Hot End Temperature Interference?

[ducky 0]

I've been playing with the ultimaker for a little while now, and and my last remaining issue seems to be with temperature. I think i have found what has been throwing me off. I searched, and found some stuff about temperature fluctuations but nothing solid with what i have been seeing.

My problem seems to be interference from when the stepper motors are on and the thermocouple readings (big black wire). I have seen this behavior when the print starts and enables the steppers for homing after heat up cycle.

Initial symptoms:

When i first turn on the ultimaker, it reports 24 C which is expected for room temp.

When i auto home the system the temperature instantly jumps to 10C and slowly climbs to 15-16c and stabilizes. And finally if i disable the stepper motors, the system will jump back to 24C instantly.

After i finally made the connection with the stepper motors, i now have the thermocouple wires, running outside of the ultimaker, instead of running through the insides, which i'm assuming they are supposed to be. I still get a 2C drop, A lot better than 10-15C. But i also have a huge wire randomly hung up on the outside. (With the steppers on i can move the wires closer and further from the y axis stepper and watch it fluctuate 2-5C more.

I check the temperatures through both the ulticontroller and pronterface console. And have verified all the wiring on the thermocouple board on the extrusion head is tight.

I'm worried i may have something wrong, or a grounding issue with the thermocouple wires. Also i'm assuming the thermocouple wiring is supposed to be routed along one of the back sides with a stepper motor? (it is rather long). Has anyone seen this behavior or have any suggestions?

 

[gr5 2,167]

I've seen other posts of this problem but don't know if they found a solution but I recommend you search and post in that thread to see if the original poster figured it out.

 

[ducky 0]

Just to update and not leave a problem unsolved: i have had little time to look into the problem, but i have put a scope on the signal wire, and did not see any interference besides a lowering of voltage. possibly interference from magnetic inductance of the motors?

Either way, i have mitigated the drop by routing the wire through the front, away from the stepper motors. Since it is was long enough. The temperature response and prints have been absolutely fantastic since then.

I'm surprised others would not have this issue though when routed by the stepper, even if to a different degree. A quick way to check,when steppers are off, is to send G28 (autohome) through pronterface and closely watch the temperatures(should jump instantly).

 

[calinb 11]

You're not alone. I've always had this problem too. It certainly causes the TC signal to "command" erroneous PID controller adjustments, but I just live with it. However, it is a shame to have a nice, linear, and accurate TC (instead of a mere thermistor), and then toss the advantage out the window by tolerating this unsolved engineering problem but, in my opinion, the electronics and cabling are not the Ultimaker's and Ulticontroller's strong suit!

Thanks for your posts, Ducky. Your findings indicate that the problem is likely not caused by stepper motor load induced "ground bounce" but rather it's caused by EMI/RFI.