Firmware Update request - Safety Cutoff on Thermistor Failure

I was just printing something and noticed that the thermistor #1 reading went from 200 degrees to 6 in an instant. Very quickly after that the printer started smoking. It turned out that the thermistor wire had come loose and snagged on the print which disconnected it. The printer was reading lower than desired temperature and just continued heating. If I wasn't in the room at the time this could have resulted in a fire.

I have since tightened up the cable tie that should have kept the wire well away from the print, but i'm wondering if a safety cutout could be written into the firmware to cater this. A sudden dramatic drop in temperature, or perhaps a failure to heat up would indicate a problem with the thermistor. At this point the heaters could be switched of and the print cancelled or paused.

I'm currently running DC42's firmware 1.09a.

Hi Crouchy
I agree with you.. I had the same experience time ago.
Fortunately it has happened during the day... I'm printing even at night when it is needed.

My solution is solder and isolate....

Dario

Edited 1 time(s). Last edit at 07/13/2015 02:50AM by Ormerod187.

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Ormerod 187
Firmware Electronics: Duet 0.6
Firmware Version:1.18.1 (2017-04-07)
Web Interface Version:1.15a
Slic3r 1.2.9a and Simplify3D 4.0.0
[www.dropbox.com]

Strange, in my case the Extruder heating was turned off with an Error and this I saw already sometimes ago as I used the firmware from DC42. So what is the difference? Okay a shortcut would be one possibility.
So the emergency shutdown could happen if the temperature changes quite fast to catch up a shortcut for example.
What kind of wiring do you use?

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Slicer: Simplify3D 4.0; sometimes CraftWare 1.14 or Cura 2.7
Delta with Duet-WiFi, FW: 1.20.1RC2; mini-sensor board by dc42 for auto-leveling
Ormerod common modifications: Mini-sensor board by dc42, aluminum X-arm, 0.4 mm nozzle E3D like, 2nd fan, Z stepper nut M5 x 15, Herringbone gears, Z-axis bearing at top, spring loaded extruder with pneumatic fitting, Y belt axis tensioner
Ormerod 2: FW: 1.19-dc42 on Duet-WiFi. own build, modifications: GT2-belts, silicone heat-bed, different motors and so on. Printed parts: bed support, (PSU holder) and Y-feet.
Ormerod 1: FW: 1.15c-dc42 on 1k Duet-Board. Modifications: Aluminium bed-support, (nearly) all parts reprinted in PLA/ ABS, and so on.

I had a similar issue when the heater slipped halfway out of its place: the hotend was unable to reach the 200 C while half of the heater cartridge ran horribly hot.
I don't feel safe leaving the printer working unattended, leaving alone construction mistakes, a single driver failure can become a fire hazard.
I would welcome an hot end design including (physical) thermal cutoff for both the hot end and heated bed.
These inexpensive devices are found on almost every appliance that incudes an heater in Europe, smaller ones are about 4 mm diameter and 10 mm long and look like this [www.digikey.com]

I would guess that this problem only occurs when using another z-probe where the thermistor is connected. As the signal is grabbed the Duet may not recognize that one wire is broken. That depends on the broken wire (which one).
So I just had this issue, I left home, I came back the print was garbage, I paused the print, the wire was pulled off the connection and I got an error and the heater shut down. I use the original connection, but I will replace this soon to a more secure connection.
Nevermind if your peinter starts burning than you have something that is not original and you modified something that causes this burn.

But a hardwired thermal shutdown like this above is indeed a good way, but where to place at which temperature? I added such kind of thing for a motor. As we could not place it inside the motor I could place it at the motor control card. There was one place that nearly had identically temperatures as the motor windings. I know this is not perfect and that is what I mean. Inside the heater block is no space and outside you will have damages before the thermal switch shut off.
Second problem: When it cools down it resets - the heater starts again until it is burning, thermal shutdown and so on.

---

Slicer: Simplify3D 4.0; sometimes CraftWare 1.14 or Cura 2.7
Delta with Duet-WiFi, FW: 1.20.1RC2; mini-sensor board by dc42 for auto-leveling
Ormerod common modifications: Mini-sensor board by dc42, aluminum X-arm, 0.4 mm nozzle E3D like, 2nd fan, Z stepper nut M5 x 15, Herringbone gears, Z-axis bearing at top, spring loaded extruder with pneumatic fitting, Y belt axis tensioner
Ormerod 2: FW: 1.19-dc42 on Duet-WiFi. own build, modifications: GT2-belts, silicone heat-bed, different motors and so on. Printed parts: bed support, (PSU holder) and Y-feet.
Ormerod 1: FW: 1.15c-dc42 on 1k Duet-Board. Modifications: Aluminium bed-support, (nearly) all parts reprinted in PLA/ ABS, and so on.

Quote
Treito
Strange, in my case the Extruder heating was turned off with an Error and this I saw already sometimes ago as I used the firmware from DC42. So what is the difference? Okay a shortcut would be one possibility.
So the emergency shutdown could happen if the temperature changes quite fast to catch up a shortcut for example.
What kind of wiring do you use?

I'm using dc42 single nozzle probe. I have a dual nozzle hotend, but had swapped it out for the single nozzle due to the quickset nozzles frequently blocking up. The second nozzle actually read error while disconnected but the first just dropped to 6 degrees.

The thermistor connector is just the push on connection as shipped with the printer, but i'm also contemplating soldering it on so this is less likely to occur again.

But you connect the thermistor to the single nozzle probe? So that can be a problem. I am not 100% sure as I do not exactly know how the thermistor is connected to the Duet, but the circuit of the single nozzle probe may deliver a false signal to the Duet if one of the thermistor wire is missing. But to be sure I would also have to take a loom at the internal circuit of the used Attiny and it also depends on the settings of this chip and so on.
I have planned to connect directly the wires (after extensioning by soldering) to the 6 pole connector. I do not think that the 1-pole connector is intended to use for this kind of connection. I also soldered the Y-end-stop as the wires always lost connection as this connection is far away from a tight fit.

---

Slicer: Simplify3D 4.0; sometimes CraftWare 1.14 or Cura 2.7
Delta with Duet-WiFi, FW: 1.20.1RC2; mini-sensor board by dc42 for auto-leveling
Ormerod common modifications: Mini-sensor board by dc42, aluminum X-arm, 0.4 mm nozzle E3D like, 2nd fan, Z stepper nut M5 x 15, Herringbone gears, Z-axis bearing at top, spring loaded extruder with pneumatic fitting, Y belt axis tensioner
Ormerod 2: FW: 1.19-dc42 on Duet-WiFi. own build, modifications: GT2-belts, silicone heat-bed, different motors and so on. Printed parts: bed support, (PSU holder) and Y-feet.
Ormerod 1: FW: 1.15c-dc42 on 1k Duet-Board. Modifications: Aluminium bed-support, (nearly) all parts reprinted in PLA/ ABS, and so on.

The hot end will cut out if the temperature drops below -10C (which it does in the case of a disconnection) or if it goes above 300C (I think that's the current firmware setting). Anything between this is regarded as the working range. A fault that leaves the temperaure in this range is problematic; how is the firmware to know if the temperature change is normal or abnormal?

There is now a 'heat up time' control, ie if the hot end doesn't get to temperature within a certain time (M570 - [reprap.org] ). I guess control could be extended to see sudden drops in temperature as faults as well, ie those that are not within the normal rate of change of temperature cool down or heat up. However, this means tracking temperature over longer periods of time, and assessing if the current temperature fits the pattern. Probably not impossible to do, just someone needs to sit down and write the firmware...

It has generally been our policy that, while you could add extra layers of redundancy (extra thermistors, hardware heater cutouts etc) these add to the cost to pick up a relatively tiny proportion of cases, and would probably lead to many more false positives than catching failures.

