Temperature Measurement


Accurate noncontact IR temperature measurement

August 2014 Temperature Measurement

To ensure accurate noncontact infrared temperature measurement, these five factors must always be kept in mind:

* Distance to target (spot) ratio.

* Field of view.

* Environmental conditions.

* Ambient temperatures.

* Emissivity.

Distance to target (spot) ratio: The optical system of an infrared sensor collects the infrared energy from a circular measurement spot and focuses it on the detector. Optical resolution is defined by the ratio of the distance from the instrument to the object, compared to the size of the spot being measured. The larger the ratio the better the instrument’s resolution, meaning a smaller spot size can be measured from a greater distance. A recent innovation in infrared optics is the addition of a close focus feature, which provides accurate measurement of small target areas without including unwanted background temperatures.

* Field of view: Make sure that the target is larger than the spot size the unit is measuring. The smaller the target, the closer you should be to it. When accuracy is critical make sure that the target is at least twice as large as the spot size.

Environmental conditions: Watch for environmental conditions in the working area. Steam, dust, smoke, etc., can prevent accurate measurement by obstructing the unit’s optics. Noise, electromagnetic fields, or vibration are other conditions that should also be considered before installation begins. A protective housing, air purging and/or water cooling can protect the sensor and ensure accurate measurements. For this reason, some Raytek products, such as Thermalert and Marathon series sensors include air purging.

Ambient temperature: If the thermometer is exposed to abrupt ambient temperature differences of 20 degrees or more, allow it to adjust to the new ambient temperature for at least 20 minutes. Raytek fixed sensors are specified for performance within certain ambient temperature ranges. For example, the Raytek MIH can withstand ambient temperatures (without water or air cooling) up to 180°C. For high ambient temperatures, Raytek offers air and water cooling options as well as accessories such as a Thermojacket.

Emissivity: This is the measure of an object’s ability to emit infrared energy. Emitted energy indicates the temperature of the object and emissivity can have a value from 0 (shiny mirror) to 1 (blackbody).

For more information contact R&C Instrumentation, 086 111 4217, info@randci.co.za, www.randci.co.za



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