Why are there two types of SA11 for pH measurements (P1 and P2)?

For the VP connector, the designation of the pins is fixed. That is why P1 for conventional pH sensors and P2 for differential pH sensors was created. It was possible to create an internal switch in the connector, but with a specification of up to 125°C leakage currents can be expected and when measuring at very low levels this could be a potential measurement integrity problem. That is why there are two versions.