AVO AVOMETER 8 Руководство по эксплуатации - Страница 11
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Using the 30kV Probe Multiplier
A
30kV de
Multiplier is available for use in series with the
meter set to its 1 OOOV de range,
readings
being made
direct
in
kV
on
the 0-100 scale and multiplied by 300. It is most
important
to
ensure that the
meter is kept in
the
earthy end
of
the
circuit
and the
multiplier connected
to
either
the
positive or negative terminal whichever is at
high
potential.
This
method
of
connection to get forward pointer indica-
tion with the meter
earthy is recommended as
we
do
not
think it desirable to use the moving
coil
reverse button
when measuring
high voltage.
A special lead is
provided
with the
multiplier
for connection
to the high potential point.
HEAVY
AC CURRENT
MEASUREMENT
AC
Currents between
1
OA and 600A may be measured by
use of the AVO Multi-range Current Transformer ( Pt.
No.
45869).
Full
operating
instructions
for its use
are
packed
with the
optional
accessory.
HEAVY DC CUR RENT MEASUREMENT
D.C.
currents between
1
OA and
600A may be measured
by
use
of the appropriate
AVO
DC Shunt
accessory.
When used
with
the
AVOMETER
8 Mk
5,
the
shunts
produce a voltage
drop of
1
OOmV when
pas.
s ing
current
at their
maximum
rating.
The
Shunt
should
be
connected by means of
its two
main
terminals
in series with
the
circuit
to
be measured. The
meter set
to
its
50!1-A
(1 OOmV) de position should
then be
connected to the
two small studs on the shunt end
blocks.
The
AVOMETER
when so set, consumes only 5011-A
at full
scale deflection,
a value which is
negligible
in comparison
with the
full
scale current of the shunt.
The
millivolt
drop
across the
shunt
is directly
proportional
to
any
current
which may flow through it
and since
the
deflection
on the
meter is
directly proportional
to the
millivolt
drop across
the terminals, the instrument indicates correctly over
its
entire scale length.
NON-SINE WAVEFORMS
In as much as rectifier moving
coil
instruments give readings
on 'ac' proportional to
the
mean
and
not the r.m.s. value
of
the waveform with which they
are
presented,
they
depend
for their accuracy, not
only
upon their
initial
calibration,
but also upon
the
maintenance
of a
sinusoidal
waveform.
Since the form factor (r.m.s. value divided by mean value)
of a sine wave is 1.11, this has been taken into account in
calibrating
the
meter,
which
does,
therefore,
indicate
r.m.s.
values
on the assumption that the normal
sine wave
will
be
encountered. Generally
speaking, considerable waveform
distortion
can occur without appreciably affecting
the form
factor
and resulting accuracy of measurement, but
the
user
should
recognise
the possibility
of some error
when
using
distorted
waveforms, squarish waveshapes
producing
high
readings
and peaky
ones,
low
readings.
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