2471F INSTRUCTION MANUAL
56-101-00220-B
CH. 2
09
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Page 11 of 13
(9) Sometimes insulation tests are required in polarized circuits that will exhibit low resis-
tance when subjected to an opposite polarity. Consult the test specifications for polar-
ity. The
RED
probe is always positive polarity from the megohmmeter. If in doubt,
make a test with probes connected in one manner and then reversed for a second test.
A substantial difference in reading will indicate a polarized circuit.
(10) If the megohmmeter indicates either an upward or downward scale reading with the
probes connected, but with the pushbutton released, the circuit under test is ener-
gized. (Small potentials may not produce a reading without button pressed but will in-
troduce erroneous readings). Make certain that all power to the device has been re-
moved and that all capacitances have been discharged. Some devices will retain re-
sidual voltages long after the power has been removed.
(11) Some tests require that jumpers be placed between two or more points on the device
under test while making insulation tests. This is generally done to prevent possible
damage to portions of the circuit that are not designed for high voltage application, or
to make an overall insulation test for a number of circuits simultaneously. Be certain to
follow the test specification procedures when jumpers are indicated.
3. CARE AND MAINTENANCE
The 2471F megohmmeter is designed to give lasting accurate performance provided rea-
sonable care is exercised in operating and handling.
(1) Keep test set in its carrying case at all times to reduce the danger of damage from vi-
bration, shock, and moisture. Exercise reasonable care to avoid dropping or excessive
shock. Protect from rain and exposure.
(2) Store in cool, clean, dry place to reduce contamination and battery deterioration.
RE-
MOVE BATTERIES IF TEST SET IS TO BE STORED FOR PROLONGED PERIODS.
(3) Do not subject megohmmeter to electrically energized circuit. The 2471F is safe from
damage from externally applied AC or DC voltages up to 300 volts, but high voltages
may be dangerous to the operator and will produce erroneous readings.
(4) Two sets of batteries are used. The three smaller AA cells (Eveready E91, or equiva-
lent) provide the positive 4.5 volts for the operational amplifier and triggering of the bat-
tery transistor switches. The three larger C cells (Eveready E93, or equivalent) provide
the negative 4.5 volts for the operational amplifier and high voltage converter. The
2471F is designed for operation with alkaline type cells, but conventional zinc carbon
cells may be used as temporary replacements.
(5) The
B1
position of the
FUNCTION
switch connects the meter for testing the condition
of the C cells, and the
B2
position for the AA cells. A reading below the
BATT. OK
ra-
dial on the meter scale is an indication of unsatisfactory battery condition. A more sig-
nificant test may be made by observing the meter on the
B1
and
B2
positions with the
probe pushbutton depressed. The pointer will drop slightly on the
B1
position, but
should remain above the
BATT. OK
radial. There should be no more than a barely
perceptible drop on
B2
with the button depressed.
Содержание 101-00220
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