KROHNE OPTISYS CL 1100 EN - Manual (Page 37)

TECHNICAL DATA
7
37
OPTISYS CL 1100
www.krohne.com 01/2013 - 4002492301 - MA OPTISYS CL 1100 R02 en
7.1 Measuring principle
The sensor has three electrodes: a measuring electrode (gold), a counter electrode (gold), and a
reference electrode (Ag/AgCl). A precise potential is built up between the measuring and the
counter electrode. The measuring electrode starts polarising, i.e. negative charges collect close
to the measuring electrode. After polarisation the electrical current decreases to 0 mA as long
as the polarising layer is not changed.
Free chlorine molecules that hit the surface of the measuring electrode take a defined portion of
the charge with them, changing the potential of the measuring potential. The signal converter
constantly measures the potential between measuring and reference electrode and immediately
readjusts the potential as soon as it begins to change. The current needed to maintain a constant
potential is directly correlated to the free chlorine concentration in the measuring medium.
Free chlorine measurement
Figure 7-1: Free chlorine measurement
1 Reference electrode
2 Voltage measurement
3 Current needed to maintain the constant potential
4 Counter electrode
5 Measuring electrode