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Question about TC4 ambient temperature/cold junction MCP3424/MCP9800
sebiiksbcs
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Posted on 03/26/2021 2:42 AM
I was wondering if the ambient temperature required for accurate cold junction calculation has to be the temp near the MCP3424 (the MCP9800 is placed next to it so I'm guessing yes), or the general ambient temperature outside the thermocouples (if that makes any sense)?

I am asking because I have my TC4 put in an enclosure with a Raspberry Pi and as the Rasp runs warm it obviously changes the ambient readings of the TC4's MCP9800 (sometimes to +10 deg C difference compared to ambient temp during startup), thus also changing the cold junction?

Needless to say doesn't this sort of mess up Artisan's ambient temp logging as I am measuring the temp inside my case not the outside temp (which I would want to have logged so I can see how my roasts turn out in hot or cold weather)?

Hope my questions make sense and thanks all!
 
renatoa
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Posted on 03/26/2021 5:09 AM
Cold junctions (at least two!) are where you connect the two (different!) TC wire metals to your circuit.
When connector attached, the cold junction is inside the connector.
For TC4 board, if you are using provided TC terminals block, it is placed close enough to MCP9800 to consider the temperature measured as AT pretty relevant.
If TC connecting screws are placed outside enclosure, thus closer to the ambient than MCP9800 ... then we have a problem...
I would try to check this by measuring boiling water, if showing 99-101C then compensation is done ok, else you need to dial an offset, there is a place somewhere in code for this purpose, search for amb.setOffset.
 
sebiiksbcs
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Posted on 03/27/2021 6:50 AM
Crystal clear reply! Thanks Renatoa. By the way are you still working on your ESP32 port? Thinking about switching since the old ATMEGA328 is nearly overloaded doing the basic TC4 tasks.
 
renatoa
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Posted on 03/27/2021 7:20 AM
Still working as in... weekly using ? smile
If already using a TC4 shield, I can sketch an Uno layout adapter board to host the ESP, and able to accept TC4 shield with no changes, if possible.
 
sebiiksbcs
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Posted on 03/27/2021 9:28 AM
I always meant make an adapter board for the TC4 shield to connect to the Blue Pill (STM32F1) or even STM32 Discovery Board (STM32F4) but you're right, it's a better idea to use an ESP like yours because you already have working code.
 
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