TM 11-6625-599-12
c. Increases in observed voltage are indi-
i n t r o d u c e d by the recorder, This condition
can only be remedied by utilizing another re-
cated by right deflection, and decreases by left
corder.
deflection.
d. Disconnect the standard cell from the
E x a m p l e : With the vtvm connected to a 450-volt dc
vtvm common input terminal and the input
p o w e r supply and set up to observe the excursions,
the following conditions were observed:
terminal.
RANGE switch at 500.
e. Place the RANGE switch at 5 0 , the
NULL switch at 10.
NULL switch at 10, and the voltage-divider
Voltage-divider switches A through E at
switches to indicate 10.000.
4, 4, 5, 5, and O, respectively.
f. Connect the vtvm common input terminal
VOLTS meter needle (varying) at .2 to
and the input terminal together. The VOLTS
O to .2 on lower scale.
meter will indicate full-scale deflection.
Indicates that the actual output of the
g. Adjust the GAIN ADJ RI control on the
dc power supply being observed was
rear panel of the vtvm for the desired amount
445.5 volts dc. The excursions about
of recorder deflection corresponding to full-
the nominal voltage w e r e 2 volts,
scale deflection of the vtvm.
which meant that the output voltage
h, Set up the vtvm to observe the excursions
varied from 443.5 to 447.5 volts. This
of a voltage (para 28).
information would be used to deter-
i. When the recording has been completed,
mine that the output was stable within
turn off and disconnect the voltage under meas-
an allowable 1/2 of 1 percent.
urement from the common input terminal and
d. Turn the NULL switch to VTVM.
the input terminal and the Teflon leads from
e. Turn off and disconnect the voltage under
the recorder output terminals.
measurement from the common input terminal
and the input terminal.
2-10. Measuring High Resistance
2-9. Recording Voltages Excursions
Perform the following procedures to deter-
mine the value of an unknown resistance be-
Provisions for connecting a recorder to the
tween 1 and 500,000 mehoms. In this appli-
vtvm are included on the rear panel. If a re-
c a t i o n a known voltage, indicated by the
corder is to be used to record excursions, care-
fully perform the following procedures:
voltage readout dials, is applied to a series cir-
a. Select a recorder with at least 10,000
cuit consisting of the unknown resistance and
megohms resistance between the recorder and
the known input resistance of the vtvm. The
ground.
voltage across the known input resistance is in-
b. Insure that the recorder output terminals
dicated by the VOLTS meter. (The scale of
the VOLTS meter is indicated by the NULL
switch. )
recorder input terminals are isolated from
ground.
c. Connect the recorder with Teflon leads
5).
and make the following checks:
b. Set the RANGE switch to 500 and the
(1) Connect a standard cell between the
NULL switch to 10.
common input terminal and the input
c. Connect the unknown resistance to the
terminal on the front panel of the
common input terminal and the input termi-
vtvm.
nal. Use short insulated leads to prevent meas-
(2) Measure the standard cell potential.
uring leakage resistance between leads.
(3) Alternately connect and disconnect
d. Adjust
voltage-divider
switches A
the recorder leads.
t h r o u g h E for full-scale deflection of the
(4) Check to see that there is no more
VOLTS meter. (The indicator meter will de-
than one-fourth of a small division
flect left. ) Set NULL switch to 1 or .1 if full-
deflection of the volts meter indica-
scale deflection cannot be obtained with NULL
tor.
switch set to 10. Determine the value of the
N o t e : E x c e s s i v e VOLTS meter indicator
unknown resistance from the following chart
d e f l e c t i o n as the recorder is connected and
when full-scale deflection is obtained:
disconnected indicates that leakage has been
15
