method for measuring the mass flow of a gas through an orifice, a meter for measuring the mass flow

专利摘要:
METHOD FOR MEASURING THE GAS MASS FLOW THROUGH A HOLE, METER FOR MEASURING THE GAS MASS FLOW THROUGH A COMPUTER PROGRAM PRODUCT EXECUTABLE BY A PROGRAMMABLE PROCESSING EQUIPMENT, AND USABLE STORAGE MEDIA. A meter is provided to measure the flow of a gas, the meter comprising a conduit through which the gas flows in use, the conduit having a flow restriction through which the blocked flow occurs in use, the flow restriction orifice dividing the conduit in a portion upstream of said orifice and a portion downstream of said orifice, the meter further comprising a sensor assembly including a piezoelectric crystal oscillator in said upstream portion so that said first piezoelectric oscillator is in contact with said gas when the meter, in use, a second piezoelectric crystal oscillator in said downstream portion such that said second piezoelectric crystal oscillator is in contact with said gas when the meter, in use, said sensor assembly is being arranged: activate the first and second piezoelectric crystal oscillators in such a way that the first and (...).
公开号:BR112014029056B1
申请号:R112014029056-3
申请日:2013-05-23
公开日:2021-01-26
发明作者:Neil Alexander Downie
申请人:Air Products And Chemicals, Inc.；
IPC主号:

专利说明:

[0001] The present invention relates to a method of, and an apparatus for, measuring the mass flow of a gas. More particularly, the present invention relates to a method of, and an apparatus for, measuring mass flow of a gas through a flow restriction orifice using a piezoelectric oscillator.
[0002] The methods and apparatus described herein can be applied to systems in which fluids of relatively high pressure (for example, about 10 bar or higher) are present, such as, for example, the supply of fluids in high pressure cylinders or factories that use high pressure fluids. The present invention relates particularly to "clean" gases, that is, gases with little or no impurities or contaminants such as water vapor or dust.
[0003] The present invention is particularly applicable to permanent gases. Permanent gases are gases that cannot be liquefied by pressure alone and, for example, can be supplied in cylinders at a pressure of up to 450 bar g (where bar g is a measure of pressure above atmospheric pressure). Examples are argon and nitrogen. However, this is not to be taken as limiting and the term gas can be considered to cover a wider range of gases, for example, a permanent gas and a vapor from a liquefied gas.
[0004] Vapors of liquefied gases are present above the liquid in a compressed gas cylinder. Gases that liquefy under pressure as they are compressed to fill a gas cylinder are not permanent and are more accurately described as liquefied gases under pressure or as vapors of liquefied gases. As an example, nitrous oxide is supplied inside a cylinder in liquid form, with an equilibrium vapor pressure of 44.4 g bar at 15 ° C. Such vapors are not permanent or true gases, as they are able to be liquefied by pressure or temperature around environmental conditions.
[0005] A compressed gas cylinder is a pressure vessel designed to contain gases at high pressures, that is, at pressures significantly higher than atmospheric pressure. Compressed gas cylinders are used in a wide range of markets, from the low cost of the industrial market in general, to the medical market, for high cost applications, such as the manufacture of electronic products that use corrosive, toxic or highly purified special gases. pyrophoric. Pressurized gas containers commonly comprise steel, aluminum or composite materials and are capable of storing compressed, liquefied or dissolved gases, with a maximum filling pressure of up to 450 bar g for most gases, and up to 900 bar g of gases like hydrogen and helium.
[0006] In order to distribute the gases effectively and controlled from a gas cylinder or other pressure vessel, a valve or regulator is required. Often, the two are combined to form a valve with integrated pressure regulator (VIPR). The regulator is able to regulate the gas flow in such a way that the gas is distributed at a constant, or variable, pressure from the user.
[0007] For many applications, it is desirable to know the gas flow from a gas cylinder. This can be critical for many applications; for example, medical applications. A number of different mass flow meter arrangements are known.
[0008] A class of mass flow meters that are commonly used in many industrial applications are mechanical mass flow meters. These meters include mechanical components that move or rotate to measure mass flow. Such a type is the inertial flow meter (or Coriolis flow meter) that measures the flow of the fluid through the effect of the fluid in shaped tubes. Coriolis meters can handle a wide range of flow rates with high accuracy. However, in order to detect the flow, complex systems are necessary, such as activation, detection, electronic and computational characteristics.
[0009] Alternative mechanical mass flow meters are diaphragm meters, rotary meters and turbine meters. However, these types of gauges are generally less accurate and involve moving parts that can be subject to wear and tear. In addition, meters as rotary meters are only useful for measuring relatively low flow rates.
[00010] An alternative class of mass flow meters are electronic flow meters. There are two main types are thermal meters and ultrasonic meters. Thermal flow meters measure heat transfer through a heated tube to measure flow. Ultrasonic flow meters measure the speed of sound in a gaseous medium, on average, sometimes the speed of sound through various paths within the tube. However, both types of electronic flow meters in general require significant signal processing hardware and are generally expensive items.
[00011] According to a first aspect of the present invention, there is provided a method of measuring the mass flow of a gas through an orifice, the method using a first piezoelectric oscillator in contact with the gas upstream of the orifice and a second piezoelectric oscillator in contact with the gas downstream of the orifice and comprising; a) activate the first and second piezoelectric crystal oscillators such that each of the first and second piezoelectric crystal oscillators resonates at the respective resonant frequencies; b) measure the resonance frequency of the first piezoelectric oscillator and the resonance frequency of the second piezoelectric oscillator; and c) determine, from the resonance frequency of the first piezoelectric oscillator and the resonance frequency of the second piezoelectric oscillator, the mass flow of gas through said orifice.
[00012] In providing such a method, the mass flow of a gas through a restrictive orifice can be easily determined using a robust and relatively inexpensive piezoelectric crystal oscillator, for example, a quartz crystal oscillator. The piezoelectric crystal oscillator will oscillate at a resonant frequency that is dependent on the density of the gas in which the oscillator is immersed. Since, under flow restriction conditions, the density of the gas upstream of the orifice is proportional to the mass flow through the orifice, a crystal oscillator can be used to measure the mass flow. In addition, by providing a crystal oscillator further downstream of the orifice, more accurate measurement can be achieved.
[00013] Such functions of an oscillator as a source of excitation (for oscillating in response to being triggered by a drive circuit) and a detector (for having a single resonant frequency that is dependent on the environment in which the oscillator is located) . In addition, a crystal oscillator is robust and, as a result, is not relatively affected by environmental disturbances. In addition, the components that are required to operate as an oscillator are low cost and compact.
[00014] In one embodiment, step c) further comprises :) determining, from the resonance frequency of the first piezoelectric oscillator and the resonance frequency of the second piezoelectric oscillator, the density of the gas upstream of the orifice and the density of the gas downstream of the hole.
[00015] In one embodiment, step c) further comprises: d) determining the relationship between the density of the gas upstream of the orifice and the density of the gas downstream of the orifice.
[00016] In one embodiment, when the ratio is equal to or greater than a predetermined value, the flow through said orifice is determined to be blocked and the mass flow is calculated from the density of the gas upstream of the orifice alone.
[00017] In one embodiment, when the ratio is less than a predetermined value, the mass flow is calculated from the density of the gas upstream of the orifice and from the density of the gas downstream of the orifice.
[00018] In one embodiment, when the ratio is less than a predetermined value, the mass flow is calculated from the density of the gas upstream of the orifice alone and the method further comprises the step of: e) providing a notification that the determination of the mass flow can understand errors.
[00019] In one embodiment, the gas is distributed from a pressure regulator or valve located upstream of the piezoelectric crystal oscillator.
[00020] In one embodiment, the pressure regulator or valve is controlled electronically, in response to the measured mass flow of the gas through said orifice. In one embodiment, the method further comprises determining the temperature of the gas upstream of the orifice.
[00021] In an arrangement, the gas is distributed from a pressure regulator or valve located upstream of the piezoelectric crystal oscillator.
[00022] In an arrangement, the pressure regulator is controlled electronically, in response to the measured mass flow of gas through said orifice.
[00023] In one embodiment, said piezoelectric oscillator comprises a quartz crystal oscillator.
[00024] In one embodiment, the quartz crystal comprises at least one tooth. In one variation, the quartz crystal comprises a pair of planar teeth.
[00025] In one embodiment, the quartz crystal is AT cut or SC cut.
[00026] In one variation, the surface of the quartz crystal is directly exposed to the gas.
[00027] According to a second aspect of the present invention, a meter is provided to measure the mass flow of a gas, the meter comprising a conduit through which the gas flows in use, the conduit having a flow, through which the blocked flow in use occurs, the flow restriction orifice dividing the duct into an upstream portion, upstream of said orifice and a downstream portion, downstream of said orifice, the meter further comprises a sensor assembly includes a first piezoelectric crystal oscillator in said upstream part such that said first piezoelectric oscillator is in contact with said gas when the meter in use, a second piezoelectric crystal oscillator in said part downstream of such that the said second piezoelectric oscillator is in contact with said gas when the meter in use, said sensor assembly being arranged: to conduct the first and second piezoelectric crystal oscillators rich so that each of the first and second piezoelectric crystal oscillators resonates at the respective resonance frequencies; measure the resonance frequency of the first piezoelectric oscillator and the resonance frequency of the second piezoelectric oscillator; and determining, from the resonance frequency of the first piezoelectric oscillator and the resonance frequency of the second piezoelectric oscillator, the mass flow of gas through said orifice.
[00028] By providing such an arrangement, the mass flow of a gas through a restrictive orifice can be easily determined using a robust and relatively inexpensive piezoelectric crystal oscillator, for example, a quartz crystal oscillator. The piezoelectric crystal oscillator will oscillate at a resonant frequency that is dependent on the density of the gas in which the oscillator is immersed. Since, under flow restriction conditions, the density of the gas upstream of the flow restriction orifice is proportional to the mass flow through the orifice, a crystal oscillator can be used to measure the mass flow. In addition, by providing a crystal oscillator further downstream of the orifice, more accurate measurement can be achieved.
[00029] Such functions of an oscillator as a source of excitation (for oscillating in response to being triggered by a drive circuit) and a detector (for having a single resonance frequency that is dependent on the environment in which the oscillator is located) . In addition, a crystal oscillator is robust and, as a result, is not relatively affected by environmental disturbances. In addition, the components that are required to operate as an oscillator are low cost and compact.
[00030] In one embodiment, the sensor assembly comprises a drive circuit. In one variation, the sensor assembly comprises a unit circuit comprising a Darlington pair arranged in a common emitter amplifier feedback configuration.
[00031] In one embodiment, the sensor assembly comprises a power source. In an arrangement, the power source comprises a lithium-ion battery.
[00032] In one embodiment, the sensor assembly comprises a processor.
[00033] In an arrangement, said piezoelectric crystal oscillator comprises at least two planar teeth.
[00034] In one embodiment, said piezoelectric crystal oscillator has a resonance frequency of 32 kHz or greater.
[00035] In an arrangement, the meter also comprises one or more of a drive circuit, a processor and a power source.
[00036] In one embodiment, said piezoelectric oscillator comprises a quartz crystal oscillator.
[00037] In one embodiment, the quartz crystal comprises at least one tooth. In one variation, the quartz crystal comprises a pair of planar teeth.
[00038] In one embodiment, the quartz crystal is AT cut or SC cut.
[00039] In one variation, the surface of the quartz crystal is directly exposed to the gas.
[00040] In one embodiment, the sensor assembly comprises a drive circuit. In one variation, the sensor assembly comprises a unit circuit comprising a Darlington pair arranged in a common emitter amplifier feedback configuration.
[00041] In one embodiment, the sensor assembly comprises a power source. In an arrangement, the power source comprises a lithium-ion battery.
[00042] In one embodiment, the sensor assembly comprises a processor.
[00043] In an arrangement, the drive circuit comprises a Darlington pair arranged in a feedback configuration of a common emitter amplifier.
[00044] In an arrangement, the meter also comprises a temperature sensor arranged to determine the temperature of the gas adjacent to said piezoelectric oscillator.
[00045] In an arrangement, the meter is arranged downstream of a pressure regulator or valve.
[00046] In another arrangement, the meter is arranged to electronically control the pressure regulating valve, or in response to the mass flow measured through the flow restriction orifice.
[00047] In an arrangement, said piezoelectric crystal oscillator comprises at least two planar teeth.
[00048] In an arrangement, said piezoelectric crystal oscillator has a resonance frequency of 32 kHz or higher.
[00049] According to a third embodiment of the present invention, there is provided a computer program product executable by a programmable processing apparatus, which comprises one or more portions of software to perform the steps of the first aspect.
[00050] According to a fourth embodiment of the present invention, a usable computer storage medium having a computer program product according to the fourth aspect stored therein is provided.
[00051] Modalities of the present invention will now be described in detail with reference to the accompanying drawings, in which: Figure 1 is a schematic diagram of a gas cylinder and assembly of the regulator; Figure 2 is a schematic diagram showing a regulator assembly and a meter assembly according to a first embodiment of the invention; Figure 3 shows a graph of the quartz crystal frequency (kHz) on the Y axis as a function of density (kg / m3) for a number of different gases; Figure 4 shows a graph of the quartz crystal frequency (kHz) on the Y axis as a function of the mass flow rate (in liters / minute), through an orifice; Figure 5 shows a graph of the flow as a function of density / pressure for measured values and for two predictive models; Figure 6 shows a graph of the flow as a function of density / pressure for a predictive model and two extremes of operational behavior; Figure 7 is a schematic diagram showing a regulator assembly and a controller assembly according to a second embodiment of the invention; Figure 8 is a schematic diagram showing a regulator assembly and a controller assembly according to a third embodiment of the invention; Figure 9 is a schematic diagram of a drive circuit for use with any of the first to third modes; Figure 10 is a schematic diagram, showing an alternative to the drive circuit for use with any of the first to third modes; Figure 11 is a schematic diagram showing, alternatively, the drive circuit for use with any of the first to third modes; Figure 12 is a schematic diagram showing a regulating drive circuit for use with any of the second or third modes; Figure 13 is a flow chart illustrating a method of operating the first embodiment; Figure 14 is a flow chart that illustrates a method of operating the second or third modalities; Figure 15 shows a graph of the frequency behavior of different types of crystals; Figure 16 is a schematic diagram, showing an alternative sensor assembly comprising two quartz crystals; and Figure 17 shows an alternative arrangement that uses an electronic remote data unit.
[00052] Figure 1 shows a schematic view of a gas cylinder assembly 10 according to an embodiment of the invention. Figure 1 shows a schematic view of a situation in which the present invention can be used. A gas cylinder 100, regulator 150 and mounting gauge 200 are provided.
[00053] The gas cylinder 100 has a gas cylinder body 102 and a valve 104. The gas cylinder body 102 comprises a generally cylindrical pressure vessel that has a planar base 102a arranged to allow mounting of the cylinder of gas 10 not supported at rest on a flat surface.
[00054] The body of the gas cylinder 102 is formed from steel, aluminum and / or composite material and is adapted and arranged to withstand internal pressures of up to about 900 bar g. An opening 106 is located at a proximal end of the gas cylinder body 102 opposite base 102a and comprises a screw thread (not shown) adapted to receive valve 104.
[00055] The gas cylinder 100 defines a pressure vessel that has an internal volume V. Any suitable fluid can be contained within the gas cylinder 100. However, the present modality refers to, but is not limited to, exclusively , permanent purified gases that are free of impurities, such as dust and / or moisture. Non-exhaustive examples of such gases may be: oxygen, nitrogen, argon, helium, hydrogen, methane, nitrogen trifluoride, carbon monoxide, carbon dioxide, Krypton, neon or mixtures that behave in the manner of permanent gases.
[00056] The valve 104 comprises a housing 108, an outlet 110, a valve body 112 and a valve seat 114. The housing 108 comprises a complementary screw thread for engagement with the opening 106 of the gas cylinder body 102. The outlet 110 is adapted and arranged to allow the gas cylinder 100 to be connected to other components of a gas assembly; for example, hoses, tubes or other pressure valves or regulators. Valve 104 may optionally include a VIPR (valve with Integrated Pressure Reduction). In this situation, regulator 150 can be omitted.
[00057] The valve body 112 can be adjusted axially in the direction or away from the valve seat 114 by rotating a manipulable handle 116 selectively to open or close the outlet 110. In other words, the movement of the body valve 112 towards or away from valve seat 112 selectively controls the area of the communication passage between the interior of the gas cylinder body 102 and the outlet 110. This, in turn, controls the flow of gas from the interior of the gas cylinder assembly 100 to the external environment.
[00058] A regulator 150 is located downstream of output 110. Regulator 150 has an input 152 and an output 154. Input 152 of regulator 150 is connected to an input tube 156, which provides a communication path between the output 110 of gas cylinder 100 and regulator 150. Inlet 152 of regulator 150 is arranged to receive high pressure gas from outlet 110 of gas cylinder 100. This can be any suitable pressure; however, in general, the pressure of the gas leaving outlet 110 will be in excess of 20 bar and more likely to be in the region of 100-900 bar.
[00059] Outlet 154 is connected to an outlet tube 158. A coupling 160 is located at the distal end of outlet tube 158 and is adapted for connection to tubes or devices (not shown) for which gas is required.
[00060] A meter assembly 200 is located in communication with outlet tube 158 between outlet 154 and coupling 160. The meter assembly 200 is located immediately downstream of regulator 150 and is arranged to determine the flow rate of mass of gas supplied to outlet 160.
[00061] Regulator 150 and meter assembly 200 according to a first embodiment of the present invention are shown in greater detail in Figure 2.
[00062] In this embodiment, regulator 150 comprises a single diaphragm regulator. However, the person skilled in the art would be readily aware of the variations that can be used with the present invention; for example, a two-diaphragm regulator or other arrangement.
[00063] Regulator 150 comprises a valve region 162 in communication with inlet 152 and outlet 154. The region 162 of the valve comprises a pressure regulating valve 164 located adjacent to a valve seat 166. Pressure regulating valve 164 it is connected to a diaphragm 168 which is configured to allow the translational movement of the pressure regulating valve 164 towards and away from the valve seat 166 to open and close, respectively, an opening 170 between them. Diaphragm 168 is bent elastically by a spring 172 located around an axis 174.
[00064] Regulator 150 can be operated to receive gas from outlet 110, at full cylinder pressure (for example, 100 bar), but to supply gas at a substantially constant low fixed pressure (for example, 5 bar) for outlet 154. This is achieved by a feedback mechanism through which the gas pressure downstream of opening 170 is operable to act on diaphragm 168 as opposed to the pressure force of spring 172.
[00065] The gas pressure in the adjacent region of diaphragm 168 must exceed the specified level, diaphragm 168 is operable to move upwards (in relation to Figure 2). As a result, the pressure regulating valve 164 is moved closer to the valve seat 166, reducing the size of the opening 170 and, consequently, restricting the flow of gas from inlet 152 to outlet 154. Generally speaking, the forces that compete with the resistance of the spring 172 and the pressure of the gas will result in an equilibrium position of the diaphragm and, therefore, the release of a constant pressure of gas at the outlet 154.
[00066] A manipulable cable 176 is provided to allow a user to adjust the pressure force of the spring 172, thereby moving the position of the diaphragm 168 and, as a result, adjusting the spacing balance between the pressure regulating valve 164 and valve seat 166. This allows adjustment of the dimensions of opening 170 through which the flow of high pressure gas from outlet 110 can pass.
[00067] The meter assembly 200 includes a body 202, a first sensor assembly 204 and a second sensor assembly 206. Body 202 can comprise any suitable material; for example, steel, aluminum or composites. The body 202 comprises a conduit 208, a first housing 210 and a second housing 212. The conduit 208 is in communication with the interior of the outlet tube 158 and is arranged to connect thereto. Conduit 208 provides a communication path between output 154 and coupling 160 (and, concomitantly, user devices or applications connected to coupling 160).
[00068] Orifice plate 214 is located inside the conduit 208. Orifice plate 214 comprises a wall that delimits a limited orifice 216. Orifice plate 214 forms a flow restriction within conduit 208. The orifice 216 has a cross-sectional area A which is small in relation to the cross-sectional area of conduit 406 so that the flow rate through orifice 216 is in a blocked condition, as will be described later.
[00069] Although orifice plate 214 is shown as a thin-walled plate in Figure 2, this need not be so. The orifice plate 214 can take any suitable form of wall and can have a tapered profile, or can have a greater thickness than shown. Alternatively, any suitable flow restriction can be used in place of orifice plate 214. For example, the flow restriction may comprise a portion of a tube of a narrower diameter than the rest of it. The skilled person would be readily aware of alternative flow restrictions that can be used to provide a flow restriction orifice 216, through which, in use, blocked flow occurs.
[00070] In the present embodiment, conduit 208 has a length of the order of a few centimeters. Orifice plate 214 delimits an orifice 216 that has a diameter in the range of 0.1 mm - 4 mm. This is sufficient to provide a blocked flow condition and to provide a gas flow through orifice 216 of between 1 and 40 eu liters / minute for gases, such as nitrogen or argon. For a gas that has a lower molecular weight, the orifice diameter 216 can be reduced to achieve a similar flow rate. Alternatively, for higher flow rates, orifice 216 can be increased proportionally, as long as the upstream pressure is sufficiently higher than the downstream pressure to create flow restriction conditions through orifice 216.
[00071] Orifice plate 214 divides the interior of conduit 208 upstream to a section 218 upstream of orifice plate 214, and a section downstream 220 downstream of orifice plate 214. In use, when gas is flowing from outlet 154 of regulator 150 in the upstream part 214 of conduit 208, the orifice plate 214 will act as a flow restriction, resulting in a pressure differential between portions upstream 218 and downstream 220 of conduit 208. For Consequently, the upstream part 21 of conduit 208 is at a first pressure Pi and density pi and the downstream part of conduit 220 is at a second (and, in use, necessarily lower) pressure P2 and density p2. This will be described in detail later.
[00072] The first housing 2i0 is located adjacent to the upstream portion 2i4 of conduit 208 and is arranged to contain at least part of the first sensor assembly 204. The interior of the first housing 2i0 can be either atmospheric pressure or it can be in communication with the interior of the conduit 208 and, consequently, in the same pressure as the interior of the outlet tube i58. This would eliminate the need for a pressure feed between housing 2i0 and the interior of conduit 208.
[00073] Alternatively, the first housing 2i0 can be provided as part of conduit 208. For example, a part of conduit 208 can be extended to accommodate the mounting of sensor 204.
[00074] The second housing 2i2 is located adjacent to downstream of portion 2i4 of conduit 208 and is arranged to contain at least part of the second sensor assembly 206. The interior of the second housing 2i2 may be atmospheric pressure or it can be in communication with the interior of the conduit 208 and, consequently, in the same pressure as the interior of the portion downstream of the outlet pipe i60. This would eliminate the need for a pressure feed between the second housing 2i2 and the interior of the conduit 208.
[00075] Alternatively, in common with the first housing 210, the second housing 212 can be omitted and the second sensor assembly 206 located in a part of conduit 208 or coupling 160. For example, the part downstream of conduit 208 may be extended to accommodate the 206 sensor mount.
[00076] These arrangements are feasible because the inventors have found that only some components of the first and second sensor assemblies 204, 206 are sensitive to high pressure. In particular, larger components such as batteries may be susceptible to high pressures. However, lithium batteries have been found to perform particularly well under the high pressures found within the upstream and downstream portions 218, 220 of conduit 208. However, suitable alternative energy sources would be readily contemplated by the specialist.
[00077] The potential location of the first and / or second sensor assemblies 204, 206 completely inside the conduit 208 provides additional flexibility when configuring the 200 meter assembly. In particular, the location of relatively fragile electronic components entirely within the walls metal or composites of the body 202 without the need for a protrusion, as the housing 210 provides considerable protection against environmental or accidental damage. This is particularly important, for example, in storage areas or warehouses, where gas cylinders may be located adjacent to other gas cylinders, heavy machinery or rough surfaces. The relatively small size of the mounting sensors 204, 206 allows internal location to be easily achieved.
[00078] In addition, the internal location of the first and / or second sensor assemblies 204, 206 protects these components from environmental conditions, such as salt, water and other contaminants. This would allow, for example, a high impedance circuit that is highly sensitive to salt and water damage to be used as part of the first and / or second sensor assemblies 204, 206.
[00079] The meter assembly 200 is arranged to measure the mass flow of the gas that passes through the orifice 216. This is measured using the first and second sensor assemblies 204, 206, as described below.
[00080] The mass flow rate of gas through orifice 216 can be determined using only the first sensor assembly 204 under particular conditions with precision. The accuracy of such a determination is dependent upon the existence of a blocked flow condition through orifice 216 as will be described below. For many applications, perhaps using orifice structural parameters 216 as described above, this will be the case in most operating conditions. However, at lower flow rates this condition cannot be satisfied and the mass flow rate, as determined by the first sensor assembly 204, may be less accurate.
[00081] In order to improve the accuracy of, or to indicate the validity of, the determination of the mass flow, the second sensor assembly 206 is provided. The second sensor assembly 206 is operable to determine the downstream density to improve the accuracy of the mass flow determination and, in addition or alternatively, to determine whether the blocked flow condition is satisfied. Therefore, the second assembly of sensor 206 is operable to provide, in conjunction with the first assembly of sensor 204, confirmation that the mass flow determined by the assembly of meter 200 is accurate.
[00082] The first sensor assembly 204 comprises a crystal quartz oscillator 222 connected to a drive circuit 224, a temperature sensor 226 and a battery 228.
[00083] In this modality, the quartz crystal oscillator 222 and temperature sensor 226 are located in communication with the interior of the upstream portion 218 of the conduit 208, while the other components of the sensor assembly 204 are located inside the housing 210 In other words, the quartz crystal oscillator 222 is immersed in the gas upstream of the orifice plate 214. A microprocessor 238 can also be supplied, either separately or as part of the drive circuit 224.
[00084] The second sensor assembly 206 is substantially similar to the first sensor assembly 204, although, in this case, a temperature sensor is not required. The second sensor assembly 206 comprises a quartz crystal oscillator 230, a drive circuit 232 and a battery 234. The second sensor assembly 206 is connected to microprocessor 238.
[00085] In this modality, the quartz crystal oscillator 230 is located in communication with the interior of the downstream portion 220 of conduit 208, while the other components of sensor assembly 206 are located inside housing 212. In other words, the quartz crystal oscillator 230 is immersed in the gas downstream of the orifice plate 214.
[00086] The specialist would easily be made aware of the changes to the arrangement described above. For example, the second sensor assembly 206 may simply comprise a quartz crystal oscillator connected to the drive circuit 224 of the first sensor assembly 204. In other words, the first and second sensor assemblies 204, 206 may share a circuit of common drive and / or battery and / or microprocessor.
[00087] The drive circuits 224, 232 and the quartz crystal oscillators 222, 230 will be described in detail later with reference to Figures 6 and 7. The temperature sensor 226 includes a thermistor. Any suitable thermistor can be used. High precision is not required from the thermistor. For example, an accuracy of 0.5 ° C is suitable for this mode. Therefore, cheap and small components can be used.
[00088] In this arrangement, quartz crystal oscillators 222, 230 are constantly under isostatic pressure within conduit 208 and, consequently, do not experience a pressure gradient. In other words, any mechanical stress arising from the pressure difference between the outside atmosphere and the inside of the body 202 of the meter assembly 200 is expressed throughout the body 202.
[00089] The theory and operation of sensor assembly 204 will now be described with reference to Figures 3 and 4.
[00090] The quartz crystal oscillators 222, 230 each have a resonant frequency that is dependent on the density of the fluid in which it is located. Exposing an oscillating pitch of the fork-like planar crystal oscillator to a gas leads to a damping change in the crystal's resonance frequency (when compared to the crystal's resonance frequency in a vacuum). There are a number of reasons for this. Although there is no gas dampening effect on the crystal oscillations, the gas adjacent to the vibrating teeth 222a, 230a (as shown in Figure 7) of the respective crystal oscillator tuning 222, 230 increases the effective mass of the oscillator. This leads to a reduction in the resonance frequency of the quartz crystal oscillator according to the movement of an elastic beam

