Principle and classification of gas flow meter detectors

In order to ensure that the difference between the air temperature in the bell jar and the liquid temperature in the liquid tank meets the specified requirements, the temperature of the detector should be strictly controlled. Therefore, five temperature sampling points are set up, and temperature and humidity sensors are added to monitor the on-site calibration environment. All signals monitored by the detector are as follows: ① Bell jar, five-way temperature including the top temperature of the jar, the upper, middle and lower temperatures in the jar, and the liquid temperature; ② The flow meter being tested, the temperature, pressure, differential pressure, and analog flow meter signal before the flow meter is calibrated; ③ Environment, room temperature and humidity; ④ Pulse signal, bell jar grating ruler, baffle, limit, and pulse flow meter signal.

The standard volume of the bell jar is obtained by measuring the displacement of the bell jar. The automatic measurement of the displacement of the bell jar is an important part of the detector (bell jar device). The grating ruler is a high-precision displacement measuring element, which has been widely used in precision instruments, high-precision precision machining and other fields. The grating ruler is used in the detector as a displacement sensing element of the bell jar measuring cylinder, which can accurately correspond to the volume of the bell jar. The principle of the water pump test detector is that when the bell jar descends, the gas in the bell jar flows through the flow meter to be tested through the connecting pipeline. When the bell jar descends, the height of the bell jar descending is converted into a pulse signal through the grating ruler, which is conditioned by the hardware interface circuit and transmitted to the computer. The computer converts it into a gas standard volume or volume flow rate after compensation and correction. In addition, the calibrated detector is equipped with a baffle and a photoelectric sensor. The volume between the two baffles of the bell jar is fixed. The time taken for the baffles to pass through the photoelectric sensor can be measured, and the standard volume or volume flow rate of the exhaust gas can also be obtained. By comparing the measured value with the volume or flow indicated by the flow meter to be tested, the basic error of the flow meter to be tested can be obtained. The

bell-type gas flow standard device is one of the main forms of gas flow standard devices. It is relatively simple to use it to calibrate the flow meter when the pressure is not high (generally less than 10kPa) and the flow rate is not large. The device can be divided into exhaust type and intake type according to the direction of air flow. Its characteristics are: ① It is suitable for calibrating gas flow meters with low pressure and small flow; ② In the exhaust type device, the gas pressure flowing through the flow meter to be tested is very low, close to atmospheric pressure, and the gas humidity is very high, which affects the calibration result, so humidity correction is necessary; ③ The intake type device requires a dry and stable gas source to ensure that the dryness of the calibration gas meets the specified requirements and to ensure that the air flow pressure, temperature and flow rate of the test pipe section are constant, which makes it more difficult to establish an intake type device than an exhaust type device; ④ Since the internal pressure of the bell jar is only determined by its own gravity, the gravity of the test system and the device counterweight in the mobile phone development, the buoyancy of the liquid and the tension of the compensation mechanism, the internal pressure is constant regardless of whether it is an exhaust type or an intake type.