15
f.
Do not work alone on high voltage circuits. Make certain that someone ca-
pable of giving aid is nearby and alert.
g.
Do not handle the Instrument, its test leads, or the circuitry while high voltage
is being applied.
h.
Hands, shoes, floor, and workbench must be dry. Avoid making measure-
ments under humid, damp, or other environmental conditions that could
effect the dielectric withstanding voltage of the test leads or Instruments.
i.
Do not change switch settings or test lead connections while the circuit is
energized. A mistake could result in damage to the Instrument and personal
injury.
j.
Locate all voltage sources and accessible current paths before making con-
nections to circuitry. High voltages may appear unexpectedly or in unex-
pected 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.
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 Instruments 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.
4.2
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 50
μ
A/250mV, 1 volt, or
10 amp range, polarity can be corrected only by reversing the test leads.
4.3
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.
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