This month I would like to discuss infrared thermometers. These are often called "laser thermometers," however, the laser dot is only for aiming or teasing animals, and it has nothing to do with temperature measurement or the size of the area being measured.

There are many different types of IR Thermometers. Many are inexpensive and will do the simple jobs, others are more complex for increasingly critical tasks, and some are even National Institute of Standards & Technology certified for accuracy.

All infrared thermometers measure the surface temperature of the subject object. Shiny surfaces or dirt can effect measurements so checking several areas is a good idea when these conditions exist. If pointed at a transparent surface such as glass, the IR Thermometer will measure the surface temperature of the glass, not the outdoor temperature. All infrared thermometers work the same way; the internal optics sense emitted, reflected and transmitted energy from the object being measured and translate this data into a temperature measurement.

Another item to consider is the Distance to Spot Size ratio. Most inexpensive IR Thermometers have a D:S ration of 8 to 1. This means the area being measured is approximately 1-inch in diameter at a distance of 8-inches. The spot size increases to 2-inches when the object is 16-inches from the thermometer and so on. A key item to remember is the object being measured must always be larger than the spot size otherwise the temperature measurement will be skewed by perimeter surfaces that may be different temperature. As you can see, it is critical to consider spot size when using an IR Thermometer for accurate measurements.

Kaplan makes available reasonably priced IR Thermometers for its customers. Check out the RayTek MiniTemp. This unit has a D:S ratio of 8:1.

We'll talk next month,

Mike Casey
Kaplan Professional Schools
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