Nickel resistance thermometer

Nickel resistance thermometer. This thermometer has been adapted satisfactorily in industrial applications for a temperature range from -100 to 300°F. The nickel resistance thermometer is less stable than platinum thermometers, but its low cost favors its usage. 

FIG. 8-61 Typical resistance-thermometer curves for platinum, copper, and nickel wire, where Rj = resistance at temperature T and Rq = resistance at 0 C. 

Resistance thermometers are made of a pure metal, such as platinum, nickel, or copper. The electrical resistance of such a material is almost linearly dependent on temperature. Resistance thermometers are stable, having a small drift. A widely used and the best-known resistance probe is the IW-100 probe, which is platinum, having a resistance of 100 ohms at the temperature of 0 °C. Other resistance values for PT probes are available. The resistance versus temperature values as well as tolerances for platinum probes are standardized. The shape and size of a resistance probe can vary considerably, resulting in changes in probe dynamics. 

Very recently, Bailey and Richards (23) have shown that a high degree of sensitivity for adsorbed species can be achieved by measuring the absorption of infrared radiation on a thin sample cooled to liquid helium temperature. The optical arrangement used in these studies is shown in Figure 10. The modulated beam produced by the interferometer is introduced into the UHV sample chamber and reflected off a thin slice of monocrystalline alumina covered on one side by a 1000 k film of nickel or copper. Radiation absorbed by the sample is detected by a doped germanium resistance thermometer. The minimum absorbed power detected by this device when operated at liquid helium temperature is 5 x 10 14 W for a 1 Hz band width. With this sensitivity absorbtivities of 10"4 could be measured. 

RTDs are constructed of a resistive material with leads attached and placed into a protective sheath. Platinum resistance thermometers are the international standard for temperature measurements between the triple point of H2 at 13.81 K (24.86°R) and the freezing point of antimony at 630.75°C (1,167.35°F). The RTD elements include platinum, nickel of various purities, 70% nickel/30% iron (Balco), and copper, listed in order of decreasing temperature range. Their features and relative performance characteristics in comparison with other sensors are tabulated in Table 3.169. 

Pt resistance thermometers can be used from -200°C to 850°C, and they are used to interpolate between the IPTS-68 fixed points. The measurement of the resistance of Pt yields a temperature precision of 0.001 K. Nickel can also be used its resistance changes by 0.6%/°C. 

The bolometer is another type of thermal detector that can offer extreme sensitivity for specialized applications, t This is essentially a resistance thermometer, usually with a platinum, nickel, carbon, or germanium element, although a semiconductor thermistor can also be used. Typically, two elements are used in a bridge circuit with one exposed to radiation and the other kept dark as a reference. The germanium bolometer provides exceptional... 

For industrial purposes, resistance thermometers are made usually either of platinum or of nickel, the latter material being fairly satisfactory for temperatures below 300 C. In the form of platinum thermometer made by Leeds Northrup Co. about 40 cm. of fine wire is wound upon a mica frame into a spiral coil about 4 cm. in length and 0.7 cm. in diameter. The length of the wire is so adjusted that the resistance of the coil is about 8.3 ohms at 0°C. The frame is made of crossed strips of thin mica notched at the edges to hold the wire in place. From the ends of this coil lead wires of platinum or gold are carried to the terminal head of the thermometer. The lead wires are insulated and held apart by mica discs through which the wires are threaded. 

Another type of resistance thermometer uses metal oxides, instead of metals it is frequently referred to as a thermistor. Electrical resistance of these metal oxides changes rapidly with even rather small temperature changes. Hence, thermistors are often emplyed to measure small temperature changes such as 1°C to 5 °C. The thermistor proper tends to have low purchase prices. Metal oxides, which are semiconductors, include mixtures of the following oxides nickel, manganese, copper, cobalt, tin, germanium, etc. [1]. 

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. 

A bolometer is a type of resistance thermometer constructed of strips of metals, such as platinum or nickel, or of a semiconductor. Semiconductor bolometers are often called thermistors. These materials exhibit a relatively large change in resistance as a function of temperature, The responsive element is kept small and blackened to absorb radiant heat. Bolometers are not so extensively used as other infrared transducers for the mid-infrared region, Flowever, a germanium bolometer. operated at 1..3 K, is nearly an ideal transducer for radiation in the. 5 to 400 cm (2000 to 2.3 pm) range. 

The first bolometer produced by Langley in 1880 used a platinum resistance element and later other metals (such as nickel) were used. These metals are still used for resistance thermometers where their high long term stability is an essential requirement. For infrared detectors, however, the older metal film bolometers have been replaced by semiconducting elements which have a much larger temperature coefficient. 

The best-known resistance thermometer is the platinum resistance thermometer, mentioned in Fig. 3.2 as the instrument for the maintenance of the ITS 90. As a typical metal, its resistivity increases approximately linearly. Over a wide temperature the change is 0.4% of the resistance per degree. In order to make a platinum resistance thermometer, a wire is wound non-inductively, so that the total thermometer has a resistance of 25.5 n at 273.15 K. Under this condition, the resistance of the thermometer will change by about 0.1 n/K. The precision that has been achieved with platinum resistance thermometers is 0.04 K at 530 K and 0.0001 K at 273.15 K, and decreases to 0.1 K at 1700 K. Similar resistance thermometers have been built out of nickel, phosphor-bronze and copper. 

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