Thermometer bimetallic

An industrial standard method has been developed to test the lightfastness of polymers in accelerated test equipment [103]. The apparatus consists of a quartz-xenon tube with a special optical filter between the light source and the specimen to produce light that resembles window glass-filtered daylight [104], Samples are mounted at a specific distance from the arc and are supported on a frame which revolves around the arc 1 to 5 times per minute for uniform exposure. A blower unit in the base provides a flow of air which makes it possible to maintain a black panel temperature of 45°C, measured by a black panel thermometer which is positioned at level with the samples. A black panel unit consists of a bimetallic thermometer mounted on a steel frame. Both faces of the frame plate and also the stem of the thermometer are coated with a heat-resistant glossy black enamel. The relative humidity level in the exposure cabinet is closely controlled. 

Liquid-in-glass thermometers Bimetallic thermometers Filled-system thermometers Phase change... 

Liquid-in-glass thermometers used mercury or alcohol as the liquid that expands as it gets warmer. Most countries mandate the removal of any mercury-filled devices due to its extreme toxicity, but alcohol and other fillings are still used. The expansion rate is linear with temperature and can be accurately calibrated. Bimetallic thermometers bond two dissimilar metals with different coefficients of expansion to produce the bimetallic element in thermometers, temperature switches, and thermostats. Filled System Thermometers can be filled with either liquid or vapor. Liquid-filled units are the most popular although they require compensation for the weight of the liquid head and for capillary length. Vapor-filled elements cannot be used if the operating temperature crosses the vapor/liquid point. 

Bimetallic Thermometers. These use two metals of different coefficients of thermal expansion that are bonded together their heating bends the device, and an electrical contact can then be made or broken. Thermometer coils that expand/contract with temperature and make or break contact with a mercury electrode are used in household thermostats and industrial control apparatus. 

Other Thermometers. Among the many other types of thermometers, we will briefly discuss the following bimetallic thermometers, noise thermometers, resonant-frequency thermometers, and semiconductor diode thermometers... 

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. 

The 2>4 sensitive element of the bimetallic thermometer is immersed only IW in the flowing stream within the line. Use when indicating temperature is of secondary importance. 

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). 

Knilppel, Strang, Puppe Walzpuppe Rohling billet roll Knilppelwalze bimetallic thermometer Bimetallthermometer bimodal distribution/ two-mode distribution bimodale Verteilung binary mixture Zweistoffgemisch binder/... 

The most widely used thermometer in polymer technology is the resistance temperature detector (RTD). For higher temperatures or with point measurements, the thermocouple is often preferred. Mechanical contact thermometers (expansion thermometers, rod thermometers, or bimetallic thermometers) are nearly always used only for local measurements. For optical thermometers, radiation pyrometers are used. 

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. 

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... 

Secondary standards are liquid-in-glass thermometers and base-metal thermocouples. They are calibrated by comparing them with primary-standard platinum-resistance thermometers or standard platinum-rhodium versus platinum thermocouples at temperatures generated in comparators. These secondary standards are used in turn for the calibration of other devices, such as liquid-in-glass thermometers, bimetallic thermometers, filled-system thermometers, and base-metal thermocouples, in which the highest degree of accuracy is not required. Optical pyrometers as secondary standards are compared with primary-standard optical pyrometers, and they are then used for calibration of r ular test pyrometers. 

There are three main families of temperature sensors thermocouples, resistance thermometers and thermistors. Some old reactors still have bimetalic thermometers (binary or with local readings), but it is suggested that they be replaced in order to allow the operator to follow closer any temperature transient from the control room. Other temperature sensors, like semi-conductor thermometers, consisting of doped germanium sensors, have a complex resistance temperature relationship and are useful only for very low temperature measurements. 

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