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Philips PM2519 - Page 24

Philips PM2519
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2-6
2.3.2.3.
DC
current
measurement
In
the
function
mA,
two
ranges
(20
mA,
200
mA)
are
available.
The
ranges
are
determined
by
shunt
R1301
and
R1303
and
the
input
impedance
of
the
ADC.
The
ranges
are
protected
by
fuse
F1300
(630
mA).
If
in
case
of
measuring
voltages,
the
function
switch
is
changed
to
the
(m)A
function
with
the
voltage
still
on
the
input
terminals,
then
due
to
the
low
resistance
of
the
shunts
a
high
current
is
switched,
which
would
normally
damage
the
function
switch.
To
prevent
this,
the
(m)A
function
is
protected
by means
of
a
switch
position
(m)A*.
In
this
case
the
input
is
first
connected
with
resistor
R1300.
If
the
input
voltage
at
the
input
is
too
high
then
fuse
F1300
will
blow.
The
high
currents
2
A,
20
A
to
be
measured
are
supplied
to
the
A-socket.
The
ranges
are
determined
by
the
shunt
R1303
and
the
input
impedance
of
the
ADC.
When
inserted,
the
X1003
input
socket,
tinks
the
input
socket
with
the
base
of
transistor
V1700,
which
sends
a
logic
0
to
the
!/O
port
of
the
microcomputer,
to
signal
that
the
high
current
ranges
have
been
selected.
1002
VoImA
O-
INPUT
IMPEDANCE
ADC
x1003
‘
fon
ce
81409
A
O—F
oo0068A
eile
124,
CAMS
RMS
CIRCUIT
|_
tov
J
AB
To
ADC
wont
cro
la
ah
cars,
2n?
E]
ae
se:
ho
C1405,
—¢Y
1302
ev
oi
cog,
p—t—)
|
our
fouRReNT
cele
100)
Lt
oe}
cRcuT
fo
x1001
eT
0
©
nhewor
[$
eae
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Vv
rues
ve
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TO!
1243
P———]
converter
RMS
CONVERTER
crn
dance.
ST4402
‘
re.
80713
Fig.
2.5.
AC/DC
current
measurements
INPUT
SENSITIVITY
INPUT
ADC
mA
socket
mA
socket
A
socket
A
socket

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