[00091] Where f is the oscillation frequency, f0 is the vacuum oscillation frequency, ρ is the gas density, and M0 is a constant.
[00092] The density ρ will, in almost all cases, be small when compared to M0, so that the formula can be approximated by the linear equation:
which can again be expressed in terms of the frequency deviation Δf from f0, defined in equation 3):

[00093] Therefore, to a good approximation, the change in which the quartz crystal oscillator is exposed. Figure 10 shows, for a series of different gas / gas mixtures, that the resonance frequency of the quartz crystal oscillator 222, 230 varies linearly as a function of density.
[00094] In general, the sensitivity of the quartz crystal oscillator 222, 230 is that a 5% change in frequency is seen with, for example, oxygen gas (having a molecular weight of 32 AMU) at 250 bar, when compared to atmospheric pressure. Such gas pressures and densities are typical of the storage cylinders used for permanent gases, which are typically between 137 and 450 bar g for most gases, and up to 700 bar or 900 g of helium and hydrogen.
[00095] The quartz crystal oscillator 222 is particularly suitable for use as a density sensor forming part of a mass flow meter, for commercially supplied gases. In order to correctly perceive the density of a gas, it is necessary that the gas be free of dust and liquid droplets, which is guaranteed with commercially supplied gases, but not with air or in most pressure monitoring situations.
[00096] Since the density value is obtained from the quartz crystal oscillator 222, the mass flow rate of gas through the orifice 216 can be determined. The mass flow rate, Q, through an orifice is defined as:

[00097] Where k is a constant, v is the velocity of the gas, pi is the density of the gas upstream and A is the cross-sectional area of hole A. However, from Bernoulli's equation 5):

[00098] As the cross-sectional area of an orifice decreases, the gas velocity will increase and the gas pressure will be reduced.
[00099] The determination of mass flow through orifice 2i6 using only a single quartz crystal oscillator upstream 222 depends on a condition known as "suffocated" or "critical" flow. Such situation arises when the gas velocity reaches sonic conditions, that is, when the flow restriction caused by the orifice plate 2i4 is such that the velocity of the gas that flows through the orifice 2i6 reaches the speed of sound. This occurs when the pressure ratio through orifice 2i6 (i.e., Pi / P2) is approximately 2 or more. As an alternative measure, this condition is generally applicable when the absolute pressure Pi upstream is at least i bar g higher than the downstream pressure absolute P2, where the pressure is atmospheric.
[000100] Once this condition is met, there is very little additional increase in air velocity through orifice 2i6. Therefore, in the blocked flow condition, where v = c (the speed of sound in the gas in question), Equation 4) becomes:

