Abstract: This article introduces a new automotive gas turbine flow meter verification system. The system consists of a computer-controlled nozzles NC switching valve, the flow meter can choose 11-caliber automatic Nozzles the speed of sound in the one pair of gas turbine flowmeters in the working conditions under the test, while the system is also available in a gas Chromatography and the speed of sound complete with nozzle gas mass flow of computing. The article also introduced a certification by the speed of sound nozzle of the gas turbine flowmeter mass flow formula plot and passenger traffic formula, the verification system and process plans. The system test using gas turbine flowmeter, by the computer directly to temperature, pressure amendments to improve the accuracy of testing.

First. Introduction

Arkla Pipeline Group, a research vehicle nozzle test the speed of sound devices, can in practical work under the conditions of certification Flowmeter gas turbine, the test flow meter in diameter 3-16 in. This verification system and gas chromatography combined to complete gas mass flow calculation.
This verification system than in the past methods have greatly improved. In most cases, the atmospheric pressure in the test turbine flowmeter for work status, the original instrument constant drift will occur. The nozzle used in the actual speed of sound pressure, temperature test under the condition to overcome this shortage. In addition, the speed of sound use of natural gas nozzle system for the medium rather than air, but also removed the air from the introduction of error.
Car test system can test the turbine metering system, not just testing a turbine flow meter. This means that the error caused by fluctuation can be detected, it is any other verification system can not do.
Second, the definition of
Nozzle flow speed of sound basic definition is: in other parameters remain unchanged under the circumstances, when the nozzle to reduce the pressure on the lower reaches a certain point, even if the pressure continues to drop downstream, they will not create nozzle pipes to further increase the quality of traffic. At this point, the gas nozzle in the pipes for the speed of sound velocity, known as the "critical flow", "the speed of sound flow" or "Choke." The quality of gas flow in the nozzle can be accurately identified the pipe out. Early, to be in the nozzle of the pressure of imports and exports decreased 50 percent, to get the speed of sound, but now can be little pressure drop to 5 percent, while the typical voltage drop no more than 10 per cent, or can get the speed of sound.
Third, automotive test equipment installed
1, a car-room, its partition into a computer, the valve block, between air compressors and power between. This can be dangerous and non-hazardous areas separate.
2, a computer control system, including a IBM. Computer 386, with 120 trillion drive 32 printers and a remote terminal (RTU). Remote Computer terminals are the interface with the NC valve, which has control of output, state input and output analog input control switch electromagnetic pneumatic valve - each nozzle has a solenoid valve. Each actuator by the two tongue reed switch to provide input signal status, reflecting the implementation of the position, determined by the computer in which the nozzle working conditions.Air compressor from the state of the input signal can be directed to the air pressure is reduced to 751 b / in 2 (table) below, the pressure valve of the NC is the smallest operating pressure. Analog input on behalf of Turbine Flowmeter temperature and pressure of work (two input), the valve import and export of pressure (3:00 input) and the temperature valve imports (1:00 input).
3, Daniel a gas chromatograph, in its verification system is a key equipment. GC every 6 min of gas to conduct a real-time component analysis and the results through an RS. 232 communications transmitted to the computer interface. Computer Application of 100 component calculated formula for the quality of the two variables. Gas chromatography of the type recorders and controllers installed in non-hazardous areas of computer room. Chromatography sampling probe installed in a dangerous region of NC valve on the pipeline.
4,2-verification system so that power supply unit to maintain operations. A 2.8 kW unit drive small loads, such as chromatography, computers and RTU. A 7 kw of a motor driven air compressors and air conditioners.
5A 1 hp air compressor to provide the 100 lb / in 2 (form) of air pressure to the NC valve solenoid valve for the operation of the nozzle. The gas source also used to activate the small hand tools.
6Connecting pipeline, from two-calibre for 4 in, for the 14 ft long tube connecting the torsion was seized instruments and verification system. A table to link the seizure of imported testing equipment, and the other root verification device connected to return to the export pipeline. Each connector used high-pressure fast joints, and pipelines to pressure the work of 550 lb / in 2 (table).

7, NC switching valve, as shown in Figure 1 of the NC-valve 1100 lb, it has 11 nozzles for the choice of the speed of sound channels, in binary mode control. As the two largest nozzle into the most functional and logical access control. Binary control valve to the NC 10 bit resolution. The result is the incremental flow-to-order 58.7 Ac-hoon. RIU the electronic control signals control the pneumatic solenoid valve switching, control of air operations at the same time, the electromagnetic valve so that the speed of sound nozzle into the working conditions. In the middle of the cylinder valve, with sufficient energy, even if the air supply valve so that rotation can still be interrupted twice.
NC valve connecting on four holes: two import and export 2. Ports for connecting to the temperature of the transmitter of imports and import and export of pressure transmitter. As import pressure should be very accurate, an import should be installed two pressure transmitter, its range is the range of 0-75 lb / in 2 (Table) and 0-200 lb / in 2 (table). When the pressure reached a pressure transmitter range of 95 percent, the computer will be pressure instruments from the first pressure switch to the second variable pressure change. Once a nozzle open, gas from the entrance into the nozzle, from the shell of the four outflow into the mouth of the shell-and outflow valve.

