Gas flow meter use precautions

Gas flow meter is a commonly used flow meter, which is installed in the pipeline to record the amount of gas flowing through. It can measure air, nitrogen, natural gas, liquefied petroleum gas, hydrogen peroxide and other media. What should users pay attention to when using gas flow meter? The following editor will introduce the precautions for using gas flow meter in detail, hoping to help everyone.

Gas flow meter use precautions

1. When the working conditions of the instrument change (such as changing the medium, the ambient temperature changes greatly, etc.), the zero position of the instrument should be readjusted. At the same time, the instrument's conduit must be installed horizontally and calibrated with a level. Otherwise, the impact of the change in working conditions on the zero drift will increase. The frame must not vibrate or sway, so it is not suitable for use on ships.

2. A large amount of test data in the range of 0-100kg/cm2 pressure and 0-7 standard liters/hour flow (air) is correlated, and the linear regression equation is obtained using the principle of least squares method. The correlation coefficient λ value is in the range of 0.999-0.9999, proving that the instrument has good linearity. However, the linearity and range size are related. The larger the flow rate, the more serious the nonlinearity. Therefore, the range is generally limited to 0-4 standard liters/hour (air) to ensure good linearity. In order to measure large flow rates while ensuring linearity, the flow splitting principle can be used to expand the range of the instrument. If bypass pipes, Venturi tubes, orifice plates, etc. are used in combination, the range can be expanded to tens, hundreds, thousands of standard liters per hour, and even tens of thousands of standard cubic meters.

3. Although the specific heat of real gas varies with pressure and the fluctuation range of some gases is even relatively large (see Table 1), the measurement accuracy of the instrument can still be maintained within a certain range (see Table 2).

4. In addition to considering corrosion resistance, it is better to choose materials with good thermal conductivity when choosing the material of the conduit. Taking nitrogen as an example, the measurement accuracy of nickel tubes is 2-2.5% and that of stainless steel is 3-4% (the thermal conductivity of nickel is about three times that of stainless steel).

5. Since the gas flow meter can only work normally when the gas specific heat is relatively stable, it is not suitable to use this instrument when the gas composition is unstable, the gas has mist in the center, and the working conditions are close to the critical zone of gas liquefaction, because the specific heat value is very unstable. For example, the critical point of ethylene liquefaction is 50 kg/cm2 and 9.9℃. When the pressure exceeds 30 kg/cm2 during the test, the instrument reading begins to become unstable.

6. If you change a gas medium, it is best to recalibrate. In the manual of the instrument, it is often introduced that it is not necessary to recalibrate, but only to convert the uncalibrated gas flow according to the specific heat of the two gases. Although it is simple and convenient, it will cause a large error, especially when working under high pressure. We found that the sensitivity of the instrument is not completely proportional to the specific heat. It is better to recalibrate the meter.

7. This instrument must be preheated before use. Before it is fully preheated, the instrument will be unstable. For better models, the preheating time is within two hours.

8. During use, when the gas flow rate suddenly changes, the temperature in the tube must be redistributed through heat transfer, so it takes a certain amount of time for the output signal to stabilize again. In order to reduce this lag phenomenon, manufacturers often add a differential network to the electrical circuit of the instrument to make the output signal respond quickly. This is especially necessary when cooperating with other instruments for flow rate automatic control.