Siemens is liable for the safety of its equipment only if maintenance, repair, and modifications are performed by
authorized personnel, and if components affecting the equipment's safety are replaced with Siemens spare parts.
Any modification or repair not done by Siemens personnel must be documented. Such documentation must:
• be signed and dated
• contain the name of the company performing the work
• describe the changes made
• describe any equipment performance changes.
It is the responsibility of the user to contact Siemens to determine warranty status and/or liabilities if other than
an authorized Siemens Service Representative repairs or makes modifications to medical devices.
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Chapter 1: Introduction
1Introduction
1.1 Service Strategy
1.2 Replaceable Parts
In keeping with the service strategy for the SC6002XL, this service manual
provides the necessary information required to service an SC 6002XL patient
monitor in the field. The SC 6002XL is both a stationary and a portable
monitor designed to monitor patient vital signs (refer to user’s guide for
monitoring options). For stationary operation near a bedside, the monitor is
connected to an AC/DC power adapter or placed on a specially designed
docking station attached to a shelf, wall, or rolling stand that securely locks
it into place. While on the docking station, the monitor is powered by a CPS
or an IDS power supply. When the monitor is detached from a CPS or IDS, it
is powered by a lead acid battery or by an optional Lithium ion battery. The
monitor is reattached to the AC/DC Power Adapter or placed back on a
CPS or IDS to recharge the battery.
The monitor has been designed for high reliability, with an estimated
MTBF of 50,000 hours (5.7 yrs.) of continuous operation.
Therefore, the service strategy is based on few failures in the field, a clear
definition of failure analysis by field service personnel, and a quick repair
turnaround. The field repair philosophy is based on the distributed and
approved spare parts list. Refer to Appendix A: Replaceable Parts.
This manual is intended to serve as a source of technical information, for
qualified field service personnel to use in servicing SC6002XL patient
monitor in accordance with the Siemens Service Strategy. Field service is
expected to be successful “First-Time Every Time.”
SC 6002XL monitors have several replaceable subassemblies, each of
which also has replaceable subassemblies and/or components.
1.3 Technical Manual
Conventions
• Front Bezel Subassembly
• Front Panel PC Board
• TFT-LCD Display Subassembly,
• Main Processor Subassembly,
• NBP Subassembly, and
• Rear Housing Subassembly with integrated serial number chip.
Individual “consumable” replaceable parts include the battery, fluorescent
backlight, and NBP filters. A complete listing of spare parts is included in
Appendix A: Replaceable Parts of this manual. Replacement of components
other than those listed in Appendix A should be performed only at Siemens
service depots in Danvers, MA, U.S.A. or in Solna, Sweden, where
specialized repair and testing equipment can assure product reliability.
The following conventions are employed in this manual:
A NOTE calls attention to items of special interest or provides additional
related information about a specific topic:
Note: Attempting to repair any PC board to the component level may
void any warranty, either express or implied.
A Caution indicates a potentially hazardous situation which, if not avoided,
may result in minor or moderate property damage. It may also alert against
unsafe practices.
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Caution
3
Printed circuit boards in these monitors contain components that
are easily damaged by static electricity. Open monitors only in a
static-protected environment. Observe proper procedures to
prevent damage to the equipment resulting from static discharge.
A Warning indicates a potentially hazardous situation which, if not avoided,
may result in death or serious injury.
Warning
Do not operate this product in the presence of flammable gasses
or liquids. If this device is operated where flammable anesthetics,
skin cleansers, or disinfectants are used, the possibility of an
explosion cannot be excluded. This product must be operated
only in strict conformance with local fire prevention regulations.
2Product Overview
2.1 Monitored Patient
Parameters
2.2 SC 6002XL Monitor
Controls
SC 6002XL Patient Monitors are light-weight, battery-equipped, hand-held
or semi-permanently mounted devices for general purpose monitoring of
a preconfigured set of physiological parameters. When not connected to a
hospital’s main ac power, they use a battery with approximately 1¼ hours
(3 hrs. for Li option battery) of operating time. A power adapter, CPS/
docking station combination, or IDS, which also charges the battery, can
be used to operate the monitor from the hospital’s main ac power circuit.
The SC6002XL monitors the following physiological parameters:
All functions are controlled by a 16-position rotary knob and nine front
panel fixed keys - Alarm Silence, Record, Alarm Limits, NBP Start/Stop, All
Alarms Off, Zoom, Main Screen, Menu, and ON/OFF. Turning the rotary
knob locates different menu items, and pressing the knob in selects the
item. Depending on the item selected, pressing the knob in may either
bring up another menu or initiate an action. See Section 5. For detailed
operating instructions, consult the SC 6002XL Patient Monitor User Guide
applicable to the installed software.
via PodComm Port (locked option)
2
and PR)
2
2.3 TFT-LCD Display
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The SC 6002XL monitor has a 6.5 inch (16.5cm), 3-channel color TFT-LCD
display. Waveforms display in Erase Bar mode at 25 ±20% mm/s (except
for respiration and etCO
All displays for a given parameter (label, unit of measure, and waveform)
are in the same color. If a waveform is not displayed for a parameter, its
label is gray.
waveforms which display at 6.25 ±20% mm/s).
