0

MAX31856 temperature wrong
Moderators: adafruit_support_bill, adafruit

Please be positive and constructive with your questions and comments.

MAX31856 temperature wrong

by PhMar on Sat Feb 06, 2021 7:27 pm

I recently ordered the MAX31856 Universal Thermocouple Amplifier. I've got it connected to an MSP430 launchpad with a Type K thermocouple. Initially it was reading more or less correctly, about 17 to 18 C. The ambient room temp is actually around 19.5 C. I let it run for an hour or so, and it started to drift up. Shut the system down, left it over night, and it started out ok again, but started drifting up. So I started checking code, wiring, everything I could think of. Now even initially it is consistently reading around 24-25 C, and there is no way the room temp is that high. Throughout this whole time (a couple of weeks of effort) I've checked code and wiring multiple times. I can write and read the control registers, fault mask register, and status register properly, I read back what I write, so I'm pretty sure the SPI bus is working correctly. I am unsure of the thermocouple polarity, so I've tried both and one direction is even worse.

Has anybody seen this behavior before? Any ideas where to look? Thanks.
Mike

PhMar
 
Posts: 2
Joined: Sat Feb 06, 2021 7:11 pm

Re: MAX31856 temperature wrong

by mikeysklar on Mon Feb 08, 2021 5:37 pm

Mike,

You have an unusual situation where things mostly work, but not quite.

Maybe you can try the Thermocouple setup on one of the controllers we sell to help narrow down if this is a MSP430 issue, library or hardware thermocouple/amplifier side configuration issue.

mikeysklar
 
Posts: 4920
Joined: Mon Aug 01, 2016 8:10 pm

Re: MAX31856 temperature wrong

by PhMar on Tue Feb 09, 2021 1:51 pm

I looked at the documentation again and it notes that the accuracy can be as much as +/- 6 C, so I think I'm going to see if I can search up a different thermocouple and try that. Maybe it is an accuracy problem. Thanks for the reply
Mike

PhMar
 
Posts: 2
Joined: Sat Feb 06, 2021 7:11 pm

Please be positive and constructive with your questions and comments.