TEMPERATURE - DESCRIPTION AND OPERATION

** ON A/C NOT FOR ALL

1. General

T495 Thermocouple Wiring Harness ** ON A/C NOT FOR ALL

The engine Exhaust Gas Temperature (EGT) is sensed and averaged by nine thermocouple probes (chromel/alumel). They are installed through one specific nozzle segment of the stage 2 nozzle assembly located in the Low Pressure Turbine (LPT) case.

A. The T495 thermocouple wiring harness consists of:

Three identical and interchangeable thermocouple lead assemblies with two probes.
One thermocouple lead assembly with three probes.
One upper extension lead.
One lower extension lead.
One main junction box assembly.

B. Description

T495 Thermocouple Wiring Harness ** ON A/C NOT FOR ALL

Wiring Diagram of the Harness of the T495 Thermocouple ** ON A/C NOT FOR ALL

(1) The T495 thermocouple wiring harness has two internal technology standards. The first internal technology uses impedance matching by diameter cable adjustment and the second uses impedance matching by resistance adjustment.

(2) Each segment of the two-probe lead assembly has:

Two rigid metal tubes (Con-o-clad), each equipped at one end with a thermocouple probe and an integral flange for attachment to a related boss on the LPT case.
A junction box at the other end of the rigid metal tubes with a receptacle for the connection to the main junction box assembly (for two of the three lead assemblies) and to the lower lead assembly (for the third one). The junction box has a flange for attachment to the LPT mounting flange S.

(3) Each segment of the three-probe lead thermocouple assembly consists of the items which follow:

(a) Three rigid metal tubes, each equipped with one thermocouple probe at one end and an integral flange for attachment to a related boss on the LPT case.

(b) A junction box at the other end of each rigid metal tube with a receptacle connector for connection to the upper extension lead and a flange for attachment to the LPT mounting flange A8.

(4) The upper extension lead has:

One rigid metal tube (Con-o-clad), equipped at each end with a mobile elbow-connector for connection to the main junction box assembly, and one of the three two-probe thermocouple lead assemblies.

(5) The lower extension lead has:

One rigid metal tube (Con-o-clad), equipped at each end with a mobile elbow-connector for connection to the main junction box assembly, and to the three-probe thermocouple lead assembly.

(6) The main junction box assembly has:

Two rigid metal tubes (Con-o-clad), each equipped at one end with a mobile elbow-connector to the related two-probe lead assembly, and at the other end to a junction box. The junction box is equipped with two receptacles connectors for connection to the extension leads and one interface receptacle connector.

C. The electromotive force is averaged first in each of the individual lead assembly (2 probes and 3 probes), then in the main junction box assembly at the level of the interface connector.
The resultant averaged electromotive force is then sent to the ECU through the CJ13 harness and the HJ13 harness.

** ON A/C NOT FOR ALL

2. EGT indication

Upper Display Unit of the ECAM System - EGT Indication ** ON A/C NOT FOR ALL

The EGT indication appears on the upper display unit of the ECAM system.
The ECAM provides the EGT indication:

in analog form thru a pointer which deflects in front of a dial,
in digital form, in the lower section of the dial.

The indication is normally green.
The index flashes amber above 855 deg.C (or above 725 deg.C during start sequence).
The index and the numerical value flash red above 890 deg.C, the MASTER CAUT light comes on accompanied by the repetitive chime, the following message appears on the ECAM: ENG 1(2): EGT OVERLIMIT
If the EGT has exceeded 890 deg.C:

the maximum value reached is memorized,
a small red line remains positioned on the analog scale, at that value (max pointer). The red line will disapear after a new take off or maintenance action through the MCDU.

[Rev.10 from 2021] 2026.04.01 13:05:30 UTC