CMN1000 thermometer

The CMN1000 is a precision thermometer for the range of < 10 mK to 2 K using the temperature dependence of the susceptibility of powdered Cerium Magnesium Nitrate (CMN).

  • The CMN sample is mounted in a sealed capsule to prevent dehydration. It is thermally connected to plate [1] via a silver foil heat exchanger;

  • A set of detector coils produces a signal proportional to the CMN susceptibility; 

  • Adapter [2] eases mounting and positioning in a measurement set-up. SRD1000 and CMN1000 sensors can be mounted close together at one adapter piece;

  • A protective cylinder with niobium shield [3] reduces  magnetic couplings to the detector coils;

  • The shielded sensor leads [4] are terminated by filtered connectors [5] to reduce rf-interference.

Sensor characteristics: 

  • T ≈ d + B / ( VMIDS - A ) (Eq. 1), with T the sensor temperature and  VMIDS  the output voltage of the detection electronics;

  • Parameters A, B, d of (Eq. 1) have to be derived experimentally using the SRD1000 reference points;

  • Typical values are A: -100 ... 100 mV, B: 1.5 104 mV.mK and d = 1 mK;

  • A fitting error for < 0.5 % may be achieved for T in the range 15 mK to 1.2 K;   

  • Sensor resolution: about 4 mK at 2 K, 0.2 mK at 500 mK and 10-4 mK at 10 mK;

  • (self-)Heating effects are negligible;

  • Thermal relaxation time < 5 s at 10 mK and less at higher temperatures;

  • Reproducibility during a cool-down is within the noise level, and better than 0.2 % after a cycle to room temperature.

Example: measured data points VMIDS versus 1 / (T-d)