Novametrix 7300 Service Manual

Model 7300

Service Manual

Aug 27, 1999

Part Number 9226-90-00

Novametrix Medical Systems Inc.

P.O. Box 690

5 Technology Drive

Wallingford, Connecticut, U.S.A. 06492.

Service Policy

Novametrix Medical Systems Inc. provides 24-hour a day access to technical support
through its Technical Support Department in Wallingford, Connecticut, and company
Service Representatives located throughout the United States. (Outside the U.S.,
primary technical support is handled through our qualified international sales and
service distributors.)

Novametrix will provide Warranty Service support within 48 hours of receiving a request
for assistance. Contact the Technical Support Department by telephone toll free at 800­243-3444, or 203-265-7701; by facsimile at 203-284-0753; or, by e-mail at
[e-mail]. After hours telephone support requests (before 8:00 AM
and after 5:00 PM Eastern Time) will be responded to promptly by the Technical
Support on-call staff. After hours facsimile and e-mail requests will be answered the
next business day. It is suggested that any person calling in for technical support have
the equipment available for product identification and preliminary troubleshooting.

Novametrix reserves the right to repair or replace any product found to be defective
during the warranty period. Repair may be provided in the form of replacement
exchange parts or accessories, on-site technical repair assistance or complete system
exchanges. Repairs provided due to product abuse or misuse will be considered “non­warranty” and invoiced at the prevailing service rate. Replaced or exchanged materials
are expected to be returned to Novametrix within 10 days in order to avoid (additional)
charges. Return materials should be cleaned as necessary and sent directly to
Novametrix using the return paperwork and shipping label(s) provided (Transferring
return materials to a local sales or dealer representatives does not absolve you of your
return responsibility.).

Novametrix manufactures equipment that is generally field serviceable. When repair
parts are provided, the recipient can call Technical Support for parts replacement
assistance and repair assurance. In the event a replacement part requires increased
technical capability, Technical Support may request Biomedical assistance, provide on­site technical support or complete replacement equipment. If the customer requires the
return of their original product, the exchange material will be considered “loaner
material” and exchanged again after the customer equipment is repaired.

Novametrix promotes customer participation in warranty repairs, should they become
necessary. A longer useful product life, and quicker, more cost-effective maintenance
and repair cycles—both during and after the warranty period, are benefits of a smooth
transition into self-maintenance. The Technical Support Department can provide
technical product support at a level appropriate to your protocol and budget
requirements.

Please contact Technical Support for information on these additional programs and
services:

• Focus Series Technical Training Seminars

• Test Equipment and Test Kits

• Service Contract / Parts Insurance Plans

• On-Site Technical Support

• “Demand Services” including:
Flat rate parts exchange
Flat rate return for repair
Time and material,
Full warranty, discounted replacement sensors.

Rev. 00

Model 7300 Service

Manual

iii

Warranty

Equipment manufactured or distributed by Novametrix Medical Systems Inc., is fully
guaranteed, covering materials and workmanship, for a period of one year from the
date of shipment, except for certain disposable products and products with stated
guarantees other than one year. Novametrix reserves the right to perform guarantee
service(s) at its factory, at an authorized repair station, or at the customer’s installation.

Novametrix’ obligations under this guarantee are limited to repairs, or at Novametrix’
option, replacement of any defective parts of our equipment, except fuses, batteries,
and calibration gasses, without charge, if said defects occur during normal service.

Claims for damages during shipment must be filed promptly with the transportation
company. All correspondence concerning the equipment must specify both the model
name and number, and the serial number as it appears on the equipment.

Improper use, mishandling, tampering with, or operation of the equipment without
following specific operating instructions will void this guarantee and release Novametrix
from any further guarantee obligations.

Service Department

For factory repair service:

Call toll free: 1-800-243-3444

To Call Direct: [phone]

Facsimile [phone]

http://www.novametrix.com

[e-mail]

iv

Model 7300 Service

Caution:

the order of a licensed medical practitioner.

Manual Rev. 00

Federal (U.S.A.) law restricts this device to sale, distribution, or use by or on

Copyright ©1999. Novametrix Medical Systems Inc.,

5 Technology Drive, Wallingford, Connecticut, 06492.

All rights reserved.

Table of Contents

Safety ..............................................................................................................................................................1

Warnings ..................................................................................................................................................1

Cautions ...................................................................................................................................................2

Notes ........................................................................................................................................................2

Introduction ....................................................................................................................................................5

About this manual .....................................................................................................................................5

Front and Rear Illustrations ......................................................................................................................5

NICO Monitor Technical Description ........................................................................................................6

Manufacturing Quality & Safety ................................................................................................................6

Declaration of Conformity with European Union Directive ........................................................................6

Trademarks and Patents ..........................................................................................................................6

Manual Revision History ...........................................................................................................................6

Theory of Operation ...................................................................................................................................... 7

NICO Model 7300 Non-Invasive Cardiac Output Monitor .........................................................................7

Digital Board 2763 ....................................................................................................................................7

Microprocessor ..................................................................................................................................7

Background Mode Debugging and Application Development .........................................................11

System Memory ..............................................................................................................................11

User Interface Control Circuitry .......................................................................................................12

Real Time Clock, Power on RESET Generation and Glue Logic .................................................... 12

Power Supply 2764 (Power Supply and Communications) .................................................................... 13

Serial Communications UART .........................................................................................................13

Pulser Source Drive ................................................................................................................15

CO

2

CAPNOSTAT Case and Detector Heater Control ...........................................................................16

Saturation LED Power Generation and LED Drive ..........................................................................17

Power Supply and Voltage Reference Generation ..........................................................................17

Logic and Input / Output Signal Control ..........................................................................................20

Analog Board 2765-01 ............................................................................................................................20

CAPNOSTAT Interface ...................................................................................................................20

Input Signal Path .....................................................................................................................20

CO

2

Case and Detector Heater Regulation ....................................................................................21

CO

2

Flow Zeroing and Patient Line Purging ........................................................................................... 22

Flow Circuitry ...................................................................................................................................22

Barometric and Airway Pressure .....................................................................................................23

Patient Airway Adapter Type Sensing .............................................................................................23

NICO Sensor Rebreathing Valve Control ........................................................................................24

Saturation Input Signal Path and Signal Conversion ...................................................................... 24

Functional Testing .......................................................................................................................................25

Equipment Required ...............................................................................................................................25

Functional Test .......................................................................................................................................25

Accuracy Tests ............................................................................................................................................29

Equipment Required ...............................................................................................................................29

