LTH Electronics MTD75, Operation Manual

Page: 257 / 266

Appendix H
MTD75 Operation Guide
- 255 -
Appe
ndix H
The pH Sensor Reading Is Constantly Over-range or Under-range

Ensure that the sensor and temperature input is correctly connected (See page 47) and that the
sensor is not faulty or damaged.

Check the temperature compensation state (See page 107). 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.
The pH Sensor Reading Is Incorrect

Check that no error messages are being displayed. Check that the sensor cable has been correctly
connected (See page 47).

Check that the Temperature reading is correct.

Check the instrument calibration using a pH simulator, Adjust the pH calibration if necessary (See
page 125).

Use another instrument to check the sensor.
The pH Sensor Is Not Functioning Correctly

Check that the sensor glass is 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 Temperature Reading Is Incorrect

Check that the temperature sensor is correctly attached (See Installation Section).

Check that the temperature sensor type is correctly selected in the Sensor Setup menu.

Where practical check the temperature sensor resistance against the table on page 183.
Current Output Is Incorrect or Noisy

Check that the maximum load for the current loop has not been exceeded. (750

).

Check that the terminals have been wired correctly.

Check that the cable screen is attached to Earth at one end and that the cable does not pass too
close to a power cable.

Check that he current output has been configured properly.
Relays Appear to Malfunction

Check that the controller’s sensors are “On-Line” in the Sensor Setup menu.

Check that the relay configuration is correct.

Ensure that the relays are connected properly see Installation section.

Check that the instrument input cables are not picking up excessive noise.

Check that the front panel fuses are in working condition (See page 31).
Instrument display appears to malfunction

Switch the instrument power off and on again.

Check that the display back-light is on, indicating power is reaching the unit.

See that it displays meaningful text (Issue number etc.) in its start-up sequence, indicating
processing activity.