# Precations of Using A Gas Flow Meters

The gas meter is a commonly used gas flow meter, which installed in the pipeline, can measure the air, nitrogen, natural gas, liquefied petroleum gas, hydrogen peroxide etc.Now, here are some tips for you when you are using it.Hope it will be useful.

Precautions of using flow meters for gas

1.If the working conditions' changing(such as the change of media environment, the large variation of temperature etc.), you should readjust the zero position.Meanwhile, the tube of the instrument must stay in the horizontal position with the level or the adjusting will be useless.So as the rack shouldn't shake or anything, it means it will not be used on a ship.

2.If you operate the pressure over 0 to 100 kg/cm2 and the air flow within 0 to 7 standard liters per hour with the method of least squares to get the linear regression equation, and the value of the correlation coefficient is in the range of 0.999 to 0.9999, that means the instrument is good linearity.But, for the nonlinearity increase with the increase of the rate of flow, so you should limit it within 0-4 standard liters per hour(of air) to ensure good linearity.In order to ensure the linearity and the measurement of large flow, you can extend the range of the meter by shunt principle.For example, cooperating the bypass pipe, Venturi tube, orifice plate and so on, the measuring range can expend to tens, hundreds, thousands, up to several thousand cubic meters per hour.

3.Although the specific heat of real gas varies with different pressure, and sometimes it is relatively large, but the measuring accuracy can still be maintained within a certain range.

4.As for the choice of the pipe material, in addition to considering the corrosion resistance, the material with good heat conduction performances is better.Take measuring the nitrogen as example, at the same condition of the pressure go within 0 to 100 kg/cm2 and the flow range from 0 to 7 standard liters per hour, the measurement accuracy is range from 2 to 2.5 percent for the material nickel, as for stainless steel it is from 3 to 4 percent.(thermal conductivity of nickel is about three times of stainless steel)

5.The flow meter gas only work normaly at the enviroment of stable specific heat, so, as long as the testing gas is
in such condition, the meter could be useless.For instance, as the critical point of ethylene liquefaction is 50kg/cm2, 9.9 degrees, once the presure surpass 30kg/cm2, the meter reading began to instability.

6.If the gas is changed, it is better to renew the calibration.But in the instruction, there is nothing about renewing, instead of the simpler
convenient of the specific heat of two kinds of gas, which could cause large errors, especially under the big pressure, the sensitivity is not completely proportional to the specific heat, so it's better to calibrate.

7.A preheated
is must, and the instrument is unstable before it is fully preheated.As a good meter, the warm-up time within two hours.

8.During the operation, when the gas flow is suddenly changed, the temperature of the pipe should be redistribution by heat transfer, so it will take some time to stable again.In order to reduce the lag phenomenon, the manufactory always add differential network in the electric line, so that could rapid reaction, which is necessary when its work with other meters.

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