Bimetallic Thermometer

Basic Principle:


These thermometers use the following two principles:

1. All metals change in dimension, that is expand or contract when there is a change in temperature.
2. The rate at which this expansion or contraction takes place depend on the temperature co-efficient of expansion of the metal and this temperature coefficient of expansion is different for different metals.Hence the difference in thermal expansion rates is used to produce deflections which is proportional to temperature changes.

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Optical pyrometer( Disappearing filament Type)

Monochromatic brithness radiation thermometer

Basic Principle of optical pyrometer:


The principle of temperature measurement by brightness comparision is used in optical pyrometer. A colour variation with the growth in temperature is taken as an index of temperature.

This optical pyrometer compares the brightness of image produced by temperature source with that of reference temperature lamp. The current in the lamp is adjusted until the brightness of the lamp is equal to the brightness of the image produced by the temperature source. Since the intensity of light of any wave length depends on the temperature of the radiating object, the current passing through the lamp becomes a measure of the temperature of the temperature source when calibrated.

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Important terms with respect to Instrumentation:

There are two different terms which should be considered in the instrumentation, they are static terms and dynamic terms.

Static Terms:


Range:


An instrument is calibrated to read values of physical variable being measured between two values. One is the higher calibration value Hc and the other is the lower calibration value Lc. This region between which the instrument is to operate is called range.

Range = Lc to Hc.

We can say that the range of the instrument (thermometer) is 0'C to 100'C.


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Strain gauge load cell

Basic Principle of Strain gauge load cell


When steel cylinder is subjected to a force, it tends to change in dimension. On this cylinder, if the strain gauges are bonded, the strain gauge also is stretched or compressed, causing a change in its length and diameter. This change in dimension of the strain gauge causes its resistance to change. This change in resistance or output voltage of the strain gauge becomes a measure of applied force.

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Piezo-electric Crystal based Acceleration measuring device.

Piezo Electric Concept:

This device which you will build is based on piezo electric effect. Let me expain you in detail, when a piezo-electric crystal is subjected to a mechanical force or stresses along specific planes, a voltage is generated across the crystal. If the force on the crystal is due to acceleration, a measure of the voltage across the crystal becomes a measure of the acceleration when calibrated.

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