EasyManua.ls Logo

Hill-Rom Isolette C2000 - Humidity Measurement

Hill-Rom Isolette C2000
93 pages
Save Page as PDF
Print Icon
To Next Page IconTo Next Page
To Next Page IconTo Next Page
To Previous Page IconTo Previous Page
To Previous Page IconTo Previous Page
Loading...
Theory
of
Operation
Chapter
3:
Theory
of
Operation
Resistor
R43
is
an
additional
check
to
the
circuit.
It
provides
a
resistance
simulating
98.57Ā°F
(36.99Ā°C).
The
sensor
module
supports
three
air
temperature
sensors
on
the
sensor
board:
signals
AIRTE,
AIRTC
and
AIRTM.
These
signals
are
interfaces
via
J2-6
to
J2-8.
These
thermistors
are
then
routed
to
temperature
multiplexer
US
and
U6,
which
provide
analog
signal
processing
into
the
A/D
converter.
The
skin
temperature
probes
contain
dual
thermistors.
The
sensor
module
can
support
two
probes,
which
can
be
plugged
into
connectors
J6
and
J7.
The
two
thermistors
are
connected
to
SKNTXM
and
SKNTXC
(X
is
either
1
or
2),
with
a
common
connector
at
AGND.
Both
probes
have
high
frequency
filtering
by
inductor
networks
LN1
and
LN2.
In
addition,
each
skin
probe
has
a
resistor
that
is
input
to
the
multiplexers.
These
signals
(SKNT1D
and
SKNT2D)
are
used
by
the
microcontroller
to
determine
whether
the
probes
are
installed.
Humidity
Measurement
Humidity
measurement
originates
with
the
humidity
sensor
on
the
sensor
P.C.
board,
connected
to
J2-5
and
J2-14
(AGND
and
HS2,
respectively).
The
sensor
is a
capacitive
type,
which
changes
capacitance
as
a
function
of
humidity
(the
net
range
of
capacitances
is
from
approximately
160
pF
to
200
pF).
The
sensor
is
connected
to
amplifier
U7A/U8A,
which
is
set
up
as
a
multi-vibrator.
The
sensor
capacitance
is
allowed
to
charge
up
through
R20
and
R21
up
to
a
threshold
voltage
established
by
R30
and
R26.
When
the
capacitor
voltage
teaches
the
threshold,
capacitor
U7A/U8A
goes high
(to
2.5V
as
controlled
by
R19
and
R28)
which
turns on
Q2.
This
then
discharges
the
humidity
sensor
through
R20,
until
it
reaches
the
lower
threshold
established
by
R24,
R26,
and
R30.
The
capacitor
voltage
goes
from
approximately
0.2
V
to
0.7V.
At
this
point
the
comparators
output
goes
low,
releasing
the
drive
to
Q2
and
allowing
the
humidity
to
start
charging
again.
This
effectively
produces
a
frequency
output
as
a
function
of
capacitance,
such
as
humidity.
The
output
signal,
which
is
only
2.5V
peak,
is
then
input
into
U7B/U8B
to
condition
the
5V
signal.
Hysteresis
is
provided
through
the
use
of
R23,
R29
and
R32
to
insure
stable
frequency
switching.
The
output
signal
JUMPUL
is
then
sent
to
the
microcontroller
for
processing.
A
typical
frequency
would
be
around
37
KHz.
Page
3
-
14
IsoletteĀ®
Infant
Incubator
Service
Manual
(man223rf)

Table of Contents

Related product manuals