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    • 专利摘要:
    METHOD TO MEASURE THE MASS OF A GAS UNDER PRESSURE, USING A PIEZOELECTRIC OSCILLATOR, DETECTOR ASSEMBLY, VALVE ARRANGEMENT, GAS CYLINDER TO CONTAIN A GAS UNDER PRESSURE, A PRODUCTABLE PROGRAMMABLE PRODUCT PROGRAMMABLE BY APPLYING A MANUFACTURABLE PROGRAMMABLE PRODUCT BY APPLYING A PROCESSABLE PROGRAMMABLE PRODUCT BY APPLYING A PROCESSABLE PROGRAMMABLE PROGRAMMABLE BY APPLYING A MANUFACTURABLE PROGRAMMABLE PROGRAMMABLE PROGRAMMABLE PRODUCT. USABLE IN COMPUTER. A method and apparatus for measuring the mass of a gas under pressure using a piezoelectric oscillator is presented. The gas is contained within a pressure vessel (100) having a fixed internal volume (V), and the piezoelectric oscillator (202) is immersed in the gas within the pressure vessel (100). The method comprises: a) using said piezoelectric oscillator (202) to measure the density of the gas inside the high pressure vessel (100); b) determining, by measuring the density and the internal volume (V) of said pressure vessel, the mass of the gas inside the pressure vessel (100). through the provision of this method, the actual content (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. This allows a determination of mass, by directly obtaining the density of the gas in the cylinder, reducing the need for sensors or (...).
    公开号:BR112013013326B1
    申请号:R112013013326-0
    申请日:2011-11-28
    公开日:2021-02-17
    发明作者:Neil Alexander Dowie；Marcel Behrens；Lateef Olusegun Adigun Obadun
    申请人:Air Products And Chemicals, Inc.；
    IPC主号:
    专利说明:

    [0001] [0001] The present invention relates to a method and apparatus for measuring the actual content of a gas cylinder under pressure. More particularly, the present invention relates to a method and apparatus for measuring the actual contents of a cylinder, using a piezoelectric oscillator. The methods and apparatus described here can be applied to systems, where gas of relatively high pressure (for example, about 10 bar or more) is present, such as, for example, the supply of gases in high pressure cylinders or factories using high pressure gases. The present invention relates particularly to "clean" gases, that is, gases with little or no impurity or contaminants, such as water vapor or dust.
    [0002] [0002] A compressed gas cylinder is a pressure vessel designed to contain gases at high pressures, that is, at pressures significantly above atmospheric pressure. Compressed gas cylinders are used in a wide range of markets, from the generally low-cost industrial market, through the medical market, to higher-cost applications, such as the manufacture of electronic products using special corrosive, toxic or pyrophoric gases , of high purity. Normally, pressure gas 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.
    [0003] [0003] The present invention is particularly applicable to permanent gases. Permanent gases are gases, which cannot be liquefied by separate pressure and, for example, can be supplied in cylinders at pressures up to 450 bar g. Examples are argon and nitrogen. However, this is not to be considered as limiting, and the term gas can be considered to encompass a wider range of gases, for example, a permanent gas and a vapor from a liquefied gas. Vapors of liquefied gases are present above the liquid within a cylinder of compressed gas. Gases that liquefy under pressure, as they are compressed to fill a cylinder, are not permanent gases, and are more precisely described as liquefied gases under pressure, or as vapors of liquefied gases. As an example, nitrous oxide is supplied inside a cylinder in liquid form, with an equilibrium vapor pressure of 44.4 bar g at 15 ° C. These vapors are not permanent or real gases, as they are liquefiable by pressure or temperature around environmental conditions.
    [0004] [0004] In many cases, it is necessary to check the contents of a given cylinder pressure vessel, or to determine the amount of gas remaining. This is particularly critical in situations, such as healthcare applications.
    [0005] [0005] It is known to calculate, in accordance with gas laws, the actual content of a cylinder, based on knowledge of the gas pressure inside a cylinder. Pressure measurement is a well-known art and there are a wide variety of devices that work to measure pressure. The most conventional type uses an elastic diaphragm equipped with deformation measuring elements. However, despite being one of the lowest cost pressure sensors made today, these sensors tend to be relatively large in size, and have a mechanical structure that, despite being produced using mass production methods by photolithography, it is still relatively complex and expensive to do. They also have a degree of fragility and require calibration and temperature compensation before they can be used.
    [0006] [0006] Another manometer normally used is a Bourdon meter. Such a meter comprises a fragile closed tube, with a flattened thin wall, which is connected to the hollow end of a fixed tube containing the fluid pressure to be measured. An increase in pressure causes the closed end of the tube to arc. Such a meter comprises delicate components, which are vulnerable to damage caused, for example, by exposure to high pressures.
    [0007] [0007] A problem, which makes it difficult to accurately measure the amount of gas in a gas vessel, is the temperature-pressure ratio of the gases contained within the cylinder. According to gas laws, the pressure exerted by a given amount of gas in constant volume is directly proportional to its temperature. Therefore, when the temperature of a gas increases, the pressure of the gas also increases.
    [0008] [0008] Consequently, the pressure measurement, using a pressure gauge, such as a Bourdon gauge, rises and falls proportionally to the absolute temperature, for example, from an initial temperature of 20 ° C to, for example , 50 ° C in a lighted environment, the pressure indicated on a Bourdon meter will increase by 10%.
    [0009] [0009] An additional problem is that, in order to determine the contents of a cylinder using a pressure measurement, it is necessary that the pressure gauge be corrected for the gas compressibility. This is complicated, due to the fact that the behavior of a gas at high pressure does not agree with the behavior of an ideal gas.
    [0010] [00010] 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, the application of tension to them results in a slight compression or elongation of the solid, and vice versa.
    [0011] [00011] "An Accurate and Robust Quartz Sensor based on Tuning Fork Technology (SF6) - Gas Density Control" Zeisel et al., Sensors and Actuators 80 (2040) 233-236, discloses an arrangement whereby a Quartz crystal is used to measure the density of SF6 gas in medium and high voltage electrical equipment at low gas pressure. 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, in which pressures up to 8 bar g are used.
    [0012] [00012] US patent 4,644,796 describes a method and apparatus for measuring the pressure of a fluid, through a quartz crystal oscillator, housed within a variable volume housing, comprising a bellows arrangement. The internal volume of the housing varies due to the compression / expansion of the bellows by pressure from the external fluid. Therefore, the density of the fluid inside the housing varies, as the internal volume of the housing varies. The density inside the housing can be measured using a quartz crystal oscillator.
    [0013] [00013] The above arrangements describe the use of a solid state sensor, such as a quartz crystal oscillator. However, none of the above devices and methods is suitable for accurately measuring the mass of gas in a pressure vessel, such as a gas cylinder. Therefore, known measurement arrangements suffer from a technical problem, in that they are not able to provide an accurate measurement of the mass of the gas in a compartment, such as a gas cylinder, where high pressures are encountered.
    [0014] [00014] According to a first aspect of the present invention, a method is provided for measuring the mass of a gas under pressure through a piezoelectric oscillator, said gas being contained within a pressure vessel with a fixed internal volume and the piezoelectric oscillator being immersed in the gas inside the pressure vessel, the method comprising: a) using said piezoelectric oscillator to measure the density of the gas inside the high pressure vessel; b) determining, from the measurement of density and the internal volume of said pressure vessel, the mass of the gas within the pressure vessel.
