Thermocouple compensation

thermocouple compensation thermistor

I am designing a project. I use ADC for reading small voltage of thermocouples. My project need to used for multi-type of thermocouples. So I need to compensate cold-junction of the thermocouples but I don't know how to. Please advise me, if I use software compensator by using a thermistor at cold-junction.

Also I don't understand about isothermal connector box.

Please help me.

00684a.pdf

Both issues, the thermocouple compensation and the isothermal block, are descrbed in details in the following publication:
"Single Supply Temperature Sensing with Thermocouples"
https://ww1.microchip.com/downloads/en/AppNotes/00684a.pdf

Regrads,
IanP

Dear IanP

For the isothermal block that has temperature sensor for compensation. I can buy it (terminal block + temperature sensor)?, or I need to build by myself ?.

Both options are possible: build one or buy one ..
Here is an example:
**broken link removed**

Regrads,
IanP

Could you give me your website or companies that sale the isothermal block?.

Or some one more details about how to build it.

you can use CYPRESS PSOC,
look at application note AN2148 .
i built this circuit and tested (between room temperature and 400 degree )
it works OK.

You may not need an isothermal block.

If you locate your reference sensor (e.g., a semiconductor device like the LM335 will work quite well) in close proximity to the tc cold junction, all you must do is ensure that the sensor and tc are at the same temperature.

The function of an isothermal block is to cause the reference sensor and tc to be at the same temperature by means of an enormous thermal mass, but there are other ways to force their temperatures to track. For example, you can simply wrap bubble-pack around the tc junction and its reference sensor; this will permit the tc and sensor to reach thermal equilibrium while protecting against thermal transients such as breezes from open windows, etc.

As far as supporting multiple tc types, you can use the above arrangement as follows:
1. Using adc, measure the LM335 output.
2. Convert measured LM335 output into equivalent tc voltage for your target tc type.
3. Measure tc voltage using adc.
4. Add together tc voltage and LM335's equivalent tc voltage to get the "corrected" tc voltage.
5. Convert corrected tc voltage to temperature.

I have used this technique and achieved better than 0.2 °C accuracy across full operating range for both J and K types.