Wiring loom resistance

The cold temp of my head thermistor regularly reads between -11.2c and +6.8c, I know it is not as accurate out of its operating range however when connected directly to the pins on the duet it reads nearer 17c to 20c, I therefore measured the resistance in the loom cables that run to the thermistor, they both measured 1.3ohms, I this high? normal? I've no idea what to expect from such a short length of cable, could someone please test theirs for comparison please?

Matt

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Limited Edition Red RS Ormerod 1 #144 of 200 - RRP 1.09fw
iamburnys Ormerod Upgrades Github
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1.3 ohms extra resistance would be undetectable, since the resistance at room temperature is 100K or more and the ADC is run in 10-bit mode. Are you sure that the thermistor wasn't being warmed by your fingers or by heat radiated from the stepper driver chips when you connected it directly to the pins on the Duet?

Edited 1 time(s). Last edit at 01/20/2014 05:50AM 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].

It is totally possible that my warm fingers increased the reading, i'll replace the cables and see how it goes i think.

it doesn't seem to affect my prints at all, just being fussy i guess

Matt

Edited 1 time(s). Last edit at 01/20/2014 06:10AM by iamburny.

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

My finding was that the legs of the thermistor have to be fully isolated else they could touch the heating block which results in false reading (my guess only). After covering the legs with only the resistor left free, I got pretty accurate readings.

@adsoftware: You didn't put the ptfe heatshrink on the hot end thermistor? It should cover it completely, leaving just the wire ends free, to hold it in the hot end, and insulate it. A better picture of the ideal is in the Tricolour Mendel instructions: [www.reprappro.com]

Ian
RepRapPro tech support

Indeed, I cut the middle and left it open a tiny bit and the reading is quite accurate. In fact, I get the same temp result as from my other thermometers.