Robo-Tank pH circuit accuracy

[servus]

I signed up with adafruit, captured data for tonight. The pH measurement started being stable after a reef-pi reload, however after about 2 hours it went back to improper measurements (see chart below). I have no clue what's going on here, I cannot think of anything that changed on the electrical side between correct and erratic measurements.

 

[robsworld78]

Ah that's

Forgot to mention in the initial post: by "turning off" a device, I meant actually turning off all individual switches on the power strips.

Anyways, I unplugged every device today, and that was the ONLY way I got a SOMEWHAT close and stable reading. As soon as I even plugged in a device, even with the power strip switch off, the reading started jumping around.

1 - unplugged ALL devices
2 - measured with probe outside the sump, in a vial, pH reading about 7.4 (CORRECT!!!)
3 - placed probe back in the sump
4 - about half between 3 and 4 moved robotank, so the pH wire is not close to ANY other wire
4 - right after 4 plugged in the InkBird controller, without the power strip switch turned on
4 to 5 plugged back in all devices and turned on
5 - all devices plugged back in and turned on, pH reading about 6.4

That's not looking so good, it certainly seems voltage related. Do you have a voltage meter you can use to test your water. If you set the voltage meter to measure AC and then put the black probe in a ground on one of your AC sockets and then the other probe touch the water. See what you get. On my tank I have 0.4v, I'm thinking you'll be much higher.

 

[robsworld78]

oh, forgot that. Is the schematic opensourced ?

Not at the moment but if I ever have to leave the scene I'll be sure to post everything.

 

[servus]

Hi Rob,

I did measure voltage in the tank... and of course I get high readings without a grounding probe... with the ground probe in, the measurement is negligible, similar to yours. I have experience with LV/HV/controls/software... that's pretty much my life.

I could not identify yet any consistencies between any factors at this point and correct/incorrect pH reading, except measuring in a bottle outside the tank. Again, what puzzled me was that after a reef-pi reload all of the sudden got 2 hours of proper readings, without anything changing on the tank except light intensity.

I will keep investigating, will keep you posted in relation to any new finds.

 

[robsworld78]

Hi Rob,

I did measure voltage in the tank... and of course I get high readings without a grounding probe... with the ground probe in, the measurement is negligible, similar to yours. I have experience with LV/HV/controls/software... that's pretty much my life.

I could not identify yet any consistencies between any factors at this point and correct/incorrect pH reading, except measuring in a bottle outside the tank. Again, what puzzled me was that after a reef-pi reload all of the sudden got 2 hours of proper readings, without anything changing on the tank except light intensity.

I will keep investigating, will keep you posted in relation to any new finds.

I think there has to be something in that tank, if I really thought it was the circuit I would be quick to send another but I think something is causing. It's not fun but the only other test I can think of is slowly removing things physically from the tank until it's like a cup of water, surely that would help identify something.

 

[servus]

LOL I went through that exercise, I will keep on trying.
By no means I am thinking it's the circuit, on the contrary, since it obviously works perfectly with the probe in the cup. I am just puzzled, and don't have experience with pH measuring. It was very interesting that with everything unplugged, except the robo-tank and the probe, I still had weird readings.
Again, by no means do I believe it's the measuring system, observations definitely point to something in the tank... improper grounding? Electrical panel and grounding AND earthing seem ok.
I will look more into it when I have time, as it is very puzzling.

 

[robsworld78]

LOL I went through that exercise, I will keep on trying.
By no means I am thinking it's the circuit, on the contrary, since it obviously works perfectly with the probe in the cup. I am just puzzled, and don't have experience with pH measuring. It was very interesting that with everything unplugged, except the robo-tank and the probe, I still had weird readings.
Again, by no means do I believe it's the measuring system, observations definitely point to something in the tank... improper grounding? Electrical panel and grounding AND earthing seem ok.
I will look more into it when I have time, as it is very puzzling.

I wonder about another possibility, maybe it's a noisy AC adapter powering the controller but still wouldn't explain why it's good in a cup. If you have a long extension cord maybe try plugging controller in a different circuit in your house.

 

[Sral]

Bumping my thoughts about this:

- maybe you have some ground loops, as soon as you connect devices, you create a loop
- if you measure in a cup, try sticking the ground probe into the cup as well
- test all the ground-pins in your AC, we fried a 6000$ antenna because a ground clamp was broken off, so our 100V power source had a floating ground ...

 

[KonradTO]

any updates?

 

[Sral]

any updates?

@PlantedAquaChicago had a similar problem in the reef-Pi main Thread. He did use an EZO circuit however.

He had consistent readings of pH 20-24 in the tank, whereas the calibration liquid read normal. Once he connected his tank to his circuits ground, the readings went to normal. He also notes that his circuit had a floating ground.

