Hi There!
PH sensors is something I've never worked with, and now I face a real necessity where I need to use one.
I need to measure pH values in a vegetables cooling tank.
Preferred specs are:
-Needs to be permanently submerged into the water
-Should not be too fragile (some have a LARGE glass end tip, some glass is fine but not too much)
-Should be reliable enough. giving +/- 0.1--0.2 readings compared to chemical tests
-Long life, not needing to be cleaned or changed in some months....
Usual projects for arduino with pH sensors (like for hydroponics, fish tanks, etc) use really cheap hobby grade pH sensors, I would like some one step above and something I can trust that's going to be providing accurate values for some months and is not in the $K range
Any advice will be helpful
Thanks:
PS: So far this is the one option I've found: LINK
-Long life, not needing to be cleaned or changed in some months....
pH sensors worth buying are precision devices, very delicate and easily destroyed by contamination. If you are at all interested in accuracy, the probes need to be cared for, cleaned and calibrated frequently. We do so on a daily basis.
Please describe the tank, its size and solution content and how quickly you think the pH will change. It is very likely that you will need a good pH meter for only occasional confirmation of results from cheap test strips. Otherwise, plan on spending $$$ for an industrial setup.
jremington:
pH sensors worth buying are precision devices, very delicate and easily destroyed by contamination. If you are at all interested in accuracy, the probes need to be cared for, cleaned and calibrated frequently. We do so on a daily basis.
Please describe the tank, its size and solution content and how quickly you think the pH will change. It is very likely that you will need a good pH meter for only occasional confirmation of results from cheap test strips. Otherwise, plan on spending $$$ for an industrial setup.
You clean&calibrate daily? Seems like lots of work, I was trying to save work to this company
This tank is an overflow compartment, connected & attached to the side of a tank where corn cobs will be cooling down after boiling. Cold water is applied to let them cool down while they travel along a long line.
There could be some minor solid remain from the corn, and probably some foam from the boiling.
The water getting into the overflow subtank won't have any major remains as the connection between one and other is a perf surface that prevents corn cobs from getting out of the cooling line
Water is expected to be <45ºC and ir constantly running.
Main point in analyzing pG is to determine how much citric acid to add to the water in order to keep it slightly acid, as a preserver for the corn before it is vacuum packed.
pH usually doesn't change too quickly, probably 0.2 an hour? Just my guess
Client has already received quotes for devices in the range of $5000 and he's not willing to pay that much, and shows open now to experience with cheaper solutions, thus I'm offering to biuld one that I can provide that can also upload the reading to the cloud.
Calibration of pH probes does change over time. Daily calibration sounds like too much to me but it depends on what level of accuracy you're expecting. The amount of cleaning necessary also depends on the environment they're in. Biweekly or monthly may be good enough.
I'm using a pH probe that cost me the equivalent of 20, 25 USD or so. I'm using my own developed sensor board with it, fully electrically isolated. The same board operates an EC sensor and water temperature sensor as well. The pH sensor works fine but it still affects the EC sensor... Getting there! It's not easy to work with sensors that are so sensitive to stray electric connections, yet must make electric contact with the water to work... pH readings are very stable, and have been for over a month now. pH probe simply submerged in the tank. It's a hydroponic setup, by the way.
wvmarle:
Calibration of pH probes does change over time. Daily calibration sounds like too much to me but it depends on what level of accuracy you're expecting. The amount of cleaning necessary also depends on the environment they're in. Biweekly or monthly may be good enough.
I'm using a pH probe that cost me the equivalent of 20, 25 USD or so. I'm using my own developed sensor board with it, fully electrically isolated. The same board operates an EC sensor and water temperature sensor as well. The pH sensor works fine but it still affects the EC sensor... Getting there! It's not easy to work with sensors that are so sensitive to stray electric connections, yet must make electric contact with the water to work... pH readings are very stable, and have been for over a month now. pH probe simply submerged in the tank. It's a hydroponic setup, by the way.