    [0015] [00015] By providing such a method, the actual content (ie, mass) of gas (such as a permanent gas) in a pressure vessel, such as a cylinder, can be measured directly, without the need to compensate for factors such as such as temperature or compressibility. This allows the determination of mass by directly obtaining the density of the gas in the cylinder, reducing the need for additional sensors or complex compensations and approximations to be made. In addition, 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 fully immersed in the gas, in contrast to conventional pressure gauges (such as a Bourdon gauge), which requires a pressure differential in order to function.
    [0016] [00016] In one embodiment, step a) comprises: activation, by means of a driving circuit, of 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 vessel.
    [0017] [00017] In one embodiment, steps a) and b) are repeated one or more times, so that a series of measurements of the gas density within the pressure vessel over a period of time is obtained, said series of measurements being used to determine the change in gas mass within the pressure vessel during that period of time.
    [0018] [00018] In one embodiment, said piezoelectric oscillator comprises a quartz crystal oscillator.
    [0019] [00019] In one embodiment, the quartz crystal is composed of at least one tooth. In a variation, the quartz crystal comprises a pair of flat teeth.
    [0020] [00020] In one embodiment, the quartz crystal is cut in AT or SC.
    [0021] [00021] In a variation, the surface of the quartz crystal is directly exposed to the gas.
    [0022] [00022] In one embodiment, the detector assembly comprises a drive circuit. In a variant, the detector assembly comprises a drive circuit, which comprises a Darlington pair arranged in a feedback configuration from a common emitter amplifier.
    [0023] [00023] In one embodiment, the detector assembly comprises a source of energy. In one arrangement, the power source is made up of a lithium battery.
    [0024] [00024] In one embodiment, the detector assembly comprises a processor.
    [0025] [00025] In one embodiment, the pressure vessel comprises a high pressure vessel. A high pressure vessel is a vessel designed to withstand internal pressures generally greater than 10 bar.
    [0026] [00026] In one variation, the pressure vessel comprises a gas cylinder.
    [0027] [00027] In accordance with a second aspect of the present invention, a detector assembly is provided for measuring the mass of a gas under pressure inside a pressure vessel with a fixed internal volume, the detector assembly comprising a piezoelectric oscillator for immersion in the gas inside the pressure vessel, the detector assembly, when so immersed, being arranged to measure the density of the gas inside the pressure vessel and being configured to determine, from the measurement of density and the internal volume of said pressure vessel , the mass of the gas inside the pressure vessel.
    [0028] [00028] By providing such an arrangement, the actual content (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. This allows a determination of the mass by directly obtaining the density of the gas in the cylinder, reducing the need for additional sensors, or performing complex calculations. In addition, the piezoelectric oscillator is a solid state device, which is resistant to high pressures or sudden changes in pressure and, as such, is less likely to be damaged by pressure "creep" or other environmental factors. The structure of the piezoelectric oscillator allows the piezoelectric oscillator to be fully immersed in the gas, in contrast to conventional pressure gauges (such as a Bourdon gauge), which requires a pressure differential in order to function.
    [0029] [00029] In one variation, said piezoelectric oscillator includes a quartz crystal oscillator.
    [0030] [00030] In a variation, the gas is a permanent gas.
    [0031] [00031] In one arrangement, the high pressure vessel is a gas cylinder.
    [0032] [00032] In one embodiment, the detector assembly comprises a drive circuit. In a variant, the detector assembly comprises a drive circuit, which comprises a Darlington pair arranged in a feedback configuration from a common emitter amplifier.
    [0033] [00033] In one embodiment, the detector assembly comprises a source of energy. In one arrangement, the power source is made up of a lithium battery.
    [0034] [00034] In one embodiment, the detector assembly comprises a processor.
    [0035] [00035] In one embodiment, the detector assembly is arranged to drive the piezoelectric oscillator, so that the piezoelectric oscillator resonates at a resonant frequency, and measures said resonant frequency over a predetermined period of time, to determine the density of the gas in said pressure vessel.
    [0036] [00036] In one embodiment, the detector assembly is further arranged to perform repeated measurements of the gas mass 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, more often, such that a series of measurements of gas density within the pressure vessel over a period of time is obtained, said series of measurements being used to determine the change in mass of gas within the pressure vessel during said period of time.
    [0037] [00037] According to a third aspect of the present invention, a valve arrangement is provided, comprising the detector assembly of the second 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 being arranged to allow selective filling of the pressure vessel with gas, or distribution of gas from the pressure vessel.
    [0038] [00038] According to a fourth aspect of the present invention, there is provided a pressure vessel, which contains a gas under pressure, the pressure vessel with a fixed internal volume and comprising: a pressure vessel body that defines an internal volume fixed; a valve arrangement connected to said vessel body and arranged to allow selective filling of the pressure vessel with gas, or distribution of gas from said vessel; and the detector assembly of the second aspect.
    [0039] [00039] In one embodiment, the detector assembly comprises a drive circuit. In one embodiment, the detector assembly comprises a source of energy. In one variation, the power source is made up of a lithium battery.
    [0040] [00040] In one embodiment, the detector assembly is located entirely within the fixed internal volume of the pressure vessel.
    [0041] [00041] In one arrangement, the pressure vessel body comprises a gas cylinder.
    [0042] [00042] According to a fifth embodiment of the present invention, there is provided a computer program product executable by a programmable processing apparatus, which comprises one or more segments of software to perform the steps of the first aspect.
    [0043] [00043] In accordance with a sixth embodiment of the present invention, a storage medium usable on a computer is provided, having a computer program product, according to the fourth aspect, stored therein.
    [0044] [00044] 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, according to a first embodiment of the invention; Figure 3 is a schematic diagram, showing an upper part of the gas cylinder assembly, according to a second embodiment of the invention; Figure 4 is a schematic diagram of a drive circuit for use with the first or second embodiments; Figure 5 is a schematic diagram, showing an alternative to the drive circuit for use with the first or second embodiments; Figure 6 shows a graph of the frequency of a quartz crystal (kHz) on the Y axis as a function of density (kg / m3) for a number of different gases; Figure 7 shows a graph of the gas mass (in kg) on the Y axis as a function of pressure (bar g) on the X axis for argon, oxygen and a mixture of argon: carbon dioxide; Figure 8 shows a graph of the gas mass (in kg) on the Y axis as a function of density (in kg / m3) on the X axis for the same three gases (argon, oxygen and a mixture of argon: dioxide carbon), as shown in Figure 7; Figure 9 shows a graph of frequencies (in kHz) on the Y axis as a function of time (in min) on the X axis for a flow rate of 12 l / min by a 50 l gas cylinder at a pressure 100 bar g; Figure 10 shows a graph of calculated flows (in liters per minute) on the Y axis as a function of time (in min) on the X axis for a 50 liter cylinder at a pressure of 100 bar g; Figure 11 shows a graph of frequencies (in kHz) on the Y axis as a function of the mass of the gas cylinder (in kg) on the X axis for a typical gas cylinder; Figure 12 is a flow chart illustrating a method, according to a described embodiment; Figure 13 shows a graph of the frequency behavior of different types of crystals; Figure 14 is a schematic diagram showing an alternative detector assembly, comprising two quartz crystals; and Figure 15 shows an alternative arrangement that uses a remote electronic data unit.
