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The EEC changes the analog data into ARINC 429 digital data. The EDIU receives the digital data and sends ARINC 629 data to the AIMS.
The EEC also sends analog N1 and N2 signals. Analog N1 signals go to the EDIU and the AVM signal conditioner. Analog N2 signals go to the AIMS and the AVM signal conditioner.
The AIMS uses the analog N2 signal when there is no digital N2 signal.
The AVM signal conditioner uses the analog speed signals in its vibration calculations.
The EDIU uses the analog N1 signal for thrust asymmetry compensation (TAC). See the rudder control section for more information about TAC (SECTION 27-21).
Indication
The EICAS and secondary engine displays show N1 and N2. The data also shows on the performance maintenance page. Percent rpm are the units for the data.
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ENGINE INDICATING -ENGINE TACHOMETER -GENERAL DESCRIPTION

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ENGINE INDICATING -ENGINE TACHOMETER -N1 SPEED (P2.5/T2.5) PROBE

N1 Speed Probe
The N1 speed (P2.5/T2.5) probe supplies the EEC with electrical signals of N1 and T2.5, and a pneumatic signal of P2.5. The probe attaches to the intermediate case above the fan duct inner wall liner at the 5:00 position.
The N1 speed probe has a sensing head that is near a wheel with teeth on the N1 shaft. The probe gets electro-magnetic pulses as the teeth go by the sensing head.
When you install a new N1 speed probe, you must do a check of the distance between the sensing head and the teeth on the N1 shaft. You use shims to adjust the distance between the sensing head and the teeth.
Training Information Point
Loosen and tighten the attachment bolts in small increments.
You  use  jackscrews  to  move  the  probe apart  from  the 
intermediate case. 
CAUTION: DO  NOT  TURN  THE  PROBE  UNTIL  YOU 

DISENGAGE THE PROBE FROM THE INNER BRACKET. IF YOU DO, DAMAGE TO THE PROBE OR THE ENGINE CAN OCCUR.
CAUTION:  MAKE SURE YOU INSTALL THE PROBE WITH THE ELECTRICAL CONNECTOR REARWARD. IF YOU DO NOT, DAMAGE TO THE PROBE OR ENGINE CAN OCCUR.
CAUTION:  DO NOT TURN THE PROBE WHEN YOU INSTALL IT. IF YOU DO, DAMAGE TO THE PROBE OR THE ENGINE CAN OCCUR.
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ENGINE INDICATING -ENGINE TACHOMETER -N1 SPEED (P2.5/T2.5) PROBE

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ENGINE INDICATING -ENGINE TACHOMETER -FUNCTIONAL DESCRIPTION

N1 Speed Signal
The N1 speed signal comes from a speed probe with two sensing circuits. One N1 signal goes to channel A of the EEC. The other signal goes to channel B. The LP shaft has a wheel with teeth that cause electromagnetic pulses as they go by the speed probe.
　
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