Temperature measurement is an essential part of automotive diagnostics. Temperature is a core input for powertrain management and HVAC operation. Knowing the exact component temperature eliminates guesswork when evaluating system performance.

Temperature measurement is also important for component failure troubleshooting. Excessive heat is the enemy of many vehicle components—from the engine to the brakes. Heat removal is so critical to component longevity that many vehicles now have multiple heat exchangers in addition to the radiator and heater core. Smaller “coolers” pull heat away from transmission and hydraulic fluids in power accessories. Cooled EGR is commonplace in modern diesels.

Clearly, we have ample need for fast and accurate temperature measurement.



When Your Aim is Fast, Accurate Measurement
The infrared, point and shoot thermometer (also commonly referred to as an infrared pyrometer) is a lifesaver, especially when it's impractical or dangerous to use a conventional contact thermocouple. Just point and shoot. Focus the laser on the target, and view the temperature reading, displayed digitally in degrees F or C. We'll look at the AIR1200 from UEI as an example.

AIR1200 Features

Squeeze and hold the trigger for constant updates, refreshed at 1 second intervals. Release the trigger to hold the last reading. Toggle between C and F temperature readings with the press of a button. The MAX recorded value is stored automatically.

This UEI AIR 1200 has its 12:1 D:S ratio, emissivity level, and temperature range are printed on its side. The spot size at different distances is also shown so you can guesstimate the optimum range for best Field of View accuracy.


The AIR 1200 has a UV work light that spots UV dyes. This kills two birds when you are troubleshooting radiator and ac condenser blockages after dye has been added. CAUTION: Never shine the laser at anyone's eyes. Permanent eye damage can result.

So How's It Work? A Look at Emissivity
Infrared energy is electromagnetic radiation, often referred to as heat radiation. Unlike heat transfer from conduction or convection, radiant heat energy can travel through a vacuum.


The military uses this to its advantage when using infrared sensors for target acquisition. That's how hi-tech smart bombs locate enemy forces lurking in a forest to avoid detection.

So how does the infrared work? It uses something called emissivity. The amount of energy radiated back by an object is compared to a theoretical object called a blackbody. The emissivity of the theoretical blackbody is assigned a value of 1.0.  All emissivity values for other objects then fall into a measurement range between 0.0 and 1.0.

Bounceback
Okay, hombre, point your infrared at an object and pull the trigger. The IR thermometer sees what you can't. It measures the radiation bouncing back from the object, compares it to its calibrated emissivity standard, and calculates the temperature—instantly.

Different materials have different emissivity. This affects the way objects radiate energy. The hotter the object, the more watts of energy per unit of area it radiates. Admittedly, emissivity plays a direct role in the limiting the amount of radiation generated by a substance at a given temperature.

CAUTION: Some objects with low emissivity are hard to measure with IR. A highly polished metallic surface or mirror are harder to measure accurately using a an IR thermometer calibrated for common materials. Fortunately, most objects like wood, cloth, and plastics have an emissivity close to 0.95.

The emissivity of the AIR 1200 infrared is calibrated to a fixed 0.95. That number is selected as a general purpose setting since it approximates the emissivity of most components we'll encounter in an automobile. Some IR thermometers have adjustable emissivity. This lets you look up a material on an emissivity chart and then dial in the correct calibration for greater accuracy. (Click here to open a reference chart listing the emissivity of common materials.)

If you are concerned about accuracy when measuring the temperature of a component that has a highly reflective surface, attach a piece of masking tape to the object and point the IR at the tape. Another option is to apply a coat of flat black paint, a less desirable option when tesing inside the vehicle.

Things that Affect Accuracy:
• Field of View
Each IR thermometer has internal optics that regulate its field of view. (Think of standard and wide angle camera lenses for reference.) The optics create a cone-shaped field of view that widens over distance. This can cause problems if the field of view is not completely filled by the object having its temperature taken. (Again, think of a camera, and how background objects at a greater distance are often out of focus.)

Based on the distance of the IR thermometer from the object, try to calculate whether the object will fill the field of view. If not, move the IR in or out to change the size of the field of view. Ideally, the object whose temperature is being measured should fill the field of view.

• Distance to Spot Ratio
The IR collects infrared energy from a circular target spot, and then focuses the energy from that location back onto the IR detector. The ratio of the distance from the object—to the size of the spot—determines the instrument resolution. This is called the D:S ratio. The larger the ratio, the better the instrument's resolution. For example, 12:1 is better than 6:1.

• Airborne Pollutants
On a clear day, you can see forever. But steam, smoke, or airborne particles can block the IR temperature reading.

• Rapid Changes in Ambient Temperature
An IR thermometer may render inaccurate readings if exposed to large and rapid changes in temperature (20 degrees F or more). Refer to manufacturers' recommendations, and let the IR thermometer acclimate for several minutes after being exposed to big changes in temperature.

Common Uses
• Exact readings are useful, but so are comparisons. For instance, a quick comparison of caliper and brake drum temperatures after a road test can isolate a dragging brake that generates excessive amounts of heat.

• Shoot the runners on a diesel engine exhaust manifold. A misfiring cylinder has a cooler exhaust.

• Wonder if that ECT reading is accurate? Point and shoot at the ECT sensor location and compare it to the ECT PID in datastream.

Have a favorite use for your IR thermometer? Let us know.
 

AIR 1200 Features/Specs
• 12:1 Distance To Spot Ratio
• Temperature Range: -58 to 1200F
• UV Leak-Detecting Work light
• Laser Targeting
• MAX Value Capture
• Fixed Emissivity (0.95)
• Backlit Display

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The UEI AIR 1200 is available from AES.

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