15
ments. A mistake could result in damage to the Instrument and possible
personal injury.
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 upon is properly grounded
and fuses are of the proper type and rating.
l. Check and double check switch positions and jack connections before apply-
ing power to the Instrument.
m. Always 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 VOM’s designed for this purpose.
4.3 Polarity Reversing
The function switch provides a convenient means to reverse polarity of the inter-
nal battery to facilitate testing semiconductor devices. The +DC and –DC posi-
tions transpose internal 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 cir-
cuit, 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, polarity can be corrected only by reversing the test leads.
4.4 Measurement of Unknown Voltage or Current
Sometimes the approximate voltage or current to be measured is known and the
correct range may easily be selected. It is often the case, however, particularly
when working upon faulty equipment, when the voltage or current is either un-
known or may be much higher than normal and anticipated. Whenever working
upon unfamiliar or unknown equipment, always begin a measurement using the
highest range available on the Instrument. Once it is determined that the voltage
is within the limits of a lower range, change to the lower range.
4.5 Test Leads
These are provided with accessory screw-on alligator clips which may be attached
to the probe tips. Aside from the convenience of eliminating the need to hand-
hold test prods to a circuit for extended periods, the test clips provide a means of
reducing hand proximity to a high voltage circuit while energized. Circuit power
must of course be turned off and any charged capacitors discharged before con-
necting or disconnecting clips to or from the current.
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