Fluid vapor pressure apparatus and related methods

Abstract

To provide a method for measuring the vapor pressure of a fluid.SOLUTION: Providing a meter 5 having meter electronics, wherein the meter 5 is at least one of a flow meter and a density meter and flows a process fluid through the meter 5; A pressure of the process fluid is measured. The pressure of the process fluid is adjusted until the single-phase / two phase boundary is reached. The streaming vapor pressure of the process fluid is measured at the single phase / two phase boundary.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to vibrometers, and more particularly to methods and apparatus for real-time vapor pressure measurements. [Background technology]

[0002] Reid Vapor Pressure (RVP) is one of the most widely recognized properties for measuring and enforcing fuel quality standards. Flowing vapor pressure is an important property in applications dealing with the flow and storage of volatile fluids such as gasoline, natural gas liquids, and liquefied petroleum gas. Vapor pressure provides an indication of how a volatile fluid may behave during handling and further indicates conditions under which foaming and pressure buildup may occur. Thus, measuring the vapor pressure of volatile fluids enhances safety and prevents damage to shipping containers and transportation infrastructure.

[0003] If a fluid's vapor pressure is too high, cavitation can occur during pumping and transfer operations. Additionally, the vapor pressure of a vessel or process line can increase beyond safe levels due to temperature changes. Therefore, it is often necessary to know the RVP before storage or transportation. Typically, RVP is determined by taking samples, transporting them to a laboratory, testing, and measuring values ​​from the samples. This creates challenges in enforcing regulatory fuel quality standards due to delays in obtaining final results, the cost of maintaining the laboratory, and the safety and forensic vulnerabilities associated with sample processing. Flowing vapor pressure is often measured using this same process, and then converted from the laboratory-measured RVP to flowing vapor pressure at the flowing temperature by relying on lookup tables and databases based on empirical measurements.

[0004] Therefore, there is a need for an in-line device or system capable of measuring flow vapor pressure and / or RVP continuously, in real time, under process conditions. This is provided by the present embodiments, representing an advancement in the art. On-site measurement is more reliable because it eliminates the need for periodic sampling and completely eliminates the risk of fluid property changes between the time of sample collection and the time of laboratory assay. Furthermore, real-time measurement improves safety because unsafe conditions can be immediately remedied. Furthermore, regulatory enforcement can be accomplished through a simple on-site check, saving costs, and inspection and enforcement decisions can be made with little delay or process downtime. Summary of the Invention [Means for solving the problem]

[0005] According to one embodiment, a method for measuring the vapor pressure of a fluid is provided. The method includes providing a meter having meter electronics, the meter including at least one of a flow meter and a density meter. A process fluid is flowed through the meter and a pressure of the process fluid is measured. The pressure of the process fluid is adjusted until a single-phase / two-phase boundary is reached, and a flowing vapor pressure of the process fluid at the single-phase / two-phase boundary is measured.

[0006] According to one embodiment, a system for measuring the flowing vapor pressure of a process fluid is provided. The system includes a meter comprising at least one of a flow meter and a density meter. A pressure regulator is in fluid communication with the meter. The system includes a pressure sensor. Meter electronics are in communication with the meter and the pressure sensor, the meter electronics being configured to receive the measured pressure. The meter electronics are configured to control the pressure regulator to adjust the pressure of the process fluid until a single-phase / two-phase boundary is reached and measure the flowing vapor pressure of the process fluid at the single-phase / two-phase boundary.

[0007] Aspects According to one aspect, a method for measuring the vapor pressure of a fluid includes providing a meter having meter electronics, the meter comprising at least one of a flow meter and a density meter; flowing a process fluid through the meter; measuring a pressure of the process fluid; adjusting the pressure of the process fluid until a single-phase / two-phase boundary is reached; and measuring the flowing vapor pressure of the process fluid at the single-phase / two-phase boundary.

