If you need a precision measurement at low temperatures, do not look any further than Hart Scientific. 

The 5623A, precision “freezer probe,” is specially sealed from the sensing element to the end of the probe cable, preventing ingress of moisture when exposed to temperatures as low as –200°C. The entire assembly withstands temperatures over its full range (–200°C to 156°C), which is ideal for verification of freezers or autoclaves where a thermo-well isn't available. The 5623A assembly can be fully immersed in fluids when the application may require use in a liquid bath. The 5623A is available in a 0.25" (6.35 mm) dia. × 6" (125 mm) long Inconel™ sheath. With accuracy (that includes calibration uncertainty and short-term drift) of ±0.05°C over its full range, the 5623A is just right as a secondary standard for calibration of other process sensors. 

Most Hart Scientific readouts make an excellent companion for the 5623A. We recommend the use of the 1521, 1522, 1502A, 1529, or 1560 thermometer readouts. 

With each 5623A, you receive a full calibration report traceable to NIST and compliant with ANSI/NCSL Z540. This report includes test data and ITS-90 calibration coefficients to enter into your Hart Scientific thermometer readout. Contact Hart if you need a NVLAP-accredited calibration.