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7
Fig. 3.
Measurement
flow-chart
The
various
circuit
functions
are
now
described together with explanations of
basic principles as necessary.
1.3.2.
Analog
section (standard
measurements)
1.3.2.
1.
Direct voltage
measurements
The
unknown
voltage to
be
measured
is
passed to the
a.c./d.c.
voltage attenuator
where by means
of
resistors
switched
by
relay
contacts controlled
from
the n?, the attenuation factor
is
changed
from
the basic
2V
range
to
give
20V,
200V
and
2000V
ranges.
The
200mV
range
uses
the
2V
range attenuator
position,
but
the
ADC
is
switched
to
the
lOOmV
position to
give
the necessary
xIO
gain
factor.
From
the
voltage attenuator the
signal
is
fed to
an
active
filter,
which
stabilises
the voltage passed to the
ADC.
The
ADC
converts
this
analog
voltage into
digital
form
for the
/iP
to measure.
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