There are many industries that utilise temperature sensors in day to day operations. Mostly there are two distinct varieties of contact sensor used for the purpose; these are the thermocouple and resistance temperature detector or RTD. Measurement usually takes place in liquids or with contact with the target surface. Contact is not however a prerequisite, there are some temperature sensors out there that operate without contact with the target material; instead measuring the ionisation of the air caused by heat.

When selecting which type of sensor to use there a myriad of considerations that must be made depending specifically on the application. Additionally however when selecting a sensor it is important to consider the temperature range, the required accuracy and response time as these will vary with different measuring methods. When accuracy is of prime importance an RTD sensor is preferable although for those with an eye on finances, thermocouples are clearly the cheaper, more affordable option. Hopefully the following break down of the RTD, thermocouple and infrared thermometer will help operatives make the decision.

The basics of RTD operation rely on the increase of resistivity that occurs when the temperature of a material is increased. Normally RTD sensors are manufactured from metals such as platinum, nickel and copper. Predominantly copper and nickel variants are used for measuring lower temperatures while platinum, although more expensive has a wide temperature range that is useful for a variety of purposes. Normally RTDs are constructed simply, a sensing element is connected a non-conducting element made from ceramic, glass or mica. The element measures the resistance and from this reading a temperature result is gained.

Thermocouples differ from RTDs in that they utilise two different metals that are joined at one end to produce a voltage that can be converted into a temperature reading. Where the two metals meet is called the sensing junction, this junction can be connected to extension wires meaning that the physical range of the thermocouple is large. Any two metals can be used in the construction of thermocouples making them more affordable than RTD sensors. Thermocouples however can produce inaccurate results if other components are introduced into the electrical circuit as they rely upon voltage to measure temperature.

As previously stated there are other forms of sensor on the market although the two aforementioned are predominant. Increasingly infrared thermometers are being used for temperature measurement. These work through a non contact method and are subsequently used for specific applications that require remote temperature measurement. Usually they consist of a lens to focus the infrared light on a source and then using the light to take a temperature reading. As they do not need contact to measure they are frequently used as a control thermometer when calibrating thermostats and inbuilt thermometers. As well as this the infrared technology is often used in researching the heating and cooling properties of certain materials.

Hopefully this information has given the uneducated a clearer idea of the types of temperature sensor out there on the market today. Depending upon which applications they are to be used for, all three have various benefits and restrictions. Cost naturally varies but in most cases the extra cost is a necessary sacrifice to achieve greater levels of accuracy. Whether using RTDs, thermocouples or infrared spot thermometers all can produce valid and accurate results; once you have decided which will suit your needs most effectively take time to research the models out there to find the perfect solution to your temperature measurement requirements.