Backyard Aquaponics
A place to discuss aquaponics

Hi,

I have posted on here before with a question about using a DS3234 RTC, I got that all figured out and now I want to introduce a pH probe into my system. I bought an Atlas Scientific pH probe (linked below).
The problem I am having is that after I calibrate it and put it into my tank it gives me random readings, however when I put it into the calibrating solution it gives me the correct readings.

Has anybody here tried using an Atlas Scientific pH probe before and experienced the same or a similar problem?
Are there any other pH probes from other companies that would be recommended?

pH probe: http://www.atlas-scientific.com/product_pages/probes/ph_probe.html

Are the readings actually random or do they just fluctuate all over the place. I'm thinking this has something to do with all the particulates in the system water and the turbulence created by the pumps. If you take a sample out of the tank and let it settle, then measure, how does the pH come out?

Note: You'll probably see a gradual pH drift so only let the sample settle for a fairly short period.

When you say "random readings", do you mean:

(a). Rapid reading fluctuations, ie: the reading is rapidly bouncing all over the place.
(b). When testing the reading is stable, but varies quite a bit between tests.

Electrical discharge from submersible pumps, heaters etc, can cause erratic, rapid fluctuations in the reading. Try taking a sample of the water from the system in a clean glass and see if you still get fluctuations when testing that. If not, then your pump etc may be giving of a small electrical discharge.

Thanks that's handy too know, I gave up on mine because it gave a totally different reading to the test kit and couldn't be trusted. I'll resurrect it and see how it performs.

This is something I've not seen. I would have thought using a magnetic stirrer within an inch or two of a pH probe, which I've done in the lab, would cause the same problems. If this is the cause it must be dependent on the type of probe.

What I mean by "random readings" is that they fluctuate all over the place. I have tested the pH probe by putting it in a glass of tank water away from the pump and the numbers I get are all over the place. I have tried doing this with different liquids with different pH, but the readings I get fluctuate all over the place. Like I said in the first post, the only time I get the correct readings is when I put the pH probe in the calibrating solution.

I have 4 of the atlas scientific probes and 4 of the EZO pH circuits they sell. I have tested all of them and they all do the same thing. Is it possible that they are all defective?

EZO pH circuit: http://www.atlas-scientific.com/product ... zo_ph.html?

From reading the manual it sounds like the EZO pH circuits are very sensitive to interference. It does seem odd that it only happens with the samples, not the buffer.

If you know of any water testing labs or a school lab around you might ask them if you can try out one of your probes on their meter just to see if it actually works (take some of your sample water since the buffer has been reading without problems). BNC connectors are fairly common on pH probes (but not universal)

Are you doing this using a breadboard or are the EZO pH circuits already soldered in (in other words is it beyond warranty)? Any chance of posting a pic of the EZO and your current interface to the pH probe? I'm not an electronics type but there's a good chance someone here knows quite a bit more and who knows, I might notice something. Is the EZO throwing any codes and is the lighting sequence going off as it should.

I apologize for not listing everything I am using in my first post. I also bought carrier board for the EZO circuit. http://www.atlas-scientific.com/product ... rrier.html?

So I am using this carrier board to connect it to my Arduino UNO. I had to solder the carrier board together, but there was no soldering done on the EZO circuit itself. Here are some pictures of how I have my pH probe, EZO circuit and microcontroller connected together. I am confident in my soldering skill and I have checked the circuit carrier many times to make sure I have soldered everything correctly.

I was also trying to see if I could get it to work earlier and I encountered another problem. When calibrating the probe the readings the probe was giving me are now staying at 7.00 no matter what calibrating solution or other liquid I test it on. I have not done anything different from the way I was testing and calibrating in the past.

A few other thoughts

Check to see if the tip of the probe is cracked - seems the most likely cause of the reading being stuck at 7.

Check for air bubbles near the tip of the pH electrode. Under maintenance and storage questions here - http://www.phmeters.com/FAQ.html. This would cause reading fluctuations as well.

Any idea how long ago the probes were made?

http://thesource.hach.com/fileSendAction/fcType/0/fcOid/27757037020023703/filePointer/27757037020023732/fodoid/27757037020023728/markspencerwaterqualityinstrumentationwhitepaper.pdf

The section on grounding and the one on RF interference seem likely as the culprit for the original problem, even with all the cross checking you've done.

I do notice that the readings stabilize a lot faster in calibration solutions that in water. I think it is because the ionization is stronger or something to that effect. My water readings do not jump around as your do though. I would guess that the power supply is not clean or picking up noise. The first thing I would try is shorten the power leads and clean the flux from the board where you soldered with hot water and toothbrush.

Did you try a factory reset? Send the ascii string "factory".

Did you do a three point calibration?
Cal,mid,7.00
Cal,low,4.00
Cal,high,10.00

Is you UNO's power stable? Try powering it from an external 5VDC supply.

I'd put my money on this. Make sure the power supply has enough amps to drive the arduino, and the probes.

The uno takes a 7-12 volt supply through the DC jack, if you're giving under that (or not using a adapter with enough amps), it could be the cause of your issues.

Thanks for everyone that replied. I found out that the reason I was getting readings that fluctuated a lot was due to the carrier board I was using for the EZO pH circuit. What happened was that there was some soldering flux residue on the underside of the board which was causing it to short out and give me incorrect readings. What I did to solve this problem was dip the board in 70% isopropyl alcohol and used a toothbrush to clean off the flux residue. After cleaning it off and letting it dry I tested the probe and it began to give me the correct readings.

Glad we could get you sorted out.