[0008] Preferably, the step of adjusting the pressure of the process fluid until the single phase / two phase boundary is reached comprises reducing the pressure at a valve located upstream of the meter. Preferably, the step of adjusting the pressure of the process fluid until the single phase / two phase boundary is reached comprises increasing the pressure at a valve located downstream of the meter. Preferably, the method includes measuring the temperature of the process fluid and calculating the Reid vapor pressure from the temperature and the vapor pressure of the fluid. Preferably, the step of calculating the Reid vapor pressure from the temperature and flow vapor pressure includes referencing a Reid vapor pressure value stored in the meter electronics using the Reid vapor pressure from temperature.

[0009] Preferably, the Reid Vapor Pressure values ​​stored in the meter electronics comprise a look-up table. Preferably, the Reid Vapor Pressure value stored in the meter electronics is calculated from the curve. Preferably, the method includes using the measured drive gain to determine the presence of entrained gas in the process fluid. Preferably, the method includes determining the presence of entrained gas in the process fluid by measuring the density of the fluid. Preferably, the method includes determining the presence of entrained gas in the process fluid using a combination of the measured drive gain and the measured density.

[0010] According to one aspect, a system for measuring the flowing vapor pressure of a process fluid includes a meter comprising at least one of a flow meter and a density meter. A pressure regulator is in fluid communication with the meter. The system includes a pressure sensor. Meter electronics are in communication with the meter and the pressure sensor, and are configured to receive the measured pressure, control the pressure regulator to adjust the pressure of the process fluid until a single-phase / two-phase boundary is reached, and measure the flowing vapor pressure of the process fluid at the single-phase / two-phase boundary.

[0011] Preferably, the system includes one or more conduits, at least one driver attached to the one or more conduits configured to generate a vibration signal in the one or more conduits, and at least one pick-off attached to the one or more conduits configured to receive the vibration signal from the one or more conduits. Preferably, the system includes a temperature sensor configured to measure a temperature of the process fluid, and the meter electronics is configured to calculate the Reid vapor pressure from the measured temperature and flow vapor pressure of the process fluid.

[0012] Preferably, the meter electronics includes a Reid Vapor Pressure reference value stored therein. Preferably, the Reid Vapor Pressure reference values ​​stored in the meter electronics include a look-up table. Preferably, a Reid Vapor Pressure reference value stored in the meter electronics is calculated therein. Preferably, the meter electronics is configured to use the measured drive gain to determine the presence of entrained gas in the process fluid. Preferably, the meter electronics is configured to use the measured density to determine the presence of entrained gas in the process fluid. Preferably, the meter electronics is configured to determine the presence of entrained gas in the process fluid using a combination of the measured drive gain and the measured density. [Brief explanation of the drawings]

[0013] [Figure 1]FIG. 1 illustrates a flow meter sensor assembly according to one embodiment. [Figure 2] FIG. 1 illustrates meter electronics according to one embodiment. [Figure 3] FIG. 1 illustrates a vapor pressure measurement system according to one embodiment. [Figure 4] FIG. 1 illustrates a vapor pressure measurement method according to one embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0014] 1-4 and the following description depict specific examples to teach those skilled in the art how to make and use the best mode of the invention. Some conventional aspects have been simplified or omitted in order to teach inventive principles. Those skilled in the art will appreciate variations from these examples that fall within the scope of the invention. Those skilled in the art will appreciate that the features described below can be combined in various ways to form multiple variations of the invention. Consequently, the present invention is not limited to the specific examples described below, but only by the claims and their equivalents.

[0015] Vibration sensors, such as vibratory densitometers and Coriolis flow meters, are commonly known and are used to measure mass flow rates and other information about materials flowing through a conduit containing a flow meter or densitometer. Exemplary flow meters are disclosed in U.S. Pat. Nos. 4,109,524, 4,491,025, and Reissue Patent No. 31,450 (all to J.E. Smith et al.). These flow meters include one or more conduits in a straight or curved configuration. For example, each conduit configuration in a Coriolis mass flow meter has a set of natural vibration modes, which can be simple bending, torsional, or coupled. Each conduit can be driven to vibrate in a preferred mode.

