Maquet Servo Ventilator 900 D, Servo Ventilator 900 E, SERVO VENTILATOR 900 C Service Manual

servo ventilator 900 C/D/E

Service Manual

Contents

Introduction . . . . . . . . . . . . . . . . . . 4 Principle diagram. . . . . . . . . . . . . . . . 6

Pneumatic unit

Gas flow through the ventilator . . . . . . . .	.	8
Gas supply. . . . . . . . . . . . . . . .	.	9
Bellows and spring assembly. . . . . . . . .	. 10
Gas supply unit.		11
O2cell . . . . . . . . . . . . . . . . . .	. 12
Relief/safety valve and working
pressure manometer.		12
Flow transducer. . . . . . . . . . . . . .	. 14
Pressure transducer .		15
Inspiratory valve and step motor.		16
Expiratory valve and pull magnet .		17
Non-return valve. . . . . . . . . . . . . .	. 17
Transducer interface.		18

Electronic unit

Principle of operation. . .	. . .	. . . . .	.	. 19
Reference level generation.	. . .	. . . . .	.	. 20
Regulation of inspiration. .	. . .	. . . . .	.	. 23
Timing. . . . . . . . .	. . .	. . . . .	.	. 28
Monitoring . . . . . . .	. . .	. . . . .	.	. 33
Regulation of expiration. .	. . . . . . . .		.	. 39
Voltage supply .				41
Input/output.				42

The Servo Ventilator 900 was orginally manufactured and sold by Siemens. Responsibility for the product was assumed by MAQUET Critical Care in 2003. Manufacturing of the product was discontinued in 2004.

Please note that this Service Manual has only been re-labeled from Siemens to MAQUET. No further significant changes are made. Thus, some information in the Service Manual may be outdated.

In case of questions, please contact your local MAQUET representative

Your local MAQUET representative supplies factory calibrated and tested plug-in circuit boards as well as other spare parts indicated in the spare parts list. When exchanging spare parts, always state serial number of the apparatus and fault-symptom.

Note that the Operating Manual is an indis-­ pensable complement to the Service Manual for proper servicing.

Disassembling

Disassembling the pneumatic unit . .	. .	. . . . 44
Disassembling the electronic unit.. .	. .	. . .	. 44
Replacement of step motor assembly
and pull magnet. . . . . . . . .	. . . . .		. 45
Replacement of power supply unit .			45
Replacement of safety catches . . .	. . . . .		. 45
Replacement of flow transducer .			46

Adjustments

Adjustment of meters Z1 and Z2.	46
Adjustment of valve arm. . . . . . . .	. . . . 46
Replacement and adjustment of R5.	47
Removing the front panel knobs .	47
Front panel potentiometer adjustments. .	48
Troubleshooting.	49
Index.	52
Block diagram. . . . . . . . . . . . .	. . . . 56

To the responsible service personnel

The contents of this document are not binding. If any significant difference is found between the product and this document, please contact MAQUET for further information.

We reserve the right to modify products without amending this document or advising the user.

We recommend using MAQUET authorized personnel for all service and repairs and the use of MAQUET exchange parts or genuine spare parts. MAQUET will not otherwise assume responsibility for the materials used, the work performed or any possible consequences of same.

About this manual

This Service Manual is intended for Servo Ventilator 900 C, D and E. When reading the manual, please note:

SV 900 C	SV 900 D		SV 900 E
Read all	Do not read		Do not read
information	information out-		information in
	lined in red		shaded areas

2

Product information program

This Service Manual is a part of a comprehensive in­ formation program for Servo Ventilator 900 C/D/E. The program is planned to contain the following:

Promotional and Scientific Publications

Brochure		Servo Ventilator		Application		Product Leaflet		Reprints
		Concept		Brochures:
				Intensive Care,
				Anesthesia,
				Transportation

Operating and Service Instructions

Operating		Brief Operating		Wall Diagram		Service Manual		Circuit Diagram
Manual		Instructions
				for Cleaning

Product Training Material

Training		Advisory		Slide Series		“I am breathing		The Patient’s
Instructions		Booklet for		including		through a		ABSee@
		Instructors		Textbook		ventilator”		Cards and
						Film and		Poster
						Booklet

Front Panel		Panel Block		Trainee’s Set		Video
­Flip-chart						programs,
						Video guide,
						Video news

3

Introduction

Pneumatic unit

Electronic unit SV 900 C

Electronic unit SV 900 D

Electronic unit SV 900 E

Principle of operation

The Servo Ventilator 900 C/D/E consists of two sepa-­ rate units.

