1515
j. Locate all voltage sources and accessible current paths before making con-
nections to circuitry. High voltage may appear unexpectedly or in unexpected
locations in faulty equipment. An open bleeder resistor, for example, may
result in a capacitor retaining a dangerous charge.
k. Make certain that the equipment being worked on is properly grounded and
fuses are the proper type and rating.
l. Double check switch positions and jack connections before applying power
to the Instrument.
m. Remain alert for low voltage circuits which may be floating at high voltage
with respect to earth ground and for composite voltages (AC + DC) such as
are found in r-f amplifiers. The floating voltage or composite voltage must not
exceed the Instrument’s rated maximum circuit-to-ground voltage.
n. Do not make electrical measurements where the air may contain explosive
concentrations of gas or dust such as in mines, grain elevators, gasoline
stations or in the presence of charging batteries until determined to be safe
by qualified personnel. Note that even metallic dusts can be explosive.
o. No General Purpose VOM is to be used to make electrical measurements on
blasting circuits or blasting caps. Use only VOMs designed for this purpose.
4.2 Polarity Reversing
The function switch conveniently reverses polarity of the internal battery to facili-
tate testing semiconductor devices. The +DC and –DC positions transpose inter-
nal connections to the COMMON and +jacks and therefore can also be used to
reverse polarity of external voltages and currents connected to these jacks (only).
Because polarity reversing momentarily interrupts the circuit, it should not be
done while measuring current or voltage without first turning off the circuit power.
When making measurements on the 50mA/250mV, 1 volt, or 10 amp range, po-
larity can be corrected only by reversing the test leads.
4.3 Measurement of Unknown Voltage or Current
The approximate voltage or current to be measured is sometimes known and the
correct range can easily be selected. However, particularly when working upon
faulty equipment, the voltage or current can either be unknown or higher than
normal or anticipated. When working upon unfamiliar or unknown equipment,
always begin a measurement using the highest range available on the Instru-
ment. Once it is determined that the voltage is within the limits of a lower range,
change to the lower range.
4.4 Test Leads
Test leads are provided with accessory screw-on alligator clips which may be
attached to the probe tips. Eliminating the need to hand-hold test prods to a
circuit for extended periods, the test clips also reduce hand proximity to a high
voltage circuit while energized. Circuit power must, of course, be turned off and
any charged capacitors discharged before connecting or disconnecting clips to
or from the current.
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