Ian
RepRapPro tech support

Crouchy, normally, a disconnected thermistor will give a reading of -273C using my fork, resulting in an immediate error. So the question is, why did it give a reading of 6C instead? Do you know which wire it was that became disconnected? Can you reproduce the 6C reading?

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

The thermistor pulled out of the socket on the green wire and bent back past your probe, perhaps it shorted on the probe?

I have a print running now which looks like it will run most of the night. I will experiment with it tomorrow and let you know what happens.

Maybe you should consider isolating the probe if your test result shows you that there has been some kind of short circuit. But isolating is always a good idea.

---

Slicer: Simplify3D 4.0; sometimes CraftWare 1.14 or Cura 2.7
Delta with Duet-WiFi, FW: 1.20.1RC2; mini-sensor board by dc42 for auto-leveling
Ormerod common modifications: Mini-sensor board by dc42, aluminum X-arm, 0.4 mm nozzle E3D like, 2nd fan, Z stepper nut M5 x 15, Herringbone gears, Z-axis bearing at top, spring loaded extruder with pneumatic fitting, Y belt axis tensioner
Ormerod 2: FW: 1.19-dc42 on Duet-WiFi. own build, modifications: GT2-belts, silicone heat-bed, different motors and so on. Printed parts: bed support, (PSU holder) and Y-feet.
Ormerod 1: FW: 1.15c-dc42 on 1k Duet-Board. Modifications: Aluminium bed-support, (nearly) all parts reprinted in PLA/ ABS, and so on.

I am definitely for a firmware update. It just hit me. The connection got lost (the original connection wire with socket connection) and the firmware did not react. The readed value jumped between 185 and 250°C and the heater heated permanently. I had burning marks on the printed parts and I hope that is the whole damage.
(Sorry for the language @screenshot)

---

Slicer: Simplify3D 4.0; sometimes CraftWare 1.14 or Cura 2.7
Delta with Duet-WiFi, FW: 1.20.1RC2; mini-sensor board by dc42 for auto-leveling
Ormerod common modifications: Mini-sensor board by dc42, aluminum X-arm, 0.4 mm nozzle E3D like, 2nd fan, Z stepper nut M5 x 15, Herringbone gears, Z-axis bearing at top, spring loaded extruder with pneumatic fitting, Y belt axis tensioner
Ormerod 2: FW: 1.19-dc42 on Duet-WiFi. own build, modifications: GT2-belts, silicone heat-bed, different motors and so on. Printed parts: bed support, (PSU holder) and Y-feet.
Ormerod 1: FW: 1.15c-dc42 on 1k Duet-Board. Modifications: Aluminium bed-support, (nearly) all parts reprinted in PLA/ ABS, and so on.

I have done some more testing with this problem.

I heated the nozzle up and then set the temp to zero before I started so it would not overheat.

When I disconnected one wire of the thermistor the temperature actually dropped to toggle between -4.8, -3.8 and -2.9 degrees. The dc42 probe's LED cycled through off, bright and dim, possibly in time with the temperature reading changes, until I reconnected the thermistor, so it appears to have detected the fault, but has not set the temperature to -273.

There's a video onthe link below That shows what happens, you can see the LED changes and temperature readings. The two gaps in the temperature graph correspond to thermistor disconnection.

[www.dropbox.com]

But that means you have connected the thermistor to the probe sensor board? What happens if you connect the thermistor directly to the Duet?
As I said I normally get directly an error. Okay I had bad luck above as the contact was only loose and so the Duet was able to "read" some temperature due to the measuring procedure. Meanwhile I soldered the connection you have interrupted in the video.

