Temperature measurement Principles of temperature measurement the triple

Principles of temperature measurement • the triple point of equilibrium hydrogen 259. 34°C •

Instruments to measure temperature can be divided into separate classes according to the physical

Thermoelectric effect sensors (thermocouples) Thermoelectric effect sensors rely on the physical principle that, when

Varying resistance devices • Varying resistance devices rely on the physical principle of the

Resistance thermometers, which are alternatively known as resistance temperature devices (or RTDs), rely on

Thermistors are manufactured from beads of semiconductor material prepared from oxides of the iron

Semiconductor devices, consisting of either diodes or integrated circuit transistors, have only been commonly

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Temperature measurement

Principles of temperature measurement • the triple point of equilibrium hydrogen 259. 34°C • the boiling point of oxygen 182. 962°C • the boiling point of water 100. 0°C • the freezing point of zinc 419. 58°C • the freezing point of silver 961. 93°C • the freezing point of gold 1064. 43°C (all at standard atmospheric pressure)

Instruments to measure temperature can be divided into separate classes according to the physical principle on which they operate. The main principles used are: The thermoelectric effect Resistance change Sensitivity of semiconductor device Radiative heat emission Thermography Thermal expansion Resonant frequency change Sensitivity of fibre optic devices Acoustic thermometry Colour change Change of state of material.

Thermoelectric effect sensors (thermocouples) Thermoelectric effect sensors rely on the physical principle that, when any two different metals are connected together, an e. m. f. , which is a function of the temperature, is generated at the junction between the metals

Thermocouple

Varying resistance devices • Varying resistance devices rely on the physical principle of the variation of resistance with temperature. The devices are known as either resistance thermometers or thermistors according to whether the material used for their construction is a metal or a semiconductor, and both are common measuring devices

Resistance thermometers, which are alternatively known as resistance temperature devices (or RTDs), rely on the principle that the resistance of a metal varies with temperature according to the relationship:

Resistance thermometer, RTD

Thermistors are manufactured from beads of semiconductor material prepared from oxides of the iron group of metals such as chromium, cobalt, iron, manganese and nickel. Normally, thermistors have a negative temperature coefficient, i. e. the resistance decreases as the temperature increases, according to:

Semiconductor devices, consisting of either diodes or integrated circuit transistors, have only been commonly used in industrial applications for a few years, but they were first invented several decades ago. They have the advantage of being relatively inexpensive, but one difficulty that affects their use is the need to provide an external power supply to the sensor