Using an Imaging Thermometer

Introduction: Using an Imaging Thermometer

15-20 years ago imaging thermometers were price prohibitive. They were also bulky and hard to use. In the past few years the cost and size of these devices has come down so much every HVAC technician, electrician and interested handyman can afford to have one.

The thermometer I will be using here is a FLIR TG-165 which is a handheld general use device which can be used to identify different temperatures by the colors of the objects imaged with the reds being the hottest with the coldest being dark blue. There are two laser pointers that highlight the area being measured and the temperature in degrees F or C being shown in the photo. The temperature given on the picture is the average between the two dots.

Step 1: Understanding Infrared Vs Visible Light.

Our eyes are sensitive to visible light in the 400-700 nm wavelength range (nm being nanometer or 1 x 10-9 meters). Infrared light has a longer wavelength at 700 nm to 1 mm. Wavelengths longer than 1 mm are classified as radio waves. Above visible light or shorter than 400 nm, is the ultraviolet band. Smartphone cameras are sensitive to both optical and infrared light so a filter must be put in front of the CCD array to make it less sensitive to near infrared.

Infrared radiation is from 700 nm to 1 mm in wavelength, the band is very large and is further divided up into five divisions. Each of these divisions have special properties, that have certain advantages and disadvantages. Here they are summarized:

1) Near Infrared-750-1400 nm- used in fiber optic communications, "night vision" scopes or image intensifiers and near- infrared spectroscopy.

2) Short-Wavelength Infrared-1400-300 nm- used in earth observation and mineral exploration.

3) Mid-Wavelength Infrared-3000-8000 nm- also known as "thermal infrared" used in heat seeking missile technology.

4) Long-Wavelength Infrared-8000-15000 nm- also known as the "thermal imaging" region. This is where the FLIR thermometer works detecting passive heat radiation from objects that are slightly higher in temperature than those around it. Like mid-wavelength infrared, this band is part of the "thermal infrared region".

5) Far-Infrared-15000 nm -1 mm- experimental biomedical applications.

Step 2: Emissivity

Emissivity is defined as the ratio of thermal radiation emitted by a surface to that of a blackbody. The FLIR thermometer has a range of Emissivity settings between .01 and .99. The default setting is .95.

A black body or blackbody is an idealized physical body that absorbs all incident electromagnetic radiation, regardless of frequency or angle of incidence. (It does not only absorb radiation, but can also emit radiation. The name "black body" is given because it absorbs radiation in all frequencies, not because it only absorbs.) A white body is one with a "rough surface that reflects all incident rays completely and uniformly in all directions.

Step 3: Example 1: Human Body

Examples shown above show that the human body surface is of slightly different temperatures caused by factors such as thickness of skin, amount of blood flow to that region, underlying tissues such as muscle or bone and whether or not there is swelling in that particular region.

Note that the hottest areas in the pictures are reddish and the coldest regions are blue. The temperature of the region that is being aimed at is displayed in degrees F. and the Emissivity setting in this case is .95, the default of the FLIR thermometer.

Instruments of this type are used by airport authorities around the world to identify persons with fever (possibly Covid 19) carriers.

Step 4: Using the Thermometer in Heating and Plumbing.

There are many uses for the instrument in heating, plumbing and cooling. The far left picture shows a hot water copper pipe coming out of the top of a water heater. Note the differences in colors between the straight piece and the elbow. The soldered portions of the elbow show varying differences in the amount of heat being released. The solder that dripped down from the elbow in the first picture looks cooler than the copper parts. The different colors are probably due to the different heat properties of the solder alloy as compared to the copper pipe. Note the dark blue color of the cold water pipe inlet in the background and how uniform the blue color is.

Note the picture taken of the whole water heater showing areas that are yellow. These are the window where the pilot flame can be seen, the gas inlet area, the water pressure relief valve on the top side, and the hot water outlet on the top. These are areas that are of different colors than the white painted tank surface which looks relatively uniform.

The fourth picture shows the inside of an upright forced air natural gas furnace burner assembly.

The fifth picture shows horizontally a vertical vent stack where two pieces are joined together. Note the coolest temperature (blue), intermediate (yellow) and hot (red) areas on the stack.

This instrument can be used to quickly see areas around a building that have poor insulation, drafts, heat losses around windows and looking for buried radiant heat water pipes under floors.

Step 5: Using the Thermometer for Troubleshooting Electrical Systems

The first two pictures show the opposite ends of fluorescent tubes and where the hottest regions in the bulbs are. The ends have a hot area in red with a cooler area colored yellow. The actual bulbs run much cooler showing up in blue. This is a normal bulb and fixture but if there were any other areas that were excessively hot (such as a shorted ballast) that area would be revealed.

The third picture shows a lightly loaded breaker panel with the yellow colors showing the areas that heat up the most are where the copper wires are tightened under the screws and the wires themselves are cooler with the background blue denoting the cooler steel box. If the screws holding the wires down were excessively red or yellow, it could be a cause for concern as it could eventually start a fire. Doing regular preventative maintenance checks of electrical conductors that conduct lots of current can see problems early so they can be corrected.

Step 6: Imaging Miscellaneous Objects

First picture is a tea kettle on a stove taken from 15 feet away.

Second picture is the cool sky behind warmer trees taken at night.

Third and fourth pictures are of a person taken at 30 feet at night. Person is wearing a black jacket so the area covering the upper torso looks coolest.

The fifth picture shows an open laptop computer showing the hottest area being the keyboard area because most of the heat generating chips are below it. In this laptop, the air is sucked from this area and blown out the side.

Step 7: Conclusion

It has been shown in this Instructable the uses for an imaging thermometer in a number of areas. The FLIR T-165 is a basic model with more advanced models allowing a visible light picture to be taken and an infrared one to overlay it so you can pinpoint which objects are the hottest such as in electrical fuse boxes or circuit breaker boxes. It takes some practice to get used to the temperature coloring system used by FLIR with red being the hottest and yellow being one step below it in temperature. In reality, white hot is the hottest, followed by yellow, then red, dull red and then darker colors. Nevertheless, this does not take away from the usefulness of the thermometer. Pictures can be saved and downloaded to your computer for later viewing.

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