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2.4 Alarms
2.5 Monitor/Software
Tracking
3Preventative
Maintenance
3.1 General
Alarm limits can be set either on a user-definable setup table, or
automatically based on current parameter values. Three alarm grades,
each with a distinct alarm tone, announce alarm situations of varying
severity:
• life-threatening (asystole or ventricular fibrillation - red)
• serious (parameter limit alarms - yellow)
• advisory (technical alarms - white)
The message field background and parameter field of the parameter in
alarm are displayed in the color associated with the alarm grade as given
above.
Each monitor has a unique ID chip installed in its rear housing for diagnostic
and tracking purposes, and un/locking optional software features.
SC 6002XL monitors require replacement of the lead-acid battery (12 months),
NBP air intake filter (24 months) and fluorescent bulb (45K - 50K hours).
Siemens recommends that a full functional verification be performed
annually. See Chapter 4: Functional Verification and Calibration. Also, some
national jurisdictions require that a temperature calibration (see Section
1.8.2 in Chapter 4) and an NBP calibration be performed at least every two
years. Refer to Section 3, Calibrating NBP System in Chapter 4 for the NBP
calibration procedure.
3.2 Battery
Note: Replace the internal manifold filter on the NBP subassembly
only if the NBP subassembly should fail characterization.
To obtain maximum life from a new lead-acid battery, install the battery
into the monitor and run the monitor on battery power for a period of 15
minutes. After the 15 minute period, either plug in the monitor’s power
adapter or lock the monitor onto a powered docking station and charge the
battery, or remove the battery from the monitor and connect the battery to
an external charger. (This initial sequence is not needed for Li batteries.)
When in storage or not in use for an extended period of time, lead-acid
batteries self-discharge and develop a “float-charge” as a characteristic of
the self-discharge process. The “float charge” must be drained off before
the battery can be properly charged. If a new battery is immediately placed
on a charger, the “float charge” provides an incorrect indication of the
battery’s charge condition, and the charger may not fully charge the battery.
Between discharges, the lead-acid battery must be recharged as soon as
possible. Once charged, it can be stored for ª 4 months without recharging.
Siemens recommends that the battery charge be maintained at >80% to
maximize the battery’s capacity and cycle life. Starting at a 100% charge
level, at room temperature the battery will self-discharge below the
acceptable minimum in about 6 months on a shelf and in about 2 months
in an unpowered spare monitor.
Warning
Dispose of used batteries in accordance with local regulations
governing disposal of hazardous materials.
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4Technical Data
Technical Data included in this Section is as of publication date of this
Manual. Changes are reported in User Guide applicable to installed SW.
4.1 General
Table 1-1General Specifications
ParameterSpecification
Power Requirements100-250 VAC through AC power adapter
Mains Frequency50/60 Hz
AC Power Consumption60 VA AC
Battery TypeLead-acid: PANASONIC LC-T121R8PU or equivalent
Lithium-ion: Siemens Li+ Battery Pack
DC Input11 - 14 V; 32 W continuous, 49 W peak
Battery Operating Time (means
running with NBP measurement
every 15 min @ 25°C temperature,
no etCO
Battery Recharging TimeLead-acid: 5 ½ hours, typical
Battery Charge/Discharge/Charge:Lithium-ion only (operating as defined above): 2 hours, charging for 2
running
2
Lead-acid: 75 mins
Lithium-ion: 180 mins
Lithium-ion: 8 hours, typical
hours, operating 2 hours
Patient Leakage Current<10 µA @ 110 V and 60 Hz (per UL 544)
<10 µA @ 220 V and 50 Hz (per IEC 601-1)
Chassis Leakage Current with
battery eliminator
<100 µA @ 110 V and 60 Hz (per UL 544)
<500 µA @ 220 V and 50 Hz (per IEC 601-1)
4.2 Environmental
Table 1-2Environmental Specifications
ParameterEnvironmental Specification
Cooling MethodConvection and cooling chimney (no fan)
Temperature:
Operating
Storage
Relative Humidity:
Operating
Storage
Altitude:
Operating
Storage
0°C to +40°C (without recorder)
-20°C to +50°C
>30% and <95%, non-condensing
>10% and <95% non-condensing
-381 to +3048 m (-1250 to 10,000 ft.)
525 to 795 mmHg (70.0 to 106 kPa)
-381 to 5486 m (-1250 to 18,000 ft.)
