Spurious heater faults and how to avoid them

bilsch

Yes the pigtail to 4 wires is a good idea. Most likely the wires are picking up interference from stepper motor or (just possibly)) heater in the same cable run.

Been forever since I came back to check for a response - oops!

I'm just using standard hookup wire ( not solid core ). I continue to have the issue so want to track it down.

Your comment on noise in the line from stepper is interesting however I only notice ( not to say its not happening ) during the initial heatup. I do have all of the wires bundled together in a long (ish, 600mm ) run to the controller for all things on the x carriage so power, therm, fans etc - eg a lot of potential for noise in that line. Its just a simple wire mesh wrap.

Any suggestions on just how sensitive to noise the pt100 is? Should I wrap the sensor wires in aluminum or something? Good enough to just move the pt100 wire out of the bundle? Could it be a cable length problem? Bad sensor, bad board etc?

I'm going to try a few of the above and see how it goes

Dougal1957

use screened cable for the PT100 and it will prob cure the issue (I Had the same and going to 4 core screened cured the problem)

PropellerHat

Hi

Just this morning I found a huge fail in the printer. I was printing 4 pieces at a time and heater number 1 had an error (15 degrees of).

The printer had stopped there, but everything else but the heater number 1 was still hot, leaving the 3 functioning hot ends to burn the plastic of their prints. It would be great that all the heaters (but maybe not 0, to be able to continue) would go off as the printer stops, and that Z would leave a gap between the prints and nozzles. I have 1.19 in the printer, I think. All the heaters are calibrated, going to do it again today for the number 1 though.

I know it´s a dangerous habit to leave the printer alone and I do it on my own risk, but I was surprised to find the 3 heaters still going and the bed height unchanged after the security function had initiated.

edit: Oh yes, the error was probably a deflected air cooling the hotend too much, so no real problem. Looks to work normally.

dc42

I'm surprised that the print stopped there, because normally a heating fault just turns off the heater concerned and then continues (which isn't generally useful). In the next 1.20 beta I intend to have the firmware execute the pause script as well when a heating fault occurs.

EDIT: I forgot, in firmware 1.19 a heating fault cancels the print.

PropellerHat

I see. Pause script would be great. Even the continuing with the 3/4 extruders would have been OK in this case.

Thanks!

Vlad

@dcaron hey, were you able to make that dyze thermistor work? This seems to be very close in specs to thermistor that I use too. Having calibration problems now. Can't figure out C value for it.

@elmoret PT100 and thermocouple is more of a workaround, not really an upgrade.
Adds complexity, requires additional circuits, can be affected by EMI from steppers, much more inert/slow etc etc etc.
Also resolution is worse than some good thermistors.
Dyze guys cover the topic pretty good actually: https://dyzedesign.com/2016/06/comparison-temperature-sensors-used-3d-printers-part-1/

dc42

Some of the figures in that table are misleading, and some are plain wrong:

Thermistor resolution "Up to 0.16°C" doesn't mention that for a wide-range thermistor, the resolution is likely to drop to 10C or even worse towards the extremes of the range. This makes it difficult or impossible for the firmware to know whether the thermistor is present before turning the heater on.
Thermistor accuracy "1°C without calibration" is only likely to be true over a very limited temperature range, e.g. close to 25C (or whatever temperature the nominal resistance is specified at)
RTD resolution "1.2C" is completely wrong, for the Duet3D PT100 daughter board it is 0.03125°C
Thermocouple resolution "0.5C" is likewise wrong, for the Duet3D thermocouple daughter board it is 0.0078125°C
The response time of any type of temperature sensor is completely dependent on the packaging

Thermistors are for budget 3D printers. If you want to know your hot end temperature accurately, use a PT100, or a thermocouple if you need to measure very high temperatures. A PT1000 may also be a reasonable option if you don;t mind the resolution being a little lower than for a PT100. See our advice at https://duet3d.dozuki.com/Wiki/temperature_sensors.