Mesa 7i76e and pt100 temp sensor

It would work, but with low resolution.
THCAD would be much better.
Or, if anyone wants to venture into a bit of coding, use audio inputs, there are at least 2 very high resolution inputs on every PC, audio line inputs, and some have separate microphone inputs. Those are usually at least 24 bit, line in is usually 1V peak to peak.

Tarja wrote:

You suggest to connect the pt100 first to a thcad?

Yes, but that would be overkill.
Probably an ESP32 (not 8266) has 12 bit analog inputs, so using that to measure temperature and output pulsed speed dependent on temperature over to Mesa 7i76E encoder input would be cheap, easy, and plenty of resolution.
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I might be overthinking this, the spindle thermistor is there just to alert when the temperature is to high, right?
For that the Mesa 7i76E input should do just fine.
Sorry for going off at a tangent if this is what you asked.

Yeah, that would be nice to have on screen inside the GUI, so yes again, Mesa inputs can be used for that, then have a VCP panel showing the temperature and a bar or dial or LED's with different colors ...
linuxcnc.org/docs/devel/html/gui/qtvcp-vcp-panels.html
or even this
www.anderswallin.net/2012/12/dual-needle-pyvcp-meter/
There is also the possibility of using that at any certain value to slow down the feed rate or to stop the motion so the spindle cools down and continue after it is cooled.

Look on eBay / Amazon / Adafruit / Aliexpress for one of the MAX31865 boards. They are used in some 3D printers and are pretty cheap.

You could set up a Wheatsone bridge for 0.4V output at 100C from a 5V supply. (Using the PT100 and 3 x 100Ω resistors)
www.allaboutcircuits.com/tools/wheatstone-bridge-calculator/

Running the bridge at 24V gives more output, but at the risk of damaging the input if the wiring goes wrong. Also that's about 5W of power dissipated in the resistors/PT100 too so there might be self-heating.

The 31855 is for thermocouples.

I imagine that the module could be re-configured for the 31865.

The 31855 is for thermocouples.

I imagine that the module could be re-configured for the 31865.