Max 31850K and thermocouple non linear Temp. curve ??

B

Buzz

Well-known member
I use a Max 31850K one wire board and a thermocouple K type for an oven we make , we tried to calibrate it and we are getting a non linear response , at 40 deg C we calibrate and offset in code so the display matches the Temp. Gun when we go up to 150 deg C it is off by 8-10 deg !! ?? or more .

Any ideas as to what could cause this offset ? the tolerances from the Board and thermocouple should only be maybe 3 deg max .

Max31859K board
https://www.adafruit.com/product/26...UUqiqD0zUgi_0hYZBFRfuTSZx1iZSIpxoCU_AQAvD_BwE

the product

https://nanometer.com/curing-oven
 
It is absolutely vital that the MAX31850 and the cold junction be at the same temperature. What steps have you taken to assure that?
 
UhClem said:
It is absolutely vital that the MAX31850 and the cold junction be at the same temperature. What steps have you taken to assure that?
Click to expand...

Max 31850K has internally compensated cold junction built in right ?? this is in an oven so maybe the board is getting hotter than it should. actually looking at the spec sheet from 0-100 degC there is a 0.3 deg variation.
 
Last edited:
The cold junction on that breakout is where you solder the thermocouple wires to the board. This may not be at the same temperature as the guts of the IC. Especially if it is located badly.
 
UhClem said:
The cold junction on that breakout is where you solder the thermocouple wires to the board. This may not be at the same temperature as the guts of the IC. Especially if it is located badly.
Click to expand...

looking at the spec sheet the IC from 0-100 degC there is a 0.3 deg variation.
 
That specification assumes that the internal IC temperature is identical to that of the cold junction. You have to make sure that is true.
 
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