Precautions for using gas flowmeters.

After choosing the brand and model of the gas flowmeter, it is also very important to use the gas flowmeter correctly. In this paper, the points for attention in the use of gas flowmeter are analyzed based on the description of the common gas flowmeter of American VTON.

1. When the working conditions of the instrument change (such as medium change, environmental temperature change, etc.), the zero position of the instrument should be readjusted. At the same time, the catheter of the instrument must be mounted horizontally and calibrated with a horizontal instrument. Otherwise, changes in working conditions will increase the impact on zero drift. The frame cannot vibrate or swing and therefore should not be used on a ship.

2. The equivalent of 0-100kg/cm2 pressure. 0-7 liters/hour flow (air) in the range of a large number of test data correlation operation, according to the principle of small square to find out the linear regression equation, the correlation coefficient λ value in the range of 0.999~0.9999, proving that the instrument has good linearity. But the larger the flow rate of linear and range size, the more serious the nonlinearity, so the range is generally limited to 0~4 L/h (air) to ensure good linearity. In order to measure large flow and ensure linearity, the shunt principle can be used to expand the range of the instrument. If a bypass pipe is used. Venturi tube. Orifice plate, etc. It can scale up to dozens of units per hour. Hundreds of them. Thousands of liters to tens of thousands of cubic meters.

3. Although the specific heat of real gases varies with pressure, and even some gases have relatively large variation ranges (see Table 1), the measuring accuracy of the instrument can still be maintained within a certain range.

4. In addition to corrosion resistance, it is best to choose materials with good thermal conductivity. In the case of mesh nitrogen measurement, the measurement accuracy of stainless steel is 2 to 2.5%(the thermal conductivity of nickel is about three times that of stainless steel) when tested in the range of 0-100kg/cm2 pressure and 0-7 L/h flow.

5. Because the gas flowmeter can only work normally when the specific heat of the gas is relatively stable, the gas composition is unstable. Gas flowmeters are not suitable because the specific calorific value is very unstable. If the critical point of ethylene liquefaction is 50kg/cm2.9 ° C, the meter reading begins to be unstable when pressure above 30kg/cm2 is found during the test.

6. If the gas medium is replaced, recalibrate the flowmeter. In the general instrument instruction manual, it is usually introduced that the uncalibrated gas flow is simple and convenient, but only according to the specific heat conversion of the two gases, but it will cause a large error. Especially when working under high pressure, we found that the sensitivity of the instrument was not completely proportional to the specific heat and was more suitable for recalibration.

7. Before use, the machine must be turned on to preheat. Before preheating, the instrument is unstable. Better models, its startup preheating time in less than two hours.

8. In the process of use, when the gas flow suddenly changes, it must be redistributed through heat transfer and temperature in the pipeline, so it takes a certain amount of time for the output signal to be re-stabilized. To reduce this lag, manufacturers often add differential networks to the electrical wiring of the instrument to quickly respond to the output signal. This is especially necessary for flow control in conjunction with other instruments.