Philips PM2517E - CIRCUIT DESCRIPTION; Overall Circuit Overview

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3.
CIRCUIT
DESCRIPTION
3.1.
GEN
ERAL
The
circuit
of the
PM
2517
can be subdivideci
into
three main sections:
-
Analog
section
-
Analog
to digital
convertor
-
Digital
section
Each
section
is described
separately with
reference
to the overall
circuit diagram.
Basic circuit diagrams
of the
varlous
stages
are inserted
in the
text
wherever
necessary
as
an aid
for
better
understanding of the overall
circuit diagram.
The circuitry of the
PM
2517 consists of special made
integrated
circuits
(LSl),
discrete components and
integrated
circuits used
for
display control.
The discrete components are used:
-
To convert the input signals supplied to the
input
terminals
into
suitable
signals
(attenuation)
for the
LSI circuits.
-
As
signal conditioning between the LSI circuits.
As LED display
control
lC's
are
used:
-
HEF
4511, BCD to 7 segm^nt latch/decoder/driver
-
HEF
4555, Dual 1 of 4 decoder demultiplexer.
The
LSI circuits used
in
the
PM
2517 are:
OQ 0055. character decoder driver for LED or LC display
bO 0059,
aigital
control
for ADC
and autoranging circuit
OO
0060, switching
part
for ADC with Delta lvlodulation
principle
(used
in combination
with OO 0064)
OO 0061.
a.c. to
d.c.
convertor
(calculated
Rl\4S)
OO 0063,
programmable
current source for resistance measurements
OO 0064, voltage to current convertor for ADC
with
Delta
lModulation
principle
(used
in combination
with OO
0060).
From
the integrated
circuits the data sheets are
given
at the end of this chapter.
PRINCIPLE
OF OPERATION
(Fis.
10)
3.2.
3-2.1. General
The Pl\tl
2517 consists of:
Analog section
-
Input circu its
-
Dc
attenuator
-
Ac
attenuator
-
Ac/dc
convertor
(OO
0061)
-
Shunt
-
Current source
{OO
0063)
-
Temperature bridge
3-2.2-
Analog
section
Switch
ing
part
{OO
0060)
v
-
| convertor
(oo
0064)
Digital
section
-
Display
-
ADC control
(OO
0059)
-
Display d rive(OO 0055)
-
D isplay
control
ADC
3.2.2. |. Direct voltage measurements
J
f
The unknown d-c. voltage
is supplied to the d.c. attenuator. Dependent on the
range selected
the
input L
,
voltage is attenuated x10 or x1000, From
the attenuator the attenuated voltage
is directly supplied
to the
-J
ADC which has a
sensitivitv of 0.1 V or 1 V.
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