[000101] Therefore, for an orifice with a fixed cross-sectional area A, the mass flow through orifice 216 is dependent only on the upstream density. This is the parameter that the 222 quartz crystal oscillator is willing to measure.
[000102] Furthermore, the speed of sound c is proportional to the square root of the absolute temperature, VT. However, as previously described, in this embodiment the temperature sensor 226 does not need to be particularly accurate. For example, if the temperature error is 0.5k to 300k, this only translates to a 1: 1200 error in the calculated speed of sound. Thus, for many applications, the 226 temperature sensor is not necessarily necessary.
[000103] Figure 4 illustrates the experimental data of mass flow measurement. Figure 4 is a graph of the resonance frequency (in kHz) on the Y axis as a function of gas flow (in liters / minute) on the X axis by nitrogen gas. As shown, the graph is highly linear and shows that the mass flow can be accurately measured using the 222 quartz crystal oscillator.
[000104] In addition, the high precision of the 222 quartz crystal oscillator allows the measurement of a very high precision, with a resolution of parts per million. Together with the linear response of the 222 quartz density sensor at high densities and pressures, the high accuracy allows the mass flow of very light gases such as H2 and He to be accurately measured.
[000105] However, as described above, the measurement of mass flow using the quartz crystal oscillator 222 will only be accurate under conditions of flow restriction, that is, when the flow velocity through orifice 216 is close or equal to the speed of sound in the gas. This, in practice, requires the user to maintain a minimum gas flow determined for the meter 200 in order to provide an accurate measurement.
[000106] As a result, a single quartz crystal upstream of oscillator 222 operating alone is unable to provide an indication of whether a blocked flow condition is present in orifice 216. Therefore, the second quartz crystal oscillator 230 ( formation of at least a part of the second sensor assembly 206) is provided. The use of piezoelectric sensors, both upstream and downstream of orifice 216 allows accurate flow measurement to be achieved.
[000107] As previously established in relation to equation 7), the mass flow rate Q is proportional to the upstream density pi, if the speed of the fluid flow through the orifice 2i6 is sonic or close to sonic. As stated above, this condition is satisfied if generally the ratio of the upstream pressure to the downstream pressure (i.e., Pi / P2) is approximately 2 or greater.
[000108] However, in practice, the pressure ratio may be insufficient. Application of the Bernoulli equation and established theory of blocked flow and speed of sound leads to equation 7)
where k 'is a dimensionless constant, A is the orifice area, pi is the upstream density and p2 is the downstream density.
[000109] Clearly, if pi / p2> 2 then equation 7) can be approximated by equation 6) above, because a blocked flow condition is considered to be present through orifice 2i6.
[000110] Therefore, in this case, the measurement from only the first sensor assembly 204 can be used to provide an accurate indication of the mass flow in situations where pi / p2> 2.
[000111] However, if the ratio is less than this, then equation 7) can be used to calculate the mass flow rate using both the first and second sensor assemblies 204, 206 to measure the upstream and downstream pi density. downstream of density p2, respectively, and to determine mass flow at flow rates through orifice 2i6 below blocked flow conditions.
[000112] Alternatively, meter 200 can merely provide a reading in addition to the first sensor assembly 204 (that is, a mass flow based solely on an upstream density measurement) and the second sensor assembly 206 (including the oscillator quartz crystal 230) can be implemented to provide an indication that the mass flow measurement is working outside a precise operating regime.
[000113] Figure 5 shows experimental data (diamonds), comprising the flow of helium gas in liters / min, through a 0.5 mm orifice. The straight line shows a linear relationship between upstream density pi and flow for a upstream / downstream density ratio of well over 2: 1 fits the data (equation 6)). The curve shows how the flow in lower density proportions can be predicted with good precision using equation 7), which takes density downstream into account p2. This curve is obtained by gradually interrupting, from equation 7) to equation 6), over a range of about 1 bar g, the critical density in the proportion of 2: 1, as an increase in flow.
[000114] Therefore, the provision of a second sensor assembly has an advantage when the meter output is almost or completely blocked. In this case, the second sensor would force the meter to adopt equation 7) (low ratio) and correctly indicate low or zero flow. Without the second sensor, the device may erroneously indicate flow as if no blockage had occurred.
[000115] Figure 6 shows the advantage of precision taking into account the downstream density. Figure 6 shows the adjustment line from Figure 5. In addition, the upper curve shows the relationship that would be expected from an upstream sensor only if the downstream density was atmospheric (this line is shown in short strokes) ). The deviation from the correct value is so small that it can be neglected at high flow rates, but is significant at low flows.
[000116] The bottom line (long lines) shows the curve that would predict whether the downstream pressure in relation to the atmosphere was twice as high as in the experimental measurement. Again, the deviation is small, except at low flows.
[000117] A second embodiment of the invention is shown in Figure 7. The characteristics of the second embodiment shown in Figure 7, which are in common with the first embodiment of Figure 2 are assigned the same reference numbers and will not be described again in this case.
[000118] In the mode of Figure 7, regulator 300 differs from regulator 150 from the mode of figure 2, in which regulator 300 is arranged to provide automatic control of gas from outlet 154 by means of a solenoid valve 302. In addition, only a single sensor assembly 204 is provided, in contrast to the first modality. In other words, the second sensor assembly is omitted in this mode. The solenoid valve 302 comprises an armature 304 that is movable in response to an electric current through the coils (not shown) of the solenoid valve 302. Armature 304 is movable to directly open or close the pressure regulating valve 164 and, consequently, the opening 170. The solenoid valve 302 is, in this mode, continuously variable (known as “approximately proportional”) to regulate the gas flow through regulator 300.
[000119] The solenoid valve 302 shown in Figure 5 is in the normally open condition. In other words, in the absence of an electrical current through the solenoid valve 302, the armature 304 is in an extended position, such that the pressure regulating valve 164 is open, i.e., the opening 170 is opened. If a current is applied to the solenoid valve 302, the armature 304 will retract and the pressure regulating valve 164 closes.
[000120] The specialist would be readily aware of alternative variations of the solenoid valve, which can be used with the present invention. For example, the solenoid valve can be digital, in response (ie, on / off or open / closed). Alternative structures can be implemented; for example, frame 304 can act directly on the diaphragm, or it can control the flow through a narrow duct in communication with outlet 154, in order to regulate the movement of diaphragm 168. Alternatively, the pressure regulating valve could be eliminated and diaphragm 168 itself could be the valve member that directly controls the flow of gas from inlet 152 to outlet 154.
[000121] The second mode comprises a controller 350. The components of controller 350 in common with the 200 meter assembly are assigned the same reference numbers for clarity.
[000122] Controller 350, in the mode of Figure 7, comprises only a single sensor assembly 204 located upstream of orifice 216 and the second sensor assembly of the first mode is omitted.
[000123] Controller 350 further comprises an electronic solenoid unit 352 connected to solenoid valve 302 and sensor assembly 204. Solenoid unit 352 is arranged to receive a signal from sensor assembly 204 and to control the solenoid valve 302, in response to that signal and, consequently, control the flow through the regulator 300.
[000124] The solenoid unit 352 can comprise any drive circuit suitable for controlling the solenoid valve 302. A suitable circuit can be an operational amplifier arrangement that has an input from the sensor assembly 204 to the negative terminal of the operational amplifier. Therefore, a variable resistor designed to provide a constant reference level and act as a comparator could be connected to the positive terminal.
[000125] An input from sensor assembly 204 to solenoid unit 352 will cause solenoid valve 302 to function. For example, if the input signal from sensor assembly 204 (or, alternatively, processor 240) exceeds a level determined threshold, solenoid 352 drives can energize solenoid valve 302. This will be described in detail below. The solenoid valve 302 can be controlled in a digital way (i.e., on or off) where a DC voltage is varied between a minimum and a maximum value. This is known as pulse width modulation (PWM). Alternatively, the DC voltage from the solenoid unit 352 can be continuously variable (e.g., proportional) to adjust the position of the pressure regulating valve 164 precisely in an analogous manner.
[000126] In addition or alternatively, the solenoid unit 352 can control the solenoid valve 302 by means of a DC output comprising an AC component. Since the extension of armature 304 of solenoid valve 302 is approximately proportional to the current applied, this causes armature 304 of solenoid valve 302 to oscillate. Such oscillations mitigate “static friction” of the reinforcement 304, that is, assist in preventing the reinforcement 304 from being stuck or jammed.
[000127] Alternatively, other control devices, such as microprocessor FETs or ASICs can be used appropriately to control the operation of the solenoid valve 302. In addition, as discussed, the solenoid valve 302 can operate in any mode of digital converter (i.e., on / off) or analog (i.e. continuously variable) to allow exact movement of the seat valve 164 or similar.
[000128] The operation of controller 350 will now be described. As described above, sensor assembly 204 (including quartz crystal oscillator 222) can be used as part of a feedback loop to control pressure electronically.
[000129] The sensor assembly 204 output is connected to the solenoid valve 302 in a feedback cycle. As shown above, the resonance frequency of the quartz crystal oscillator 222 is proportional to the density of the gas upstream of orifice 216, and that, under conditions of flow restriction, the density of the gas upstream of orifice 216 is proportional to the mass flow rate Q through the orifice.
[000130] Therefore, a special resonance frequency, the quartz crystal oscillator 222 will correspond to a particular density of gas upstream of the orifice and, under conditions of flow restriction, a particular mass flow through orifice 216. For therefore, a feedback cycle can be implemented in controller 350 which is operable to maintain the resonance frequency of quartz crystal oscillator 222 at a particular joint frequency and, concomitantly, to maintain the flow of gas through orifice 216 at a flow rate of constant mass.
[000131] The general principle of operation is like this: the quartz crystal oscillator 222 is defined for a certain frequency. If the upstream density drops, then the resonance frequency of the 222 quartz crystal oscillator will increase. Controller 350 will then open solenoid valve 302 to increase the gas pressure downstream of solenoid valve 302. This will increase the pressure and, at the same time, the density of the gas upstream of orifice 216. This will then decrease the frequency resonance of the quartz crystal oscillator 222 until the frequency setpoint is restored, which corresponds to a desired mass flow rate of gas through orifice 216. In other words, controller 350 implements a feedback circuit to minimize the difference between the assembly of the punctual mass flow rate and the actual mass flow.
[000132] Controller 350 also controls solenoid valve 302 depending on the temperature. In this, the feedback loop is arranged to maintain the pressure not equal to a constant, but equal to a constant divided by the square root of the absolute temperature, 1 / VT, measured in degrees Kelvin.
[000133] The electronic gas pressure controller made in this way can be connected to an orifice downstream will offer a constant flow of gas mass. The ratio of pressures (upstream / downstream) through the orifice should be sufficient, about 2 or more, to maintain the critical flow orifice, whereby we observe that, at the narrowest point of the gas flow, it is approximately sonic in speed. This can be seen from equation 7).
[000134] In equation 6), the speed of sound in the gas, c can be expressed as stated in equation 8):
where Y is the ratio of specific heat Cp / Cv, R is the gas constant, T is the temperature and M is the molecular weight. Therefore, replacing the expression with c) in equation 6) generates:
where pi is the upstream density, as measured by the quartz crystal oscillator 222.
[000135] In general, only density and temperature are variable in the applications relevant to the present invention. Therefore, an amount of p can be defined as established in equation i0):

[000136] Replacing this expression in equation 9), it provides:

[000137] Therefore, since
a constant for packaged gases, k is a constant for any particular gas, and the area A of the orifice is a constant, the flow rate can be determined from p '. Consequently, the mass flow can be controlled based on the density divided by the square root of the temperature or, in practice, the resonance frequency of the quartz crystal oscillator 222 divided by the square root of the temperature measured by the temperature sensor 226.
[000138] Therefore, if the sensor assembly 204 is operable to control solenoid valve 302 to keep p 'substantially constant, the mass flow through orifice 216 will be kept constant. In other words, the solenoid valve 302 can be controlled based on both the measured resonance frequency of the quartz crystal oscillator 222 and the measured temperature.
[000139] The first or second modalities may additionally comprise a display (not shown) to show a user the results of measurements made on the detected gas. Alternatively, the display can be located away from the meter assemblies 200, 350 and the relevant data can be communicated remotely.
[000140] In order for the 222 quartz crystal oscillator to provide an accurate measurement, the 222 quartz crystal oscillator must be kept free of dirt, moisture and other contaminants. While this is not an issue for commercially supplied packaged gases (which are extremely clean), the 350 controller can be used in situations where environmental contamination can be a significant problem.
[000141] Therefore, the meter assembly 200, 350 is provided with a filter 354 located between the quartz crystal oscillator 222 and the main gas flow. The filter 354 can be of any suitable pore size. The pore sizes in the range of 5 - 10 μm are particularly suitable for this application. The 354 filter (or a similar filter) can be applied to the first embodiment described above.
[000142] Alternatively, filter 354 can be omitted if the quartz crystal oscillator 222 is located behind an opening that is small enough to prevent the penetration of dirt or other contaminants. For example, a mesh opening size of 0.25 mm would be suitable for use without a filter, as long as the pressure upstream of the gas can be measured in this way.
[000143] A third embodiment of the present invention is shown in Figure 8. The third embodiment comprises a controller 450. The components of controller 450, in common with the meter assembly 200 and controller 350 are assigned the same reference numbers for further clarity.
[000144] Controller 450, in the mode of Figure 8, comprises only both in a first sensor assembly 204 located upstream of orifice 216 and a second sensor assembly 206 in common with the first mode. Therefore, the third modality is a combination of the characteristics of the first and second modalities.
[000145] Controller 450 further comprises an electronic solenoid unit 452 connected to solenoid valve 402 and for sensor assemblies 204, 206. Solenoid unit 452 is arranged to receive a signal from sensor assemblies 204, 206 and to control the solenoid valve 402 in response to that signal and, consequently, control the flow through regulator 400.
[000146] The solenoid unit 452 can take the form of the solenoid unit 352 and any variants thereof and will not be described further here. An input from sensor assemblies 204, 206 to solenoid unit 452 will cause solenoid valve 402 to function. For example, if the input signal from sensor assembly 204 (or, alternatively, processor 240) exceeds one determined threshold level, solenoid unit 352 can energize solenoid valve 302. This will be described in detail below. The solenoid valve 302 can be controlled in a digital way (i.e., on or off) where a DC voltage is varied between a minimum and a maximum value. Alternatively, the DC voltage from the solenoid unit 352 can be continuously variable (e.g., proportional) to adjust the position of the pressure regulating valve 164 precisely in an analogous manner.
[000147] In addition or alternatively, the solenoid unit 452 can control the solenoid valve 302 by means of a DC output comprising an AC component. Since the extension of armature 304 of solenoid valve 302 is approximately proportional to the current applied, this causes armature 304 of solenoid valve 302 to oscillate. Such oscillations mitigate the “static friction” of the reinforcement 304, that is, they help to prevent the reinforcement 304 from being stuck or jammed.
[000148] Alternatively, other control devices, such as FETs or microprocessors or ASICs can be used appropriately to control the operation of the solenoid valve 302. In addition, as discussed, the solenoid valve 302 can operate in either converter mode digital (i.e., on / off) or analog (ie continuously variable) to allow exact movement of the pressure regulating valve 164 or similar.
[000149] The operation of controller 450 will now be described. As described above, sensor mount 204 (including quartz crystal oscillator 222) and sensor mount 206 (including quartz crystal oscillator 230) can be used as part of a feedback loop to control pressure electronically .
[000150] The output of the first sensor assembly 204 and the second sensor assembly 206 is connected to the solenoid valve 302 in a feedback cycle. As shown above, the resonance frequency of the quartz crystal oscillator 222 is proportional to the density of the gas upstream of orifice 216, and that, under conditions of flow restriction, the density of the gas upstream of orifice 216 is proportional to the mass flow rate Q through the orifice.
[000151] Therefore, a special resonance frequency, the quartz crystal oscillator 222 will correspond to a particular density of gas upstream of the orifice and, under conditions of flow restriction, a particular mass flow through orifice 216. For therefore, a feedback cycle can be implemented in controller 450 which is operable to maintain the resonance frequency of quartz crystal oscillator 222 at a particular set frequency and, at the same time, to maintain the flow of gas through orifice 216 at a flow rate. of constant mass.
[000152] Controller 350 also controls solenoid valve 302 depending on the temperature. In this, the feedback loop is arranged to maintain the pressure is not equal to a constant, but equal to a constant divided by the square root of the temperature, 1 / VT.
[000153] The electronic gas pressure controller made in this way can be connected to an orifice downstream will offer a constant mass flow of gas. The ratio of pressures (upstream / downstream) through the orifice must be sufficient, about 2 or more, to maintain the critical flow orifice, whereby we observe that, at the narrowest point, the gas flow is close to the sonic in velocity. This can be seen from equation 6).
[000154] In equation 8) above, the speed of sound in the gas, c is expressed. Therefore, replacing the expression of c in equation 7) generates the equation:
where pi is the upstream density, as measured by the quartz crystal oscillator 222, and p2 is the downstream density, as measured by the quartz crystal oscillator 230.
[000155] In general, as stated above, only the upstream and downstream densities and temperature are variable in the applications relevant to the present invention.
[000156] Therefore, as for the second modality, an amount of ρ '' can be defined as established in equation 13):

[000157] Replacing this expression in equation 9), it provides:

[000158] Therefore, once
which is a constant for the packaged gases, k is a constant and the area A of the orifice is a constant, the mass flow can be determined only from ρ “. Therefore, sensor assemblies 204 and 206 are operable to control solenoid valve 402 to maintain substantially constant p ”. In other words, the solenoid valve 302 can be controlled based on the resonance frequency of the first quartz crystal oscillator 222, the resonance frequency of the second quartz crystal oscillator 230 and the square root of the temperature measured by the temperature sensor 226 .
[000159] The first, second or third modalities can additionally comprise a display (not shown) to show a user the results of measurements made on the detected gas. Alternatively, the display can be located away from the meter 200 and controllers 350, 450 assembly and the relevant data can be communicated remotely.
[000160] For example, the first, second or third modalities may also comprise an antenna (not shown) for remote communication with, for example, a base station. This will be discussed later. In this case, the antenna can be located outside the body 202 and is connected to the sensor assembly 204 by means of a wire connector or equivalent.
[000161] The antenna itself can be adapted and arranged in order to use any appropriate communication protocol; for example, a non-exhaustive list can be RFID, Bluetooth, Infrared (IR), 802.11 wireless, frequency modulation (FM) transmission or a cellular network.
[000162] Alternatively, wired communication can be implemented. Wired communication requires only a single metallic conductor to communicate: the circuit's “return” path is provided by means of capacitive coupling through the air between the communication devices. The specialist would be readily aware of the alternatives of the antenna (and associated transmission hardware), which could be used with the modalities discussed here.
[000163] For example, the communication can be carried out by means of acoustic transmission from inside the housing 210. A transmitter located inside the housing 210 can carry out the acoustic transmission. The transmitter may comprise, for example, a simple fixed frequency piezoelectric resonator.
[000164] A complementary receiver is also required and this component can be located away from the 200 meter assembly or the controller 350, 450 and can comprise hardware, such as, for example, a phase lock circuit tone detector with a microphone integrated.
[000165] Sensor assembly 204 will now be described in greater detail with reference to Figures 9, 10 and 11. Although the following description refers to sensor assembly 204, it should be understood that this also applies to sensor assembly 206 , which can be structurally and similar in electronic configuration.
[000166] The quartz crystal oscillator 222 comprises a flat section of quartz cut. Quartz shows piezoelectric behavior, that is, the application of a tension through the crystal causes the crystal to change its shape, generating a mechanical force. On the other hand, a mechanical force applied to the crystal produces an electrical charge.
[000167] Two parallel surfaces of the 222 quartz crystal oscillator are metallized in order to provide electrical connections throughout the crystal. When a voltage is applied through the crystal, through metal contacts, the shape of the crystal changes. When applying an alternating voltage to the crystal, the crystal may be forced to oscillate.
[000168] The physical size and thickness of the quartz crystal determines the characteristic or resonant frequency of the quartz crystal. Indeed, the characteristic or resonant frequency of crystal 222 is inversely proportional to the physical thickness between the two metallized surfaces. Quartz crystal oscillators are well known in the art and thus the structure of the 222 quartz crystal oscillator will not be described here further.
[000169] In addition, the frequency of resonant vibration of a quartz crystal will vary, depending on the environment in which the crystal is located. In a vacuum, the crystal has a specific frequency. However, this frequency is changed in different environments. For example, in a fluid, the vibration of the crystal will be dampened by the surrounding molecules and these will affect the resonance frequency and the energy required to oscillate the crystal to a given amplitude.
[000170] In addition, the adsorption of gases or the deposition of surrounding materials on the crystal will affect the mass of the vibrating crystal, changing the resonance frequency. Such adsorption or deposition of material forms the basis for the commonly used selective gas analyzers in which an absorbent layer is formed on the crystal and increases in mass as the gas is absorbed.
[000171] However, in the present case, no coating is applied to the 222 quartz crystal oscillator. In fact, the deposition of material on the 222 quartz crystal oscillator is undesirable in the present case, since the measurement accuracy can be affected.
[000172] As shown in Figure 9, the quartz crystal oscillator 222 of the present embodiment is tuned in the shape of a fork and comprises a pair of teeth 222a approximately 5 mm in length arranged to oscillate at a resonance frequency of 32.768 kHz. Teeth 222a are formed in the planar section of quartz. The fork teeth 222a oscillate normally in their fundamental mode, in which they move synchronously to and away from each other at the resonance frequency.
[000173] Fused (or non-crystalline) quartz has a very low temperature-dependent coefficient of expansion and a low elasticity coefficient. This reduces the dependence on the fundamental frequency of the temperature and, as will be shown, the effects of the temperature are minimal.
[000174] In addition, it is desirable to use quartz, which is AT cut or SC cut. In other words, the planar section of quartz is cut at specific angles, so that the temperature coefficient of the oscillation frequency can be arranged so as to be parabolic with a wide peak close to around room temperature. Therefore, the crystal oscillator can be arranged in such a way that the slope at the top of the peak is precisely zero.
[000175] These quartz crystals are commonly available at a relatively low cost. In contrast to most quartz crystal oscillators, which are used in a vacuum, in the present embodiment the quartz crystal oscillator 222 is exposed to gas under pressure in conduit 208.
[000176] The drive circuit 224 for driving the quartz crystal oscillator 222 is shown in Figure 9. The drive circuit 224 must meet a series of specific criteria. First, the quartz crystal oscillator 222 of the present invention can be exposed to a range of gas pressures; potentially, pressures can range from atmospheric pressure (when gas cylinder 100 is empty) to about 900 bar g, if the gas cylinder contains a pressurized gas such as hydrogen. Thus, the 222 quartz crystal oscillator is required to operate (and restart after a period of non-use), under a wide range of pressures.
[000177] Therefore, the quality factor (Q) of the 222 quartz crystal oscillator will vary considerably during use. The Q factor is a dimensionless parameter related to the damping rate of an oscillator or resonator. Equally, it can characterize the bandwidth of a resonator in relation to its central frequency.
[000178] In general, the higher the Q factor of an oscillator, the lower the rate of energy loss in relation to the stored energy of the oscillator. In other words, the oscillations of a high oscillator Q factor decrease in amplitude more slowly in the absence of an external force. Sinusoidally driven resonators with higher Q factors resonate with greater amplitudes in the resonance frequency, but have a lower frequency bandwidth around that frequency so that they resonate.
[000179] The drive circuit 224 must be able to drive the 222 quartz crystal oscillator, despite the change in Q factor. As the pressure in the gas cylinder 100 increases, the oscillator of the 222 quartz crystal oscillator. it will become more and more dampened, and the Q factor will fall. The falling Q factor requires a greater gain to be provided by an amplifier in the drive circuit 224. However, if it is too high an amplification is provided, the drive circuit 224, the response from the quartz crystal oscillator 222 can become difficult to distinguish. In this case, the drive circuit 224 can simply oscillate with an unrelated frequency, or the frequency in a non-fundamental way of the quartz crystal oscillator 222.
[000180] As an additional limitation, the drive circuit 224 must be of low power, in order to work with small low power batteries for a long time, with or without supplementary power, such as photovoltaic cells.
[000181] The drive circuit 224 will now be described with reference to Figure 9. In order to drive the quartz crystal oscillator 222, the drive circuit 224 essentially takes a voltage signal from the quartz crystal oscillator 222, amplifies it, and feeds the signal back to the quartz crystal oscillator 222. The fundamental resonance frequency of the quartz crystal oscillator 222 is, in essence, a function of the rate of expansion and contraction of the quartz. This is determined, in general, by the cut and size of the crystal.
[000182] However, external factors also affect the resonance frequency. When the energy of the generated output frequencies corresponds to the losses in the circuit, an oscillation can be sustained. The drive circuit 224 is arranged to detect and maintain this oscillation frequency. The frequency can then be measured by the microprocessor 238, used to calculate the proper gas property required by the user and, if necessary, the output to an appropriate visualization medium (as will be described later).
[000183] Drive circuit 224 is powered by a 6 V 228 battery. Battery 228, in this mode, comprises a lithium battery. However, alternative sources of energy will be readily apparent to the person skilled in the art; for example, other types of rechargeable and non-rechargeable batteries and an array of solar cells.
[000184] Drive circuit 224 further comprises a common emitter amplifier of Darlington pair 250. A Darlington pair comprises a composite structure consisting of two bipolar NPN transistors configured in such a way that the current amplified by a first of the transistor is amplified even more per second. This configuration allows a higher current gain to be obtained when compared to each transistor being taken separately. Alternative PNP bipolar transistors can be used.
[000185] A pair of Darlington 250 is arranged in a feedback configuration from a single common emitter amplifier transistor (T1) 252. A bipolar junction NPN transistor is shown in Figure 7. However, the person skilled in the art would be aware of alternative transistor arrangements that can be used; for example, a PNP bipolar junction transistor or Metal Oxide Semiconductor Field Effect Transistors (MOSFETs).
[000186] Drive circuit 224 comprises another transistor follower of NPN T2 emitter that acts as a buffer amplifier 254. The buffer amplifier 230 is arranged to function as a buffer between the circuit and the external environment. However, this feature is optional and may not be mandatory; for example, a FET can be directly connected to drive circuit 220.
[000187] A capacitor 256 is located in series with the quartz crystal oscillator 222. Capacitor 232, in this example, has a value of 100 pF and allows the drive circuit 224 to trigger the quartz crystal oscillator 222 in situations where the crystal has been contaminated, for example, salts or other deposited materials.
[000188] In addition, drive circuit 224 can be optimized for the quick start of quartz crystal oscillator 222. In order to achieve this goal, another additional resistor and capacitor can be connected between the base of transistor D1 and ground. These components can comprise, for example, a 10 MQ resistor and a 10 nF capacitor.
[000189] An alternate drive circuit 240 will now be described with reference to Figure 10. Drive circuit 240 can be used in place of drive circuit 204 described above. In contrast to drive circuit 204 described above, drive circuit 240 includes a common metal oxide semiconductor field effect transistor amplifier (MOSFET) drain 242 instead of the Darlington pair of the circuit in Figure 9. MOSFET 242 functions as a high impedance input that allows the input impedance of the amplifier stage to be compensated with the high impedance of the 202 quartz crystal oscillator. In other words, MOSFET 242 provides a unit gain with a high input impedance for reduce the electrical charge on the 202 quartz crystal oscillator.
[000190] The output of the 242 common drain MOSFET amplifier is fed to two successive single transistors (Q2, Q3) 244 common emitter amplifiers. The resistors R6 and R8 provide negative feedback and current bias to the transistors. The common emitting amplifiers 244 provide a high gain to amplify the oscillations of the quartz crystal oscillator 202 and, in this embodiment, comprise bipolar junction NPN transistors. However, the person skilled in the art would be aware of alternative transistor arrangements that can be used; for example, a bipolar or MOSFET PNP junction.
[000191] A capacitor 246 is connected between the 202 quartz crystal oscillator and the ground. Capacitor 246, in this mode, is operable to increase the unit for the quartz crystal oscillator 202.
[000192] A resistor 248 is connected in series with the quartz crystal oscillator 202. Resistor 248, in this modality, has a value of 56 kQ and dampens oscillations of quartz crystal oscillator 202, in order to allow the circuit oscillates over a wide range of pressures with only gradual changes in the waveform.
[000193] Drive circuit 240 is powered by a 3 V 249 battery. Battery 249, in this mode, comprises a lithium battery. However, alternative energy sources will be readily apparent to the person skilled in the art; for example, other types of rechargeable and non-rechargeable batteries and an array of solar cells. Alternatively, an electrical supply arrangement can be used after DC rectification and appropriate voltage reduction.
[000194] An alternate drive circuit 260 will now be described with reference to Figure 11. The drive circuit shown in Figure 8 is configured similarly to a Pierce oscillator. Pierce oscillators are known from digital IC clock oscillators. In essence, the drive circuit 260 comprises a single digital inverter (in the form of a transistor) T, three resistors R1, R2 and Rs, two capacitors C1, C2, and the quartz crystal oscillator 222 (or oscillator 230).
[000195] In this arrangement, the 222 quartz crystal oscillator functions as a highly selective filter element. Resistor R1 acts as a load resistor for T transistors. Resistor R2 acts as a bias feedback resistor, the T inverter in its linear region of operation. This effectively allows the T inverter to function as a high-gain inversion amplifier. Another resistance Rs is used between the output of the T converter and the quartz crystal oscillator 222 to limit the gain and to dampen unwanted oscillations in the circuit.
[000196] The quartz crystal oscillator 222, in combination with C1 and C2 forms a P1 network bandpass filter. This allows for a 180 degree phase shift and voltage gain from the output to the input at approximately the resonance frequency of the 222 quartz crystal oscillator. The drive circuit described above 260 is reliable and inexpensive to manufacture, since which comprises relatively few components. This circuit is also especially applicable to low pressure applications.
[000197] As discussed above, the sensor assembly 204 can include a microprocessor 238 that receives inputs from the quartz crystal oscillator 222 and drive circuit 224. The microprocessor 238 can comprise and arrange properly, such as an ASIC or FPGA. The microprocessor 238 is programmed to calculate and, if necessary, present and communicate the determination of the mass flow rate of the gas through the orifice 216.
[000198] When used with the quartz crystal oscillator 222, the microprocessor 238 can be configured to measure the frequency f or period of the drive circuit signal 224. This can be achieved, for example, by counting oscillations over time fixed, and convert that frequency to a density value using an algorithm or a look-up table. This value is transmitted to the microprocessor 238.
[000199] The microprocessor 238 also receives the temperature T measured from the temperature sensor 226. The microprocessor 238 is arranged to perform, based on the inputs provided, a calculation to determine the mass flow of the gas through the orifice 216 .
[000200] Once the mass flow has been determined, this data can be stored in a local memory, can be displayed on a display screen or can be transmitted to a remote station.
[000201] The microprocessor 238 can optionally be designed for mass production to be identical in all 200 meter assemblies, with different characteristics of the software and hardware enabled for different gases.
[000202] In addition, microprocessor 238 can also be configured to minimize energy consumption through the implementation of standby or "standby" modes that can cover microprocessor 238 and additional components, such as drive circuit 224 and crystal oscillator of 222 quartz.
[000203] Various schemes can be implemented; for example, microprocessor 238 can be at rest for 10 seconds every 1 second. In addition, the microprocessor 238 can control the quartz crystal oscillator circuit 222 and drive unit 224 in such a way that these components are put into standby mode most of the time, just exchanging the most energy-hungry components for ^ second every 30 seconds.
[000204] Figure 12 shows a regulator drive circuit 270 suitable for use with the second or third embodiments of the present invention. The drive circuit of regulator 270 is operable to receive an input frequency from the quartz crystal oscillator 222 (and / or the quartz crystal oscillator 230 in the case of the third mode) to a NAND quad gate. The NAND gate also receives a setpoint frequency from an oscillator connected to a voltage regulator. The NAND quad gate functions as an XOR gate.
[000205] The difference between these frequencies is then introduced in a frequency-voltage converter to convert this to a voltage output. The output voltage is then amplified by an amplifier 741 and used to control the position of the solenoid valve 302, in order to maintain the frequency input of the quartz crystal oscillators 222, 230 at the setpoint frequency, as defined by the voltage in the 10K pot shown in Figure 12.
[000206] A method of operating the first embodiment of the present invention will now be described with reference to Figure 13. The method described below is applicable to the first embodiment alone. Step 500: Initialize measurement
[000207] In step 500, the measurement of the mass gas flow through orifice 216 is initialized. This can be activated by, for example, a user pressing a button outside the housing 210. Alternatively, the measurement can be initiated via a remote connection, for example, a signal transmitted over a wireless network and received by mounting meter 200 through an antenna.
[000208] As an alternative, or in addition, the 200 meter assembly can be configured to start up remotely or on a timer. The method proceeds to step 502. Step 502: Activate the quartz crystal oscillators
[000209] Once started, drive circuits 224, 232 are used to drive the respective quartz crystal oscillators 222, 230. During initialization, each drive unit 224, 232 applies a random noise AC voltage throughout respective quartz crystal oscillator 222, 230. At least a portion of said random voltage will be at an appropriate frequency to cause the respective quartz crystal oscillator 222, 230 to oscillate. Each quartz crystal oscillator 222, 230 then begins to oscillate in sync with the respective signal.
[000210] As will be appreciated, quartz crystal oscillators 222, 230 are, in essence, detectors and independent conductors since the resonance frequency of each crystal is itself what is being measured.
[000211] Through the piezoelectric effect, the movement of the quartz crystal oscillators 222, 230 will generate a voltage in the resonance frequency band of the respective quartz crystal oscillator 222, 230. The respective drive circuit 224, 232 in It then amplifies the signal generated by the quartz crystal oscillator 222, 230, such that the signals generated in the frequency quartz crystal resonator band 222, 230 dominate the output of the control circuit 224, 232. The band narrow quartz crystal resonance filters all unwanted frequencies and the drive circuit 224, 230 then drives the respective quartz crystal oscillator 222, 230 at the fundamental resonance frequency f. Once the respective quartz crystal oscillator 222, 230 has stabilized at a particular resonance frequency, the method proceeds to step 504. Step 504: Measure the resonance frequency of the quartz crystal oscillator
[000212] Resonance frequency f is dependent on environmental conditions within the upstream portion 214 of conduit 208. In the present modality, the change in resonance frequency Δf is, for a good approximation, proportional in magnitude to the change in gas density in the upstream part 214 of conduit 208 and will decrease with increasing density.
[000213] In order to carry out a measurement, the frequency of the quartz crystal oscillator 222 is measured over a period of approximately 1 s. This is to allow the reading to stabilize and for sufficient swings to be counted to determine an accurate measurement. The frequency measurement is performed on the microprocessor 238. The microprocessor 238 can also record the time, T1, when the measurement was started.
[000214] Once the frequency has been measured, the method proceeds to step 506. Step 506: Measure the temperature of the gas
[000215] In step 506, the temperature sensor measures the temperature 226 of the gas within the upstream part 214 of conduit 208. This measurement is necessary in order to accurately determine the speed of sound in the gas flow.
[000216] As previously described, the temperature measurement need not be particularly accurate. For example, if the 226 temperature sensor is accurate at 0.5 ° C, then this corresponds to an error of only about one part in twelve hundred on the absolute value of the temperature required for calculating the speed of sound. .
[000217] Alternatively, this step may simply involve a fixed temperature value to be entered into the microprocessor 238. This can occur, for example, in situations where a known temperature environment is used, or where a high temperature is not required degree of accuracy. In this case, the 226 temperature sensor is not necessary. Step 508: Determine the mass flow of gas
[000218] This is done using equation 8) above, where the density pi of the gas upstream of the orifice 216, the density p2 of the gas downstream of the orifice 216 and, optionally, the temperature T of the gas are known. Thus, knowing the resonance frequencies, as measured in step 504, the (optional) gas temperature T measured in step 406, an accurate measurement of the mass flow through orifice 2i6 can be performed. This applies even if the blocked flow condition (established in equation 7)) is not met because it can be used upstream and downstream of the densities. The method then proceeds to step 510.
[000219] Alternatively, mass flow measurement can be done using equation 7) for flow restriction conditions, where the pi density of the gas upstream of orifice 216 and, optionally, the gas temperature T is known . Therefore, knowing the resonance frequency of the quartz crystal oscillator 222, as measured in step 504, the known (optional) gas temperature T measured in step 406, a measurement of the flow mass Q, through orifice 216 can be done. In addition, the measurement of the gas density p2 of the gas downstream of the orifice 216 by the quartz crystal oscillator 230 can then also be used to provide an indication of the accuracy of the measurement made by the quartz crystal oscillator 222. The method then proceeds to step 510. Step 510: Communicate and store results
[000220] The mass flow rate of the gas can be presented in a number of ways. For example, a screen (not shown) attached to housing 210, body 202 or regulator 150, 300 can display the mass flow rate of the gas through the orifice 216 (and, as a consequence, the mass flow rate of gas exiting the coupling 160). Alternatively, the mass flow measurement could be remotely communicated to a base station or to a meter located on an adjacent fitting, as will be described later.
[000221] As yet an additional alternative, the mass flow rate of gas at time T1 can be stored in a local memory for said microprocessor 238 to generate a time record.
[000222] As stated above, in the alternative mode, a warning message may be presented to the user to indicate that the mass flow rate as a measure may be inaccurate because the flow rate is too low for a blocked flow condition to exist through orifice 216 .
[000223] The method then proceeds to step 512. Step 512: Disconnect sensor assembly
[000224] It is not necessary to keep the 200 meter assembly operational at all times. On the contrary, it is beneficial to reduce energy consumption by turning off the 200, 350 meter assembly when not in use. This extends the life of the 228 battery.
[000225] The configuration of the drive circuit 224 allows the quartz crystal oscillator 222 to be restarted, regardless of the pressure of the upstream portion 214 of the conduit 208. Therefore, the meter assembly 200, 350 can be turned off as and when necessary in order to save battery power.
[000226] A method of operating the second and third embodiments of the present invention will now be described with reference to Figure 14. The method described below is applicable to the second and third embodiments alone. Step 600: Initialize the measurement
[000227] In step 600, the measurement of the mass gas flow through orifice 216 is initialized. This can be activated by, for example, a user pressing a button outside the housing 210. Alternatively, the measurement can be initiated via a remote connection, for example, a signal transmitted over a wireless network and received by controller 350, 450 through an antenna.
[000228] At this time, a desired mass flow of particular gas is introduced by the user. This is then stored by controller 350, 450 and regulator drive circuit 270 programmed appropriately to achieve a specified setpoint frequency of quartz crystal oscillator 222 (quartz crystal and oscillator 230 in the case of the third mode) and to maintain the quartz crystal oscillator 222 at that particular frequency, in order to maintain a determined gas flow.
[000229] Alternatively, or in addition, controllers 350, 450 can be configured to start up remotely or by a timer. The method proceeds to step 602. Step 602: Activate the quartz crystal oscillators
[000230] Once started, the drive circuit 224 is used to drive the quartz crystal oscillator 222. In the case of the second mode, the drive circuit 232 is also used to drive the quartz crystal oscillator 230. During initialization, each drive circuit 224, 232 applies an alternating voltage of random noise between the respective quartz crystal oscillators 222, 230. At least a portion of said random voltage will be at an appropriate frequency to cause the respective crystal oscillator quartz 222, 230 oscillate. Each quartz crystal oscillator 222, 230 then begins to oscillate in sync with the respective signal.
[000231] As will be appreciated, quartz crystal oscillators 222, 230 are, in essence, detectors and independent conductors since the resonance frequency of each crystal is itself being measured.
[000232] By means of the piezoelectric effect, the movement of the quartz crystal oscillators 222, 230 will generate a voltage in the resonance frequency band of the respective quartz crystal oscillator 222, 230. O, or the respective drive circuit 224, 232 then amplifies the signal generated by the quartz crystal oscillator 222, 230, such that the signals generated in the frequency band of the quartz crystal resonator 222, 230 dominate the output of the drive circuit 224, 232. A narrow quartz crystal resonance band filters all unwanted frequencies and drive unit 224, 230, then drives the respective quartz crystal oscillator 222, 230 at the fundamental f resonance frequency. Once the respective quartz crystal oscillator 222, 230 has stabilized at a particular resonance frequency, the method proceeds to step 604. Step 604: Measure the resonance frequency of the quartz crystal oscillators
[000233] Resonance frequency f is dependent on environmental conditions within the upstream portion 214 of conduit 208. In the present modality, the change in resonance frequency Δf is, for a good approximation, proportional in magnitude to the change in density of the gas in the upstream portion 21 of conduit 208 (for quartz crystal oscillator 222) and will decrease with increasing density. The same applies to the 230 quartz crystal oscillator in the case of the third modality.
[000234] In order to perform a measurement, the frequency of or each quartz crystal oscillator 222, 230 is measured over a period of approximately 1 s. This is to allow the reading to stabilize and sufficient swings to be counted to determine an accurate measurement. The frequency measurement is performed on the microprocessor 238. The microprocessor 238 can also record the time, T1, when the measurement was started.
[000235] Once the frequency has been measured, the method proceeds to step 606. Step 606: Measure the temperature of the gas
[000236] In step 606, the temperature sensor measures the temperature 226 of the gas within the upstream part 218 of conduit 208. This measurement is necessary in order to accurately determine the speed of sound in the gas flow. Step 608: Maintain feedback loop
[000237] Controller 350, 450 can be operated to maintain a feedback cycle according to equation 11) above; that is, using the oscillation frequency of the quartz crystal oscillator 222 (or equation 13), if the third modality is used, including the oscillator 230, if desired) to achieve a particular mass flow.
[000238] In other words, the ratio of the pi density of the gas upstream of the orifice 216 divided by the square root of the temperature T (in the second embodiment), or a function of the pi density of the gas upstream of the orifice 216 and the density p2 of the gas downstream of orifice 2i6 divided by the square root of temperature T (in the third embodiment) is used to allow a proportional gas flow to be generated.
[000239] Therefore, the resonance frequency of quartz crystal oscillator 222 (or a function of oscillator 222 and oscillator 230 in the third mode) divided by the square root of a signal proportional to temperature can be maintained at a predetermined value by proportional opening / closing solenoid valve 302 to maintain a steady flow of gas through orifice 216. Step 610: Communicate and store results
[000240] A user can specify a particular mass flow rate of the gas. Therefore, as long as this condition is met, no further display is required. However, optionally, the current mass flow of the gas can be presented in a number of ways. For example, a screen (not shown) attached to housing 210, body 202 or regulator 150, 300 can display the mass flow rate of the gas through the orifice 216 (and, as a consequence, the mass flow rate of gas exiting the coupling 160). Alternatively, the mass flow measurement could be remotely communicated to a base station or to a meter located on an adjacent fitting, as will be described later.
[000241] As yet an additional alternative, the mass flow rate of gas at time T1 can be stored in a local memory for said microprocessor 238 to generate a time record.
[000242] As stated above, in the alternative mode, a warning message may be presented to the user to indicate that the mass flow rate as a measure may be inaccurate because the flow rate is too low for a blocked flow condition to exist through orifice 216 .
[000243] The variations of the above modalities will be evident to the person skilled in the art. The exact configuration of the hardware and software components may be different and still be within the scope of the present invention. The specialist would be readily aware of alternative configurations that can be used.
[000244] For example, the modalities described above used a quartz crystal oscillator, having a fundamental frequency of 32.768kHz. However, crystals that operate at alternative frequencies can be used. For example, quartz crystal oscillators that operate at 60 kHz and 100 kHz can be used with the modalities described above. A graph showing the change in frequency with the density of different crystals is shown in Figure 15. As an additional example, a crystal oscillator that operates at a frequency of 1.8 MHz can be used.
[000245] Higher frequency operation allows the pressure to be monitored more frequently because a short period of time is necessary to prove a certain number of cycles. In addition, higher frequency crystals allow a shorter duty cycle to be used in a crystal “standby” mode. As an explanation, in most cases, the crystal circuit and unit will spend most of the time switched off, only being switched on for a second or so, when a measurement is necessary. This can happen, for example, once a minute. When a higher frequency crystal is used, the pressure can be measured faster. Therefore, the time in which the crystal is operational can be. This can reduce power consumption and, at the same time, improve battery life.
[000246] In addition, the above modes have been described by measuring the absolute frequency of a quartz crystal oscillator. However, self-contained electronics incorporated in an associated gas cylinder regulator, can advantageously measure the change in sensor frequency by comparing that reference frequency with a crystal of the same type, but closed in a vacuum or pressure package. The package can contain the gas pressure at a selected density, the gas in atmospheric conditions or it can be opened to the outside atmosphere of the gas cylinder.
[000247] A suitable sensor assembly 700 is shown in Figure 16. The sensor assembly 700 comprises a first quartz crystal oscillator 702 and a second quartz crystal oscillator 704. The quartz crystal oscillator 702 is first a reference crystal that is located inside a vacuum-sealed 706 container. The first 702 quartz crystal oscillator is driven by a 708 drive circuit.
[000248] The second quartz crystal oscillator 704 is a crystal similar to crystal 222 described in the previous embodiments. The second quartz crystal oscillator 704 is exposed to the gas environment inside housing 210. The second quartz crystal oscillator 704 is driven by a drive circuit 710.
[000249] This comparison can be performed using an electronic mixer circuit 712 that combines the two frequency signals and produces an output with a frequency equal to the difference between the two crystals. This arrangement allows small changes in the sequence of, for example, temperature to be negated.
[000250] In addition, the circuits used in the assembly of sensor 204 can be simplified, because it is only necessary that the difference frequency be measured. In addition, this approach is particularly suitable for use with a high frequency (MHz) crystal oscillator, where it can be difficult to directly measure the frequency of the crystal.
[000251] In addition, all electronic components necessary to measure and indicate density, mass or mass flow do not need to be mounted on or inside the gas cylinder. For example, electronic functions could be divided between units mounted on the cylinder permanently and units mounted on the station of use or from a customer or temporarily mounted on the outlet of the cylinder, as the position normally used for a conventional flow meter.
[000252] An example of this arrangement is shown with reference to figure 17. The arrangement comprises a gas cylinder assembly 80 comprising a gas cylinder 800, an regulator 802 and a mass flow meter 804. The gas cylinder 800 , regulator 802 and a mass flow meter 804 are substantially similar to those of gas cylinder 100, regulator 150 and meter assembly 200 or controller 350, 450, substantially as previously described with reference to the previous embodiments.
[000253] In this modality, the mass flow meter 804 comprises a quartz crystal oscillator and the drive circuit (not shown) similar to the quartz crystal oscillator 222 and drive circuit 224 of the previous modalities. An antenna 806 is provided for communication via any communication protocol at the appropriate distance; for example, Bluetooth, infrared (IR) or RFID. Alternatively, wired communication can be used.
[000254] As an additional alternative, acoustic communication methods can be used. The advantage of such methods is that remote communication can be carried out without the need for an external antenna.
[000255] A connection pipe 808 is connected to the outlet of the gas cylinder 800. The connection pipe is terminated by a quick connection connection 810. The quick connection connection 810 allows to connect the hose or components to be connected and disconnected with ease and speed of the gas cylinder 800.
[000256] A quick connect unit 850 is provided for connection to gas cylinder 800. A complementary quick connect connector 812 is provided for connection to connector 808. In addition, the quick connect unit 850 is equipped with a data 852. The data unit 852 comprises a display 854 and an antenna 856 for communication with the antenna 804 of the gas cylinder assembly 80. The display 854 may comprise, for example, an LCD, LED or display readable by the para light. minimize energy consumption and maximize the visibility of the display.
[000257] The data unit 852 can record various parameters as measured by the sensor assembly 802 of the gas cylinder assembly 80. For example, the data unit 852 can record the mass flow as a function of time. This record can be useful, for example, for welding contractors who want to verify that the gas flow was present and correct during long gas welding procedures on critical components, or to provide an assembly of company data on the use of a particular customer.
[000258] As an alternative, data from data unit 850 can be output to a computer-enabled welding machine (for welding applications) or other gas consuming equipment, to allow calculation of derived parameters, along with messages from Warning.
[000259] In addition, the data unit 850 can be arranged to provide the following functions: providing an audible or visual alarm if the type of gas changes; contain and display data on gas use; providing multimode operation, for example, a supplier / filling mode and a customer mode; to allow data entry; providing data such as the number of cylinders, the type of gas, a certificate of analysis, a history of the customer (who had the cylinder on those dates), safety data and operational tips can be performed in summary form on the cylinder.
[000260] As an alternative, all of the above examples can optionally be transformed, stored or obtained from a system entirely located at (or inside) the gas cylinder 800 or housing 210, as discussed in terms of meter assembly 200 or 350, 450 controllers.
[000261] Although the above modalities have been described with reference to the use of a quartz crystal oscillator, the person skilled in the art would be readily aware of the alternative piezoelectric materials that could also be used. For example, a non-exhaustive list may include crystal oscillators comprising: lithium tantalate, lithium niobate, lithium borate, berlinite, gallium arsenide, lithium tetraborate, aluminum phosphate, germanium bismuth oxide, polycrystalline ceramic zirconium oxide titanate, high alumina ceramic, zinc oxide silicon composite, or dipotassium tartrate.
[000262] Modalities of the present invention have been described with particular reference to the illustrated examples. While specific examples are shown in the drawings and are described in detail here, it should be understood, however, that the drawings and detailed description are not intended to limit the invention to the particular form described. It will be appreciated that variations and modifications can be made to the examples described in the scope of the present invention.

