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  • Author Author: jw0752
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Exploring an Inexpensive Thermal Imager

jw0752

In early November told us that his NVR had died. In the course of the discussion and Ralph's experiments it was speculated that there was a short on the board that was pulling down the power supply. Over the years as I have serviced equipment this has always been a challenge to find the point or component that is the source of a short on a circuit board. In the past I have followed traces and cut them as needed to step by step find my way to the source of the problem. I have often thought how nice it would be to just have a magic viewer that would highlight the source of the short. The challenge of finding a short on a board has only gotten more difficult as the boards have gotten more complex.

 

In early November, just as Ralph was having the NVR failure, I had pre-ordered an inexpensive Thermal Imager from a Chinese source. I had no idea what to expect but the price was right and I wanted to see what it could do. The Imager arrived today and so I read the manual and familiarized myself enough that I could do some simple experiments. Here is the Thermal Imager.

 

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My plan for this experiment was to find a big simple circuit board with a fairly long trace that I could put some power into and see if the Thermal Imager could see it. The board that I selected was originally from a TV and I had already pretty much salvaged all the parts from it. After spending several minutes trying to find a long trace with good connection points I gave up and tried a different approach.

 

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My next approach was to put one lead of the ohmmeter on a jumper wire and then drag the other probe across the board hitting the other jumpers and watching for a meter deflection. After a short time I was rewarded with a needle jump from my analog meter. When I explored a little further I was delighted to find that not only were the two contact points across the board from each other but there was actually a diode between them. Since there were a few scatter components still on the board I had luckily found one that had a component in the circuit.

 

The next step was to see if my new Imager could find the diode that tied my two contact points together. At this point I had no idea where it was. I hooked up my power supply as you can see on the picture above so that my current from the power supply was forward biased through the diode. With the power supply on constant current I brought the current up to 250 mA. The voltage was about 1 volt. I then used the Imager to scan the component side of the board for hot spots and I was not disappointed.

 

   imageimage

 

At this point you can see that I got what I paid for with respect to the resolution of the Imager. Between the two images I was however able to identify the diode in question. Good old D155 was where the heat in my image was coming from. I looked at the trace side of the board with the Imager but the 250 mW of power that the power supply was dumping into the circuit was pretty much all showing up in the diode.

 

image

 

The next step was to take a jumper wire and short across the diode. At 250 mA I was pretty certain that I would not be able to put any more current into the diode without frying it. With the jumper in place across the diode I brought the current up to 1.5 amps and about 0.7 volts. This put about a Watt of power into the circuit and I knew that a lot of it would be going into the traces connecting my two power attachment points. Now when I looked at the trace side of the board there was a definite green glow that came down the left side, across the bottom and then snaked its way to the vicinity of the second contact point.

 

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I have to admit that I was hoping for a little better resolution than I am getting but it is a whole lot better than I had before. At least now I have a general direction and area to deal with. If it was important to actually identify the trace in question I would have to get out a fine point marker and use the old method of marking it as I followed it with my eyes. Over all I am pleased with this experiment and the new Thermal Imager. I am retired now and the volume that comes across my bench is a trickle compared to when I was working. This Imager is perfect for me at this stage and it will give me an additional diagnostic tool when I am occasionally looking for a short on a circuit board. If I was back doing the volume that I used to do it would probably make sense to spend a little more money so that components and traces could be more easily resolved in the images.

 

John

 

 

  • in reply to jw0752

    The Flir One camera that I have has the same 160 x 120 resolution as the TG297, so the image quality should be similar to the thermal images I have in my blogs. Hopefully though the TG297 should have overall more user friendly operation and better battery life.

     

    Kind regards

  • in reply to koudelad

    Hi David,

     

    The resolution on mine is 32 X 32 and I wish it were better but I did not want to pay for the better so I will have to deal with it. It would be fun to see the difference in what could be seen with yours as opposed to mine on the same experiment.

     

    John

  • Thanks for showing us the experiment!

     

    I am currently waiting to get my hands on this new FLIR TG297FLIR TG297 camera. They recently introduces a cheaper series with 160x120 pixels resolution.

     

    Another approach to find the shorts is to put some alcohol on the board and see at which places it evaporates the fastest.

     

    David

  • in reply to jw0752

    Thanks John for running the test.

     

    It does offer some possibilities for troubleshooting. I would tend to use other methods for locating cable and their routing. I do like the idea of using the technique on a printed circuit board. Still trying to wrap my head around practical applications.

  • in reply to colporteur

    Hi Sean,

     

    I ran an experiment involving the electric wiring. I measured the heat of an exposed 12-2 cable in my shop and then I put a space heater and a hot plate on it for 15 minutes. I am estimating about 1800 Watts or about 15 Amps was flowing in the 120 VAC circuit.

     

    image

    The cable begins at the same temp as the environment which makes it hard to see.

     

    image

    I was quite surprised to see this much change in temperature. This is an exposed cable so there is no intervening wall. This technique can be useful to me in the future. I was able to use the Thermal Imager to follow the warm wire all the way through the rafters of my shop and back to the distribution box. This will be another way to trace a circuit. I am sure that if the wire were behind a wall the temperature of the wire would eventually warm the wall slightly but the image of the wire would not come through. Heat radiation is not like x-rays where it would penetrate the wall directly. Instead the thermal energy from the wire would warm the wall which would then diffuse the energy by conduction and re-radiate it over a much larger surface area. The movies would sometimes lead us to believe that a thermal imager can see people and other warm items through walls and roofs but this is just Hollywood Physics.

     

    John