This could be a similar problem, that some part of the circuit or an external disturbance causes the circuit‘s ground (or the tanbk's) to fluctuate, which causes a voltage difference to the tank, leading to a disturbance in the pH reading, as that’s electrically connected to the tank. Also: the calibration liquid typically comes in a plastic container, which isn't conductive and would therefore be much less sensitive to disturbances.

solution might be better isolation on the pH circuit, grounding the tank or grounding the circuit. Maybe @PlantedAquaChicago has some news by now

 

[KonradTO]

@PlantedAquaChicago had a similar problem in the reef-Pi main Thread. He did use an EZO circuit however.

He had consistent readings of pH 20-24 in the tank, but not in the calibration liquid. Once he connected his tank to his circuits ground, the readings went to normal. He also notes that his circuit had a floating ground.

This could be a similar problem, that some part of the circuit or an external disturbance causes the circuit‘s ground to fluctuate, which causes a voltage difference to the tank, leading to a disturbance in the pH reading, as that’s electrically connected to the tank.

solution might be better isolation on the pH circuit, grounding the tank or grounding the circuit. Maybe @PlantedAquaChicago has some news by now

I am very interested in following the discussion at this point. I get some (stray) voltage in my tank. It's about 12 volts, 6 of which are induced by an old heater and the rest go down when I disconnect the temperature probe and the kessil jack from the Robotank. Since it's stray voltage only and its low I did not do much about it, but since I will soon add a pH probe to my Robotank board I might have some problems as well... I never grounded my tank before (shops don't even sell the grounding probes here in EU and no one I know does use the grounding probe) but I will try to find one online when my pH readings go weird

 

[robsworld78]

I am very interested in following the discussion at this point. I get some (stray) voltage in my tank. It's about 12 volts, 6 of which are induced by an old heater and the rest go down when I disconnect the temperature probe and the kessil jack from the Robotank. Since it's stray voltage only and its low I did not do much about it, but since I will soon add a pH probe to my Robotank board I might have some problems as well... I never grounded my tank before (shops don't even sell the grounding probes here in EU and no one I know does use the grounding probe) but I will try to find one online when my pH readings go weird

Let us know how it goes, hopefully it's not a problem, normally it isn't.

 

[InactiveAcct]

@robsworld78 Pretty amazed at what I've been seeing with your ph circuit. Wondering if you know whether it's compatible with pi pico and if you have a library for that? I was looking at your code and it was importing arduino - new to microcontrollers, thought I'd ask.

 

[servus]

I haven't been following this thread regularly, as I did not have any updates. Here's my update from today, after a few radical changes:
- moved to new tank
- sump in the basement
- new tank and sump on separate, independent circuit, directly from the panel, grounded properly (as far as I measured it)
- different lights, powerheads, heaters, return pump, skimmer
- same erratic pH readings (!!!!!!!); read pH in a cup - 7.9, stable; read pH in the sump - around 6.5, with drops to 6.2, 6.1 sometimes
- placed grounding probe in the sump, right next to the pH probe, same results
- turning off 2 months old Vectra pump, pH reading 7.7

The fact that I can't identify where it's coming from is killing me! It's got to be from the circuit somehow.

I was thinking about grounding the probe BNC connector - good idea?

I looked at the main thread, will follow some of the recommendations and post conclusions here.

 

[servus]

I am happy to report:
- grounding the GND pin of the "Feeder" connector (basically DC ground) fixed the problem!!!!

It appears the ground is not properly connected, most likely inside the power supply purchased from Amazon. Thanks, guys!!!!!

 

[robsworld78]

@robsworld78 Pretty amazed at what I've been seeing with your ph circuit. Wondering if you know whether it's compatible with pi pico and if you have a library for that? I was looking at your code and it was importing arduino - new to microcontrollers, thought I'd ask.

Good to hear, it is compatible with any microcontroller that has I2C but currently I don't have any code for a Pico, I believe that uses python so it will be quite different. I'll have to get one and get it working, good reason to buy the new Pico W with wifi. The idea is an "R" character followed by a zero will return the pH. I attached a sketch for an Arduino as an example.

 

[robsworld78]

I am happy to report:
- grounding the GND pin of the "Feeder" connector (basically DC ground) fixed the problem!!!!

It appears the ground is not properly connected, most likely inside the power supply purchased from Amazon. Thanks, guys!!!!!

Right on, thanks for sharing. Just to clarify where did you ground it to?

 

[servus]

Right on, thanks for sharing. Just to clarify where did you ground it to?

Earth ground... at the moment it's just a piece of wire going to the outlet ground.

 

[robsworld78]

Earth ground... at the moment it's just a piece of wire going to the outlet ground.

It doesn't matter now but I'm thinking the DC adapter powering the controller doesn't have a ground, maybe if it did that wouldn't be needed.

 

[Sral]

It doesn't matter now but I'm thinking the DC adapter powering the controller doesn't have a ground, maybe if it did that wouldn't be needed.

Depends on the internal wiring I guess. I am using your 12VAC/DC Converter with LM2596 DC/DC step down to 5V. The LM2596 is not isolated completely, so the GND is the same on all my 12V and 5V rails.

The AC/DC Converter has a Earth connection, but only uses that to earth its cage, not to give a defined GND level. I’ll have to earth that using a resistor and capacitor as well, I think.