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12. Calibration
Note.
Set the FUNCTION SELECTOR
switch of Modulator MD83A/ARN (signal
a. Preliminary Calibration Procedure. Be-
g e n e r a t o r ) to CAL, and the SPECIFIC SIG-
fore using the resolver test set, calibrate it to
N A L SELECTOR switch to 30-VAR to o b -
t a i n a variable-phase 30-cps output signal of
produce the exact phase shift required for
variable amplitude at the MOD OUTPUT con-
proper omnirange zeroing of resolvers. Cali-
nector.  T h e amplitude of the variable-phase
brate the resolver test set weekly, each time
o u t p u t is then adjusted with resistor R138,
troubleshooting is performed, and each time it
and the amplitude of the reference-phase out-
has been moved or handled extensively, since
put is adjusted with R151. Adjust the ampli-
tude of the signal at each output to the values
vibration could disturb the control settings.
s p e c i f i e d in (2) through (10) below.
(1) Set the controls of the resolver test
(2) Adjust the signal generator variable-
set to the positions listed in the fol-
phase output (with R138) to provide
lowing chart:
an output of 1.5 volts as indicated on
the ac voltmeter attached to the re-
solver test set VAR connector.
(3) Remove the ac voltmeter cable from
the VAR tee connector and recon-
nect it to the REF. tee connector (2,
fig. 4) and adjust the signal generator
(2) Connect all equipment as shown in
reference-phase output (with R151)
figure 4 with the ac voltmeter con-
to provide an output of 7 volts as indi-
netted to one end of the VAR tee
cated on the ac voltmeter.
connector (1, fig. 4). Be sure that
the hot lead of the oscilloscope is con-
(4) Remove the ac voltmeter cable from
nected to the red terminal of the filter.
the REF. tee connector and recon-
Note. Since the course indicator or course selector
nect it to the VOLTMETER connector
serves only as a load for the 30-cps reference signal, it
(3, fig. 4) ; adjust the INPUT LEVEL
i s not necessary to use a course indicator or course
control to obtain 4.25 volts as ob-
selector that has had previous O R Z a d j u s t m e n t
served on the ac voltmeter.
(3) Using a screwdriver, remove the pro-
(5) Remove the ac voltmeter from the
tective caps on the front panel cover-
VOLTMETER connector and recon-
ing the CAL. E and CAL. controls
nect it to the OUTPUT connector (4,
(fig. 3) and loosen the locknuts so
that the shafts are free to turn.
(6) Turn the CAL. E control fully clock-
(4) Connect the ac voltmeter (TM 11-
wise.
6625-320-12), oscilloscope (TM 11-
6625-219-12), and signal generator
(7) Alternately adjust the signal gener-
to the power source.
ator phase dial and CAL. E. control
on the resolver test set to obtain a
(5) Energize all test equipment and allow
minimum-amplitude signal indication
15 minutes warmup time.
(null) on the oscilloscope. This will
b. Calibration Procedure.
occur near a reading of 180 on the
Note. In the process of obtaining a null in the follow-
phase dial of the signal generator.
ing procedure, start with a relatively high range setting
Note the exact phase dial reading
o n t h e ac voltmeter and a high gain setting on the
where the null occurs.
o s c i l l o s c o p e . As the null is aprpoached, the range set-
ting of the ac voltmeter is decreased so that the reading
Notes.
t a k e s up more than one-third of the scale used. The
1. When adjusting the phase dial of the
o s c i l l o s c o p e gain setting remains constant. The most
s i g n a l generator, a l w a y s approach the point
accurate null indication will be on the oscilloscope.
where the null occurs, using the same direction
of dial rotation to minimize possible errors due
Set the signal generator phase dial to
(1)
to mechanical backlash.
0 and the output frequency to 30 cps.
2. During the calibration and test proce-

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