ASSEMBLY OF SENSORS TO MEASURE PHYSICAL PROPERTIES OF A GAS UNDER PRESSURE WITHIN A GAS CYLINDER COM

专利摘要:
assembly of sensors for measuring physical properties of a gas under pressure within a gas cylinder comprising a gas cylinder body and a valve arrangement defining a fixed internal volume of the gas cylinder, and gas cylinder for containing a gas under pressure. a sensor assembly (200) is provided for measuring the physical properties of a gas under pressure within a pressure vessel (100). the sensor assembly (200) comprises a housing and a piezoelectric oscillator (202) for immersion in the gas within the pressure vessel (100). the sensor assembly (200) is arranged, when immersed in said gas, to measure the density of the gas within the pressure vessel (100). The housing comprises a first chamber and a second chamber. the first chamber is in fluid communication with the second chamber and substantially houses said piezoelectric oscillator. the second chamber is in fluid communication with the interior of the pressure vessel. by providing such an array, the true contents (ie mass) of the fluid in a pressure vessel such as a cylinder can be measured directly and accurately. the housing of the present invention alleviates noise and errors generated by convection currents within a gas cylinder 100, allowing an accurate determination of mass, or rate of change in mass, through direct derivation of the density of the gas in the cylinder.
公开号:BR112014029058B1
申请号:R112014029058-0
申请日:2013-05-23
公开日:2021-06-22
发明作者:Neil Alexander Downie；Clayton Mathew Ludik
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 true contents of a cylinder of gas under pressure. More particularly, the present invention relates to a method of, and apparatus for, accurately measuring the true contents, or rate of change of true contents, of a gas cylinder using a piezoelectric oscillator and housing shield.
[0002] The methods and apparatus described herein can be applied to systems where relatively high pressure gases (for example, about 10 bar or higher) are present, such as, for example, the supply of gases in high pressure or high pressure cylinders. factories that use high pressure gases. The present invention is particularly concerned with "clean" gases, i.e. gases with little or no impurities or contaminants such as water vapor or dust.
[0003] A compressed gas cylinder is a pressure vessel designed to contain gases at high pressures, ie at pressures significantly greater than atmospheric pressure. Compressed gas cylinders are used in a wide range of markets, from the low-cost general industrial market, to the medical market, to high-cost applications such as the manufacture of electronic products that use toxic, high-purity, corrosive specialty gases or pyrophoric. Typically, gas under pressure containers comprise steel, aluminum or composites and are capable of storing compressed liquefied or dissolved gases, with a maximum filling pressure of up to 450 bar g (where bar g is a measure of pressure (in bar) above atmospheric pressure) for most gases, and up to 900 bar g for gases such as hydrogen and helium.
[0004] 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. Examples are argon and nitrogen. However, this should not be taken as limiting and the term gas can be considered to encompass a wider range of gases, for example a permanent gas and a vapor of a liquefied gas. Liquefied gas vapors are present above the liquid in a compressed gas cylinder. Gases that liquefy under pressure as they are compressed to fill a cylinder of gases are not permanent and are more accurately described as liquefied gases under pressure or as liquefied gas vapors. As an example, nitrous oxide is supplied within 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 apt to be liquefied by pressure or temperature around ambient conditions.
[0005] In many cases, it is necessary to control the contents of a particular cylinder or pressure vessel to determine the amount of gas remaining. This is particularly critical in situations such as healthcare applications.
[0006] It is known to calculate, in accordance with gas laws, the true content of a cylinder from knowledge of the gas pressure inside a cylinder. Pressure measurement is a well known technique and there are a variety of devices that work to measure pressure. The more conventional type uses an elastic diaphragm equipped with tension measuring elements. However, despite one of the lowest cost pressure sensors currently made, these sensors tend to be relatively large in size, and have a mechanical structure that despite being produced by mass production methods of photolithography is still relatively complex and expensive to make. They also have a degree of brittleness and require calibration and temperature compensation before they can be used.
[0007] Another measure of pressure used is a Bourdon gauge. Such a meter comprises a fragile, flat, thin-walled, closed-end tube which is connected to the hollow end of a fixed tube containing the pressure of the fluid to be measured. An increase in pressure causes the closed end of the tube to describe an arc. Such a meter comprises delicate components, which are vulnerable to damage caused by, for example, exposure to high pressures.
[0008] A problem that makes it difficult to accurately measure the amount of gas in a gas vessel is the temperature-pressure relationship of the gases contained within the cylinder. According to gas laws, the pressure exerted by a given quantity of gas at constant volume is directly proportional to its temperature. Therefore, as the temperature of a gas increases, so will the pressure of the gas.
[0009] Consequently, measuring pressure using a pressure gauge such as a Bourdon gauge goes up and down proportionally to the absolute temperature, for example, from an initial temperature of 20°C, to, for example , 50°C in a bright environment, the pressure indicated on a Bourdon gauge will increase by 10%.
[00010] An additional problem is that in order to determine the contents of a cylinder using a pressure measurement, the pressure gauge is required to be corrected for the compressibility of the gas. This is complicated because the behavior of a gas at high pressure does not conform to the behavior of an ideal gas.
[00011] An alternative type of device used to measure the physical properties of gases is a piezoelectric device such as a quartz crystal. Quartz crystals demonstrate piezoelectric behavior, that is, applying tension to them results in slight compression or elongation of the solid, and vice versa.
[00012] "A Precise and Robust Quartz Sensor Based On Tuning Fork Technology For (SF6)-Gas Density Control" Zeisel et al., Sensors and Actuators 80 (2000) 233-236 discloses a scheme in which a quartz crystal sensor is used to measure SF6 gas density in high and medium voltage electrical equipment at low gas pressures. Measuring the density of SF6 gas is essential for the safety of the device. This document describes a low pressure application for quartz sensor technology where pressures up to 8 bar g are used.
[00013] The US patent US 4,644,796 discloses a method and an apparatus for measuring the pressure of a fluid through a quartz crystal oscillator housed within a housing of variable volume, comprising a bellows assembly. The internal volume of the housing varies due to compression/expansion of the bellows by external fluid pressure. Therefore, the density of fluid within the housing varies as the internal volume of the housing varies. Density inside the housing can be measured using a quartz crystal oscillator.
[00014] The above arrangements describe the use of a solid state sensor such as a quartz crystal oscillator. However, none of the above provisions and methods are suitable for accurately measuring the mass of gas in a pressure vessel such as a gas cylinder.
[00015] An additional complication with regard to measuring the physical properties of a gas contained in a gas bottle is the movement of the gas inside the cylinder. For example, if the top of a gas cylinder is cold, vigorous convection currents can be set up that can distort measurements of the physical properties of the gas.
[00016] The Grashof number (Gr) is a dimensionless number that approximates the ratio of buoyancy to viscous force acting on a fluid. The value of Gr provides an indication of the probability of convection occurring in particular fluids - the higher the value of Gr, the more likely convection is to occur.
[00017] The Gr value of, for example, argon gas at a pressure of 300 bar g pressure inside a gas cylinder is too large. Argon at such high pressures has a density approaching water, but has a significantly lower viscosity (about fifty times lower than water). Also, argon has a much greater tendency to expand when heated than water. As a result, even small negative temperature gradients (ie where the top of the cylinder is cooler) can trigger strong convection of the gas in the gas cylinder.
[00018] A temperature gradient along the length of a cylinder can occur in a number of circumstances in use. For example, if a cylinder is newly filled, if it is moved between environments at different temperatures, or in a situation where a flow is drawn from a valve connected to the cylinder, the top of the cylinder may be significantly cooler than the volume of the cylinder. The temperature gradient can be many times greater than 10°C and even as high as 30°C. At the moment, Integrated Pressure Reduction Valves (VIPRs) are becoming increasingly popular.
[00019] However, these valves get particularly cold as the gas expands from the storage pressure. Therefore, as a result of these temperature differences, convection will often occur inside a cylinder. Convection occurs in a turbulent manner, with random modulations of density and temperature, such that p ~ 1/T, with almost no change in pressure.
[00020] In general, one approach to measuring the physical properties of a gas inside a cylinder is to place a sensor inside the gas cylinder itself. This allows the sensor to monitor gas properties in the center of the cylinder.
[00021] However, when the flow is drawn from a gas cylinder using a cylinder that has a VIPR, strong convection currents are generated. Convection currents lead to excessive noise when measuring the properties of gases, such as the rate of change in the mass content of a cylinder, making measurement results inaccurate or even meaningless. Therefore, known measurement arrangements suffer from a technical problem that they are unable to provide an accurate measurement of the physical properties of a gas in a container such as a gas cylinder where convection is likely to be encountered.
[00022] According to a first aspect of the present invention, there is provided an assembly of sensors for measuring physical properties of a gas under pressure within a gas cylinder comprising a gas cylinder body and a valve arrangement defining a Fixed internal volume of the gas cylinder, the sensor assembly comprising a housing, a piezoelectric oscillator for immersion in the gas within the gas cylinder, and a drive circuit can be operated to drive the piezoelectric oscillator so that the piezoelectric oscillator resonates at a resonant frequency, the sensor assembly being arranged to determine the density of the gas within the gas cylinder from the resonant frequency of the piezoelectric oscillator, when immersed in said gas, in which, in use, the The housing is located within the fixed internal volume of the gas cylinder and comprises a first chamber and a second chamber, the first chamber being in fluid communication. a with the second chamber and substantially enclosing said piezoelectric oscillator, and the second chamber being in fluid communication with the interior of the gas cylinder.
