RADIOMETER TCM3 - Page 65

TCM3
and
TCM30
Service
Manual
2.
TCM3
Analog PCB, continued
Electrode
Input/
Three
electrode
terminals
are
used
for
coding,
Output Circuit
(continued)
Electrode
Pin
10
Pin
16
Pin
18
E5277,
E5280
-
pO./pCO,
1
0
0
E5247,
E5250
-
pO.
1
0
1
E5237
-
pCO,
1
1
0
Electrode
Simulator
0
1
1
A/D
Conversion
The
PCB
includes
two
similar
A/D
converters.
A/D1
converts
the
signals
from
the
100RNR.1
input
multiplexer.
A/D2
is
dedicated
to
the
temperature
signal
from
termistor
1.
The
following
description
refers
to
A/D
1.
The
converter
consists
of
an
integrator
and
a
D-Flip/Flop.
The
FF
is
clocked
bya
symmetrical
100
kHz
square
wave.
When
the
FF
Q-output
is
low,
the
integrator
output
voltage
will
increase
until
the
triggering
level
of
the
D-FF,
is
reached.
At
the
next
positive
clock-pulse
edge,
the
Q-output
will
go
high
causing
the
integrator
output
and
QA7a
pin
1
to
tum
and
-
decrease to below
the D-FF triggering
level.
At
the
next
clock-pulse
the
Q-output
will
go
low
and
a
new
cycle
commences.
‘The
part
of
the
time
in
which
Q
is
high
is
called
the
duty-cycle,
d.
D-FF Q- output Γη Г] Г]
(002.5)
TRIGG
Ramp -voltage SZ 一 一 一 一 一 一 LEVEL
(aA7a.1]
Clock signal 100Khz
(002,3)
'
D
Example of A/D converter signals. Duty-cycle = 0.25.
Continued on next page
92-40