Measuring cell with coulometric phosphorus
The core of the device is the coulometric sensor with
a hygroscopic phosphorus pentoxide coating (P2O5) which
absorbs the water transported in the carrier gas.
A voltage is applied to 2 platinum electrodes and the
water is broken down by means of electrolysis into hydrogen
(H2) and oxygen (O2). The amount of electrical charge
required for this is proportional to the quantity of
water and is determined. The amount of charge can be
directly converted into the amount of water by means
of Faraday's Law. Therefore, measurement is an absolute
measurement which can be carried out without calibration.
In practice it is nevertheless advisable to perform
a calibration measurement for the purpose of quality
control. This ensures that water is detected selectively.
The P2O5 coating reforms and thus the sensor regenerates
itself. The device is therefore always ready to use.