[00023] The arrangement of the present invention relates to a sensor assembly. The sensor assembly includes a piezoelectric oscillator enclosed within a housing. The housing is a self-contained structure comprising at least two chambers and is arranged to be placed within a pressure vessel such as a gas cylinder. This allows for optimal placement of the sensor assembly inside the pressure vessel, where it can be, for example, spaced from the vessel walls, where temperature variations or boundary layer flux can affect, for example, the density measurement .
[00024] According to an embodiment, a sensor assembly for measuring physical properties of a gas under pressure within a pressure vessel is provided, the sensor assembly comprising a housing and a piezoelectric oscillator for immersion in the gas within of the pressure vessel, the piezoelectric oscillator being arranged, when immersed in said gas, to measure the density of the gas within the pressure vessel, wherein the housing comprises a first chamber and a second chamber, the first chamber in fluid communication with the second chamber and substantially enclosing said piezoelectric oscillator, and the second chamber which is in fluid communication with the interior of the pressure vessel.
[00025] By providing such an arrangement, the actual contents (ie mass) of fluid in a pressure vessel such as a cylinder can be measured directly, without the need to compensate for factors such as temperature or compressibility. The housing of the present invention alleviates noise and errors generated by convective currents within a gas cylinder, allowing an accurate determination of the mass, or mass rate of change, by direct derivation from the density of the gas in the cylinder.
[00026] In addition, the piezoelectric oscillator is a solid state device, which is resistant to high pressures or sudden pressure changes and as such is less likely to become damaged by "strain" pressure, or other environmental factors . The piezoelectric oscillator structure allows the piezoelectric oscillator to be fully immersed in the gas, in contrast to conventional gauges (such as a Bourdon gauge) which require a pressure differential to function.
[00027] In one embodiment, the sensor assembly further comprises a drive circuit operable to drive the piezoelectric oscillator so that the piezoelectric oscillator resonates at a resonant frequency and to measure said resonant frequency over a period of predetermined time to determine the density of the gas in said pressure vessel.
[00028] In one embodiment, the pressure vessel has a fixed internal volume and the sensor assembly is further configured to determine, from the density measurement and the internal volume of said pressure vessel, the mass of the gas inside the vessel depression.
[00029] In one embodiment, the sensor assembly is further arranged to perform repeated measurements of the mass of the gas within the pressure vessel at discrete time intervals, to obtain a plurality of measurements, and to determine from said plurality of measurements, the mass flow of gas to/from the pressure vessel during discrete time intervals.
[00030] In one modality, the discrete time intervals are on the order of seconds.
[00031] In one modality, numerical filtering is applied to said measurements.
[00032] In one embodiment, the first chamber has a wall comprising a first opening that allows fluid communication between the first and second chambers, and the second chamber has a wall comprising a second opening to allow fluid communication between the second chamber and the interior volume of the pressure vessel.
[00033] In one embodiment, the first and/or second opening has dimensions less than or equal to 0.35 mm.
[00034] In one embodiment, the first and/or second opening has dimensions less than or equal to 0.22 mm.
[00035] In one embodiment, the housing is substantially cylindrical.
[00036] In one embodiment, the housing has a length of 230 mm or less.
[00037] In one embodiment, the housing has a length of 80 mm or less.
[00038] In one embodiment, said piezoelectric oscillator comprises a quartz crystal oscillator.
[00039] According to a second aspect of the present invention, there is provided a gas cylinder for containing a gas under pressure, the gas cylinder comprising: a gas cylinder body defining a fixed internal volume; a valve arrangement connected to said gas cylinder body and arranged to permit selective filling of the gas cylinder with gas or dispensing gas from said gas cylinder; and mounting the first aspect sensor.
[00040] According to an embodiment, there is provided a pressure vessel for containing a gas under pressure, the pressure vessel having a fixed internal volume and comprising: a pressure vessel body defining a fixed internal volume; a valve arrangement connected to said vessel body and arranged to permit selective filling of the pressure vessel with gas or dispensing gas from said vessel; and mounting the first aspect sensor.
[00041] In one embodiment, the sensor assembly is located entirely within the fixed internal volume of the pressure vessel.
[00042] In one embodiment, the pressure vessel is shaped like a gas cylinder.
[00043] According to a third aspect of the present invention, there is provided a method for measuring the mass of a gas under pressure, using a sensor assembly comprising a piezoelectric oscillator and a housing, said gas being contained within a vessel with a fixed internal volume, the piezoelectric oscillator being immersed in the gas within the pressure vessel, the housing comprises a first chamber and a second chamber, the first chamber in fluid communication with the second chamber and substantially enclosing said piezoelectric oscillator, and the second chamber being in fluid communication with the interior of the pressure vessel, the method comprising: a) using said piezoelectric oscillator to measure the density of the gas within the high pressure vessel; b) determining, from the measurement of density and the internal volume of said pressure vessel, the mass of the gas inside the pressure vessel.
[00044] By providing such a method, the true contents (ie mass) of gas (as a standing gas) in a pressure vessel such as a cylinder can be measured directly, without the need to compensate for factors such as temperature or the compressibility. This allows a mass determination by direct derivation from the gas density in the cylinder, reducing the need for additional sensors or complex compensations and approximations to be performed. Furthermore, the piezoelectric oscillator is a solid state device, which is resistant to high pressures, sudden pressure changes or other environmental factors. The piezoelectric oscillator is operable to be entirely immersed in the gas, in contrast to conventional gauges (such as a Bourdon gauge) which require a pressure differential in order to function.
[00045] In one embodiment, step a) comprises: driving, by means of a drive circuit, the piezoelectric oscillator so that the piezoelectric oscillator resonates at a resonant frequency; and measuring said resonant frequency over a predetermined period of time to determine the density of the gas in said high pressure reservoir.
[00046] In one embodiment, steps a) and b) are repeated one or more times so that a series of measurements of the density of the gas inside the pressure vessel over a period of time is obtained, said series of measurements be used to determine the change in the mass of gas within the pressure vessel during said period of time.
[00047] In one embodiment, said piezoelectric oscillator comprises a quartz crystal oscillator.
[00048] In one embodiment, the quartz crystal comprises at least one tooth. In a variation, the quartz crystal comprises a pair of planar teeth.
[00049] In one modality, the quartz crystal is AT cut or SC cut.
[00050] In a variation, the surface of the quartz crystal is directly exposed to the gas.
[00051] In one modality, the sensor assembly comprises a drive circuit. In a variation, the sensor assembly comprises a drive circuit comprising a Darlington pair arranged in a feedback configuration of a common emitter amplifier.
[00052] In one embodiment, the sensor assembly comprises a power source. In one arrangement, the power source comprises a lithium ion battery.
[00053] In one embodiment, the sensor assembly comprises a processor.
[00054] In one embodiment, the pressure vessel comprises a high pressure vessel. A high pressure vessel is a vessel arranged to withstand internal pressures generally in excess of 10 bar.
[00055] In a variation, the pressure vessel comprises a gas cylinder.
[00056] In a variation, said piezoelectric oscillator comprises a quartz crystal oscillator.
[00057] In a variation, the gas is a permanent gas.
[00058] In one arrangement, the high pressure reservoir is a gas cylinder.
[00059] In one embodiment, the sensor assembly comprises a drive circuit. In one embodiment, the sensor assembly comprises a drive circuit comprising a Darlington pair disposed in a feedback configuration of a common emitter amplifier.
[00060] In one embodiment, the sensor assembly comprises a power source. In one arrangement, the power source comprises a lithium ion battery.
[00061] In one embodiment, the sensor assembly comprises a processor.
[00062] In one embodiment, the sensor assembly is arranged to drive the piezoelectric oscillator so that the piezoelectric oscillator resonates at a resonant frequency and to measure said resonant frequency over a predetermined period of time, to determine the density of the gas in said pressure vessel.
[00063] In one embodiment, the sensor assembly is further arranged to perform repeated measurements of the mass of the gas within the pressure vessel at discrete time intervals, to obtain a plurality of measurements, and to determine from said plurality measurements, the mass flow of gas to/from the pressure vessel during discrete time intervals, more often so that a series of gas density measurements within the pressure vessel over a period of time is obtained, said series of measurements being used to determine the change in the mass of gas within the pressure vessel during said period of time.
[00064] According to a fourth aspect of the present invention, there is provided a valve arrangement comprising assembling the sensor of the first aspect, the valve arrangement being for connection to a pressure vessel body to form the pressure vessel with a fixed internal volume, the valve arrangement arranged to permit selective filling of the pressure vessel with gas or dispensing gas from the pressure vessel.
[00065] In one modality, the sensor assembly comprises a drive circuit. In one embodiment, the sensor assembly comprises a power source. In one variation, the power source comprises a lithium ion battery.
[00066] In one embodiment, the sensor assembly is located entirely within the fixed internal volume of the pressure vessel.
[00067] In one arrangement, the pressure vessel body comprises a gas cylinder.
[00068] According to a fifth embodiment of the present invention, there is provided a computer program product executable by a programmable processing apparatus, comprising one or more portions of software for performing the steps of the third aspect.
[00069] According to a sixth embodiment of the present invention, there is provided a computer-usable storage medium having a computer program product, according to the fifth aspect stored therein.
