Temperature sensing element

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. 

Temperature Measurement This is usually simple, and standard temperature-sensing elements are adequate for continuous use. Because of the high abrasion wear on horizontal protection tubes, vertical installations are frequently used. In highly corrosive atmospheres in which metallic protection tubes cannot be used, short, heavy ceramic tubes have been used successfully. 

It follows, that if the detector was to be effective and produce the true Gaussian form of the eluted peak then, (Ca), must at all times be unity and consequently the detector must have the same plate capacity as that of the column. This means that the detector must employ the same absorbant, have the same geometry and be packed to give the same plate height as the column. It is obvious to accomplish this, the column must also be the detecting cell and the temperature sensing element must be placed in the column packing itself. 

In the 1950 s the confluence of two factors gave new impetus to the field one was the appearance of simple calorimeters based on thermistors as the temperature sensing elements, and the other was the impact of other surface chemistry developments which pointed the way to what could be achieved through heat-of-immersion measurements. 

Zettlemoyer et al. provided a detailed study of the use of a thermistor connected to a Mueller bridge as the temperature-sensing element in immersional calorimetry. Thermistor calorimeters have since gained wide use because of the simple construction and operation they make possible. Brief... 

Thermocouples are constructed by joining two dissimilar metals. Such a junction will produce a potential which is proportional to the temperature. These couples are almost always used in pairs and connected to oppose each other s potential. One is kept at a fixed temperature (usually the melting point of ice), and the other is used as the temperature-sensing element. The potential between the two couples, measured with a potentiometer, will be proportional to the temperature difference between the reference temperature and the observed temperature. 

It is permissible to switch the flame supervision out of the safety circuitry for a furnace zone when the zone temperature is at or above 1400°F (760°C), per NFPA 86 (sect. 5-9.1). Burners without flame supervision shall be interlocked to prevent their operation unless the furnace is at or above 1400°F (760°C). A MOOT (760°C) bypass controller must be used for this purpose per NFPA 86 (sect. 5-17). The bypass controller and temperature-sensing element must be independent from any other controller or element. Failure of the element must cause the bypass controller to sense a temperature below MOOT (760°C) and therefore shut off the combustion system. Visual indication must be provided to indicate that the bypass controller action is in effect. 

In so-called power-compensation DSC, sample and reference are completely isolated from each other (Fig. 3.2). Both the sample and reference crucible have their own heating element and temperature sensing element. With the aid of a temperature programmer, both sample and reference are heated and always have the same temperature. As soon as changes in the sample occur, extra (or less) heat will be needed to maintain the set heating rate. With the aid of specialized electronic circuitry, extra (or less) power is now sent to the sample holder in order to keep the temperature difference zero. In this way, power and consequently heat flow and enthalpy changes are measured. 

The most common are thermocouples, resistance bulb thermometers, and thermistors. All provide measurement in terms of electrical signals. Independently of their constructional differences, their basic dynamic behavior can be examined in terms of the temperature profiles in Figure 13.6a and b. The temperature-sensing element is always inside a thermowell (Figure 13.7). In the first case (Figure 13.6a) we assume... 

Tabata O (1986) Fast-response silicon flow sensor with an on-chip fluid temperature sensing element. IEEE Trans Electr Device ED33(3) 361... 

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