Section II. 0PERATI0N UNDER USUAL CONDITIONS

TM 55-4920-411-13&P

Section II. 0PERATI0N UNDER USUAL CONDITIONS

CAUTION

To prevent damage to equipment, do not operate Temperature and

Speed Simulator at Ambient Temperatures of -25C, or lower.

3-2. Preliminary Starting Procedure.

j. Adjust TEMP OUTPUT potentiometer to produce

simulated temperature that lights the CAUTION light

a. Place POWER switch (S1) OFF.

on annunciator panel.

b. Place LOP/HI OIL TEMP switch (S3) to NORM.

k. Place the OIL PRESSURE switch in OFF position

c. Turn FUNCTION SWITCH (S2) to 0%.

and L 1 through L6 will turn off.

d. Turn VAR FREQ ADJ (F1) to 0.

1. The SECONDS display provides a means of

measuring start cycle duration in seconds (0 to 99). The

e. Connect Simulator as shown in Figure 2-2.

START/STOP/RESET switch, adjacent to the display,

allows the operator to start, stop, or reset the display.

3-3. Operation Procedure.

NOTE

3-4.

Procedures for Shutdown.

Additional operational checks of APU

a. Place POWER switch (S1) OFF

system is listed in TM 55-1520-237-23-3.

Disconnect Simulator cables.

a. Place POWER switch in OFF position.

3-5.

General Theory of Operation.

b. Turn FUNCTION SWITCH to 0%.

a. Signal Generator Board,

c. Turn VAR FREQ ADJ to O.

(1) The output of the 1 MegaHertz oscillator on the

d. Connect BH18604A test cable to SIGNAL OUT-

signal generator board (figure 3-2) is divided down to 768

PUT connector and to appropriate connector on APU as

Hz by a frequency divider consisting of Z1, Z2, and Z7.

shown in figure 2-2.

The output of the frequency divider provides the refer-

e. Connect BH2833 power cable to POWER connec-

ence signal for phase-locked loop Z6, Function switch S2

tor and to a 115 vac, 50 to 400 Hz power source.

and variable frequency adjust F1 preset a program-

mable frequency divider ( N). The output of the phase-

f. Place POWER switch and OIL PRESSURE switch

locked loop (VCO out) is defined by the equation fVCO

in ON position. Power lamp should illuminate and SEC-

= N x 768 Hz. An additional frequency divider (Z7)

ONDS display should read 00.

makes the signal unit output frequency = N x 768 or

g. Press LAMP TEST switch Lamps L1 through L6

48N. Since 100% rpm = 4800 Hz, N = 100 at 100% rpm.

should illuminate.

h. Determine at what frequencies the events L1

(2) The temperature output adjust controls the gain

through L6 occur in the APU under test.

of operational amplifier A5 in the temperature signal

generator. Two thermal resistors cancel the thermocou-

i. Select frequencies using the FUNCTION SWITCH

ple effect created by the joining of the thermocouple out-

and VAR FREQ ADJ.

put leads to the copper wiring of the signal generator.

NOTE

b. Display Board. One megahertz from the signal

The FUNCTION SWITCH selects out-

generator board is divided down to 1 Hz by Z6-Z8. This 1

puts of 5, 15, 70, 90, or 110% rpm. The

Hz signal is then counted, decoded and displayed.

VAR FREQ ADJ increases or decreases

Switch monitoring lamps L1-L6 are excited by 28 vdc

these outputs by + 1, 2, 3, 4, or 5% rpm.

from the APU. Load resistors R1-R6, located on a heat

An exception occurs when the FUNC-

sink in the bottom of the signal unit, provide the re-

TION SWITCH is at 5% and the VAR

quired load for the APU switches.

FREQ ADJ is at -5, the frequency output

is 1% rpm (not 0% rpm), equivalent to 48

Hz.

3-3