An infrared thermometer is a thermometer which infers temperature from a portion of the thermal radiation emitted by the object being measured. They are sometimes called laser thermometers if a laser is used to help aim the thermometer, or non-contact thermometers or temperature guns, to describe the device’s ability to measure temperature from a distance. By knowing the amount of infrared energy emitted by the object and its emissivity, the object’s temperature can often be determined.

The most basic design consists of a lens to focus the infrared thermal radiation on to a detector, which converts the radiant power to an electrical signal that can be displayed in units of temperature after being compensated for ambient temperature. This configuration facilitates temperature measurement from a distance without contact with the object to be measured. As such, the infrared thermometer is useful for measuring temperature under circumstances where thermocouples or other probe type sensors cannot be used or do not produce accurate data for a variety of reasons.

The actual area being measured is determined by the distance-to-spot ratio of the IR thermometer you are using and this varies from model to model. As the distance from the object being measured increases, the spot size of the area being measured also increases.

For example this Sper Scientific’s IR Pen has a distance to spot ratio of 1:1 meaning that at 1" from the target it will measures the temperature of a 1" circle. At 2" it will measure a 2" diameter and so forth.

Spot Size : Distance

IR thermometers provide non-contact temperature measurement making them particularly useful in circumstances where the object to be measured is moving; where the object is surrounded by an electromagnetic field, as in induction heating; where the object is contained in a vacuum or other controlled atmosphere; or in applications where a fast response is required, an accurate surface temperature is desired or the object temperature is above the recommended use point for contact sensors, or contact with a sensor would mar the object or the sensor, or introduce a significant temperature gradient on the object's surface.

They can be used to serve a wide variety of temperature monitoring functions. A few examples provided include:

• Checking mechanical equipment or electrical circuit breaker boxes or outlets for hot spots.
• Checking heater or oven temperature, for calibration and control purposes.
• Detecting hot spots / performing diagnostics in electrical circuit board manufacturing.
• Monitoring materials in process of heating and cooling, for research and development or manufacturing quality control situations.