LTH Electronics MTD75, Operation Manual

Page: 256 / 266

Appendix H
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MTD75 Operation Guide
Appe
ndix H
The Redox Sensor Is Not Functioning Correctly

Check that the sensor not broken or cracked.

Check the reference probe KCl (where applicable) for leakage or contamination.

Ensure all probe protective caps have been removed.

Check that any junction boxes used are correctly connected.

Check that a suitable high impedance, low noise cable has been used.

Check for damaged or broken cables.

Check for damp, grease, or liquids near connectors, junction boxes, or terminations.

Where extension cables have been used, try connecting the sensor directly to the instrument.
The Electrodeless Conductivity Sensor Reading Is Constantly Over-range or Under-range

Ensure that the sensor and temperature inputs are correctly connected (See page 42) and that the
sensor is not faulty or damaged.

Check that the correct sensor type or cell constant has been entered within the Channel Setup
menu (See page 101).

Check the temperature compensation state (See page 101) If the compensation is set to “Manual”
check that the fixed temperature is at the correct level. If the compensation is “Automatic” check
that the temperature reading on the main display is correct.

Check that the sensor is “seeing” a representative sample, trapped air will give a low reading.

Ensure the input is correctly connected and the sensor is not faulty or damaged.

Check the sensor and its cable for possible short circuits. Consider the fact that the conductivity may
be higher than the range of the instrument.

Check the Pt1000 RTD temperature sensor connections.

Check that any in-line junction boxes and extension cables have been fitted and wired up correctly.
The Electrodeless Conductivity Sensor Reading Is Incorrect

Low reading due to incomplete immersion.

There may be some trapped matter within the sensor bore.

High conductivity readings caused by a short circuit or leakage of liquid contamination into the
sensor moulding.

Low conductivity can be caused by accumulation of trapped air or gas coming out of solution.
Check that no "air traps" exist in the sensor installation.

High conductivity readings caused by leakage of solution into the sensor. This usually indicates that
the sensor material has been fractured and the sensor must be replaced.

First check that the temperature resistance is correct, otherwise the temperature compensation
circuit will cause false or erratic readings. Temporarily switching out the temperature compensation
can help to show if this is the cause of the problem.

If another electrodeless sensor is available, this can be used to determine whether the fault lies with
the instrument or the sensor.

Check that the sensor cable is not damaged or broken and that the outer screen does not make
contact with any other terminals or metal work.

Check that the sensor cable is sufficiently distant from power cables or electrical noise sources.

Check that the correct sensor type has been installed.

Check that the correct range has been selected.

Check that the correct sensor loop resistor calibration value (500Ω) has been used.

Check that the calibration procedure has been followed precisely.

Check that the temperature compensation has been set up as required.

Check that the sensor cable does not exceed the maximum specified length (sensor 5m + extension
95m).