Types and principles of level gauges

According to the image, this level gauge is a type of level gauge known as a radioactive level gauge. It works on the principle of using a radioactive source (such as cesium-137 or cobalt-60) to emit radiation downward through the liquid, which then interacts with detectors at the bottom. When the liquid level is above the radioactive source and the detector, these rays are absorbed by the liquid, thereby reducing the amount of radiation that reaches the detector. By measuring these reduced amounts of radiation, the height of the liquid level can be determined. Therefore, this level gauge does not belong to the insert-type level gauge. As for the use of purge hydrogen at both ends, it may be because hydrogen is present in the liquid, and hydrogen needs to be used for purging and evacuation. .

Pneumatic level gauge: The principle of pneumatic level measurement is as follows: A pneumatic tube is inserted into an open container. Air or an inert gas such as nitrogen, which serves as the gas source, passes through a filter and is then reduced in pressure by a adjustable pressure regulator (whose function is to bring the supply pressure to a constant value; this constant pressure depends on the height of the liquid level being measured), thereby ensuring that the pressure at the inlet for the pneumatic gas remains constant. The clean air is then blown into the liquid being tested via a float flow meter, a constant flow valve, and an air supply tube. The blowing flow rate is indicated by the float flow meter, and the magnitude of this flow rate is set using the flow control valve on the float flow meter. The gas at a constant flow rate escapes from the lower end of the air supply tube inserted into the liquid, forms bubbles, and is discharged into the atmosphere through the liquid. When a small amount of bubbles (about 150 per minute) are discharged from the lower end of the blowing pipe (since the bubbles are minimal and the gas flow rate is low, the frictional losses of air within the blowing pipe can be ignored; as a result, the pressure inside the blowing pipe is almost equal to the static pressure of the liquid level), the pressure value indicated by the differential pressure transmitter can thus reflect the liquid level height.

It seems that the level gauge LT21801B below is the one connected to the nuclear source, while LT21801A above is not connected to the nuclear source

Dear expert, may I ask why there is only one pressure tapping pipe here but two purge hydrogen pipes?

The method of operation should be blow-type, but the connection of the air supply for the blow-type level gauge is incorrect; one should be placed above and the other below