TB 55-4920-389-34
e. Connect test equipment as shown in figure 4-1.
f.
Allow equipment to warm up and stabilize.
Section IV. CALIBRATION PROCESS
NOTE
Unless otherwise specified, verify the results of each test and take corrective action
whenever the test requirement is not met before continuing with the calibration.
4-1. Tachometer Indicator.
a. Performance Check.
(1) Set the test instrument POWER switch to START.
(2) Adjust test instrument SPEED ADJUST 0-700 RPM control clockwise (CW) to indicate 500 RPM on the low
scale of test instrument tachometer indicator, while holding TACH RANGE SEL switch to LOW position.
(3) Adjust stroboscope (Al) RPM controls until a single motionless image of the back tape appears. Stroboscope
will indicate between 485 and 515 RPM. If not, perform b(1) and (2) below.
(4) Set the TACH range selector to HIGH.
(5) Set the SPEED ADJUST 0-700 RPM fully clockwise (CW).
(6) Adjust test instrument SPEED ADJUST 700-50000 RPM control clockwise (CW) for each test instrument
tachometer indicator indications as listed in table 4-1. Stroboscope will indicate within the limits specified. If not, perform
b(3) and (4) below.
(7) Set test instrument DRIVE ROTATION control counterclockwise (CCW) position.
(8) Repeat techniques (2) thru (6) above. Indications will be within the limits specified.
b. Adjustments.
(1) Set the stroboscope to indicate 500 RPM.
(2) Adjust the test instrument SPEED ADJUST 0-700 RPM control until a single motionless image of the black
tape appears on stroboscope. Adjust the test instrument TACH CAL LOW potentiometer (located behind the tachometer
indicator) for 500 RPM on the tachometer, while holding TACH RANGE SEL switch to LOW position,
(3) Set the stroboscope to indicate 4500 rpm.
(4) Adjust the test instrument SPEED ADJUST 700-5000 RPM control until
4