Quick guide on which temperature sensor to choose for low-temperature experiments
Choosing the correct temperature sensor can be difficult especially for the very first low-temperature experiment. However, different sensor types have certain universal properties that can be useful for choosing the right sensor.
Silicon diodes of the S950 series are the best choice for the general cryogenic use between 1.4 K and 400 K. All sensors are exchangeable (they follow a standard curve) and come in rugged sets of various setups (see fig. 1). The design is simple and cost-efficient. They are used in a broad range of cryogenic applications like cryogenic coolers, laboratory cryogenics, cryo-gas production and space satellites. Platinum RTDs (resistance temperature detectors) are an industrial standard and are also used from 14 K to 1235 K by the American National Institute of Standards and Technology (NIST). They follow an industrial standard curve up to 30 K with good sensitivity over the entire bandwidth. At lower temperatures, RTDs must be individually calibrated. Thanks to their outstanding reproducibility, they are used in many precision measurements.
Platinum RTDs have a limited design, are cost-efficient and require only simple instrumentation. They are widely used in applications with liquid nitrogen or at higher temperatures.
Ruthenium oxide RTDs can be used to 50 mK and below. Their unparalleled advantages are the low magnetic resist and a standard curve. Their upper temperature limit lies at 40 K (Cernox sensors are better in magnetic fields over 2 K). Ruthenium oxide RTDs are used in applications that require a standard curve in magnetic fields, like MRI systems. Apart from germanium, they are the only cryogenic temperature sensors that can be used below 100 mK. GaAlAs diodes offer high sensitivity over a wide range (1.4 K to 500 K). They are well suited in moderate magnetic fields and offer many of the advantages of silicon diodes. However, since they don’t follow any standard curve, silicon diodes are frequently preferred, except for moderate magnetic field applications. Choose Cernox sensors for the latter, as they may be used from 100 mK to 420 K with great sensitivity over the entire temperature range. The have low magnetic reluctance and are first choice for applications with magnetic fields up to 30 T (at temperatures above 2 K). Furthermore, Cernox sensors are resistant against ionizing radiation. Further sensors are thermal elements and capacitive sensors. However, they are less accurate and thus less suited for low-temperature experiments. Thermal elements follow a standard curve and can be used in rugged environments over a broad spectral range. Capacitive sensors are well suited as control sensors in strong magnetic fields, as they show almost no magnetic field dependence.
During thermal cycles, small variations in the capacitive and temperature curves will occur. We recommend measuring the temperature in the zero field with other cryogenic temperature sensors and using the capacitive sensors as control unit.
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Please note that we can only offer silicon diode temperature sensors and platinum and ruthenium RTDs.