PH electrodes have an extremely high impedance. Their typical resistance lies between 100 M_ and 800 M_. The entire measuring system must be suitable for this resistance range. This is the reason why special measuring cables, connectors and junction boxes are used for both pH and redox measurement.
CPK 9-NBZ1A – PH Measuring Cable
Measuring cable CPK 9 (pH electrodes with ESA / ESS plug-in head, high-temperature applications, IP 68 / NEMA 6X)