Since surface temperature is often a good indicator of how well users' equipment or processes are running, regular temperature measurement should be an essential element of any industrial process control application.
General considerations
Some considerations for you 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 will the sensor be located?
* What area of the process needs to be measured?
* What is the ambient temperature?
* Are accessories required to protect the sensor?
* What display capability is required?
* What output signal capability is required?
Target size and distance considerations
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 you 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.
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.
Rule of thumb
* For temperatures up to 900°C use 8-14 μm wavelength.
* For temperatures over 900°C use 1-3 μm wavelength.
With these considerations in mind users are on the way to selecting the correct instrument for the application.
To receive a free guide on infrared technology, 'Principles of Non-Contact Temperature Measurement', readers can send an e-mail to [email protected] with their name, company, address and contact details. R&C will send this 29 page illustrated booklet by post or e-mail.
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