Philips pm2521 - Analog Section (Standard Measurements)

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
NOTE:
The
OQ
integrated
circuits used in this instrument
are specially
designed LSI
circuits for multimeter
appiications
to
ensure
high accuracy and
stability.