    [0045] [00045] Figure 1 shows a schematic view of a gas cylinder assembly 10, according to an embodiment of the invention.
    [0046] [00046] The gas cylinder 100 has a gas cylinder body 102 and a valve 104. The gas cylinder body 102 comprises a generally cylindrical pressure vessel, having a flat base 102a arranged to allow the gas cylinder assembly gas 10 stand on a flat surface.
    [0047] [00047] The body of the gas cylinder 102 is formed from materials of steel, aluminum and / or composites, and is adapted and arranged to withstand internal pressures 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 helical thread (not shown) adapted to accommodate the valve 104.
    [0048] [00048] The body of the gas cylinder 102 and the valve 104 define a pressure vessel (in this embodiment, in the form of a gas cylinder 100), having an internal volume V. The internal volume V is fixed. For this reason, it is understood that the structure of the gas cylinder 100 is such that its internal volume V (and, concomitantly, the volume of a gas contained therein) can be assumed to be non-variable to a significant degree in its 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 gas cylinder assembly. gas 10, where gas is kept under pressure.
    [0049] [00049] Any suitable fluid can be contained within the gas cylinder 100. However, the present embodiment relates, but is not limited to, purified permanent gases, which are free of impurities, such as dust and / or moisture. Non-complete examples of such gases may be: oxygen, nitrogen, argon, helium, hydrogen, methane, nitrogen trifluoride, carbon monoxide, krypton or neon.
    [0050] [00050] 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 helical thread for engagement with the opening 106 of the gas cylinder body 102. The outlet 110 is adapted and arranged, to allow the gas cylinder 100 to be connected to other components in a gas assembly; for example, hoses, tubes, or other valves or pressure regulators. Valve 104 can optionally comprise a VIPR (Valve with Integrated Pressure Regulator).
    [0051] [00051] Valve body 112 can be adjusted axially near or away from valve seat 114 by rotating a lever 116 to selectively open or close outlet 110. In other words, the movement of the valve body valve 112 near or away from valve seat 112 selectively controls the area of the pass-through medium between the inside of the gas cylinder body 102 and the outlet 110. This, in turn, controls the flow of gas from the interior of the gas cylinder assembly 100 to the external environment.
    [0052] [00052] 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 conduit 120, which allows components (such as wires) to be conducted from the outside of the gas cylinder 100 to the interior of the gas cylinder 100. the duct 120 acts as a high pressure seal, maintaining the integrity of the gas cylinder 100.
    [0053] [00053] The gas cylinder assembly 10 is provided with a detector assembly 200. The detector assembly 200 is arranged to measure the density of the gas within the internal volume V of the gas cylinder 100. The detector assembly 200 is shown in greater detail. in Figures 2 and 3, and comprises a quartz crystal oscillator 202 connected to a drive circuit 204 and a battery 206 by appropriate wiring 208. A processor 220 (not shown in Figures 2 and 3) can also be provided, either separately , or as an integral part of the drive circuit 204. This will be described later.
    [0054] [00054] In the embodiment shown in Figure 2, the quartz crystal oscillator 202 is located inside the internal volume V of the gas cylinder 100, and the drive circuit 204 is located outside the gas cylinder 100. Therefore, at least a part of the detector assembly 200 is located in the through-hole 118. The quartz crystal oscillator 202 and the drive circuit 204 are connected by wiring 208, which passes through the high-pressure conduit 120.
    [0055] [00055] 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 through conduit 120.
    [0056] [00056] An alternative embodiment is shown in Figure 3. The characteristics of the embodiment shown in Figure 3, which are in common with the embodiment in Figure 2, are assigned the same reference numbers, and will not be again described here.
    [0057] [00057] In the embodiment of Figure 3, the entire detector assembly 200 is located within the internal volume V of the gas cylinder 100. Thus, the quartz crystal oscillator 202, the drive circuit 204 (and the processor 204 , if provided) and battery 206 are all located inside the internal volume V of the gas cylinder 100. The components of the detector assembly 200 are completely immersed in the gas and are under isostatic pressure of gas inside the gas cylinder 100. For Therefore, the detector assembly 200 experiences the total gas pressure of the gas inside the gas cylinder 100.
    [0058] [00058] In this embodiment, conduit 120 can be optionally suppressed. Alternatively, the detector assembly 200 can be connected to an antenna 250 for remote communication, for example, with a base station. This will be discussed later. In this case, the antenna 250 can be located outside the gas cylinder 100 and connected to the detector assembly, by means of a cable or equivalent connector. The cable can be passed through the conduit 120, in order to make a connection between the antenna 250 and the detector assembly 200.
    [0059] [00059] The antenna 250 itself can be adapted and arranged to use any suitable communication protocol; for example, a non-complete list can be RFID, Bluetooth, Infrared (IR), 802.11 wireless, frequency modulation (FM) transmission, or a cellular network.
    [0060] [00060] Alternatively, wired communication can be implemented. Wired communication needs only a single metallic conductor to communicate: the "return" path of the circuit is provided by capacitive coupling through the air between the communication devices. The expert should be readily aware of the alternatives of the antenna 250 (and associated transmission hardware), which can be used with the embodiments discussed here.
    [0061] [00061] The inventors found that only some of the components of the detector assembly 200 are sensitive to high pressure. In particular, larger components, such as batteries, may be susceptible to high pressures. However, lithium batteries have been found to behave particularly well under the high pressures that arise within the gas cylinder 100. Consequently, battery 206 contains lithium ion cells. However, suitable alternative energy sources will be readily contemplated by the qualified person.
    [0062] [00062] The location of the complete detector 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 resistant metal or composite wall of the cylinder of gas 100 provides considerable protection against environmental or accidental damage. This is particularly important, for example, in storage areas or depots, where gas cylinders 100 are located adjacent to other gas cylinders 100, heavy machinery or rough surfaces.
    [0063] [00063] Furthermore, the location of the electronic components of the detector assembly completely within the internal volume V of the gas cylinder 100 allows larger components to be supplied, which, otherwise, might not be suitable for use on the external surface of a cylinder 100. For example, a larger battery can be provided in order to increase the operational life of the detector assembly 200.
    [0064] [00064] In addition, the internal location of the detector assembly 200 protects electronic components from environmental conditions, such as salt, water and other contaminants. This will allow, for example, a high impedance circuit, which is highly sensitive to salt and water damage, to be used as an integral part of the detector assembly 200.
    [0065] [00065] However, in a variation of the above embodiments, part of the detector assembly may be located within the internal volume V of the gas cylinder 100, and a part may be located outside the same. For example, drive circuit 212 and processor 200 may be located inside gas cylinder 100, while battery 206 may be located outside gas cylinder 100. This arrangement allows more fragile components of the detector assembly to be protected against damage and contaminants, while the 206 battery is easily accessible for maintenance and replacement.
    [0066] [00066] With respect to external communication, in one configuration, an aerial or external antenna (such as antenna 250) is not explicitly demanded. For example, communication can be carried out by means of acoustic transmission from inside the 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 fixed frequency piezoelectric resonator .
