Thermocouple wiring - effect of adding connectors

[Alex Gibson]

Hi all

 

Some of my work 3D printers use K-type thermocouples.  The way they are integrated into the wiring harness makes maintenance annoying – they are fragile, screw into the heater block and complete replacement requires pulling the printer from its home and upending it on a table and faffing about with zip ties a lot. It would be useful to be able to place a connector near to the thermocouple like other functions.

 

I’m aware that interrupting a thermocouple wire with dissimilar metal connectors effectively makes additional thermocouple junctions, which will complicate things and at least reduce accuracy.  I’ve also read that the closer to the thermocouple end this happens, the worse – hence the TC reading chip being right next to the screw terminals – and I’m thinking of 5cm from the TC junction, about 80cm from the PCB end.

 

The ‘right way’ to do this would be to use dedicated thermocouple connectors, which use the same metals as the TC wires - but they’re so bulky they defeat the point.

 

BUT – I’ve read that if generic connectors are used, the additional thermocouple effects on each leg of the wire somewhat cancel out.  Accuracy may be affected, but relative temperature still reads.  Is that true?

 

I already mentally/in slicer offset the temperatures reported by Makerbots by 10 degrees compare to thermistor based printers – so I’m wondering whether it’s worth trying to just do it, use a standard Molex Micro-fit 3.0 connector and see what the impact is… as long as the hot end temperature is anywhere in the range the firmware will accept, I can adjust to it.

 

Before sacrificing one for science and just testing it, I wonder if anyone can speak from experience about the likely outcome, or has any tips?

 

Would using a small choc-block style connector to directly connect the thermocouple wires similar metal to similar metal be a big improvement?  I might try this first…

 

Cheers,

 

 

Alex Gibson

 

+44 7813 810 765    @alexgibson3d    37 Royal Avenue, Reading RG31 4UR

 

admg consulting

 

edumaker limited

 

·         Project management

·         Operations & Process improvement

·         3D Printing

 

[Brad DrunkenTraitor]

Many moons ago, talking to an engineer fixing an ice machine i had a very similar conversation. 

His take on it was that if you strip the conductors back far enough and make sure it goes all the way through the connector block, the ends of the two conductors will contact each other in the middle, leaving the connector as a simple mechanical connection rather than an electrical one. It leaves the reading close enough for an ice machine, but in that case the exact reading wasnt critical. 

In theory, the material used for the connector becomes near irrelevant. 

Maybe print up some plastic clamps that deal only with the conductors, and without any extra metallic material to interfere?

I havent personally investigated, but the theory stands to reason.