Development and experiment of high-precision temperature and pressure calibrating system

PTU devices (devices measuring pressure, temperature and humidity simultaneously) was typically applied to weather observation systems, wrist computers, study of humidity generation technology and calibration of metering equipment. At the moment, a number of sensors or equipments are directly exposed to severe and complex environment conditions, so more comprehensive environmental parameters are inevitably affected by the surrounding environment when these sensors or equipments are working. With the peripheral environment change, not only accuracy and reliability of these sensors or instruments are hard to ensure, but also they can't work when the environment changes beyond sensor or instrument calibration range. Hence, to obtain more comprehensive data of sensors or equipments, a set of device or system which can be used to measure pressure, temperature and humidity simultaneously is urgently required. However, it is pity that there are hardly any commercial calibration systems to be available for low temperatures (<0℃) for the PTU devices at present. As for this situation that there are absent for commercial calibration systems which can be used to calibrate the temperature, pressure and humidity simultaneously at low temperatures (<0℃), a new high-precision temperature and pressure calibration system was developed based on the two-temperature and two-pressure humidity generation principle. In this temperature and pressure calibration system, pressure and temperature can be controlled simultaneously. On the one hand, the temperature and pressure calibration for sensors and apparatus can be achieved simultaneously, on the one hand, it can provide the theoretical basis and more comprehensive experimental data for the further research of the calibration system of temperature, pressure and humidity. After introducing the structure of the system and operating principle, mathematical models of temperature system and pressure system were developed, and compound control strategy of bang-bang and improved PID(proportional-integral-differential) was given. Finally, field tests were carried out. Experimental results indicated that when the absolute pressure is from 30kPa to 130 kPa and temperature is from -70℃ to 80℃, temperature measurement absolute error and control absolute error were less than 0.02℃ and 0.03℃, respectively; measurement absolute error and control absolute error of pressure were less than 15Pa and 18Pa, respectively; The target uncertainty (k=2) of the temperature and pressure are 0.06 ℃ and 10 Pa, respectively. These results further showed that the calibration system had the advantages such as high control precision, strong stability and high reliability. This calibration system can be used to calibrate sensors and apparatus as well as evaluate ground equipments and radiosonde instruments.