-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.
Atlas Scientific Gravity Analog pH Kithttps://www.atlas-scientific.com/product_pages/kits/gravity-ph-kit.html
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.
I don't to spend even $25 if the results are going to be unusable
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.