Odd Temperature Readings with multiple probes


 
C

CSchaaf

TVWBB Member
I've been using my HM without issue for a few months now, but hadn't ever tried more than 2 probes (thermocouple and a single food probe) until the other day when I tried connecting a second probe.

I did some boiling water tests today and here are my results.

I have three probes
  1. Probe A = Thermocouple
  2. Probe B = Food probe always using Port 1 in these examples
  3. Probe C = Food probe always using Port 3 in these examples

Here is the first example of me testing Probes A and B


Now A, B, and C - you can see that C's temp is way off, and it also caused probe A to read high


Now A and C - both are high


Now just C and it's back to normal.


Any ideas? What other tests can I do?

Thanks!
 
Questions / things to try:

  • Do you have the Vishay 10k thermistor soldered onto any of the jacks?
  • Verify that the correct probe presets are selected on the config screen.
  • Swap the 2 thermistor probes, B and C between the jacks they're plugged into and re-run the same tests.
  • Do the temps fluctuate if you touch the external braid on the probe cable?
  • Try a different power supply.
  • Try the "A/C input line noise filter" in the config.
  • Run the hm-noise firmware to see if it provides any insight.
  • Inspect the HeaterMeter PCB for any suspect solder bridges near/around the probe jacks and surrounding components.
 
As Steve said, swap around the probes to see if the odd temps move with the probes or stay with the probe jacks. (Never submerge probes, that is a sure fire way to make them flake out) If the odd readings stay with the probe jacks rather than move with the probes then you probably have a HM issue rather than a probe issue, and vice versa...
If it turns out to be a HM problem check all the stuff Steve mentioned, if no joy then do a reflow on the solder of all the parts between the ATMega and the edge of the board where the probe jacks are (including the probe jacks). Pay particular attention to the resistors and caps that are standing on end, and also reflow the solder on the last four pins of the ATMega (the ones on the corner near the TC amp parts). After doing the reflow clean the board with isopropyl alcohol and a soft brush (like a tooth brush) or some flux remover. Make sure to let the solvent dry out before you power the HM up again.
 
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