Parameters Determining Current - Mettler Toledo InPro 6850i Bedienungsanleitung

36
As a consequence of the reaction at the cathode and
the anode, a current flows between cathode and an-
ode (4 electrones per oxygen molecule), which is
proportional to the oxygen partial pressure at the
cathode.
The amperage of the current flow depends on the
surface of the cathode. Typical values are:
6800
6850(i)
6900(i)
6950i
This current is measured and converted and indicat-
ed in the transmitter into an oxygen value. In ISM
sensors this computation takes place in the sensor
and the transmitters displays this value.

10.3 Parameters determining current

The quantity of oxygen diffused in and the magnitude
of the electrode current are influenced by the follow-
ing parameters:
– Oxygen partial pressure of the solution
– Membrane material and thickness
– Size of cathode
– Polarization voltage
– Temperature
– Flow conditions in the solution
Fick's law gives the mathematical relationship be-
tween these parameters:
InPro 6850i, 6900i, 6950i
52 206 349
InPro 6850i / 6900i / 6950i O
Air current
50 – 110 nA
50 – 110 nA
250 – 500 nA
2500 – 6000 nA < 0.025
Sensor 12 / 25 mm
2
Zero current in %
of the air current
< 0.1
< 0.1
< 0.03
© 02 / 09 Mettler-Toledo AG
Printed in Switzerland