Below 30K, these sensors must be individually calibrated. Platinum sensors conditioned for cryogenic use should never be exposed to temperatures above 420K. Cryo-con controllers and temperature monitors have the IEC751 calibration curves built in for Alpha values of 0.00385, 0.00375 and 0.003902. These curves assume 100 Ohms at 0C but can be easily adapted to sensors with other 0C resistance values by using the Multiplier field in the sensor definition table. For example, a multiplier field of 10 would map a 100 Ohm curve to a 1000 Ohm curve. Curves for other Alpha values are generally be obtained directly from the sensor manufacturer.
Ratiometric measurement is a high accuracy technique for measuring resistance.
The resulting balanced circuit cancels the DC drift and low frequency noise components of the reference and essentially reduces the measurement to a ratio between the unknown resistance and the internal calibration standard resistance. This is an important technique in a cryogenic control application since the canceled low frequency noise and drift are often within the bandwidth of the control loop, causing the loop to track reference noise as well as sensor temperature. However, the technique is not always used since the measurement circuitry is more complex. Home Products Support Contact About Us Specifications subject to change without notice.