Pyrometers: Non-contact Temperature Measurement

Pyrometers come in handy for applications
such as heat treating.

Non-contact temperature measurement technology allows process operators and technicians to evaluate the temperature of process materials, machinery, or piping by measuring their electromagnetic radiation. Through inferential calculation and one or more radiation measurements, specialized instruments can determine temperature without contacting the subject material or surface. While the concept of non-contact measurement technology has existed for many years, more recent advancements in non-contact temperature sensing and the evolution of the pyrometer have allowed temperature measurement at a distance to become popular throughout industrial process operations.

Pyrometers can commonly concentrate light from an object onto a temperature sensing element. The sensed elevation in temperature is proportional to the infrared optical energy. Different instruments may have varying arrangements of concentrating lenses and sensors, but the operating principle is the same. The physical law behind the pyrometer's operating principle operates on an exponential mathematical basis that is non-linear. This results in one of the limitations of the pyrometer. A single pyrometer can only, with high accuracy, deliver a comparatively narrow range of target temperature. If the need for accuracy is reduced, the applicable temperature range widens. Innovative manufacturers have developed instruments with technology and features overcoming many of the limitations imposed by the physics, delivering instruments with accuracy and applicable temperature range usable in a wide array of applications.

One of the advantages to using a non-contact pyrometer is that their calibration is independent of the distance between the sensor and the object being evaluated. This phenomenon is due to the fact pyrometers have a field of view and can be filled with the target object in a way independent of distance. While the radiation emanating from the target object may be decreasing, the field of view of the pyrometer is measuring a greater portion of the object which is proportional to the amount of radiation being lost, essentially canceling out the distance and allowing the pyrometer to provide useful output. An example of a practical application of a pyrometer in industry would be its use to check the temperature of a ventilation system in the HVAC field.

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