---

Slicer: Simplify3D 4.0; sometimes CraftWare 1.14 or Cura 2.7
Delta with Duet-WiFi, FW: 1.20.1RC2; mini-sensor board by dc42 for auto-leveling
Ormerod common modifications: Mini-sensor board by dc42, aluminum X-arm, 0.4 mm nozzle E3D like, 2nd fan, Z stepper nut M5 x 15, Herringbone gears, Z-axis bearing at top, spring loaded extruder with pneumatic fitting, Y belt axis tensioner
Ormerod 2: FW: 1.19-dc42 on Duet-WiFi. own build, modifications: GT2-belts, silicone heat-bed, different motors and so on. Printed parts: bed support, (PSU holder) and Y-feet.
Ormerod 1: FW: 1.15c-dc42 on 1k Duet-Board. Modifications: Aluminium bed-support, (nearly) all parts reprinted in PLA/ ABS, and so on.

Quote
Crouchy
I have done some more testing with this problem.

I heated the nozzle up and then set the temp to zero before I started so it would not overheat.

When I disconnected one wire of the thermistor the temperature actually dropped to toggle between -4.8, -3.8 and -2.9 degrees. The dc42 probe's LED cycled through off, bright and dim, possibly in time with the temperature reading changes, until I reconnected the thermistor, so it appears to have detected the fault, but has not set the temperature to -273.

There's a video onthe link below That shows what happens, you can see the LED changes and temperature readings. The two gaps in the temperature graph correspond to thermistor disconnection.

[www.dropbox.com]

I have just tried to reproduce that fault, without success. I have a dual nozzle hot end board on my Ormerod and I am using firmware 1.09c-dc42. After turning on the printer and connecting the web interface, if I disconnect either thermistor from the hot end board, then the fan starts running and the web interface shows "error" for that heater.

Please can you try each of the following:

1. Instead of disconnecting the thermistor from the hot end board, disconnect the 2-pin thermistor lead from the Duet, and see what the reading is. This is to check whether the hot end board is affecting the behaviour.

2. If you have a M305 P1 command with a nonzero H parameter in config.g, try setting H to zero (you can just send the new M305 command via the web interface) and see what the reading is when you disconnect the thermistor.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

I tried disconnecting the thermistor on the duet shield and got similar results, around -5.8 degrees.

Unfortunately, I've now hit another problem that's put me out of action for the moment. See attached pictures. Not being electrically minded I have no idea if this is related at all.

I would guess you have somehow a short circuit between the extruder heating cartridge and the thermistor probably at the hot-end block at the nozzle. That would explain your strange readings and maybe your Duet is broken.

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Slicer: Simplify3D 4.0; sometimes CraftWare 1.14 or Cura 2.7
Delta with Duet-WiFi, FW: 1.20.1RC2; mini-sensor board by dc42 for auto-leveling
Ormerod common modifications: Mini-sensor board by dc42, aluminum X-arm, 0.4 mm nozzle E3D like, 2nd fan, Z stepper nut M5 x 15, Herringbone gears, Z-axis bearing at top, spring loaded extruder with pneumatic fitting, Y belt axis tensioner
Ormerod 2: FW: 1.19-dc42 on Duet-WiFi. own build, modifications: GT2-belts, silicone heat-bed, different motors and so on. Printed parts: bed support, (PSU holder) and Y-feet.
Ormerod 1: FW: 1.15c-dc42 on 1k Duet-Board. Modifications: Aluminium bed-support, (nearly) all parts reprinted in PLA/ ABS, and so on.

If just one of the heater pins was charred, I would say the most likely cause was a poor crimp connection to the socket on that pin. As several pins carrying the heater current are affected, I suspect either an internal short in the heater cartridge, or several poor crimp connections. I suggest you replace the heater cartridge, and either replace the Molex connectors on the board yourself, or return the board to me and I will replace them. I can send you the connectors if you can't source them locally. I suggest you also check the other end of the hot end loom for signs of charring on the connections to the orange and yellow wires.

Edited 1 time(s). Last edit at 07/21/2015 04:16PM by dc42.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Thanks dc42. I replaced the burnt connectors on both the cable and the probe and the printer is functional again. I actually soldered the wires to the crimps as the crimp tool I have is sub-standard.

If I disconnect the thermistor now the temperature shows "Error" in the web interface and turns the heater off.

I can only conclude that a bad crimp was responsible for my original problem as well.