Thermocouple Amplifier with Cold Junction Compensation Explained
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- Опубликовано: 5 май 2024
- A Thermocouple Amplifier with Cold Junction Compensation Circuit is explained in this video that is an example of thermoelectrical temperature sensor signal conditioning circuit design and analysis. This K-Type Thermocouple Amplifier is designed to perform two tasks of signal amplification and zero adjusting to set the intercept to zero for the overall temperature transfer function of the circuit. The circuit is designed with two op amps, a 2.4 volt Zener diode with -0.085% per degree Kelvin temperature coefficient that results in -40.8 micro volt per degree C temperature coefficient which is nearly matching the 40.7 micro volt per degree Seebeck coefficient of Peltier-Seebeck Thermoelectric voltage generation in order to compensate for the unwanted effect of the cold temperature (the non-zero temperature of the copper wire at PCB temperature). The designed Type-K Thermocouple Amplifier maps measured temperature range of 0 to 400 degree Celsius to the 0 to 4 volt range at the output of the circuit achieving a 10 mV per degree Celsius temperature coefficient for the overall amplifier.
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Very interesting circuit. I have a couple of thermocouples in a box waiting for me to get time to use them. I wonder how this circuit compares practically against the off-the-shelf modules that can be purchased from Adafruit and other places.
I worked on the installation of a new furnace in an aluminum foundry and installed thermocouples and the associated devices, but there was no opportunity for me get any insight into the circuit design.
Also, if anyone is interested, there is at least one easy to deal with supplier of trustworthy, USA made thermocouples, if you don't want to take your chances on Amazon or other such places.
Glad that you liked this Thermocouple Amplifier video. Thanks for the comment and sharing your thoughts. Here are a few related sensor amplifier videos: Thermometer Sensor Circuit Explained ruclips.net/video/5jmbZ9ak6EI/видео.html
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I hope these circuits are interesting as well.
Very nice and fascinating.
Thank you. Glad that you liked this video. For related sensor signal conditioning and amplifier videos please see ruclips.net/p/PLrwXF7N522y7Ut9bm8TXAOhIWqL__FGlj which is the collection of Sensors & Instrumentation Amplifiers Videos.
Good !
But i didn't get the use of the 1 meg resistor.
I also wondered about that
Thanks! Good question, we want to avoid leaving the thermocouple terminal float in the circuit.
@@STEMprof Thanks ! A kind of pull up résistor ?
Yes, you are welcome.
@@STEMprof but it is tied to ground through the 100 Ohm resistor
Is the zener temp coeff. value accurate at all? The part is specified for 2.4V Zener. There is no binning from production not any uncertainty. Have you built this circuit, and confirmed the accuracy?
Good question, Yes for 2.4v Zener and for the cold (PCB/copper) temperature range of 0 to 50 degree Celsius that matters. Note that Zener Diodes between 1.8v to 3.3v have remarkably stable temperature coefficients assuming proper DC Bias current (say 6-10 mA).
A Thermocouple Amplifier with Cold Junction Compensation Circuit is explained in this video. For more sensor signal conditioning and amplifiers see ruclips.net/p/PLrwXF7N522y7Ut9bm8TXAOhIWqL__FGlj and the following videos: PT100 RTD Temperature Detector with Error Compensation ruclips.net/video/Fsd-X69awFk/видео.html
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For more analog circuits and signal processing examples see: ruclips.net/p/PLrwXF7N522y4c7c-8KBjrwd7IyaZfWxyt
I hope these sensors circuits videos are interesting and useful.
Why not use the 3.9 & 4.3 Zeners in series (with higher drive voltage & higher divider etc., as that would be near 0 temp issues?
Never mind, I see they are using it to compensate connection issues.
@@stevenbliss989 Correct, 2.4 volt Zener Diode is intentionally used since its -0.085% per degree C temperature coefficient results in -40.8 micro volt per degree voltage sensitivity which nicely compensates for the unwanted effect of non-zero cold junction temperature Tc as explained around minute 8:00
How to use J-Type Thermocouple in this design?
Good Question, While you can use both Type J and Type K thermocouples in this example, J-Type can operate well at lower temperature and in vacuum. It is not preferred in very high temperature or very corrosive environments where K-type is a better choice. For more sensor signal conditioning and amplifiers see ruclips.net/p/PLrwXF7N522y7Ut9bm8TXAOhIWqL__FGlj video playlist.
Good morning.
What is a composite amplifier ?
Good morning as well. Composite Amplifier usually means cascade of more than one stage. More examples ruclips.net/p/PLrwXF7N522y7Ut9bm8TXAOhIWqL__FGlj are posted in the sensor signal conditioning and amplifiers playlist.