Pronterface heatbed temps showing strangely...

Can't find a forum to stick Pronterface questions in so here it is...

I have an issue with my Gen7 1.3 (modded with constant temp sensing on standby 5v), running Marlin.

Pronterface keeps showing random drops in the heat on the heatbed. I can't see how it could be the thermistor as that is firmly siliconed to the bottom of the board with heatpaste as well. Here is an image of it acting up strangely.

Any ideas on what it may be... And should I worry?

Check to make sure that your thermistor wire connections are good on the end that connects to your Gen7. Also, double check that all open wire was properly covered with heatshrink. My first guess is that you have a lose connection or some form of contact with your thermistor wire.

I haven't needed heatsink grease for my thermistors, but that shouldn't be causing the rapid drops in your readings. Does the rest of your system appear to function properly?

Strange,

Are your Heat Resistor wires wrapped around your thermistor wires?

The high current from the Heat Resistor turning on and off creates a pretty good magnetic field, and could be affecting the low voltage reading of the thermistor.

I was having the same issue on my hot end.

I replaced the thermistor wires with shielded twisted pair, and added a tantalum capacitor just before the ramps board, and the drops have all gone away.

This was after throwing a scope across the thermistor line and seeing how bad the noise was...

-Rob A>

Very interesting. Would of never thought of that. My wires are running together (zip tied).
I'll look it next time I get time.

Sorry to bring this back to the top but I needed to add that I just had the printer apart and while I was there I took the zip ties off the two sets of wires, wrapped the sensor wire in aluminium foil (1 to 2 layers, nothing really clean or tidy), sticky tapped it on, zip tied the wires back together and now Pronterface shows an accurate steady reading.

Cheers for the help!