SLE SLE2000 HFO, Service Manual, Page: 10 / 84

SLE2000 HFO Service Manual
Doc No. SM/0001: Issue 7.0
Page 10 of 84
PTR1 monitors proximal airway pressure in the range -60 to +60 cmH
2
O. The resultant voltages serve two
purposes:
The first is to present a voltage in the range 1.22V to 4.78V to the ADC U18/26 on the A0702/02 PCB,
for trigger and high pressure fresh gas dump functions.
The second presents a voltage in the range 0.42V to 6.42V to the HFO CPU PCB (A0736/01), to
compare against CPAP, CYCLE FAIL and HIGH PRESSURE alarm settings, and also to drive the LCD
pressure display.
Fresh gas failure pressure transducer PTR2 monitors the fresh gas supply pressure and activates the
audible alarm BZ2 and also drives the leak alarm LED should the pressure fall below 17.5 cmH
2
O. If the
pressure rises above 80 cmH
2
O then the block LED is operated and the audible alarm will activate.
3.1.4 HFO M
AIN
B
OARD
A
SSEMBLY
(A0736/01)
3.1.4.1 Motor Stall Alarm
This circuit is active in all HFO modes. Jet rotation is monitored using two opto interrupter devices which
under normal operation shall provide two pulse trains. One of these signals sets a bistable and the other
resets it (U25A and B). The output from the bistable is monitored by an LM2917 tachometer IC (U26).
Should the pulse train stop, then T4 is switched off and the HFO solenoid (SV4) is de-energised thus
cutting off the gas supply to the rotating jet assembly.
In addition, during normal HFO operating conditions, T4 is periodically switched off by T3 in response to
an HFO modulation voltage generated by U21. This uses the I:E solenoid (SV1) energisation voltage to
switch SV4 according to expiratory, inspiratory or continuous HFO modes.
3.1.4.2 HFO Rate
This circuit uses the signal generated by the tachometer circuit (ref 3.1.4.3) to display the HFO rate on the
LCD display. This is achieved by using a TC9401(U20) in a frequency to voltage configuration. The
derived voltage is input to the processor system via the ADC0809 (U5).
3.1.4.3 HFO Pressure Activity Monitor
This circuit uses a voltage representing the pressure wave (taken from the A0702/02 buffered transducer
output) to monitor a minimum level of HFO pressure activity using an LM2917N tachometer IC. The
alarm output is produced when the peak to peak pressure drops below 3cmH
2
O or the frequency drops
below 3Hz. This circuit is only activated when both CPAP mode and either expiratory or continuous