Testing ............................................................................................................................................29

CO

2

Testing ..........................................................................................................................................30

SpO

2

Flow Testing ...........................................................................................................................................31

Time / Date Setting .................................................................................................................................31

Electronic Tests ...........................................................................................................................................33

Rev. 00

Model 7300 Service

Manual

v

Equipment Required ...............................................................................................................................33

Power Supply ......................................................................................................................................... 34

Voltage Checks ...................................................................................................................................... 35

Testing ............................................................................................................................................ 37

CO

2

Testing .......................................................................................................................................... 37

SpO

2

Flow, Barometric Pressure and Rebreathe Valve Testing ......................................................................38

Serial / Analog Testing ........................................................................................................................... 40

Safety Testing ........................................................................................................................................ 40

Maintenance ................................................................................................................................................. 41

General .................................................................................................................................................. 41

Maintenance Schedules ......................................................................................................................... 41

Cleaning and Sterilization ....................................................................................................................... 41

Monitor ............................................................................................................................................ 41

Finger Sensor ........................................................................................................................41

SpO

2

SpO

Y-Sensor .............................................................................................................................. 42

2

Y-Strip Tapes and Foam Wraps ........................................................................................... 42

SpO

2

Ear Clip ........................................................................................................................................... 42

NICO Sensors ................................................................................................................................. 42

CAPNOSTAT CO

Sensor .............................................................................................................. 42

2

Disassembly ........................................................................................................................................... 43

Equipment Required ....................................................................................................................... 43

Disassembling Unit ......................................................................................................................... 43

Reassembling Unit ................................................................................................................................. 44

Battery Maintenance .............................................................................................................................. 44

Replacing the Internal Battery ................................................................................................................44

Mains Voltage Configuration ..................................................................................................................45

Fuse Replacement .......................................................................................................................... 46

Software Update Instructions ................................................................................................................. 47

Equipment Required ....................................................................................................................... 47

Setup ............................................................................................................................................... 47

Procedure ........................................................................................................................................ 48

Specifications .............................................................................................................................................. 51

General ................................................................................................................................................... 51

NICO ...................................................................................................................................................... 51

CO

2 ................................................................................................................................................................................................51

Flow Sensor ........................................................................................................................................... 52

SpO

2 ..............................................................................................................................................................................................52

Monitor Specifications ............................................................................................................................ 52

NICO Accessories ....................................................................................................................................... 53

Parts Lists .................................................................................................................................................... 55

9226-00 Non-Invasive Cardiac Output Monitor, Model 7300 .................................................................55

9226-01 Main Assy ................................................................................................................................. 55

2763-01 Digital Board Assy .................................................................................................................... 56

2764-01 Power Board Assy .................................................................................................................... 58

2765-01 Analog Board Assy ................................................................................................................... 62

2766-01 CO

Input Board Assy ..............................................................................................................65

2

9392-01 Pump W Rsvr Assy .................................................................................................................. 65

Drawings ...................................................................................................................................................... 67

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Model 7300 Service

Manual Rev. 00

1

Safety

1.1 Warnings

For maximum patient and operator safety, observe the following warnings, cautions
and notes.

WARNING:

Indicates a potentially harmful condition that can lead to personal injury.

!

• Explosion Hazard: Do not use the NICO monitor in the presence of flammable
anesthetics. Use of this instrument in such an environment may present an
explosion hazard.

• Electrical Shock Hazard: Always turn the NICO monitor off before cleaning it. Do
not use with a damaged external power source. Refer servicing to qualified
service personnel.

• Connect the AC Mains power cord to a properly grounded hospital-grade outlet.
The NICO monitor should be connected to the same electrical circuit as other
equipment in use on the patient. Outlets of the same circuit can be identified by
members of the hospital’s engineering department.

• Failure of Operation: If the monitor fails to respond as described, do not use it
until the situation has been corrected by qualified personnel.

• Reuse (disassembly, cleaning, disinfecting, resterilizing, etc.) of the NICO
sensor may compromise the device functionality and system performance and
cause a potential patient hazard. Performance is not guaranteed if the NCIO
sensor is reused.

• Inspect the CO
to be damaged or broken.

• Do not attempt to rotate the NICO sensor in the breathing circuit by grasping the
pneumatic tubes exiting the flow sensor.

• Do not apply excessive tension to any cable or the NICO sensor pneumatic
tubing.

• Periodically inspect NICO sensor tubing lines for kinks.

• Replace the NICO sensor if excessive moisture or secretions are observed in the
tubing.

• Do not use the NICO monitor if it is unable to properly identify the NICO sensor.
If the condition persists, refer the monitor to qualified service personnel.

• The NICO sensor connector should be properly inserted into the front panel
receptacle prior to connecting the NICO sensor to the breathing circuit, in order
to avoid a circuit leak, or occlusion of the NICO sensor tubing.

, SpO2 and NICO sensors prior to use. Do not use if they appear

2

Rev 00

Model 7300 Service Manual

1

1 Safety

1.2 Cautions

!

Cautions

• In the event the message NICO SENSOR FAILURE is displayed, remove the NICO
Sensor from the patient circuit.

• Patient Safety: Care should be exercised to assure continued peripheral
perfusion distal to the SpO

• Inspect the SpO
hours.

• When applying sensors take note of patient’s physiological condition. For
example, burn patients may exhibit more sensitivity to heat and pressure and
therefore additional consideration such as more frequent site checks may be
appropriate.

• Do not position sensor cables or tubing in any manner that may cause
entanglement or strangulation.

• The NICO monitor is not intended to be used as a primary apnea monitor.

Indicates a condition that may lead to equipment damage or malfunction.

sensor site for adequate circulation at least once every four

2

sensor site after application.

2

CAUTION:

1.3 Notes

• Use only Novametrix approved sensors and accessories with the NICO monitor.

• Do not operate the NICO monitor when it is wet due to spills or condensation.

• Do not operate the product if it appears to have been dropped or damaged.

• Never sterilize or immerse the monitor in liquids.

• Do not sterilize or immerse sensors except as directed in this manual.

• No tension should be applied to any sensor cable or tubing.

• To avoid the effects of excessive moisture in the NICO sensor, insert it in the
ventilator circuit with the pneumatic tubes upright. Excessive moisture in the
NICO sensor may affect the accuracy of the measurements.

• Operate the monitor at temperatures between 10 to +40° C (50 to 104° F),
10-95% R.H. non-condensing.

