Bimetal Thermometers

Other nonelectrical thermometers are bimetal, fiHed-system, and pyrometric cone thermometers. In bimetal thermometers, two strips of metal of differing expansion characteristics are welded together face-to-face. If one end of such a strip is fixed, the strip bends in response to temperature change as the... 

In addition to the mercuiy-in-glass thermometer, other temperature-sensing elements may be used for psychrometers. These include resistance thermometers, thermocouples, bimetal thermometers, and thermistors. 

Bimetal thermometer A thermometer that uses two dissimilar bars of metals (with different rates of linear thermal expansion) riveted together. A variation in temperature produces a bending moment on the bar, which is magnified by a lever to record temperature on a dial. 

If larger displacements are required, an arrangement as shown in Fig. 9.7, the bimorph, can be applied. The principle is similar to the bimetal thermometer. Two thin plates of piezoelectric material are glued together. By applying a voltage, one plate expands and the other one contracts. The composite flexes. 

Fig. 9.7. Bimorph. Although the word bimorph is a trade name of Vernitron, Inc., it was described and analyzed by Curie (1889a). The most common mode of connection is to ground the two outer electrodes and to apply a voltage to the center electrode. The operation is similar to the bimetal thermometer. (By courtesy of Morgan Matroc, Inc., Vernitron Division, Bedford, Ohio.)...

BIMETAL THERMOMETER. Thermostatic bimetal can be defined as a composite material, made up of strips of two or more metals fastened together, which, because of the different expansion rates of the components, lends lo change iLs curvature when subjected to a change in lemperaLure. 

Bimetal thermometers are made in ranges from + 1000°F (538°C) down to — 300°F (— 184°C) to and lower. However, at low temperatures, the rate of deflection drops off quite rapidly. Because of its long-term instability at high temperatures, the maximum temperature for continuous use is about 800°F (427°C). However, special bimetal thermometers can be obtained for continuous use up to 1200°F (649°C). Good bimetal thermometers retain their accuracy indefinitely. Usually industrial bimetal thermometers read with an accuracy of 1% at any point on the scale. The speed ot response of bimetal thermometers is generally about the same as that for liquid-in-glass thermometers in similar ranges. 

Fig. 2. Principal configurations of elements used in bimetal thermometers (a) flat spiral, (b) single helix, (c) multiple helix...

Bimetal thermometer Turbine Bellow Magnetically coupled Infrared (IR) spectroscopy... 

Fig. 2.29 Bimetal thermometers use two metals of different expansion to create spiral thermometers.

Resistance thermometers Filled-system thermometers Bimetal thermometers low temperatures... 

Temperature measurement Thermocouples Bimetal thermometer Resistance thermometer Radiation pyrometer Infrared measurement Conductivity pH Viscosity Infrared analyzer Mass spectrometer Radiation analyzer Chromatographic analyzer Ultraviolet analyzer Photonic measurement... 

Bimetal thermometer Vortex-shedding — diaphragm coupled Raman spectroscopy... 

---