(b)  
Open circuit input signal conditions or out of range values of oil quantity are signalled by slewing the display indication to zero, holding the indication for 2 seconds, then displaying "dashes". If the oil quantity returns to within range, the display automatically indicates the new value.

 (8)  
Engine Vibration

 (a)  The engine vibration signal is derived from the Airborne Vibration Monitor and is a dc current proportional to the vibration level. The signal conditioning consists of applying the input current to a resistive load and amplifying the developed voltage with a differential amplifier. The amplifier output is applied to an analog to digital converter, via a multiplexer. The digitized values are processed to compute the vibration level, formatted and displayed on an LED pointer, under the interrupt control of the microprocessor.
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 ú ú 04 Page 23 ú Mar 15/91
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A 737-300/400/500MAINTENANCE MANUAL
 (b)  Open or short circuit input signal conditions, or out of range values of engine vibration are signalled by slewing the pointer to zero, holding the setting for 2 seconds, then "blanking" the display. If the vibration returns to within range, the display automatically indicates the new value.
 (9)  
Hydraulic Oil Pressure

 (a)  
The hydraulic oil pressure signal is derived from an 11.8v, 400 Hz, 3 wire synchro. The rotational angle of the synchro representing hydraulic pressure. The signal conditioning consists of full wave rectification of two of the synchro line-to-line voltages with respect to the synchro 400 Hz power supply. The rectified voltages (VA and VB) are smoothed and routed to an analog to digital converter (ADC), via a multiplexer. The digitized ADC output values are processed to determine the synchro angle, which is then used to compute the hydraulic pressure. The microprocessor system formats the hydraulic pressure value and displays it on an LED pointer, under interrupt control of the microprocessor.

 (b)  
Open circuit input signal conditions or out of range values of hydraulic pressure are signalled by slewing the display indication to zero, holding the setting for 2 seconds, then "blanking" the display. If the hydraulic pressure returns to within range, the display automatically indicates the new value.

 (10)
 Hydraulic Oil Quantity

 (a)  The hydraulic oil quantity signal is derived from a float-operated linear potentiometer assembly. The three wire potentiometer input is applied to two differential amplifiers, from which two ouput voltages VA and VB are derived, the voltages are dependent upon the wiper position and hence the oil quantity. The voltages are applied to an analog to digital converter, via a multiplexer and the digitized values used to compute the percentage of oil in reservoir. The computed value is formatted and displayed on a 2 1/2 digit 7 segment display, under the interrupt control of the microprocessor. The interrupt rate (200 Hz approx) is such that flicker-free operation is ensured.
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 ú ú 04 Page 24 ú Mar 15/91
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500MAINTENANCE MANUAL
 (b)  
The "left" channel processes SYSTEM B hydraulic oil quantity, and the "right" channel processes SYSTEM A hydraulic oil quantity.

 (c)  
Open circuit or short circuit input signal conditions, or out of range values of oil quantity are signalled by slewing the pointer to zero, holding the setting for 2 seconds, then displaying "dashes". If the hydraulic oil quantity returns to within range, the display automatically indicates the new value.

 (d)  
The hydraulic oil refill level (RF88%) is defined as 88% of full and is presented as a legend above the BITE test button.

 (11) BITE/Operational Test
 (a)  
An unmarked, recessed push switch is located in the bottom of the front bezel. Operation of this switch will, when both engine oil pressure are below 13 psi, initiate a BITE sequence.
　
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