• Avoid storing the monitor at temperatures less than -10q C or greater than +55q
C (<14q F or >131q F) 10-95% R.H. non-condensing

• Observe precautions for electrostatic discharge (ESD) and electromagnetic
interference (EMI) to and from other equipment.

• Where electromagnetic devices (i.e., electrocautery) are used, patient
monitoring may be interrupted due to electromagnetic interference.
Electromagnetic fields up to 3 V/m will not adversely affect system performance.

• Caution: Federal (U.S.A.) law restricts this device to sale, distribution, or use by
or on the order of a licensed medical practitioner.

2

Model 7300 Service Manual

NOTE:

A point of particular interest or emphasis intended to provide more efficient or convenient
operation.

• In order to ensure proper monitoring of oxygenation and ventilation:

• The use of pulse oximetry is recommended during NICO monitoring.

• Setting of ETCO

and SpO2 alert limits is recommended.

2

Rev. 00

Notes

Safety

1

• A “NO RESPIRATION” alert is not generated when both the CAPNOSTAT CO2
sensor and the NICO sensor are disconnected from the NICO monitor.

• Be certain that the monitor is not in Demo Mode while monitoring. Demo Mode
can be identified by the flashing DEMO MODE label in the General Message
area of the display. To exit Demo Mode and return to normal monitoring mode,
turn the power off and back on.

• The NICO monitor contains no user serviceable parts. Refer servicing to
qualified service personnel.

• Do not attach an SpO

sensor distal to a blood pressure cuff. Valid data cannot

2

be processed when the cuff is inflated. Attach the sensor to the limb opposite to
the site used for the blood pressure cuff.

• This product and its accessories which have patient contact are free of latex.

• The NICO monitor is Year 2000 compliant.

• Data Validity: Inaccurate SpO

and Pulse Rate values may be caused by;

2

• Incorrect application or use of a sensor

• Significant levels of dysfunctional hemoglobin; carboxyhemoglobin or

methemoglobin

• Significant levels of indocyanine green, methylene blue, or other intravascular

dyes

• Exposure to excessive illumination such as surgical lamps—especially ones

with a xenon light source, or direct sunlight

• Excessive patient movement

• Venous pulsations

• Electrosurgical interference

• Use of an IABP.

• NICO measurements will occur provided the following conditions are met:

• The NICO sensor is properly installed in the patient’s breathing circuit.

• Valid flow and CO

•VCO

•ETCO

is greater than 20 mL/min.

2

is between 15 and 70 mmHg (2.0 - 9.0 kPa or %)

2

signals are detected with no significant signal artifact.

2

• The tidal volume is greater than 200ml.

• The respiratory rate is between 3 and 60 br/min.

• The STOP/CONTINUE REBREATHING key is not illuminated.

• NICO is not paused by the monitor for any other reason (displayed in the C.O.

message area)

• When a new CAPNOSTAT CO

sensor is attached to the monitor, or is moved

2

from one monitor to another, it must be adapter zeroed before use.

• After the life cycle of the equipment and accessories has been met, disposal
should be accomplished following national/local requirements.

• There is no screen indication during monitoring, except on start-up (or when the
SET ALERTS screen is displayed), as to when the NICO alert settings are off.

Rev. 00

Model 7300 Service Manual

3

1 Safety

Notes

[This page intentionally blank.]

4

Model 7300 Service Manual

Rev. 00

2

Introduction

2.1 About this manual

This document contains information which is proprietary and the property of
Novametrix Medical Systems Inc., and may not be reproduced, stored in a retrieval
system, translated, transcribed, or transmitted, in any form, or by any means, without
the prior explicit written permission of Novametrix Medical Systems Inc. Novametrix
reserves the right to change specifications without notice.

2.2 Front and Rear Illustrations

Front panel keys

Knob

Display screen

NICO sensor input connection

SpO2 sensor input connection

CAPNOSTAT CO

Power cord entry module

(power cord receptacle

Rear panel power switch

Power cord retainer

(secure power cord)

Equipotential connection

(connection to monitor chassis)

sensor input connection

2

and fuse housing)

Operate/standby key

Serial number label

Rear panel
power connectors

Rev 00

Model 7300 Service Manual

5

2 Introduction

2.3 NICO Monitor Technical Description

2.4 Manufacturing Quality & Safety

2.5 Declaration of Conformity with European Union Directive

NICO Monitor Technical Description

Per requirements of IEC 601-1, the NICO monitor is classified as class II equipment,
internally powered, with type BF applied part, and an enclosure protection rating of
IPX0. The NICO monitor is Year 2000 compliant.

Transport/Storage: -10 to +55° C (14-131° F), 10-95% R.H. non-condensing
Operating Conditions: 10 to +40° C (50 to 104° F), 10-90% R.H. non-condensing

The Novametrix Medical Systems Inc. manufacturing facility is certified to both
ISO 9001 and EN46001 (MDD93/42/EEC Annex II). Novametrix’ products bear the
“CE 0086” mark. The product is certified by Underwriter’s Laboratories (UL) to bear the
UL mark; and tested by TÜV Rheinland to IEC 601-1/EN60601-1.

The Authorized Representative for Novametrix equipment is:

D.R.M. Green
European Compliance Services Limited,
Oakdene House,
Oak Road,
Watchfield
Swindon, Wilts SN6 8TD
United Kingdom

2.6 Trademarks and Patents

CAPNOSTAT CO2 Sensor is a registered trademark (®) and NICO, NICO2 and the
stylized NICO
output confidence bar), SuperBright and Y-Sensor are trademarks (™) of Novametrix
Medical Systems Inc. Other trademarks and registered trademarks are the property of
their respective owners.

