Hot end thermistor problems

Hi

So far it appears we nearly have a fully functional printer, but we are having some problems with the hot end thermistor.

If we install as instructed we are getting the error message Temperature measurement fault for the hot end sensor. We have removed this and checked the resistance and get a reading of around 90 which decreases if we hold the thermistor so it gets warmer.

We continued with the rest of the commissioning instructions and everything else functions except the hot end will not heat up i guess due to not having a good reading from the thermistor.
After checking and checking again we decided to hold the thermistor in the fingers to warm it up and the error message went away - this then enabled us to heat up the hot end a bit so it had some heat. We then turned of the machine replaced the thermistor in the block and then it all works.

My question is what could be causing the problem in the first place? and how can we resolve it?

The unit has jp9 in place.

Thanks

Martin

1. When it reports the error, what temperature does it give, and what is the actual temperature? If it reads below -30 then it considers that an error and the heater won't come on.

2. Which firmware version are you using? The latest (V0.53) firmware corrects an over-sensitivity in the interpretation of the thermistor resistance, which typically results in more accurate (higher) temperature readings at low temperatures. So if you are using an older version of the firmware then it may be worth upgrading. You need to update the files on the SD card as well.

---

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].

Hi

1. The temperature is initially showing at -273 in the error, but after being manually warmed up we do not get any errors.

2. We are using v0.53 firmware and was still the same in v0.50.

Thanks
Martin

Quote
msavage
Hi

1. The temperature is initially showing at -273 in the error, but after being manually warmed up we do not get any errors.

2. We are using v0.53 firmware and was still the same in v0.50.

Thanks
Martin

Sounds like one of the thermistor wires have come off, check the thermistor connections and make sure they are connected correctly and snug.

Paul

---

RS Ormerod No 436

Hi Martin

How are you powering the board? Low 5V voltage can cause various anomalies. See: [www.reprappro.com]
If you're one of the first 220 Ormerod owners, see this: [forums.reprap.org]

Ian
RepRapPro tech support

All wiring checks out and if I was to put a resistor in place of the thermistor there are no errors.

We are powering with the PSU and jp9 in place and we still have a usb connected.
When it was powered from USB only we always struggled to get more than 4.5v on pin 1 even if we used a powered usb hub.

We have machine number 267.

Edited 1 time(s). Last edit at 01/10/2014 07:39AM by msavage.

Hi Martin

It sounds like a bit of a loose connection. Check through the wiring. Check that all the crimps are pushed into the crimp housings in the loom, and that the connections are tight on the ends of the thermistor.

Ian
RepRapPro

okay, but would that explain why it works after warming the thermistor manually (between the fingers) then replacing it into the block?
Once it has a temperature close to body temperature it continues to work until the heating block is turned of for a period of time then we have to go through the same process again.

I have a similar experience with the hot end thermistor.

Morning start up, the hot end often reads -273 (e.g. [°C] = [K] − 273.15) i'm pretty sure its not 0 degrees Kelvin in my room!!
To rectify this I zero Z axis then warm up bed first, do a Duet reset then the 100k hot end thermistor is kicked into life, don't ever touch the wiring. The warmth from the bed must be similar to msavage "massaging" his thermistor =D

Seems to be a bit like my on Austin Mini, hates early morning cold starts!

Matt

Edited 1 time(s). Last edit at 01/10/2014 10:41AM by iamburny.

---

Limited Edition Red RS Ormerod 1 #144 of 200 - RRP 1.09fw
iamburnys Ormerod Upgrades Github
Follow me on ThingiVerse My Designs

Sounds like a good idea - I will give that a go.

Thanks

If it's saying -273 then that corresponds to an analog reading of zero. Looks to me like either the thermistor circuit has an intermittent open circuit, or an intermittent short circuit to ground.

You could try measuring the voltages at either end of the thermistor while the Duet is reporting -273C. Should be 3.3V at one end, and some fraction of a volt the other end (at room temperature).

---

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].