375 to 795 mmHg (50.0 to 106 kPa)
Water ResistanceDrip-Proof
Dimensions (H x W x D):196 x 223 x 134 mm (7.7 x 8.8 x 5.3 in) (w/ rotary knob)
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Table 1-2Environmental Specifications (Continued)
ParameterEnvironmental Specification
Weight:
SC 6002XL (w/o etCO
)
2
3.42 kg (7.54 lb) w/ lead-acid battery
3.22 kg (7.10 lb) w/ lithium-ion battery
2.87 kg (6.32 lb)) w/o battery
Battery
Lead-acid: 0.55 kg (1.22 lb)
Lithium-ion: 0.35 kg (0.78 lb)
Finish:
according to Siemens
Corporate Design Guidelines
Front: white
Rear and Handle: anthracite gray
Material: ABS Polycarbonate Blend (injection molded plastic)
4.3 Display
Table 1-3Display Specifications
ParameterSpecification
TypeColor Thin Film Transistor - Liquid Crystal Display (TFT-LCD)
Size170 mm (6.7 in) diagonal
Resolution640 x 480 pixels
Active Viewing Area132.5 x 99.4 mm
Pixel pitch0.207 mm x 0.207 mm
Sweep Speedsfixed 25 mm/s ±20% for ECG, SpO
fixed 6.25 mm/s ±20% for Rsp and etCO
, and IBP curves
2
curves
2
Display ModeErase bar (updates waveforms from left to right)
4.4 Outputs
Table 1-4Output Specifications
ParameterSpecification
QRS Synchronization:
Timing:
Output Pulse:
Alarm Output12 V Open collector output for external alarm indicator
RecorderUART interface w/ recorder through interface plate or docking station
Debug PortUART interface w/ a PC to retrieve diagnostic information through
External VGAVideo signals sent to external VGA display for remote viewing of
NetworkSerial connection to Infinity Network through Infinity Serial Hub interface
For heart rates from 30 to 250 [1/min], with QRS widths from 40 to 120
msec and QRS amplitudes from 0.5 to 5 mV, a sync pulse is delayed no
more than 35 msec from peak of R-wave for each valid QRS complex.
+12 V, 100 ms duration
connector
interface plate or docking station connector
SC6002XL screen. -- not available when Infinity Serial Hub interface plate
in use.
not available when Infinity Serial Hub interface plate in use.
plate or docking station connector.
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4.5 Connectors
Table 1-5Connector Specifications
ParameterSpecification
DC InputSiemens 2-pin power connector
Docking StationSiemens 28-pin connector to provide Alarm Output, Recorder, Debug
Note: For patient parameter specifications, refer to User Guide applicable to installed software version.
7-pin shielded female PodComm connector
5Monitor Controls
5.1 Main Screen Key
5.2 Menu Key
The rotary knob in the lower right corner of the front panel is a pointing and
selecting device. Turn the knob to select a screen area or menu item or to
change a default value, and press the knob in to confirm your selection and
to set a default value. Press Main Screen key to return to the MAIN screen.
Note: Instructions in this chapter are intended to provide only a
cursory overview of basic monitor controls for accessing and
performing service-related functions. Refer to the User Guide for the
installed software version for complete operating information.
Pressing the Main Screen key exits the current menu or screen and
displays the home screen.
-- provides access to the Main menu. In general, functions of direct
concern to the CSE or Biomed are accessed via Monitor Setup →
Biomed on the Main menu. Password-protected service-related
functions are to be performed by only authorized technical
personnel. Use Biomed password (375) to access the following:
• Save Setups - Confirm or Cancel
• Locked Options - four locks into which monitor-specific 2-digit codes
must be entered to enable locked options
• Diagnostic Logs
•Units
-Temperature - °C or °F
-Pressure - mmHg or kPa
• Service - requires Service password. (The password is given on the
Service Setup Instructions for the installed software version.)
-Update Software
-Line Frquency - set the frequency equal to the ac mains line
according to local conditions (50 or 60 Hz).
Note: An incorrect setting of line frequency can cause artifact or excessive waveform noise on the ECG waveform.
-Language - selection appropriate for clinical site
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-Test Pulse - Confirm or Cancel, one-shot test pulses for ECG
(1mV spike) and Temp (–5°C and +50°C, respectively). An
additional test is performed for IBP, Resp Pulse, and SpO
indication is reported in the trend table.)
•Exit
. Test
2
5.3 Alarm Limits Key
5.4 Alarm Silence Key
5.5 All Alarms Off Key
5.6 NBP Start/Stop Key
5.7 Zoom Key
5.8 Record Key
-- calls up a setup table for alarms.
1) Turn rotary knob to select desired parameter field and limits, and
press knob in to activate your selection.
2) The number representing the limit value turns black on a blue background, indicating that you can change it. Turn knob to change value.
3) When desired setting is displayed, press knob in to set value.
4) Press MAIN Screen key to return to MAIN screen.
-- silences an active alarm tone for 1 minute ±5 seconds, and turns active
blinking parameter areas into active steady parameter areas
-- suspends alarms for a fixed 3-minute ±5 second period.
-- starts and stops non-invasive blood pressure measurement.
-- used for fast access to all parameters or NBP parameter box bottom
channel screen setups, choice made from a user menu.
With an R50™ recorder connected, press the Record fixed key to start a
manual, timed recording.
Note: If a recorder is not connected, pressing the Record fixed key
writes 15 seconds of waveform and vital signs information to internal
memory. SC 6002XL monitors can store up to five recordings, which
are automatically printed as soon as the recorder is connected.