The pneumatic unit comprises the gas conduction system with two pressure transducers, two flow transducers and two servo valves.

Each transducer, continuously delivers its actual value to the electronic unit.

The servo valves are used as CONTROLLING ­ ELEMENTS­ for the control of inspiratory and expiratory gas conduction.

The electronic unit comprises three controlling systems, two for regulation of inspiration and one for regulation of expiration.

The three controlling systems will be in use, one at a time, depending on the TIMING control and the selected­ ventilation MODE.

4

Introduction

Feedback control

(= regulation system)

Each of the controlling systems comprises its PID- ­controller, (P=Proportional action, I=Integral action and D=Derivative action), as shown in the picture.

The CONTROLLING ELEMENT will be positioned by the PID-CONTROLLER (output).

P-action gives a continuous basic positioning. (Thereby the ACTUAL VALUE will correspond to the DESIRED VALUE).

I-action gives a slowly varying positioning com­ pensation for small long time error (in the ACTUAL VALUE).

D-action gives a speed-up positioning reaction at fast changes (in the ACTUAL VALUE).

The actual value from the TRANSDUCER in use is compared with the desired value from REFERENCE LEVEL. The difference between the ACTUAL VALUE and the DESIRED VALUE results in an ERROR SIGNAL, which is converted to a positioning signal for the CONTROLLING ELEMENT (inspiratory and expiratory valve respectively). The valve in use will then be moved

into such a position that the error will be corrected­. In this way, the desired value is maintained independently of changes in the airways and the lungs.

5

Principle diagram

!

Reference level

The main block REFERENCE LEVEL generates the DESIRED VALUE for each regulating system, corre­ sponding to the settings on the front panel.

@

Regulation of inspiration

The regulation of inspiration is done by means of the FLOW SERVO LOOP in the following modes: VOL. CONTR. VOL. CONTR. + SIGH. MAN., each mandatory inspiration during SIMV + PRESS. SUPPORT and each mandatory inspiration during SIMV.

The actual value for the controller in this loop comes from the FLOW TRANSDUCER in the inspiratory channel. The regulation of inspiration is done by means of the PRESSURE SERVO LOOP in the following modes: PRESS SUPPORT. PRESS. CONTR., CPAP, each spontaneous

inspiration during SIMV + PRESS.SUPPORT and each spontaneous inspiration during SIMV.

The actual value for the controller in this loop comes from the PRESSURE TRANSDUCER in the inspiratory channel.

The ERROR SIGNAL from the controller in use (flow or pressure), is fed to a converter, common to both inspiratory servo loops, which delivers the valve control signal to the inspiratory valve (positioning).

For both servo loops, the inspiratory valve is the controlling element in regulation of inspiration.

#

Timing

Reference timing pulses (START SIMV CYCLE, CLOCK, INSP.TIME and EXP.TIME) are generated in this main block.

The TIMING gets some command variables from the front panel settings.

$

Monitoring

The monitoring of all values that are displayed on the panel meters and the digital display takes place in this main block.

Some of the readings are compared with preset alarm limits and visual and audible alarms are activated­ if the preset limits are exceeded.

The monitoring system is independent of the regulating systems.

The pressure limiting system is included in this main block.

%

Regulation of expiration

The regulation of expiration is done by means of the PRESSURE SERVO LOOP during expiration in all modes when using PEEP.

The actual value for the controller in this loop comes from the PRESSURE TRANSDUCER in the expiratory channel.

The error signal from the controller is fed to a con­ verter which delivers the valve control signals for the expiratory valve (positioning).

The expiratory valve is the controlling element in regulation of expiration.

^

Power supply

The four regulated supply voltages are; +5V, ±15V and +24V.

&

Input/output

Output signals are buffered in this main block. Some of the functions of the ventilator can be

externally controlled via inputs in this block.

= Not valid for SV 900 D		= Not valid for SV 900 E

6

Principle diagram

%

$

! @

# ^

&

7

Pneumatic unit

Gas flow through the ventilator

The flap valve prevents back flow of gases in the expiratory tubing. It is essential for the trig function

The gas flow to the patient is measured

The safety valve opens if the bellows is overfilled or if the pressure in the bellows exceeds approximately 120 cm H2O

The airway pressure is measured

The gas conduction from the patient is regulated

From patient

The gas flow from the patient is measured

To patient

The gas is filtered

O2 concentration in the gas is measured

The gas supply is regulated so that a constant filling volume is maintained in the bellows

Gas inlets

The working pressure is mechanically adjusted

The working pressure is shown on a manometer

The gas conduction to the patient is regulated

A more detailed description of the pneumatic unit is found in the Training Instructions

8

Pneumatic unit

Gas supply

The lower gas inlet is used for high pressure gases 250700 kPa). The inlet can be connected either via a gas mixer or directly to the hospital central gas supply, to gas bottles or to a compressor.

