pixelpixi
Guest
I got a shiny new pH probe because I thought that maybe my old one was shot. In the meantime I also switched to new hardware. I'm now using a tiny pc ( http://www.fit-pc.com/new/ ) and a USB IO device ( http://www.labjack.com/labjack_u3.php?prodId=52 ). I got linux installed, ported my software to use the drivers for the new device, and hooked up my temperature and ph probe amplifier. I calibrated the probe and it with the calibration solutions it appeared to give solid accurate repeatable readings. Sweet.
Then I put the pH probe back in the tank and got a reading of... 7.1!
That's clearly not right, so I tested the calibration solutions again. They were spot on.
I suspected that maybe the probe is too close to a powerhead, so I took a sample of tank water in a container and measured it outside the tank. It read 7.85. I thought, "Okay, that must be it."
I turned off the powerhead near the ph probe. The probe still read 7.1
I turned off and disconnected EVERYTHING (pumps, powerheads, lights, heaters) and still got reading around 7.1 in the tank and 7.85 outside the tank.
I took my multimeter and stuck one probe in the tank and the other on the ground of the data acquisition module. Surprisingly (or maybe not, given these problems) it registered about .5VAC. The source of that voltage has me totally baffled, though.
Any thoughts as to what might be causing this? The only thing I can think of at this point is that maybe electrical wires near the tank are inducing an electric current and that's throwing off the ph probe. Would a grounding probe help or hurt my efforts here?
Then I put the pH probe back in the tank and got a reading of... 7.1!
That's clearly not right, so I tested the calibration solutions again. They were spot on.
I suspected that maybe the probe is too close to a powerhead, so I took a sample of tank water in a container and measured it outside the tank. It read 7.85. I thought, "Okay, that must be it."
I turned off the powerhead near the ph probe. The probe still read 7.1
I turned off and disconnected EVERYTHING (pumps, powerheads, lights, heaters) and still got reading around 7.1 in the tank and 7.85 outside the tank.
I took my multimeter and stuck one probe in the tank and the other on the ground of the data acquisition module. Surprisingly (or maybe not, given these problems) it registered about .5VAC. The source of that voltage has me totally baffled, though.
Any thoughts as to what might be causing this? The only thing I can think of at this point is that maybe electrical wires near the tank are inducing an electric current and that's throwing off the ph probe. Would a grounding probe help or hurt my efforts here?
