Pediatric Ventilator Stephanie Technical Manual January 2003 1
Pediatric Ventilator
Stephanie
Technical Manual January 2003
1
CONTENT Basic Principles .........................................................................................................................4
1.1 Structure ....................................................................................................................4 1.1.1 Control Unit Module .............................................................................................5 1.1.2 Electronic Module .............................................................................................5 1.1.3 PC Module............................................................................................................8 1.1.4 Electric Power Supply Module ............................................................................8 1.1.5 Battery Module..................................................................................................9 1.1.6 Pneumatics Module ...........................................................................................9 1.1.7 Patient Component ..........................................................................................10 1.1.8 Test Module.....................................................................................................10 1.1.9 Valve Actuation...............................................................................................11
1.2 Functional Operation...............................................................................................11 1.2.1 Gas Supply ......................................................................................................12 1.2.2 Electric Power Supply.....................................................................................12
Technical documentation Power Pack/Mains Power ..............................................................12 1.2.3 Generation of the Ventilation Pattern .............................................................16 1.2.4 Heating and Humidifying Ventilatory Gases ..................................................17 1.2.5 Monitoring...........................................................................................................18 1.2.6 Control.............................................................................................................18
2 Mechanical Structure ......................................................................................................19 2.1 General ....................................................................................................................19 2.2 Assembly and Disassembly.....................................................................................20 2.3 Assembly pictures for Exchange of Stephanie-Moduls ..........................................21
3 Pneumatics ......................................................................................................................42 3.1 General ....................................................................................................................42 3.2 Pneumatics module .................................................................................................42
3.2.1 Pneumatics schema .....................................................................................43 3.2.2 Sensor Electronic..........................................................................................44
3.2.2.1 Signal designation .......................................................................................44 3.2.2.2 Operating function.......................................................................................44
3.2.3 Assembly and Disassembly.............................................................................46 3.3 Test Block ...............................................................................................................47
3.3.1 General ............................................................................................................47 3.3.2 Assembly and Disassembly.............................................................................48
3.4 Patient Component ..................................................................................................49 3.4.1 General ............................................................................................................49 3.4.2 Functional operation........................................................................................49 3.4.3 Assembly and Disassembly.............................................................................51
3.5 Patient Hose System................................................................................................51 3.6 Measurement of Pressure and Volume Flow ..........................................................52 3.7 Aerosol System .......................................................................................................53 3.8 Ventilatory-Gas Humidifying .................................................................................53
4 Electronic ........................................................................................................................53 4.1 General ....................................................................................................................53 4.2 Control Unit.............................................................................................................54
4.2.1 Therapy Control Module.................................................................................54 4.2.2 Monitor Control Module .................................................................................55
4.3 PC Module...............................................................................................................55
2
4.3.1 PC Circuit Boards............................................................................................55 4.3.2 VGA Card .......................................................................................................55 4.3.3 PC Interface.....................................................................................................55
4.3.3.1 Signal Designations.....................................................................................56 4.3.3.2 Operational functioning...............................................................................56
4.4 Electronics Block ....................................................................................................58 4.4.1 Microcomputer ................................................................................................58
4.4.1.1 Signal designations......................................................................................58 4.4.1.2 Operational functioning...............................................................................60
4.4.2 Monitoring (watchdog.....................................................................................61 4.4.2.1 Signal designations......................................................................................61 4.4.2.2 Functional operation....................................................................................62
4.4.3 Sensor Module.................................................................................................64 4.4.3.1 Signal Designations.....................................................................................64 4.4.3.2 Operational functioning...............................................................................65
4.4.4 Power amplifier ...............................................................................................67 4.4.4.1 Signal designations......................................................................................67 4.4.4.2 Operational function....................................................................................68
4.5 Power Supply ..........................................................................................................72 4.5.1 Power supply module ......................................................................................72
4.5.1.1 Signal designations......................................................................................72 4.5.1.2 Operational function....................................................................................73
4.5.2 Battery Module....................................................................................................73 4.6 Valve Actuation.......................................................................................................74
5 Safety Concept ................................................................................................................75 5.1 General ....................................................................................................................75 5.2 Safety Design of the Ventilators .............................................................................75 5.3 Mandatory Parameters to be monitored and tested .................................................76 5.4 Adjustment and Treatment of Limit Valves............................................................76
5.4.1 General ............................................................................................................76 5.4.2 Pressure ...........................................................................................................76 5.4.3 Respiratory Minute Volume............................................................................77 5.4.4 Insp. O2 concentration: ...................................................................................77 5.4.5 Temperature ....................................................................................................78
5.5 Alarm Response ......................................................................................................78 5.5.1 General ............................................................................................................78 5.5.2 Alarm suppression...........................................................................................79 5.5.3 Status graphic of the alarm system..................................................................79 5.5.4 Alarm table......................................................................................................81
6 Failure Mode Analysis ....................................................................................................84 6.1.1 Control Unit.....................................................................................................84
3
Basic Principles
1.1 Structure
Using the modular structure, this section will briefly deal the individual functional modules
and their interaction.. Detailed descriptions and explanations of the individual functionalities
of the modules are given in the sections that follow.
As shown in the Appendix (modular display, Stephanie), theStephanie consists of several
components or modules :
• Control unit module,
• Electronic module,
• PC module,
• Pneumatics module,
• Electric power supply module,
• Patient component,
• Actuator for the ventilator valve.
4
1.1.1 Control Unit Module
The control unit module is positioned on the front side of the Stephanie unit. It is lectern-
shaped and is comprised of all the adjustment and settings elements in the form of switches,
potentiometers and keys (push-buttons). Furthermore, these are grouped for the various
therapy settings and for monitoring.
The control unit module, ie the control elements, transmits the information to the central
controller in the electronic block module.
On a 10.4" TFT flat screen, all monitoring results are displayed in alphanumerical form of all
ventilation parameters being monitored; time functions of ventilatory pressure, volume flow
and volume are displayed in graphical form.
The screen display is directly controlled by the PC module.
1.1.2 Electronic Module
The electronic module consists of the circuit boards: pressure sensor circuit boards, power
amplifier, monitoring (watchdog) as well as the central processing unit.
5
The sensor circuit board has two pressure sensors for regulating and monitoring ventilatory
pressure, one differential pressure sensor that, together with the pneumotachograph head,
carries out volume measurement, and amplifiers for evaluating thermistor signals for
ventilatory-gas humidifying.
The Microcomputer (MC) is the essential core of the unit controlling all therapy
functionalities provided by the Stephanie unit. It processes the information given via the
control module received from the adjustment and settings elements and transfers these on to
the serial port interface RS 232 to the PC module.
The microcomputer generates the digital control algorithms for pressure regulation and
volume regulation. For doing this, it receives information from the pressure and volume flow
sensors of the sensor ciruit board as actual values and compares these to the pre-set or target
values of the ventilatory pattern generator. As a result of the control algorithm, a corrective
signal is generated, which – amplified by the power amplifier – activates the valve actuation.
This changes the pistion position of the inspiration/expiration valve until the target and pre-
set values precisely correspond to each other.
The microcomputer also takes on the regulation of respiratory-gas humidifying. Temperature
signals provided by the sensor circuit board serve as actual values, and the target value is
generated by the temperature control algorithm. Depending on regulating deviations, power
6
transistors located in the electric power module switch on or off the heating element in the
humidifier and/or hose.
The power amplifier amplifies the analogue signal generated by the microcomputer which, in
turn, activates the valve actuation. By means of feedback of the path signal of a positional
transducer coupled with the valve actuation, a path control loop is created, which greatly
improves the dynamic of the valve actuation.
Circuit board monitoring / supervision (watchdog) serves functionality monitoring, and
oversees the microcomputer, the power supply as well as the PC module. It contains the so-
called watchdogs, that are rhythmically activated by both units, and if failure occurs, switches
the entire unit over to an emergency mode, in which the safety valve is activated and the
patient can at least spontaneously breathe ambient air.
If the alarm limit is exceeded, it activates an audible alarm.
In addition, this circuit board contains the power transistors for activation of the magnetic
valve (solenoid).
7
1.1.3 PC Module
h00000000
120 240
Sauerstoffsensor
®
M - 11
2x4AT
Reset
h00000000
12024 0
Sauerstoffsensor
®
M - 11
2x4AT
Reset
The PC Module houses a complete personal computer, 586 DX 66.
It fulfills two tasks:
• Monitoring of the microcomputer,
• Monitoring of ventilatory parameters and pre-set alarm limits.
The sensor signals generated by the sensor circuit board are evaluated independent of the
microcomputer and the monitoring parameters are alphanumerically displayed in a dedicated
field on the monitor display screen.. It coordinates the visual alarm with the alarm status, that
are recognized either by the PC module itself or by the microcomputer.
In addition, the PC module generates the screen display of ventilatory pressure, volume and
volume flow as a function of time.
1.1.4 Electric Power Supply Module
The electric power supply module supplies the electric current necessary for the operation of
the ventilation unit. It contains all monitoring switching devices as well as power transistors
for switching on/off the heating elements of the respiratory-gas humidifier and ventilation
hoses.
8
1.1.5 Battery Module
h00000000
120 240
Sauerstoffsensor
®
M - 11
2x4AT
Reset
The battery module contains a 24 V lead storage battery, which, in the event of power failure,
ensures continued operation of the ventilation unit for a short period of time.
1.1.6 Pneumatics Module
Pneumatik-Block
The pneumatics module contains all the pneumatic components that are necessary for
processing the respiratory gas, including respiratory gas mixer, valves, pressure regulator, etc.
It is pneumatically connected to the patient component via a plug coupling.
