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Reading thermocouple in contact with 18V metal tab
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batteryboy
- Newbie
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- Joined: Mon Jan 08, 2024 3:44 pm
Reading thermocouple in contact with 18V metal tab
Hi,
We wish to measure the temperature of the 18V metal tab of a SOT223 transistor.
Is it OK to use TC-08, and we can just momentarily turn off the power supply and then read the thermocouple on the TC-08 software, and then turn the product back on again.
As you know, we wont be able to read the thermocouple when the 18V is on the tab.
We could just put kapton round the thermocouple end, but that will cause temperature inaccuracy.
We wish to measure the temperature of the 18V metal tab of a SOT223 transistor.
Is it OK to use TC-08, and we can just momentarily turn off the power supply and then read the thermocouple on the TC-08 software, and then turn the product back on again.
As you know, we wont be able to read the thermocouple when the 18V is on the tab.
We could just put kapton round the thermocouple end, but that will cause temperature inaccuracy.
Re: Reading thermocouple in contact with 18V metal tab
Hi batteryboy,
The answer is yes, but you should ensure that the TC-08 ON period doesn't overlap with the transistor powering ON period.
Alternatively, you could avoid any potential problems, and perhaps make life easier by either:
(a) Using a Laptop running on Batteries to power the TC-08.
or
{b) Rather than Kapton, using a heat transferring, electrical spacer, i.e. a substance that has high thermal conductivity, and low electrical conductivity, made into a rigid, thin surface, to thermally and safely sandwich between your thermocouple tip and the plate of the transistor.
A potential promising substance is Aluminium (or Aluminum) Oxide, which has a thermal conductivity of 30W/mK, in comparison to Kaptons 1.76 W/mK for a thickness of 273 µm. If you want to accurately track the changes in heat, you would need to use as thin a spacer as practically possible, and ensure that the rate of heat transfer through the spacer is faster than the rate of change of heat in the transistor, during your measurement.
Note also that in the past Beryllium Oxide, and Boron Nitride have been recommended as they have very impressive thermal conduction and electrical insulation properties (300 & 800 W/mK respectively). However Beryllium Oxide is now classified as a highly hazardous substance (in particular in powder form) and although there is limited data for boron Nitride, it's powder is also generally considered toxic. So, to avoid the consequences of accidentally scraping powder from one of these compounds machined into an electrical spacer, you should, absolutely, never use these. (I only mention them here in case any forum user decides to do their own research, after reading this.)
Regards,
Gerry
The answer is yes, but you should ensure that the TC-08 ON period doesn't overlap with the transistor powering ON period.
Alternatively, you could avoid any potential problems, and perhaps make life easier by either:
(a) Using a Laptop running on Batteries to power the TC-08.
or
{b) Rather than Kapton, using a heat transferring, electrical spacer, i.e. a substance that has high thermal conductivity, and low electrical conductivity, made into a rigid, thin surface, to thermally and safely sandwich between your thermocouple tip and the plate of the transistor.
A potential promising substance is Aluminium (or Aluminum) Oxide, which has a thermal conductivity of 30W/mK, in comparison to Kaptons 1.76 W/mK for a thickness of 273 µm. If you want to accurately track the changes in heat, you would need to use as thin a spacer as practically possible, and ensure that the rate of heat transfer through the spacer is faster than the rate of change of heat in the transistor, during your measurement.
Note also that in the past Beryllium Oxide, and Boron Nitride have been recommended as they have very impressive thermal conduction and electrical insulation properties (300 & 800 W/mK respectively). However Beryllium Oxide is now classified as a highly hazardous substance (in particular in powder form) and although there is limited data for boron Nitride, it's powder is also generally considered toxic. So, to avoid the consequences of accidentally scraping powder from one of these compounds machined into an electrical spacer, you should, absolutely, never use these. (I only mention them here in case any forum user decides to do their own research, after reading this.)
Regards,
Gerry
Gerry
Technical Specialist
Technical Specialist