SLE 2000 HFO, Руководство по обслуживанию

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Page 64 of 258 Issue 10 (01/10/2004)
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.
15.0.6 Alarm Board Assembly (A0738/02)
15.0.6.1 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 A0702/04 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.
15.0.6.2 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 A0702/04 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 A0702/04 PCB is de-energised, as
would happen in the event of a power failure.
15.0.6.3 Power Supply Monitor
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.