权利要求:
Claims (15)
[0001]
1. METHOD FOR MEASURING THE GAS MASS FLOW OF A GAS THROUGH A HOLE, the method characterized by using a first piezoelectric oscillator (222) in contact with the gas upstream of the orifice and a second piezoelectric oscillator (230) in contact with the gas downstream of the orifice and comprising; a) actuating the first and second piezoelectric crystal oscillators such that each of the first and second piezoelectric crystal oscillators resonates at the respective resonant frequencies; b) measure the resonance frequency of the first piezoelectric oscillator and the resonance frequency of the second piezoelectric oscillator; and c) determine, from the resonance frequency of the first piezoelectric oscillator and the resonance frequency of the second piezoelectric oscillator, the mass flow of gas through said orifice.
[0002]
Method according to claim 1, characterized in that step c) further comprises: d) determining, from the resonance frequency of the first piezoelectric oscillator and the resonance frequency of the second piezoelectric oscillator, the density of the gas upstream of the orifice and the density of the gas downstream of the orifice.
[0003]
Method according to claim 2, characterized in that step c) further comprises: e) determining the relationship between the density of the gas upstream of the orifice and the density of the gas downstream of the orifice.
[0004]
Method according to claim 3, characterized in that when the proportion is equal to or greater than a predetermined value, the flow through said orifice is determined to be blocked and the mass flow is calculated from the density of the gas at orifice amount alone.
[0005]
Method according to claim 3 or 4, characterized in that when the proportion is less than a predetermined value, the mass flow is calculated from the density of the gas upstream of the orifice and from the density of the gas downstream the hole.
[0006]
6. Method according to claim 3 or 4, characterized in that when the proportion is less than a predetermined value, the mass flow is calculated from the density of the gas upstream of the orifice alone and the method further comprises the step of : e) provide a notification that the mass flow determination may comprise errors.
[0007]
Method according to any one of claims 1 to 6, characterized in that the gas is distributed from a pressure regulator or valve located upstream of the piezoelectric crystal oscillator.
[0008]
Method according to claim 7, characterized in that the pressure regulator or valve is controlled electronically in response to the measured mass flow of gas through said orifice (216).
[0009]
9. METER FOR MEASURING A GAS MASS FLOW, the meter characterized by comprising a conduit (208) through which the gas flows in use, the conduit having a flow restriction orifice (216), through which occurs the flow in use, the flow restriction orifice dividing the duct into an upstream portion (218), upstream of said orifice and a downstream portion (220), downstream of said orifice, the meter further comprises an assembly sensor (204, 206) including a first piezoelectric crystal oscillator (222) in said upstream part such that said first piezoelectric oscillator is in contact with said gas when the meter in use, a second piezoelectric crystal oscillator (230) in said downstream part such that said second piezoelectric oscillator is in contact with said gas when the meter is in use, said sensor assembly being arranged: to drive the first and second piezoelectric crystal oscillators of mod the one where each of the first and second piezoelectric crystal oscillators resonates at the respective resonance frequencies; measure the resonance frequency of the first piezoelectric oscillator and the resonance frequency of the second piezoelectric oscillator; and determining, from the resonance frequency of the first piezoelectric oscillator and the resonance frequency of the second piezoelectric oscillator, the mass flow of gas through said orifice.
[0010]
10. The meter according to claim 9, characterized in that the meter also comprises a drive circuit comprising a Darlington pair arranged in a feedback configuration of a common emitter amplifier.
[0011]
11. Meter according to claim 9 or 10, characterized in that it is arranged downstream of a pressure regulator or valve.
[0012]
Meter according to claim 11, characterized in that the meter is arranged to electronically control the pressure regulating valve, or in response to the mass flow measured through the flow restriction orifice.
[0013]
Method or meter according to any one of claims 9 to 12, characterized in that said piezoelectric oscillator comprises a quartz crystal oscillator.
[0014]
Method according to any one of claims 1 to 8, or a meter according to any one of claims 9 to 13, characterized in that said piezoelectric crystal oscillator comprises at least two planar teeth.
[0015]
15. LEGIBLE MEDIA BY COMPUTER, characterized in that it comprises being adapted to execute the method presented in claims 1 to 8.