    [0067] [00067] A complementary receiver is also required, and this component may be located away from cylinder 100, and may comprise hardware, such as, for example, a circuit tone detector with phase lock integrated into a microphone. Such an acoustic arrangement provides the advantage that no through conduit is necessary (as is the case for the antenna 250), and that all electronic components can be entirely located inside the cylinder 100.
    [0068] [00068] The benefits of the internal location of the detector assembly 200 are unique to solid-state detector devices, such as the quartz crystal oscillator 202. For example, a conventional pressure sensor, such as a Bourdon meter, cannot be located that way. 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 prevents the location of a conventional pressure gauge entirely within a gas cylinder 100.
    [0069] [00069] Detector assembly 200 will now be described in more detail with reference to Figures 2 to 4. The quartz crystal oscillator 202 comprises a small thin section of cut quartz. Quartz shows piezoelectric behavior, that is, the application of a voltage through the crystal causes the crystal to change its shape, generating a mechanical force. On the other hand, a mechanical force applied to the crystal produces an electrical charge.
    [0070] [00070] Two parallel surfaces of the 202 quartz crystal oscillator are metallized in order to provide electrical connections through the raw crystal. When a voltage is applied through the crystal through the metal contacts, the crystal changes shape. By applying an alternating voltage to the crystal, the crystal may be forced to oscillate.
    [0071] [00071] The physical size and physical thickness of the quartz crystal determine the characteristic or resonant frequency of the quartz crystal. Indeed, the characteristic or resonant frequency of crystal 202 is inversely proportional to the physical thickness between the two metallized surfaces. Quartz crystal oscillators are well known in the art, and thus the structure of the quartz crystal oscillator 202 will not be described in detail here.
    [0072] [00072] The resonant frequency of vibration of a quartz crystal will vary, depending on the environment in which the crystal is located. In a vacuum, the crystal will have a specific frequency. However, this frequency will change in different environments. For example, in a fluid, the crystal's vibration will be attenuated by the fluid's neighboring molecules, and this will affect the resonant frequency and energy required to oscillate the crystal in a given amplitude.
    [0073] [00073] In addition, the adsorption of gases or deposition of adjacent materials on the crystal will affect the mass of the vibrating crystal, changing the resonant frequency. This forms the basis for the normally used selective gas analyzers, in which an absorbent layer is formed on the crystal and increases in mass when gas is absorbed on the absorbent layer. However, in the present case, no coating is applied to the quartz crystal oscillator 202. In fact, the adsorption or deposition of material on the quartz crystal oscillator 202 is undesirable in the present case, since the measurement accuracy can be affected.
    [0074] [00074] The quartz crystal oscillator 202 of the present embodiment is in the form of a tuning fork and comprises a pair of teeth 202a (Figure 4) approximately 5 mm long, arranged to oscillate at a resonant frequency of 32.768 kHz. The tines 202a of the tuning fork normally oscillate in their fundamental mode, in which they move synchronously close to and away from each other at the resonant frequency.
    [0075] [00075] In addition, it is desirable to use quartz, which is cut in AT or SC. In other words, the flat section of quartz is cut at selected specific angles, so that the temperature coefficient of the oscillation frequency can be arranged to be parabolic with a broad peak close to room temperature. Thus, the crystal oscillator can be arranged in such a way that the slope at the top of the peak is precisely zero.
    [0076] [00076] These quartz crystals are commonly available at a relatively low cost. In contrast to most quartz crystal oscillators, which are used under vacuum, in the present embodiment, quartz crystal oscillator 202 is exposed to gas under pressure in the internal volume V of gas cylinder 100.
    [0077] [00077] The drive circuit 204 to drive the quartz crystal oscillator 202 is shown in Figure 4. The drive circuit 204 must meet a series 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 pressurized gas, such as hydrogen. Thus, the quartz crystal 202 is required to operate (and restart after a period of non-use) under a wide range of pressures.
    [0078] [00078] Therefore, the quality factor (Q) of the quartz crystal oscillator 202 will vary considerably during use. The Q factor is a dimensionless parameter related to the attenuation rate of an oscillator or resonator. Equally, it can characterize a resonator's bandwidth relative to its central frequency.
    [0079] [00079] In general, the higher the Q factor of an oscillator, the lower the rate of energy loss in relation to the stored energy of the oscillator. In other words, the oscillations of an oscillator with a high Q factor are reduced 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 lower frequency bandwidth around that frequency, to which they resonate.
    [0080] [00080] The drive circuit 204 should be able to drive the quartz crystal oscillator 202, despite the variation of the Q factor. As the pressure in the gas cylinder 100 increases, the oscillator of the quartz crystal oscillator 202 will becomes more and more attenuated, and the Q factor drops. The falling Q factor requires that a greater gain be provided by an amplifier in the drive circuit 204. However, if a very high amplification is provided in the drive circuit 204, the response from the quartz crystal oscillator 202 can make difficult to distinguish. In this case, the drive circuit 204 can simply oscillate at an unrelated frequency, or at the frequency in a non-fundamental way of the quartz crystal oscillator 202.
    [0081] [00081] As an additional limitation, the drive circuit 204 must be of low power, to operate with small low power batteries for a long time, with or without supplementary power, such as photovoltaic cells.
    [0082] [00082] 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 receives a voltage signal from the quartz crystal oscillator 202, amplifies it, and feeds that signal back to the quartz crystal oscillator 202. The fundamental resonant frequency of the quartz crystal oscillator 202 is, in essence, a function of the rate of expansion and contraction of the quartz. This is determined, in general, by the cut and size of the crystal.
    [0083] [00083] However, external factors also affect the resonant frequency. When the energy of the generated output frequencies coincides with the losses in the circuit, an oscillation can be sustained. The drive circuit 204 is arranged to detect and maintain that oscillation frequency. The frequency can then be measured by processor 220, used to calculate the appropriate gas property required by the user and, if necessary, emitted to an appropriate display medium (as will be described later).
    [0084] [00084] The drive circuit 204 is powered by a 6 V power source 206. The power source 206, in this embodiment, comprises a lithium battery. However, alternative energy sources will be readily apparent to one skilled in the art; for example, other types of rechargeable and non-rechargeable batteries and an array of solar cells.
    [0085] [00085] Drive circuit 204 still comprises a common emitter amplifier with a Darlington pair 210. A pair of Darlington comprises a composite structure, consisting of two bipolar NPN transistors configured in such a way that the current amplified by a first transistor is amplified even more by the second. This configuration allows a higher current gain to be obtained, when compared to each transistor separately. Alternatively, bipolar PNP transistors can be used.
    [0086] [00086] The Darlington pair 210 is arranged in a feedback configuration by a common transistor emitting amplifier (T1) 212. A bipolar NPN junction transistor is shown in Figure 4. However, the person skilled in the art should be aware of alternative transistor arrangements, which can be used; for example, a bipolar PNP junction transistor or transistors with a metal oxide semiconductor field effect (MOSFETs).
    [0087] [00087] The drive circuit 204 comprises another transistor T2 following the NPN emitter, which acts as an attenuator amplifier 214. The attenuator amplifier 214 is arranged to function as an attenuator between the circuit and the external environment.