[00070] Embodiments 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 assembly; Figure 2 is a schematic diagram showing an upper part of the gas cylinder assembly in accordance with an embodiment of the invention; Figure 3a is a schematic diagram showing the housing of the sensor assembly of the embodiment of Figure 2; Figures 3b to 3f are schematic diagrams showing alternative variations of housing suitable for use with the sensor assembly of the embodiment of Figure 2; Figure 4 is a schematic diagram of a drive circuit for use with embodiments of the invention; Figure 5 is a schematic diagram showing an alternative drive circuit for use with embodiments of the invention; Figure 6 is a schematic diagram showing another alternative drive circuit for use with embodiments of the invention; Figure 7 shows a graph of quartz crystal frequency (kHz) on the Y axis versus density (kg/m3) for a number of different gases; Figure 8 shows a graph of gas mass (in kg) on the Y axis versus pressure (bar g) on the X axis for argon, oxygen, and an argon:carbon dioxide mixture; Figure 9 shows a graph of gas mass (in kg) on the Y axis versus density (in kg/m3) on the X axis, with the same three gases (argon, oxygen and a mixture of argon: Carbon Dioxide) , as shown in Figure 7; Figure 10 shows a graph of frequency (in kHz) on the Y axis versus time (in minutes) on the X axis for a flow rate of 12 1/min from a 50 liter gas cylinder at a pressure of 100 bar g; Figure 11 shows a graph of the calculated flow (in liters per minute) on the Y axis as a function of time (in minutes) on the X axis for the 50 liter cylinder at a pressure of 100 bar g; Figure 12 shows a graph of frequency (in kHz) on the Y axis versus gas cylinder mass (in kg) on the X axis for a typical gas cylinder; Figure 13 is a graph of flow (in liters/minute divided by two) as a function of time (on the X axis), in seconds, for a flow measurement using a quartz crystal oscillator without a housing; Figure 14 is a graph of flow (in liters/minute divided by two) as a function of time (on the X axis), in seconds, for a flow measurement using a quartz crystal oscillator, surrounded by a housing, according to the first modality; Figure 15 is a graph of flow (in liters/minute divided by two) as a function of time (on the X axis), in seconds, for a flow measurement using a quartz crystal oscillator, surrounded by a housing, according to the first modality (squares) and for the same data passed through a numerical filter (diamonds); Figure 16 is a flowchart illustrating method, according to a described embodiment; Figure 17 shows a graph of the behavior of different types of frequency crystals; Figure 18 is a schematic diagram showing an alternative sensor assembly comprising two quartz crystals; and Figure 19 shows an alternative assembly that utilizes an electronic remote data unit. Figure 1 shows a schematic view of a gas cylinder assembly 10, in accordance with an embodiment of the invention.
[00071] The gas cylinder assembly 10 comprises a gas cylinder 100 having a gas cylinder body 102 and a gas cylinder valve 104. The body 102 comprises a generally cylindrical vessel having a flat base 102a arranged to allow the gas cylinder 100 to be supported on a flat surface.
[00072] The gas cylinder body 102 is formed from steel, aluminum and/or composite materials 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 the base 102a and comprises a screw thread (not shown) adapted to receive the valve 104.
[00073] The gas cylinder body 102 and valve 104 define a pressure vessel (in this embodiment, in the form of gas cylinder 100) having an internal volume V. The internal volume V is fixed. This is to say that the structure of the gas cylinder 100 is such that the internal volume V of it (and, concomitantly, the volume of a gas contained therein) cannot be assumed to vary, to a significant degree, in use, storage or depending on environmental conditions such as temperature, pressure and humidity. The internal volume V of the gas cylinder 100 is intended to include the entire volume within the body of the gas cylinder 102 and the valve 104. In other words, the internal volume V is the total internal volume within the cylinder assembly. gas 10, where the gas is kept under pressure.
[00074] Any suitable fluid may be contained within the gas cylinder assembly 100. However, the present embodiment refers to, but is not limited exclusively to, permanent purified gases that are free of impurities such as dust and/or moisture . Non-exhaustive examples of such gases could be: oxygen, nitrogen, argon, helium, hydrogen, methane, nitrogen trifluoride, carbon monoxide, carbon dioxide, krypton, neon or mixtures thereof (eg argon and carbon dioxide).
[00075] 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 connect to other components of a gas assembly; for example, hoses, tubes or other pressure valves or regulators. Valve 104 can optionally include a VIPR (valve with integrated pressure regulator).
[00076] The valve body 112 can be adjusted axially towards 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 the valve seat 112 selectively controls the area of the communication passage means between the interior of the gas cylinder body 102 and the outlet 110. This, in turn, controls the flow of gas from the inside of the 100 gas cylinder assembly to the outside environment.
[00077] A through hole 118 is formed in the housing 108 downstream of the outlet 110. The through hole 118 is closed by means of a conductor 120 that allows the components (such as wires) to be fed through the external gas cylinder 100 to the interior of gas cylinder 100. Conductor 120 functions as a high pressure seal to maintain the integrity of gas cylinder 100.
[00078] The gas cylinder assembly 10 is provided with a sensor assembly 200. The sensor assembly 200 is arranged to measure the density of gas within the internal volume V of the gas cylinder 100. The sensor assembly 200 is shown in Figure 2 and comprises a quartz crystal oscillator 202 connected to a drive circuit 204 and a battery 206 by appropriate wiring. A processor 220 (not shown in Figure 2) may also be provided, either separately or as part of the drive circuit 204. This will be described later.
[00079] In the embodiment of Figure 2, the entire sensor assembly 200 is located within the internal volume V of the gas cylinder 100. Therefore, the quartz crystal oscillator 202, the drive circuit 204 (and the processor 220, if provided) and battery 206 are all located within the internal volume V of gas cylinder 100. The components of the sensor assembly 200 are completely immersed in the gas and are under isostatic gas pressure within the gas cylinder 100. Consequently, the sensor assembly 200 experiences the full gas pressure of the gas within the gas cylinder 100.
[00080] As shown in Figure 2, the sensor assembly 200 can be connected to an antenna 230 for remote communication with, for example, a base station. This will be discussed later. In this case, the antenna 230 can be located outside the gas cylinder 100 and connected to the sensor assembly via a wire connector or equivalent. The wire can be passed through the conductor 120 so as to make a connection between the antenna 230 and the sensor assembly 200.
[00081] The antenna 230 itself can be adapted and arranged to use any appropriate communication protocol; for example, a non-exhaustive list might be RFID, Bluetooth, Infrared (IR), 802.11 wireless, frequency modulation (FM) broadcast, or a cellular network.
[00082] Alternatively, one-wire communication can be implemented. A wired communication needs only a single metallic driver to communicate: the "return" path of the circuit is provided via capacitive coupling through the air between the communication devices. The skilled person would be readily aware of antenna 230 alternatives (and associated transmission hardware) that could be used with the modalities discussed herein.
[00083] The inventors have discovered that only a few components of the sensor 200 assembly are sensitive to high pressure. In particular, larger components such as batteries can be susceptible to high pressures. However, it has been found that lithium ion batteries perform particularly well under the high pressures found within gas cylinder 100. Therefore, battery 206 comprises lithium ion cells. However, suitable alternative energy sources would readily be contemplated by the qualified person.
[00084] The location of the complete sensor assembly 200 entirely within the gas cylinder 100 provides additional flexibility when configuring gas cylinders 100. In particular, the location of relatively fragile electronic components entirely within the strong metal or composite walls of the cylinder 100 gas provides considerable protection from environmental or accidental damage. This is particularly important, for example, in storage areas or warehouses, where gas cylinders 100 are located adjacent to other gas cylinders 100, heavy machinery or rough surfaces.
[00085] In addition, locating the sensor assembly electronics completely within the internal volume V of the gas cylinder 100 allows larger components to be supplied otherwise which may not be suitable for use on the outer surface of a cylinder 100. For example, a larger battery can be provided in order to increase the operational lifetime of the sensor assembly 200.
[00086] In addition, the internal location of the sensor 200 assembly protects the electronics 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 sensor assembly 200.
[00087] However, while the sensor assembly 200 is shown in Figure 2 located inside the cylinder, it should be understood that other locations are suitable. For example, the sensor assembly 200 can be mounted on valve 104 adjacent to conductor 120 or form a separate section of valve 104. What is important is that the quartz crystal oscillator 202 is exposed to gas in the internal volume V of the cylinder. of gas 100.
[00088] Additional variations are within the scope of the present invention. For example, the quartz crystal oscillator 202 can be located inside the internal volume V of the gas cylinder 100 and the drive circuit 204 located outside the gas cylinder 100. Therefore, at least a part of the sensor assembly 200 is located throughout an orifice 18. Quartz crystal oscillator 202 and drive circuit 204 are then connected by wiring 208 that passes through high pressure conductor supply 120.
[00089] In another variation, other parts of the sensor assembly can be located inside the internal volume V of the gas cylinder 100 and a part can be located outside of it. For example, the drive circuit of processor 212 and 220 can be located inside gas cylinder 100, while battery 206 can be located outside gas cylinder 100. This arrangement allows for the most fragile components of the sensor assembly are protected from damage and contamination, while the 206 battery is easily accessible for maintenance and replacement.
[00090] With respect to external communication, in one configuration, an aerial or external antenna (such as antenna 230) is not explicitly required. For example, communication can be carried out by means of acoustic transmission from inside cylinder 100. Acoustic transmission can be carried out by a transmitter located inside the gas cylinder 100. The transmitter can comprise, for example, a simple piezoelectric frequency resonator fixed.