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Chapter 2: Functional Description
Overview
1
SC 6002XL monitors are configured patient monitors running on one
processor, an MPC821 Power PC processor, which attends to all
monitoring functions, controls all graphics functions, generates video and
timing signals for the LCD screen, and interfaces with the PCMCIA. It also
performs several peripheral control functions, such as NIBP control, audio
volume control, and timing generation for the front end. See Figure 2-1.
SpO
IBP1
IBP2
Temp
Resp
2
ECG
M
U
X
LED Drive
M
U
X
NIBP
A
D
C
Front End
Record
Debug
Export
To
etCO
2
Front Panel
Double
Xducer
Meas.
Safety
A
S
I
I
s
C
o
l
a
t
i
o
n
CUFF
NIBP
Driver
µController
(68HC11)
832 16
SRAM
Memory
(512KB)
AudioKeyboard
LCD
Control
CP
Processor
(MPC821)
DRAM
Memory
(4MB)
Video
DAC
Network
(HDLC/
CEPT)
PCMCIA
Card
Flash
Memory
(2MB)
LCD
(640 x 480)
X
F
M
R
Quad
UART
PodCom
Option
RGB
Network
+12
11 - 15v
POWER
CONVERSION
+3.3V
+5V
+18
+42
-5V
BATTERY
CHARGER
(Li or Pb)
Main Board
Figure 2-1SC6002XL Patient Monitor Block Diagram
2 Parameter Inputs
The data acquisition front end acquires and digitizes signals derived from a
three-, five-, or six-electrode ECG patient lead set, a Nellcor® SpO
2
transducer, an Impedance respiration measurement system, a thermistorbased Temperature transducer, and two strain-gauge IBP transducers
(IBP2 = locked option). The NIBP main transducer signal is digitized
together with the rest of the front end parameters. See Section 4 and
Section 5 for more detailed information.
3 Main PC Board
The Main MPC821 Power PC processor not only attends to monitoring
functions, but also controls all graphics functions, generates the video and
timing signals for the LCD screen, interfaces with the PCMCIA, and
controls the network link. In addition, it performs a host of peripheral
control functions, such as NIBP control, audio volume control, and timing
generation for the front end.
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3.1 LCD Control
3.2 Network Interface
3.3 Front Panel Circuitry
3.4 Pod Interface
3.5 Battery Control and
ON/OFF Control
A set of buffer/drivers are used to drive the 6.5” screen. In parallel, a triple
video DAC generates analog RGB signals for an external monitor (typically
a CRT).
The SC 6002XL monitor interfaces with the physical interface device (e.g.,
CPS, IDS or IHUB) automatically when connection to the device has been
detected. Connections to I
maintained by software components resident on both the SC 6002XL and
the physical interface device.
The front panel circuit processes the audio information, drives the
fluorescent tubes on the LCD, implements a secondary alarm in case the
unit resets or turns off, and routes the video and timing signals to the
screen. It also routes the UART signal coming from the Pod interface to the
main board Quad UART.
The Pod Interface generates an isolated voltage to power the pod and also
converts the Pod Comm protocol from the pod into a UART stream that can
be interpreted by the microprocessor.
The Pb-acid or Lithium battery charging and discharging cycles are
controlled by a special charger circuit. The circuit initiates a charge cycle
when commanded by the microcontroller. The charge cycle for a Pb-acid
consists of a bulk charge period in which the battery is being supplied a
constant current of ~400mA, a constant voltage period in which the battery
voltage is held constant at ~14.8V and the current is allowed to diminish as
the charge approaches 100%, and a float cycle in which the voltage is
maintained at ~13.7V. For Lithium batteries, the charger circuit acts as a
constant voltage source of 16.8V. The battery is charged from a switching
supply controlled by the charger chip. The microcontroller also reads the
front panel keys and the rotary knob, encodes the information coming from
them, and routes it to the main processor. When the On/Stdby key is
pressed, it turns the monitor on and off. In addition, the microcontroller
controls the NIBP safety timer.
NFINITY
network services are established and
3.6 BOOT Process, Flash
Memory, and DRAM
3.7 SRAM
3.8 68HC11
Microcontroller
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The BOOT EPROM contains the boot code and must be preprogrammed
at the factory. It cannot be programmed after being installed on the Main
board, and therefore cannot be updated in the field via a software
download.
The executable software normally resides as compressed operational code
in Flash memory. When the 68HC11 microprocessor senses that the on/
off switch on the front panel has been pressed, it turns on (or turns off) the
3.3V and 5V supplies. As the 3.3V supply turns on, it wakes up the MPC821
main processor, which begins execution from the BOOT PROM. During
boot initialization, the main processor attempts to read the Memory Card
to detect legal software. If a legal software memory card is present, the
software is loaded from the card. Otherwise, the main processor loads
software from the Flash to the main processor DRAM, from which it
completes initialization and enters operational mode. DRAM contains
expanded operational code, and data space variables and stacks.
The 512K x 8 SRAM is battery backed up and is used for error logs, trends,
recordings and other non-volatile memory uses.
