TM 11-6625 -444-14-1
The following procedures describes operation of the
b. Connect the voltmeter to an ac source. (Ac
AN/GSM-64B as an rms voltmeter. To operate the
source must have outputs of 1, 10, 100, and 1,000
voltmeter in other modes, refer to Chapter 3.
volts at 500 Hz 0.03 percent. )
a. If it is desired to change input coupling,
c. Set the voltmeter RANGE switch to AUTO.
remove the voltmeter dust cover and set the input
Set the ac source to the following voltages at 500
coupling switch to ac or dc.
Hz. Check to see that the voltmeter readout is
within tolerance listed:
source.
Ac source output
Voltmeter indication
c. Disconnect the test leads from the INPUT
0.99870 to 1.00130
1 vrms
terminals.
9.9870 to 10.0130
10 vrms
100 vrms
99.870 to 100.130
(1) POWER switch to ON.
1000 vrms
998.70 to 1001 .30
(2) SAMPLE RATE control fully clockwise.
d. Set the ac source
to
zero
output
and
e. Push VDC pushbutton and 10 RANGE push-
disconnect the voltmeter.
button.
f. Connect shorting jumper between HI and LO
a. To change the input coupling, remove the
INPUT terminals. Check to see that GUARD
voltmeter top cover and set the INPUT coupling
terminal is connected to LO INPUT terminal.
switch to ac or dc.
g. Rotate DC ZERO control to obtain a readout
b. Connect the voltmeter line cord to power
of 00.0000.
source.
h. Disconnect the shorting jumper from the
c. Press the VAC pushbutton and desired
INPUT terminals and reconnect test leads.
RANGE pushbutton.
i. Press the VAC pushbutton and desired
d. After completing ac voltage measurements,
RANGE pushbutton.
place the voltmeter in standby or shutdown status
7-8. Initial Adjustments
by following the procedure given in paragraph 3-11
The following checks can be performed to check
or 3-12, respectively.
correct operation of the ac converter.
FUNCTIONING OF PL-1370 / GSM-64B
Section II 1.
7-10. Introduction
b. The ac converter consists of a range amplifier
and rms detector. The output voltage from the
This section describes the functioning of Plug-In,
range amplifier is 1 volt rms maximum, for a full
Electronic Test Equipment PL-1370/GSM-64B. It
scale input voltage. A scaled output voltage from
covers the interaction between the major circuit
the range amplifier is applied to the rms detectors
elements of the ac converter through a block
balance amplifier where any negative-going signals
diagram and detailed circuit description. Refer to
are inverted. The output of the balance amplifier is
summed with the output of the range amplifier at
for the detailed schematic diagram of the ac
the summing junction of the squaring amplifier.
converter.
This action provides a rectified version of the
7-11. Block Diagram Description
range amplifier output. The rectified signal is
a. The ac converter provides a dc voltage,
processed by the squaring amplifier, integrating
proportional to the rms value of the applied input
amplifier, and square root amplifier, respectively.
voltage, to the A/D converter of the AN/GSM-
These three amplifiers perform squaring, in-
64B. This dc voltage is digitized by the A/D
tegrating, and square rooting functions which
converter and subsequently displayed as a front
result in a dc voltage proportional to the rms value
panel readout. A simplified diagram of the circuits
of the INPUT terminal voltage.
involved in the rms conversion process is shown in
Change 1 7-3