[0016] Some types of mass flow meters, particularly Coriolis flow meters, can operate by performing a direct measurement of density to provide volumetric information from the quotient of mass divided by density. See, for example, U.S. Patent No. 4,872,351 to Ruesch for a Net Oil Computer that uses a Coriolis flow meter to measure the density of an unknown multiphase fluid. U.S. Patent No. 5,687,100 to Buttler et al. teaches a Coriolis effect densitometer that corrects density measurements for mass flow effects in a mass flow meter operated as a vibrating tube densitometer.

[0017] Material flows into the flow meter from a connected pipeline on the inlet side of the flow meter, is directed through the conduit, and exits the flow meter on the outlet side of the flow meter. The natural vibration modes of the vibrating system are defined in part by the combined mass of the conduit and the material flowing within the conduit. When there is no flow through the flow meter, a driving force applied to the conduit causes all points along the conduit to oscillate with the same phase, or a small "zero offset," which is the time delay measured at zero flow rate. When material begins to flow through the flow meter, Coriolis forces cause each point along the conduit to have a different phase. For example, the phase at the inlet end of the meter lags the phase of the central driver position, while the phase at the outlet leads the phase of the central driver position. Pickoffs on the conduit generate sinusoidal signals that represent the motion of the conduit. The signal output from the pickoffs is processed to determine the time delay between the pickoffs. The time delay between two or more pickoffs is proportional to the mass flow rate of material through the conduit.

[0018] Meter electronics connected to the driver generate drive signals to operate the driver and to measure the mass flow rate and / or other properties of the process material from signals received from the pickoff. The driver can have one of many well-known configurations. However, magnets and opposing drive coils have been very successful in the flow meter industry. An alternating current is passed through the drive coil to vibrate the conduit at a desired conduit amplitude and frequency. It is also known in the art to provide a pickoff as a magnet and coil configuration very similar to the driver configuration. However, while the driver receives a current to induce motion, the pickoff can induce a voltage using the motion provided by the driver. The magnitude of the time delay measured by the pickoff is very small, often measured in nanoseconds. Therefore, the transducer output must be very accurate.

[0019] FIG. 1 illustrates a flow meter 5, which may be any vibratory meter, such as, for example, without limitation, a Coriolis flow meter or a density meter. The flow meter 5 includes a sensor assembly 10 and meter electronics 20. The sensor assembly 10 responds to the mass flow rate and density of a process material. The meter electronics 20 connects to the sensor assembly 10 via leads 100 and provides density, mass flow rate, and temperature information, as well as other information, across a path 26. The sensor assembly 10 includes flanges 101 and 101′, a pair of manifolds 102 and 102′, a pair of parallel tubes 103 (first conduit) and 103′ (second conduit), a driver 104, a temperature sensor 106, such as a resistance temperature detector (RTD), a pair of pickoffs 105 and 105′, such as a magnet / coil pickoff, a strain gauge, an optical sensor, or any other pickoff known in the art. Conduits 103 and 103' have inlet legs 107 and 107' and outlet legs 108 and 108', respectively. Conduits 103 and 103' bend at least one symmetrical location along their lengths and are essentially parallel throughout their lengths. Each conduit 103, 103' oscillates about an axis W and W', respectively.

[0020] Legs 107, 107', 108, 108' of conduits 103, 103' are fixedly attached to conduit mounting blocks 109 and 109', which are in turn fixedly attached to manifolds 102 and 102'. This provides a continuous, closed material path through sensor assembly 10. When flanges 101 and 101' are connected to a process line (not shown) carrying the process material being measured, the material enters flowmeter 5 at first end 110 through a first orifice in flange 101 (not visible in FIG. 1 ) and is directed through manifold 102 to conduit mounting block 109. Within manifold 102, the material is split and directed through conduits 103 and 103'. Upon exiting conduits 103 and 103', the process material is recombined into a single stream within manifold 102' and then directed to exit second end 112, which is connected to the process line (not shown) by flange 101'.

