Probe noise

I occasionally see the probe noise icon appear in yellow on the dash.
This is what it looks like when I click it 1622303875292.png

Is this amount of noise ok, or bad?

I have the AC noise filter to 50hz (UK) and I'm using a cheap isolated thermocouple from eBay.

Bryan Mayland

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Oof the numbers would be easier to read if you didn't post a 2000 pixel wide image :LOL:

It's not perfect due to the line noise, but it isn't terrible either with 3 ticks peak-to-peak. 1 is normal, 2 is still fine, 4 is where I'd say you'd want to do something about it.
haha sorry about that.

I've just received a better quality thermocouple so trying that instead.

I've double checked my soldering and replaced the wires that go from the PCB to the thermocouple socket.

I'm not quite sure how you read the image below. Is it supposed to be a sine wave? - you count the spikes between each peak?

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Bryan Mayland

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It is not supposed to be a sine wave, but that's what you get when there is power line noise getting into the system. What you should see is more like this

How to get rid of it is sort of a mystery, because the frequency is too low for hardware filtering to be effective. Trying different outlets can help here in the US since our outlets are mostly not GFCI protected and that seems to be the kind that produce the most issues. Most outlets in the EU/UK are protected by some means (RCD / GFCI / arc fault?) so you might have a harder time with it. I'm not sure how it gets in or how to get rid of it unfortunately.

I'd say your latest image is in the unusable territory considering over the course of 20ms the temperature has varied by roughly 4C which is more than HeaterMeter can deal with even after software filtering.
Thanks. Makes a bit more sense now. I'm trying a cook with it connected to a car battery instead. I cant see the yellow warning icon anymore so I think it must be the power line noise.

How do I bring up the noise graph without clicking on the the little yellow/red icon
they came out very well thanks :)

I had a thought. Audiophiles tend to use some sort of EMI/noise smoothing on the AC input to audio equipment.
Would something like this work for probe noise? - supressing noise before it hits the ac/dc converter.



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Bryan Mayland

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Maybe? I'm really not sure where it comes from to begin with. I can reproduce it in my kitchen if the probe sheath touches the metal of my toaster oven despite my probe being isolated (no continuity from the sheath to either of the thermocouple pins). That system works perfectly with no noise at all out at the grill or if the sheath isn't touching the toaster. How to get rid of it is just a giant mystery to me.