AVO AVOMETER 8 Інструкція з експлуатації Посібник з експлуатації - Сторінка 6
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Друкувати сторінкуOPERATION
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 introduced
if
the
instru-
ment
is
touched during
a
reading.
On de ranges, the meter
consumes
only 50 microamps at
full scale deflection
corresponding
to 20,0000/V.
In the
case of ac ranges above 1 OV, full scale deflection is ob-
tained with
a
consumption of 0.5mA
(20000/V).
The
1
OV
range
is 1 0000/V. The 3V
ac
range
consumes
1
OmA
at full scale deflection. The meter maintains a high degree
of accuracy
for
audio frequency
tests
up to 15kHz
on
ranges up
to 300V ac. All
current
consuming voltmeters,
however sensitive, draw current to varying degrees from
the circuit
under test,
thus causing the voltage to
fall
at
the
point
of
measurement.
Owing
to
the
high sensitivity of the Model 8 on de ranges.
this
effect is unlikely to be of importance except
in
a
very
few instances.
It
might effect the measurement of e.h.t.
voltage on a television
set
or the tapping on a potential
divider, where the resistances are comparable with the
resistance of the meter on the range in use. It is generally
possible to use
a meter on a
higher
range
than
absolutely
necessary where the
higher meter resistance
causes less
disturbance. At the
same
time
adequate
pointer deflection
for reasonable
accuracy should
be attained.
4
When
it
is essential to obtain an accurate indication of the
voltage developed
across
a
high
value
resistor
it is
some-
times preferable to
insert
the meter
in
series with
it
and to
measure the current flowing
.
The
reading
in milliamps,
multiplied by the value of the
resistance in
thousands of
ohms, will give the developed
voltage.
RESISTANCE MEASUREMENT
There
are three self-contained ranges covering from
1 ohm
to 20 megohms and provision is made
for
upward
ex-
tension
of these
limits.
On resistance ranges, the
meter must have, in addition to
the normal
instrument zero a resistance zero corresponding
to the
full scale
deflection
of
the
meter.
Before carrying
out tests
for
resistance, a check should
be
carried out
to
ensure that the
meter actually
indicates
zero ohms
irres-
pective
of
the
condition of
the
battery (within the limits
of adjustment
described
later).
The accuracy, should be within 3% of the
reading
about
centre scale. increasing up
to about
10% of the
indication
around deflections corresponding
to
10% and 90% of
full scale deflection.
Resistance tests should never
be
carried out on
components
which are already
carrying current.