In the fields of industrial production, scientific research experiments and product quality control, high and low temperature coolant testing machines play a crucial role. It can simulate a variety of extreme environmental conditions and carry out rigorous testing of product performance. In this paper, the units of temperature, humidity and pressure commonly used in high and low temperature coolant testing machines and their conversion methods are introduced in detail.

　　1. Temperature unit and conversion

　　Temperature is a physical quantity that measures the cold and heat of an object, and the temperature units commonly used in high and low temperature coolant testing machines are Celsius (℃), Fahrenheit (℉) and Kelvin (K). Here is the conversion formula between them:

　　Celsius to Fahrenheit conversion:

　　F = (9/5) x C + 32 (F for Fahrenheit, C for Celsius)

　　C = (5/9) × (F - 32)

　　Celsius to Kelvin conversion:

　　K = C + 273.15 (K for Kelvin, C for Celsius)

　　C = K - 273.15

　　Two, humidity units and conversion

　　Humidity indicates the content of water vapor in the air, and commonly used humidity units are relative humidity (RH) and absolute humidity (AH). Relative humidity is the ratio of the actual content of water vapor in the air to the saturated water vapor content at the same temperature, expressed as a percentage; Absolute humidity refers to the absolute mass or volume of water vapor in the air.

　　In high and low temperature coolant testing machines, relative humidity is the most commonly used humidity index. It should be noted that relative humidity is closely related to temperature, so at different temperatures, the corresponding water vapor content of the same relative humidity is different.

　　3. Pressure unit and conversion

　　Pressure represents the vertical force on a unit area, and the commonly used pressure units in high and low temperature coolant testing machines are PASCAL (Pa), bar (bar), MPa (MPa) and standard atmospheric pressure (atm). Here is the conversion formula between them:

　　Pasca and bar conversion:

　　1 bar = 100,000 Pa

　　PASCAL to mpa conversion:

　　1 MPa = 1,000,000 Pa

　　Standard atmospheric pressure and PASCAL conversion:

　　1 atm = 101,325 Pa

　　It should be noted that in practical applications, the selection of pressure units should be determined according to test requirements and equipment specifications. At the same time, when performing pressure conversion, it should be ensured that the correct conversion factor is used to avoid errors.

　　In short, the temperature, humidity and pressure units commonly used in high and low temperature coolant testing machines and their conversion methods are of great significance for the correct use of the equipment and the accurate evaluation of product performance. In the actual operation process, the user should choose the appropriate unit according to the specific needs and equipment specifications, and master the corresponding conversion method.