[00091] A complementary receiver is also required and this component may be located away from cylinder 100 and may comprise hardware such as a phase closed circuit tone detector with an integrated microphone. Such an acoustic arrangement provides the advantage that a conductor is not required (as is the case for antenna 230) and that all electronics can be located entirely within cylinder 100.
[00092] Alternatively, the sensor assembly 200 can be connected to a display device (not shown) mounted on the gas cylinder itself. This can take the form of a digital display, which is operable to display the mass of gas remaining in cylinder 100 or, for example, the gas utilization rate.
[00093] In this arrangement, the quartz crystal oscillator 202 is constantly under isostatic pressure within the internal volume V of the gas cylinder 100 and, consequently, does not experience a pressure gradient. In other words, any mechanical stress arising from the pressure difference between the internal volume V of the gas cylinder 100 and the external environment is across conductor 120.
[00094] The benefits of the internal location of the sensor assembly 200 are unique to solid state sensing devices such as the quartz crystal oscillator 202. For example, a conventional pressure sensor such as a Bourdon gauge cannot be located in this form. Although a crystal-based sensor can operate fully immersed in the gas at constant pressure, a conventional pressure sensor is not capable of measuring isostatic pressure and requires a pressure gradient in order to function. Therefore, a conventional pressure gauge must be located between the high pressure to be measured and the atmosphere. This precludes locating a conventional pressure gauge entirely within a gas cylinder 100.
[00095] The sensor assembly 200 will now be described in greater detail with reference to Figures 2 and 3a to 3f. The 202 quartz crystal oscillator comprises a small, thin section of quartz cut. Quartz demonstrates piezoelectric behavior, that is, the application of a voltage across the crystal causes the crystal to change shape, generating a mechanical force. On the other hand, a mechanical force applied to the crystal produces an electrical charge.
[00096] Two parallel surfaces of the 202 quartz crystal oscillator are metallized in order to provide electrical connections across the entire crystal. When a voltage is applied across the crystal, through metal contacts, the crystal changes shape. By applying an AC voltage to the crystal, the crystal can be caused to oscillate.
[00097] The physical size and thickness of the quartz crystal determines the characteristic or resonant frequency of the quartz crystal. In effect, the characteristic or resonant frequency of the crystal 202 is inversely proportional to the physical thickness between the two metallized surfaces.
[00098] The resonant frequency of the 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 changes in different environments. For example, in a fluid, the crystal's vibration will be dampened by the fluid's neighboring molecules and these will affect the resonant frequency and energy needed to oscillate the crystal at a given amplitude.
[00099] In addition, the adsorption of gases or deposition of surrounding materials on the crystal will affect the mass of the vibrating crystal, changing the resonance frequency. This forms the basis for commonly used selective gas analyzers in which an absorbent layer is formed over the crystal and increases in mass as the gas is absorbed into the absorbent layer. However, in the present case, no coating is applied to the quartz crystal oscillator 202. Indeed, adsorption or deposition of material on the quartz crystal oscillator 202 is undesirable in the present case, since the measurement accuracy can be affected.
[000100] The quartz crystal oscillator 202 of the present embodiment is the fork-shaped fit and comprises a pair of teeth 202a (Figure 3a) approximately 5 mm in length arranged so as to oscillate, in this embodiment, at a resonant frequency of 32.768 kHz. Fork tines 202a normally oscillate in their fundamental mode, where they move synchronously to and away from each other at the resonant frequency.
[000101] In addition, it is desirable to use quartz, which is AT cut or SC cut. In other words, a planar quartz section is cut at certain selected angles so that the temperature coefficient of the oscillation frequency can be arranged to be parabolic with a broad peak near the ambient temperature. Therefore, the crystal oscillator can be arranged such that the slope at the top of the peak is precisely zero.
[000102] These crystals are commonly available at relatively low cost. In contrast to most quartz crystal oscillators which are used in a vacuum, in the present embodiment the quartz crystal oscillator 202 is exposed to gas under pressure in the internal volume V of the gas cylinder 100.
[000103] The sensor assembly 200 further comprises a housing 250. The housing 250 can be operated to place the quartz crystal oscillator 202 and, in use, is located in the internal volume V of the gas cylinder 100. The housing 250 can be operated to reduce the effect of convection currents within the gas cylinder 100 on measurements taken by the sensor assembly 200. The housing 250 of Figure 2 is shown in more detail in Figure 3a.
[000104] Referring to Figure 3a, the housing 250 comprises, in this embodiment, a first portion 252 and a second housing portion 254. The first housing portion 252 has a substantially cylindrical side wall 256, a distal end wall 258 and a proximal end wall 260 adjacent to the quartz crystal oscillator 202 and sealing the proximal end of the housing 250. The walls of the first housing portion 252 define a first chamber 262. The first chamber 262 substantially surrounds the quartz crystal oscillator 202 and is located adjacent the proximal end of housing 250.
[000105] The first housing portion 254 may comprise a conventional pressure housing as commonly available for quartz crystal sensors. This can reduce manufacturing costs. However, alternative configurations can be used, some possible variations of which are illustrated in Figures 3b to 3f.
The second housing portion 254 has a substantially cylindrical side wall 264, a distal end wall 266 and a proximal end wall 268. The walls of the second housing portion 254 define a second chamber 270. In this embodiment, the second housing portion 254 is cylindrical with a diameter of approximately 6 mm and a length of approximately 80 mm. However, this should not be taken as limiting and the dimensions and cross-sectional shapes can be varied as required.
The second chamber 270 is located adjacent the first chamber 262 and is in fluid communication therewith via a through hole 272 in the distal end wall 258 of the first portion 252. In this embodiment, the hole 272 has a diameter of approximately 0.35 mm. However, other shapes and dimensions of the through hole can be used as needed. Furthermore, a plurality of through holes 272 could be provided, if necessary.
[000108] Another through hole 274 is formed in the side wall 264 of the second housing portion 254 such that the second chamber 270 is in fluid communication with the gas within the volume V of the gas cylinder 100 and outside the housing 250. In this embodiment, the additional hole 274 has a diameter of 0.22 mm. However, an alternative size through 0.35mm through holes 274 has also been shown to achieve good results. The skilled person would be readily aware of the through hole configurations, dimensions and shapes that could be used with the present invention. In addition, a plurality of through holes 274 could be provided.
[000109] The structure of the housing 250 is such that the first and second chambers 262, 270 are in fluid communication in series with each other and with the volume V of the interior of the gas cylinder 100. In other words, the gas, in the to which the quartz crystal oscillator 202 is exposed has to pass from the internal volume V of the gas cylinder 100, through the second chamber 270 to the first chamber 262, before it reaches the quartz crystal oscillator 202.
[000110] In the embodiment shown in Figures 2 and 3a, the first and second chambers 262, 270 formed by housing 250 are formed as separate structures. However, this need not be the case and a single common housing 250 can be used.
[000111] Figures 3b to 3f show alternative embodiments of housing 250 within the scope of the present invention. For clarity, reference numerals referring to features in common with the modality in Figure 3A have been omitted.
[000112] Figure 3b shows a second embodiment of the housing 250. The second embodiment is structurally similar to the first embodiment, except that the through hole 274 is formed in the distal end wall 266 of the second housing portion 254.
[000113] Figure 3c shows a third embodiment of housing 250. The embodiment of Figure 3c is structurally similar to the first and second embodiments of housing 250, except that the second housing portion 254 has an extended length. In this embodiment, the second housing portion 254 has a length of approximately 230 mm. While Figure 3c is shown with through hole 274 at a distal end, through hole 274 could also be formed in sidewall 264 of second housing portion 254.
[000114] The embodiments of Figures 3d to 3f show different structures of the housing 250. The fourth embodiment of the housing 250 shown in Figure 3d differs from the previous embodiments in that the housing 250 is a cylindrical unitary element and comprises an outer wall 276, a wall of distal end 278 and a proximal seal 280.
[000115] The walls 276, 278, 280 delimit an interior of the housing 250. The housing 250 further comprises an inner wall 282, which divides the interior of the housing 250 into a first and a second chamber 284, 286. The first chamber 284 substantially surrounds quartz crystal oscillator 202 and is located adjacent to the proximal end of body 250.
[000116] The second chamber 286 is located adjacent to the first chamber 284 and is in fluid communication therewith via a through hole 288 in the inner wall 282. In this embodiment, the hole 288 has a diameter of approximately 0.35 mm. However, other shapes and dimensions of the through hole can be used as needed. Furthermore, a plurality of through holes 288 could be provided, if necessary.
[000117] Another through hole 290 is provided to allow fluid communication between the second chamber 286 and the internal volume V of the gas cylinder 100. In common with the first embodiment, the hole 290 is provided in the side wall 276 of the housing 250 .
[000118] A fifth mode of housing 250 is shown in Figure 3e. The fifth embodiment of housing 250 is structurally similar to the fourth embodiment; however, through hole 290 is provided in distal end wall 278 of housing 250 and housing 250 is of greater length (in this embodiment, 230 mm) such that second chamber 286 has a greater internal volume. Any of these variations can be applied to the fifth modality.
[000119] A sixth embodiment of the housing 250 is shown in Figure 3f. The sixth mode of housing 250 is structurally similar to the fifth mode; however, a second inner wall 292 is provided. Second inner wall 292 has a through hole 294 formed therein and divides the interior of housing 250 into three chambers - a first chamber 284, a second chamber 286 and a third chamber 296.
