To assure accurate noncontact infrared temperature measurement keep in mind the following:
- Distance to Target (Spot) Ratio
- Field of View
- Environmental Conditions
- Ambient Temperatures
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 (D:S ratio). The larger the ratio number the better the instrument's resolution, and the smaller the spot size that can be measured from 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.
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.
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 that reason some of Raytek products, such as Thermalert and Marathon Series sensors, include air purging.
Ambient Temperatures (the surrounding 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-mounted 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 (356°F). For high ambient temperatures, Raytek offers air cooling and water cooling options as well as accessories, such as Thermojacket.
Emissivity is the measure of an object's ability to emit infrared energy. Emitted energy indicates the temperature of the object. Emissivity can have a value from 0 (shiny mirror) to 1.0 (blackbody). Learn more about emissivity and emissivity values for various materials.