9
1.1.7 Patient Component
The patient component contains all the pneumatic components of the patient circuit (loop),
which must be sterilised. In particular, these are: the inspiration/expiration valve housed in a
ventilation valve unit, safety valve as well as an injector. It additionally integrates the
heater/humidifier of the patient gas.
1.1.8 Test Module
The test module contains an electromagnet via which the safety valve of the patient
component is activated; it also contains a lever for switching the ventilator over to manual
operation, as well as for calibration for Compliance and Resistance, for testing the entire
system during the unit system selftest.
10
1.1.9 Valve Actuation
The valve actuation is carried out by an electrodynamic converter. It is activated by the power
amplifier and is coupled with the ventilatory valve unit by means of magnetic force.
1.2 Functional Operation
"Operational Diagram, Entire System"
Gassupply
Pistonvalve
Watch dogforCPU
Ventilationpres.Ventilationflow
Pressuresensor(control circuit)
Flowsensor(control circuit)
TubesystemPatient
(Monitor)
Gasblender
DAC1 El. dyn.Drive
Bidirectionel Transfer of all Adjustmentparameter and Alarms
HP-Alarm
HP-Alarm
FiO2-Sensor
Sensor 2
MP-Alarm
Supervisionof
vent. pressure
Supervision of- Apnoe- Diskonnektion-Temperatur
-FiO2
Supervisor-Programm of Microcomputer Supervisor-Programm ofPC - Module
- FiO2,- Apnoe- Diskonnektion- Temperatur
visual display of- Information
- AlarmsGraphical indication
of breathingcurves
and ventilation parameter
Plausibilitycheck of
Adjustments
Ext. watch dog
für Monitor
LP-Alarm
presuresensorAir and O2
Net voltage
"disk on chip"for Programm
Zeroing ofFlowsensor
cycl.Zeroing.
Supervision
reg.distanceSensor 1Way measurement
system (WMS)
Valves forAir and O2
Manual ventilationoutlet
switch over valveManual-mechanical
manualhandleautomatic
Substitution in case oflGasfailure
watchdog
ADC
ADC
DAC2
ADC
8bitBus
ADC of PC
Micro-Computer PC-Modul
mitMonitor
Emergencyvalve
Funktion diagram of hole unit"STEPHANIE"
audibleSignal
Supervision ofaudible Signals
Speaker 1
Speaker 2
internalVoltage forSupervision
watchdogPC
poweramplifier
Display-ElementsUser-Elements
Front panelADC
Akku-Modul
Temperatur
Patient gashumidifier
and warmer
ADC Temp.-Sensor Temp.-Sensor(Monitor)
Voltagesupervision
Voltage generator
Power supply
Floppy disk
Hard disk
Pneumatik - Modul
ADC
in Pn.-Module
Monitorparameter
SafetyRelais
Pressuresensor
reg.distance
(control circuit)
Supervision- transmissionerror MC/PCUserelements
Supervision ofSupervision
ofvent. pressure
Emergency valve
11
1.2.1 Gas Supply
The gas supplies, compressed air (Air) and oxygen (O2) are fed in the pneumatics module via
magnetic valves (solenoids) to the oxygen/air mixer and can be used either for mechanical or
manual ventilation. The current (actual) oxygen concentration is monitored by the oxygen
sensor and evaluated by the PC module.
Pressure sensors, together with the central processor, monitor supply pressures for CA and
O2.
1.2.2 Electric Power Supply
Technical documentation Power Pack/Mains Power 1. General description The power pack module of the STEPHANIE provides the equipment with the necessary
supply voltage 5 V, +/- 12 V and 24 V, and regulates the charging of the internal battery as
well as the switch-over from mains power supply to battery operation. Furthermore, it
generates monitoring signals including re-set signals for the controller of the STEPHANIE.
All voltages are generated with switching regulators from a unstabilized intermediate circuit
voltage in the range of 22 – 28 V, that is taken either from rectified secondary voltage of a
transformer, or from the internal battery of the equipment.
2. Transformer A safety transformer from the company Marek is used to generate the secondary voltage. The
transformer can be operated on 230 V or 100 V respectively, and provides secondary 22 V at
7 A. Compliance with the requirements of EN 60601 for equipment with a protective rating of
1 has been tested. In addition, the transformer is equipped with an over-heating safety device.
The rectified secondary voltage serves as intermediate circuit voltage for generating other
supply voltages as well as directly providing power supply for the heating system.
12
3. Generating supply voltages The supply voltages necessary for the STEPHANIE (5V / 4A and +/-12/2A) are taken from
the intermediate circuit voltages with switching regulators (see circuit diagram, sheet 1).
Types LM2679 from National Semiconductor (NSC) were used. Voltages of 5V and 12V are
generated by the downwards adjustment control, the 12 voltage by means of inversion of the
+12V voltage. The load on the 12V regulator does not increase in this case, because the 12V
supply is essentially only alternately loaded. The design of the switching and the selection of
additional components is in accordance with the circuit recommendations of NSC. Cooling of
the regulator is effected by means of a copper surface on the printed circuit board. The
maximal measured temperature in immediate proximity of the 5V regulator (having the most
load) amounted to approximately 70ºC. (maximal permissible temperature, 115ºC).
The thermal load on the other components is lower.
Additionally, all voltages are filtered through a LC module. Because of a special sensitivity of
the power amplifier to interference of the –12V supply (leads to noise at the patient
component), a significantly greater inductivity (4mH) was used than that for the other
voltages.
The 5V and 12V regulators can be switched off via a shut-down input (STB2) (see "Control").
4. Charging circuit, switch-over to battery operation For maintaining voltage supply in the event of mains power failure, the STEPHANIE is
equipped with two series connected batteries (each 12V /1.3 ampere hour). A voltage of
approximately 27.6V is necessary to charge the batteries which slightly difffers according to
temperature.
As the intermediate circuit voltage from the mains can lie below as well as above this value, a
regulator is used for battery charging that operates both upwards and downwards (component
at U5, Circuit Diagram, sheet 1). The circuit is similar to an application of the company
Linear Technologies.
The maximal output current of the charging circuit is limited to a value of approximately 0.3A
via R16 and Q3. Battery charging can also be switched on or off via a shut-down signal (AK-
SHDN).
The switch-over between mains power supply and battery operation is effected by a relay
(K1, Circuit Diagram, sheet 1). By means of this relay, the equipment can also be switched
off in the event of error or malfunctioning, by using the Re-set key S1. This forces the relay
13
into the mains position. If the mains power is also switched off, the STEPHANIE software
shuts the equipment down.
5. Heating Control The circuit breaker for the two heating systems of the STEPHANIE are also built in to the
power pack module. They are Profets from the company, Infineon: (U6, U7, Circuit Diagram,
sheet 1). They are Mosfets with protective and monitoring functions.
The components are short-circuit proof and equipped with thermal overload protection.
They switch the intermediate circuit voltage over to heating resistors.
6. Control
Monitoring of the power pack and the generation of the control signals for the controller is via
the microprocessor (Motorola 68HC11, ICI, Circuit Diagram, sheet 2).
Because of practicality, the processor is used as the use of assembled discrete components is
somewhat costly. The possibility of programming proves to be useful as well, because the
temporal control of the signals has proven to be critical. The program is written in Assembler
and filed (stored) in the program memory of the processor.
Generated and evaluated are the following signals:
14
Outputs:
- Two power OK signals (POK1/2) These signals are set when all supply voltages lie within the default limits. These are: 5V :4.8 – 5.2V 12V :11 – 13V -12V :-11 – -13V Intermediate circuit voltage : 18- 37V The voltages are led through voltage multipliers to the A/D converter inputs of the processor and the processor controls the compliance with the limit values. The POK signals are logical HIGH (5V) for correct functioning, and LOW (0V) for malfunctioning. POK1 is used as RESET for the controller of the STEPHANIE. A correct start of the controller was only achieved, when this signal was set with a delay of 200 ms.
- Two signals for battery check (BATOK, BATLOW) These signals serve as watchdog for the battery. BATOK becomes HIGH, when the battery voltage is at least 22V. BATLOW becomes LOW, when the voltage fall below 18V.
- A mains power failure signal (PFAIL)
This output becomes LOW, when the secondary voltage of the transformer falls below 18V.
- Inputs: Mains switch-off/shut-down (SHDN) This signal causes the STEPHANIE to shut down the power supply unit. The mains/battery switch-over relay is put into battery operation mode, in this mode battery charging is switched off. SHDN is used to briefly switch over to battery operation during the test routine after starting up the equipment to test the flawless functioning of the battery.
- Standby operation (STB)
In standby mode, all functions of the equipment, apart from battery charging, are deactivated. Input corresponds to a software shutdown. The switch-over mains/battery is put into mains position, the voltage regulator for supply voltages are switched off (the internal control signal STB2 is set to LOW). Battery charging mode remains on. Evaluation of standby signal proved to be problematic, because the STEPHANIE switching circuit generated no clearly defined signal. During normal operational mode, there is a voltage of approximately 4V, that drifts to smaller values after switch-over to standby, without a clear switch-over. Therefore, the evaluation takes place also with a A/D converter. If the voltage exceeds 3V, normal operation is switched off. Switch-over to standby takes place when the voltage falls below 2V.
15
- Inputs for heating control (HZ1ON, HZ2ON, HZDIS) HIGH signals at HZ1ON, HZ2ON switch on the respective heating, under the condition that HZDIS is not activated and the unit is being operated on mains power. In battery operation, the heating systems are switched off to increase operation time.
7. Actions to be taken in the event of power failure
If the processor detects a fall in secondary voltage below 18V, there is an automatic switch-
over to battery-powered operation via the switching of relay K1. Here, a relay can be used,
because of the large supportive condensator at the input (C22, 10000uf), the intermediate
circuit voltage only falls slowly.
As soon as mains power has been restored, switch-over to mains power takes place and
battery charging is switched on once again.
8. Safety controls
For protection against transient interruptions, all voltage outputs are equipped with voltage
surge diodes. Secondary and battery voltages are secured with 47V protection diodes, the +/-
12V voltages with 15V diodes and the 5V with 6.8V diodes.
Problems with reversed polarity are kept below approximately 0.7V.
1.2.3 Generation of the Ventilation Pattern
The central control regulates the pressure, volume flow regulating circuits for generating the
ventilation pattern desired.
It receives from the control elements of the control unit the desired ventilation parameters and
from these generates, via the controller program, all the analogue and digital control signals
necessary for carrying out the tasks involved in the therapy.
For this purpose, actual values of ventilation pressure and volume flow are collected by the
analogue-digital converter (ADUs) of the central control (microcomputer) and are via control
16
algorithms converted into an analgoue control signal for the power amplifier. This regulates,
via the valve actuation, the control valve in the patient loop.
Mandatory monitoring of the ventilation pressure is carried out by the PC module via a
second pressure sensor.
To ensure a high quality of performance of monitoring the pressure and volume flow
regulator circuits, a high valve actuation dynamic is of absolute necessity. For this, there is
the path control circuit, in which the position of the control valve is tracked by means of an
optical positional transducer, and is fed back to the input of the power amplifier.
For reasons of safety, the positional transducer is a dual system and the position signal is fed
to the central control by System 2. By comparing the pre-set (target) valve (output DAC1 of
the central control) with the actual position, a complex monitoring of the ADU – DAU path of
the central control is obtained including power amplifier, actuator and control valve.
1.2.4 Heating and Humidifying Ventilatory Gases
Heating and humidifying ventilatory gases are also coordinated by the central control. A
temperature sensor at the exit side of the humidifying chamber and one at the exit side of the
inspiration hose heating element provide the actual temperature valve to the central control.
The central control generates, according to a pre-set temperature value and according to a
temperature control algorithm, the control signal, from which the power transistors for both
heating circuits are switched.
A third temperature sensor serves as monitor. For safety reasons, it is also evaluated by the
PC module.
17
1.2.5 Monitoring
Together with the display screen, the PC module serves and supports
• monitoring of the proper functioning of the central control, and
• monitoring of the ventilation pattern
• alphanumerical display of measured ventilation parameters as well as alarm statuses.
The PC is coupled with the central control via a serial interface port and receives the setting
parameters of the control unit, including those of the alarm statuses of the central control, and
also transmits its own alarm statuses as well as the monitoring parameters to the central
control..
1.2.6 Control
The central control and PC module take on, independent of one another, the monitoring of
safety-relevant parameters and statuses in line with current standards.
Both units classify alarm statuses via independent alarm systems, into alarms of high and
medium priority and then feed these data to the circuit board. This triggers an audible alarm
and, should the situation or error be endangering, switches off the emergency air valve for
reasons of patient safety.
Monitoring the central control and PC module themselves is carried out by watchdogs, that, in
the event of malfunctioning or failure, also lead to shut-down followed by appropriate
corrective action.
The audible warning system has a backup system so that in the event of failure of the first
audible system, the second system will trigger the alarm.
18
2 Mechanical Structure
2.1 General
„Mechanical Structure“.
The Stephanie consists of the housing, in which a rack is inserted. Positioned on this rack are
the PC module, pneumatics module and electric power supply module arranged as plug-ins.
The circuit boards of the electronic module are individually inserted in the lower tier of the
rack. The latter are covered at the rear side of the unit by the battery module.
The control unit serves as the front cover of the housing unit.
Connections between the individual electronic units are in the form of wiring backplane, ie
circuit boards, and connection cables. A specific of the Stephanie is the drive of the
oxygen/air mixer positioned in the pneumatics module. As the setting element belonging to it
is positioned on the control unit, a toothed-belt drive serves as a mechnical coupling to both
components.
All functional units of the patient circuit such as valve actuation, patient component and the
test module are mounted to a robust mounting plate on the right-hand sidewall of the
Stephanie. The valve actuation is positioned inside the patient component and the test module
on the exterior of the housing.
Below the lowest tier insert, there are two blowers mounted for providing cooling of the
inside of the unit. RPMs of the blowers and therewith the cooling performance, are regulated
by thermistors that are positioned at temperature-critical points in the unit.
19
2.2 Assembly and Disassembly
The housing consists of an L-shaped basic body, formed by the right sidewall and the base
plate, the left sidewall and the housing cover. Normally, it need not be completely
disassembled for servicing.
If it is necessary to gain access to the backplane or to the control unit, only the cover need be
removed.
To remove the cover, loosen the two long hexagon socket screws (3mm) that are accessible
through the large bores on the rear wall of the cover. The cover is carefully pulled forward
approximately 3 mm, so that the tongues located on the underside of the cover can be freed
from the pins mounted to the housing. Following this, the cover can be lifted from the
housing. Make sure that the control unit does not tip forward. After loosening M4
countersunk screws on the lowerside of the control unit, the control unit is carefully pulled
forwards and hung in the hing pins of the unit. Now the control unit can be swung forward
and all components of the backplane as well as the control unit are accessible.
Assembly is carried out in reverse order. Only make sure that while inserting the control unit,
the potentiometer axis of the FiO2- drive must be inserted into the correct sleeve.
20
2.3 Assembly pictures for Exchange of Stephanie-Moduls
Please take care and secure, that all cables and screws you remove will be reconnected in
exactly the same way and position.
1.
2.
21
3.
2 1
4.
22
5.
6.
23
7.
8.
24
9.
10.
25
11.
12.
26
13.
14.
27
15.
16. Pneumatic-Modul
28
17.
18.
29
19.
20.
30
21.
22.
31
23.
24.
32
25.
26.
33
27.
28.
34
29.
30.
35
31.
32.
36
33. PC-Modul
34.
37
35.
36.
38
37. power supply unit
38.
39
39. battery unit
40.
40
41.
41
3 Pneumatics
3.1 General
The pneumatic system of the Stephanie consists of three main componnents, the pneumatics
module, patient component together with the patient loop, and the test block.
3.2 Pneumatics module
„Pneumatics module, top view“,
The pneumatics module is an insert that contains all the pneumatic elements that do not
directly belong to the patient loop. In addition, sensors are located in the pneumatics module.
These sensors measure the pressures of the supply gases, the inspiratory oxygen concentration
as well as the inner temperature of the module.
Structurally, the pneumatics module is a hermetically closed unit within the ventilation unit.
Should it, in the event of malfunctioning or failure, result in an unacceptably high oxygen
concentration within the module, the high oxygen concentration cannot escape to other parts
of the unit. Such concentrations can escape through a number of wide slits in the front plate of
the pneumatics module.
42
3.2.1 Pneumatics schema
Dat um Name ( Ur spr . : ( Er s . f : )Bl .
Bl at t
Nor m
Gepr .Bear b.
Dat um Name
( Ar t i kel nummer
( Benennung)
Maást ab
Wer k s t of f / Hal bz eugHal bf er t i gt ei lRoht ei l
)
Žnder ungZust .
A NA E S T HE S I E
A T E MT HE R A P I E
P Ž DI A T R I ES t eph an
ng)
Mainusch Pneumatic-Block
Stephanie
1 035 65 053
6.10.00
O2-Kalb.21%
Duese
O,3
Air
R1/8 O2
Injektor M5
D1
V2
V3
V4
M5O2-Zelle
MischerR1/8
MischerR1/8
M5Pilot Druck
Mischerausgang
R1/8 Air
M5Drucksensor
V1
R1/8
NW 0.8
NW 0.8
NW 0.8NW 2
R�cksclagventil OV10/DN8
NC
NC
NC
NC
V7 Ventil stromlos ge”ffnet
24 Volt 2 WATT
Druckbereich 2.5 - 6bar
V1 V2 V3 V4 V5 V6 Ventile stromlos geschlossen
V2-V7
V1
Aerosol M5V6
NW 0.8
NC
Flow = 1-40 l/min
P=min ca.2.8bar
NW 0.8
V7NO
Handbeatmung M5
ca 10 l max.
V5R1/8
NW 2
NCDruckregler 150 mbar
O,5
D2
2.8 bar
43
3.2.2 Sensor Electronic
3.2.2.1 Signal designation
Operating voltages
SV_P12LV
SV_P12
SV_N12
Control signals
/ÜW_VPL Actuation of compressed-air valve (-12V)
/ÜW_VO2 Actuation of oxygen valve (-12V)
/ÜW_VINJ1 Actuation of injector valve 1(-12V)
/ÜW_VINJ2 Actuation of injector valve 2 (-12V)
/ÜW_VSubst Actuation of substitution valve (-12V)
/ÜW_VAerosol Actuation of aerosol valve (-12V)
Outlet signals
PM_UP120 Pressure sensor 120 mbar admission pressure
PM_UPl Pressure sensor, compressed-air admission pressure
PM_UO2 Pressure sensor, oxygen admission pressure
PM_UFiO2 FiO2 sensor signal
PM_UTemp Temperature-sensor signal
3.2.2.2 Operating function
The electronics integrated in the pneumatics module is made up of sensors for measuring:
• Oxygen concentration (FiO2),
• Temperature inside the pneumatics module.
• Supply pressure of compressed air,
• Supply pressure of oxygen,
• Admission pressure of ventilatory-gas mixture.
44
All sensors apart from the oxygen sensor and their respective electronic components are fitted
to a circuit board. (see Operating Plan „Electronics, Pneumatics Module“ in Appendix 6).
This circuit board is located inside the pneumatics module in such a way, that a SUB-D plug
connector mounted to the rear side of the circuit board – hermetically sealed – protrudes
through the rear side of the pneumatics module. This allows all electrical connections to be
effected outside the pneumatics module.
Oxygen partial pressure and thus oxygen concentration of the ventilatory-gas mixture (after
pressure regulator PR2) is converted by means of a sensor KE25 (Unitronic) into an electric
current that is amplified by the amplifier U1 by a factor of 100 and held as signal PM_UFiO2
at the outlet.
The thermistor amplifier U2 is, together with thermistor R4, located on the circuit board, a
temperature voltage converter, and serves to determine the inner temperature of the
pneumatics module. Its output signal PM_UTemp is evaluated by the central control. If the
limit value for the inner temperature of 50°C is exceeded an audible and a visual alarm are
triggered.
The pressure sensors for the admission pressure of the compressed air and oxygen as well as
the ventilatory-gas mixture are sensors with integrated electronic, that directly provide the
pressures of the assigned currents PM_UPl, PM_UO2 and PM_UP120 at the outlet.
45
3.2.3 Assembly and Disassembly
Removing the pneumatics module is effected in the following way:
1. Remove the supply hoses for compressed air and oxygen,
2. Position Hand/Ventilator, switch in Ventilator position,
3. Remove patient component,
4. Loosen pneumatic connection sleeve for patient component from the right sidewall with
hexagon socket wrench,
5. Open housing (see Pt. 2.2),
6. Remove toothed belt from toothed gear of the pneumatics module,
7. Remove SUB-D plug from the rear side of the pneumatics module,
8. Remove plug-coupling hose for nebulizer outlet from the inner right sidewall,
9. Loosen the 4 screws on the front plate of the pneumatics module,
10.Pull out the pneumatics module.
After loosening the screws and removing the cover, all components of the module are now
accessible.
If only an inspection of the pneumatics module is to be carried out during ooperation, the
entire module need not be pulled out. It is only necessary to remove the cover and to unscrew
the upper module rails. After that, the module cover can be opened as described above and the
inner parts of the pneumatic module are accessible.
46
3.3 Test Block
3.3.1 General
„Test block, side view“
The so-called test block is mounted on the right sidewall of the basuc unit. On the underside
of the test block there is a screw-on bottle attached filled with copper wool that serves as test
Compliance. Via a pneumatic resistance, it is connected to a connecting union (pipe) found on
the rear side of the test block. When the unit is not in operation or when running the test
program, the Y-piece of the ventilation hose is attached to this connecting union.
47
Using the lever „Hand / Resp“, the unit can be switched over between manual ventilation and
ventilator operation. When the lever is in „Resp“ position, the ventilatory-gas mixture reaches
the patient via the patient component and the patient is mechanically ventilated. When the
lever is in the „Hand“ position, a tappet rod found in the pneumatics module switches the unit
over to manual ventilation. The ventilatory-gas mixture is then provided at the connecting
union below this lever and is led via a hose to the manual ventilation bag. By using a
screwdriver, the volume flow for manual ventilation can be adjusted at the flow control valve.
This becomes visible when the lever is in the „Hand“ position. Otherwise, it is covered by the
lever.
When the lever is in the „Hand“ position, an electric contact is simultaneously activated.
Once activated the optical message "Attention Manual Ventilation!" appears on the display
screen.!“. In addition, the emergency air valve as well as the injectors in the patient
component are switched off, whereby the patient can, generally, spontaneously breathe
ambient air.
Furthermore, the test block is equipped with an electric lifting magnet. When activated, this
closes, via a valve reed, the emergency air valve of the patient component. (see. Patient
component).
3.3.2 Assembly and Disassembly
The test block can be disassembled by loosening the hexagon socket screws that are
accessible at the side. After loosening the screws the test block can be pulled off and the plug
connection between the test block and housing removed.
When re-assemblying, make sure that the tappet rod of the switch-over "Hand/Ventilator" is
centrally positioned on the tappet of the pneumatics module.
When replacing the electromagnet (solenoid), loosen the ring nut between the patient
component and the test block by using box or socket spanner (wrench).
48
3.4 Patient Component
3.4.1 General
„ Patient component, inside view“,
The patient component is the actual connection (interface) between the ventilator and the
patient. It is attached on the sidewall of the basic unit in front of the test block and locked in
using a lever.
All pneumatic components of the patient loop are found in the patient component; all these
components must undergo sterilisation.
3.4.2 Functional operation
The ventilatory-gas mixture in the pneumatics module is pressurized to approximately 110
mbar. It is led via a plug coupling, hermetically sealed with o-rings, through the inlet of the
patient component. The ventilatory gas flows through the humidifying bottle filled with
water, and then, warmed and humidified, proceeds to the inspiration valve Vin and from there
is led via the inspiration outlet through the inspiration hose to the Y-piece. The exhaled
ventilatory gas flows through the expiration hose and the expiration inlet to the expiration
valve Vex and from there into the ambient air via an injector.
Valves V1, V2, V3, V4 and V5 form the safety system within the patient component and
prevent, in the event of mechanical malfunctioning, any endangering of the patient.
By means of the excess pressure safety valve V1, the maximum possible excess pressure at
the inspiration outlet is mechanically limited. Here, the opening pressure of valve V1 is
49
adjustable in the range from 20 mbar to approximately 80 mbar by using the toggle found on
the front side of the patient component.
The negative pressure safety valve V4 limits the maxium negative pressure at the expiration
inlet to approximately -10 mbar. It is pre-set by the manufacturer and the opening pressure
cannot be adjusted by the user.
The inspiration outlet and the expiration inlet are connected to the emergency air valve via the
check valves V2 and V3. During normal operation of the ventilator, a lifting magnet
(solenoid) in the test block presses a valve head against the outlet of V5. This disables V2 and
V3. In the event that the unit detects an operational disturbance, the solenoid is deactivated,
the valve head opens the emergency air valve, and the patient can inhale via valve V2 and
exhale via valve V3, whereby the effective dead space is less than 2.5 ml.
The inspiration valve Vin and the expiration valve Vex structurally form a single unit, in that
the inspiration valve opens when the expiration valve closes, and vice versa. This valve unit is
actuated by a valve actuation that is found in the basic unit. The mechanical connection
between actuation and valve unit is by means of magnetic forces. Here, a small magnetic
clamp is attached to the actuation and the side of the valve pistion facing the actuation is
equipped with a thin soft iron plate. When the patient componenet is locked onto the right
side of the housing, the magnetic clamp attracts the valve piston above the soft iron plate and
in this way forms a tight (free of play) connection between actuation and valve unit. Through
a slight crowned design of the soft iron plate, slight tilting of the patient component can be
compensated for, without endangering the safety of the mechanical connection.
When the patient component is separated from the basic unit, the moving part of the valve
actuation found in the basic unit is pulled against a stop until it overcomes the maximum
magnetic force, and the connection between actuation and valve is mechanically broken.
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3.4.3 Assembly and Disassembly
The patient component can be completely disassembled.
The bell-shaped valve and the safety valve can be unscrewed by using a coin to loosen the
screws.
3.5 Patient Hose System
"Patient hose system, complete“.
The patient hose system, consisting of heated inspiration hose and expiration hose, is attached
to the ventilatory-gas connection pipes found on the front side of the patient component.
51
Here, it must be ensured that the red hose sleeve coupling of the inspiration hose is on the red
inspiration outlet. At the end of the inspriation hose, a nebulizer pot can be attached, which
then can be connected via an additional hose with the Y-piece.
At the patient end, the temperature sensor is also inserted in to the bore marked red.
The plugs for heating and temperature sensor are pluged into the respective sockets located in
the connection block for heating, pressure measurement and aerosol.
3.6 Measurement of Pressure and Volume Flow
The measurement of pressure and volume flow takes place near the patient between Y-piece
and tube connector. For this, a pneumotachograph head is inserted between both parts. The
differential pressure resulting above the resistor of the PNT-head is a rate for the volume
flow. The differential pressure is led, via two thin tubes, to the pressure sensors (ventilation
pressure) of the sensor circuit board found in the basic unit, and to the differential pressure
sensor (volume flow). The mechanical connection of these hoses to the basic unit is via a Luer
Lock coupling.
For reasons of safety, the measurement of ventilation pressure is via two pressure sensors.
Via valves, the pressure measurement ports of the differential pressure transducer can be
intermittently switched over to ambient air, and during this short time period a zero set
compensation of the volume flow can be carried out. A precise explanation of this calibration
procedure can be found in subpoint 4.3.3 (Sensor Module).
52
3.7 Aerosol System
On the right sidewall there is also a connection union (pipe) for aerosol (see also Pneumatics
Module) and Fig. 3.5.3. When the nebulizer function is activated the therapy ventilatory-gas
mixture at this connection is under a pressure of approximately 2 bar. It is fed to the nebulizer
chamber via a hose attached to this connection. This is to be placed, near the patient, on the
end of the inspiration hose (see also Hose System).
3.8 Ventilatory-Gas Humidifying
Humidifying the ventilatory gas takes place by means of a state-of-the-art procedure, in that
humidifying and warming of the ventilatory gas is done in two steps and via two separate
loops.
4 Electronic
4.1 General
The entire electronic system is housed in the basic unit.
• Control unit,
• Monitor,
• Electric power supply,
• Pneumatics Module,
• Actuator
53
The operational functioning of the individual electronic components can best be described
using the following logic diagrams.
The signal designations are based on the following principle:
The first two letters refer to the signal sources. They are followed by a sub-hyphen and the
subsequent characters that should, if possible, identify the significance of the signal.
Serving as signal sources:
MC : Microcomputer (central control),
PC : PC Module,
ÜW : Monitoring,
LV : Power amplifier,
SM : Sensor module,
PM : Pneumatics module,
SV : Electric power supply module,
AM : Battery module,
RV : Backplane circuit board,
GG : Basic unit.
4.2 Control Unit
The control unit is the communications level (interface) between the user and the equipment.
On the one hand it contains all control elements necessary for the therapeutic operation of the
Stephanie (Therapy Control Module), on the other hand, it also contains the monitor,
consisting of a display screen and its control elements (Monitor Control Module), via which
the user can access all information pertaining to the patient and equipment.
4.2.1 Therapy Control Module
Setting and adjustment elements for the individual parameters are:
• Potentiometer: Tins, Trigger, Vt, Pmax, PEEP, Temp, FiO2, V’osz, fosz, Rv und Ev,
• Switch: Operation mode, inspiration pattern,
• Incre. transmitter: Tex.
• Keys: Insp. Hold, Aerosol, NVI, PVI,
54
The switches are equipped with resistor networks, so that their position, including that of the
potentiometer, is recorded and transmitted to the microcomputer by an analogue-digital
converter via a 16 ibt databus (MC_D0..MC_D15).
The switching state of the keys is stored in a switching circuit and also transmitted via the
databus.
The control signals from the microcomputer for the temporal coordination of the query of the
control elements as well as signalling the LEDs are transmitted via the same databus. The
logic necessary for this is carried out by two programmable logic arrays (PAL).
A failure mode analysis of the control unit is discussed in Section 5.
4.2.2 Monitor Control Module
The following belong to the Monitor Control Module:
Incremental transmitter for menu control of the monitor, as well as the
Keys for Stop, Print, LFD1, Reserve, Alarm Mute.
These signals are evaluated by the PC module and the central control (MC).
4.3 PC Module
The PC module contains a complete industrial standard PC, consisting of the PC circuit
board, a VGA card, floppy-disk drive, harddisk and a bus card as interface between the
processor and the PC. All circuit boards are mounted on a backplane.
4.3.1 PC Circuit Boards
The PC circuit boards supply a PC (486 -33 DX2) and contain all necessary drives and
interfaces for the keyboard and storage systems.
The actual monitoring program is stored on a semiconductor memory (silicon disk). As the
PC card is a commerically manufactured circuit board that is not subject to servicing, its
functioning will not be detailed in this technical manual.
4.3.2 VGA Card
The VGA card contains the entire electronics necessary to drive TFT-VGA display screen.
For detailed information, refer to manufacturer's technical data..
4.3.3 PC Interface
The PC provides the interface between the PC and the ventilator.
55
4.3.3.1 Signal Designations
Operating voltages
SV_P5, SV_0V
Input signals
AIN0...AIN7 8 Analogue inputs
DI0...DI15 16 digital inputs
IGRa, IGRb Inputs for an incremental transmitter
Output signals
DAC0...DAC3 4 Analogue outputs
D01...D15 16 digital outputs
Bus signals
D0...D15 16 Databus signals
A0...A10 11 Addressbus signals
OSC,/IOW, /IOR, BALE, AEN,
RESET.DRV, /IOCS16
Controlbus signals
4.3.3.2 Operational functioning
The PC interface card provides the connection between the address bus and the databus of the
PC as well as analogue and digital input/output signals of the processor.
The analogue-to-digital converter (A3 and A4) allows the AD conversion of 8 analogue
signals with a word size of 12 bits in a voltage range of +/-12V.
Two digital-to-analogue converters (A1, A2) generate four analogue output signals in a
voltage range of +/- 5V using a word size of 12 bits. The exact setting of the reference voltage
is effected via the settings control R1.
56
Via circuits D6 and D7, 16 digital inputs can be read and via D8 and D11 an additional 16
digital outputs can be recorded.
The sequential and combinational control logic for these processes is provided by PALs D3,
D4 and D5.
57
4.4 Electronics Block
4.4.1 Microcomputer
4.4.1.1 Signal designations
Operating voltage
SV_P5, SV_0V
Analogue input signals 10bit (0.5V)
SM_UTemp1 Ventilatory gas conditioning, Temperature 1
SM_UTemp2 Ventilatory gas conditioning, Temperature 2
SM_UTemp3 Ventilatory gas conditioning, Temperature 3
PM_UPl Supply pressure, compressed air
PM_UO2 Supply pressure, O2
PM_UTemp Temperature in pneumatics module
RV_UP4 Battery voltage 4V
LV_Usumm1 Positional transducer: cumulative voltage 1
LV_Usumm2 Positional transducer: cumulative voltage 2
Analogue input signals 12 bit (+/-10V)
SM_UP1 Pressure, near patient sensor
SM_UP2 Pressure, near unit sensor
SM_UFlow Volume flow of PNT
PM_UP120 Admission pressure 120 mbar
LV_Us2 Positional transducer: path 2
PM_UFiO2 FiO2 sensor signal
Analogue output signals 12 bit (+/- 12V)
MC_ UDAC1, Analogue output 1
MC_UDAC2 Analogue output 2
58
Digital input signals
/ÜW_RSTMC Restart Microcomputer
SV_PGLV Power amplifier
/NMI Not assigned
/ÜW_5VBFail
/ÜW_PCWD watchdog for PC fail
/RV_SMan Switch, manually switched on
Digital output signals
MC_SD Shut down signal for power supply
MC_INSP Inspiration phase for mechanical ventilation
MC_Heiz1 Heating, humidifier chamber, ON
MC_Heiz2 Heating, hose, ON
MC_RSTAus Blocking of Restart function of ÜW
MC_LVEin Relay on power amplifier, ON
MC_Spk1Ein Signal transmitter 1 on ÜW, ON
MC_NL Emergency air magnet, normal operation
MC_WD Control signal for watchdog on ÜW
MC_HP Alarm, high priority
MC_MP Alarm, medium priority
Bus signals
MC_D0...MC_D15 16 Databus signals
MC_A0...MC_A7 8 Address bus signals
MC_RD, MC_WR, MC_CLK, MC_SEL Control bus signals
Serial interface ports
TXD0, RXD0, TXD1, RXD1 Interface port signals
59
4.4.1.2 Operational functioning
The circuit board of the microcomputer is made up of the following components:
• The actual microcontroller (80C166 from Siemens) with an integrated 10 bit ADU,
• 12 bit ADU, 8 channels (D ),
• 12 bit DAU, 2 channels (D ),
• PAL (D ),
• ROMs (D ),
• RAMs (D ),
• 2 Latch (D ),
• Bi-directional bus driver (D ).
The analogue input signals are collected by the two ADUs and together with the digital input
signals further processed by the microcomputer in line with the program.
At its outputs, it furnishes the corresponding digital control signals and provides the DAU the
information for its analogue output data.
Address bus and databus signals are transmitted via the respective drivers to the outside.
Coordination of the internal processes is ensured by the processor, and by the PAL. In
particular, it generates control signals for the peripheral components.
By means of the adjusting rheostat R1, the reference voltage of the DAU and by means of R6
that of the 10 bit ADU can be set.
The microcomputer is equipped with two ports for serial data transmission RS232.
60
h00000000
120240
Sauerstoffsensor
®
M - 11
2x4AT
Reset
4.4.2 Monitoring (watchdog
4.4.2.1 Signal designations
Operating voltage
RV_P12, SV_0V, SV_N12LV
Analogue input signals
SA_SPEECH Tone signals for voice output
(not yet installed)
Digital input signals
SV_AkkLOw Battery LOW signal (Ubatt < 21 V)
SV_PG Power good for processor voltage
SV_PGLV Power good for LV voltage
/MC_RSTAus Blocking of Restart function of ÜW
MC_Spk1Ein Signal transmitter 1 on ÜW ON
MC_NL Emergency air magnet, normal operation
MC_WD Control signal for watchdog on ÜW
MC_HP Alarm, high priority
MC_MP Alarm, medium priority
PC_RSTEin Restart_function enable
PC_RSTDrive
Digital output signals
/ÜW_5VBFail Internal voltage 5V fail
/ÜW_5VB1fail Internal voltage 5VB1 fail
/ÜW_RSTMC Restart Microcomputer
/ÜW_RSTPC Restart PC
/ÜW_PCWD PC watchdog responded
/ÜW_MCWD MC watchdog responded
/ÜW_NL Emergency air signal, normal operation
61
ÜW_Spk1_1 Output voltage 1 for speaker 1
ÜW_Spk1_2 feedback input signal 2 from speaker 1
ÜW_SPK2 Output signal for speaker 2
Valve control signals
/ÜW_V0.../ÜW_V10 Negative control signals for the valves
Bus signals
MC_D0...MC_D15 16 data bus signals
MC_A7 Address bus signal
MC_RD, MC_WR, MC_SEL Control bus signals
4.4.2.2 Functional operation
The watchdog circuit board has the following tasks to fulfil:
• Monitoring the proper functioning of PC and MC by processing and evaluating watchdog
signals,
• Generating audible signal sequence for alarm,
• Generating the actuation signal for the emergency air,
• Actuating all magnetic valve in the pneumatics module and basic unit.
Internal power supply
For reasons of safety, the internal voltages for 5V are doubled and the DC-DC transformer
converts the externally supplied voltage RV_P12 into IC21 (5VB) and IC22 (5VB1).
Watchdog monitoring
The PC module and the controller independently transmit, in the course of properly
processing their respective program and at intervals of approx 100..200 ms, watchdog signals
PC_WD and MC_WD, that are evaluated by the watchdog for the PC signal (IC8) and that for
MC signal (IC9). In the event of errors in the program run, the watchdog signal cease and the
PC and/or MC are restarted. During this time a HP (high priority) alarm is triggered, and the
patient has the possibility to spontaneously breathe ambient air via the emergency air valve.
The precise time for running this routine can be read from the status graphs for the watchdog
automaton. It is identical for both the PC and MC systems.
