PT100 weirdness
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Hmmmm so my new daughter board arrived last week.
I mounted it and all seemed fine. Tested with resistors first, both 220 Ohms, both read ~316° C.
Ok so up for a print, worked, did come calibration, next print.
And this one failed, second hotend didn't extrude because of a heater error. Temp reading was 2000° C. So I moved the second hotend by hand and I had a fine reading again, I moved the PT100 cable near the hotend and bam again 2000° C.
So I assumed a damaged cable.
Switched the PT100 whic was still the original BigBox old style in silver cable one to a new E3D one just like on the first hotend.
At room temperature first read 21.7° C, new one 17.1° C. Didn't think much about it just ran PID tuning and now again the filament boiled out of the hotend. The heater reached "240° C" what I wanted to tune but apparently was hotter.
So back to resistors in both ports of the daughter board and…..
316° C on the first, 206° C on the second.
Can this be?! Another damaged chip on the daughter board in just under one week and litterally no usage?
I checked my cabling, all fine, no problem, no accidentially shortage or possible voltage on the PT100 ports...This sucks, now I got my box mechanically fixed and in a shape I like and now I have electronic problems...
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I find this very strange:
- Your report of a faulty daughter board is the first one I've ever seen.
- Getting readings differing by 3C when both sensors are at room temperature is most definitely wrong.
- According to the manufacturer of the MAX31865 chips, the inputs are protected against overvoltage faults of up to +/-45V.
So at this stage I am considering 2 possibilities:
1. A firmware bug that is affecting the reading of the second sensor in your configuration. Can you stack your 2 boards together, connect 100 ohm resistors to all 4 inputs, and see what readings you get? Then stack them in the opposite order and compare the readings.
2. A short or leakage in your wiring or in the PT100 sensor itself, that is damaging the sensor chip somehow, despite the manufacturer's claim that the inputs are protected to +/-45V.
Can you confirm that in both cases, it is the second channel of the daughter board that has the problem, and it was connected to the second hot end?
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Will try all later but so far I can confirm that the first board had the fault on port 1, the new one on port 2…
So not what you wrote, each board a different port affected... -
Just to add this I used the sensors I replaced for a while also in long prints with the RUMBA and with the Duet later. Now I have two new gen E3D cartridge PT100 mounted I had on my alternate Volcano Hotends which I used with the RUMBA…
If you say the chips are protected up to 45V I have no idea even if I have a shortage how simple PT100 can damage the chips... -
Ok I did some further testing.
I prepared parallel resistor bundles in the range of about 107-108 Ohms to get a tempereratur about room temperature.
So on the old board I had 107 on port 1, 107 on port 2, new board 106.4 on port 1 and 108 on port 2.I don't tell you all the details, I tested both boards alone and stacked, on the DuetWifi and on the DueX2.
Always about the same results:
Old board port 1: 12.5° C
Old board port 2: 15.8° C
New board port 1: 16.3° C
New board port 2: 12.5° CSo old board port 1 and new board port 2 are off, well port 2 of the old board seems off a little too.
Port 1 of the new board is the best…On the old board I had two old PT100s connected and later on port 1 a new generation E3D PT100, on the new board just on port 2 an old one...
But again, I can't imagine that a simple resistor (PT100) can damage the chip...I could now print using the "good" ports of both boards but still this is a strange situation....
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Oh BTW out of curiosity I downgraded to 1.18.2 too but also the same result…
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So any ideas what can be wrong with my setup?
It worked a long time, I didn't do anything to the cabling as I have fixed cabling from top of the back of the box to the board which I didn't change for almost a year. And the cabling from print head to the connection point is free floating in the air also bundled cabling which I didn't change. All cables are bundled, the PT100 cables from top back are in a sleeve and still the original silver PT100 cables with a heavy isolation and internal metal sleeve… So all that could have happened is a broken cable to the PT100 itself. An inspection didn't show any other cable damaged or contacting the PT100 cables... -
Please ask for your new PT100 board to be replaced under warranty. When you receive it, before you connect the sensors, test both inputs with the same resistor, one at a time. The readings should be within 0.5C of each other, and typically much closer than that.
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Just to be sure what to do now, I ordered from you/Tony so I write to info@duet3d.com or what?
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Just to be sure what to do now, I ordered from you/Tony so I write to info@duet3d.com or what?
Yes.
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Ok got the new daughter board today. At first thanks to Tony/David for the quick replacement!
Tested with two resistors on the DWF first and the readings have been reasonable.
I monitored the PT100 connections for any leak voltage when moving carriages, switching on heaters and fans to be sure there is not voltage on the heater channel by accident. No voltage could be monitored so.
Then connected both PT100 and looks good for now:
