Significant error in temperature reported by instrument

[Chuck - Raymarine - Moderator]

Significant error in temperature reported by instrument

Incorrect temperature values reported by an instrument may result from any of the following:
- Temperature offset not configured
- Poor connection of the temperature sensor leads to the instrument or iTC-5
- Thermistor failure
- Failure of Temperature sensing circuitry of instrument or instrument pod

Raymarine instruments support up to +/- 9.9 degrees of temperature offset within the configuration settings of the instrument display. Should the temperature sensing transducer be interfaced directly to an instrument display, then the temperature offset must be configured via the user interface of the instrument display which it has been interfaced to. Should the temperature sensing transducer be interfaced directly to an iTC-5 or instrument pod, then the temperature offset must be configured via the user interface of Master Multifunction Instrument Display (i70, ST70, ST70+, etc.).

Temperature sensing transducer employ a thermistor as their sensing element. The impedance through a thermistor will change as the thermistor temperature changes. Increases in temperature will cause a decrease in impedance through the thermistor. Correspondingly, decreases in temperature will cause an increase in impedance through the thermistor. The table below identifies the nominal resistance values across the transducers thermistor leads (white and brown) for the reported temperatures. Should measured resistance correspond to a temperature which is more than 9.9 degrees from the actual temperature, then the transducer's thermistor would be deemed to be failing and necessitate replacement of the transducer or transducer insert (for transducers with removable speed/temp inserts).



Should the transducer's thermistor pass the test described above, then instrument display's or instrument pod's temperature sensing circuitry may performed as follows:
1) Power down the instrument
2) Disconnect the BROWN and WHITE transducer leads from the instrument display or pod.
3) Install a 10,000 Ohm resistor across the BROWN and WHITE terminals of the instrument display or instrument pod
4) Power on the instrument
5) Verify that the instrument display reports a temperature of approximately 77 degrees F.

Should the instrument display not respond as indicated above, then the instrument display or instrument pod has failed and should be serviced by Raymarine’s Product Repair Center.

RAYFAQ#