62
The normal state is state 1, the emergency air valve is closed (/ÜW_NLok). If there is no
watchdog signal within the set time-window, the status graph goes over to state 2: the
emergency air valve opens and the PC or MC are restarted via signals /ÜW_RSTPC or
/ÜW_RSTMC. If restartup is successful, the automaton goes over to 3, in which the
emergency air remains open. Only when the next proper WD signal is received, will state 1 be
activated again. If restart was unsuccessful, the WD automaton goes over to state 4, which
can only be exited again by switching the unit off: the emergency air valve remains open and
the HP alarm remains activated.
Generating the audible alarm signal
The audible alarm signal is also generated in an alarm automaton. The signal sequence is
stipulated according EN 475 and for alarms of medium priority (PC_MP, MC_MP) is distinct
from those alarms of high priority (PC_HP, MC_HP). The alarm automaton is made up of the
PALs IC1 and IC2 in connection with a clock generator (IC5).
The output signal of the automaton activates the signal generator SPK1 via the power
amplifier (IC10). This is found in the basic unit and is electrically switched between outputs
ÜW_SPK1_1 and ÜW_SPK1_2. This allows, via the signal (ÜW_SPK1_2) to determine
whether current is actually flowing through the signal generator SPK1 on request/prompt for
audible signaling.. In this respect, signal ÜW_SPK1_2 is actually an input signal and serves
towards monitoring the audible signal routing from input of watchdog switching down to
signal generator SPK1.
In the event of any error within this routing, alarm automaton 2 kicks in and triggers the
audible alarm (ÜW_SPK2) via signal generator 2.
Valve actuation
The magnetic valves (solenoids) in the pneumatics system are actuated by bus signals
(MC_D0..MC_D10) and the respective control. Both registers IC11 and IC12 store the
databytes sent by the MC and control, on their part, the MOSFET power transistors T2..T11
via the optical coupler IC15..IC17. Via their outputs, they switch (ÜW_V0.../ÜW_V10) the
solenoids to - 12V (SV_N12LV). In high-impedance state of the transistors, the valves are
switched off.
Here, there is also a check as to whether the desired switching operation has been at least
electrically executed, or not. For this, there are, in parallel to the outputs of transistors
T0...T10, the control inputs of the optical couplers (IC 18...IC20) are switched via RLC
63
components. When the transistors are in off status low current flows through each solenoid,
which, however, suffices to activate the optical coupler. This signal is transmitted via the bus
drivers IC13 and IC14 and the MC bus signals (MC_D0 ...MC_D10) to the MC. When the
MC generates a control signal for actuating the solenoids, a check is run by the MC after a
transient period of about 10 ms, whether the respective valve has actually been switched. This
provides information on the electrical functional capability of the path, MC - ÜW - valves –
MC, including the respective software.
The emergency air valve is of particular importance among the solenoid valves, as it is not
activated via the bus, but by the alarm automaton and the WD automaton. The emergency air
valve can only be actuated when all units are functioning properly and do not signal a
malfunctioning.
The logic equations for activating the emergency air valve can be found in the operational
diagram.
4.4.3 Sensor Module
The sensor module is a circuit board on which all sensors necessary for the proper functioning
of the Stephanie are mounted, including their respective electronic components. They are the
following:
1 Differential pressure sensor for measuring volume flow,
2 Pressure sensors for ventilatory pressure (HCMX100),
3 Thermistor amplifier for measuring ventilatory-gas temperature,
1 Instrument amplifier,
2 Amplifier.
4.4.3.1 Signal Designations
Operating voltages
SV_P12LV, SV_P12, SV_N12, SV_0V
64
Input signals
MC_UDAC2 MC: DAC-Signal 2
/ÜW_VPNT ÜW: zero point valve PNT ON
GG_UIn1 GG: analogue input 1
GG_UIn2 GG: analogue input 2
GG_Ures1 GG: analogue reserve input 1
GG_Ures2
GG_Rth11 GG: Thermistor 1, terminal1
GG_Rth12 GG: Thermistor 1, terminal2
GG_Rth21 GG: Thermistor 2, terminal1
GG_Rth22 GG: Thermistor 2, terminal2
GG_Rth31 GG: Thermistor 3, terminal1
GG_Rth32 GG: Thermistor 3, terminal2
Output signals
SM_UP1 SM: voltage, pressure 1
SM_UP1Out SM: k. fixed voltage, pressure 1
SM_MP1 SM: measuring pt. 1 (refer. voltage 1.23 V)
SM_UP2 SM: voltage, pressure 2
SM_UFlow SM: voltage, volume flow
SM_UFlowOut SM: k. fixed voltage volume flow
SM_UOut1 SM: output voltage 1
SM_UOut2 SM: output voltage 2
SM_UTemp1 SM: voltage, temperature sensor 1
SM_UTemp2 SM: voltage, temperature sensor 2
SM_UTemp3 SM: voltage, temperature sensor 3
SM_Ures SM: voltage, reserve
GG: analogue reserve input 2
4.4.3.2 Operational functioning
The functioning of the sensor module is discussed in the following on hand of the operational
diagram FP_SM.
65
Differential pressure sensor
Determining the volume flow is carried out pneumotachographically, whereby the volume
flow to be measured flows through a pneumotachograph head (PNT) and the resulting fall in
pressure above the PNT (the difference between proximal and distal pressure) is converted
into an electrical signal by a piezoresistive differential pressure sensor. The differential
pressure sensor as well as the two sensors for measuring the ventilatory pressure are, from a
pneumatic view, symmetrically arranged. This is necessary so that the ventilatory pressure
does not impede the measurement of the volume (common mode pressure suppression).
The proximal supply pressure P1 reaches, via a distributing manifold, to the proximal
pressure sensor (sensor 2) and via the solenoid valve (valve 2), to the pressure inlet of the
differential pressure sensor (sensor 1).
In the same way the distal supply pressure P2 reaches, via a second distributing manifold, the
distal pressure sensor (sensor 3) and via the solenoid valve (valve 1), the second pressure inlet
of the differential pressure sensor.
The output signal of the differential sensor (sensor 1) is amplified by the instrument amplifier
U1 and is resident at the output as signal SM_UFlow.
A second amplifier A1D provides a short circuit-proof signal SM_UFlowOut for connecting
external equipment.
Bridge supply current for the differential pressure sensor is generated by the reference voltage
source (A1A) in connection with amplifier A1B.
Solenoid valves Valve1 and Valve 2 are electrically actuated in order and switch in
deactivated state a respective pressure inlet of the differential pressure sensor to ambient air.
During normal operation the valves are switched on (/ÜW_VPNT= -12V) and connect the
pressure inlets of the differential pressure sensor with the pressure port for the proximal and
distal pressure.
During a periodical zero point correction, the valves, via the signal /ÜW_VPNT, are
switched off for the duration of approximately 50 ms and the pressure inlets of the differential
pressure sensor are switched over to ambient air. The microcomputer measures the ouput
voltage SM_UFlow and in a compensating procedure, via the control signal MC_UDAC2, the
bridge zero point is modified until SM_UFlow Null reaches zero.
66
Pressure sensors for ventilatory pressure
The output signal of the proximal pressure sensor (sensor 2) is amplified via amplifier A2B (
V=2) to signal SM_UP1 and via a second amplifier A2A (V=1) short circuit-proof to signal
SM_UP1Out.
The distal pressure signal of sensor 3, however, is only converted via amplifier A2C (V=2) to
signal SM_UP2.
The pressure voltage transfer function is:
U/V = 1 + 0.04 * P/mbar.
Thermistor amplifier (temperature measurement)
The instruments amplifiers U3 to U5 form, in connection with the reference voltage source
(MP1) and the bridge resistors R11..R15, a resistive voltage converter by means of which the
signals of the externally located temperature sensors (thermistors) are converted to electical
voltages (SM_UTemp1, SM_UTemp2, SM_UTemp3). The temperature voltage transfer
funtion is:
U/V = 2 + 0.1 *(T/°C - 20°C).
Discrete amplifier (Reserve)
The instruments amplifier U2 enables the amplification of a random signal by the factor
V=100. (use for the measurement of FiO2 in Pulmostar)
Both amplifiers A1C (V=2) and A2D (V=1) are for reserve purposes.
4.4.4 Power amplifier
4.4.4.1 Signal designations
Voltages
SV_P12, SV_N12, SV_P12LV, SV_N12LV Operating voltages
Input signals
WM_I1PSD1 WM: current 1 from PSD 1
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WM_I2PSD1 WM: current 2 from PSD 1
WM_I1PSD2 WM: current 1 from PSD 2
WM_I2PSD2 WM: current 2 from PSD 2
MC_UDAC1 MC: Analogue voltage 1
MC_LVEin MC: power amplifier ON
Output signals
LV_USum1 LV: cumulative voltage of positional transd. 1
LV_USum2 LV: cumulative voltage of positional transd. 2
LV_Us1 LV: voltage, path 1
LV_Us2 LV: voltage, path 2
LV_UEDA1 LV: output voltage 1 for EDA
LV_UEDA2 LV: output voltage 2 for EDA
4.4.4.2 Operational function
The power amplifier amplifies the analogue signal supplied by the microcomputer (MC) and
through that controls the moving-coil (electrodynamic) actuation (EDA) for the ventilatory
valve.
In addition, electronic components are on the circuit board for two positional transducers, by
means of which the exact position of the valve piston is determined and with that, via path
feedback, the natural frequency of the EDA can be significantly increased.
Explanatory note on the positional transducer system (Wegmeßsystem/WMS)
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Wegmess-Systemmit allen Anschlußbelegung
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The actual positional transducer system is found on the right sidewall of the Stephanie. It
consists of two position measurement paths, each of which are formed by a luminescence
diode (LED), an optic system and a position sensitive device (PSD). The lightband generated
by the LED and optic is covered by the PSD opposite a crevice located on the valve piston, so
that at the point of the crevice only a narrow light spot appears on the PSD. This spot of light
generates two photoelectric currents, the strength of which both in intensity as well as the
position of the spot of light on the active surface of the PSD can be determined.
The following explains the principle of signal processing. Definitions are
l: Length of the active path of the PSD
x: Position of the lightspot on on the PSD with reference to the initial starting point
I1: Current 1
I2: Current 2,
L: Photo-current of the lightspot.
Equations for the photo-currents:
I1 = k * L * x/l; I2 = k * L * (1-x)/l (Eq1)
Resulting cumulative currents:
Is=I1 + I2 = k * L * 1/l (Eq2)
and the differential current
Id = I1 - I2= k * L * (1-2*x)/l (Eq3)
When the quotients are formed from Id and Is, one receives
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S = Id/Is = 1 - 2*x. (Eq4)
According to this, the Eq. 4 signal obtained is only proportional to path x and within a certain
range independent of photo-current and physical properties of the PSD.
The following description of circuit design refers to positional transducer system WMS 1.
The operational function of WMS2 is the same.
The photo-currents WM_I1PSD1 and WM_I2PSD1 are converted by amplifiers A1A and
A1B, in connection with resistors R1 and R2, into current-proportional voltages. A1C forms
the sum Us and A1D the difference Ud of these currents. The analogue division curcuit A2
then realises Eq.4 by quotient formation of Us and Ud. Its output signal LV_Us1 is a
measurement for the position of the lightspot on the PSD and is therefore proportional to the
path travel (position) of the piston..
Signal LV_Usumm1 corresponds to the 0.33 fold cumulative voltage after A1C. It serves to
monitor the optical path of the WMS. By means of the adjuster ER1, the electrical zero point
of WMS can be shifted.
The setting of the transfer function of WMS is fixed at U/V = 2 * s/mm, i.e. 1mm travel
difference corresponds to a voltage difference of 2 V.
Power amplifier
The actual power amplifier (LV) is realised by a TDA 2050 (A6). In connection with the
feedback resistors (R33, R41) it has for the input signal an amplification of V=13.6. Input
resistor R33 is, via relay REL1 in its activated state, switched to control input MC_UDAC1
and in deactivated state, via R40, switched to the output of A6. The activation of REL1 is by
means of transistor T1 and the control signal MC_LVEin. The sense of this circuit is that for
reasons of load, the LV and therewith the EDA are only activated when necessary. In certain
emergency situations or when using the Stephanie as a pulmonary-function unit, the LV is
switched off by the MC via the signal MC_LVEin=LOW. This means that the LV can no
longer be activated via its input, and the output current through EDA sinks to values less than
30 mA, which no longer create thermal load.
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Travel feedback
The output signal of positional transducer 1 is led via a transfer link with PD behaviour (A5A,
A5B) to a further control input for the power amplifier. Der P-part carries back a travel-
proprtional part, and the D-part a speed-proportional part. Via the travel-proportional part, the
overall transfer factor of LV and EDA, concerning travel, and via the speed-proportional part
(ER3) the attenuation can be stipulated. Due to the high loop amplification of this system, the
transfer function LV-EDA is practically only dependent on that of the positional transducer
system, and results
s / Uein = 1 / KWMS = 0.5 mm/V.
This achieves, that, independent of intraindividual parameter fluctuations between the
individual moving-coil actuators, a constant transfer behaviour of the valve actuator is
ensured. That is to say, a change in voltage of MC_UDAC1 by 1 V leads to a change in
position of the EDA of 0.5 mm.
By means of the ER4, an additional stability of the system can be influenced at high
frequencies.
Safety observations
Since the positional transducer system is designed as a dual system, one system is for the
feedback, a second is for checking the system.. Thanks to the good coordination between the
control voltage of the MC (MC_UDAC1) and the position of the control valve, a check can be
run, via the second positional transducer system, as to whether the desired position has
actually been achieved. This comparison check takes place in the MC. This monitoring check
is very complex and entails the entire path MC - LV - actuator – control valve - MC. Its
operational function is: within a certain temporal and voltage error span, the MC checks
whether the generated control voltage of the MC agrees with the voltage of positional
transducer system 2. In the case of deviation, an alarm with high priority is triggered along
with activation of the emergency air system.
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4.5 Power Supply
4.5.1 Power supply module
4.5.1.1 Signal designations
Voltages:
SV_P5, SV_P12, SV_N12 Operating voltages for the computers
SV_P12LV, SV_N12LV Operating voltages for power amplifier and valves,
SV_P24 Intermediate circuit voltage (24...28V)
SV_HEIZ1 Activated voltage for heating and humidifier,
SV_Heiz2 Activated voltage for hose heating
Monitoring signals:
SV_PG Power good signal of computer voltages
SV_PGLV Power good signal of LV voltages
SV_Netzok Mains voltage is OK
SV_Akkok Battery voltage is OK
SV_AkkLow Battery voltage is less than 20 V
Control voltage:
MC_SD MC: Shut down
/BE_SBER BE: switch position not ready
MC_HEIZ1 MC: Heating 1 ON
MC_HEIZ2 MC: Heating 2 ON
/UW_NL ÜW: emergency air valve not activated
Switch signals
SV_S1a, SV_S1b Switch contact of mains power switch
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4.5.1.2 Operational function
For an explanation of the operational function, see Appendix 7.2: Operational Diagram
FP_SV.
Voltage generation
The input voltage of 220 V is led, via the fuses and the mains power switch to a primary
voltage regulator. If the signal is MC_SD=LOW, it generates an intermediate circuit voltage
of 24 V...28 V (otherwise it is zero). At the same time the charging current for the 24 V lead
battery is generated and the battery is charged.
In the case of /BE_SBER =HIGH, the secondary voltage regulators for the computer voltages
and the power amplifier are switched on.
A contact of the mains power switch is on the outside.
Substitution switch of the battery voltage
If there is a power failure during operation on mains power supply (SV_Netzok=LOW), the
intermediate circuit voltage through the primary regulator becomes zero, and the battery
voltage (24V) is switched via a MosFet to the intermediate circuit. This ensures that there
continue, with no break, all output voltages of the power supply.
Only the heating is not supplied with current during a power failure.
The battery voltage is monitored for compliance within certain voltage parameters and its
state is determined via the respective signals.
Heating voltage generation
The voltages for respiratory gas humidifier and hose heating are obtained via the power-
MosFets directly from the intermediate circuit voltages. Prerequisite for provision of these
heating voltages is that the mains power is on and the systems monitor does not detect an
emergency air situation (SV_Netzok * /UW_NL=HIGH). If this is the case, heating voltages
1 and 2 from the MC can be switched via signals MC_Heiz1,2.
4.5.2 Battery Module
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The battery module is made up of a 24 V rechargeable lead battery, of which the output
voltage (AM_P24) is secured by a 4 A fuse, and is led to the identical inputs of the power
supply module.
4.6 Valve Actuation
The valve actuation is realised by a moving-coil converter similar to that of a loudspeaker.
The drive coil is held by two centering diaphams and is frictionlessly guided.
This drive coil is closed in the direction of the ventilation valve unit by a plate, on which a
small magnetic clamp (D=8.5 mm) is stuck. This magnet forms, in connection with the soft-
iron plate on the valve piston, the mechanical coupling between the valve actuator and the
ventilation valve unit.
When the patient component is connected to the housing, both parts come into magnetic
contact and form a tight hysteresis-free mechanical coupling.
The executed positional feedback, in connection with the valve actuator, has already been
explained in Section 4.3.4. In addition, it allows to check the integrity of the connection
between the valve actuation and the valve piston.
The assembly of the valve actuation is carried out within the unit, whereby using an
adjustment gauge, the adjustment of the position of the positional transducer and the
ventilation valve unit can be conducted.
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5 Safety Concept
5.1 General
The safety concept for the Stephanie is so designed, that it detects a simple error and even in
the case of a double error, switches the ventilator over to a status where the patient is not at all
endangered.
At this stage of development we understand the status of "fail save"; that means that the
patient is secured by the safety valve being activated and this allows the patient to
spontaneously breathe ambient air.
Depending on the cause of the error or malfunctioning, and in line with EN 475, the unit
introduces various forms of visual and audible error signalling and corrective action.
Causes of error and malfunctioning are various. These can be:
• Unit defect of the ventilator des Ventilators (break-down),
• Faulty use of the unit (e.g. disconnection),
• Threatening situation on the patient's side (e.g. apnea),
5.2 Safety Design of the Ventilators
Concerning safety design, the Stephanie is structured as a dual-channel system. The diagram
shows that the microcomputer (central control) and the PC module almost completely, but
independent of one another, take over the mandatory monitoring parameters of the unit and
patient, and when errors are detected trigger audible alarms as well as introduce corrective
action.
In addition, many functional units such as actuator, audible alarming, valve control, etc., are
subject to very complex selftests, the functioning of which has been described in the
respective sections.
Furthermore, the test function of the Stephanie, that must be conducted before using the unit
on the patient, provides a very comprehensive test of the unit. After the test has been
successfully carried out, the unit, based on reliability predictions, can be classified as being
new equipment (prerequisite: constant failure rate).
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5.3 Mandatory Parameters to be monitored and tested
According to DIN EN 794, the mandatory parameters to be monitored and tested are:
1. Functional capability of the equipment.
2. Operating voltages
3. Gas pressure of the central respiratory gas supply
4. Alternative or reserve power supply
5. Inspiratory oxygen concentration
6. Air-passage pressure
7. Minute volume
8. Disconnection
9. Apnea
10. Respiratory gas temperature
5.4 Adjustment and Treatment of Limit Valves
5.4.1 General
The mandatory limit values to be monitored are preferably set by hand (see Operating
Instructions). This has the disadvantage of being time-consuming compared with
automatically set defaults dependent on the preset ventilation parameters. On the other hand,
it has the advantage that a mistakenly false setting of these parameters triggers an alarm, thus
avoids any endangering of the patient.
After the unit has been switched on, limit values are set according to the setup routine.
5.4.2 Pressure
During machine ventilation, the respective peak pressure is monitored in relation to upper and
lower limit values.
During proper functioning of the pressure loop, the upper limit value will normally not be
reached.
Pressure falling below the lower limit value, in the case of disconnection or in comparison to
the preset value of Pmax and VT, will result in "soft lung".
Setting Limit Value
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Setting the limit value is carried out manually.
Setup: Pgob = 30 mbar,
Pgun = 10 mbar.
Error corrective action
Pgob-Alarm:
Visual: "Peak pressure too high !!!"
Audible: HP-Warning tone
Technical: opening of safety valve
Pgun-Alarm:
Visual: "Peak pressure too low, Disconnection ?"
Audible: Warning tone
Technical: no response.
5.4.3 Respiratory Minute Volume
The expiratory minute volume V'ex is monitored in all modes of operation.
Approximately 15 s are selected as a monitoring timeframe.
Setting limit values
Manual setting,
Setup: V’max = 2 l/min,
V’min = 0.2 l/min
Error corrective action
Visual: "Minute volume too low ! Disconnection?"
" Minute volume too high !"
Audible: HP- or MP alarm,
Technical: none
5.4.4 Insp. O2 concentration:
Since a pneumatic mixer is used, the actual preset value is recorded by coupling the mixer
rotary head with an transmitter (Potentiometer).
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The voltage value, corresponding to the potentiometer setting, is the target value, and is
compared to the actual value which is measured by the O2 sensor.
Setting limit values
Manual setting,
Setup: FiO2 ob = 50%
FiO2un = 20 %.
5.4.5 Temperature
Setting limit values
Setting limit values is carried out manually.
Setup: Tun = 33 °C,
Tob = 38 °C.
Error corrective actions
Visual: " Respiratory gas temperature too high!"
„ Respiratory gas temperature too low!“
Audible: MP - Alarm for a temperature >= 40°C
Technical: For excess temperature > 41 °C longer than 2 min., heater is switched off.
5.5 Alarm Response
5.5.1 General The individual alarm ratings correspond to, in line with DIN EN 475, the various alarm
responses regarding the audible and visual alarm signals as well as the response of the safety
system.
In line with this, there is a distinction between alarms of medium priority and those of high
priority. An alarm of at least medium priority (MHP) means that the alarm begins as medium
priority and then goes over to an alarm of high priority.
The safety system responds by switching off the emergency air valve ( /ÜW_NL), the two
valves for compressed air (/ÜW_VPL) and oxygen (/ÜW_VO2), the central gas supply as
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well as the injector valve (/ÜW_VInj1, /ÜW_VInj2). In this event the patient can at least
spontaneously breathe ambient air.
Visual alarm signalling is via alphanumeric display on the monitor screen. In the event of an
alarm of low and medium priority, it is yellow, alarms of high priority are displayed in red.
Alarm situations that have ended, but have not yet been acknowledged, are displayed in
green.
5.5.2 Alarm suppression
The audible components of alarms of high and medium priority can be suppressed for the
duration of 2 minutes by pressing the "Alarm mute" key.
This suppression applies, however, only for current alarms. When the cause triggering the has
been, in the meantime, remedied, but recurs before this suppression elapses, it is treated as a
new alarm. This also applies to alarms arising due to other causes.
The status of the audible alarm suppression is visually displayed.
5.5.3 Status graphic of the alarm system The behaviour of the alarm automaton can best be described by means of a status graphic.
This also applies to those of the MC and PC..
(Graphic) Glossar
MPALneu MPALneu
MP-OptAnzeige
Gelb
Grün
MP-OptDisplay
Yellow
green
MP-Signalton MP-Signal tone
Kein Alarm No alarm
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Kein Alarm
HP-SignaltonHP-OptAnzeige
(rot)
HP-OptAnzeigeHPAL : rot
/HPAL : grün
HPAL_neu + HPAL_old*Tmute
/HPAL* Mute
/HPAL
MPAL + MHPAL
MP-SignaltonMP-OptAnzeige
MP-OptAnzeigeMPAL: gelb/MPAL: grün
MPALneu +MPALold*Tmute
/MPAL
MHPALold*Tmhp + HPALneu
HPAL/MPAL* Mute
Mute
Mute
HPAL
The status graphic describes the transitions between the individual states/statuses depending
on the kind of (MP, MHP, HP) as well as temporal occurance and the effect of T-Mute key.
The designations in the nodes denote which action is taken during a particular status. The
edge lines represent the condition under which a status transition occurs..
In detail:
HPAL: presence of a HP-Alarm condition
MPAL: presence of a MP-Alarm condition,
MHPAL: presence of a MHP-Alarm condition,
Tmute: Alarm-Mute duration has elapsed,
Mute: Activation of Mute key
Tmhp: Time for transition from a MP-Alarm to HP-Alarm.
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5.5.4 Alarm table The following is a table of Alarm Events evaluated by the Stephanie.
To apply this table:
The alarm designation is identical to the visual alarm message.
The category designates the priority of the alarm (MP, MHP, HP) including the kind of
audible signalling.
Columns 5 and 6 refer to the particular monitoring unit.
The column "Condition" refers to the condition that triggered the alarm event.
The various responses of the safety system are listed in the last column. Definitions
• Safety status 1: the switching off of all valves, including the emergency air valve, so that
the patient can breathe ambient air or be manually ventilated.
• Safety status 2: For CMV ventilation with standard values for CPAP mit PEEP = 2mbar.
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No. Alarm designation Rating Monitoring. Condition Safety system response
Primary energy supply
1 „Mains power failurel“ MHP MC PC /SV_Netzok
2. „Compressed air failure“ MHP MC PC P_Pl < 2.8 bar
3. „Oxygen failure“ MHP MC PC P_O2 < 2.8 bar
4. „Primary gas failure“ HP MC PC (P_Pl < 2.8 bar) & ( P_O2 < 2.8 bar) Stage 1 (all valves OFF)
5. „Respiratory gas failure“ HP MC PC P_120 < 70 mbar Stage 1
6. „Battery discharge“ HP MC PC RV_AkkuLow & /SV_NetzOk Stage 1
Ventilatory parameters
7. „Peak pressure“ When Plim_max is reached for longer than
0.1 s for MC and for longer than 0.2s for
PC
MC switches after 0.1 s to
PEEP level.
PC switches off emergency
air after 0.2s
8. „Cont. high pressure“ HP MC PC Pmean > Pmean lim for longer than 15 s /V_NL for 1sec. After that
start of new inspiration.
Max. 3 attempt, then
/V_NL,/V_PL, /V_O2,
9. „pressure low, Disconn ?“ MHP MC PC Pendinsp < Pmax during machine
inspiration
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No.
Alarm designation Rating Monitoring. Condition Safety system response
10. „AMV high“ MP MC PC Amv > AMV lim max
11. „AMV to low“ MHP MC PC AMV < AMV lim min
12. „Apnea“ MHP MC PC no inspiration start within 15 s
Respiratory gas conditioning
13. „FiO2 too high“ MP MC PC FiO2 > FIO2 lim max
14. „FiO2 too low“ MP MC PC FiO2 < FiO2 lim min
15. „ Temperature too high“ MP MC PC Temp > Temp lim max
16. „ Temperature too low“ MP MC PC Temp < Temp lim min
17. „Temperature > 41°C“ MHP MC PC Temp > 41°C Heating OFF
Hardware error
20. „Controller error “ HP ÜW PC watchdog error Safety status 1
21 „PC error „ almost imposs.. HP ÜW MC watchdog error Safety status 1
21. „Valve error n “ MHP MC No electrical response of valve n
22. „Potentiometer n“ HP MC Potentiometer makes no contact Safety status 2
23. „power supply error“ HP MC,
ÜW
PC /SV_PG + /SV_PGLV Safety status 1
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6 Failure Mode Analysis
6.1.1 Control Unit
The failure mode analysis for the control unit is found in the following table.
No. Failure/error type Detec.. Explanation
F_BE1 Contact error of the contact of
the Pot. und Schalter
yes see 1 and 2
F_BE2 LED defect yes Detection during unit selftest
F_BE3 Incr. transmitter Tex defect ja no reaction of expiration time to
change in IGR. Detection also during
unit selftest.
F_BE4 Line break in databus yes see 3.
F_BE5 Keys defect yes see 4.
F_BE6 Incr. transmitter monitor
defect
yes No reaction of menu bar to change in
IGR. Detection also during unit
selftest.
F_BE7 Display screen defect yes Detection during operation and during
unit selftest.
1. The potentiometer and switch receive a primary voltage that is 90% that of the reference
voltage. In addition, all ADU inputs are connected, via high-impedance resistors, with the
reference voltage. In the case of line break or interruption in the contact, the ADU
measures the primary voltage, which is evaluated as a nonplausible setting and thus as an
error. In this event, the new value is not accepted, the unit continues to operate with the old
value, however, it triggers a HP alarm with error description.
2. During the unit selftest, all settings of the potentiometer and switch are displayed in a
menu item. These settings are to be confirmed by the tester.
3. Only the databus lines MC_D0...MC_D9 are used. During the unit selftest all LEDs are
switched on and off, and the numeric display is activated. Thus, and in connection with
point 2, the entire databus is tested. This must be confirmed by the tester.
4. During the unit selftest all keys must be tested and the response of each checked by the
illumination of the respective LED. In this fashion, a complete check, including the
respective component of the microcomputer necessary for this function, is carried out.
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By means of this test, all errors possibly occuring in the control unit can be detected.