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chipgarner / MultiZoneKilnController

Multi zone kiln contrer based on refactoring and re-writing kiln_controller https://github.com/jbruce12000/kiln-controller
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MAX31855 Numerous errors at high temperatures. #24

Open chipgarner opened 5 months ago

chipgarner commented 5 months ago

The MAX31855 hits a lot of errors but keeps working at high temperatures.

The board sends errors like short to ground, short to power, over and over. Connecting the TC to a Fluke or a '56 shows no errors. The errors come more and more often as the temperature increases. The errors continue in the same manner as the kin is cooling, with the high voltage switching shut off. I have tried different software - my software graphs the errors real time. To further define "errors", the board sends out a set of bits that corresponds to a specific error as defined in the board documentation. This has been desc

Around 1600F my thermocouple started getting lots of errors [which is normal] and since the variable was named incorrectly, my setting in config.py was ignored and the code ended my schedule because it though there was an emergency. These errors are caused by plasma in the kiln making it my tc appear to have a short circuit. @jbruce

I have done a lot of testing of this error and will post what I have tried in about two weeks.

chipgarner commented 5 months ago

@rondoc I have reproduced this error with two different kinds of TC boards connected to the same TC and only see the errors on the '55. It is very reproducible and Jason thinks it is just normal. kiln-controller works fine even if it is only getting one good response out of every 10 requests.

I have tried warming the TC board itself and was not able to reproduce the problem.

You may be right that this is in how we read the board. The low level software that does the reading is in the Adafruit library that does the SPI communications. We are using two different libraries, one (bitbangio) that does SPI using any GPIO on the Pi, and another that uses the Pi hardware SPI pins. (This is because users have wired there controllers in different ways.) It is possible that there is shared code in these two libraries that has an error in it. We have the Adafruit code, and I am planning to look into this.

The only other possibility I can think of is that the errors are coming from the TC board itself. What do you think?

And thanks!

rondoc commented 5 months ago

@Chip Garner @.***> you seem to understand the problem. Can you write the code to read the 55 and or the 56 board to the pi? Adafruit code might have a timing error either too fast for the pi or not truly synchronous if it needs to be. I am totally unable to know as I have zero coding skills. May be reading tc can be done in a different way. For an idea. Take tc output and convert to a linear scale using the well defined voltage vs temp. for the type of tc. Then use an A to D converter that will give a digital output that can be read by the pi. Although I think the pi has A to D capabilities itself. From here on out its all yours! At least you would have no errors..Hopefully. Ronald.

On Tue, Apr 2, 2024, 1:07 PM Chip Garner @.***> wrote:

@rondoc https://github.com/rondoc I have reproduced this error with two different kinds of TC boards connected to the same TC and only see the errors on the '55. It is very reproducible and Jason thinks it is just normal. kiln-controller works fine even if it is only getting one good response out of every 10 requests.

I have tried warming the TC board itself and was not able to reproduce the problem.

You may be right that this is in how we read the board. The low level software that does the reading is in the Adafruit library that does the SPI communications. We are using two different libraries, one (bitbangio) that does SPI using any GPIO on the Pi, and another that uses the Pi hardware SPI pins. (This is because users have wired there controllers in different ways.) It is possible that there is shared code in these two libraries that has an error in it. We have the Adafruit code, and I am planning to look into this.

The only other possibility I can think of is that the errors are coming from the TC board itself. What do you think?

And thanks! Y

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