The P1 is for conventional pH with one pH glass bulb and one reference junction. P2 is for differential pH measurements with two pH glass bulbs. The pin layout on the variopin is different, therefore there are two different types of SA11.
The P1 is for conventional pH with one pH glass bulb and one reference junction. P2 is for differential pH measurements with two pH glass bulbs. The pin layout on the variopin is different, therefore there are two different types of SA11.