MAX31855 Issues

Breakout boards, sensors, Drawdio, Game of Life, other Adafruit kits, etc.

Moderators: adafruit_support_bill, adafruit

Please be positive and constructive with your questions and comments.
Post Reply
User avatar
mangus580
 
Posts: 5
Joined: Tue Nov 22, 2016 9:30 pm

MAX31855 Issues

Post by mangus580 »

Having issues with the MAX31855. I have 4 of them each running off their own ESP8266. Using Type K thermocouples. I am getting (more and more frequently) a ton of high values (out of limit?)

Using these to monitor oven temperatures in the ambient to @700° F range. As seen in the picture below, you can see how the temp reading keeps randomly spiking (see the graphs) to what appears to be an impossible #.

I am not sure whats causing this, it was very minimal when first setup, now that they have been in place for a month or 2, they are getting worse and worse. BTW, this is taking a temperature reading somewhere around every 30 seconds,

I need help - any suggests are greatly appreciated!
Attachments
427fa163-6387-4be6-a30a-be8b53a5c69f.jpg
427fa163-6387-4be6-a30a-be8b53a5c69f.jpg (922.64 KiB) Viewed 110 times

User avatar
mikeysklar
 
Posts: 8378
Joined: Mon Aug 01, 2016 8:10 pm

Re: MAX31855 Issues

Post by mikeysklar »

Can you show the MAX31855 connections? The soldering on the boards and to the probes? This sounds like a physical connection deterioration issue based on your description.

User avatar
mangus580
 
Posts: 5
Joined: Tue Nov 22, 2016 9:30 pm

Re: MAX31855 Issues

Post by mangus580 »

This is the only photo I have that shows how I set this up.

How likely would it be that I would have connection issues on all 4 of them though?
Attachments
2022-05-30 11.49.22.jpg
2022-05-30 11.49.22.jpg (135.37 KiB) Viewed 90 times

User avatar
mikeysklar
 
Posts: 8378
Joined: Mon Aug 01, 2016 8:10 pm

Re: MAX31855 Issues

Post by mikeysklar »

There is a good summary in the forums from another MAX31855 user diagnosing the issue around high air temperature causing an increase in conductivity.

viewtopic.php?f=31&t=169135&p=830405&hi ... gs#p830405
Problem: when using MAX31855 for temperature measurement in furnaces or kilns with a heating coil exposed to air, once the temperature reaches around 900-1000C, MAX31855 starts reporting fault codes 2, 4 , 6 (thermocouple shorted to ground, VCC or both), while the actual temperature readings continue to be accurate. Some Arduino libraries for MAX31855 do not report the temperature value when one or more fault conditions are present, and the temperature is then reported as NaN.

Why this is happening: As the air heats up to about 1000C and above, it becomes slightly electrically conductive. A leakage path is then introduced from the exposed heating coil through the thermocouple to the common ground. MAX31855 detects this leakage current as a fault. MAX31855 needs just 50 microamps of leakage current to report a fault. To test this condition, connect a 9V battery via a 150k resistor between the thermocouple and the ground plug on the power cord of your kiln. MAX31855 will immediately report a fault. A similar leakage current develops from the exposed heating coil to the thermocouple when the air heats up to around a 1000C.
I know you were reporting bizarre high values, but was the raw data coming into the AIO feed as NaN or max value?

User avatar
mangus580
 
Posts: 5
Joined: Tue Nov 22, 2016 9:30 pm

Re: MAX31855 Issues

Post by mangus580 »

I have not had the opportunity to get down to the plant where this setup is running, but reading back through your quote... I wonder if maybe I should be using a different library.

Suggestions on the appropriate library? I think I used the one from the Adafruit tutorial on it if I recall....

User avatar
mikeysklar
 
Posts: 8378
Joined: Mon Aug 01, 2016 8:10 pm

Re: MAX31855 Issues

Post by mikeysklar »

The Adafruit MAX31855 is the right library to be using. There is an open issue which has some suggestions block out alarm faults. The code was not merged into the library due to conflicts, but might be enough to help you put together a solution.

https://github.com/adafruit/Adafruit-MA ... ry/pull/31

User avatar
mangus580
 
Posts: 5
Joined: Tue Nov 22, 2016 9:30 pm

Re: MAX31855 Issues

Post by mangus580 »

Does this apply even when using the MAX31855 from Adafruit?

User avatar
mikeysklar
 
Posts: 8378
Joined: Mon Aug 01, 2016 8:10 pm

Re: MAX31855 Issues

Post by mikeysklar »

The github issue mentions third party MAX31855 boards, but @xonxoff99 thread was based on Adafruit boards showing faults at higher temperatures.

viewtopic.php?p=827564

Post Reply
Please be positive and constructive with your questions and comments.

Return to “Other Products from Adafruit”