Bimetallic strip thermometer

The principle of the expansion of a solid is employed in bimetallic-strip thermometers, which are comprised of strips of two different metals bonded together, side by side. Since the metals selected for this use have... 

Bimetallic strip thermometers are preferred for monitoring oven temperatures. Mercury thermometers should not be mounted through holes in the tops of ovens so that the bulb hangs into the oven. Should a mercury thermometer be broken in an oven of any type, the oven should be closed and turned off immediately, and it should remain closed until cool. All mercury should be removed from the cold oven with the use of appropriate cleaning equipment and procedures (see Chapter 5, section 5.C. 11.8) in order to avoid mercury exposure. After removal of all visible mercury, the heated oven should be monitored in a fume hood until the mercury vapor concentration drops below the threshold limit value (TLV). 

Changes in dimension. With such devices, a change in physical dimension occurs with a change in temperature. In this category are liquid-in-glass or other fluid-expansion thermometers, bimetallic strips, and others. 

No particular difficulties are experienced in controlling temperatures in the region from room temperature up to 300°C. Bimetallic strip devices, Wheatstone bridge circuits (thermistor activated) or mercury thermometers with capacitance devices connected to relays can be used for control of bath temperatures. For good control, the immersion heater should have the lowest possible heat capacity and the bath should have as large a volume as possible. Should the bath volume be small for whatever reason, the heat capacity of the heater should also be low to prevent flirther bath temperature rise after the current is shut off. A thin Pt wire, woimd aroimd a frame, may be used as a heater in these cases it may be placed directly in the bath without any Insulation. Vigorous agitation of the liquid in the bath is important. Bath temperatures somewhat below room conditions may be maintained by means of an immersed copper coil with a constant... 

Determine the radius of curvature of a metallic strip thermometer s bimetallic strip, composed of yellow brass and chrome. The two metals are sealed at 60 °C and each band has a thickness of 0.20 mm. The strip has a length of 15.0 cm when exposed to a temperature of 250 °C. J. Tran... 

Bimetallic thermometer (bimetallic strip which shows a deflection due to differential expansivity that is proportional to temperature—frequently used for temperature control by coupling the bimetallic strip to a mechanical switch to control the chosen device). 

Temperature measurement thermometers, thermistors, thermocouples, radiation pyrometers and bimetallic strips. 

The principle of the thermal expansion of solids is used in bimetallic thermometers, which consist of two metal strips of different materials with different coefficients of expansion firmly connected together. Temperature differences bend these bimetallic springs and they are usually wound in spirals or coUs. The useful measuring range is from —73 to - -537°C with an accuracy of +1% of full scale [4). Bimetallic strips are used for temperature compensation in mechanical instrument movements. They are also used in switching relays to indicate whether a limiting value is exceeded. 

Bimetallic thermometers measure temperature by the change in physical dimension of the sensor. They have often been used [80]. The sensor consists of a composite strip of material, normally in a helical shape, formed by two different metals Differences in the thermal expansion of the two metals cause the curvature of the strip to be a function of temperature. The strip is used as a temperature indicator with a self-contained scale. Bimetallic thermometers have been used at temperatures from -185 to 425°C. The precision and accuracy of such thermometers are described in Ref. 81. 

A bimetallic thermometer (Fig. M-7) consists of an indicating or recording device, a sensing element called a bimetallic-thermometer bulb, and a means for operatively connecting the two. Operation depends upon the difference in thermal expansion of two metals. The most common type of bimetallic thermometer used in industrial applications is one in which a strip of composite material is wound in the form of a helix or helices. The composite material consists of dissimilar metals that... 

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