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Topic: pH controller unstable in field measurements (Read 15235 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
^
^
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!!!!

quangduc191

Hello.

Anyone can update the final way can solve this problem.

I have try many ways but still can not make the PH measurement stability. It just stability when put the probe to a cup of water, when put the probe to the tank it always variant about 7.3-7.8 .

we are try to build a system for smart agriculture but we meet a lot of problem with sensor field. So i think why we don't connect together and make some sensor for everybody can use it. The commercial sensor is expensive and some time the manufacture, the don't sell the sensor only they want to sell the sensor include the controller for more expensive.

Finally, now i need some of this sensor as below that can connect to ardruino board, if you can help me please let me know:   

air: temperature, humidity, light, Co2, rain

Water: PH, Conductivity, temperature

Soil: humidity, conductivity, temperature

my email: quangduc191@gmail.com

PalfiZsolt

Hi quartapound,

I'm very newby in electrical topics and your solution is not exactly clear for me. Where should I connect the LPF exactly?

Thanks.

ieee488

Hi quartapound,

I'm very newby in electrical topics and your solution is not exactly clear for me. Where should I connect the LPF exactly?

Thanks.
On the power Vcc.

ODwyerPW

if money is not too much of an issue, take a look at these fine circuits for quantifying several water quality attributes.

http://www.atlas-scientific.com

Lots of good stuff available.
Quiero una vida simple en Mexico...nada mas.

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