Faults
MXD70 Dissolved Oxygen
Setup and Operating Guide
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Faults
The Sensor Condition Is Showing “Fault”
The “Fault” setting on the sensor condition is caused by the sensor output current being too high
when a zero calibration was performed. Check for the following possible causes:
Wiring fault. Disconnect the sensor from the instrument and confirm that the reading goes to zero.
Possible faulty sensor connector. Check to see if sensor connector pins are covered with liquid or
dirt. If the connector appears clean try a new cable or a different sensor.
Membrane is broken on mechanical tension is to low. Visually inspect membrane for any tears and
replace if present. Alternatively perform an electrolyte refill and check that the resistance between
the cathode and electrode is low.
Polargraphic sensor polarization time to short. Ensure that the sensor has been polarized for the
length of time as recommended by the manufacturer and that the bias voltage has been set
correctly in the instrument.
Possible contamination in sensor body. Follow manufacturer’s sensor cleaning guidelines.
The calibration sample is not completely oxygen free.
Check that the probe type, bias voltage and membrane correction factor have been set correctly in
the instrument. Also ensure all sensor protective caps have been removed.
If using manual pressure and temperature compensation ensure that the correct values have been
entered.
The Sensor Condition is Showing “Refill”
The sensor output was too low at span calibration to provide sufficient sensor accuracy. Follow the
sensor manufacturer’s electrolyte service guidelines. If the condition persists check for the following
possible causes:
Membrane is broken. Visually inspect membrane for any tears and replace if present.
Contaminated membrane. Gently clean the membrane surface with a soft clean cloth or tissue
wetted with distilled or D.I. water, if fouling is still present replace the membrane.
Cathode contamination. If the membrane has been ruptured the cathode can become
contaminated with the sample media. Follow the sensor manufacturer’s cleaning guidelines.
Polarization voltage is incorrect. Check the “Bias Voltage” value in the input channels setup menu
matches the value given by the sensor manufacturer.
Cathode and Anode wired wrong way round. Check the installation section of this manual.
Check that the probe type, bias voltage and membrane correction factor have been set correctly in
the instrument. Also ensure all sensor protective caps have been removed.
If using manual pressure and temperature compensation ensure that the correct values have been
entered.
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