Why we need temperature Measurement ?
Different way of Temperature Measurement
Some Implemented devices of temperature Measurement
•Thermocouple Temperature Measurement Sensors
Thermocouples consist essentially of two strips or wires made of different metals and joined at one end. Changes in the temperature at that juncture induce a change in electromotive force (emf) between the other ends. As temperature goes up, this output emf of the thermocouple rises, though not necessarily linearly.
Thermocouples consist essentially of two strips or wires made of different metals and joined at one end. Changes in the temperature at that juncture induce a change in electromotive force (emf) between the other ends. As temperature goes up, this output emf of the thermocouple rises, though not necessarily linearly.
•Resistance
Temperature Devices(RTD)
Resistive temperature devices capitalize on the fact that the electrical resistance of a material changes as its temperature changes. Two key types are the metallic devices (commonly referred to as RTDs), and thermistors. As their name indicates, RTDs rely on resistance change in a metal, with the resistance rising more or less linearly with temperature. Thermistors are based on resistance change in a ceramic semiconductor; the resistance drops nonlinearly with temperature rise.
Resistive temperature devices capitalize on the fact that the electrical resistance of a material changes as its temperature changes. Two key types are the metallic devices (commonly referred to as RTDs), and thermistors. As their name indicates, RTDs rely on resistance change in a metal, with the resistance rising more or less linearly with temperature. Thermistors are based on resistance change in a ceramic semiconductor; the resistance drops nonlinearly with temperature rise.
•Infrared Temperature Measurement Devices
Infrared sensors are non-contacting devices. They infer temperature by measuring the thermal radiation emitted by a material.
Infrared sensors are non-contacting devices. They infer temperature by measuring the thermal radiation emitted by a material.
Bimetallic Temperature Measurement
Devices
Bimetallic devices take advantage of the difference in rate of thermal expansion between different metals. Strips of two metals are bonded together. When heated, one side will expand more than the other, and the resulting bending is translated into a temperature reading by mechanical linkage to a pointer. These devices are portable and they do not require a power supply, but they are usually not as accurate as thermocouples or RTDs and they do not readily lend themselves to temperature recording.
Bimetallic devices take advantage of the difference in rate of thermal expansion between different metals. Strips of two metals are bonded together. When heated, one side will expand more than the other, and the resulting bending is translated into a temperature reading by mechanical linkage to a pointer. These devices are portable and they do not require a power supply, but they are usually not as accurate as thermocouples or RTDs and they do not readily lend themselves to temperature recording.
•Fluid-Expansion Temperature Measurement Devices
Fluid-expansion devices, typified by the household thermometer, generally come in two main classifications: the mercury type and the organic-liquid type. Versions employing gas instead of liquid are also available. Mercury is considered an environmental hazard, so there are regulations governing the shipment of devices that contain it. Fluid-expansion sensors do not require electric power, do not pose explosion hazards, and are stable even after repeated cycling. On the other hand, they do not generate data that is easily recorded or transmitted, and they cannot make spot or point measurements.
Fluid-expansion devices, typified by the household thermometer, generally come in two main classifications: the mercury type and the organic-liquid type. Versions employing gas instead of liquid are also available. Mercury is considered an environmental hazard, so there are regulations governing the shipment of devices that contain it. Fluid-expansion sensors do not require electric power, do not pose explosion hazards, and are stable even after repeated cycling. On the other hand, they do not generate data that is easily recorded or transmitted, and they cannot make spot or point measurements.
- Change-of-State Temperature Measurement Devices
Resistance Temperature Detector (RTD)
Bimetallic Thermometers
# The Bimetal Thermometer employs a bimetallic sensing element which reacts consistently to temperature change, producing an accurately calibrated temperature measurement.
—#The
sensing element consists of two dissimilar metals welded together (in the form
of a coil), and encased in a stainless steel stem.
—#When
the stem is exposed to temperature change, the coil expands or contracts, and
the corresponding reaction is transmitted to the pointer, thereby indicating
the temperature of the process.
Three
fundamental principles are:
1.All the metals expand or contract with
change in temperature
2.The temperature coefficient of
expansion or contraction is not the same for all the metals
3.The difference in the expansion rates
is used to produce a deflection proportional to temperature change
Constructed
by bonding two different metals such that they cannot move relative to each
other
Construction
#The bimetallic thermometer consists of a bimetallic strip.
—#A bimetallic strip is
made of two thin strips of metals which have different co efficient of
expansion.
—#The two metal strips
are joined together by brazing, welding or riveting so that the relative motion
between them is arrested.
—#The bimetallic strip
is in the form of a cantilever beam. An increase in temperature will result in
the deflection of the free end of the strip as shown i diagram.
—#This deflection is
linear and can be related to temperature changes.
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