NICO and its sensors and accessories are covered by one or more of the following USA
patents: 4,859,858, 4,859,859, 4,914,720, 5,146,092, 5,153,436, 5,190,038,
5,206,511, 5,251,121, 5,347,843, 5,369,277, 5,379,650, 5,398,680, 5,616,923,
5,693,944, 5,789,660. Other patents pending.

with CO2 shadow, NICO Sensor, NICO Loop and CObar (cardiac

2

2.7 Manual Revision History

7-Aug-99 Release

6

Model 7300 Service Manual

Rev. 00

3

Theory of Operation

3.1 NICO Model 7300 Non-Invasive Cardiac Output Monitor

The NICO model 7300 monitor measures cardiac output based on changes in
respiratory CO
measurement of cardiac output is accomplished by interpreting data collected by
proprietary sensors that measure flow, airway pressure, and CO
then combining these signals to calculate CO
technique known as Fick partial rebreathing is applied to calculate cardiac output.
NICO can be used with mechanically ventilated patients in the operating room,
intensive care, or emergency departments.

concentration caused by a brief period of rebreathing. The

2

elimination. Using these variables, a

2

3.2 Digital Board 2763

3.2.1 Microprocessor

Refer to sheet 1 of the 2763-03 schematic.
The generation of the logic and control signals for the purpose of acquiring the raw

physiological parameters, and management of the data needed to produce an accurate
Non-Invasive Cardiac Output, are the responsibilities of microprocessor IC1. This
device, a Motorola MC68332, is a highly integrated 32-bit microcontroller that
combines high-performance data manipulation capabilities with powerful peripheral
subsystems. These subsystems include circuitry for timing generation, peripheral chip
selection and data control, interrupt generation, as well as synchronous and
asynchronous serial communication. Also included is a sophisticated timing co­processor, the TPU (Time Processor Unit), that can generate complex timing
waveforms independent of the main processor. In general, the signals for subsystems
are functionally grouped into ports which can be independently programmed by
software to be a pre-defined port function or discrete I/O. Additionally, the functionality
for several ports (Ports C, E and F) can be pre-defined by the state of specific data bus
lines on system power-up. Included is a special “background mode” port that allows the
device to be externally controlled, facilitating system debugging and testing. Also
integrated on-chip are several activity monitors as well as a software watchdog to
ensure proper device and system operation. Refer to table 1.

concentration, and

2

Port Defined Function Functionality & Power-up Control

TPU
16 Channels

Rev 00

Timing Signal Generation Each channel independently user

Table 1: CPU Port Functions

Model 7300 Service Manual

programmable as TPU function or as
Discrete I/O

7

3 Theory of Operation

Digital Board 2763

QSM
4 Synchronous Serial
Chip Selects & one
asynchronous serial
channel

Background Mode System debugging Allows an appropriate external device

C Chip Selects D0: CSBOOT* Data Width, 8 or 16-

E Bus Control D8: Control Signals or Discrete I/O

F MODCK and Interrupts D9: MODCK & IRQ or Discrete I/O

Serial Communications Port:
QSPI: Queued Serial Peripheral
Interface
SCI: Serial Communications
Interface

QSPI chip selects independently user
programmable, can be used as
Discrete I/O or decoded to create up
to 16 chip selects. SCI transmit can
be programmed as Discrete I/O

to control the microprocessor and
system

bit
D1: CS1*-CS3* or BR*,BG*,BGACK*
D2: CS3*-CS5* or FC0-FC2
D3-D7: CS6*-CS10* or A19-A23

Table 1: CPU Port Functions

The operating frequency of the system clock in the

system is 24.117 MHz. It is

NICO

generated by an internal VCO (Voltage Controlled Oscillator) derived from Y1, a

32.768KHz watch crystal, and is software programmable. The Timing Processor Unit
(TPU) co-processor of the MC68332 provides complex timing functions generated from
the system clock. This feature is utilized to control the precise timing required for the
acquisition of the End Tidal Carbon Dioxide (etCO

) and saturation (SpO2) signals.

2

The TPU is also used to generate the PWM (Pulse Width Modulation) control for the
Capnostat Case and Detector heaters, and to provide the frequency generation for the
audio tones. See Tables 2 and 3

Signal Name Function / Timing

CO2AZ Auto Zero Clears the Sample/Hold circuitry prior to data

acquisition.
Active High, 90 us

CO2PWENB Pulse Width Enable Defines the active time for both phases of the bipo-

lar source pulse, used for pulse width protection
circuitry.
Active High, 810 us

SRCDRV0 Source Drive 0 First source drive signal.

Active High, 405 us

CO2CSHL Current Sample/Hold Enables circuitry for source current measure-

ment. Sample is taken when SRCDRV0 is active.
Low = Sample, 90 us, High = Hold

SRCDRV1 Source Drive 1 Second source drive signal delayed for 10 micro-

seconds after SRCDRV0 ends.
Active High, 395 us

CO2SSH Signal Sample/Hold Enables circuitry for CO

data acquisition.
Low = Sample, 90 us, High = Hold

CASEPWM Case Heater PWM PWM control for the case heater servo

and Reference channel

2

Table 2: TPU Timing Generation for the etCO2 subsystem

8

Model 7300 Service Manual

Rev. 00

Digital Board 2763

Theory of Operation

DETPWM Detector Heater PWM PWM control for the detector heater servo

TOUT1, TOUT2 Tone Generation Variable frequency outputs to generate system

audio

3

Table 2: TPU Timing Generation for the etCO

Signal Name Function / Timing

ASAMPL Auto Zero Clears the Sample/Hold circuitry prior to data

acquisition.
Active Low

RDLEDL Red Channel LED control pulse Defines the active time for the Red LED. Active

Low

IRLEDL Infra-Red Channel LED control pulse Defines the active time for the Infra-Red LED.

Active Low

RSAMPL Red Channel Sample/Hold Enables circuitry for the Red Channel signal mea-

surement. Sample is taken when SRCDRV0 is
active.
Low = Sample, 90 us, High = Hold

ISAMPL Infra-Red Channel Sample/Hold Enables circuitry for the InfraRed Channel signal

measurement. Sample is taken when SRCDRV0
is active.
Low = Sample, 90 us, High = Hold

Table 3: TPU Timing Generation for the SpO2 subsystem

subsystem

2

To help reduce and suppress the radiation of electromagnetic interference, ferrite filters
(L1-L11) have been placed on clock signals with fast rise and fall times. Other digital
signals, including address and data lines, are rise-time limited by the addition of small
valued resistors and / or capacitors. In addition, good EMI/EMC design techniques
have been incorporated in the component layout and printed circuit board manufacture.

Table 4 lists the chip select, control and discrete I/O functions for the NICO system
module. On power-up, Ports E and F are programmed as discrete inputs by pulling
down their controlling data lines, DB8 and DB9. After power-up, the software sets up
each pin function individually and performs a series of self-tests to check the integrity
of the system. During this period, the MPU holds the SYSUP line low which keeps the
system in the initialization state. The state of configuration inputs on Port E (CNFG0,
CNFG1 and CNFG2) and on data input buffer IC10 (see sheet 2 on 2763-03 schematic)
(JP1, JP2, JP2, JP4, TP4, TP5 and TP6) are read. These inputs allow the software to
identify different operating conditions, such as Manufacturing Diagnostic Mode, or to
recognize different hardware configurations. After the initialization period is complete
and all system functions have been set, the MPU brings the status signal SYSUP high,
indicating that the system is ready for patient monitoring operation.

