Development of A Cryocooler based Variable Temperature Setup for Calibration of Temperature Sensors

Measurement of temperature is an important aspect of any system such as an experimental system, equipment or any process involving the temperature. The measurement and control of temperature is quite important for the proper functioning of the process, device, or the equipment. Especially, in the field of cryogenics, there is a need to measure temperatures of fluids entering or exiting systems such as a Joule Thompson (JT) valve, an expansion engine or a turbine to assess the performances and improve them. Measurement of temperatures in the cryogenic range is carried out by different transducers such as the Resistance Temperature Detectors (RTD)s (also known as Resistance Thermometers, such as Platinum resistance thermometer (PT500)), thermocouples, Cernox, Silicon diodes and Germanium sensors etc. The sensors produce an output proportional to the variation of some physical property with temperature. The temperature calibration of the above sensors is best done against a pre-calibrated temperature sensor.

In this work, we present the development of a variable temperature experimental setup using a two stage Gifford McMahon (GM) cryocooler, which provides the refrigeration to cover the temperature range from 4.2 K to 300 K needed for the temperature sensor calibration. The sensors to be calibrated are mounted within the holes of an Oxygen Free High Conductivity (OFHC) copper thermal block, which accommodates a maximum of eight temperature sensors. Its design is such that different types of temperature sensors such as Silicon / Germanium diodes, RTDs, Thermocouples, Cernox sensors, Carbon resistors etc. can be calibrated using a pre-calibrated Silicon diode temperature sensor. The sensor leads from the vacuum jacket of the experimental cryostat are connected to the measuring instruments which consist of a current source (Source meter), Data AcQuisition System (DAQ), a Temperature controller and a computer. An in-house developed LabVIEW based software is used for the temperature control of the copper lock and data collection. The results of calibration of typical temperature sensors along with their measurement accuracies are presented. This set up is in regular use for the calibration of various types of temperature sensors.