The upper gas inlet is used for low pressure gases, e.g. from an anesthesia circuit or a flowmeter. Normally,­ only one of the two inlets is used at a time.

In any case, the gases pass a one-way valve, an O2 cell and a bacteria filter. The bacteria filter removes­ 99.998% of all particles down to a size of 0.3 microns­.

When an anesthesia vaporizer is used, the gas supply unit has a different construction with three nipples. For further information, see the Operating Manual for the vaporizers.

When the gas is supplied via the high pressure inlet, a constant filling volume is obtained in the bellows by means of the gas inlet regulatory function of a controlled inlet valve. A constant working pressure is obtained by the action of the spring assembly­.

9

Pneumatic unit

Bellows and spring assembly

The bellows are placed in a double coil spring set between two metal plates. The lower plate is movable and spring tensioned. The upper plate acts as a lid, which is firmly positioned above the bellows.

A double coil spring set is arranged to give a constant pressure to the bellows, independent of the plate position. The pressure is set by the adjustment handle­ PRESET WORKING PRESSURE.

Coil springs

10

Pneumatic unit

Gas supply unit

The gas supply unit contains an on-demand valve for the high pressure gas, a controlled inlet valve, two one-way valves, the O2 cell holder and a bacteria filter­.

Normally, the high pressure inlet is used and the bellows are filled through the controlled inlet valve, a oneway valve and the bacteria filter.

Mechanically actuated gas supply unit

The pressure plate acts upon the controlled inlet valve via the lever arm. Before connecting the gas supply, the bellows are empty, the pressure plate in top position and the controlled inlet valve open. When connecting high pressure gas, the bellows fills, the actuating tab on the right edge of the pressure plate goes down against the lever arm until the controlled­ inlet valve has closed. The pressure plate is then in its regulating position, which means that during inspiration, gas is continuously fed to the bellows. Thus a constant gas volume is kept in the bellows when using the high pressure inlet.

When a constant gas flow (from a flowmeter) is supplied via the low pressure inlet, excess gas will be let out from the bellows by the relief valve (surplus function).

Gas supply unit for Vaporizer with magnets

When using Vaporizer 950, 951 or 952, a gas supply unit with three gas inlets has to be used and the actuating tab on the pressure plate must be replace by a magnet kit.

Electronic gas supply unit for vaporizer

The gas is normally supplied via a gas mixer at the lower gas inlet. This inlet is controlled by a 24 V electromagnetic inlet valve.

The built-in PC-board has two Hall-sensors, sensing the position of the pressure plate magnet. When the magnet reaches up to the upper Hallsensor, the inlet valve will open. When the magnet reaches down to the lower Hall-sensor, the inlet valve will close.

Also when there is no power, the inlet valve is kept closed.

= Not valid for SV 900 E

11

Pneumatic unit

O2cell

The O2 cell used in the ventilator gives an output voltage­ proportional to the partial pressure of O2 at the cell. At constant sum of barometric pressure and WORKING PRESSURE (and constant temperature), the output voltage is proportional to the relative O2 CONCENTRATION­.

For each O2 cell, the variable output will stay at a fairly constant level during the life time of the cell (approximately 800 000 %xhours).

The output voltage level from the cell is usually within 7-15 mV in normal air.

Relief/safety valve and working pressure manometer

The working pressure manometer is connected to the safety valve via a plastic tube. A bacteria filter protects­ the manometer from contamination.

12

Pneumatic unit

Relief/safety valve for gas evacuation

A special reief/safety valve has to be used for gas evacuation.

For detalíls, see corresponding Operating Manual.

The relief/safety valve may be opened in two ways. Firstly, if the bellows tend to overfill, a metal rod will push the lever to let out excess volume (surplus function)­ . Secondly, if the working pressure exceeds approximately 120 cm H2O, the valve will let out excess pressure (safety function).

= Not valid for SV 900 E

13

Pneumatic unit

Flow transducer

The inspiratory and expiratory flow transducers have the same construction. The gas flows through the flow transducer in two parallel channels, one large main channel, and one small measuring channel.