Rev. 00

Port Pin Functions System Signal

Table 4: Chip Select, Control and Discrete I/O

Name

1

I/O Comments

Model 7300 Service Manual

9

3 Theory of Operation

Digital Board 2763

CDATA0 thru

DATA7

CSBOOT* ROMOEL O Program PROM Chip Select

CS0* / BR* UBRAMWRL O Upper Byte SRAM Write Enable

CS1*/ BG* LBRAMWRL O Lower Byte SRAM Write Enable

CS2* / BGACK* SRAMOEL O SRAM Read Enable, Word

CS3* / PC0 / FC0 ROMWRL O FLASH PROM Write Enable, Word

CS4* / PC1 / FC1 UARTCSL O High Speed quad UART Chip Select

CS5* / PC2 / FC2 BOOTWE O Port C Discrete Output, prevents

CS6* / PC3 / A19 A19 O High Address line A19

CS7* / PC4 / A20 RTCCSL O Real Time Clock Chip Select

CS8* / PC5 / A21 DISPCSL O EL Display Chip Select

CS9* / PC6 / A22 VRAMCSL O Video Memory Chip Select

O D0-D7 pulled high, Pins are Chip Select

on power-up

Word (16-bits) wide mode, D0 = HIGH

Allows for byte (8-bit) or word writes

Allows for byte (8-bit) or word writes

unintentional writes to FLASH EPROM.
This signal must be asserted before
ROMWR* in order to overwrite the FLASH

CS10* / ECLK /
A23

E DATA8 O D8 pulled low, Discrete I/O on power-up

DSACK0* / PE0 CNFG2 I Configuration Switch 2

DSACK1* / PE1 DS1L I Data and Size Acknowledge 1*

AVC* / PE2 CNFG0 I Configuration Switch 0

RMC* / PE3 CNFG1 I Configuration Switch 1

DS* / PE4 DSL O Data Strobe

AS* / PE5 ASL O Address Strobe

SIZ0* / PE6 SIZ0 O Signifies current operation is 8-bit data

SIZ1* / PE7 CNFG2 I Configuration Switch 2

R/W* RDL O Data Read Strode

CASCADEL O Cascaded Chip Select for Additional

Parallel Peripherals

WRL O Data Write Strobe

Table 4: Chip Select, Control and Discrete I/O

10

Model 7300 Service Manual

Rev. 00

Digital Board 2763

Theory of Operation

F DATA9 O D9 pulled low, Discrete I/O on power-up

MODCLK / PF0 LED O LED CPU Activity Indicator

IRQ1* / PF1 SYSUP O System Initialization Complete

IRQ2* / PF2 CSOFTOT O Case Heater Over Temperature Shut

Down

IRQ3* / PF3 DSOFTOT O Detector Heater Over Temperature Shut

Down

IRQ4* / PF4 UARTIRQL I External UART Interrupt

IRQ5* / PF5 EXTDCIN I Indicates external AC MAINS power

operation

IRQ6* / PF6 PWRDWN O System power down enable

IRQ7* / PF7 NMIL I Non-Maskable Interrupt

Table 4: Chip Select, Control and Discrete I/O

1.Signal names with an “L” suffix are active low signals.

3

3.2.2 Background Mode Debugging and Application Development

Refer to sheet 1 on 2763-03 schematic.
Background debugging of the system during applications development or during

system testing is possible by connecting an appropriate external device (emulator or
debugger) to header J1. The signals present on this header enable an external device
to halt the current microprocessor bus activity. This turns control of the microprocessor
system over to the external device, placing the microcontroller into Background
Debugging Mode. In this mode, the internal MPU registers can be viewed and altered,
special test features can be invoked and the system’s memory, and peripherals can be
read and written to.

Refer to sheet 2 on 2763-03 schematic.
In addition to the inherent debugging capabilities of the microprocessor, the digital

board also contains circuitry to monitor events during application development. Output
latches IC15 and IC17 along with Profiling header J4 are used to determine CPU
utilization during system development, latching various status bits out on the header.

3.2.3 System Memory

Refer to sheet 1 on 2763-03 schematic.
A 16-bit wide data path is used for FLASH PROM and SRAM transfers to maximize

system throughput. Non-volatile memory, used for the storage of the boot-up and main
program code, is contained in IC4, a 1024K x 8-bit, 5V FLASH ROM. To initiate the
data transfer process, the MPU brings the ROMOEL output signal LOW, causing a
word of program data stored in the FLASH ROM to be sent out on the data bus from
the appropriate memory address. Program data may be updated by commanding the
device to erase a block of its present programmed data then using the ROMWRL signal
to place new program data into the address specified by the MPU. The FLASH ROM
is internally protected from unintentional overwrites of the boot code by requiring an
independent signal, BOOTWE, going active in addition to ROMWRL. The BOOTWE
line must be high prior to writing new boot code into the FLASH device. Two 128K x 8­bit Static RAMs (IC3 and IC6) contain volatile data storage for use as a temporary data
scratch pad during system operation and for recording patient trend information. To

Rev. 00

Model 7300 Service Manual

11

3 Theory of Operation

3.2.4 User Interface Control Circuitry

Digital Board 2763

retain patient trending data during periods of power down, the SRAMs are battery
backed to retain their contents. A 2.5 Volt level VBACK generated from the main
battery via IC30 on the 2764 Power Board, is supplied when the system is turned off
and removed from the AC MAINS. During this battery backed-up state, transistor Q1
keeps the chip enable control line of the SRAMs high and in a low power, inactive state.
This forces the SRAMs data bus to a high impedance state, isolating the parts from the
rest of the system. True non-volatile storage for system parameters is provided by a
serial EEPROM (IC8), which has the ability to retain programmed information in the
absence of power.

Refer to sheet 3 on 2763-03 schematic.
The user interface features a high contrast, 320 row by 240 column Electroluminescent

Display module. Patient and system information is presented in both graphical and
textual formats organized into several screen configurations. An integrated display
controller, IC19, works in conjunction with the MC68332 MPU, and provides the
necessary timing signal generation and housekeeping functions to display the visual
information generated by the system. Programmable logic device IC2 is designed to
condition the logic signals between the MPU and display controller, making sure that
the critical timing specifications of the two devices are met. SRAMS IC18 and IC22
provide video RAM storage for the display system. In addition to buffering the signals
for the display interface, CPLD IC2 also decodes chip selects for the system input
buffers and output latches off of CASCADEL. If required, IC2 can be reprogrammed
in-circuit using header J9.