    [0088] [00088] A capacitor 216 is located in series with the quartz crystal oscillator 202. Capacitor 216, in this example, has a value of 100 pF and allows the drive circuit 204 to activate the quartz crystal oscillator 202, in situations where the crystal is contaminated, for example, by salts or other deposited materials.
    [0089] [00089] An alternate drive circuit 260 will now be described with reference to Figure 5. The drive circuit shown in Figure 5 is configured similarly to a Pierce oscillator. Pierce oscillators are known from digital clock IC oscillators. In essence, the drive circuit 260 comprises a single digital converter (in the form of a transistor) T, three resistors R1, R2 and RS, two capacitors C1, C2, and the quartz crystal oscillator 202.
    [0090] [00090] In this arrangement, the 202 quartz crystal oscillator functions as a highly selective filter element. The resistor R1 acts as a load resistor for the transistor T. The resistor R2 acts as a feedback resistor, polarizing the inverter T in its linear region of operation. This effectively allows the T inverter to function as a high gain inverter amplifier. Another resistance Rs is used between the output of the inverter T and the quartz crystal oscillator 202, to limit the gain and to attenuate unwanted oscillations in the circuit.
    [0091] [00091] The quartz crystal resonator 202, in combination with C1 and C2, forms a Pi 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 drive circuit 260 described above is reliable and inexpensive to manufacture, since it comprises a relatively small number of components.
    [0092] [00092] As discussed above, the detector assembly 200 may include a processor 220, which receives input from the quartz crystal oscillator 202 and the drive circuit 204. The processor 220 may comprise a suitable arrangement, such as an ASIC or FPGA. Processor 220 is programmed to calculate, present and communicate useful parameters to users of cylinder 100.
    [0093] [00093] When used with the quartz crystal oscillator 202, the processor 220 can be configured to measure the frequency f or period of the signal from the drive circuit 204. This can be achieved, for example, by counting the oscillations to the over a fixed time, and converting that frequency to a density value, using an algorithm or a look-up table. This value is transferred to processor 220, which is configured to perform, based on the inputs fed, a calculation, to determine the mass of the gas in the gas cylinder 100.
    [0094] [00094] Processor 220 can optionally be designed, so that mass production is identical in all cylinders, with different software and hardware characteristics enabled for different gases.
    [0095] [00095] In addition, processor 220 can also be configured to minimize power consumption, by implementing standby or "sleep" modes, which can cover processor 220 and additional components, such as drive circuit 204 and the 202 quartz crystal oscillator.
    [0096] [00096] Various schemes can be implemented; for example, processor 220 may be at rest for 10 seconds every 11 seconds. In addition, processor 220 can control quartz crystal oscillator 202 and drive circuit 204 in such a way that these components are put on hold by it most of the time, with only the components most in need of power being activated by ½ second every 30 seconds. Alternatively or additionally, communication components, such as antenna 250, can be turned off, as needed, or used to activate detector assembly 200.
    [0097] [00097] The theory and operation of the detector assembly 200 will now be described with reference to Figures 6 to 9.
    [0098] [00098] The quartz crystal oscillator 202 has a resonant frequency, which is dependent on the density of the fluid, in which it is found. The exposure of a flat crystal oscillator of the type oscillating tuning fork to a gas leads to a displacement and attenuation of the resonant frequency of the crystal (when compared to the resonant frequency of the crystal in a vacuum). There are a number of reasons for this. Although there is an attenuation effect of the gas on the oscillations of the crystal, the gas adheres to the vibrating teeth of the pitch-type crystal oscillator 202, which increases the 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, unilateral elastic beam:
    [0099] [00099] The two parts of equation 1) relate to: a) mass of gas additive on the teeth of the 202 quartz crystal oscillator and b) shear forces that arise in the outermost layer of the teeth during oscillation.
    [0100] [000100] The equation can thus be rewritten in terms of frequency and simplified to:
    [0101] [000101] It was discovered by the inventors that a good approximation can be adequately obtained by the approximation: 4) Δf ≈Δρ
    [0102] [000102] Therefore, for a good approximation, the change in frequency is proportional to the change in gas density, to which the quartz crystal oscillator is exposed. Figure 6 shows, for a series of different gases / gas mixtures, that the resonant frequency of the quartz crystal oscillator 202 varies linearly as a function of density.
    [0103] [000103] In general, the sensitivity of the 202 quartz crystal oscillator is that a 5% change in frequency is seen, for example, with oxygen gas (having a molecular weight of 32 AMU) at 250 bar, when compared with atmospheric pressure. Such gas pressures and densities are typical of cylinders used for storing permanent gases, which are typically between 137 and 450 bar g for most gases, and up to 700 or 900 bar g for helium and hydrogen.
    [0104] [000104] The quartz crystal oscillator 202 is particularly suitable for use as a density sensor for commercially supplied gases. Firstly, in order to correctly detect the density of a gas, it is necessary that the gas be free of dust and liquid droplets, which is guaranteed with commercially supplied gases, but not with air or in most control situations. pressure.
    [0105] [000105] Secondly, due to the fact that the gas pressure inside a cylinder can only be changed slowly during normal use (ie, while the gas is expelled through outlet 110), the fact that the quartz crystal oscillator 202 taking a short period of time (about 1 second) to obtain a reading does not affect the accuracy of the measurement. The time period of approximately 1 s is necessary, because of the need to count the oscillations and because of the need for a quartz crystal oscillator 202 to reach equilibrium at a new gas pressure.
    [0106] [000106] This method may be less accurate, if the gas in the gas cylinder 100 is not uniform - for example, if the gas is a non-uniform mixture, as can occur inside a cylinder partially filled with liquid, or in the case of a freshly prepared or insufficiently mixed mixture of light and heavy gases. However, this is unlikely to occur in most conditioned gas applications.
    [0107] [000107] As previously described, the internal volume V of 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 has been obtained from measurement by the detector assembly 200, the mass M of the gas in the cylinder can be obtained from the following equation: 5) M = pV
    [0108] [000108] Direct measurement of the gas density p, therefore, allows the calculation of the mass of gas remaining in the gas cylinder 100.
    [0109] [000109] The measurement of the mass of gas, in this way, has a number of advantages over the known arrangements. For example, the measured mass, according to an embodiment of the invention, is intrinsically corrected with respect to temperature. In contrast, the measurement of pressure, using, for example, a Bourdon gauge, varies proportionally with absolute temperature. Therefore, the present arrangement does not require measurement and / or correction, as is the case with known provisions.
    [0110] [000110] In addition, the gas mass, measured according to an embodiment of the present invention, is intrinsically corrected with respect to Z compressibility. In a conventional arrangement, for example, using a Bourdon meter, in order to obtain gas content from the pressure, the compressibility of the gas needs to be corrected. This is particularly important at high pressures, where the Z compressibility is not proportional to the gas pressure in the expected form of an ideal gas.
    [0111] [000111] Automatic compensation for compressibility is illustrated with reference to Figures 7 and 8. Figure 7 shows a graph of the gas mass (in kg) on the Y axis as a function of pressure (bar g) for argon, oxygen and a mixture of argon: carbon dioxide. As shown in Figure 7, the masses of the different gases vary with increasing pressure. In addition, at high pressures greater than 250 bar g, there is no longer a linear relationship between mass and pressure.
