Sensors & Transducers

Selecting the right infrared sensor

November 2004 Sensors & Transducers Education (Industry)

Since surface temperature is often a good indicator of how well your equipment or process is running, regular temperature measurement should be an essential element in any industrial process control application.

Some considerations to make before choosing an infrared sensor:

* What is the temperature range of the process or maintenance application?

* What type of material is being measured?

* How far away from the process to be measured is the sensor?

* What area of the process needs to be measured?

These are the main questions to ask when choosing the correct Raytek temperature sensor for an application. Environmental and operating conditions, for example ambient temperature, will determine other sensor specifications, such as the need for protective accessories or display and output capability.

Consider target size and distance

Raytek offers a variety of products with specific temperature range features. Single wavelength infrared temperature sensors need a clear line of sight between the instrument and the target. Sighting options allow the user to aim the sensor on the target. Some Raytek units have a built in laser that pinpoints the target, which is very helpful when the target is very small, or in dark inaccessible areas. A two-colour or ratio instrument is most effective when the target is very small or is moving in and out of the field of view. A fibre-optic unit, whose cable can snake around obstructions, is best in a harsh environment or if a direct line of sight between the instrument and the target is otherwise impossible. For single wavelength sensors, the measurement target should be larger than the field of view by at least 50%. If the target is smaller than the field of view, background temperatures will affect the reading.

Consider surface characteristics

The target materials temperature range, emissivity and surface characteristics determine the response or wavelength needed in a sensor. Emissivity is the ability of the material to emit IR energy. Most organic, painted or oxidised surfaces have emissivity values close to 0,95, which is already pre-set in some of the Raytek products. Other Raytek sensors have adjustable emissivity to ensure accuracy when measuring materials outside this value, such as metals, glass and thin film plastic.

R&C Instrumentation is offering free copies of the booklet: Infrared technology, principals of non-contact temperature measurement - and will send this 29-page illustrated booklet by post or e-mail - whichever is preferred. Those wanting a copy should e-mail with your name, company, address and contact details - and whether you would prefer e-mail or hard copy.

For more information contact R&C Instrumentation, 032 946 2805,,


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