Calibration

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

fig. 4).

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-