An appropriate analyzer is used to test and troubleshoot the aircraft thermocouple system at the first indication of trouble, or during periodic maintenance checks.

1. Troubleshooting EGT System and
Tachometer System
Published By:- Kim Bishop

2. Table Of Contents
• Introduction
• Superior Labs Inc
• Troubleshooting EGT System
• One or more inoperative thermocouples in engine parallel
harness
• Engine thermocouples out of calibration
• EGT indicator error
• Resistance of circuit out of tolerance
• Shorts to ground
• Shorts between leads
• Troubleshooting Aircraft Tachometer System
• Contact Us

3. Introduction
• An appropriate analyzer is used to test and
troubleshoot the aircraft thermocouple system at the
first indication of trouble, or during periodic
maintenance checks.
• The test circuits of the analyzer make it possible to
isolate the troubles listed below

4. Superior Labs Inc
• Superior Labs Inc. manufactures the aircraft
tachometers for all general aviation aircraft.
• We can also offers the custom screen printed dials,
internal lighting, anti-glare glass, and pre-set engine
hours.
• Contact us now!

5. Troubleshooting EGT System
• Following the list is a discussion of each
trouble mentioned.
• One or more inoperative thermocouples in engine parallel
harness
• Engine thermocouples out of calibration
• EGT indicator error
• Resistance of circuit out of tolerance
• Shorts to ground
• Shorts between leads

6. Troubleshooting EGT System
1.One or More Inoperative Thermocouples in Engine
Parallel Harness:-
• This error is found in the regular testing of aircraft
thermocouples with a hot heater probe and is a broken
lead wire in the parallel harness, or a short to ground in the
harness.
• In the latter case, the current from the grounded
thermocouple can leak off and never be shown on the
indicator. However, this grounded condition can be found
by using the insulation resistance check.

7. Troubleshooting EGT System
2. Engine Thermocouples Out of Calibration:-
• When thermocouples are subjected for a period of time to
oxidizing atmospheres, such as encountered in turbine
engines, they drift appreciably from their original
calibration. On engine parallel harnesses, when individual
thermocouples can be removed, these thermocouples can
be bench-checked, using one heater probe.
• The temperature reading obtained from the
thermocouples should be within manufacturer’s tolerances.

8. Troubleshooting EGT System
3. EGT Circuit Error:-
• This error is found by using the EGT and comparing the
reading of the aircraft EGT indicator with the analyzer
temperature reading.
• The analyzer and aircraft temperature readings are then
compared.

9. Troubleshooting EGT System
4. Resistance of Circuit Out of Tolerance
• The engine thermocouple circuit resistance is a very
important adjustment since a high-resistance condition
gives a low indication on the aircraft EGT indicator.
• This condition is dangerous, because the engine is
operating with excess temperature, but the high resistance
makes the indicator read low.
• It is important to check and correct this condition.

10. Troubleshooting EGT System
5. Shorts to Ground/Shorts Between Leads:-
• These errors are found by doing the insulation check using
an ohmmeter. Resistance values from zero to 550,000
ohms can be read on the insulation check ohmmeter by
selecting the proper range.

11. Troubleshooting Aircraft Tachometer System
• The rpm check circuit in the analyzer is used to read engine speed
during engine run-up with an accuracy of ±0.1 percent. The
connections for the rpm check are the instrument cable and
aircraft tachometer system lead to the tachometer indicator
• If the difference between the readings of the aircraft tachometer
indicator and the analyzer rpm check circuit exceeds the tolerance
prescribed in applicable technical instructions, the engine must be
stopped, and the trouble located and corrected.

12. Contact Us
• Superior Labs Inc
• Address:5783 Central Ave.
• Hot Springs, AR
• 71913
• Phone:501-525-6688
• Fax:501-525-7733
• Email: superiorlabsinc@gmail.com
• Website: http://www.superiorlabsinc.com
• Resource: https://goo.gl/PfM3be