About the working principle of the bell-type gas flow standard device, do you know how to solidly promote the instrument industry?

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The bell-type gas flow standard device is a standard equipment for calibrating gas flow meters with air as the medium. It is a relatively classic gas flow standard device. When the pressure is not high and the flow rate is not large, the device is relatively simple to use. Therefore, it has been widely used in the field of domestic gas flow measurement.

The gas of constant volume and constant pressure in the bell jar flows through the tested sampler through the experimental pipeline, and the volume value of the gas flowing out of the bell jar is compared with the indicated value of the tested sampler to realize the verification and calibration of the tested sampler.

The working principle of the bell-type gas flow standard device is that a movable bell and a fixed liquid tank form a sealed cavity with variable volume. During the descending process of the bell, a pressure compensation mechanism is used to keep the internal gas pressure at a constant value, which does not change with the depth of the bell immersed in the sealing liquid. The volume between the two baffles of the bell is fixed, and the instantaneous flow can be calculated by measuring the time that the two baffles pass through the photoelectric transmitter successively. During the verification process, the gas temperature θ in the bell jar, the gauge pressure ρ', the gas temperature θm and the gauge pressure ρ'm at the measured flowmeter are measured with a thermometer and a pressure gauge. Since the volume between the two baffle plates of the bell jar has been determined in advance through verification (that is, the volume at 20°C and zero gauge pressure) VN, the volume of the bell jar to be verified is:

V=VS[1+(2αB+αSC)(θ-20)] where: V——the volume of the bell jar under test conditions; VS——the standard volume of the bell jar; α B——the expansion coefficient of the bell jar material ; αSC——the linear expansion coefficient of the scale; θ——the temperature during verification.

The gas used in the bell-type device is preferably indoor air. The gas entering the bell-jar must be given a certain constant temperature for a special gas source, and the gas pressure in the bell-jar should not deviate from the specified value.

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