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**Dual function sensors**

*№46 Laboratory of Physical and technological problems sensor electronics**V.F. Mіtіn*

**1. Applications: **

Dual function sensor (DFS) is intended for concurrent measurements of temperature and magnetic fields in cryogenic applications. The DFS approach can also be applied to the problem in cryogenic thermometry of temperature measurements in high magnetic fields, since, by simultaneous, direct measurements of temperature and local magnetic field, it enables computational correction of the field effects on the thermometer.

**2. Description:**

The DFS consists of a Ge-on-GaAs film resistance thermometer and an InSb-on-GaAs film Hall-effect magnetic field sensor, which at constant current provides an output voltage proportional to magnetic field induction. These sensors are incorporated in a parallelepiped package, made from gold plated copper, sealed with epoxy. The dimensions of this package are 3.5 mm wide, 2.2 mm high and 10.1 mm long. The DFS has eight copper contact leads:- four leads for the resistance thermometer and four leads for the Hall-effect magnetic field sensor. Two models of the DFS have been developed and produced for use in the 1.5 to 400 K (DFS-1) and 0.1 to 400 (DFS-2) temperature ranges.

**3. Main advantages:**

• wide temperature range for operation (0.1 to 400 K)

• monotonic response over a wide temperature and magnetic field range

• high sensitivity

• high accuracy

• small temperature reading errors for operation in magnetic fields

• high radiation tolerance

• high quality and low price

**4. Operating characteristics:**

DFS specification

Operating temperature range for:

DFS-1 1.5 to 400 K

DFS-2 0.1 to 400 K

Resistance of DFS-1 thermometer at 1.5 K 100 kΩ

Resistance of DFS-1 thermometer at 400 K 30 Ω

Resistance of DFS-2 thermometer at 0.1 K 100 kΩ

Resistance of DFS-2 thermometer at 400 K 30 Ω

Input resistance of Hall-effect magnetic field sensor at 300 K 10 to 20 Ω

Output resistance of Hall-effect magnetic field sensor at 300 K 15 to 30 Ω

Magnetic sensitivity of Hall-effect magnetic field sensor at control current of 0.5 mA 5 to 6 mV/Tesla

Zero field offset voltage of Hall-effect magnetic field sensor at control current of 0.5 mA 0.1 (max.) mV

Temperature coefficient of magnetic sensitivity of Hall-effect magnetic field sensor 0.03 (max.) %/K

Magnetic field-induced temperature errors of DFS-1 thermometer without correction, ΔT/T, at 4.2 K in magnetic fields:

2.5 Tesla 0.5 %

4 Tesla 0.37 %

6 Tesla -0.44 %

8 Tesla -2.0 %

Error in the thermometer reading, ΔT/T, at 4.2 K after gamma radiation dose 0.76 Grad -2 %

Resistance vs. temperature curves for DFS-1 and DFS-2 thermometers that are intended for operation in the 1.5 K to 400 K and 0.1 to 400 K temperature ranges, respectively | Voltage vs. magnetic field curves for DFS Hall-effect magnetic field sensor at control current of 0.5 mA and temperatures 4.2 K, 77.4 K and 298 K |