[000120] The first, second and third chambers 284, 286, 296 are in fluid communication in series with each other and with the interior of the gas cylinder 100 external to the housing 250. In other words, the gas, in which the oscillator quartz crystal 202 is exposed has to pass sequentially and consecutively from the internal volume V of the gas cylinder 100, through the third chamber 296, the second chamber 286 to the first chamber 284, before it reaches the quartz crystal oscillator 202.
[000121] The arrangement of a series of chambers as shown in the first to sixth embodiments of the housing 250 described above allows pneumatic damping of the convection currents within the gas cylinder 100. As described above, a result of temperature differences within the cylinder 100 is that convection will often occur within a cylinder. Convection occurs in a turbulent manner, with modulations of density and temperature (such that p ~ 1/T), with almost no resultant change in pressure.
[000122] The inventors understand the operating principle of the housing 250 as follows. Housing 250 defines an internal volume of gas, which tends to average changes in density and temperature. In principle, there will be no flow through the through holes in housing 250, due to the lack of pressure change. Therefore, the system will provide a constant output at a constant pressure as density and temperature vary just outside of it. Only if housing temperature 250 changes will the density change be measured. However, this is limited in practice because of the large thermal mass of the gas volume within the interior of the housing 250.
[000123] However, the inventors have found that the housing 250 responds differently to observed pressure fluctuations, for example, when the flow is drawn from the gas cylinder 100. In this case, the through holes are sufficiently large for said corresponding pressure change to be communicated almost instantaneously through fluid flow through the through holes.
[000124] It has been found that, in order to obtain the above-described advantages, a housing 250 comprising at least two chambers is required. A one-chamber setup has been shown to be ineffective in providing sufficient insulation from the density and temperature changes resulting from convection currents within the cylinder.
[000125] The drive circuit 204 to drive the quartz crystal oscillator 202 is shown in Figure 4. The drive circuit 204 must meet a number of specific criteria. First, the quartz crystal oscillator 202 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 quartz crystal 202 is forced to function (and restart after a period of non-use) under a wide range of pressures.
[000126] Therefore, the quality factor (Q) of the 202 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. Equivalently, it can characterize the bandwidth of a resonator in relation to its center frequency.
[000127] In general, the larger 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, oscillations of a high Q factor of the oscillator reduce in amplitude more slowly in the absence of an external force. Sinusoidally driven resonators with higher Q factors resonate with greater amplitudes at the resonant frequency, but have a smaller frequency bandwidth around that frequency for them to resonate.
[000128] The drive circuit 204 must be able to drive the 202 quartz crystal oscillator despite the Q factor change. As the pressure in the gas cylinder 100 increases, the oscillation of the 202 quartz crystal oscillator it will become more and more muted, and the Q factor will drop. The falling Q factor requires a higher gain to be provided by an amplifier in the drive circuit 204. However, very high amplification is provided, the drive circuit 204, the response from the quartz crystal oscillator 202 may become if difficult to distinguish. In this case, the drive circuit 204 may simply oscillate at an unrelated frequency, or at the non-fundamental frequency of the quartz crystal oscillator 202.
[000129] As an additional limitation, the drive circuit 204 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.
[000130] The drive circuit 204 will now be described with reference to Figure 4. In order to drive the quartz crystal oscillator 202, the drive circuit 204 essentially takes one. voltage signal from the quartz crystal oscillator 202, amplifies it, and feeds the signal back to the quartz crystal oscillator 202. The fundamental resonance frequency of the quartz crystal oscillator 202 is, in essence, a function of the rate of expansion and contraction of quartz. This is generally determined by the cut and size of the crystal.
[000131] However, external factors also affect the resonant frequency. When the energy of the output frequencies generated matches the losses in the circuit, an oscillation can be sustained. The drive circuit 204 is arranged to detect and maintain this oscillation frequency. The frequency can then be measured by processor 220, used to calculate the proper gas property required by the user and, if necessary, output to an appropriate display medium (as will be described later).
[000132] The drive circuit 204 is powered by a power supply of 6 V 206. The power supply 206, in this modality, comprises a lithium ion 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.
[000133] The drive circuit 204 further comprises a common emitter amplifier Darlington pair 210. A Darlington pair comprises a composite structure consisting of two bipolar NPN transistors configured such that the current amplified by a first of the transistor is further amplified 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.
[000134] The Darlington 210 pair is arranged in a feedback configuration from a single transistor (Ti) common emitter amplifier 212. A bipolar NPN junction transistor is shown in Figure 4. However, the expert would be aware of the arrangements transistor alternatives that can be used; for example, a PNP bipolar junction transistor or Metal Oxide Semiconductor Field Effect Transistors (MOSFETs).
[000135] The drive circuit 204 comprises another NPN emitter follower transistor T2 which acts as a buffer amplifier 214. The buffer amplifier 214 is arranged to function as a buffer between the circuit and the external environment.
[000136] A capacitor 216 is located in series with the quartz crystal oscillator 202. The capacitor 216 in this example has a value of 100 pF and allows the drive circuit 204 to drive the quartz crystal oscillator 202 in situations where the crystal has been contaminated, for example, salts or other deposited materials.
[000137] An alternate drive circuit 240 will now be described with reference to Figure 5. The drive circuit 240 can be used in place of the drive circuit 204 described above. In contrast to the drive circuit 204 described above, the drive circuit 240 includes a common drain Metal Semiconductor Oxide Field Effect Transistor (MOSFET) amplifier 242 instead of the Darlington pair of the circuit of Figure 6. The MOSFET242 functions as a high input impedance 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, the MOSFET242 provides a unity gain with a high input impedance to reduce load electrical in the 202 quartz crystal oscillator.
[000138] The output of common drain MOSFET amplifier 242 is fed to two successive single transistors (Q2, Q3) Common Emitter Amplifiers 244. Resistors R6 and R8 provide negative feedback and current bias for the transistors. Common emitter amplifiers 244 provide a high gain for amplifying the oscillations of the quartz crystal oscillator 202 and, in this embodiment, comprise NPN bipolar junction transistors. However, one skilled in the art would be aware of alternative transistor arrays that can be used; for example, a bipolar PNP transistor or MOSFET junction.
[000139] A 246 capacitor is connected between the 202 quartz crystal oscillator and ground. Capacitor 246 in this mode is operable to increase the drive to quartz crystal oscillator 202.
[000140] A resistor 248 is connected in series with the quartz crystal oscillator 202. The resistor 248, in this mode, has a value of 56 kQ and damps the oscillations of the quartz crystal oscillator 202, in order to allow the circuit oscillates over a wide range of pressures, with only gradual changes in waveform.
[000141] The drive circuit 240 is powered by a 3V 249 battery. The 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 current supply arrangement can be used after DC rectification and appropriate voltage reduction.
[000142] Another alternative drive circuit 300 will now be described with reference to Figure 6. The drive circuit shown in Figure 6 is configured similarly to a Pierce oscillator. Pierce oscillators are known from digital IC clock oscillators. In essence, the drive circuit 300 comprises a single digital inverter (in the form of a transistor) T, three resistors Ri, R2 and Rs, two capacitors Ci, C2, and the quartz crystal oscillator 202.
[000143] In this arrangement, the 202 quartz crystal oscillator functions as a highly selective filter element. Resistance Ri acts as a load resistance for transistors T. Resistance R2 acts as a bias feedback resistor, the inverter of T in its linear operating region. This effectively allows the T-inverter to function as a high-gain inverting amplifier. Another resistor Rs is used between the output of the converter T and the quartz crystal oscillator 202 to limit the gain and to dampen unwanted oscillations in the circuit.
[000144] The quartz crystal resonator 202, in combination with Ci and C2 forms a Pi network bandpass filter. This allows for a 180 degree phase shift and voltage gain from the output to the input at approximately the resonant frequency of the quartz crystal oscillator. The above-described drive circuit 300 is reliable and inexpensive to manufacture since it comprises relatively few components.
[000145] As discussed above, the sensor assembly 200 may include a processor 220 which receives inputs from the quartz crystal oscillator 202 and drive circuit 204. The processor 220 and may comprise suitable arrangement such as a specific integrated circuit of application (ASIC) or Field Programmable Gate Array (FPGA) . Processor 220 is programmed to calculate, display and communicate parameters useful to cylinder 100 users.
[000146] When used with the quartz crystal oscillator 202, the processor 220 can be configured to measure the frequency f or period of the signal of the drive circuit 204. This can be achieved, for example, by counting oscillations over a time fixed, and convert this frequency to a density value using an algorithm or a lookup table. This value is transferred to processor 220, which is configured to perform, based on the inputs provided, a calculation to determine the mass of gas in gas cylinder 100.
[000147] The 220 processor can optionally be designed for mass production to be identical across all cylinders, with different software and hardware features enabled for different gases.
[000148] In addition, processor 220 can also be configured to minimize power consumption by implementing standby or "sleep" modes that can encompass processor 220 and additional components such as drive circuit 204 and crystal oscillator. quartz 202.
[000149] Several schemes can be implemented; for example, processor 220 may be idle for 10 seconds every 1 second. In addition, the processor 220 can control the quartz crystal oscillator circuit 202 and the unit 204 such that these components are placed in a standby state so that most of the time, being only in power switching of hungry components per h. second every 30 seconds. Alternatively or additionally, communication components such as antenna 230 can be turned off as needed or used to activate the sensor assembly 200.
[000150] The theory and operation of the sensor assembly 200 will now be described with reference to Figures 7 to 14.
