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Topic: pH controller unstable in field measurements (Read 12433 times) previous topic - next topic

quartapound

#30
Mar 29, 2017, 10:52 pm Last Edit: Mar 29, 2017, 11:08 pm by quartapound
... I am going to try to fit a LPF in there, with a 100K resistor, 50 nF capacitor, for a T of 5 ms and a cutoff frequency of ~30 Hz
...
low pass-filters at 10 Hz before the ADC
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^
THIS!!!  Totally worked for me.  I had severe ground loop/Galvanic isolation issues trying to monitor pH in my saltwater tank.  Powering the arduino (and the probe) from a laptop on battery power confirmed this was the issue because the numbers were rock solid until I plugged in the laptop AC adapter, or attached the external PSU to the arduino... at which point the numbers would deviate.


....to replicate your 10Hz low pass filter I used a 220k resistor and 70nF capacitor....BINGO!

now I'm getting the same stable numbers on mains power as I did on laptop battery power!! I've been banging my head against the wall all week trying to fix this issue, THANK YOU SO MUCH!!!!

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