    [0112] [000112] Figure 8 shows a graph of the gas mass (in kg) on the Y axis as a function of density (in kg / m3) for the same three gases (argon, oxygen and a mixture of argon: carbon dioxide ), as shown in Figure 7. In contrast to Figure 7, it can be seen that the gas mass as a function of density is identical for each gas / gas mixture. In addition, the relationship is still linear at high densities. Accordingly, the quartz crystal oscillator 202 can be high resolution and highly linear with density.
    [0113] [000113] As mentioned above, the arrangement of the present invention allows measurement at very high precision, with a resolution of parts per million. Together with the linear response of the 202 quartz density sensor to high densities and pressures (as illustrated in Figures 7 and 8), the high precision allows very light gases, such as H2 and He, to be accurately measured.
    [0114] [000114] In addition to measuring static pressure inside a gas cylinder 100, detector assembly 200 is capable of measuring mass flow into or from gas cylinder 100. This can be useful in situations where it is necessary to use the gas rate from the gas cylinder 100, perhaps, to calculate the time remaining until the cylinder is emptied. Alternatively or additionally, the mass flow can be monitored in order to deliver precise amounts of gas.
    [0115] [000115] Gas density at atmospheric pressure is only on the order of 1 g / liter, and normal gas usage rates are often only 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 out of the gas cylinder 100 to be measured by changing the indicated density. The mass flow
    [0116] [000116] Figures 9 and 10 illustrate experimental data for mass flow detection. Figure 9 shows a graph of frequency (kHz) on the Y axis as a function of time (in minutes) on the X axis for a flow rate of 12 liters per minute from a 50 liter cylinder at ~ 100 bar pressure indicated. Figure 10 shows a graph of the calculated flow rate (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.
    [0117] [000117] These figures illustrate that, for the most normal uses, the mass flow rate of gas, from a gas cylinder 100, can be determined by measuring a change in density over time. Consequently, the mass flow rate can be calculated with sufficient precision and time resolution using the quartz crystal oscillator 202 and the drive circuit 204.
    [0118] [000118] Figure 11 illustrates further experimental data, showing the operation of the present invention. Figure 11 shows a graph of the frequency (in kHz) on the Y axis as a function of the total mass (in kg) of the cylinder on the X axis. As can be seen, the graph is, with a high degree of accuracy, approximately linear. Therefore, Figure 11 shows that the mass of gas inside the gas cylinder 100 can be accurately measured with the quartz crystal oscillator 202.
    [0119] [000119] A method, according to an embodiment of the present invention, will now be described with reference to Figure 12. The method described below is applicable to each of the first and second embodiments described above with reference to Figures 2 and 3. Step 300: initialize measurement
    [0120] [000120] In step 300, the measurement of the mass of gas in the gas cylinder 100 is initialized. This can be activated, for example, by a user, by pressing a button on the outside of the gas cylinder 100. Alternatively, the measurement can be initiated by means of a remote connection, for example, a signal transmitted over a network without wire and received by detector set 200, via antenna 250 (see Figure 3).
    [0121] [000121] As another alternative, or in addition, the detector assembly 200 can be configured to start up remotely, or with a timer. The method proceeds to step 302. Step 302: activate the quartz crystal oscillator
    [0122] [000122] Once started, the drive circuit 204 is used to drive the quartz crystal oscillator 202. During initialization, the drive circuit 204 applies a random noise AC voltage across the crystal 202. At least a portion of the said random voltage will be at an appropriate frequency, to cause the crystal 202 to oscillate. Crystal 202 will then begin to oscillate in sync with that signal.
    [0123] [000123] Through the piezoelectric effect, the movement of the quartz crystal oscillator 202 will then generate a voltage in the resonant frequency range of the quartz crystal oscillator 202. The drive circuit 204 then amplifies the generated signal by the quartz crystal oscillator 202, in such a way that the signals generated in the frequency band of the quartz crystal resonator 202 dominate the output of the drive circuit 204. The narrow resonant band of the quartz crystal removes by filtration all the unwanted frequencies and the drive circuit 204 then drives the quartz crystal oscillator 202 at the fundamental resonant frequency f. Once the quartz crystal oscillator 202 has stabilized at a particular resonant frequency, the method proceeds to step 304. Step 304: Measure the resonant frequency of the quartz crystal oscillator
    [0124] [000124] The resonant frequency f is dependent on the conditions within the internal volume V of the gas cylinder. In the present embodiment, the change in resonant frequency Δf is proportional in magnitude to the change in gas density within the gas cylinder 100, and will decrease with increasing density.
    [0125] [000125] In order to make a measurement, the frequency of the quartz crystal oscillator 202 is measured over a period of approximately 1 s. This is to allow the reading to stabilize, and for sufficient swings to be counted, in order to determine an accurate measurement. Frequency measurement is performed on processor 220. Processor 220 can also record time T1 when the measurement was started.
    [0126] [000126] Once the frequency has been measured, the method proceeds to step 306. Step 306: determine mass of gas in the gas cylinder
    [0127] [000127] Since the frequency of the quartz crystal oscillator 202 was measured satisfactorily in step 303, processor 220 then calculates the mass of gas in the gas cylinder 100.
    [0128] [000128] This is done using equation 5) above, in which 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 308. Step 308: Store measurement results
    [0129] [000129] Once the mass of gas has been calculated, the mass can simply be recorded in an internal memory associated with processor 220 of detector set 200 for future retrieval. As yet another alternative, the gas mass at time T1 can be stored in a local memory for said processor 220.
    [0130] [000130] The method then proceeds to step 310. Step 310: Communicate results
    [0131] [000131] As an optional step, the mass of the gas can be presented in several ways. For example, a display connected to the gas cylinder 100, or valve 104, can display the mass of the gas contained in the gas cylinder 100. Alternatively, the measurement of the gas mass can be remotely communicated to a base station, or the a meter located on an adjacent accessory.
    [0132] [000132] The method then proceeds to step 312. Step 312: turn off detector assembly
    [0133] [000133] It is not necessary to keep detector set 200 operational at all times. On the contrary, it is beneficial to reduce energy consumption by switching off detector assembly 200, when not in use. This extends the 206 battery life.
    [0134] [000134] The configuration of the drive circuit 204 allows the quartz crystal oscillator 202 to be restarted, regardless of the gas pressure in the gas cylinder 100. Therefore, the detector assembly 200 can be turned off, when necessary, in order to save battery power.
    [0135] [000135] The method of operating an embodiment of the present invention has been described above with reference to steps 300 to 310 above. However, optionally, the following additional steps can also be taken: Steps 314 - 318: make additional mass determination
    [0136] [000136] It may be desirable to calculate the mass flow of gas to / from gas cylinder 100. At a time T2, which is after T1, steps 314, 316 and 318 are carried out. Steps 314, 316 and 318 correspond to steps 304, 306 and 308, respectively, performed at time T2. The values resulting from steps 314, 316 and 318 are stored in the internal memory of processor 220, as a mass of gas at time T2.
    [0137] [000137] The time interval between T1 and T2 can be very short, in the order of seconds, as illustrated in Figure 9. Alternatively, if the flow rate 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 T1 and T2 can be considerably longer; for example, in the order of minutes, hours, or days.