Ok, and this being an industrial plant with lots of motors, heaters, fans, and whatnot, will I get absolutely random values in my meter? I don't to spend even $25 if the results are going to be unusable...
Is your ph probe continously submerged in water or only when you request a measurement? The one that was quoted to us had a method of flushing th probe tip with a blow of compressed water every X hours with a timer and s valve conected to the plant's air system
I don't to spend even $25 if the results are going to be unusable
You need some experience with the probes in order to judge. Buy the kit suggested in reply #2 (which comes with pH calibration solutions), stick it in the cooling water and see how the calibration changes over time. That is cheap education! Temperature compensation is required if the temperature changes.
Needless to say, your client won't be impressed if the device you build does not work.
edugimeno:
Ok, and this being an industrial plant with lots of motors, heaters, fans, and whatnot, will I get absolutely random values in my meter? I don't to spend even $25 if the results are going to be unusable...
Is your ph probe continously submerged in water or only when you request a measurement?
It's been in the tank for almost a month now I think. Time to check the calibration, see how much it drifted (if at all). I should also do something about temperature compensation, my water cools down to like 8-9° at night, warming up to 20-23° during the day. The effect of temperature is not nearly as bad as for the EC sensor but it still does affect the readings.
It all depends on the nature of your water. Is it clean? Lots of dirt in it that may stick to the sensor?
Best thing to do is just get yourself a sensor and try it out, gain experience with your system. pH sensors need maintenance, there is simply no way around that.
wvmarle:
It's been in the tank for almost a month now I think. Time to check the calibration, see how much it drifted (if at all). I should also do something about temperature compensation, my water cools down to like 8-9° at night, warming up to 20-23° during the day. The effect of temperature is not nearly as bad as for the EC sensor but it still does affect the readings.
It all depends on the nature of your water. Is it clean? Lots of dirt in it that may stick to the sensor?
Best thing to do is just get yourself a sensor and try it out, gain experience with your system. pH sensors need maintenance, there is simply no way around that.
Yes I guess I will have to do my own internal tests before I get it out to the customer-
Most sensor I've been reading specs about show that they measure temperature also to do some correction, is this correction not really worth?
Thanks
Error from temperature is not much; 0.1-0.2 pH points or so for a 10 C range. I don't remember the exact number but something like that, and I think it even depends on how far off neutral you are. The formula is also kinda complex. I looked into it, and as my hydroponics is usually (should be, at least) about 5.5-6, decided it's not worth the effort. I still have it in mind to implement, though. Sometime in the future.
Most of my systems are running outdoors, so see such temperature changes. I've another installation indoors, there the temperature changes by a few degrees only, that's not going to affect pH readings significantly.
A DS18B20 is cheap and easy to implement, so why not
EC changes 2% per degree C, so that's a whole different story.
Ok, I'm still not sure about my client's expectations about accuracy, probably 0,2% is about right.
I will probably order the $200 probe I linked above, as the other one seems to have a large block of glass, and being for the food industry, the less glass exposed to the risk of breaking, the better
Thanks to last 2 comments, but I'm not measuring the pH of the corn, I'm measuring the pH of the water used to wash the corn, to make sure it is slightly acid
Still. pH sensor in direct contact with water that is in direct contact with the food.
Check your local government's regulations, very likely it will state it must be food safe. Just like the pipes that washing water is running through, as any contamination there will end up in the corn just the same. Even if not in the regulations, it's just good practice.
Standard pH probes are not designed to stay in water for long time.
They work using a reference electrode that must be in contact with water, usually with a ceramic plug (or a very small hole sometimes). Unfortunately osmosis happens so water will enter in the reference electrode and some liquid in the reference electrode go out. The time it will happens depends on many factors.
For this reason there are pH probes for special uses, for example they have a big reference electrode so it became diluted by water in long time.
But they are not cheap.
For example these ones by Mettler Toledo