A 5-switch silicon keypanel and multifunctional rotary encoder provide operator control
of screen selection, patient data entry, and user selectable input. The keypanel also
contains several LEDs which represent various system conditions such as input power
status (AC or Battery) and alarm state. Control of the user interface is generated from
the CASCADEL chip select signal along with the appropriate address line state and
WRL signals from the microprocessor. IC10 and IC13 (sheet 2 on schematic) are input
buffers, which read in the present state of the keypanel and rotary encoder. Depressing
a key or activation of the encoder causes the signal line associated to be pulled low, in
contrast to its normally high state. Input buffer IC14 provides a latched output for
controlling the front panel LEDs as well as several other latched control outputs.

To supplement the visual indicators associated with the membrane keypanel and
display, an audio output signal is generated to provide an additional mode to convey
information to the user. The TPU processor of the MC68332 (TOUT1 and TOUT2) can
generate two-tone frequencies. These signals are fed into separate reference inputs
of the Quad 8-bit DAC, IC20, providing a means for independently attenuating each
signal under CPU control. From the DAC, the individual signals are summed together
by IC21B and filtered by L11 and C50. Audio amplifier IC23 drives the system speaker
to produce system audio. Inverter IC7F, controlled by the SYSUP signal from the MPU,
disables the audio amplifier until system initialization has been completed. DAC IC23
also supplies an output voltage level SPO2VLED to set the current gain of the
saturation drive circuit which is found on the
associated with the DACB output (including IC21A, Q3 and J6) is presently not used.

Power PCB, 2764-01. The circuitry

NICO

3.2.5 Real Time Clock, Power on RESET Generation and Glue Logic

12

Model 7300 Service Manual

Refer to sheet 2 on 2763-03 schematic.
Time keeping for date and time stamping of patient trend information is provided by

Real Time Clock IC16. This device contains a built in crystal for precise time and date

Rev. 00

Power Supply 2764 (Power Supply and Communications)

measurement. The NICO system has been designed and tested for Y2K compliance.
In the absence of digital power, the time keeping function is maintained by the battery
backed-up supply, VBACK.

On power-up, the system is forced into a RESET state by IC9 (sheet 1 on schematic).
This chip creates the master active low system reset signal SRST*, holding up system
initialization until a stable 5 VDC logic level is maintained. An inverter is used to
generate RESET for devices that require an active high reset signal.

3.3 Power Supply 2764 (Power Supply and Communications)

3.3.1 Serial Communications UART

Refer to sheet 3 on 2764-03 schematic.
To enable serial communication with up to three external devices simultaneously, a

Quad UART (Universal Asynchronous Receiver/Transmitter), IC14, is provided for
buffered high-speed data communication. The connection to external, non-patient
contact-type devices is electrically isolated from the patient applied sections by optical
data couplers (IC16, IC17, IC21, IC23, IC26) and isolated winding off of the power
supply flyback transformer, T1. Transceiver IC13, located on the patient-isolated
circuit, provides signal translation between the system’s TTL logic level and the RS-232
level requirements. Serial Ports A and C (J1 and J3) are configured for a simple 3-wire
(Transmit, Receive and Ground) connection, while Serial Port B (J2) has additional
hardware handshaking capabilities. Connection to an external device is through a null­modem type of interface cable. The fourth UART channel is available on internal
connector J5 for future product expansion. In addition, the system is capable of
outputting four channels of analog output data through IC22 and receiving four
channels of analog input through buffer amplifiers IC18 and A/D Converter IC20 on
connector J4. Voltage reference IC19 supplies the analog I/O circuitry with a stable
voltage level. Connector J4 allows sensing of external cable connection by shorting
pin 15 (IOSNSE) of the external cable to ground. Refer to Tables 5 to 8 for the pinout
and signals of interface connectors.

Theory of Operation

3

Rev. 00

J1

Pin Number Signal Function

1 NC No Connection

2

3

4 NC No Connection

5

6 NC No Connection

7 NC No Connection

8 NC No Connection

9 NC No Connection

Table 5: Serial Channel A, 9-pin D-subminiature connector located on the rear panel

RxC

TxC

Isolated Ground

Serial Channel A Receive

Serial Channel A Transmit

Non-Patient Signal Ground

Model 7300 Service Manual

13

3 Theory of Operation

Power Supply 2764 (Power Supply and Communications)

J2

Pin Number Signal Function

1 NC No Connection

2 RxB Serial Channel B Receive

3 TxB Serial Channel B Transmit

4 NC No Connection

5 Isolated Ground Non-Patient Signal Ground

6 NC No Connection

7 RTSB Request to Send Channel B, Hardware Handshake

8 CTSB Clear to Send Channel C, Hardware Handshake Input

9 Isolated Power Power

Output

Table 6: Serial Channel B, 9-pin D-subminiature connector located on the rear panel

J3

Pin Number Signal Function

1

2

3

4

5

6

7

8

NC No Connection

RxA Serial Channel C Receive

TxA Serial Channel C Transmit

NC No Connection

Isolated Ground Non-Patient Signal Ground

NC No Connection

NC No Connection

NC No Connection

14

Model 7300 Service Manual

9

NC No Connection

Table 7: Serial Channel C, 9-pin D-subminiature connector located on the rear panel

J4

Pin Number Signal Function

1

2 ADCIN0 ADC Input Channel 0

Isolated
Ground

Non-Patient Signal Ground

Table 8: Analog Connector, 15-pin D-subminiature connector located on the rear panel

Rev. 00

Power Supply 2764 (Power Supply and Communications)

3 ADCIN1 ADC Input Channel 1

4 ADCIN2 ADC Input Channel 2

5 ADCIN3 ADC Input Channel 3

Theory of Operation

3

6

7

8

9

10

11 DACOUT0 DAC Output Channel 0

12 DACOUT1 DAC Output Channel 1

13 DACOUT2 DAC Output Channel 2

14 DACOUT3 DAC Output Channel 3

15 IOSNSE Cable connect sense input

Table 8: Analog Connector, 15-pin D-subminiature connector located on the rear panel

Isolated
Ground

Isolated
Ground

Isolated
Ground

Isolated
Ground

Isolated
Ground

3.3.2 CO2 Pulser Source Drive

The source drive circuitry is designed to drive the source with a bipolar signal to prevent
the migration of charges within the source that may result from unidirectional electrical
fields. The resistance of the source is monitored constantly to ensure the integrity of
the system by sampling the current through the source while it is active.

