Thermometer cryogenic

A descriptive flowchart has been prepared by Sparks (Materials at Low Temperatures, ASM, Metal Park, OH, 1983) to show the temperature range of cryogenic thermometers in general use today. Parese and Molinar (Modem Gas-Based Temperature and Pressure Measurements, Plenum, New York, 1992) provide details on gas- and vapor-pressure thermometry at these temperatures. 

TABLE III Some Cryogenic Thermometers Suitable for Use Below 4 K... 

Table 8.9 summarizes some representative characteristics of the best-known types of cryogenic thermometers. Figure 8.29 gives a graphic summary of the approximate useful range of many common cryogenic thermometers between 4 and 300... 

IR detection by bolometers and microbolometers depends on the change in electrical resistance of a material as the temperature of the material changes. The electrical resistance of carbon increases exponentially with l/T as its temperature is reduced below 5 K. This allows it to be used as an inexpensive cryogenic thermometer, and any material that can make a thermometer is a candidate for use as a thermal detector. The behavior of carbon resistors at low temperatures and their use as thermometers and bolometers are described by Clement and Quinell (1952), Boyle and Rogers (1959), and Shephard (1964). 

Meyer Tool and Manufacturing Company Website (2014) Cryogenic Thermometers - An Introduction. Accessed July 2014 at http //www.mtm-inc.com/ reduce project risk/cryogenic thennometers/... 

A cryogenic sensor is, for example, a thermometer used around a fixed temperature where it shows a high sensitivity. It does not usually need a calibration. The realization technology of sensors often differs from that of the corresponding thermometers. 

Most of cryogenic sensors have been developed in close connection with detectors and do not find different applications. This is the case of SSG (superheated superconducting granules) others have also independent applications, e.g. Ge thermometers. 

In a cryogenic experiment, one or several detectors are used for a definite goal for which they have been optimized. For example, in CUORE experiment described in Section 16.5, the sensors are the Ge thermistors, i.e. thermometers used in a small temperature range (around 10 mK). One detector is a bolometer made up of an absorber and a Ge sensor. The experiment is the array of 1000 bolometers arranged in anticoincidence circuits for the detection of the neutrinoless double-beta decay. Note that the sensors, if calibrated, could be used, as well, as very low-temperature thermometers. Also the array of bolometers can be considered a single large detector and used for different purposes as the detection of solar axions or dark matter. 

Because of their high heat capacity, only few of the thermometers described in Chapter 9 can be used as sensors for detectors. Resistance (carbon) sensors were used for the first time in a cryogenic detector by Boyle and Rogers [12] in 1959. The carbon bolometer had a lot of advantages over the existing infrared detectors [13]. It was easy to build, inexpensive and of moderate heat capacity due to the low operating temperature. 

The low-temperature thermometers based on heavily doped compensated germanium (see Section 9.6.2.1) show high stability, good reproducibility, low noise and low specific heat. Ge used for cryogenic sensors is heavily doped (1016 - 1019 atoms/cm3), with T0 of Mott s law ranging between 2 and 70K (see formula 9.6). 

A sensor is only one component of a cryogenic detector. In the simplest case, a detector consists of an absorber (for example absorber of energy) and a sensor (for example a thermometer like a TES). Nevertheless, other physical parameters than energy and temperature may be involved in a cryogenic detector. For example, in a cryogenic gravitational antenna (see Section 16.2) the absorber is the cooled bar, whereas the sensors is SQUID-capacitor system. 

In the category of electronic thermometers, the thermocouples (TCs), resistance temperature detectors (RTDs), thermistors, integrated circuitry (IC), and radiation thermometers will be discussed in separate subsections. The IC and diode detectors will be discussed in connection with cryogenic thermometry. Their characteristics are shown in Figure 3.161. 

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. 

The direct determination of the saturation pressure of the adsorptive has the advantage of providing the real p° and, with nitrogen, of allowing one to calculate the adsorption temperature to the nearest 0.01 K. Since the surface layer of a cryogenic liquid tends to become colder (because of evaporation) than the lower part of the liquid (Nicolaon and Teichner, 1968), it is necessary to condense the adsorptive in the bottom of a double-walled ampoule, so that the location of the condensation is very close to the adsorbent sample. Measurement of the sample temperature by means of a resistance thermometer is more straightforward, but requires calibration against the saturation vapour pressure thermometer. 

Resistive materials used in thermometry include platinum, copper, nickel, rhodium-iron, and certain semiconductors known as thermistors. Sensors made from platinum wires are called platinum resistance thermometers (PRTs) and, though expensive, are widely used. They have excellent stability and the potential for high-precision measurement. The temperature range of operation is from -260 to 1000°C. Other resistance thermometers are less expensive than PRTs and are useful in certain situations. Copper has a fairly linear resistance-temperature relationship, but its upper temperature limit is only about 150°C, and because of its low resistance, special measurements may be required. Nickel has an upper temperature limit of about 300°C, but it oxidizes easily at high temperature and is quite nonlinear. Rhodium-iron resistors are used in cryogenic temperature measurements below the range of platinum resistors [11]. Generally, these materials (except thermistors) have a positive temperature coefficient of resistance—the resistance increases with temperature. 

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