Because many folk may not want to get into a full computer controlled thermal bridge as outlined in my other thread, here is a simpler method that can determine the power output of your DUT.
I fabricated my build with very thin strands from type "J" ( Iron and Constantan ) thermocouple wire, wrapped and glued to 1/4 watt 100 Ohm resistors.
You could use very fine Copper and Iron, or Copper and Constantan for your thermo elements.
Each side was insulated with styrofoam to reduce the effects of air drafts, and raise the sensitivity.
The output from the self powered unit is low but is easily read on my Fluke using the uA range setting.
The first method, (direct readout) requires a calibration curve to be generated.
With the null balance method, this is not necessary. You tune your power supply voltage for null and read power output on your power supply E X I. (I prefer this method).
You could use a dual thermometer. You could also use a powered bridge with thermistors, but I wanted to keep it simple and self powered. Also it is hard to sense the heat generated by those tiny resistors.
Although designed for power under a watt, it is easily scaleable to any power level with the appropriate sized resistors.
For greater output, additional thermocouples can be wired in series, but tips must be insulated electrically.
If you really want to build a quality thermal RMS power meter, see the attached datasheet. Linear Technology made a very nice chip to do the job, it is no longer available but you can use some of the ideas presented by the late master Jim Williams. See also app note 61 by Linear Tech.
« Last Edit: 2013-03-29, 19:34:28 by ION »
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