Carbon resistor temperature sensors

Early bolometers used, as thermometers, thermopiles, based on the thermoelectric effect (see Section 9.4) or Golay cells in which the heat absorbed in a thin metal film is transferred to a small volume of gas the resulting pressure increase moves a mirror in an optical amplifier. A historical review of the development of radiation detectors until 1994 can be found in ref. [59,60], The modern history of infrared bolometers starts with the introduction of the carbon resistor, as both bolometer sensor and absorber, by Boyle and Rogers [12], The device had a number of advantages over the Golay cell such as low cost, simplicity and relatively low heat capacity at low temperatures. 

As was shown in Figure 3.159, cryogenic temperatures can be detected by integrated circuit diodes types K, T, and E thermocouples (TCs) class A and B resistance temperature detectors (RTDs) acoustic and ultrasonic thermometers germanium and carbon resistors and paramagnetic salts. As TCs and RTDs will be discussed in separate subsections, here the focus will be on the other sensors. 

Commercially available carbon resistors have been used as temperature sensors in the cryogenic temperature area near absolute zero, from about -253°C to -272°C (-424°F downward to below -458°F). One major benefit of the carbon resistor at low temperature is its lower susceptibility to adverse effects caused by a magnetic field and stray radio interference. They do require individual calibration to keep the measurement error under 1%. Carbon resistors may be incorporated into resistor networks to improve linearity. These sensors exhibit a large increase in resistance below -253°C ( 424°F). Reproducibility on the order of 0.2% is obtainable when calibrated individually. Small size, low cost, and general availability make their use attractive in cryogenic work. 

Thermistor and carbon resistor sensors performed satisfactorily, in that no false indication was noted even during the dewar filling operation and during pressurization or depressurization. Recorded response times on emergence were relatively fast. Some manufacturers have installed a separate heater w ire winding around the sensing element to speed up the temperature rise and thereby improve the recovery time. 

Since specific heat at very low temperatures is minimal, even low heat input causes a large temperature increase. For measurements requiring exact temperature recording, care must be taken to minimize both the intrinsic heat generation of thermal sensors and the heat flux along their current leads. Carbon resistors and germanium diodes (heating power <10 W) are useful below 40 K. Above that temperature, platinum resistors suffice. 

Ordinary carbon resistors can be used as temperature sensors. 

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