MAX31855 Type K thermocouple amp board

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vriz55
 
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MAX31855 Type K thermocouple amp board

Post by vriz55 »

I recently attempted to connect (in parallel) more than one device to the MAX31855 TC amp board ( a type k thermocouple internal to a coffee roaster and the LCD display on the coffee roaster) and notice that the LCD display on the coffee roaster became noisy. When I removed the MAX31855 TC amp board the LCD display on the coffee roaster was stable. The MAX is hooked up to a RPi3 and is sending temp data to the cloud for remote display on customers cell phone and works very nice. Any ideas on how to eliminate noise on customers coffee roaster LCD when MAX is hooked up in parallel with it and type k T/C in coffee roaster? Please advise....Thanks....Vic Rizzo

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adafruit_support_bill
 
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Re: MAX31855 Type K thermocouple amp board

Post by adafruit_support_bill »

I recently attempted to connect (in parallel) more than one device to the MAX31855 TC amp board ( a type k thermocouple internal to a coffee roaster and the LCD display on the coffee roaster)
I'm not sure how one would connect an LCD display in parallel to a thermocouple. Please post photos showing how you have everything wired.

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vriz55
 
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Re: MAX31855 Type K thermocouple amp board

Post by vriz55 »

Actually, we paralleled the red and yellow leads coming from the coffee roaster type k T/C to the red and yellow leads of type k wire leading to the MAX amp card at a terminal strip in the coffee roaster control box. So you are correct that the Type k T/C wire was not directly paralled to the LCD display...The problem is that it appears that the MAX amp card is inputting a small oscillating voltage into the coffee roaster terminal strip which is causing the LCD display to oscillate...Is it possible for the MAX amp card to generate voltage? Please let me know if you still need a photo...Thanks...Vic Rizzo

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Re: MAX31855 Type K thermocouple amp board

Post by adafruit_support_bill »

Theremocouples work in the millivolt range, so they are very susceptible to noise. Cross-connecting two circuits like that, you may have introduced a ground loop of some kind. Make sure you have a good ground connection between the MAX31855 to the analog ground on the roaster circuit.

Also note that all thermocouple connections should be made with the same type of wire as the thermocouple. (for type K that would be Nickel-Chromium & Nickel-Alumel). Using a different wire type will invalidate the cold-junction compensation.

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