thermocouple issues

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By godnemoz 13 April 2017 19:26

Member · 11 comments

Hi
I have a duet wifi with a thermocouple in my heated bed it keep jumping up to 2000c even when only the 5v power supply is going so I was wondering if there was a filter in the temp so it did not register just the 2000c would that work?

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By dc42 13 April 2017 19:38

Administrator · 2,672 comments

Themocouples only output about 40 microvolts per degC, so the wiring between the thermocouple and the daughter board picks up interference easily, especially by induction. Use twisted pair wiring all the way back to daughter board, and keep it away from other wiring as far as possible. If you are using a bare tip thermocouple, make sure that the thermocouple tip is insulated from the printer metalwork. If you are using a cartridge thermocouple, grounding the cartridge housing may help.


Duet WiFi hardware designer and firmware engineer
http://www.escher3d.com
https://miscsolutions.wordpress.com

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By godnemoz 13 April 2017 19:55

Member · 11 comments

Its a cartidge thermocoupling ill try earthing the heated bed to see that makes a difference
It insulated wire within a braded metal outer
The bed has a AC heating pad on witch I havent been able to try yet beause of this issue

Last edited by godnemoz (13 April 2017 20:06)

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By Shotfire 13 April 2017 20:22

Member · 8 comments

I was able to fix that problem by taking a piece of RG-59 coax (Same stuff used for cable tv) and removing the inside conductor and white insulation but leaving the wire shield in there. I helps to warm the cable up in the oven at a low temperature before pulling the the center conductor out, it helps to have two people, you have to work it out a little at a time. Then I ran the thermocouple wires through the cable, there should be plenty of room, on my dual head I ran two thermocouple's through it. Then on the Duet side solder a short wire (the shorter the better) onto the shield wires in the RG-59 coax, put some heat shrink over the connection, then connect the other end of the short wire to a ground on the Duet board, any ground should work. Problem solved. David, you may want to put this fix in the Wiki since this seems to be a re-occurring problem.

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By dc42 13 April 2017 20:54

Administrator · 2,672 comments
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By godnemoz 14 April 2017 02:49

Member · 11 comments
dc42 wrote

Themocouples only output about 40 microvolts per degC, so the wiring between the thermocouple and the daughter board picks up interference easily, especially by induction. Use twisted pair wiring all the way back to daughter board, and keep it away from other wiring as far as possible. If you are using a bare tip thermocouple, make sure that the thermocouple tip is insulated from the printer metalwork. If you are using a cartridge thermocouple, grounding the cartridge housing may help.

Is there on way to filter the noise (2000c)  out by firmware so that it ignores the 2000c reading

I tryed to strip some coax cable but the sheild wire keeped coming with it then i tryed just earthing the sheild thats already on the thermocoupling and that just gave a reading of 2000c then I connected it to a rex_c100 and that read the thermocoupling with out no nosie

Last edited by godnemoz (14 April 2017 02:49)

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By dc42 14 April 2017 06:57

Administrator · 2,672 comments

The firmware already does some filtering.

What is a rex_c100 ?


Duet WiFi hardware designer and firmware engineer
http://www.escher3d.com
https://miscsolutions.wordpress.com

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By godnemoz 14 April 2017 08:49

Member · 11 comments
dc42 wrote

The firmware already does some filtering.

What is a rex_c100 ?


rex-c100 is a Digital PID Temperature Controller

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By dintid 20 April 2017 10:52

Member · 44 comments
dc42 wrote

The firmware already does some filtering.

What is a rex_c100 ?

I'll pipe in here, as I have the same problems, only with Thermocouples on hotend.

I have tried 2 different original daughterboards, so I think we can say the fault isn't here.
I've tried both channels on both boards.

Issue:
it shows temperature fine when using short wire at 10cm. - when I put by hand around it, it starts heating up just fine.
When using long wire (up to hotend) the temprature is mostly fine when thermocoupler isn't touching anything - as soon as I touch it, it jumps to 2000c
When installing in hotend it's just at 2000c constantly.

I've run a wire away from the machine, away from any potential interference, but as soon as I touch the thermocouples the temperature jumps to 2000c.

I've tried at least 5 different thermocouplers... they all work fine on other controllers/firmware combos (marlin, smoothie etc)...

Last edited by dintid (20 April 2017 10:53)


RepRapFirmware supported G-codes: https://duet3d.com/wiki/G-code

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By dc42 20 April 2017 17:49

Administrator · 2,672 comments

Did you read the wiki page on connecting thermocouples?


Duet WiFi hardware designer and firmware engineer
http://www.escher3d.com
https://miscsolutions.wordpress.com