Philips pm2521 - 6.4.1.6. Resistance measurements (Ω); RESISTANCE MEASUREMENTS (STANDARD METHOD); RESISTANCE MEASUREMENTS IN RELATIVE REFERENCE MODE (ZERO SET)

41
1.4.4.
Analog
section
(multifunction
measurements)
1.4.4.
1.
R.M.S.
convertor
In
the
R.M.S.
convertor
the difference
in voltage between the
Vin2 and
Vini
is converted
into current
in a
dual
V-l convertor.
The
current is determined
by
Y_il!_and the state
of the RNGA signal,
(where R is either
R305 or
R
R306
+
R307).
This relay
signal from D1
908 selects
the
input
sensitivity
of
the
R.M.S. convertor.
The current in
the a.c.
to
d.c. convertor
is rectified
and
then
converted into
a
current again
by the R.M.S.
section.
This current is
proportional to the
r.m.s. value of the
input signal
V.
Capacitor
C302 is
the
integrating
capacitor for the
R.M.S.
section.
Capacitors
C303
and
C304 provide
the
automatic zero
(AZ) compensation for the
R.M.S.
convertor.
The output of the
R.M.S. convertor
is converted
into
a
voltage
by resistor network
R309-R312. The
output
voltage
can be adjusted
by R310 and is
filtered
by R314/C306. It is supplied
via relay contact
K301 to
the
active filter.
RMS
CONVERTOR
INPUT
R.M.S.
CONVERTOR
Fig.
29.
R.M.S. convertor