Mettler Toledo InPro 6000G Serie Instructions D'utilisation page 37

InPro 6800 G / 6850i G / 6900i G / 6950i G O
Type D, 4-electrodes, InPro 6950i G
The InPro 6950i G is intended for measuring perma-
nent low oxygen level down to 0.1 ppb. In terms of
measurement principle it is a combination of the
InPro 6850i G and InPro 6900i G. It consists of 4
electrodes. The anode (platinum) and reference (sil-
ver / silver chloride) are separated in two electrodes.
A guard ring is placed around the cathode. The cath-
ode has the highest diameter from all amperometric
oxygen sensors from METTLER TOLEDO
The electrodes show the following reactions:
Cathode:
Anode:
Reference: No current
Guard:
Due to the larger surface of the cathode a higher
current appears during measurement. This allows
for measurement of oxygen levels below 1 ppb.
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:
6800G
6850i G
6900i G
6950i G
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.
© 09 / 09 Mettler-Toledo AG
Printed in Switzerland
O + 2 H O + 4 e
2 2
–
4 OH O
→
2
O + 2 H O + 4 e
2 2
Air current
50 – 110 nA
50 – 110 nA
250 – 500 nA
2500 – 6000 nA < 0.025
12 mm
2
–
4 OH
→
+ 2 H O + 4 e
2
–
4 OH
→
Zero current in %
of the air current
< 0.1
< 0.1
< 0.03
InPro 6000 G – Series
–
–
–
52 206 477
37