The 68HC11 Microcontroller, with 2K of EEPROM and 256 bytes of RAM,
is powered as long as there is a main supply plugged into the system or
when the user presses the ON/OFF button. The code is stored in its
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internal flash memory, but can be downloaded from the MPC821. The
microcontroller performs the following functions:
On/Off controlWhen the ON/OFF pushbutton (either local or remote is pressed), the
microcontroller activates the 3.3V and 5V supplies, which wakes up the
MPC821 through a power-on reset. In addition, the microcontroller has
control over a flyback supply, which comes on any time the unit is plugged
into AC power (in order to charge the battery) or is turned on.
The microcontroller also reads the front panel keys and the rotary knob,
encodes the information coming from them, and routes it to the main
processor.
NBP Valve modulationWhen directed by the main processor, the microcontroller supplies
modulation signals for the two NBP manifold valves.
NBP Safety TimerWhen the pump or the valve V2 are turned on, the microcontroller initiates
a 128 sec. timer (90 sec. or 60 sec. for neonates) which, if exceeded,
produces an NBP fault and results in cut off of main 12V power to the NBP
manifold.
Battery ChargerThe microcontroller initiates a battery charge when needed, and stops the
charging process when the battery reaches full capacity. It can recognize
whether a Pb or Lithium battery is connnected into the sytem, and directs
the battery controller chip to charge to different levels depending on the
battery type. See Section 3.5. The microcontroller also acquires the battery
voltage and current for monitoring purposes.
Recorder PowerThe microcontroller controls the power applied to a stand-alone R50
Recorder.
Main Audio GeneratorThe microcontroller generates the fundamental audio frequency of the
unit’s tone generator, as directed by the main microprocessor.
4Front EndAll physiological signals (except etCO
multiplexing system and a common 16 bit ADC. The data is then
transferred through the isolation barrier to an HDLC port in the main
processor, where it is digitally filtered and processed.
4.1 NIBP Control
4.2 Safety
The NIBP main transducer signal is digitized together with the rest of the
front end parameters. However, the redundant (overpressure) transducer
is processed separately on the grounded end of the board, and the pump
on/off signal and valve enable signals are generated off of the MPC 821
microprocessor. The PWM signals for the valve flow control and the
redundant safety timer are implemented in a separate microcontroller
(MC68HC11).
• Patient isolation withstands 5kV during defib.
• Leakage currents are limited to safe values normally and during single
fault conditions.
• Patient is protected against electrosurgical burns at the electrodes.
• Defibrillation protection does not drain excessive current away from
the patient.
) are digitized through a high speed
2
• Specially shielded connectors and cables are used to provide
excellent immunity up to 1000MHz and can not be touched by the
patient even when disconnected.
• Single cable from MultiMed Pod to main SC6002XL unit reduces
clutter between bed and monitor.
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Temp
ECG
Resp
SpO
MultiMed
Protection
2
Defib
ESU
NBP
Hose
RF Filter
Lead Off
Neutral
SW
Modulator
Pressure
Transducer
Pre-
Amp
Modulator
Demodulator
LED Drive
Linearizer
Low-Pass
Filter
Bandpass
Filter
Current
Sources
Bandpass
Filter
Power Monitor
Amp
Amp
Amp
NBP
Amp
Temp
Temp Ref.
ECG
Pace
Resp
Amp
Cal Resistor
4
2
2
6
4
2
M
U
X
2
Converter
Control
Power
16 Bit
A / D
Asic
Data Control
Figure 2-2Front End
5 Physiological
Parameter Data
Acquisition
5.1 ECG/Resp
Differential
I/V
Converter
Red
Ambient
Light
Rejection
Demodulator
I/R
HDLC
(to MPC821)
Transducers gather physiological data at the patient and feed them into the
small MultiMed Pod at the bed. The MultiMed Pod in turn is connected via
a 3-meter cable to the front end in the main unit where analog ECG,
Respiration, Temperature, and SpO
signals are converted to digital form
2
and sent through isolators for processing.
The MultiMed Pod located close to the patient accepts a set of 3, 5 or 6
shielded ECG electrode leads, an SpO
(Nellcor) cable adapter, and a
2
temperature sensor. The ECG section contains RF filters, and overvoltage
clamps that include 1k series resistors to limit shunting of defibrillator
current. The SpO
and temperature sections also contain RF filters.
2
Impedance respiration is sensed through the ECG electodes. Void-free
potting and internal shielding enable compact containment of high voltage
defibrillator and electrosurgery pulses. The small interconnecting cable to
the main assembly is captive at the MultiMed POD but plugs into the
MultiMed front end via a specially shielded connector.
The front end accepts physiological signals from the MultiMed POD
connector and feeds temperature, respiration, and ECG signals via RF
filters, configuration multiplexers, and pre-amplifiers to a high-speed
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multiplexer driving a 16-bit analog-to-digital (A/D) converter. The data
stream is sent to the Main Processor board via an opto-isolator. Control
commands from the Processor are sent out to the front end on a similar
isolating link. Isolated DC power is also provided.
The ECG signals are conductively coupled to the isolated circuits via
current-limiting series resistors, whereas the SpO
isolated at the transducer. Temperature signals are doubly insulated at the
patient by disposable boots on the sensors. AC (40kHz) excitation currents
for respiration monotoring are dc-isolated by high-voltage ceramic
capacitors.
