RADIOMETER TCM3 - Page 67

TCM3
and
TCM30
Service
Manual
2.
TCM3
Analog PCB, Continued
Charging
Circuit
Automatic
Secondary
Voltage
Regulation
1nnono 1
The
battery
contains
6
NiCd
cells.
Its
nominal
voltage
is
7.2
V
(each
cell
1.2
V)
and
the
capacity
is
2
Ah
(25
°C,
360
mA).
The
charging
current
depends
upon
the
TCM3/30
consumption.
At
low
consumption,
the
charge
rate
will
be
high
and
vice
versa.
When
the
monitor
is
supplied
from
the
mains,
the
voltage
at
TP
7
will
be
9.2
V
and
OS
is
active.
The
voltage
drop
across
R93
and
R94
is
constant
0.7
V
(Vcais-
Vaz),
leaving
more
to
R94
if
Vass
drops
and
vice
versa.
The
table
below
lists
some
typical
rates
of
the
TCM3/30
consumption,
and
the
corresponding
NiCd
charging
currents.
The
figures
are
indicative
only
as
the
consumption
depends
very
much
on
the
actual
display
showing.
Situation
Current
Charging
.
consumption
current
|
Monitor
off,
battery
fully
charged
0
80
mA
Monitor
off,
battery
empty
0
300
mA
Monitor
on,
waiting
for
calibration,
battery
100
mA
300
mA
empty
|
Monitor
on,
ready
for
measuring,
electrode
300
mA
30
mA
temp..43
°C.
Monitor
on,
measuring,
electrode
temp.
43
°C
300
mA.
30
mA
If
the
monitor
is
supplied
from
the
battery
cassette
TCB3
or
BAT,
the
secondary
voltage
(TP
7)
will
decrease,
Q4
and
Q5
cut-off
and
no
charging
takes
place.
This
circuit,
which
applies
to
the
PCBs
901-835
and
902-428
only,
consists
of
the
opto-couplers
OP3
and
OP4,
O6, O7
and
QAS.
A
change
in
the
secondary
voltage
will
cause
the
regulator
voltage
to
change
via
QAS
and
OPA,
and
counteract
the
secondary
voltage
change.
If
the
monitor
is
connected
to
the
mains
via
the
mains
adapter,
the
opto-coupler
OP3
is
activated,
Q7
cuts
off
and
the
regulation
loop
will
change
the
secondary
voltage
from
8.2
to
9.2
V.
Continued on next page
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