[0021] Conduits 103 and 103' are selected and appropriately mounted in conduit mounting blocks 109 and 109' so that their mass distributions, moments of inertia, and Young's moduli about bending axes W-W and W'-W', respectively, are substantially the same. Because the Young's moduli of conduits 103, 103' change with temperature, and this change affects flow rate and density calculations, a temperature sensor 106 is attached to at least one of conduits 103, 103' to continuously measure the temperature of the conduit. The temperature of the conduit, and therefore the voltage appearing across temperature sensor 106 for a given current flowing through the conduit, depends primarily on the temperature of the material flowing through the conduit. The temperature-dependent voltage appearing across temperature sensor 106 is used by meter electronics 20 in a well-known manner to compensate for changes in the modulus of elasticity of conduits 103, 103' due to any changes in the temperature of conduits 103, 103'. Temperature sensor 106 is connected to meter electronics 20.

[0022] Both conduits 103, 103' are driven by a driver 104 in opposite directions about their respective bending axes W and W' in what is referred to as the first out-of-phase bending mode of the flow meter. This driver 104 may include any one of many well-known configurations, such as a magnet attached to conduit 103' and opposing coils attached to conduit 103, through which an alternating current flows to vibrate both conduits. An appropriate drive signal is transmitted via lead 113 to the meter electronics. The voltage is applied to the driver 104 by the device 20. While the present description is directed to two conduits 103, 103', it should be understood that in other embodiments, only a single conduit or more than two conduits may be provided. It is also within the scope of the present invention to generate multiple drivers and multiple drive signals for the drivers that drive the conduits in modes other than the first out-of-phase bending mode.

[0023] Meter electronics 20 receives the temperature signal on lead 114 and the left and right velocity signals appearing on leads 115 and 115', respectively. Meter electronics 20 generates a drive signal appearing on lead 113 to driver 104 to vibrate conduits 103 and 103'. Meter electronics 20 processes the left and right velocity signals and the temperature signal to calculate the mass flow rate and density of the material flowing through sensor assembly 10. This information, along with other information, is applied by meter electronics 20 via path 26 to a utilization means. A description of the circuitry of meter electronics 20 is not necessary for an understanding of the present invention and will be omitted for the sake of brevity. It should be understood that the description of FIG. 1 is provided merely as an example of one possible vibrometer operation and is not intended to limit the teachings of the present invention. Although the construction of a Coriolis flowmeter is described, it will be apparent to those skilled in the art that the present invention can be practiced with a vibrating tube or fork densitometer without the additional measurement capabilities provided by a Coriolis mass flowmeter.

[0024] 2 is a block diagram of the meter electronics 20 of flow meter 5 according to one embodiment. In operation, flow meter 5 provides various measurements that may be output, including one or more of mass flow rate, volume flow rate, mass flow rate and volume flow rate of individual flow components, and a measured or averaged total flow rate, which may include, for example, both volumetric and mass flow rates of individual flow components. The flow meter 5 generates a vibrational response that is received and processed by the meter electronics 20 to generate one or more fluid measurements that can be monitored, recorded, stored, totaled, and / or output.

[0025] Meter electronics 20 includes an interface 201, a processing system 203 in communication with interface 201, and a storage system 204 in communication with processing system 203. Although these components are shown as separate blocks, it should be understood that meter electronics 20 may be comprised of various combinations of integrated and / or separate components. Interface 201 is configured to communicate with sensor assembly 10 of flow meter 5. Interface 201 may be configured to couple to leads 100 (see FIG. 1 ) and exchange signals with driver 104, pickoff sensors 105 and 105′, and, for example, temperature sensor 106. Interface 201 may further be configured to communicate with, for example, an external device via communication path 26.

[0026] The processing system 203 can include any manner of processing system. The processing system 203 is configured to retrieve and execute stored routines to operate the flow meter 5. The storage system 204 can store routines including a flow meter routine 205, a valve control routine 211, a drive gain routine 213, and a vapor pressure routine 215. The storage system 204 can store measurements, received values, working values, and other information. In some embodiments, the storage system stores mass flow (m . )221 , density (ρ) 225, density threshold (226), viscosity (μ) 223, temperature (T) 224, pressure 209, drive gain 306, drive gain threshold 302, gas entrainment threshold 244, gas entrainment rate 248, and any other variables known in the art. Routines 205, 211, 213, 215 can include any of the signals mentioned and their other variables known in the art. Other measurement / processing routines are contemplated and are within the scope of this description and claims.

