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IR thermometers are small, lightweight, and require little training to use effectively. You simply point the device at the target, pull the trigger, and check the readout. The thermometer monitors surface temperature from a distance by measuring the infrared radiation naturally emitted from an object (Fig. 1, in original article). The detector reads the energy signal, and the instrument's electronics converts that reading to a temperature value; which you see displayed on an LCD. On most instruments, accuracy is 51% of the reading or 51DegrC (52DegrF).
Because you can take a precise reading from several feet away, you reduce or eliminate the risk of burned fingers, electrocution, and falling. The distance depends on the spot size desired and the focal length of the instrument.
Flexibility
There are three common ways to take readings.
• Spot measuring: This method determines the absolute surface temperature of objects. While it's an effective way of using IR devices, it's not nearly as productive as the following two methods.
• Temperature differentials: This method compares two separate spot measurements, either in different locations or at the same location over time. It's an extremely productive method, because it allows you to eliminate variables that spot measuring cannot account for. It also allows you to use trending to predict what will happen.
• Scanning: This method focuses on targets such as circuit breakers, cable connections, or transformer housings to identify hot spots (high temperature points). With this method, you simply pull the trigger and slowly move the instrument along the target. When you see sudden fluctuations in temperature, you've found hot spots.
Using the instrument. IR thermometers measure only the surface temperature of objects, and do not read through panels or covers. However, sometimes a panel will heat up, if the connections behind it are very hot. The surface temperature of motors, oil-filled transformers, and circuit breakers correlate directly to operating conditions. Let's take a look at some ways to use this instrument.
Pinpointing nuisance tripping of circuit breakers. Checking circuits inpidually by conventional means can take forever; and cause major disruptions in operations. But with an IR thermometer, you can isolate suspect circuitry just by scanning the panel.
Identifying sources of energy loss. Connectors or other components may be draining energy because of heat created by loosening and wear or by the buildup of dirt, carbon deposits, and corrosion; all of which create unwanted resistance. A portable IR thermometer allows you to check connectors and components from a variety of distances and angles. Temperature differentials of 10DegrC (18DegrF) from ambient indicate the early stages of a problem you need to investigate. Differences of 30DegrC (45DegrF) warrant immediate investigation.
Protecting electric motors. Polyphase induction motors represent about 85% of all electric motors used in industry. An industrial plant may run hundreds of these motors daily. A motor circuit has a breaker (or fuses), starter, thermal overload protection device for each phase, and the motor itself. Any one of these can overheat unexpectedly. A small voltage unbalance is lethal to a motor, but you can use your IR thermometer to verify balanced phase-to-phase power distribution; as well as check connections. IR is also ideal for checking motor bearing and gear box temperatures.
The speed and convenience of an IR thermometer gives you the ability to respond quickly to a motor shut down. Using it as a forensic tool, you can see if the problem is in power supply connections, circuit breakers, fuses, thermal overload protection devices, or elsewhere. An IR scan can even determine if you have a clogged air filter.
Protecting transformers. Regular scans of transformer housing, winding, and power terminal temperatures provide a better understanding of what's going on in this equipment. You can even detect winding flaws.