    [0138] [000138] The method then proceeds to step 320. Step 320: Calculate the mass flow
    [0139] [000139] Knowing the time difference between times T1 and T2, and the mass of gas in the gas cylinder 100 at those times, processor 220 can calculate the mass flow, in the time period between T1 and T2 from the equation 6).
    [0140] [000140] The method can then repeat steps 314 to 320, to calculate the additional mass flow, if necessary. Alternatively, the method can proceed to step 312, and the detector assembly 200 can be turned off.
    [0141] [000141] Variations of the above embodiments will be apparent to one skilled in the art. The exact configuration of the hardware and software components may be different and still fall within the scope of the present invention. An expert should be promptly aware of alternative configurations, which can be used.
    [0142] [000142] For example, the embodiments described above used a quartz crystal oscillator, having a fundamental frequency of 32.768 kHz. However, crystals can be used, which operate at alternative frequencies. For example, quartz crystal oscillators, which operate at 60 kHz and 100 kHz, can be used with the above described embodiments. A graph, which shows the frequency change with density for different crystals, is shown in Figure 13. As another example, a crystal oscillator, which operates at a frequency of 1.8 MHz, can be used.
    [0143] [000143] An operation with a higher frequency allows the pressure to be monitored more frequently, because a short period of time is necessary to sample a certain number of cycles. In addition, higher frequency crystals allow a shorter duty cycle to be used in a crystal "suspend" mode. As an explanation, in most cases, the drive circuit and the crystal will spend most of the time switched off, only being switched on for a second or less, when a measurement is needed. This can happen, for example, once a minute. When a higher frequency crystal is used, the pressure can be measured more quickly. Therefore, the time, in which the crystal is operational, can be reduced. This can reduce power consumption and, at the same time, improve battery life.
    [0144] [000144] In addition, the above embodiments have been described by measuring the absolute frequency of a quartz crystal oscillator. However, in independent electronics incorporated into a regulator associated with the gas cylinder, it may be advantageous to measure the change in the sensor frequency, by comparing that frequency with a reference crystal of the same type, but closed in a vacuum or a package of pressure. The pressure pack can contain gas at a selected density, gas under atmospheric conditions, or it can be opened to the outside atmosphere of the gas cylinder 100.
    [0145] [000145] A suitable detector assembly 400 is shown in Figure 14. The detector assembly 400 comprises a first quartz crystal oscillator 402 and a second quartz crystal oscillator 404. The first quartz crystal oscillator 402 is a reference crystal , which is located inside a vacuum-sealed 406 container. The first quartz crystal oscillator 402 is driven by a 408 drive circuit.
    [0146] [000146] The second quartz crystal oscillator 404 is a crystal similar to crystal 202 described in the previous embodiments. The second quartz crystal oscillator 404 is exposed to the gas environment within the internal volume of the gas cylinder 100. The second quartz crystal oscillator 404 is driven by a drive circuit 410.
    [0147] [000147] This comparison can be made using an electronic mixer circuit 412, which combines the two frequency signals and produces an output with a frequency equal to the difference between the two crystals. This arrangement allows small changes to be neutralized, due, for example, to temperature.
    [0148] [000148] In addition, the circuits used in a gas cylinder 100 can be simplified, because only the frequency of difference should be measured. In addition, this approach is particularly suitable for use with a high frequency (MHz) crystal oscillator, where it can be difficult to directly measure the frequency of the crystal.
    [0149] [000149] In addition, all the electronics 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 units mounted on the cylinder permanently, and units mounted on any of a customer's stations, or temporarily mounted on the outlet of the cylinder, as the position normally used for a flow meter. conventional.
    [0150] [000150] An example of such an arrangement is shown with reference to Figure 15. The arrangement comprises a gas cylinder assembly 50, comprising a gas cylinder 500 and a detector assembly 502. The gas cylinder assembly 50, gas cylinder 500 and detector assembly 502 are substantially similar to the gas cylinder assembly 10, gas cylinder 100 and detector assembly 200, substantially as described above with reference to the previous embodiments.
    [0151] [000151] In this embodiment, the detector assembly 502 comprises a quartz crystal oscillator and drive circuit (not shown) similar to the quartz crystal oscillator 202 and drive circuit 204 of the previous embodiments. An antenna 504 is provided for communication via any suitable remote communication protocol; for example, Bluetooth, Infrared (IR) or RFID. Alternatively, wired communication can be used.
    [0152] [000152] As an additional alternative, acoustic communication methods can be used. The advantage of such methods is that remote communication can be carried out, without the need for an external antenna 250.
    [0153] [000153] A connection tube 506 is connected at the outlet of the gas cylinder 500. The connection tube is closed by a quick connection 508. The quick connection 508 allows the connection tube, or the components, to be connected and disconnected with ease and speed of the gas cylinder 500.
    [0154] [000154] A quick connection unit 550 is provided for connection to gas cylinder 500. A complementary quick connection connector 510 is provided for connection to connector 508. In addition, the quick connection unit 550 is equipped with a unit data unit 552. The data unit 552 comprises a display 554 and an antenna 556 for communication with the antenna 504 of the gas cylinder assembly 50. The display 554 may comprise, for example, an E-ink display, to minimize consumption power and maximize the visibility of the screen.
    [0155] [000155] The data unit 552 can record various parameters measured by the detector set 502 of the gas cylinder assembly 50. For example, the data unit 552 can record mass as a function of time. Such a record can be useful, for example, for welding contractors who want to check whether the gas flow was present and correct during long gas welding procedures on critical components, or to provide data on the use of a particular customer.
    [0156] [000156] In addition, the data obtained from the gas cylinder 500 can be used to present data on the run time, that is, the time before the gas in the cylinder 500 is used. This is particularly critical in applications, such as a hospital oxygen cylinder used to transport patients between hospitals. Such time (Tro) can be calculated from the knowledge of the flow rate (discussed above), mass content of the cylinder 500 and the current time (Tc) using the following equation:
    [0157] [000157] As an alternative, data from data unit 550 can be transmitted to a computer-activated welding machine (for welding applications), or other equipment using gas, to allow calculation of derived parameters, along with alert messages. Non-complete examples of this could be: gas used per unit arc time, gas used per kg of welding wire (for example, with welding porosity alert), the number of standard type balloons (or to measure and calibrate welding balloons) a non-standard size), the number of welding hours remaining, the pressure display (by converting the measured density value with respect to pressure using known gas data).
    [0158] [000158] In addition, the data unit 550 can be arranged to provide the following functions: provide an audible or visual alarm, if the gas level is below a certain level or flow; display the life of the cylinder (for example, for slowly varying mixtures), or an expiration date for the cylinder; contain and display data on gas usage, that is, which types of welding, which types of welded metal, or provide links, so that mobile phones or computers can collect detailed data; providing a multimodal operation, for example, a supplier / filling mode and a customer mode; display different quantities to the customer, from those displayed by the gas company that refills the cylinders; allow data entry; provide data, such as a cylinder number, type of gas, a certificate of analysis, a history of the customer (who had the cylinder during which dates), safety and operational data can be contained in summary form on the cylinder.
    [0159] [000159] Alternatively, all of the above examples can optionally be processed, stored or obtained from a system entirely located in (or within) gas cylinder 500, as discussed in terms of detector assembly 200, 502.