[0027] The flow meter routine 205 can generate and store fluid quantification values ​​and flow rate measurements. These values ​​can include substantially instantaneous measurements or can include summed or cumulative values. For example, the flow meter routine 205 can generate mass flow rate measurements and store them, for example, in a mass flow rate 221 storage device of the storage system 204. The flow meter routine 205 can generate density 225 measurements and store them, for example, in a density 225 storage device. The mass flow rate 221 and density 225 values ​​are determined from the vibration response, as described above and known in the art. The mass flow rate measurements and other measurements can include substantially instantaneous values, can include samples, can include average values ​​over a time interval, or can include cumulative values ​​over a time interval. The time interval can be selected to correspond to a block of time during which a particular fluid state is detected, for example, a liquid-only fluid state or a fluid state including liquid and entrained gas. Additionally, other mass flow rates and volumetric flow rates and related quantification values ​​are contemplated and are within the scope of this description and claims.

[0028] As described, the drive gain 306 may be utilized as a signal indicating a no-flow / false total condition. The drive gain threshold 302 may be used to identify periods of flow, no flow, single-phase / two-phase boundaries, and entrained / mixed-phase flow. Similarly, the density threshold 226 applied to the density measurement 225 may be used, individually or in conjunction with the drive gain, to identify entrained / mixed-phase flow. The drive gain 306 may be utilized as a measure of the sensitivity of the flow meter 5's conduit vibration to the presence of fluids of different densities, such as, for example, without limitation, liquid and gas phases. The combined effect of energy input and damping on the resulting amplitude is known as the extended drive gain. This represents an estimate of the amount of power required to maintain a target vibration amplitude when more than 100% power is available. Extended Drive Gain = Drive Gain x Drive Target / Max (Left Pickoff, Right Pickoff) / Frequency (1)

[0029] For purposes of the embodiments provided herein, it should be noted that the term drive gain may, in some embodiments, refer to a measured or derived signal indicative of the drive current, pickoff voltage, or amount of power required to drive the flow conduit 103, 103′ of a particular amplitude. In related embodiments, the term drive gain may be expanded to encompass any metric utilized to detect multiphase flow, such as noise level, standard deviation of the signal, attenuation-related measurements, and any other means known in the art for detecting mixed-phase flow. In one embodiment, these metrics may be compared across the pickoff sensors 105 and 105′ to detect mixed-phase flow.

[0030] The vibrating conduits 103, 103' require little energy to maintain vibration at their first resonant frequency as long as all fluid within the conduit is uniform in density. For fluids consisting of two (or more) immiscible components with different densities, vibration of the conduit results in a difference in the magnitude of the displacement of each component. This difference in displacement is known as decoupling, and the magnitude of this decoupling has been shown to depend on the ratio of the densities of the components and the inverse Stokes number.

number

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[0031] The decoupling that occurs between the components causes damping of the tube vibrations, so that for a given energy input, more energy is required to maintain the vibrations or the amplitude of the vibrations decreases. Referring to FIG. 3 , according to one embodiment, a vapor pressure measurement system 300 is provided. A process line 303 is provided having an inlet 304 and an outlet 307 and configured to carry a process fluid entering the process line 303 through the inlet 304. An upstream pressure regulator 308 is provided to control a flow rate through the process line 303. A downstream pressure regulator 310 is provided to control a flow rate through the process line 303. A flow meter 5 having meter electronics 20 is disposed between the upstream pressure regulator 308 and the downstream pressure regulator 310 and configured to receive the process fluid flowing through the upstream pressure regulator 308. A pressure sensor 312 and a temperature sensor 314 are also present in the system 300. While the pressure sensor 312 and the temperature sensor 314 are shown downstream of the flow meter 5, these sensors 312, 314 may be disposed prior to the flow meter 5 or may be incorporated within the flow meter 5.