Refer to sheet 1 on 2764-03 schematic.
The TPU co-processor in the MC68332 generates the timing signals that drive the

power to the broadband infrared source located in the CAPNOSTAT CO
SRCDRV0 and SRCDRV1 lines are used to control the direction of the current flow
through the source. On the falling edge of CO2AZ (Auto Zero) and the rising edge of
CO2PWENB (Pulse Width Enable), the SRCDRV0 signal goes High, enabling drivers
IC1A and IC2B to turn on one half of the MOSFET H-Bridge formed by Q1 and Q2.
This causes current to flow through the P-Channel half of MOSFET Q1, through the
CAPNOSTAT source, through the N-Channel half of MOSFET Q2 and finally through
R23 to the negative supply rail, completing the first part of the Source Pulse cycle. The
duration of SRCDRV0 is 405 us (microseconds). After the SRCDRV0 line goes Low,
there is a 20 us software delay until the SCRDRV1 line goes High, enabling drivers
IC1B and IC2A to turn on the other half of the MOSFET Bridge formed by the P­Channel half of Q2 and the N-Channel half of Q1. This drives the current through the
source in the opposite direction. The 20us software delay between the SRCDRV0 and
SRCDRV1 signals is to prevent the possibility of both halves of the MOSFET bridge
being active at the same time, thus creating a low impedance path between the two
power supply rails.

When current flows through the source, it will also flow through current sensing resistor
R23, creating a differential voltage proportional to the source current. This voltage is

Non-Patient Signal Ground

Non-Patient Signal Ground

Non-Patient Signal Ground

Non-Patient Signal Ground

Non-Patient Signal Ground

sensor. The

2

Rev. 00

Model 7300 Service Manual

15

3 Theory of Operation

Power Supply 2764 (Power Supply and Communications)

measured during the last part of the SCRDRV0 period by differential amplifier IC3A,
and is inputted to IC9 (see sheet 2 on schematic), a 12-bit, 11-channel A/D Converter
after being conditioned by the sample / hold circuit consisting of IC4, IC5 and C11. The
converter output of the sample / hold is processed in software to represent the current
flowing through the CAPNOSTAT source:

V

= (VSR / RSR) * RS * A

SRC

V(DA)

where V

= voltage out of difference amplifier

SRC

proportional to current through the

source element
= 24V +/- 0.625V
= differential voltage across the source

V

R
R

A

V

SR

SR

S

V(DA)

SRC

element

= resistance of the source element

= resistance of the current sensing

resistor
= 1 ohm
= difference amplifier gain
=5
= [120 (Volts*Ohms) / R

(Ohms)]

SR

For compatibility with present Novametrix monitors, the software displays the source
current scaled by (1.1Vsrc) +17mV. In addition to monitoring the source current, the
A/D Converter IC9 also digitizes the feedback signals from the Saturation sensor and
Power Supply.

In order to prevent the source from being driven until the system is up and ready, there
is protection circuitry that inhibits the source drive until enabled. During system power­up, the RESET line keeps Q3 on, preventing source pulses by pulling down SRCDRV0
and SCRDRV1 through D3. Protection circuitry also guards against extended pulse
width as well as shortened duty cycle. On the rising edge of CO2PWENB, the trip point
of IC6B is exceeded, bringing the output of IC6B high as C12 charges through diode
D4. This allows capacitor C8 to charge up through R22. If the CO2PWENB signal does
not turn the Source Pulser off within 200 us after the 810 us pulse period, the voltage
across C8 will exceed the trip point for IC6A, pulling the CO2INH line low and turning
the Pulser off. After the CO2PWENB signal returns Low, capacitor C12 is allowed to
discharge through R26, keeping the output of comparator IC6B at the voltage acquired
during the period when CO2PWENB was High. After approximately 7.2ms, C12 will
have discharged below comparator IC6B’s trip point. The comparator output goes low,
discharging C8 and the circuit is ready for the next source pulse cycle.

3.3.3 CAPNOSTAT Case and Detector Heater Control

16

Model 7300 Service Manual

Refer to sheet 2 on 2764-03 schematic.
The temperature of the CAPNOSTAT sensor system directly affects its ability to

accurately measure CO

. Two separate heaters and control circuits are used to

2

maintain the sensor temperature at a precise value. One heater regulates the
temperature of the detectors that detect the amount of infrared energy passing through
the sample chamber; the other regulates the temperature of the transducer case (and
loosely maintains the temperature of the airway adapter). While the purpose of the
detector heater is to keep the detectors' sensitivity to infrared radiation constant, the
function of the case heater is to keep condensation from forming on the airway
windows by elevating the window temperature above the ambient airway temperature.
Both heaters use an efficient Pulse-Width Modulation scheme designed to decrease
power consumption, with the PWM timing generated by the TPU under microprocessor

Rev. 00

Power Supply 2764 (Power Supply and Communications)

control. The MPU senses the voltage output from the CAPNOSTAT case and detector
thermistors (circuit described in the Analog 2754-01 PCB discussion) and regulates the
output pulses from the TPU, creating a pulse duty cycle that is proportional to the
amount of energy required to maintain the heater temperature. Dual MOSFET Driver
IC10 buffers the TPU signals to drive the gates of Dual P-Channel MOSFET Q7. These
drive signals are AC coupled by capacitors C24 & C31 to ensure that if PWM pulses
are lost for any reason, the MOSFET gates will be pulled up by resistors R40 and R47
which will turn the MOSFETs Off, removing power to the Capnostat heaters. Dual
MOSFET Q4 also controls power to the heaters, allowing independent over­temperature cut-off of each heater by both software and hardware watchdogs. D6, L1
and C25 help turn the pulses for the Case Heater from Q7A into a steady DC output,
while D8, L2 and C32 smooth out the Detector Heater output from Q7B. Since the TPU-
generated PWM signal is based on the system clock, it is synchronized with the
generation of the source pulse timing. This minimizes the effect of any random
disturbance caused by the heater circuit on the detection of the CO
Reference signals.

3.3.4 Saturation LED Power Generation and LED Drive

Refer to sheet 2 on 2764-03 schematic.
Adjustable voltage regulator IC11 is configured as a constant current supply for the Red

and InfraRed (IR) saturation sensor LEDs. R50 limits the current to Vref/R {1.25V/26.7
ohms} or 50mA, while Zener diode D9 sets the maximum output voltage at 7.5 Volts.
Capacitors C36 and C37 provide a reservoir for providing the instantaneous current
demanded when the LEDs are turned on. Transistor Q11 allows shutting down the
power to the sensor LEDs by the microprocessor.

