Cryogenic Temperature Sensors

In the renewable energy economy, hydrogen will have an important role, and in the processing of LH2, the measurement and control of cryogenic temperatures is one of the most important tasks. 

Acoustic time domain reflectometry operates on the principle that the velocity of sound and ultrasound increases in gases and decreases in liq- 

Characteristics of silicone and gallium-aluminum-arsenide diodes. 

Silv Thii Aluminum Thin Wire er l Wire Molten Iron, 3.5% U 0 a - 

The velocity of sound increases in gases and decreases in liquids and solids as the temperature rises. 

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Lake Shore Cryotronics, WestervTUe, OH, has an extensive website www.lakeshore.com, which includes a reference manual on Thermal Resistances of Cryogenic Temperature Sensors from 1-300 K. ... 

Notwithstanding the excellent analytical features inherent in molecular phosphorimetric measurements, their use has been impeded by the need for cumbersome cryogenic temperature techniques. The ability to stabilize the "triplet state" at room temperature by immobilization of the phosphor on a solid support [69,70] or in a liquid solution using an "ordered medium" [71] has opened new avenues for phosphorescence studies and analytical phosphorimetry. Room-temperature phosphorescence (RTF) has so far been used for the determination of trace amounts of many organic compounds of biochemical interest [69,72]. Retention of the phosphorescent species on a solid support housed in a flow-cell is an excellent way of "anchoring" it in order to avoid radiationless deactivation. A configuration such as that shown in Fig. 2.13.4 was used to implement a sensor based on this principle in order to determine aluminium in clinical samples (dialysis fluids and concen-... 

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. 

Acoustical temperature sensors can theoretically measure temperature from the cryogenic range to plasma levels. Their accuracy can approach that of primary standards. Temperature measurements can be made not only in gases but also in liquids or solids, on the basis of the relationship between the sound velocity and temperature shown in Figure 3.163. The acoustic velocity can be detected by immersing a rod or wire into the fluid or by using the medium itself as an acoustic conductor. The sensor rod can measure the temperature at a point or, by means of a series of constrictions or indents, can profile or average the temperature within the medium. 

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. 

Kang et al. [28] report a space-qualified FBG system that uses FBG sensors to monitor the strains in a filament-wound CFRP tank during pressure testing. Mizutani et al. [27] describes a space-qualified on-board FBG system used to monitor the strain on a CFRP composite LH2 tank installed on a reusable launch vehicle (RLV) test article. The FBG sensors were installed on the CFRP composite tank with UV-cured polyurethane adhesive that showed good performance at cryogenic temperatures. The system (which weighs less than 2 kg) was installed, flown, and tested on the RLV typical recorded data are shown in Figure 16.15. 

Specific resistivity p and critical temperature Tc were measured by the four-probe method. For the Tc value the point in the middle of the curve of transition to the superconducting state was taken. As a temperature sensor in the cryogenic zone a germanium thermometer of the VG-type was used. The values of the lower Hci and the upper Hc2 of the critical magnetic field at the temperature of 4.2 K were determined from differential curves of magnetization similarly to [8]. 

Porous Si shows a much lower thermal conductivity than bulk crystalline Si. The measured difference is more than two orders of magnitude at room temperature, while it exceeds four orders of magnitude at cryogenic temperatures. This makes porous Si very appropriate for use as a local thermal isolation platform on the Si wafer for the integration of sensitive thermal and other devices. Existing devices to date include flow sensors, accelerometers, bolometers, gas sensors. 

There are two basic designs for engineering use immersion probes (see Fig. 8.25) and surface temperature sensors. The immersion probes feature a high-purity platinum wire encapsulated in ceramic, or securely attached to a support frame. Features such as repeatability after thermal shocks, time response in different environments, interchangeability, and mechanical shock tolerance differ between specific designs and probe fabricators. The repeatability of the typical immersion sensor is usually certified to be about 0.1 K at the ice point after several thermal cyclings to cryogenic temperatures. For most thermometers this repeatability value is conservative. 

T. Junquera et al. Neutron Irradiation Tests of Calibrated Cryogenic Sensors on Low Temperatures, CERN-LHC Project Report n°153 (1997)... 

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. 

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. 

The considered experimented set - up can be applied in two different ways. The first one is to use is as a semiconductor sensor cooler with low heat dissipation to cool the sensor down to the ambient temperature. It is interesting to be applied in cryogenic range of temperatures. The second option is related with the cooler for high energy dissipation devices (for example laser diode cooler). The first set of experiments was performed with sorption heat pipe and ammonia as a working fluid to demonstrate the basic possibility to decrease the temperature of the heat loaded wall to compare with the temperature of this wall in the phase of loop heat pipe cooling mode. 

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