Description and Operation
Engine Vibration Indicator
Engine Vibration Monitor Unit
Engine Vibration Pickup
Trouble Shooting
Adjustment/Test
Engine Vibration Pickup........................................................................................... 77-32-11 Removal/Installation
*[1] Airplanes with EGT (MILLIVOLT) system. *[2] Airplanes with EGT (SERVOED) system.
Contents 77 Jun 20/83 Page 2 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
ENGINE INDICATING - DESCRIPTION
1. General
A. The engine indicating systems described in this chapter include the engine pressure ratio (EPR) indicating system, a tachometer system to measure the speed of the low pressure compressor (N1) and high pressure compressor (N2), an exhaust gas temperature (EGT) indicating system, and an airborne vibration monitoring system.
B. Each system provides a reading of engine operating conditions on indicators located on the center instrument panel. This information enables the monitoring of engine output and maintaining a selected flight performance.
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ENGINE PRESSURE RATIO INDICATING SYSTEM - DESCRIPTION AND OPERATION
1. General
A. The engine pressure ratio (EPR) indicating system shows the engine power output and is used for setting engine thrust and for monitoring engine performance. The EPR indicating system consists of one inlet pressure (Pt2) sensing probe, six-exhaust pressure (Pt7) sensing probes, an engine pressure ratio transmitter and a pressure ratio indicator for each engine.
B. The engine inlet and exhaust pressures, sensed by the pressure sensing probes, are transmitted to the pressure ratio transmitter. The transmitter converts the exhaust and inlet pressures into a ratio, provides output signals proportional to the EPR and transmits the signals to the EPR indicator located in the flight compartment. The indicator transforms the electrical input signals into the indicator pointer shaft rotation and digital three-wheel counter to show the engine pressure ratio. A test receptacle, used to attach a master indicator, is included in the circuit to provide a means of adjusting and checking the system (Fig. 1). On airplanes incorporating EPR-activated takeoff warning system, refer to Chapter 31, Instruments, for a description.
C. On airplanes incorporating a Performance Data Computer System (PDCS), an EPR indicator incorporating a second servo loop and a driven bug is installed on the pilot's instrument panel.
2. Inlet Pressure Sensing Probe
A. The engine inlet pressure (Pt2) is sensed by a probe similar to a pitot tube. This probe is mounted through the center of the nose dome with the open end of the tube facing the inlet air stream. The vent hole in the probe functions as the probe ice detector by decreasing engine inlet pressure (increasing EPR) when icing occurs. The probe is anti-iced by the engine anti-ice system.
3. Exhaust Pressure Sensing Probe
A. Each engine has six exhaust (discharge, Pt7) pressure-sensing probes projected into the stream of turbine exhaust gases. The probes are connected to a common manifold for obtaining an average pressure of the exhaust gases. Exterior connection to the manifold is made at a single point through the fan discharge outer duct at approximately the seven o'clock position (Fig. 1).
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Engine Pressure Ratio Indicating System 567
77-11-0 Figure 1 Jan 20/83
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BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
4. Engine Pressure Ratio Transmitter
A. The engine pressure ratio transmitter converts the exhaust pressure (Pt7) and the inlet pressure (Pt2) into a ratio, and generates three-phase electrical signals corresponding to pressure changes in the engine. It consists of two bellows (multi-cell diaphragms), a sensing mechanism, an amplifier, a motor-gear train, and a synchro transmitter. The engine pressure ratio transmitters are located at STA 570 on the right and left side of the airplane in the air conditioning bay.
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