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Differential pressure transmitters have difficulty measuring the level of fluids at temperatures below -20°C. If it is necessary to measure the level of low-temperature media such as liquid ammonia or liquid nitrogen, indirect measurement with gas isolation can be employed. As shown in the figure, the level of the cryogenic medium is measured by detecting the gas pressure inside the pressure guiding tube. Since the liquid in the pressure guide tube on the high-pressure side is at a normal temperature above its boiling point. Therefore, the liquid in the pressure guide tube evaporates into gas until a saturated gas is formed inside it. When a differential pressure transmitter is chosen for measurement, the principle of hydrostatic pressure of a liquid column is still applied; in this case, the pressures on the high-pressure and low-pressure sides of the differential pressure transmitter are respectively: PH = hx×ρ + Px ； PL=Px ； Then P = PH + PL = (hx×ρ + Px) – Px = hx×ρ; its range ΔP is (hx×ρ + Px). The relationship between differential pressure and current is as follows: The differential pressure transmitter should be installed at a position higher than the highest liquid level, with the high-pressure side connected to the liquid-phase pressure guide tube. This allows the transmitter to operate in a normal temperature environment and ensures that the low-temperature liquid vaporizes fully. To facilitate the adjustment of the instrument zero point and the replacement of the instrument, a balance valve must be installed between the high-pressure and low-pressure sides of the differential pressure transmitter. After the differential pressure transmitter is installed, its zero point should be adjusted. Next, the gas-phase pressure guiding valve PL should be opened, and the zero point should be adjusted again under operating pressure. Then open the liquid-phase pressure control valve PH, wait for a moment to allow the low-temperature liquid to vaporize fully, and then close the balance valve to put the transmitter into operation. When checking or zeroing the device in use, first open the balance valve to equalize the pressures on the high and low sides of the differential pressure transmitter; then close the liquid-phase pressure guiding valve to check or adjust the zero point. If there is a danger when the vapor of the liquid being tested comes into contact with air, certain safety measures must be taken during maintenance. How should the level of low-temperature liquids be measured when the installation location for differential pressure transmitters is limited? When using a differential pressure transmitter to measure the level of low-boiling-point liquids, under normal room temperature and dry gas phase conditions, one of the pressure guiding tubes leading from the container is for the liquid phase and the other is for the gas phase. However, due to the low boiling point of the liquid being measured, vaporization occurs in the pressure guiding tube, and this vaporization affects the accuracy of the measurement values. For this purpose, there are certain requirements regarding the configuration of the pressure guiding tubes, such as the need to install gas-phase containers, as well as specific requirements for the installation location of the differential pressure transmitters; these factors increase the workload and the difficulty of construction ； What should be done in some sites where, due to environmental constraints, the installation requirements for differential pressure transmitters cannot be met? Here is a simple installation method: use a pipe to connect the gas and liquid pipes together, as shown in the figure. As can be seen from the diagram, the gas generated by the \"vaporization\" of the liquid being tested rises along the tube to the top of the container, while the liquid flows down along the tube. For this pipe, a Ф14×2 size will suffice; for use with corrosive media, a stainless steel pipe is appropriate. Adding such a tube is simple and easy, but the effect is very good. This method is applicable for measuring the level of low-boiling-point liquids using the differential pressure method. Most importantly, it imposes no strict requirements on the installation location of the differential pressure transmitter, which facilitates on-site installation.