Temperature measurement Radiation thermometers All objects emit electromagnetic

Temperature measurement

Radiation thermometers All objects emit electromagnetic radiation as a function of their temperature above absolute zero, and radiation thermometers (also known as radiation pyrometers) measure this radiation in order to calculate the temperature of the object. The total rate of radiation emission per second is given by: E = KT**4

Radiation thermometer

Thermography (thermal imaging) Thermography, or thermal imaging, involves scanning an infrared radiation detector across an object. The information gathered is then processed an output in the form of the temperature distribution across the object is produced

Thermal expansion methods • Liquid-in-glass thermometers • Bimetallic thermometer two strips of different metals are bonded together any temperature change will cause the strip to bend • Pressure thermometers PV = KT

Glass thermometer

Quartz thermometers The quartz thermometer makes use of the principle that the resonant frequency of a material such as quartz is a function of temperature, and thus enables temperature changes to be translated into frequency changes The temperature-sensing element consists of a quartz crystal enclosed within a probe (sheath). The probe commonly consists of a stainless steel cylinder, which makes the device physically larger than devices like thermocouples and resistance thermometers. The crystal is connected electrically so as to form the resonant element within an electronic oscillator. Measurement of the oscillator frequency therefore allows the measured temperature to be calculated.

Fibre-optic temperature sensors Fibre-optic cables can be used as either intrinsic or extrinsic temperature sensors Several other types of device that are marketed as extrinsic fibre-optic temperature sensors consist of a conventional temperature sensor (e. g. a resistance thermometer) connected to a fibre-optic cable so that the transmission of the signal from the measurement point is free of noise. Such devices must include an electricity supply for the electronic circuit that is needed to convert the sensor output into light variations in the cable. Thus, low-voltage power cables must be routed with the fibre-optic cable, and the device is therefore not intrinsically safe.

Acoustic thermometers The principle of acoustic thermometry was discovered as long ago as 1873 and uses the fact that the velocity of sound through a gas varies with temperature according to the equation

Colour indicators • The colour of various substances and objects changes as a function of temperature

Change of state of materials Temperature-indicating devices known as Seger cones or pyrometric cones are commonly used in the ceramics industry. They consist of a fused oxide and glass material that is formed into a cone shape. The tip of the cone softens and bends over when a particular temperature is reached. Cones are available that indicate temperatures over the range from 600°C to + 2000°C

Choice between temperature transducers The suitability of different instruments in any particular measurement situation depends substantially on whether the medium to be measured is a solid or a fluid