OPERATION
Usi
ng
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
vol
tage.
A special lead is provided
with
the multiplier for connection
to the high
potenti
al
point.
HE
AVY
AC
CURREN
T
MEASUREMENT
AC Currents between 1
OA
and
600A may be measured by
use
of
the
AVO
Multi-range Current Transformer (Pt. No.
45869).
Fu
ll operating instructions for its
use
are packed
with the
optional accessory.
HEAVY
DC
CURR
ENT
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
.sing 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
enti
re
scale length.
NON-SINE
WAV
EF
ORMS
In
as
much
as
rectifier moving coil instruments give readings
on 'ac'
proportional
to
the mean and not the r.m.s.
va
lue
of
the waveform
with
which they
are
presented, they depend
f
or
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
wil
l 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.
9
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