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EP2667159B1|2021-12-01|

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KR20150008450A|2015-01-22|

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BR112014029056A2|2017-06-27|

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法律状态:
2018-12-04| B06F| Objections, documents and/or translations needed after an examination request according [chapter 6.6 patent gazette]|

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2020-02-18| B06U| Preliminary requirement: requests with searches performed by other patent offices: procedure suspended [chapter 6.21 patent gazette]|

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2020-07-14| B06A| Patent application procedure suspended [chapter 6.1 patent gazette]|

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2020-11-24| B09A| Decision: intention to grant [chapter 9.1 patent gazette]|

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2021-01-26| B16A| Patent or certificate of addition of invention granted [chapter 16.1 patent gazette]|Free format text: PRAZO DE VALIDADE: 20 (VINTE) ANOS CONTADOS A PARTIR DE 23/05/2013, OBSERVADAS AS CONDICOES LEGAIS. |

优先权:

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申请号 | 申请日 | 专利标题

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EP12169386.5A|EP2667159B1|2012-05-24|2012-05-24|Method of, and Apparatus for, Measuring the Mass Flow Rate of a Gas|

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EP12169386.5|2012-05-24|

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PCT/EP2013/060688|WO2013174956A1|2012-05-24|2013-05-23|Method of, and apparatus for, measuring the mass flow rate of a gas|

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