[0032] Meter electronics 20 is in communication with upstream pressure regulator 308, downstream pressure regulator 310, pressure sensor 312, and temperature sensor 314. Meter electronics 20 can control upstream pressure regulator 308 and downstream pressure regulator 310. Meter electronics 20 receives pressure measurements from pressure sensor 312 and temperature measurements from temperature sensor 314. Meter electronics 20 is configured to monitor the pressure of the process fluid and reduce that pressure until flow meter 5 detects the introduction of the second phase, indicating that vapor pressure has been reached. In one embodiment, there is only a single pressure regulator 308.

[0033] Referring to FIG. 4, a flowchart 400 illustrating an example of a vapor pressure measurement scheme used by system 300 is provided. The pressure of the process fluid in system 300 is measured in step 402. This is accomplished by pressure sensor 312. The temperature of the process fluid in system 300 is measured in step 403. If the process fluid is single-phase under normal process conditions, the flow pressure can be reduced by partially closing upstream pressure regulator 308, as shown in step 404. The drive gain and / or density can be measured in step 406 and can be used to determine the presence of multiphase flow and also to determine the single-phase / two-phase boundary, as described above. As the process fluid pressure is measured 400 and the process fluid pressure is reduced 404, the introduction of a second phase is determined via the drive gain and / or density measurement 406, which also indicates that vapor pressure has been reached. Detection of the flow vapor pressure is indicated in step 408 by recording both the pressure and temperature at the time the second phase is determined. In step 410, the RVP is calculated from the measured flowing vapor pressure, taking into account the temperature at which the flowing vapor pressure was recorded.

[0034] Note that if the process fluid already contains some vapor, this can be detected by measuring the drive gain and / or density, and the downstream pressure regulator 310 can be partially closed to increase the pressure in order to measure the vapor pressure and temperature at which the second phase is no longer present. In either case, it is the single-phase / two-phase boundary and the associated temperature / pressure of the process fluid at this boundary that is utilized to indicate the flowing vapor pressure of the process fluid.

[0035] In other embodiments, other pressure regulators and methods of pressure control may be used if the upstream / downstream pressure regulator configuration does not provide sufficient pressure change to reach the vapor pressure. In other embodiments, a temperature measurement may also be included to provide the ability to convert between true vapor pressure (TVP) and vapor pressure at standard temperature (e.g., Reid Vapor Pressure (RVP)). TVP is the actual vapor pressure of a liquid product at the measured temperature. TVP is difficult to measure directly and depends on the composition and temperature of the liquid in the measurement device. Once the TVP and temperature are known, the flow vapor pressure and / or RVP at any other temperature can be calculated from empirical correlation data stored in the meter electronics 20. The empirical correlation data may include lookup tables, mathematical algorithms, and / or mathematical curves. Direct RVP measurement typically requires sending a sample for laboratory analysis.

[0036] In one embodiment, the system 300 is placed in a slipstream that only measures a sample of the main flowstream, thus reducing its impact on the material process. Because RVP is highly composition-dependent, slipstream sampling is effective when the composition is reasonably uniform. This allows for a smaller system size, lower cost, and less obtrusive.

[0037] The detailed descriptions of the above embodiments are not exhaustive descriptions of all embodiments contemplated by the inventors as being within the scope of the present invention. Indeed, those skilled in the art will recognize that certain elements of the above embodiments can be variously combined or removed to create further embodiments, and that such further embodiments will fall within the scope and teachings of the present invention. It will also be apparent to those skilled in the art that the above embodiments can be combined, in whole or in part, to create additional embodiments within the scope and teachings of the present invention.

[0038] Thus, while specific embodiments of, and examples for, the invention have been described herein for illustrative purposes, various equivalent modifications are possible within the scope of the invention, as those skilled in the art will recognize. The teachings provided herein may be applied to other vibration systems, not just the embodiments described above and illustrated in the accompanying figures. The scope of the invention should, therefore, be determined from the claims that follow.

