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4. Engine Vibration Indicator
A.  A vibration indicator shows the vibration level of an engine. It is a permanent magnet, temperature compensated dc microammeter, contained in a hermetically sealed case. The round dial face is graduated in mils (thousandths of an inch) of engine vibratory displacement (amplitude of vibration). There are two indicators, one for each engine, mounted on the center instrument panel.
5.  Operation
A.  The monitor unit and test switch utilizes ac power, however, dc power is used for integral instrument lighting.
B.  With engines running, the airborne vibration monitoring system is energized by closing the applicable circuit breakers. The vibration pickups generate alternating electrical signals proportional to the amount of engine vibration due to the relative movement of a permanent magnet and a coil in each pickup. The generated electrical signals are the input received by the monitor unit. The monitor unit integrates the input signals, filters out undesired frequencies of vibration, and amplifies and rectifies the alternating signals to pulsating dc signals. The dc signals are transmitted through sensitive relays to the corresponding vibration indicators. The indicators transform the pulsating dc signals into the pointer movements on the indicator dials. Engine vibration readings can be obtained from either the engine inlet pickups or the turbine section pickups of the two engines simultaneously by properly positioning the pickup selector switch. The accepted vibration level at any selected engine rpm will vary between engines. If at any time an indicator shows engine vibration increasing above the normal level, the test switch should be used to determine if the system is functioning properly before corrective or compensating action is taken.
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502  Airborne Vibration Monitoring System Component Location 
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Airborne Vibration Monitoring System Schematic  502 
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AIRBORNE VIBRATION MONITORING SYSTEM (CONSOLIDATED) - ADJUSTMENT/TEST
1.  Airborne Vibration Monitoring System Operation Test
A.  Test Airborne Vibration Monitoring System Operation with Engines Shut Down
(1)  
Prepare Airborne Vibration Monitoring System for Test.

(a)  
Provide electrical power.

(b)  
Open ENGINE VIB AMP and ENGINE TRIM and VIB CONT circuit breakers on circuit breaker panel P6.

(c)  
Place ENG VIBRATION PICKUP selector switch in TURBINE position.

 

(2)  
Test Airborne Vibration Monitoring System Indicator

(a)  
Observe vibration indicators to establish that each indicator pointer is within one needle width of the zero position. Replace indicator(s) if not within limits.

(b)  
Close ENGINE VIB AMP and ENGINE TRIM AND VIB CONT circuit breakers. This operation may cause a slight fluctuation and up-scale movement of indicator pointers. The final indicator pointer position should be within one needle width of zero.

(c)  
Push TEST switch and observe that pointers read between 3.5 and 4.5 mils. Check that both indicators read within 0.5 mil of each other.

(d)  
Release TEST switch.

(e)  
Place ENG VIBRATION PICKUP selector switch in INLET position.

(f)  
Repeat steps (c) and (d).

 

(3)  
Restore Airplane to Normal Configuration

(a)  If no longer required, remove electrical power from airplane.
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B.  Test Airborne Vibration Monitoring System Operation with Engines Operating
(1)  
Prepare Airborne Vibration Monitoring System for Test

(a)  
Start engines in accordance with Chapter 71, Power Plant.

(b)  
Run engines at idle.

(c)  
Close ENGINE VIB AMP circuit breaker on circuit breaker panel P6-2.

 

(2)  
Test Airborne Vibration Monitoring System Operation

(a)  
Place ENG VIBRATION PICKUP selector switch to INLET position.

(b)  
Slowly advance engine thrust lever to maximum thrust position, observing corresponding engine vibration indicators.
　
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