Fourth, the basic flow formula

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In the formula: M-conditions under the mass flow, lb;
P-Shell pressure,1b/in 2 (Absolutely)
A-Nozzle throat of the cross-sectional area, in 2 Arkla diameter nozzle of the range of 0.0620-0.9941 in, therefore, the scope of its area is about 0.003-0.776 in 2;
C-Critical flow coefficient, which is the specific heat value of the function (such as constant flow of David). It is a state with the gas flow velocity of the gas-related parameters. Arkla in the system, a representative of the critical flow of natural gas estimated value of 0.7 (dimensionless). The value and the pressure and temperature. C chromatography analysis is used to calculate the molecular weight calculated from the 100;
Cd-- Outflow coefficient, or the actual mass flow divided by the mass flow of a few. In short, it is the efficiency of the nozzle design, the different nozzles it is different and is determined by the calibration. Arkla the nozzle out of the range of 0.96-1.0 coefficient (dimensionless);
R-Gas constant, its value is 48.03 divided by the molecular gas, from gas chromatography analysis of the calculation of the molecular gas also tested for this;
T-Shell, the temperature, R (H +460).
Volume flow is divided by the density of mass flow, density equivalent to P / ZRT, volume flow rate calculated using the following formula:

In the formula : V-Volume flow;
Z-Shell, the compression factor (RCJohnson, not AGA), is a close to 1 values. GC Analysis of the molecular weight and gas components can be used for this;
Rv-Gas constant, equivalent to 2.398 molecular weight divided by the gas. GC also used to calculate the molecular weight of this. R and Rv has been adjusted to engineering units.

Fifth, Verification Process

Gas flows through the turbine flow meter, and then the NC valve and submit four signals, as shown in Figure 2. Measurement of gas pressure and temperature of the two signals, and two pulse signals from the pulse of the turbine flow meter - and from the mass flow valve NC signal. Should pay attention to the turbine flowmeter pulse conversion gear from the bottom.

Figure 2 Verification System flow chart

When the flow meter rotating lap, the computer measured installed in the turbine flow meter on the issue of the originating set of data. First-class speed gear in the middle rounds, Rockwell turbine flow meter and American Meter, and their input-output ratio of 122.0555-l. The second level is Biansuchilun gear, the input-output ratio in 1 and 2 to 1 between.
Flowmeter Register in Biansuchilun fixed at the top, according to different calibre instrument, the output shaft to each lap Register readings of 100 or 1000 Acf. To 3-6 in the flowmeter, the Register and the output shaft of the 100:1 ratio is, therefore, Biansuchilun above the output shaft to the ring on behalf of every 1 ft 3, for 8 in the flow meter or greater, with the Register The ratio between the output shaft is 1000:1. Flowmeter signal, the middle gear, Biansuchilun Register and the results are given is the actual condition of cubic feet of flow (Acf).
Pressure, volume, temperature (PVT) charts installed in the upper part of the Register and used to check Register.
Computer input temperature and pressure instruments, measuring instruments and application of the Acfh calculated Scfh (standard A 3 / h); lb for the unit to the mass flow from the computer numerical control valve in the access to data under the state divided by the standard density. In the system flows through the turbine flow meter and then through the gas valve NC, the mass flow is a constant everywhere.
However, the actual volume of cubic feet of gas flow as the composition, temperature, pressure and change. Therefore, the volume of traffic in the valve body and the turbine flowmeter different traffic volume. For a certain quality of traffic, when the gas density increased, the actual volume of traffic (Acfh) decreases. Valve in traffic volume higher than in the turbine flowmeter flow - this is because the pressure valve of imports below the turbine flowmeter pressure, fluid flow rate slightly increased. That is why the valve and flow meter pressure and temperature measurements are needed for.
Turbine Flowmeter Scfh and the instructions given by the NC valve Scfh that is the difference between the turbine flowmeter point in the flow of error. The error is relative to the percentage percentile flow mapping error. This percentage is the actual instrument error of traffic on a special instrument constant rendering of the foot. Entered into the computer through a different speed than can easily change the constant K (pulses / ft 3).
In order to get the smallest error, the software program can apply a different size of the nozzle, and can change gear transmission ratio of turbine flow meter to achieve approval. The use of software programs can save time and effort, in fact, instead of a change gear transmission ratio and the flow meter test can be repeated until a satisfactory result achieved. With 10 different points of the flow test results can be drawn detailed maps.