More details on reading noise graph


 
G

Gary V

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Brian,
Just updated my Pi from a Pi3 to the 3+. I noticed that the control is much more stabile and just seems to work better. Not sure why right now but that is what has happened. I thought is was a fluke, but swapping in the 3 and doing control and noise test, definetly showed improvement with the 3+. I suspect cpu runs hotter on 3 versus3+. 3+ now has heatsink on cpu. My main question is about the noise graph. The scale on the left is what. volts, millivolts, %, etc. Not sure what it is. I assume the bottom scale is time. As you toggle through the selection screen for different devices to monitor, the left scale values change. Is this information located on the Wiki page. I could not find it. If it is not there, could a topic be added that gives detail on what you see like the Linkmeter page shows. Being a analog guy in a digital world, i always have questions.
thanks Gary
 
That's odd. The Pi simply provides a web interface and the ability to control the HM. If you happened to update the SD card, it might have loaded a newer firmware on the ATMEGA micro controller.
 
Thanks Steve for your ideas. It is pretty strange what i have observed when changing out Pi`s.
I totally reformated the sd card prior to powering up the Pi3+ with the latest snapshot. I always keep the firmware updated. Used the same sd card. The controls work exactly like they should now. A deviation from setpoint gives smooth pulsed steps to correct back to zero. The damper moves without any extra jitter which has always plagued my control even with the capacitor added to the servo power rail. Now smooth one step at a time. I do see there are differences with the pi 3 and Pi3+. Different wifi chip, higher clock speed for processor. later processor revision, heat sink on processor. It acts like there has always been a slight issue with the data transfer from the heatermeter buss to the Pi buss. My noise is much lower now than it was before. That`s how i got going down this rabbit hole. I have gone back and forth numerous time swapping the Pi`s out with same result. The Pi 3+ when used with my heatermeter boards just works better. It would be interesting if someone else has seen this or it`s just my setup.

Still interested in what the scaling on the left side of the noise graph is. Hope someone can offer some info on that and other questions i was looking for in my original post about noise graph.
 
Gary V said:
Still interested in what the scaling on the left side of the noise graph is. Hope someone can offer some info on that and other questions i was looking for in my original post about noise graph.
Click to expand...
The scale is "ADC counts" and varies based on what you're looking at, but always represents voltage. For thermistor probes the scale is 1023 = 3.3V (or whatever the 3.3V voltage rail is). For thermocouples, it could either be that or 1023 = internal bandgap voltage, depending on the temperature. The internal bandgap is around 1.1V. It switches between the two somewhere around 400-500F but it depends on the actual bandgap voltage and if the temperature is going up or down.

Really the noise graph is just there to show you if you have noise. All points should be within 0-1 of each other for 3.3V reference, or 1-3 for bandgap reference. The button one, only the first bit of the graph is used since the buttons don't get full 255x readings the other probes do.
 
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