[000151] The 210 quartz crystal oscillator has a resonant frequency that is dependent on the density of the fluid in which it is located. Exposing a tuning of the oscillating fork-type planar crystal oscillator to a gas leads to a shift and dampening of the crystal's resonant frequency (as compared to the crystal's resonant frequency in 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 210a in fork tuning of the crystal oscillator 210 increases the effective mass of the oscillator. This leads to a reduction in the resonant frequency of the quartz crystal oscillator, according to the movement of a fixed elastic beam on one side:
where f is the oscillation frequency, f0 is the oscillation frequency in a vacuum, p is the gas density, and MQ is a constant.
[000152] The density p will, in almost all cases, be small compared to Mo, so 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):

[000153] Therefore, to a good approximation, the change in frequency is proportional to the change in density of the gas in which the quartz crystal oscillator is exposed. Figure 7 shows, for a series of different gas/gas mixtures, that the resonant frequency of the quartz crystal oscillator 210 varies linearly as a function of density.
[000154] In general, the sensitivity of the quartz crystal oscillator 202 is that a 5% change in frequency is seen with, for example, oxygen gas (having an atomic mass number 32) at 250 bar when compared with atmospheric pressure. Such pressures and densities are typical of 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 for helium and hydrogen.
[000155] The 202 quartz crystal oscillator is particularly suitable for use as a density sensor for commercially supplied gases. First, in order to accurately detect the density of a gas, it is necessary that the gas is free of dust and liquid droplets, which is guaranteed with commercially supplied gases, but not with air or in most monitoring situations of pressure.
[000156] Second, because the pressure of gas inside a cylinder can only change slowly during normal use (ie as gas is evacuated through outlet 110), the fact that quartz crystal oscillator 202 takes a small amount of time (about 1 second) to take a reading does not affect measurement accuracy. The time period of approximately 1 s is necessary because of the need to count the oscillations and because of the need for the quartz crystal oscillator 202 to reach equilibrium at a new gas pressure.
[000157] This method may be less accurate if the gas in gas cylinder 100 is not uniform - for example, if the gas is a non-uniform mixture, as may occur within a partially filled liquid cylinder or, in the case of a freshly prepared and insufficiently mixed mixture of light and heavy gases. However, this is unlikely to occur in most packaged gas applications.
[000158] As previously described, the internal volume V of the gas inside the gas cylinder 100 is fixed. Therefore, since the density p of the gas within the internal volume V of the gas cylinder 100 was obtained from measuring by the sensor assembly 200, the mass M of gas in the cylinder can be obtained from the following equation: M = pV
[000159] Direct measurement of the density p of the gas therefore allows the calculation of the mass of gas remaining in the gas cylinder 100.
[000160] Measuring the mass of gas in this way has a number of advantages over known arrangements. For example, the measured mass in accordance with an embodiment of the invention is intrinsically corrected for temperature. In contrast, measuring pressure using, for example, a Bourdon gauge varies proportionally with absolute temperature. Therefore, the present arrangement does not require temperature measurement and/or correction, as is the case with known arrangements.
[000161] In addition, the mass of gas measured according to an embodiment of the present invention is intrinsically corrected for Z compressibility. In a conventional assembly, for example, using a Bourdon meter, in order to obtain pressure contents of gas, the compressibility of the gas needs to be corrected for. This is particularly important at high pressures, where the Z compressibility is not proportional to the gas pressure in the form expected of an ideal gas.
[000162] The automatic compensation for compressibility is illustrated with reference to Figures 8 and 9. Figure 8 shows a graph of the gas mass (in kg) on the Y axis as a function of Pressure (bar g) for argon, oxygen and mixture of argon:Carbon dioxide. As shown in Figure 8, the masses of the different gases vary with increasing pressure. Furthermore, at high pressures in excess of 250 bar g, there is no longer a linear relationship between mass and pressure.
[000163] Figure 9 shows a graph of gas mass (in kg) on the Y axis versus density (in kg/m3) for the same three gases (argon, oxygen and a mixture of argon: carbon dioxide) as in Figure 8. In contrast to Figure 8, it can be seen that the gas mass as a function of density is identical for each gas/gas mixture. Furthermore, the relationship is still linear at high densities. Therefore, the quartz crystal oscillator 202 can be both high resolution and highly linear with density.
[000164] As outlined above, the arrangement of the present invention allows the measurement of mass to a very high accuracy, with a resolution of parts per million. Coupled with the linear response of the quartz density sensor 202 at high densities and pressures (as illustrated in Figures 8 and 9), the high accuracy allows very light gases such as H2 and He to be accurately measured.
[000165] In many practical situations, mass flow measurement into or from gas cylinder 100 is important. This can be useful in situations where the gas utilization rate from the gas cylinder 100 is needed, for example, to calculate the time remaining before the cylinder is emptied. Alternatively or additionally, mass flow can be monitored in order to deliver precise amounts of gas.
[000166] Gas density at atmospheric pressure is only on the order of 1 g/liter, and normal gas usage rates are often just a few liters per minute. The inventors have found that the quartz crystal oscillator 202 is sufficiently stable and accurate to allow the mass flow of gas leaving the gas cylinder 100 to be measured ÕM by means of changing the indicated density. Mass flow 01 is calculated from equation 5):
where V is the volume, Δp the change in density indicated over the time interval Δt. In this example, operation of the sensor assembly 200 requires the drive circuit 204 to integrate over a number of oscillation cycles of the quartz crystal oscillator 202.
[000167] Therefore, it is not possible to obtain an instantaneous rate of change õp of the density with time, . However, the rate of density change over time is relatively low in a gas cylinder 100 in normal operation. Therefore, the measurement taken using the sensor assembly 200 is sufficiently accurate in normal use.
[000168] Figures 10 and 11 illustrate the experimental data of mass flow detection. Figure 10 shows a graph of frequency (kHz) on the Y axis versus time (in minutes) on the X axis for a flow rate of 12 liters per minute from a 50 liter cylinder at a pressure of ~100 bar indicated. Figure 11 shows a graph of the calculated flow (in liters per minute) on the Y axis versus time (in minutes) on the X axis for the 50 liter cylinder at ~100 bar pressure.
[000169] These figures illustrate that, for most normal uses, the mass flow of gas from a gas cylinder 100 can be determined from a measurement of the change in density over time. Consequently, the mass flow can be calculated with sufficient precision and time resolution using the quartz crystal oscillator 202 and drive circuit 204.
[000170] Figure 12 illustrates other experimental data that show the operation of the present invention. Figure 12 shows a graph of frequency (in kHz) on the Y axis versus the total cylinder mass (in kg) on the X axis. As can be seen, the graph is, to a high degree of accuracy, therefore, the Figure 12 shows that the mass of gas inside the gas cylinder 100 can be accurately measured with the quartz crystal oscillator 202.
[000171] However, as described above, when the flow is drawn from a cylinder, the top of the cylinder can become significantly cooler than the rest of the cylinder, creating strong convection currents inside the cylinder. Figure 13 shows the effect of convection on measuring gas flow from a cylinder from which a gas flow has been established for 10 minutes.
[000172] In the experimental setup, the housing 250 is omitted and the quartz crystal oscillator 202 is located inside the uncovered gas cylinder 100 and directly exposed to the gas in the cylinder 100.
[000173] It can be seen from Figure 13 that convection currents cause considerable noise to the flow signal after the flow stops. The Y axis shows flow in liters/min divided by 2, while the X axis is time, with one data point per second. The noise level due to convection means that erroneous flows can be detected and little meaningful information can be collected. In particular, noise fluctuations can trigger erroneous measurements of flow rates ranging between +10 liters/min and -10 liters/minute. This is clearly unacceptable for accurate commercial use.
[000174] Figure 14 illustrates a similar measurement. However, in this case, the experimental arrangement comprises the housing 250 of the first mode, which is located around the quartz crystal oscillator 202 to act as a pneumatic damper. As shown in Figure 14, the data shows significantly less noise than gas flows (at a flow rate of approximately 12 liters/minute) and when the valve is closed.
[000175] As shown, a housing 250 in accordance with an embodiment of the present invention significantly reduces (measurement errors and resulting data) noise due to convection within a cylinder 100.
[000176] The inventors have discovered that this noise reduction cannot be effectively achieved using electronic filtering alone. For example, while applying an RC filter or an exponential digital filter results in some smoothing of the signal, it has been experimentally found that, in order to obtain acceptable results, a time constant of approximately 30 seconds is required. This slow response time is unacceptable for most typical commercial applications.
[000177] However, it has been found that the combination of housing 250 (which significantly reduces noise due to convection) and electronic filtering can provide good results. Since noise is significantly reduced by using the 250 housing, electronic filtering can be provided that weights over a shorter period of time, improving response.
[000178] An exponential averaging model was applied, using the formula of equation 6):
Where
is the previously calculated value of
(or the average value)
, current the currently registered value
and Y θ an exponential decay constant (0 to <1) .
[000179] However, exponential filtering presents a time lag for the reported values. This delay can be calculated using equation 7):
where is the period of time between readings.
[000180] Figure 15 shows an experimental measure that shows the filtering effect with a y-decay constant of 0.9. It can be clearly seen since the filter has the effect of smoothing out signal noise even more.
