Which statement about thermocouple leads is correct?

Which statement about thermocouple leads is correct?

• A. Are designed for a specific installation and may not be altered
• B. May be installed with either lead to either post of the indicator
• C. May be repaired using solderless connectors
• D. May be replaced without regard to installation

Answer: (A)

Thermocouple measurements rely on a precise, unaltered circuit. The small voltage generated by the thermocouple comes from the specific pair of metals and their connections. The extension leads and their installation are chosen to match the type of thermocouple, withstand the service environment, and preserve polarity and calibration. Because even a small change in lead material, a splice, or a different connector can introduce additional thermoelectric EMFs or alter the circuit resistance, any modification can shift the reading. That’s why these leads are designed for a particular installation and should not be altered. If damage occurs, the proper approach is to replace the entire lead assembly with an approved, identical installation rather than trying ad-hoc repairs. In contrast, swapping lead ends between posts can invert polarity and give erroneous readings; solderless repairs are generally not permitted in aviation practice due to reliability concerns; and replacing a lead without regard to how it’s routed or supported can affect heat shielding, vibration resistance, and calibration.

Thermocouple measurements rely on a precise, unaltered circuit. The small voltage generated by the thermocouple comes from the specific pair of metals and their connections. The extension leads and their installation are chosen to match the type of thermocouple, withstand the service environment, and preserve polarity and calibration.

Because even a small change in lead material, a splice, or a different connector can introduce additional thermoelectric EMFs or alter the circuit resistance, any modification can shift the reading. That’s why these leads are designed for a particular installation and should not be altered. If damage occurs, the proper approach is to replace the entire lead assembly with an approved, identical installation rather than trying ad-hoc repairs.

In contrast, swapping lead ends between posts can invert polarity and give erroneous readings; solderless repairs are generally not permitted in aviation practice due to reliability concerns; and replacing a lead without regard to how it’s routed or supported can affect heat shielding, vibration resistance, and calibration.