Packing thermometer heat

Jan. 1, 2020
When it comes to diagnostics, automotive technicians (especially flat-rate ones) always are looking for an edge. One tool that can get a lot done for not a lot of money is a non-contact infrared (IR) thermometer. The ability to measure component temp

The infrared thermometer can save you time in the bays.

underhood IR temperature thermometer vehicle diagnostics diagnosing vehicles repair shop training technician training A/C training automotive aftermarket When it comes to diagnostics, automotive technicians (especially flat-rate automotive technicians) always are looking for an edge. Techs know that the ability to pinpoint problems quickly and accurately is the key to their livelihood, and they often are willing to make investments in technology that can help them in that regard. This means careful shopping for diagnostic tools that can get them the best "bang for their buck," as the technician sorts through what items they should acquire for their personal tool box.
One diagnostic tool that can get a lot done for not a lot of money is a non-contact infrared (IR) thermometer. The ability to measure component temperatures quickly can be invaluable to the technician, especially drivability and HVAC techs. While contact-type thermometers can be more accurate, the flexibility of the IR thermometer makes it extremely attractive for automotive diagnostics.
For example, an IR thermometer can be used on moving parts and in places that are difficult to access. They also are excellent for measuring very high temperatures and hazardous objects such as high-voltage components. It is important to keep in mind, though, that while IR thermometers are flexible, their accuracy depends on how they are used. Let's take a look at how IR thermometers work and some tips on how to use them for maximum accuracy.

What is Infrared?

Infrared is electromagnetic energy that lies on the spectrum between visible light and radio waves. All objects emit infrared energy, which is invisible to the naked eye. An IR thermometer uses an optical detector that gathers infrared energy emitted by an object and converts this into an electrical signal. This signal is then displayed as a temperature reading on the IR thermometer's display.

One major advantage of IR thermometers is their speed. Samples can be taken in milliseconds, making it easy to scan over a component looking for temperature variations. Most IR thermometers are built in the shape of a pistol, so determining the temperature of a component is simply a matter of pointing it at the target and pulling the trigger. The instrument's display is located on the backside of the unit, so the technician can view temperature readings easily while taking a measurement.

Taking Accurate Measurements

While most IR thermometers can take temperature measurements from several feet away, it is important to remember that the spot (circular sampling area) of the instrument gets larger as you get farther away from the target. The size of the spot is determined by the instrument's distance from the target and its distance-to-spot (D:S) ratio.

For example, a 10:1 D:S ratio would mean that the diameter of the spot is 1/10-inch of the distance from the target. In order to achieve a ½-inch spot, the IR thermometer should be held 10 times this distance (five inches) away from the object being measured. There is a range of possible D:S ratios that are used in IR thermometers (anywhere from 4:1 to 16:1), with the higher numbers allowing a smaller spot size to be measured.

To ensure accuracy, the technician should know the D:S ratio of the IR thermometer. This is then used to determine the optimal distance to target as well as an estimate of the spot size. If the spot becomes larger than the area the technician wishes to measure, accuracy can be compromised because of background temperature variations.

To aid the technician in aiming the device, most IR thermometers incorporate laser sighting. The simplest design uses one laser beam to mark the center of the spot that is being sampled. Some IR thermometers incorporate two laser beams that converge at the optimal distance from the target. Anytime the technician sees two laser dots on the target, it means that the instrument is not at the correct distance. Simply move the instrument closer or further from the target so the dots come together, then take the reading. More expensive units use three laser beams that mark the center and the perimeter of the sampling spot. This eliminates a lot of guesswork for the technician and shows the exact area being measured.

What is Emissivity?

When using an IR thermometer, the technician must understand emissivity and how it affects the instrument's accuracy. Emissivity is an expression of a material's ability to emit infrared energy. Emissivity values range from 0 to 1. For example, if a material has an excellent ability to emit infrared, the emissivity value would be closer to 1. On the other hand, a value closer to zero (say, 0.2) would indicate that a material's ability to emit infrared energy is relatively poor.