[000181] Table 1 below shows a summary of the measurements made on the housing arrangements, according to embodiments of the present invention. As shown below, use of the various modalities of housing 250 results in up to an order of magnitude improvement in noise reduction as a result of convection currents within cylinder 100. In addition, numerical filtering can reduce flow propagation (ie, the variation in measured flow as a result of noise over the measurement signal) even more. However, numerical averaging comes at the expense of response time. Therefore, compensation is required in practice.

[000182] A method according to an embodiment of the present invention will now be described with reference to Figure 16. The method described below is applicable to each of the embodiments described above. Step 400: Initialize measurement
[000183] In step 400, measuring the mass of gas in gas cylinder 100 is initialized. This can be activated by, for example, a user pressing a button on the outside of the gas cylinder 100. Alternatively, the measurement can be started via a remote link, for example, a signal transmitted over a wireless network. and received by the sensor assembly 200 through antenna 230 (see Figure 2).
[000184] As another alternative, or in addition, the sensor assembly 200 can be configured to start remotely or by a timer. The method proceeds to step 402. Step 402: Triggering the quartz crystal oscillator
[000185] Once started, the drive circuit 204 is used to drive the quartz crystal oscillator 202. During startup, the drive circuit 204 applies a random noise AC voltage between the crystals 202. At least a portion of said random voltage will be at an appropriate frequency to cause the 202 crystal to oscillate. Crystal 202 will begin to oscillate in sync with this signal.
[000186] Through the piezoelectric effect, the movement of the quartz crystal oscillator 202 will generate a voltage in the resonant frequency band of the quartz crystal oscillator 202. The drive circuit 204 then amplifies the signal generated by the oscillator of quartz crystal 202, such that signals generated in the frequency band of the quartz crystal resonator 202 dominate the output of the drive circuit 204. The narrow band of resonant quartz crystal filters out all unwanted frequencies and the circuit drive 204 then drives the quartz crystal oscillator 202 at the fundamental resonance frequency f. Once the quartz crystal oscillator 202 has stabilized at a particular resonant frequency, the method proceeds to step 304. Step 404: Measuring the resonant frequency of quartz crystal oscillator
[000187] The resonant frequency f is dependent on the conditions inside the internal volume V of the gas cylinder. In the present embodiment, the change in resonance frequency Δf is proportional in magnitude to the change in gas density within gas cylinder 100 and will decrease with increasing density.
[000188] In order to make a measurement, the frequency of the quartz crystal oscillator 202 is measured for a period of approximately 1 s. This is to allow the reading to stabilize and for enough oscillations to be counted to determine an accurate measurement. Frequency measurement is performed on processor 220. Processor 220 may also record the time, Ti, when measurement was initiated.
[000189] The quartz crystal oscillator 202 is located inside the housing 250 of one of the previously described embodiments. Therefore, during the measurement period, the housing 250 protects the quartz crystal oscillator 202 from density and temperature variations due to convection within the cylinder 100. This situation can occur when, for example, the gas has been established from the cylinder 100 for a predetermined period and the top of cylinder 100 is cold.
[000190] Once the frequency has been measured, the method proceeds to step 406. Step 406: Determine the mass of gas in the gas cylinder
[000191] Once the frequency of the quartz crystal oscillator 202 has been satisfactorily measured in step 303, the processor 220 then calculates the mass of gas in the gas cylinder 100.
[000192] This is done using equation 5) above, where the mass of the gas can be calculated directly from the density determined in step 304 and the known internal volume V of the gas cylinder 100. The method then proceeds to step 408 Step 408: Store measurement results
[000193] Once the gas mass has been calculated, the mass can simply be written to an internal memory associated with the processor 220 of the sensor assembly 200 for later retrieval. As yet another alternative, the mass of gas in time Ti can be stored in a local memory for said processor 220.
[000194] The method then proceeds to step 410. Step 410: Communicate results
[000195] As an optional step, the gas mass can be displayed in various modes. For example, a display connected to gas cylinder 100 or valve 104 can display the mass of gas contained within gas cylinder 100. Alternatively, the mass measurement of the gas could be remotely communicated to a base station or to a meter located on an adjacent slot.
[000196] The method then proceeds to step 412. Step 412: Disconnect sensor assembly
[000197] It is not necessary to keep the sensor assembly 200 operational at all times. Conversely, it is beneficial to reduce power consumption by turning the sensor assembly 200 off when not in use. This prolongs the life of the 206 battery.
[000198] The configuration of the drive circuit 204 allows the quartz crystal oscillator 202 to be reset regardless of the gas pressure in the gas cylinder 100. Therefore, the sensor assembly 200 can be turned off, and when necessary, in order to save the battery.
[000199] The method described above is in relation to a single measurement of the contents of the cylinder 100. While the housing 250 of the present invention is arranged to protect against convective currents that primarily affect mass flow measurements, the housing 250 it will also help in measuring contents in steady state (ie a single measurement) . This is because a user may need a steady state measurement of the true contents of a cylinder of 100 after a given flow is drawn so that the remaining gas mass can be determined.
[000200] However, after the flux has been removed, the upper part of cylinder 100 may be cooler than the rest of it, creating convective currents therein. Housing 250 allows accurate measurement to be made of true mass contents, regardless of convection within cylinder 100. This improves the accuracy and speed of steady state measurements.
[000201] The method of operation of an embodiment of the present invention has been described above with reference to step 400-412 above in relation to steady state measurements. However, the following additional steps can also optionally be carried out in order to measure the mass flow from cylinder 100: Steps 414-418: Perform another mass determination I
[000202] It may be desired to calculate the gas mass flow to/from gas cylinder 100. At time T2, which is later than Ti steps 414, 416 and 418 are performed. Steps 414, 416 and 418 correspond to steps 404, 406 and 408, respectively, performed at time T2. The resulting values from steps 414, 416 and 418 are stored in the internal memory of processor 220 as a mass of gas at time T2.
[000203] The time interval between Tx and T2 can be very short, on the order of seconds, as illustrated in Figure 9. Alternatively, if the flow is slow, or if it is desired to measure the losses inside the gas cylinder 100 , due to, for example, leakage, then the time interval between Ti and T2 can be considerably longer; for example, on the order of minutes, hours or days.
[000204] The method then proceeds to step 420. Step 420: Apply numeric filtering
[000205] This step is, as described above, optional. Numerical filtering can be selected in situations where a highly accurate flow rate is required, but where the response time of the meter is less critical. Such a situation can occur when, for example, a low flow is being measured over a long period of time.
[000206] If numerical filtering is selected, it can be performed by dedicated computational hardware forming part of processor 220 or, alternatively, it can be encoded in software running on processor 220.
[000207] As described above, numerical filtering can comprise an exponential filter, which uses the measurement made in step 406 (and stored in step 408), together with the measurement made later in step 416 (and stored in step 418).
[000208] The method then proceeds to step 422. Step 422: Calculate the mass flow
[000209] Knowing the time difference between the times Ti and T2, and the mass of gas in the gas cylinder 100 at those times, the processor 220 can calculate the mass flow during the time period between Ti and T2 from the equation 6).
[000210] The method can then perform repeated steps 314-320 to recalculate the mass flow if necessary. Alternatively, the method can be moved to step 312 and the sensor assembly 200 can be moved down.
[000211] Variations of the above modalities will be apparent to the person skilled in the art. The exact configuration of the hardware and software components may differ and still be within the scope of the present invention. The expert would be readily aware of alternative configurations that could be used.
[000212] For example, the modalities described above have used a quartz crystal oscillator, having a fundamental frequency of 32.768kHz. However, crystals that operate at alternate frequencies can be used. For example, quartz crystal oscillators operating at 60kHz and 100kHz can be used with the modalities described above. A graph showing the frequency change with the density of different crystals is shown in Figure 17. As an additional example, a crystal oscillator operating at a frequency of 1.8 MHz can be used.
[000213] Higher frequency operation allows pressure to be monitored more often because a short period of time is required to sample a certain number of cycles. In addition, higher frequency crystals allow a shorter duty cycle to be used in a crystal "sleep" mode. By way of explanation, in most cases, the crystal and drive circuit will spend most of the time off, only being turned on for a second or so when a measurement is needed. This can happen, for example, once a minute. When a higher frequency crystal is used, pressure can be measured faster. Therefore, the time the crystal is operational can be reduced. This can reduce power consumption and at the same time improve battery life.
[000214] In addition, the above modalities have been described to measure the absolute frequency of a quartz crystal oscillator. However, in self-contained electronics incorporated in an associated gas cylinder regulator, it may be advantageous to measure the change in frequency of the sensor by comparing that reference frequency with an identical type crystal, but enclosed in a vacuum bag or a pressure. The package can contain gas pressure at a selected density, gas at atmospheric conditions or can be opened to the outside atmosphere of gas cylinder 100.
[000215] A suitable sensor assembly 500 is shown in Figure 18. The sensor assembly 500 comprises a first quartz crystal oscillator 502 and a second quartz crystal oscillator 504. The quartz crystal oscillator 502 is first. a reference crystal which is located within a vacuum sealed vessel 506 under. The first 502 quartz crystal oscillator is driven by a 508 drive circuit.
[000216] The second quartz crystal oscillator 504 is a crystal similar to the crystal 202 described in the previous embodiments. The second quartz crystal oscillator 504 is exposed to the gas environment within the internal volume of the gas cylinder 100. The second quartz crystal oscillator 504 is driven by a drive circuit 510.
[000217] This comparison can be performed using an electronic circuit mixer 512 that combines the signal of two frequencies 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.
