The method of measuring the cryogenic medium is that the transmitter is limited by two convenience: the low temperature resistance of the material and the electrical insulation of the transmitter. For media that exceed -20 degrees, such as frozen salt water, the liner material of the transmitter can usually be used. However, the choice of Teflon material is that the thermal expansion and cooling of PTFE are more serious. Electrodes leak easily. The main problem of measuring low temperature media is the electrical insulation of the transmitter. When the measuring tube is filled with flowing cold media, it is easy to measure the condensation of water droplets or water frost condensation in the outer wall of the measuring tube and the transmitter. In this way, the insulation resistance between the signal circuit, the excitation circuit and the shell can be reduced or even short-circuited.
In this case, we can use resin or sealant to seal the shell. By filling the transformer oil in the transmitter shell, insulation can be guaranteed, and the cavity in the transmitter shell can be filled directly with resin to isolate the electrical parts from the air.