Sral
Valuable Member
First Feature: the RoboTank pH circuit Accuracy Thread
It starts with some discussion and info on the Accuracy and reliability from members and @robsworld78 , the creator of the circuit. Interesting read if you are into it.
@servus then mentions unstable readings with his circuit:
So he get's unstable readings with other equipment in the tank, when they are connected to AC sockets, irrespective whether they are on or off. This is understandable since switches might not sever all three connections an AC socket can have: Neutral, AC lead and Ground. As soon as the plug is in you have some electrical connection doing different things, or even nothing depending on your setup.
@servus then continues with longer term measurements:
First helping suggestion from @robsworld78 to measure the voltage between the tank and the AC socket's ground
(he suggested measuring AC, but you can measure both AC and DC)
His answer is of course: yes, there is a high voltage if you don't use a grounding probe.
It starts with some discussion and info on the Accuracy and reliability from members and @robsworld78 , the creator of the circuit. Interesting read if you are into it.
@servus then mentions unstable readings with his circuit:
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
So he get's unstable readings with other equipment in the tank, when they are connected to AC sockets, irrespective whether they are on or off. This is understandable since switches might not sever all three connections an AC socket can have: Neutral, AC lead and Ground. As soon as the plug is in you have some electrical connection doing different things, or even nothing depending on your setup.
@servus then continues with longer term measurements:
Great stuff, so reef-Pi reloads and everything seems fine, but over night some problem emerged. So nothing that you would expect since nothing changed, right ? Well, there could again be several things at work here. I am thinking (and I am no expert) that maybe some electrical equipment in the house introduced a disturbance on the power line / neutral line / ground that got transferred to the tank or the circuit, or that the disturbance was there all along and just needed time to build up a potential difference that then starts to disturb the probe. Again, several things that are very setup specific.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.
First helping suggestion from @robsworld78 to measure the voltage between the tank and the AC socket's ground
(he suggested measuring AC, but you can measure both AC and DC)
His answer is of course: yes, there is a high voltage if you don't use a grounding probe.
Sadly this is where the info ends, @robsworld78 continues thinking about a faulty/noisy Power adapter, and I suggest measuring the calibration fluid with a grounding probe inside, since those are typically in a highly insulating plastic container that shields you from any electrical disturbances.
Sral
Valuable Member
So messages to take away from that:
- fluctuating and offset pH measurements in the tank when equipment is plugged into the AC sockets
- when you test something, write it down you so can describe it as accurately as possible ^^
Methods of getting info on the problem:
- measuring DC and AC voltage between the tank and the AC ground
- try also measuring DC and AC voltage between the tank and your circuit's ground
- unplug all equipment one by one and watch the pH readings and measure the DC+AC voltage as above
- see if restarting Reef-Pi has some influence
- try a grounding probe between the tank and the AC socket's ground
- again, watch the pH readings and the DC+AC voltages as described above
- try adding a grounding probe to your calibration liquid and see if that makes it worse
- try adding a probe to your calibration liquid that connects it to your tank and see if that makes it worse
Ultimately:
- Seems like and electrical disturbance on the tank or the circuit
- sadly the discussion stopped so we don't have any more specific info on this specific problem or it's solution
- fluctuating and offset pH measurements in the tank when equipment is plugged into the AC sockets
- when you test something, write it down you so can describe it as accurately as possible ^^
Methods of getting info on the problem:
- measuring DC and AC voltage between the tank and the AC ground
- try also measuring DC and AC voltage between the tank and your circuit's ground
- unplug all equipment one by one and watch the pH readings and measure the DC+AC voltage as above
- see if restarting Reef-Pi has some influence
- try a grounding probe between the tank and the AC socket's ground
- again, watch the pH readings and the DC+AC voltages as described above
- try adding a grounding probe to your calibration liquid and see if that makes it worse
- try adding a probe to your calibration liquid that connects it to your tank and see if that makes it worse
Ultimately:
- Seems like and electrical disturbance on the tank or the circuit
- sadly the discussion stopped so we don't have any more specific info on this specific problem or it's solution
Last edited:
Sral
Valuable Member
Second Feature: @Krheigh in the main reef-Pi thread
Standard question from @Ranjib :
Galvanic isolation means, that the pH circuit's power, ground and signal lines are electrically closed off from the main AC power and ground. The idea behind this is that any electrical disturbance / voltage difference between your tank and your circuit can not cause a current through the pH probe through your circuit, which will throw it's measurement off very easily.
His answer is sadly not a direct one towards Ranjib's question, so we do not know whether that was the reason:
However, the solution may actually be quite ingenious. Fill a small chamber with water from the tank, then measure that. If the small chamber is made of plastic, connected by silicone tubes and has no standing water connection to the tank, it might not be disturbed by whatever is causing the problem in the tank.
It basically achieves galvanic isolation, but on the side of the probe, not the circuit ^^
I did try to explain to him what Ranjib meant with galvanic isolation.
So he has unstable readings as well, but they seem slightly different: there are massive spikes up to pH 10.Any ideas what to do?
I recently installed a pH probe it works but it fluctuate way to much (see image)
When in calibration fluids it doesn't fluctuate at all.
Standard question from @Ranjib :
That's actually the first thing you should watch out for, so it should probably have been Feature 1 ^^
Galvanic isolation means, that the pH circuit's power, ground and signal lines are electrically closed off from the main AC power and ground. The idea behind this is that any electrical disturbance / voltage difference between your tank and your circuit can not cause a current through the pH probe through your circuit, which will throw it's measurement off very easily.
His answer is sadly not a direct one towards Ranjib's question, so we do not know whether that was the reason:
So he maybe has no isolation.
However, the solution may actually be quite ingenious. Fill a small chamber with water from the tank, then measure that. If the small chamber is made of plastic, connected by silicone tubes and has no standing water connection to the tank, it might not be disturbed by whatever is causing the problem in the tank.
It basically achieves galvanic isolation, but on the side of the probe, not the circuit ^^
I did try to explain to him what Ranjib meant with galvanic isolation.
Sral
Valuable Member
Things to take away from this:
- always try to galvanically isolate your pH circuit
- maybe you can also isolate the circuit from the tank, but sadly @Krheigh never reported whether either his separate chamber approach or the isolator was successful. Maybe he sees this and alleviates this ^^
- always try to galvanically isolate your pH circuit
- maybe you can also isolate the circuit from the tank, but sadly @Krheigh never reported whether either his separate chamber approach or the isolator was successful. Maybe he sees this and alleviates this ^^
Sral
Valuable Member
I'm happy to report that @servus from the first feature, a problem with erratic pH readings and spikes, has found a solution as explained in his Post in the Robo-Tank Accuracy Thread:
That's something I was wondering about as well, since power supplies usually don't feature grounding. So lesson here:
- try grounding your circuit !
(but try doing it over a resistor and a current sensing multimeter first, I don't want you shorting something ^^)
Great stuff !
That's something I was wondering about as well, since power supplies usually don't feature grounding. So lesson here:
- try grounding your circuit !
(but try doing it over a resistor and a current sensing multimeter first, I don't want you shorting something ^^)
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