We’re using two of the NCD pH/ORP/temperature sensor. I think that one of the two may have a fouled ORP electrode.
- pH/ORP sensor A has been used in the lab with municipal wastewater samples, for a total of a few days
- Sensor B has been used in the lab and was deployed in a sewer for about 24 hours
- Both are otherwise kept in electrode storage solution otherwise, and rinsed in water after each test.
Since the sewer deployment, sensor B’s ORP output doesn’t react much when we add a strong oxidizer to a water sample. On both sensors the pH reading behaves correctly and jumps from about 6 to 11 when we dose, but on sensor A the ORP jumps up by roughly 90 mV at that same moment, while on sensor B the ORP does not move at all. The ORP on sensor B seems to track pH (-56 mV for every unit rise in pH). This plot shows that when the oxidizer is added, both sensors’ pH rises quickly, but only sensor A shows a jump in ORP.
Sensor B still responds quickly and correctly when we move it from one solution into another, so it isn’t dead, but it seems to have lost the ability to sense oxidizers. Could the electrode have been fouled by the wastewater? Can you recommend any cleaning or restoration procedure for the ORP electrodes (I didn’t see any in the manual)?
Thanks in advance!
