AD
INSTRUMENTS
MLT1115 Galvanic Oxygen Electrode
Transducer Series
Description
The MLT1115 Galvanic Oxygen Electrode is
designed for measuring the concentration of oxygen
in aqueous solution.
Operation
Connect the electrode to the input connector of any PowerLab (or other recording
device having an input impedance of at least 1 MΩ). The unit may be connected directly
into a BNC input or alternately to a Pod Port via the supplied MLAC22 BNC to DIN
Smart Adaptor. The output in air-saturated deionized water should be 20 – 35 mV at
25 °C. The output will be larger at higher temperatures or in water saturated with pure
oxygen or Carbogen (5% CO
2
, 95% O
2
).
Note: Constant temperature must be maintained to obtain a meaningful signal.
Principle of Operation
The electrode comprizes a platinum cathode and a lead
anode connected via an internal 7.5 kΩ resistor. As oxygen
diffuses across the membrane and into the electrolyte
solution inside the electrode, the following reactions occur:
O
2
+ 2H
2
O + 4e
-
→ 4OH
-
at cathode
2Pb + 4OH
-
→ 2Pb(OH)
2
+ 4e
-
at anode
O
2
+ 2H
2
O + 2Pb → 2Pb(OH)
2
overall
For every molecule of oxygen consumed at the cathode,
four electrons are transferred from the anode. The potential
across the internal 7.5 kΩ resistor is proportional to this
current flow therefore, to oxygen concentration.
The rate of oxygen consumption by the electrode is given
by the formula:
d[O
2
]/dt = E/(4000RF)
where:
d[O
2
]/dt is the rate of oxygen consumption in mol/s
E is the output signal (potential) in mV
R is the value of the internal resistor, 7.5 kΩ
F is the Faraday constant, 96486.7 A·s/mol
Membrane
Cathode
Cover cap,
tip
Anode
Cover cap,
cylinder