Difference in Local and Remote Reading of Parameters on Ships
Values of some main engine exhaust temperatures displayed in the engine control room computer differ from those displayed on the main engine local thermometers for the same cylinders.
How to Find Which is Correct Reading
Comparisons would be made between the control room display and the local display. The simplest way of providing an accurate reading would be to exchange the local thermometer for a new unit. This new and correct reading would be used as the datum to check the control room display.
Reasons for Difference in Local and Remote Reading
The local thermometer could be defective due to:
- Vibrations
- Physical damage to the mercury in glass unit
- The control room display could be defective due to cable damage
- Physical damage to the probe
- Incorrect power supply to the display unit.
- Defective display gauge
Fault Finding
- Physical damage to the probe or thermometer would be inspected for by visual observation.
- Vibration of the mercury in glass units could be identified by the mercury column being detached internally.
- Cable damage would be inspected for by measuring the resistance of the cable to test for continuity and then an insulation test to check for insulation breakdown.
- Power supply would be checked using a multi-meter.
- To check for a defective gauge, exchange the gauge for a new spare and test by calibration test.
Preventive Maintenance
All remote engine instrumentation should be calibrated, usually within a six month period. The measuring probe would be removed and placed in a test unit that would either change the temperature or pressure depending on the probe classification. For temperature probes, the test unit temperature would be varied in stages over the expected range of the unit and the display readings examined for errors. The display unit should have zero and span adjustments, and if required these would be adjusted to ensure that accurate readings are displayed. Following the calibration and adjustment, the process would be recorded in the appropriate records.