MAX31855 problems

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adafruit_support_bill
 
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Re: MAX31855 problems

Post by adafruit_support_bill »

Looking at the library code for the begin() function, it just initializes the state of the SPI bus. It does not actually attempt to communicate with the device. So don't have any evidence of the device being responsive.

Given that there is no internal temperature reading and no error returned for the thermocouple state, I'd have to conclude that the boards are all non-functional at this point.

Since the problem began with changes to the wiring, an accidental short or crossed wire during that process would be the likely suspect.

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Jrodeghi
 
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Re: MAX31855 problems

Post by Jrodeghi »

An Update. I tried shortening the wires as I read somewhere that an SPI bus can not be longer than 0.5m(50cm) the length of the wires. So I shortened the wires and the same problem still occured.

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Re: MAX31855 problems

Post by adafruit_support_bill »

There is no fixed maximum length for an SPI bus. Longer wires are more susceptible to interference. This can be addressed with shielded and/or twisted pair wiring. Increase line capacitance is another issue. That can be addressed by slowing down the data rate.

In your case, line length does not seem to be the issue, since you tested boards individually with shorter wiring and they were all unresponsive. It sounds to me like some event during the re-wiring process killed all 9 of the boards. Perhaps an accidental short-circuit or crossed wires.

Another possibility is that they were damaged by interference picked up by the longer wiring. You have not given us any information about other equipment in the cabinet, so it is hard to speculate. But inductive loads can create damaging spikes.

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Jrodeghi
 
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Re: MAX31855 problems

Post by Jrodeghi »

Update. I switched a single thermocouple over to an Arduino Uno. I did not get any actual temperatures. What I got was the following.

Code: Select all

0xFFFFFFFF
Something wrong with thermocouple!
Internal Temp = -0.06
0xFFFFFFFF
Something wrong with thermocouple!
Internal Temp = -0.06
0xFFFFFFFF
Something wrong with thermocouple!
Internal Temp = -0.06

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Jrodeghi
 
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Re: MAX31855 problems

Post by Jrodeghi »

The other equipment in the cabinet are motor controllers and relays to control heaters. The relays operate at 120V Ac and a few 240V AC. The motor controllers and the Arduino get power from a 120v Ac to 24v Dc then the Arduino has another convertor that converts 24 to 12.

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adafruit_support_bill
 
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Re: MAX31855 problems

Post by adafruit_support_bill »

Motors, relays and most types of heaters are inductive loads. They all create current surges and voltage spikes when starting and stopping.

The current surges can cause brief 'brownouts' as the input voltage sags under load. This can cause processors to malfunction or reset. The reverse voltage spikes can feed back through the power & ground buses and cause damage to other connected devices.

But even if your circuits are electrically isolated, the radiated EMI from these devices and their wiring can still be picked up by other nearby devices and their wiring.

Kickback/snubber diodes are typically used to minimize inductive voltage spikes from relays and similar devices. Strategies to protect against radiated EMI include:

* Use shielded and/or twisted pair cabling - For offending devices, this minimizes the EMI radiated from the supply cabling. For affected devices, it minimizes the EMI received.
* Keep wire runs as short as practical.
* Keep wiring for sensitive devices well separated from wiring for devices that generate EMI.

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Jrodeghi
 
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Re: MAX31855 problems

Post by Jrodeghi »

Thank you for the help! I will get right on trying to implement these fixes.

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