The A/D samples the following parameters:
Table 2-1Parameter Sampling Table
Parameter# of Channels
signals are optically
2
ECG4
Pace2
Red1
SpO
2
IR1
SpO
2
NBP1
Resp1
Temp2
The hardware pace detector monitors the ECG signal in two of the four
channels (those not connected to the chest leads). All other signals are
decimated and filtered using digital signal processing in the MPC821. High
oversampling rate is required to minimize the requirements (and size) of
the analog anti alias filters. Superior rejection to ESU and other types of
interference is achieved with this type of design.
5.1.1 ECG• Bandwidth is set flexibly by software filters.
• Reconfigurable neutral selector can drive any electrode.
• Lead-on detection functions with even poor electrodes.
• Calibration voltages can be superimposed on patient wave-forms or
onto flat baselines.
See Figure 2-3. Composite electrocardiographic (ECG) signals generated
by the heart and by a pacemaker are filtered to reduce RF interference
from impedance respiration and electrosurgery and then injected with dc
lead-off detection currents. Over-voltage clamps protect the
semiconductors from the surges passing the sparkgaps in the MultiMed
Pod and also reduce the dc current applied to the patient due to a
component fault.
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RA
aVLaVR
LA
aVF
LL
Figure 2-3Lead-Forming Network
5.1.2 Lead SelectionA lead-forming network following the RF filter generates the necessary
reference points for electrocardiographic measurements. Both normal
leads (I, II, III, V1 and V2) and augmented leads (aVL, avR, and avF) can be
obtained. See Figure 2-3.
Four differential channels generate the main axes I, II, V1 and V2. The
remaining leads are derived mathematically as indicated in the vector
diagram of Figure 2-3.
5.1.3 Lead-Off DetectionLead-off detection is accomplished by introducing a very small current into
each patient electrode, which would drive the corresponding input high if
it were disconnected. A set of five comparators detects a lead-off
condition.
5.1.4 Low-Pass Filtering and
Common Mode
Enhancement
The ECG preamplifier has a flat frequency response of 0.5 - 40Hz, with a
software notch filter at 50/60 Hz. A 180° combined signal drives the neutral
electrode to increase the CMMR.
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5.2 Respiration
5.3 SpO
2
Impedance respiration is monitored by injecting a 40 kHz square wave of
current into the RA electrode. The resulting 40 kHz voltage drop between
the RA + LL electrodes is proportional to the impedance. Especially
balanced true current sources do not load the ECG electrodes or distort the
ECG morphology. The returning 40 kHz differential voltage is amplified,
synchronously demodulated, and low-pass filtered. An AC-coupled stage
with an “autobloc” DC restorer feeds the input to the A/D converter with
a nominal output of 60 mV per Ohm.
Figure 2-4 SpO
Functional Block Diagram
2
The pulse oximeter circuit uses a Nellcor® sensor to detect the oxygen
saturation level in arterial blood flow. Determination of the concentration
of oxygen in the blood is based upon the principle that the absorption of
red (R) light depends on the degree of oxygenation of the blood, whereas
the absorption of infrared (IR) radiation is relatively independent of
oxygenation and causes only constant attenuation. See Figure 2-4. In the
SpO
sensor, R and IR light emitting diodes (LEDs) are alternately pulsed
2
ON at a 25% duty cycle. The light is transmitted through a well-perfused
part of the body, such as a fingertip or an ear lobe. The intensity of light
(including ambient) transmitted through or scattered by the blood is
converted to a current by a photodiode in the sensor. The current that
appears when both LEDs are OFF depends mainly on the ambient light,
which is later subtracted to leave only the R or IR signal levels. The large
dynamic range of the light intensities requires constant automatic
monitoring and adjustment.
The intensities of the R and IR sources are independently controlled by two
digital-to-analog converters (DACs) attenuating the 2.5 V reference. These
levels or zero are sequentially selected by a multiplexer, and converted to
a driving current which is further guided or inverted by an output
multiplexer to the LEDs in the sensor.
5.3.1 SpO
Front EndThe primary purpose of the SpO2 front end is to convert the sensor’s
2
analog signal into individual digitized signals for the red and infrared analog
signals for processing by the microprocessor. See Figure 2-5 on page 16.
Circuitry in the front end first eliminates the non-pulsatile component in the
input signal, then demultiplexes the resulting pulsatile signal to separate
the R and IR signal components, and finally converts the demultiplexed R
and IR analog signals into serial digital data streams.
A sequence of light pulses, driven from the chopped current source in the
sensor LEDs, are passed through a finger or an earlobe to a photodiode.
The sensor LEDs are connected in an anti-parallel fashion on one pair of
wires.
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Figure 2-5 Sensor LED Timing Diagram
A timing generator controls the sensor LEDs and signal multiplexing/
demultiplexing (see Figure 2-5) by means of three control signals:
• IRONL (infrared LED)
• AMBONL (LEDS not lit)
• REDONL (red LED)
5.3.2 Input StageA preamplifier converts the photocurrent to an equivalent voltage, and
applies it to a 20 Hz high-pass filter that removes the non-pulsatile
component. The output of the preamplifier is fed to a saturation detector.
