Soni Nozzle Gas Meter Test Bench
(Camera sampling type)


This series test bench for soni nozzle gas meter is a gas flow test bench based on the critical flow Venturi nozzle theory with high accuracy, which is mainly used to test error of small-scale jet gas meter and mechanical crushing etc. It is an ideal testing device during development and production of small-scale jet gas meters.

1 .1 Features

1.1.1 Standard segment adopts the soni nozzle without movable throttle component so that the accuracy and stability of the device can be guaranteed.
1.1.2. The device contains several sets of mutually independent systems for pipelines test and error calculation, so it can test for points with different flows on several jet gas meters, then the production efficiency is improved.
1.1.3. The adoption of SCM and highly accurate A/D conversion and other technologies can detect temperature, pressure or other environmental parameters which are added to do the error correction computation, making the demand for environment reduces greatly.
1.1.4. The device can test the error on points with different flows on the jet gas meter automatically under the control of PC machine, and give the error curve, pressure loss and judgment for the testing jet gas meter. In addition, it can save, print and analyze the test result so that the automatic management of production process is realized. 
1.1.5. The device adopts the passive pressure method and uses the high quality dry-type and oil-free vacuum pump with low noise to ensure that the gas passing by the nozzle always reaches the state of critical flow.
1.1.6. The device is made of professional industrial aluminum profiles and stainless steel with good shape, delicate technology and stable structure, and it can match up to the foreign products with same kind.

2. Main performance index
2.1 Accuracy of device ≤0.5%
2.2 Flow points: 0.04 m3/h,0.32m3/h,1.6m3/h,2.5m3/h,4m3/h.
2.3 Stability of flow ≤0.1%
2.4 Measuring range of the absolute pressure sensor used in the pipeline system is 0~120KPa, and the accuracy ≤0.2%; Measuring range of micro differential pressure sensor is -2KPa~2KPa, and the accuracy ≤0.5%; Measuring range of temperature sensor is 0~50ºC, and the accuracy ≤0.2%.
2.5 The number of meters to be tested is 4.
2.6 Conditions for use:
Temperature of environment 20±2ºC
Relative humidity 45%-85%
Atmospheric pressure   86kPa-106kPa
  Power supply 220V (or 3*220V) ±20V ~50Hz
  Power dissipation 2.5kW

3. Components and operating principle
The device is mainly composed of compression gas source, control gas path, test pipeline system, error computation SCM system, operating control SCM system, soni nozzle, working platform and PC machine. The test pipeline system is shown in Fig 1.

Fig 1 The test pipeline system
The gas flow in the whole test pipeline is completed by the suction of vacuum pump. When the gas passing by soni nozzle reaches the state of critical flow, the gas mess flow passing the tested meter and nozzle keeps constant.
Controlling and operating functions are implemented by the electrical part of the device, which is mainly composed of error sampling computation CPU, operating CPU and PC machine. The electrical principle is shown in Fig 2.





Fig 2 The electrical principle of device
Abstract of working principle:
PC conveys all parameters of the tested meter and all control commands during the testing process to the main control unit of SCM through the RS232 communication port. The data processing control center (CPU) controls the testing pipeline according to the demands, then it conveys the values measured by the sensors to the error slave machines and PC machine through RS485 communication bus, then the slave machines will determine the start and end of test according to the photoelectric signal of the tested meter, and the integration of gas flow passing nozzle during the test process is performed according to operational parameters. When the test ends, the error slave machine obtains the error of tested meter according to the following formula:
 

where δi is the display relative error of the ith tested gas meter, Vi is the actually gas volume of the ith tested gas meter. The calculated error is delivered to be displayed on LED and saved by PC.

4. Diagrammatic sketch of device structure (core mode)

5. Installation and debugging

After assembling, debugging and passing inspection in the factory, in order to bring convenience to transportation to users, the device may be taken apart into several components and then be packaged. So the device will be installed and debugged once more before use.
Be cautious to place the device steady and make it connected firmly during the process of installing and debugging, especially ensuring the whole pipeline system must not have leakage.
The installation and debugging for the first time is completed by the technical staffs from factory, and the customers can send crew to participate in the process to facilitate the mending and fixing afterwards.

6. Illustration of buttons function

6.1 Power source button

The power source button is a switch button with auto-lock function and pilot lamps to unlock or turn off the power source of the device. When the button is pressed, if the red lamp of the button lights on, it means the device is in the state of opening. And when the button flicks, the pilot lamp going out indicates that the device is in the state of closing.

6.2 Lifting button

 The lifting button is used to separately control the lifting of air cylinders in the meters. When power source opens, if pressing the button, the air cylinder of the corresponding meter pushes downwards to full state and the green lamp lights on. If pressing this button again, the air cylinder moves upwards and the lamp goes out.
The lifting can be realized by the operation of PC machine.

6.3 Reset button

The reset button is used to terminate the current test and restart a new test. When the error slave machine is under the state of testing, if relevant staff notices the photoelectric sampling system makes mistake in sampling or other exception responses, the reset button can be pressed to terminate this test and start the next test.
The reset button can only do test reset to error slave machine, but have no effect on hardware reset problem of the error single-chip machine. Occasionally, when error slave machine is under the state of crashing, only turning off the power source of the device can reset the hardware.

7. Illustration of interface

7.1 RS232 interface

RS232 interface is used to connect the standard serial communication port of computer. The random-distributed communication cable is used to connect the device and computer stably before the use of device, or the computer can't be used to control the device. The specific meanings of inner wires of pins are: pin- TXD, pin- RXD and  pin- GND.

7.2 Photoelectrical sampling device interface

The interface is used to connect the photoelectrical sampling device. The specific meanings of inner wires of pins are: pin- +5V, pin- GND, pi- photoelectrical sampling device signal.

8. Pre-use preparation
8.1 When the compression gas source has no output, connect the compression gas source to the entrance of gas source of device (filtering pressure reducing valve) with proper gas pipe, then rotate the pressure reducing valve slowly, and stop rotating and lock it when pointer of the pressure gauge points to 0.5MPa.
8.2 When PC and power source of device start, the pilot lamp of device lights on, and each error slave machines display the corresponding meter number.
8.3 Press the lifting button to observe if each gas cylinder works well. The lifting velocity can be altered by adjusting the gas inlet and outlet throttle valve.
8.4 Place each meter to be tested on the testing platform and push the gas cylinder, then observe if the air inlet and outlet port of the tested meter are pointed to the port of the push downwards mechanism, or adjust the fixture of the meters to make the location of the tested meter approximate.
8.5 Adjust the rotating button of the photoelectrical sampling device to make the sampler located vertically, then adjust the bracket of the samplers one by one to make the spot emitted by the sampler pointed to the specific location on the valve cover of the tested meter. If needed, adjust the potentiometer on the photoelectrical sampler again to make it have a proper sampling sensitivity (some devices have no sampler due to different styles of meters).
Until now, the preparation is done, then you can operate the computer to test meters.

Soni Nozzle Gas Meter Test Bench
(Camera sampling type)