Analog Section (Standard Measurements) - Philips PM2521 Service Manual

1
1.
CIRCUIT DESCRIPTION
1.1.
GENERAL
The
circuit
of the
Automatic
Multimeter
PM2521
can be subdivided into three main
functional sections
as
shown
in Fig.
1
.:
—
Analog
section
—
Control section
—
Display section
Each
of the sections
is
described separately
in
conjunction with
the
overall circuit
diagrams
(Fig. 62,
63
and
64).
However,
basic circuit
diagrams of the various
stages are included, within the
text,
where
considered necessary
to
assist in a
better understanding of the
more complex
parts
of the
overall circuit.
For the
principles
of
operation of the instrument, the
reader
is
referred to the
PM2521
Operating Manual.
1.2.
SURVEY OF MAIN
SECTIONS
The
functional
circuit
blocks within the three
main
sections, analog, control and
display
and the
basic
signal
paths are
shown
in
block diagram
Fig. 2.
1.2.1.
Analog
section
The
analog section comprises the following input measuring
signal
facilities:
a)
A
voltage
measuring
path consisting
of:
—
A.C./D.C.
voltage attenuator
—
R.M.S. convertor
(00
0061
)
—
Active
filter
- ADC
(OQ 0064/00
0060)
b)
A
current
measuring
path consisting
of:
—
A.C./D.C.
active l-V
convertor
—
R.M.S. convertor
—
Active
filter
- ADC
c)
A
resistance/diode
measuring path
consisting of:
—
Current source
(OQ
0063)
—
Active
filter
-
ADC
d)
A
temperature measuring
path
consisting of:
—
Thomson
bridge
—
Current source
- ADC
e)
A
timer/counter path
consisting
of:
—
A.C./D.C. voltage attenuator
—
Trigger
level
circuit
NO
TE: The
OQ
integrated
circuits
used
in this
instrument
are specially designed LSI
circuits
for
multimeter
appiications
to
ensure high accuracy
and
stability.