Thermal gas mass flow meter gas metering selection considerations
2021-06-29
Based on the principle of thermal diffusion, the thermal gas mass flowmeter is designed by constant temperature difference method. It is a special measuring instrument for gas measurement. It has the characteristics of high precision, wide range ratio, small pressure loss, direct measurement of gas standard volume flow without pressure compensation, and many other flowmeters do not have, and has been widely used in all walks of life.
However, the following points should be noted when selecting and installing:
Thermal gas mass flowmeter constant temperature difference measurement center point is to ensure that the temperature between the two probes is constant, the heat of the medium (flow rate) and the heat supply current required for heating is proportional to the medium temperature and medium specific heat as the key parameter, the flow meter converter is stored in more than 60 kinds of conventional gas specific heat conversion coefficient, the coefficient is set as a single matrix clean gas.
However, in the actual measurement of the field, the purity of the medium is not so high, although the design accuracy of the flowmeter accuracy has not declined, but the measured value and the actual value may have a certain amount of deviation, which is why the hot gas mass flowmeter dry gas; The temperature of the medium is a major difficulty of the hot gas mass flowmeter, and it is necessary to heat the heating probe to 50 degrees higher than the medium temperature when working.
If the temperature change frequency of the medium itself is too high during the measurement, that is, the power supply current required for heating is large and small, resulting in large fluctuations in the flow rate displayed by the meter head, and its measurement accuracy will fall straight down, which is not conducive to detection.
If the temperature of the medium itself is higher, the probe requires a higher heating temperature, the flowmeter design power is less than 18w, when the heating temperature is too high, the power supply current required for heating is too large (power supply current is not enough), it will produce a variety of abnormal conditions, such as the meter head flow from small to large cyclic changes, Therefore, the thermal gas mass flowmeter is mostly used to measure the medium temperature change frequency is not high and the temperature does not exceed 400 degrees of gas.
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