Types of temperature measurement

Various types of temperature instruments available for industrial purpose and it can be used its depend upon on your requirements.

  • Resistive Temperature detector (RTD)
  • Thermocouples
  • Infrared Sensors
  • Thermometers
  • Silicon Diode

Resistive Temperature detector (RTD)

An RTD (Resistance Temperature Detector) is a sensor whose resistance changes as its temperature changes. The resistance increases as the temperature of the sensor increases. The resistance vs temperature relationship is well known and is repeatable over time. An RTD is a passive device. It does not produce an output on its own. External electronic devices are used to measure the resistance of the sensor by passing a small electrical current through the sensor to generate a voltage. Typically 1 mA or less measuring current, 5 mA maximum without the risk of self-heating.

Thermocouples

A thermocouple is a sensor that measures temperature. It consists of two different types of metals, joined together at one end. When the junction of the two metals is heated or cooled, a voltage is created that can be correlated back to the temperature. A thermocouple is a simple, robust and cost-effective temperature sensor used in a wide range of temperature measurement processes.

Infrared temperature Sensors

An infrared intemperature probe measures temperature by detecting the infrared energy emitted by all materials which are at temperatures above absolute zero, (0°Kelvin). The most basic design consists of a lens to focus the infrared (IR) energy on to a detector, which converts the energy to an electrical signal that can be displayed in units of temperature after being compensated for ambient temperature variation. This configuration facilitates temperature measurement from a distance without contact with the object to be measured.

Thermometers

The measurement of temperature is performed by the thermometer by using mercury, which – when heated – expands, and contracts in response to a fall in temperature. This causes the length of the liquid column to be longer or shorter depending on the temperature.

Silicon Diode

Diodes are highly sensitive and linear temperature sensors.Silicone and germanium diode temperature elements areavailable from − 458 to 395 ° F ( − 272 to 202 ° C). They areaccurate to 0.2 ° F (0.1 ° C) for temperatures that are above ambient and to 0.2% of their full scale range depicts the diode-based thermometer circuits of a silicone diode with a 1 mA constant current source, germanium diode with a 6-V power supply.

The current through the silicon diode thermometer read-out could be anywhere from 10 µ A to 10 mA, but becausehigher currents result in higher errors due to self-heating, thecurrents are usually kept between 100 and 500 µ A. Themeters used with germanium diodes usually have a range of0 to 50 µ A. Because of the low source impedances, a simplemicroampere indicating meter can be used.

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