Installation
MXD70 Dissolved Oxygen
Setup and Operating Guide
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Installation
Installation and Choice of Dissolved Oxygen
Sensors
The Dissolved Oxygen input of the MXD70 Series has been designed to accept a wide variety of both
Galvanic and Polargraphic Dissolved Oxygen sensors. Parameters such as membrane correction, bias
voltage and temperature sensor type can be easily programmed into the instrument.
The choice of the correct type of Dissolved Oxygen sensor, how and where to mount it so that it has a
representative sample of solution are probably the two most important considerations when installing
a Dissolved Oxygen system.
The following criteria are of great importance during selection:
The trade-off between a thin membrane giving quick response times and depending on the sample
the reduced life time of the membrane.
Galvanic sensors are less reliable in zero to low flow samples and are incompatible with certain
bioprocesses due to the present of lead in the sensor.
The use of the correct materials for corrosion resistance.
The chemical make up, temperature of the sample.
Position of the sensor for robustness and service access.
Ensuring a representative, uncontaminated solution sample.
To ensure correct sensor mounting the following conditions should be observed:
The dissolved oxygen sensor can only measure what is in the immediate vicinity of the sensor area
of the sensor.
A moderate flow is maintained to provide an “up to date” sample.
Ensure that the full area of the sensor’s membrane is in contact with the sample.
Install the sensor in an upright position to ensure that the internal electrolyte is in contact with the
membrane.
Avoid points where air can be trapped.
Avoid points of high turbulence as air bubbles will affect the measurement.
If the sample has solids present then a jet wash or equivalent cleaning system may be required to
keep the membrane in contact with the sample.
When a new dissolved oxygen sensor is first fitted or changed it must be calibrated (see page 24). Due
to the nature of dissolved oxygen sensors it will also need periodic re-calibration, the MXD70 series
provides an inbuilt count down timer which will trigger an alarm when the calibration interval has
expired (see page 34).
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