Claims

1. 1. A method for measuring the vapor pressure of a fluid, comprising: providing a meter having meter electronics, the meter including at least one of a flow meter and a density meter; flowing a process fluid through the meter; measuring the pressure of the process fluid; adjusting the pressure of the process fluid until a single-phase / two-phase boundary is reached; measuring the flowing vapor pressure of the process fluid at the single-phase / two-phase boundary; A method comprising:

2. 2. The method for measuring the vapor pressure of a fluid as recited in claim 1, wherein adjusting the pressure of the process fluid until the single-phase / two-phase boundary is reached comprises reducing the pressure at a valve located upstream of the meter.

3. 2. The method for measuring the vapor pressure of a fluid as recited in claim 1, wherein adjusting the pressure of the process fluid until the single-phase / two-phase boundary is reached comprises increasing the pressure of a valve located downstream of the meter.

4. measuring the temperature of the process fluid; calculating the Reid vapor pressure from the temperature and the flow vapor pressure; 2. The method of claim 1, comprising:

5. 5. The method of measuring the vapor pressure of a fluid as recited in claim 4, wherein the step of calculating a Reid vapor pressure from the temperature and the flowing vapor pressure comprises referencing a Reid vapor pressure value stored in meter electronics using the Reid vapor pressure from the temperature.

6. 6. The method of measuring the vapor pressure of a fluid as recited in claim 5, wherein the Reid Vapor Pressure values ​​stored in the meter electronics comprise a look-up table.

7. 6. The method of measuring the vapor pressure of a fluid as recited in claim 5, wherein the Reid Vapor Pressure value stored in the meter electronics is calculated from a curve.

8. 10. The method of claim 1, further comprising using a measured drive gain to determine the presence of entrained gas in the process fluid.

9. 10. The method of claim 1, further comprising determining the presence of entrained gas in the process fluid by measuring the density of the fluid.

10. 10. The method of claim 1, further comprising determining the presence of entrained gas in the process fluid using a combination of a measured drive gain and a measured density.

11. 1. A system (300) for measuring flowing vapor pressure of a process fluid, comprising: a meter (5) comprising at least one of a flow meter and a density meter; a pressure regulator (308) in fluid communication with said meter (5); a pressure sensor (312); and meter electronics (20) in communication with the meter (5) and the pressure sensor (312), the meter electronics (20) comprising: Receive the measured pressure, The pressure regulator (308) is controlled to control the pressure of the process fluid until the single-phase / two-phase boundary is reached. Adjust the pressure of A system configured to measure the flowing vapor pressure of the process fluid at the single-phase / two-phase boundary.

12. The meter (5) one or more conduits (103, 103'); at least one driver (104) attached to the one or more conduits (103, 103') configured to generate a vibration signal in said one or more conduits (103, 103'); at least one pick-off (105, 105') attached to the one or more conduits (103, 103') configured to receive vibration signals from the one or more conduits (103, 103'); The system (300) of claim 11, comprising:

13. a temperature sensor (106) configured to measure a temperature of the process fluid; The system (300) of claim 11, wherein the meter electronics (20) is configured to calculate a Reid vapor pressure from the measured temperature and flowing vapor pressure of the process fluid.

14. 14. The system (300) of claim 13, wherein the meter electronics (20) has a Reid Vapor Pressure reference value stored therein.

15. 15. The system (300) of claim 14, wherein the Reid Vapor Pressure reference value stored in the meter electronics comprises a look-up table.

16. 15. The system (300) of claim 14, wherein the Reid Vapor Pressure reference value stored in the meter electronics is calculated within the meter electronics.

17. The system (300) of claim 11, wherein the meter electronics (20) is configured to determine the presence of entrained gas in the process fluid using a measured drive gain.

18. The system (300) of claim 11, wherein the meter electronics (20) is configured to determine the presence of entrained gas in the process fluid using the measured density.

19. The system of claim 11, wherein the meter electronics is configured to determine the presence of entrained gas in the process fluid using a combination of the measured drive gain and the measured density.

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