Principles Of Operation - Datron 1061A User Handbook Manual

Principles of
operation
Fig
1.1
DVM
simplified block
diagram
Figure
1.1
shows
how
the
DVM
achieves
its
basic
measurement
functions,
its
advanced measurement
and computing
functions
and
the interfacing
with
other
equipment
in
systems applications.
Voltage
measurement
The
instrument comprises a
fully
floating isolation
amplifier with
electronically
switched
gain ranges
providing
a
full
range output
which
is
applied to the
analog
to digital converter.
AC
voltage
measure-
ment
is
achieved using a
True
RMS
AC
converter
which
converts
AC
signals
to
DC
and
applies the
DC
voltage
to
the analog to digital
converter.
Resistance
measurement
Resistance
measurement
is
achieved by passing the
current
from an
internal
precision current source
through
the
unknown
resistance
and
sensing the
voltage
developed
across the resistance.
Current
measurement
For
current
measurement, switched precision
shunts
are fitted internally.
The unknown
current
is
passed through these
and the resulting voltage
sensed.
Analog
to digital
conversion
The
signal
from
the
DC
isolator
or
AC
converter
is
applied to
the input of a high gain integration
amplifier.
The
integration capacitor
starts
charging
from
a zero state at
a
rate
proportional
to the
magnitude of the
incoming
signal.
The
integration
period
is
approximately
20mS
(1061) or
160mS
(1071).
Fig 1.2
Simplified
measurement
cycle
At
the
end of
this
period, a reference signal of
opposite polarity to
the
input
signal
is
applied
and
the time
taken for the capacitor
to
discharge
to
zero
volts
is
measured
(null detection),
providing
an
accurate
computation
of
the
input
signal
magnitude.
1-3