DOC AIRBUS | AMM A320FSHAFT SPEED INDICATING SYSTEM - DESCRIPTION AND OPERATION
** ON A/C NOT FOR ALL
1. Component Location
** ON A/C NOT FOR ALL 
Shaft Speed Indicating System (N1 Probe)- The N1 speed probe is installed to the Compressor Intermediate Case (CIC) at the 3:30 o'clock position.
- The N2 speed transducer is installed to the Angle Gearbox (AGB) at the 5 o'clock position.
- The Nf speed probe is installed to the CIC, through the Fan Intermediate Case (FIC) and to the No. 1 and No. 1.5 Bearing support at the 1 o'clock position.
| FIN | FUNCTIONAL DESIGNATION | PANEL | ZONE | ACCESS DOOR | ATA REF |
|---|---|---|---|---|---|
| ** ON A/C NOT FOR ALL | |||||
| 4064KS | PROBE-N1 | 400 | 73-11-00 | ||
| 4065KS | TRANSDUCER-N2 | 400 | 77-11-10 | ||
| 4066KS | PROBE-NF | 400 | 73-11-00 | ||
2. System Description
A. N1 Power Indicating.
(1) Shaft speed indicating is used to sense and transmit low rotor (N1) speed to the Electronic Engine Control (EEC).
(2) The primary engine thrust control parameter is the low rotor (N1) speed.
(3) The N1 speed probe is installed in the CIC, which is station 2.5.
(4) The probe is a dual channel sensor that has a magnet stack with two isolated coils and electrical connectors.
(5) The probe is attached with two bolts.
(6) Low rotor speed is sensed by the dual element, N1 speed sensor.
(7) The probe sends an N1 speed signal through the EEC to the Electronic Centralized Aircraft Monitoring (ECAMS).
(8) ECAM displays the N1 speed signal as a virtual gauge on the aircraft flight deck's main instrument panel.
(9) Each channel of the N1 speed probe can command the thrust level through adjustment of the N1 speed.
(10) The EEC controls all engine subsystems to get the necessary N1 speed and keep the engine operation in all approved limits.
(11) The N1 speed probe makes a waveform that is positive as the target tooth gets near and negative as it goes by. Each one of the 20 teeth on the No. 2 bearing coupling nut, which goes in front of the probe, causes a sudden change in the magnetic field.
(12) The probe gives an oscillation signal which is a signal that is in proportion to the speed that the coupling turns.
(13) The probe, if correctly installed, has a minimum space between the sensor and the exciter teeth to let a strong signal be permitted and also prevent rub.
(14) The maximum limit (or overspeed warning) is set to N1 - 100%. When the indicator shows N1 - 100%, the display changes to red, the master caution light illuminates, and a single chime goes off.
B. Nf - Shaft Speed Indicating.
(1) Shaft speed indicating is used to sense and transmit fan rotor (Nf) speed to the EEC.
(2) The Nf speed probe is installed on the No. 1/1.5 bearing support.
(3) The probe is a one-channel sensor that has a magnet stack, coil and electrical connector.
(4) The probe has a two-bolt flange with jackscrew holes to remove the probe.
(5) Fan rotor speed is sensed by the one-element N2 speed probe.
(6) The probe sends an Nf speed signal through the EEC to the PHMU where it is used with the N1 vibration pickup to measure fan vibration. This speed signal and vibration data is used for on-wing trim balance. The Nf speed signal is not displayed in the cockpit.
C. N2 - Shaft Speed Indicating.
(1) Shaft speed indicating is used to sense and transmit high rotor (N2) speed to the EEC.
(2) The EEC uses the N2 speed signal for control of fuel and ignition during start, and also to monitor an overspeed condition of the high rotor.
(3) The N2 speed transducer is a speed coil that is located on the AGB which transmits the torque from the high rotor to the Main Gearbox (MGB).
(4) The N2 speed transducer is dual channel. It makes two isolated electrical signals, with frequencies that are related to N2 speed by N2 rpm.
(5) The speed transducer sends an N2 speed signal through the EEC to the ECAM. The ECAM displays the N2 speed signal as a three-digit digital value in the lower level engine indications that are on the aircraft flight deck's main instrument panel.