The material the object is made of and its surface finish determine emissivity values. Objects with reflective surfaces emit infrared energy poorly; therefore, polished metals have very low emissivity values. If these same metals have a rough or oxidized surface, however, their emissivity will increase.

Published tables are available that list emissivity values for various materials and surface finishes. Examples of emissivity values include:

  • Polished brass – 0.03
  • Oxidized brass – 0.61
  • Polished copper – 0.03
  • Black oxidized copper – 0.78
  • Black lacquer paint – 0.96

As seen above, an ideal surface for performing IR temperature measurements is one that is painted flat black. A rule of thumb is to avoid taking IR thermometer measurements on smooth, shiny surfaces. Higher accuracy will be achieved if the surface is rough, oxidized or painted a non-reflective color.

IR thermometers are designed to take emissivity into account when making temperature measurements. Many less-expensive IR thermometers have their emissivity compensation fixed, and these often are set around 0.95. This means that the technician must pay attention to the emissivity of the object being measured, and make sure that it is as close to 0.95 as possible in order to get accurate temperature measurements.

On more expensive IR thermometers, emissivity compensation can be adjusted. With this capability at hand, the technician does not need to perform any surface preparation as long as the approximate emissivity of the object is known. The bottom line is that the technician must be aware of both the tool's capabilities as well as its proper operation.

Practical Applications

Now comes the fun part: How to use IR thermometers for fixing cars. The ability to measure temperatures quickly and accurately will come in handy for many diagnostic scenarios. In some situations, the technician already will know the temperature they are looking for. For example, when checking the accuracy of an engine coolant temperature (ECT) sensor, it would be expected that the temperature near the sensor will be close to the ECT data seen on a scan tool. If a significant difference is noted, this could point to a skewed ECT sensor.

In other situations, the technician won't have any idea of what the temperature of a component (or one area of a component) should be. However, the ability to compare temperatures using an IR thermometer is an effective approach for pinpointing the source of problems. For example, no specification exists for what the outlet temperature of a catalytic converter should be. Looking for a temperature rise between the inlet and the outlet during operation, however, can be an excellent indicator of catalyst operation.

One of the technician's trickier diagnostic situations is where a bearing at the rear of the car is making noise, but it isn't clear which side is causing the problem. The next time you run into this, try taking the car for a spirited test drive and then use an IR thermometer to look for a temperature difference between the bearing housings on each side.

Odds are good the side with the noisy bearing will have a higher temperature, saving you a bunch of work and helping improve your image with your customer.

The IR thermometer also can be used for making temperature checks on heating, ventilation and air conditioning (HVAC) systems on the car. Air discharge duct temperatures can be checked and compared quickly, keeping in mind that experts still recommend use of a regular thermometer for this application if accuracy is a priority.

Also, an IR thermometer can be used to check each individual grid line from a rear window defroster for proper operation. For maximum accuracy, the measurements should be taken from the interior of the vehicle where the actual grid lines are located. Radiators also can be checked for proper circulation by moving the IR thermometer in a vertical zigzag pattern across its surface with the engine at operating temperature. Any cool spots found will show where tubes are blocked and coolant can't circulate through.

Killer Apps

IR thermometer technology has been around for quite a long time and is now inexpensive enough that most technicians should be able to afford a fairly advanced unit. For those who must have the latest and greatest, however, the thermal imager is the coolest thing on earth. One of these units will set you back several thousand dollars, but can generate infrared images that show definitively where the high and low temperatures are.

Regardless of what instrument you decide to buy, measuring temperatures with IR technology can make automotive diagnosis quicker and more accurate. And we all know that is the technician's key to making money.

Tony Martin is an associate professor of automotive technology at the University of Alaska Southeast in Juneau, Alaska. He holds Canadian Interprovincial status as a Journeyman Heavy Duty Equipment Mechanic. He also has 19 ASE certifications, including CMAT, CMTT, L1 and L2.

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