    [0160] [000160] 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. In addition, a quartz crystal oscillator will not incorrectly read pressure changes due to changes in cylinder temperature, as is the case, when detecting leakage through a pressure gauge. In addition, embodiments of the invention can be used to detect failures, for example, in the failure detection of the residual pressure valve (for example, in a used cylinder with pressure less than 3 bar g).
    [0161] [000161] Although the above embodiments have been described with reference to the use of a quartz crystal oscillator, a person skilled in the art should be readily aware of alternative piezoelectric materials, which can also be used. For example, a non-complete list may include crystal oscillators, comprising: lithium tantalate, lithium niobate, lithium borate, berlinite, gallium arsenide, lithium tetraborate, aluminum phosphate, germanium bismuth oxide, titanate ceramic polycrystalline zirconia, high alumina ceramics, silicon oxide and zinc compounds, or dipotassium tartrate.
    [0162] [000162] Furthermore, although 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 under load or speed, the inventors of the present patent application demonstrate that the internal volume of the tire does not change significantly in use. For example, since the change in internal volume is, in this context, less than 23% of the total internal volume, the present invention is safely operable to calculate the mass of gas inside a vehicle tire.
    [0163] [000163] In addition, although many applications use air as gas inside a vehicle tire, gases, such as nitrogen, are increasingly used. The arrangements of the present invention are particularly suitable for such applications. In addition, because the mass measurement is essentially temperature independent, the arrangement of the present invention is particularly useful in situations where environmental conditions can affect the measurements.
    [0164] [000164] As an additional example, the present invention can also be applied to air suspension systems for vehicles.
    [0165] [000165] Embodiments of the present invention have been described with particular reference to the illustrated examples. Although specific examples are represented in the drawings and described in detail herein, it should be understood, however, that the drawings and detailed description are not intended to limit the invention to the particular form disclosed. It should be understood that variations and modifications can be made to the described examples, within the scope of the present invention.
    权利要求:
    Claims (10)
    [0001]
    METHOD FOR MEASURING THE MASS OF A GAS UNDER PRESSURE, USING A PIEZOELECTRIC OSCILLATOR, characterized by the fact that said gas comprises a permanent gas or a mixture of permanent gases and is contained within a gas cylinder (100) having a fixed internal volume ( V), the gas cylinder (100) comprising a gas cylinder body (102), a valve arrangement (104) connected to said gas cylinder body (102) and arranged to allow selective filling of the cylinder gas (100) with gas, or gas distribution from the gas cylinder (100) and the piezoelectric oscillator (202) being arranged in the valve arrangement (104) so that the piezoelectric oscillator (202) is located inside of the gas cylinder body (102) and immersed in the gas inside the gas cylinder (100), the method comprising: a) using said piezoelectric oscillator (202) to measure the density of the gas inside the gas cylinder (100); b) determining, from the measurement of density and the internal volume (V) of said gas cylinder, the mass of the gas inside the gas cylinder (100).
    [0002]
    METHOD, according to claim 1, characterized by the fact that step a) comprises: actuation, by means of an actuation circuit, of the piezoelectric oscillator, so that the piezoelectric oscillator resonates to a resonant frequency; and measuring said resonant frequency over a predetermined period of time, to determine the density of gas in said pressure vessel.
    [0003]
    METHOD, according to claim 1 or 2, characterized by the fact that steps a) and b) are repeated one or more times, so that a series of measurements of the gas density inside the pressure vessel over a period of time is obtained, said series of measurements being used to determine the variation in the mass of gas within the pressure vessel during said period of time.
    [0004]
    METHOD, according to claim 1, 2 or 3, characterized in that said piezoelectric oscillator comprises a quartz crystal oscillator.
    [0005]
    GAS CYLINDER, having a fixed internal volume (v) and containing permanent gas or a mixture of permanent gases under pressure, characterized in that the gas cylinder (100) comprises a gas cylinder body (102) and a valve arrangement ( 104) connected to the gas cylinder body (102), the valve arrangement (104) being arranged to allow selective filling of the gas cylinder (100) with gas, or distribution of gas from the gas cylinder ( 100), and comprising a detector assembly (200) for measuring the mass of the gas under pressure inside the gas cylinder (100), the detector assembly (200) comprising a piezoelectric oscillator (202) disposed in the valve arrangement (104) of so that the piezoelectric oscillator (202) is disposed within the body of the gas cylinder (102) and immersed in the gas inside the gas cylinder (100), the detector assembly (200), when so immersed, is arranged to measure the density of the gas inside the gas cylinder (100) and being configured used 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 (100).
    [0006]
    GAS CYLINDER, according to claim 5, characterized by the fact that it also comprises a drive circuit, which comprises a pair of Darlington arranged in a feedback configuration from a common emitter amplifier.
    [0007]
    GAS CYLINDER, according to claim 5 or 6, characterized by the fact that the detector assembly is also 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 gas cylinder.
    [0008]
    GAS CYLINDER according to any one of claims 5 to 7, characterized in that the detector assembly is further arranged to carry out 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, more times so that a series of measurements of the gas density inside of the pressure vessel over a period of time is obtained, said series of measurements being used to determine the variation in the mass of gas within the pressure vessel during said period of time.
    [0009]
    GAS CYLINDER, according to any one of claims 5 to 8, characterized in that the detector assembly is located entirely within the fixed internal volume of the gas cylinder.
    [0010]
    LEGIBLE STORAGE MEDIA BY COMPUTER, characterized by the fact that it performs the steps of claims 1 to 4.
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    同族专利:
    公开号 | 公开日
    MX2013005952A|2013-07-03|
    TW201229513A|2012-07-16|
    CA2817794A1|2012-06-07|
    KR101544291B1|2015-08-12|
    US20130306650A1|2013-11-21|
    EP2458344B1|2018-03-14|
    CN103608649B|2018-04-17|
    EP2458344A1|2012-05-30|
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    ES2671716T3|2018-06-08|
    CL2013001501A1|2014-03-28|
    PL2458344T3|2018-08-31|
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    法律状态:
    2018-12-18| B06F| Objections, documents and/or translations needed after an examination request according [chapter 6.6 patent gazette]|
    2019-08-27| B06U| Preliminary requirement: requests with searches performed by other patent offices: procedure suspended [chapter 6.21 patent gazette]|
    2020-03-10| B06A| Patent application procedure suspended [chapter 6.1 patent gazette]|
    2020-08-25| B06A| Patent application procedure suspended [chapter 6.1 patent gazette]|
    2021-01-26| B09A| Decision: intention to grant [chapter 9.1 patent gazette]|
    2021-02-17| B16A| Patent or certificate of addition of invention granted [chapter 16.1 patent gazette]|Free format text: PRAZO DE VALIDADE: 20 (VINTE) ANOS CONTADOS A PARTIR DE 28/11/2011, OBSERVADAS AS CONDICOES LEGAIS. |
    优先权:
    申请号 | 申请日 | 专利标题
    EP10192962.8|2010-11-29|
    EP10192962.8A|EP2458344B1|2010-11-29|2010-11-29|Method of, and apparatus for, measuring the true contents of a cylinder of gas under pressure|
    PCT/EP2011/071198|WO2012072588A1|2010-11-29|2011-11-28|Method of, and apparatus for, measuring the true contents of a cylinder of gas under pressure|
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