5.3.3 Brightness ControlIf the output of the preamplifier is in saturation, the gate array provides a
signal to the digital-to-analog converters (DACs), which controls the drive
current to increase or decrease the brightness of the LEDs.
Controlling LED brightness extends the system dynamic range. For a very
transparent subject it may not be possible to reduce the gain to prevent
saturation. In that event, the brightness must be reduced. An additional
purpose is to equalize the received amplitude of each wavelength. If both
LEDs are turned ON to maximum brightness, and the software finds an
extraordinary difference between the two, the microprocessor tends to
reduce that difference by equalizing the R or IR brightness signals.
5.3.4 Ambient Light Rejection
Amplifier
The ambient rejection amplifier is a synchronous detector. The signal
appied to its inverting input is a composite of R, IR, and ambient signals.
The non-inverting input is the same signal gated by the timing generator.
This synchronously multiplexes the IR, ambient, and R analog signals.
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+2.6V
-2.6V
Figure 2-6 IBP Functional Block Diagram
5.4 Invasive Blood
Pressure
The IBP circuit has been designed to be used with a strain gauge pressure
transducer. See Figure 2-6. The analog portion of the IBP circuit provides
excitation voltages for resistance bridge transducers. These voltages are
derived from a reference which is also used to derive the A/D converter
reference voltage. At the circuit input, a resistor divider network provides
for transducer unplugged detection. R-C filtering and protection diodes
limit the effects produced during electrosurgery, defibrillation, and other
such procedures. A selector multiplexer allows for the insertion of
calibration signals into the amplifier stage. The multiplexor feeds the
pressure signal to a buffer amplifier, which in turn feeds the AD converter
analog input. This allows the monitor to measure pressure signals in a
range greater than ±700 mmHg with a resolution of approximately
.02mmHg/LSB.
When no pressure transducer is plugged into the monitor, the resistor
divider network puts a negative signal into the instrumentation amplifier,
which propagates through the system to indicate the unplugged condition.
5.5 Non-Invasive Blood
Refer to Figure 2-7 on page 18.
Pressure
5.5.1 NBP SubsystemThe NBP subsystem consists of the following components:
•pump
•two modulating valves
• strain-gauge pressure transducer
• overpressure sensor
• pneumatic manifold
In addition, an electronic data acquisition and control system measures and
digitizes the pressure pulses as the cuff inflates and deflates. Pump and
valve control circuitry engage these elements as needed in the
measurement cycle. Several interlock systems and expiration timers
ensure the safety of the equipment in case of single point failures.
The SC6002XL NBP circuit uses a cuff and the oscillometric method to
determine blood pressure without using a microphone. A strain-gauge
pressure transducer is DC-coupled to a 16-bit A/D converter, so that cuff
pressure is measured with adequate resolution to detect blood pressure
pulses. This eliminates the need for a separate ac-coupled measurement
channel, with its associated distortion and long transient recovery.
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A/D
Figure 2-7 NBP Functional Block Diagram
5.5.2 NBP System DescriptionThe combination of high-resolution A/D conversion and digital filtering,
together with wide-range linear deflation control allows the circuit to
measure blood pressure very rapidly and accurately, and to recover quickly
from motion artifacts. The non-invasive pressure system is composed of
the following components:
• pneumatic assembly
• electronic circuitry, mounted on the Main CPU Board
Pneumatic AssemblyThe pneumatic assembly contains a pump, two modulating valves (V1 and
V2), two air filters (intake and manifold), and a manifold assembly which
interconnects these components. The pump provides the pressurized air
to inflate the blood pressure cuff. V1 and V2 control the air flow during the
deflation phase of a blood pressure measurement. V1 is a normally-closed
exhaust valve with a relatively small orifice (relative to V2). V2 is a normallyopen exhaust valve with a relatively large orifice. The pump speed can be
controlled to permit accurate inflation pressures for special applications.
The filters prevent potential contamination of pneumatic components by
debris coming from the cuff or hose.
Electronic CircuitryThe electronic circuitry, mounted on the Main CPU Board, contains the
electrical drivers for the pump, the valves, and its power supplies. In
addition, the readback from the pressure transducer is processed through
the floating section ADC. The software data acquisition and algorithm
processing is performed in the MPC821 main processor.
5.5.3 OperationThe measurement sequence consists of an inflation phase, in which the air
pump inflates the cuff, which has been wrapped around the patient’s limb
(typically the upper arm or thigh) to a predetermined pressure. At this
point, the blood circulation to the limb is occluded. The monitor then
linearly deflates the cuff at a software-controlled rate during which time
the blood pressure parameters are determined by digital filtering and
analysis of waveform data obtained from the pressure transducer during
the deflation cycle.
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Inflation PhaseWhen a blood pressure measurement is initiated (via software or front
panel fixed key), V2 closes, the pump turns ON, and the pressure
transducers monitor the ensuing pressure rise. When the pressure has
reached the target inflation pressure, the pump turns OFF and a dynamic
braking circuit rapidly brings the pump to a halt. The target inflation
pressure adapts to the patient’s systolic pressure, just occluding the blood
flow. The software monitors the slope of the pressure curve during
inflation to estimate the cuff volume, a factor used in the deflation
sequence.
