OPERATION
If
an overload is applied to the meter, either forward or in
reverse, the cut-out knob springs from its normal position
in the panel, thus breaking the main circuit and the
red
portion
of
the
cut-out
knob will show. This knob
has
only
to be depressed
to
render the instrument again ready for
use.
It is important
to
note that the cut-out should never
be
reset when the instrument is connected
to
an external
circuit, whilst the fault which
has
caused the overload
should be rectified before the meter is reconnected.
Although the overload mechanism giv
es
almost complete
protection
to
the meter,
it
cannot be guaranteed to com-
pletely fulfil its function in the very worst
cases
of
misuse,
such
as
the mains being connected across the meter when
set to a current range.
It
should
be
noted that mechanical
shock
to
the instrument
will
sometimes trip the
cut-out
mechanism. Additional protection is provided on resistance
ranges by a fuse connected in the
nx
1 and i1x1 00 ranges.
WARNING
Special care must be taken when using the
instrument
to
service television receivers
or
other apparatus
employing capacitors
of
large capacitance,
for
the inclu-
sion
of
such components in a circuit may mean that very
heavy peak currents may
flow
when the apparatus is
switched on.
Such surges produce a peaky wave form
and
although these peaks are only
of
a
few
milli-seconds
duration, they may, never-the-less, damage the
Instru-
ment diodes.
8
EHT
MEASUREMENT
CAUTION:
It
is recommended that neither the meter.
multiplier
nor
leads are handled whilst high voltage tests
are
in
progress.
Using
the
Combined
10kV/30kV
Multiplier
A combined 1
OkV
and 30kV de multiplier is available for
use
with the instrument .The Multiplier should
be
connected
to
the AVO METER set
to
the 1
OV
de range. It is recommend-
ed that the meter is kept as near earth potential
as
possible
and the Multiplier
used
at
the high potential end. e.g.
when measuring
an
e.h.t. voltage when the negative line is
earthy, the Multiplier should be connected between the
point of positive potential and the positive terminal of the
meter.
In
addition, the
low
potential end
of
the meter must
be
connected
to
the
low
potential
of
the supply being
measured using the
low
potential lead provided. A cap is
provided which should always
be
in position over the high
voltage terminal not in
use
.
A resistor connected permanently across the multiplier
terminals prevents the full voltage being present should the
meter be disconnected.
General Note: When measuring high ac and de voltages
(say above
SOOV)
unless the common negative terminal is
either earthy or connected
to
earth, errors
will
be intro-
duced
if
the instrument is touched during a reading.
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