SLE SLE2000 HFO, Service Manual, Page: 12 / 84

SLE2000 HFO Service Manual
Doc No. SM/0001: Issue 7.0
Page 12 of 84
This board accepts a time multiplexed signal from the HFO main Board (A0736/01)which contains the
signals for the high, fail to cycle and low alarm thresholds along with the proximal airway pressure signal.
This multiplexed signal is fed into four bargraph drivers (LM3914's) which in turn drive four 10*LED
arrays. For each level of the signal only one of the 40 LED's is illuminated.
3.1.6 A
LARM
B
OARD
A
SSEMBLY
(A0738/02)
3.1.6.1 Alarm Conditioning Circuit
The Alarm circuit comprises U1, U2 and U3. Those alarm inputs which can be muted are input to U2 via a
4066 quad analogue switch (U1), the control pins of which are connected to the mute timer output from
the A0702/02 board PLB/7b. The non mutable alarm inputs go to U2 directly. U2 is an 8-bit comparator
which outputs a logic 1 if any input differs from its reference bit. U3 is a variable gain buffer which drives
audible alarm BZ2.
3.1.6.2 O
2
Signal Processing
The pneumatic module contains a Galvanic fuel cell which monitors the oxygen concentration delivered by
the blender. The voltage output from this cell is input to U4(LT1006) and associated components, which
condition the cell output voltage to the range 0-4.5V. This voltage is then presented to the ADC U18/4
on the A0702/02 PCB and is used to display the FIO
2
.
The alarm board also contains a battery powered alarm circuit, consisting of BT1 and BZ3. The circuit is
completed when normally closed relay RL1 on the A0702/02 PCB is de-energised, as would happen in the
event of a power failure.
3.1.6.3 Power Supply Monitor (not on A0738/01 )
The circuit associated with the LM339N quad comparator is set up to give two comparison ‘windows’,
one for the 12V rail being between 11V and 13V and the other for the 24V rail being between 23V and
26V. If either of these rails falls outside the windows then the output transistor is switched on and the
buzzer is activated. The circuit requires the 5.12V supply to be present and will continue to accurately
monitor the 12V and 24V rails until the 5.12V supply drops below the brownout level.