Advice for selecting a non-contact infrared temperature sensor

Solutions Direct and Raytek offer guidelines for analyzing your application in light of available solutions.

A.J. Johnson

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All objects constantly emit infrared (IR) radiation. Infrared radiation occupies the region of the electromagnetic spectrum between visible light and microwaves. As an object becomes hotter, the frequency of the vibrations increases and the total amount of infrared energy increases significantly. The human eye is unable to detect infrared radiation; however an IR detector (a.k.a. pyrometer) converts the infrared energy into an electrical signal that generates a temperature value. Infrared or non-contact temperature sensors are very successful in measuring hot, moving, or difficult to reach objects. They are also used where conventional contact temperature sensors would damage or alter the material.

Infrared has been used successfully in a wide range of industrial applications including: heat treating, forging, glass processing, building and construction materials, packaging, thermoforming, machine condition monitoring, and food processing. Solutions Direct has put together some basic questions to help customers choose the correct fixed mount pyrometer:

• What is the temperature range to be measured as well as accuracy required?
• What is the target material? Is it shiny or dull? Highly reflective or shiny materials tend to have a low emissivity (object’s ability to emit energy) while non-metallic or organic materials have a higher emissivity. Solutions Direct has compiled an emissivity table by material type.
• What is the distance from the sensor and target size? Optical resolution is specified by the D:S ratio, which is found by comparing the distance from the object to the sensor (D) with the size (e.g., diameter) of the spot being measured (S). For example, a 1" spot on a target being measured at a distance of 10" has a D:S of 10:1.
• How much of the device’s field of view does the target fill? The more, the better.
• What are the ambient/environmental conditions? What is the ambient temp? Is there smoke, dust, or particulates? These can affect accuracy and repeatability.
• Are the parts moving (e.g., rollers, moving machinery, or conveyor belts)? If so, how fast? This influences response time requirements.
• What signal input does your controller accept? Possibilities include 4-20 mA, J or K thermocouple, or RS-485.

Solutions Direct distributes Raytek's line of fixed mount infrared thermometers for OEM’s and industrial applications ranging from -40 to 1,800 °C (-40 to 3,272 °F). These sensors are economical, easy-to-install, and integrate easily into existing process control systems. They come in a variety of temperature ranges, optical resolutions, response times, outputs, and spectral responses/wavelengths. Accessories for cooling and air purging are also available. If you have any questions or need assistance in choosing an infrared sensor for your application, please contact us.

Solutions Direct Online

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Edited by Peter Welander, pwelander(at)cfemedia.com