FAA Aviation Mechanic Powerplant (AMP)Engine InspectionEasy
A mechanic is functionally checking a resistance-bulb type cylinder head temperature (CHT) probe removed from a reciprocating engine. Using an ohmmeter, the mechanic measures the probe's resistance at a known ambient temperature and compares it to the manufacturer's resistance-versus-temperature chart. What does this check verify?
- AThat the probe's electrical resistance changes proportionally with temperature within tolerance
- BThat the probe will produce full-rated voltage output at maximum operating temperature
- CThat the probe's thermocouple junction produces the correct millivolt output
- DThat the probe's magnetic pickup generates the correct frequency signal
Show answer & explanationAnswer & explanation
Correct answer: A. That the probe's electrical resistance changes proportionally with temperature within tolerance
A resistance-bulb CHT probe operates on the principle that its electrical resistance changes with temperature. Comparing measured resistance at a known temperature to the manufacturer's chart verifies the probe is within calibration tolerance.
Why the other options are wrong
- B. Resistance bulbs do not generate voltage output; that describes a different sensor type.
- C. Thermocouple millivolt output applies to thermocouple-type EGT/CHT probes, not resistance-bulb types.
- D. Magnetic pickups apply to speed sensors, not CHT probes.
Resistance-Bulb CHT Probe Check
A functional test comparing a resistance temperature sensor's measured ohmic value at a known temperature against a manufacturer's resistance-temperature chart.
- Resistance changes proportionally with temperature
- Checked with an ohmmeter at a known ambient temperature
- Different from thermocouple-type probes which measure millivolt output
Memory trick: Resistance rises and falls with heat — match it to the chart to seal the deal.