[000218] In addition, the circuit used in a gas cylinder 100 can be simplified, because it is necessary that only the difference frequency is measured. Furthermore, this approach is particularly suitable for use with a high frequency (MHz) crystal oscillator, where it can be difficult to directly measure the crystal frequency.
[000219] 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 can be divided between permanently cylinder mounted units and units mounted at the user's or customer's station or temporarily mounted at the cylinder outlet, like the position normally used for a conventional flowmeter.
[000220] An example of this arrangement is shown with reference to Figure 19. The arrangement comprises a gas cylinder assembly 50 comprising a gas cylinder 600 and a sensor assembly 602. gas 600 and sensor assembly 602 are substantially similar to the assembly of gas cylinder 10, gas cylinder 100, and sensor assembly 200, substantially as described above with reference to prior embodiments.
[000221] In this mode, the sensor assembly 602 comprises a quartz crystal oscillator and the drive circuit (not shown) similar to the quartz crystal oscillator 202 and drive circuit 204, of previous embodiments. A 604 antenna is provided for communication via any suitable distance communication protocol; for example, Bluetooth, infrared (IR) or RFID. Alternatively, wired communication can be used.
[000222] As an additional alternative, acoustic communication methods can be used. The advantage of such methods is that remote communication can be performed without requiring an external antenna.
[000223] A connecting tube 606 is connected to the outlet of the gas cylinder 600. The connecting tube is terminated by a quick connect connection 608. The quick connect connection 508 allows connecting the hose or components to be connected and disconnected with Ease and speed of the 600 gas cylinder.
[000224] A quick connect unit 650 is provided for connection to the gas cylinder 600. A complementary quick connect connector 610 is provided for connection to connector 508. In addition, the quick connect unit 650 is equipped with a quick connect unit. data 652. Data unit 652 comprises a display 654 and an antenna 656 for communication with the antenna 604 of the gas cylinder assembly 50. The display 654 may comprise, for example, an E-ink monitor to minimize the consumption of power and maximize display visibility.
[000225] Data unit 652 can record various parameters as measured by the sensor assembly 602 of the gas cylinder assembly 50. For example, data unit 652 can record flow as a function of time. This record can be useful, for example, for welding contractors who want to verify that gas flow was present and correct during long gas welding procedures on critical components, or to provide usage data for a particular customer.
[000226] In addition, the data obtained from gas cylinder 600 can be used to present data about the run time, ie the time before the gas in cylinder 500 is used up. This is particularly critical in applications such as a hospital oxygen cylinder used for patient transit between hospitals. Such time (Tro) can be calculated from the knowledge of the flow (discussed above), the mass content of cylinder 500 and the current time (Tc) through the following equation 8):

[000227] Alternatively, data from data unit 652 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 of Notice. Non-exhaustive examples of these might be: gas used per unit arc time, gas used per kg of welding wire (For example, with warning about weld porosity), the number of standard size balloons (or for measuring and calibrating balloons of an out-of-the-ordinary size), the number of hours of welding remaining, the pressure display (by converting the measured value from density to pressure using known gas data).
[000228] In addition, data unit 652 can be arranged to provide the following functions: provide an audible or visible alarm, if the gas level is below a certain level or the flow rate; the exit of the entire life of the cylinder (for example, for slowly changing mixtures) or an expiration date of the cylinder; to contain and display data on gas usage, ie what types of welds, what types of weld metals, or generate links so that mobile phones or computers can get detailed data; to provide multi-mode operation, for example, a supplier/filler mode and a customer mode; to display different quantities to the customer from what is displayed by the gas company filling the cylinders; to allow data entry; to provide data such as the number of cylinders, the type of gas, a certificate of analysis, a customer history (who had the cylinder on which dates), safety data and operational tips can be summarized on the cylinder.
[000229] 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 600 as discussed in terms of the sensor assembly 200, 602.
[000230] In addition, the embodiments of the present invention can also be used to perform leak detection. A quartz crystal oscillator is particularly suitable for this task, due to the high sensitivity of such a sensor. Also, a quartz crystal oscillator will not incorrectly read pressure change due to changes in cylinder temperature, as is the case when sensing leaks using a pressure gauge. Furthermore, embodiments of the invention can be used to detect failures, for example, in residual pressure valve failure detection (eg in a used cylinder with pressure less than 3 bar g)
[000231] 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 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, zirconium titanate ceramic polycrystalline, high alumina ceramic, silicon oxide and zinc composite, or dipotassium tartrate.
[000232] Furthermore, while the previous embodiments have been illustrated with reference to gas cylinders, other applications of the present invention can be used. For example, the quartz crystal oscillator can be located inside the tire of a vehicle, such as a car, motorcycle, or truck. Although the shape of a vehicle tire can change in load or speed, the inventors of the present patent application have shown that the internal volume of the tire does not change significantly in use. For example, since the change in interior volume is, in this context, less than 2-3% of the total internal volume, the present invention is reliably operable to calculate the mass of gas within a vehicle tire.
[000233] In addition, although several applications use air as the gas inside a vehicle tire, increasingly, gases such as nitrogen are used. Embodiments of the present invention are particularly suitable for such applications. Furthermore, because measuring mass is essentially independent of temperature, the arrangement of the present invention is particularly useful in situations where environmental conditions can affect measurements.
[000234] As a further example, the present invention may also be applicable to air suspension systems for vehicles.
[000235] Embodiments 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 herein, it is to 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 within the scope of the present invention.

权利要求:
Claims (14)
[0001]
1. ASSEMBLY OF SENSORS TO MEASURE PHYSICAL PROPERTIES OF A GAS UNDER PRESSURE WITHIN A GAS CYLINDER COMPRISING A GAS CYLINDER BODY AND A VALVE ARRANGEMENT THAT DEFINES A FIXED INTERNAL VOLUME OF THE GAS CYLINDER(200, the assembly ) characterized by comprising a housing, a piezoelectric oscillator (202) for immersion in the gas inside the gas cylinder, and a drive circuit can be operated to drive the piezoelectric oscillator so that the piezoelectric oscillator resonates at a frequency of resonance, the sensor assembly(200) being arranged to determine the density of the gas within the gas cylinder (100) from the resonant frequency of the piezoelectric oscillator (202) when immersed in said gas, in which, in use, the housing (250) is located within the fixed internal volume (V) of the gas cylinder and comprises a first chamber and a second chamber, the first chamber in fluid communication with the second chamber and enclosing substantially said piezoelectric oscillator, and the second chamber which is in fluid communication with the interior of the gas cylinder (100).
[0002]
Sensor assembly, according to claim 1, characterized in that the sensor assembly(200) further comprises a processor prepared to determine, from the measurement of density and the internal volume (V) of said gas cylinder (100 ), the mass of the gas inside the gas cylinder.
[0003]
Sensor assembly according to claim 2, characterized in that the processor is further arranged to perform repeated measurements of the mass of the gas inside the gas cylinder at discrete time intervals, to obtain a plurality of measurements, and to determine, from said plurality of measurements, the mass flow of gas to/from the gas cylinder during discrete time intervals.
[0004]
Sensor assembly, according to claim 3, characterized in that the processor is prepared to define said discrete time intervals as in the order of seconds.
[0005]
Sensor assembly, according to claim 3 or 4, characterized in that the processor is prepared to apply numerical filtering to said measurements.
[0006]
Sensor assembly according to any one of claims 1 to 5, characterized in that the first chamber has a wall comprising a first opening allowing fluid communication between the first and second chambers, and the second chamber has a wall comprising a second opening to allow fluid communication between the second chamber and the interior volume of the gas cylinder.
[0007]
Sensor assembly according to claim 6, characterized in that the first and/or second opening has dimensions less than or equal to 0.35 mm.
[0008]
Sensor assembly according to claim 7, characterized in that the first and/or second opening has dimensions less than or equal to 0.22 mm.
[0009]
Sensor assembly according to any one of claims 1 to 8, characterized in that the housing is substantially cylindrical.
[0010]
Sensor assembly according to any one of claims 1 to 9, characterized in that the housing has a length of 230 mm or less.
[0011]
Sensor assembly according to claim 10, characterized in that the housing has a length equal to or less than 80 mm or less.
[0012]
Sensor assembly according to any one of claims 1 to 11, characterized in that said piezoelectric oscillator comprises a quartz crystal oscillator.
[0013]
13. GAS CYLINDER FOR CONTAINING A GAS UNDER PRESSURE, the gas cylinder (100) characterized by: a gas cylinder body (102) defining a fixed internal volume; a valve arrangement (104) connected to said gas cylinder body (102) and arranged to allow selective filling of the gas cylinder with gas or dispensing gas from said gas cylinder (100); and the sensor assembly(200) of any one of claims 1 to 12.
[0014]
A gas cylinder according to claim 13, characterized in that the sensor assembly is located entirely within the fixed internal volume of the gas cylinder.

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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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2019-11-26| B06U| Preliminary requirement: requests with searches performed by other patent offices: procedure suspended [chapter 6.21 patent gazette]|

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2021-05-25| B09A| Decision: intention to grant [chapter 9.1 patent gazette]|

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2021-06-22| B16A| Patent or certificate of addition of invention granted|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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EP12169387.3|2012-05-24|

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EP12169387.3A|EP2667176B1|2012-05-24|2012-05-24|Apparatus for measuring the true contents of a cylinder of gas under pressure|

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PCT/EP2013/060689|WO2013174957A1|2012-05-24|2013-05-23|Method of, and apparatus for, measuring the true contents of a cylinder of gas under pressure|

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