ABB MMCO-2 - Page 10

I
.
L
.
41
-
121.2
(
Power
Supply
Module Internal
Schematic
Figure
22
)
which is controlled
by
the
microprocessor
U
2
.
The
ranging
chip
multiplexes
the
phase
and
ground
inputs
.
Op
amp
U
1.2
,
and associated
resistors allow
for
calibration
of
the
high
level
input
voltage
to
the
microprocessor
.
The calibration
is made
by adjusting
potentiometer
P
1
so
that the
relay
pickup
and
meter
-
ing
are
correct
with
the
input
current set to
4
amps
or
greater
(
0.8
A
or
greater
with
the
1
A
ct
)
.
remains
in
the
display
mode
which
it
was
in
when the
“
EXTERNAL
SCROLL
"
switch
was
released
.
Settings
cannot
be
changed
using
the
“
EXTERNAL
SCROLL
”
button
.
6
.
CIRCUIT
DESCRIPTION
Documents
referenced
are
:
•
Current
Transformer
Module
Internal
Sche
-
matic
(
Figure
18
)
•
Microprocessor
Module
Internal
Schematic
(
Figure
20
)
•
Power
Supply
Module
Internal
Schematic
(
Figure
22
)
•
Display
Module
Internal
Schematic
(
Figure
Referring
to
Power
Supply
Module Internal
Sche
-
matic
,
Figure
22
:
A
5
-
volt
voltage
reference
for
the
A
/
D
converter
and
for
the
5
volt
power
supply
is
generated by voltage
reference
Z
6
,
Op
amp
U
2.1
and associated
discrete
components
.
24
)
•
I
/
O
Module
Internal
Schematic
(
Figure
26
)
6.1
.
CURRENT
INPUT
CIRCUITRY
Since
there
are
four
identical
sets
of
circuitry
for
phase
A
,
B
,
C
,
and
ground
only
the
circuitry
for
phase
A will
be
described
.
6.2
.
MICROPROCESSOR SUPPORT
CIRCUITRY
Referring
to
the
Microprocessor
Module
Internal
Schematic
,
Figure
20
:
Referring
to
the
ct
Module
Internal
Schematic
,
Figure
The
microprocessor
is
supported
by
chip
selector
U
11
,
address latch
U
5
,
32
K
bytes
of
EPROM
(
U
7
)
,
2
K
bytes
of
RAM
(
U
8
)
and
512
bytes
of
EEPROM
18
:
Current
is
input
to
the
relay
at
terminals
4
and
5
(
for
phase
A
)
,
stepped
down
by
current
transformer
T
1
and
full
wave
rectified
by
diode
bridge
BR
1
.
Resistors
R
1
and
R
10
convert
the
input
current
to
voltage
.
Diodes
D
1
,
D
5
and
CR
1
clamp
the
voltages
to
safe
values
.
Resistor
R
5
protects
the
microprocessor
input
(
U
2
,
on
Microprocessor
Schematic
,
Figure
20
)
.
For low level
current
inputs
,
up
to
3.75
Volts
across
resistor
R
1
,
the
input
voltage
is measured
directly by
the
analog
to
digital
(
A
/
D
)
converter
within
the micro
-
computer
chip
(
U
2
,
Microprocessor
Module
Sche
-
matic
,
Figure
20
)
.
(
U
6
)
.
A
real
-
time clock
chip
(
U
9
)
is accessed
by
the micro
-
processor
and
gives
date and time
information
.
For
relays
with
the
real
-
time clock
option
,
a
lithium
battery
(
BT
1
)
type
BR
2016
or
CR
2016
is
in
a
battery
holder
on
this
board
.
Diode
D
3
and resistor
R
44
are
in
series
with
the
battery
in
order
to
insure that the
battery
will
not
be
charged
.
Relays
without the real
-
time clock
option
do
not
have
a
battery
.
Referring
to
the
Microprocessor
Module
Internal
Schematic
,
Figure
20
:
WARNING
Each
phase
and
ground
go
to
different
pins
on
the
microprocessor
U
2
and
are
multiplexed
internally by
the
microprocessor
U
2
.
For
higher
level
signals
the
voltage
across
resistor
R
10
(
ct
Module Internal
Sche
-
matic
Figure
18
)
is scaled
by
a
ranging
chip
U
3
Replace
battery
with
ABB
Style
9648
a
03
h
01
only
.
Use
of
another
battery
may
present
the
risk
of fire
or
explosion
.
10
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