Marconi TF 933C - Chapter 3 TECHNICAL DESCRIPTION; Circuit Description

Chapter
Technical
description
3.1
CIRCUIT
DESCRIPTION
The electrical measuring circuit, as shown in Fig. 7.1, consists o! a
Wheatstone
bridge
in
which the
specimen forms one arm and the
two calibrated moisture controls
form
the ratio
arms. The
out-of-balance voltage
is applied
to the inputs
of a FET
differential
amplifier
and
displayed
on a
centre zero
meter.
the
function
switch
is
in
ZERO
position
the sample
is
disconnected and
the
'UNITS'
arm
of
the
bridge.is
shorted
out.
The
red
ZERO
control, R
19, is then
used
to
balance
the
amplifier
for
zero
output.
Preset
resistor,
R16,
is
adjusted
during
test
to
ensure
that
the
instrument
reads
correctly
when
standard
resistors
are
used
in
place
of
the
electrode.
16
933C
(1)