Most pH sensors with a glass membrane cannot be mounted upside down. To absorb the thermal expansion of the internal buffer solution there is always a sizeable air bubble inside the sensor. When the sensor is mounted upside down the reference element can lose contact with the electrolyte. The FU24 pH sensor from Yokogawa can be used in upside down application, because it has a special design that allows us to reduce the size of the air bubble. The PH18 sensor can be mounted upside down because it does not have a glass electrode or electrolyte.