The main channel is fitted with a wire mesh net, the resistance of which causes a certain proportion of the gas to flow through the measuring channel.

The flow through, and the differential pressure across, the measuring channel acts on a small metal disc (“flag”), which, via a metal pin presses on a small semiconductor strain gauge. This consists of diffused resistors on both sides of an elastic silicone rod. The resistors are connected as a part of a Wheatstone bridge, the other part of which is situated­ on the TRANSDUCER INTERFACE board (PC 765).

The more flow in the channel, the higher the pres­ sure on the strain gauge. The change in resistance in the Wheatstone bridge, is converted to a corresponding­ signal voltage.

The output signal from the flow preamplifier is a nonlinear function of the flow. The flow preamplifier signals are linearized on PC board 5 (inspiration) and on PC board 4 (expiration), respectively.

A resistor, 220 Ohms, 6W, is moulded into the transducer and is used for heating of the expiratory flow transducer. The transducer is heated to approximately­ 60°C (140°F) to prevent condensation of water vapour. The inspiratory flow transducer has the same resistor, but since it is not connected to any voltage, it will not be heated.

If water should condense in the expiratory flow transducer, the resistance of the wire mesh net increases­. Thus the output signal will increase. This can be seen on the meter EXPIRED MINUTE VOLUME, or on the digital display, as an increased reading. The accumulation of medicaments, mucus and secretions in the expiratory flow transducer gives the same result.

For details on cleaning and calibration of the flow transducer, see the chapters Routine cleaning and Calibration in the Operating Manual.

14

Pneumatic unit

Pressure transducer

The pressure transducers in the inspiratory and expiratory­ channels are of the same type.

The gas pressure acts upon a silicone rubber mem­ brane into which is moulded a strain gauge of the same type as in the flow transducers. The strain gauge

resistors are connected as a part of a Wheatstone­ bridge, the other part of which is situated on the TRANSDUCER INTERFACE board (PC 765).

The output signal voltage from the pressure amplifier is proportional to the gas pressure.

When replacing the pressure transducers, the preamplifier zero and gain have to be adjusted. For details, see the chapter Calibration in the Operating Manual.

Each pressure transducer is connected to its channel­ via a plastic tube and a bacteria filter. The bacteria­ filter and the plastic tube for the inspiratory channel should be replaced after every 1000 hours of operation.

The bacteria filter and the plastic tube for the ex­ piratory channel should be replaced after every patient.

15

Pneumatic unit

Inspiratory valve and step motor

The inspiratory valve is operated by the step motor via the logarithmically slotted cam and the lever arm.

When the step motor is in operation, a ball bearing at the end of the lever arm travels in the slot.

The lever arm squeezes the inspiratory valve tube against a fixed arm. The change in the flow is approximately 10% for each step of the step motor,

independent of the motor position as long as the airway­ pressure is unchanged.

The step motor has four coils which are fed with positioning signals from PC board 6 in the electronic unit.

When the mains voltage is switched off (or at mains voltage failure) the step motor will always end up with the inspiratory valve in fully opened position.

The maximum speed of the step motor is about 480 steps/second and the time elapsing from fully open to fully closed position is approximately 0.1 second.

The plastic case contains two PC boards, one with two miniature lamps and the other with two photo detectors. When the step motor reaches either end position of the cam slot, the light beam between the lamp and the photo detector is interrupted by the cam screen. This will generate an end position signal for the electronic circuits on PC board 6.

The position of the lamps in relation to the screen is of the utmost importance. If the lamps by any chance come out of position, this will cause the step motor to “rattle” because end positions are not properly­ indicated. The same symptom occurs if a lamp is damaged.

16

Pneumatic unit

Expiratory valve and pull magnet

The expiratory valve comprises a pull magnet acting on a lever arm which squeezes a silicone rubber valve tube against a fixed arm. The valve will close when the magnet is activated. When the supply current to the magnet is removed, the valve will open fully because­ of the spring. This ensures that the patient can always exhale through the ventilator at voltage failure.

The expiratory valve is controlled by the signals from the electronic unit. At a PEEP setting, the information­ from the pressure transducer in the expiratory channel regulates the valve position during expiration.

Non-return valve

The purpose of the flap valve is to prevent air from entering the patient circuit through the expiratory channel.

The valve is a vital part of the triggering function since a patient trig is sensed in the expiratory channel­ (pressure drop).

17