Deflation PhaseAfter the pump stops, there is a short delay to allow thermal transients to
settle. Either V1 or V2 is modulated to control the deflation rate. The choice
of V1 or V2 and the initial pulse width is made based on the estimated cuff
volume determined during the inflation cycle. The chosen valve is
modulated at a 20 Hz rate, and the pulse width (open time) is continuously
adjusted to provide a linear deflation rate. If initial deflation was started with
V1, the software may determine that it needs to switch to V2 to maintain
proper deflation. In either case, V2 opens fully (de-energizes) when the
measurement cycle is ended to allow for rapid and complete deflation.
5.5.4 NBP HardwarePump control circuitry provides the following three functions:
• limits the current to the pump when it starts, to prevent power supply
overload
• dynamically brakes the pump when the pump is shut off
• provides a closed-loop speed control for special low-flow operations
Speed ControlPump speed is controlled by measuring the back-EMF generated by the
motor winding, which is directly proportional to the speed. However, to
obtain a measurement of the back-EMF, the drop caused by copper losses
must be added to the voltage appearing on the motor winding. The speed
control effectively drives the pump at constant full speed.
Current LimitDedicated circuitry limits the current to the pump. When the current on the
pump is approx. 363 mA, the current loop takes over and limits its value.
The microprocessor and an N-channel FET turn the pump ON.
5.5.5 Valve ControlA relatively high pulse voltage is used to drive V1 and V2 to get quick
response and extend the pulse-width flow control range.
5.5.6 Power SuppliesSeparate control logic supplies voltage (+12V) to the pump and V2 to
provide them with redundant turn-off capability. Without +12V the pump
cannot run, and V2 can neither close nor remain closed. Power supplies
necessary for operation of the NBP circuitry are derived as follows:
+5V and -5V SupplyThe +5V and -5V for the NBP analog circuitry are derived from the floating
section.
+12V SupplyThe +12V drives the NBP pump and both modulating valves. The 6002XL
flyback supply produces the +12V. This circuit produces several voltages
needed for monitor operation. The main flyback regulation loop is closed
around the +12V output, therefore making it the best regulated of the
multiple voltages generated.
In operation, a resistor network samples the +12V output and feeds it into
the controller chip error amplifier, which compares it to an internal
reference. The duty cycle of the switching transistor is adjusted to null this
reference. A separate current feedback loop is used to stabilize the circuit
and provide current limiting protection.
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+36V RegulatorA +36V supply used to accelerate the energizing of the valve coils is
derived from the 42V raw supply generated by the flyback supply.
5.5.7 Power Supply MonitorThe power supply monitor circuit provides reset logic to the
microprocessor, and the redundant power switch circuit, both at power-up
and in the event of a power failure or voltage drop. The heart of the monitor
is a power supervisor chip. At power-up, the control line is held low for a
period of about 200 ms, after which the voltage rises to the +5V level. After
start-up, any dip in the +5V that causes the output to go to less than
+4.75V causes the same sequence. A resistor network is used to monitor
the +12V supply. When the voltage on the reference signal falls below
+1.25V, a reset sequence similar to the one described above ensues. The
+5V and -5V are monitored via the floating section ADC.
5.5.8 Safety TimerThe safety timer becomes active only after starting the pump at least one
time. Once the pump has been activated, the timer circuit operates
regardless of whether the pump has been turned off. Starting of the pump
is sensed by voltage developed across the pump sense resistor. If as a result
of some failure, hardware or software, the pump continues to run longer
than the timer expiration period, a microcontroller output rises and opens a
redundant switch, which causes the pump to turn off and V2 to open.
The safety timer period is derived from the microcontroller clock. Note
that, for redundancy purposes, the safety timer is implemented not in the
MPC821 but in the 68HC11 microcontroller.
Among other signals multiplexed into the floating section data stream are
power supply monitor voltages. Measuring these voltages gives an
indication of the integrity of the power supplies and the A/D converter
voltage reference.
5.5.9 Pressure ChannelsPressure fluctuations in the cuff change the balance of the pressure
measurement bridge, resulting in a differential voltage which is fed into an
amplifier. The gain of the amplifier is determined by the setting of a
calibration potentiometer. This potentiometer is initially adjusted in the
factory, and from then on the calibration should be checked every year.
The overpressure hardware is fed by a single power source. This increases
safety of the system, since a failure of the reference voltages does not
impact operation of the overpressure channel. An overpressure test is
performed at each power-up cycle to ensure that the overpressure
circuitry is working. Any error detected in the overpressure comparator
circuit is fed to the redundant power switch circuitry described above. The
software overpressure detection is completely independent of the
overpressure circuitry.
Figure 2-8 Temperature Functional Block Diagram
5.6 Temperature Circuit
Temperature measurements are made using a thermistor probe that is
electrically equivalent to YSI
400 series probes. See Figure 2-8.
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