Connector J4 on the NICO 2765-01 Analog Board connects the saturation sensor to
the monitor. Both of the saturation sensor LEDs are controlled by an amplifier
configured as a constant current driver. The voltage control for the constant current
drive, SPO2VLED, comes from DAC IC20 on the NICO Digital Board, 2763-01. The
cathode of the Red LED channel is tied to the driver consisting of amplifier IC12A,
MOSFET Q10 and resistor R57. Since the amplifier is connected as a non-inverting
amplifier, the voltage appearing at the positive terminal will also appear at the negative
terminal and across R57. This voltage, nominally 0.74V, creates a current through R50
of 225mA {0.74V/3.3 ohms} when the RDLED* signal is asserted which also flows
through the Red LED of the Saturation sensor via Q10. The driver for the IR LED
(IC12B, Q13 and R64) creates a constant current source of 111mA across R64 and is
controlled by asserting the IRLED* signal. The two control signals operate at 33 kHz
with a 10% duty cycle and are staggered so that one LED is on during the middle of the
other LED’s off time.

Theory of Operation

Data and

2

3

Rev. 00

3.3.5 Power Supply and Voltage Reference Generation

The monitor operates either on isolated AC Mains power or on the internal 12-Volt
Lead-Acid Battery. To provide isolation from the MAINS lines as well as AC/DC voltage
conversion, the NICO monitor utilizes a Medical Grade, universal input off-line
switching power supply. The DC output of this supply is 15 VDC at 40 Watts, and is
brought to the Power board on connector J6 (sheet 5 on schematic). The heart of the
power supply design for the system is a 100 kHz switching regulator, IC34 (sheet 4 on
schematic), which utilizes a flyback transformer configuration to generate the DC
supply voltages and provide the required isolation between the primary, secondary and
isolated power planes. Power On / Off control is achieved by sensing the state of the
power switch located on the front panel. A high to low transition on the PWRSW line is
debounced by C85 and IC31A, and clocked into Flip-flop IC32A, which causes the Flip-

Model 7300 Service Manual

17

3 Theory of Operation

Power Supply 2764 (Power Supply and Communications)

flop output to toggle its present state. A high output causes switching regulator IC34 to
be turned on, supplying power to the system. Flip-flop IC32B provides control over the
state of the system when the user turns the system “Off”. When the monitor is operated
from an AC MAINS power source the green AC ON indicator on the front panel is lit. If
the monitor is on, pressing the power key on the front membrane keypanel will not
power the monitor down. Instead, the monitor is placed in a standby operating mode.
The display and other non-essential control functions are inactivated by the software,
giving the monitor the appearance of power down. While in standby, however, the core
system continues to operate, keeping the Capnostat heaters within temperature
regulation. This reduces the time required to bring the system up to full operating
specifications during the following power-up cycle. While on battery operation,
depressing the Power Key on the front keypanel will turn off the switching regulator,
thus powering down the system. Stand by mode is disabled and power to the system
is turned off. The monitor enters a low power mode where only circuitry required for
SRAM and real-time clock battery back-up and Power Key sensing is kept supplied.
Power for the SRAM and Real-time clock, VBACK, is determined by the state of VDD.
When VDD is available and transistor Q23 is turned on, VDD is supplied through
transistor Q21. In the absence of VDD, VBACK drops down to a low power level
supplied through diode D36.

During system initialization, the switching frequency is synchronized to the main
system clock by the components associated with Q17 to reduce system data
acquisition errors due to power supply interference. The nominal synchronized
frequency is 156 kHz. The primary of transformer T1 is designed to accept 10 to 24 V
DC input and provides secondary outputs of nominally 5 VDC, +14 VDC, and -14 VDC.
An additional winding pair is isolated by 2KV from the other transformer windings to
provides 9VDC output for the earth connected and patient isolated serial and analog
input and output circuitry. The 5VDC supply (VDD) provides feedback to the switching
regulator by resistor divider R108 and R112. The other windings are loosely regulated
by the requirements of the 5 VDC supply by the ratio of the transformer windings,
creating semi-regulated secondary voltages for the analog supplies of approximately
+\-14VDC. The 5V supply is L-C filtered to provide clean logic supplies for both the
digital logic (VDD) and the analog sections of the Digital and Power Boards (DVDD).
Another filter isolates the 5-Volt supply for the Flow Pneumatics (VVDD) from the rest
of the system. Regulators IC33 and IC36 are designed as a tracking regulator pair to
provide a 24VDC differential voltage for powering the Capnostat source (+VSRC, ­VSRC). The voltage level of the +VA supply is monitored by IC35B to ensure that a
tight voltage range is maintained and not exceeded in the event that the +5 VDC
feedback to the switching regulator, IC34, is lost. Linear regulator IC27 provides the
logic and analog supply for the patient-isolated circuits.

Power for the CAPNOSTAT heaters and the display are derived off of the main 15 Volt
input from the offline switching regulator during connection to an AC MAINS power
source. During AC operation, the signal LINEST is High, indicating the presence of AC
MAINS. IC37, also a switching voltage regulator, and its associated circuitry provide
these functions with a well-regulated 12 VDC supply. When the monitor is operating off
of the internal battery, LINEST is Low, disabling the switching regulator and turning on
MOSFET Q19A which is controlled by voltage comparator IC35C. In this mode, the
heaters and display are supplied directly with battery power, minimizing power losses
that occur during the conversion of one voltage level to another. The output from
comparator IC35C also controls the Reset input to Flip-flop IC32B, determining
whether the monitor is in AC stand-by or DC Power Down operating mode.

Charging the battery takes place as long as the unit is connected into a viable source
of AC MAINS power and the power entry module switch is in the “On” position. In order

18

Model 7300 Service Manual

Rev. 00

Power Supply 2764 (Power Supply and Communications)

to charge the battery as quickly and efficiently as possible, a two-step charging process
is employed. Assuming the battery is in a depleted charge state, feedback to the low
drop-out linear regulator, IC39, sets the voltage output at a fast-charge level of
approximately 14 VDC. Sensing the voltage drop across R144, comparator IC40A
monitors the current draw of the battery, limiting it to approximately 250mA for a
maximum charge rate of C/10. If the battery tries to draw current in excess of the
amount allowed, IC40A turns off the regulator, thus limiting the charging current. As the
battery reaches a fully charged state and the current draw decreases to approximately
50mA, IC40B turns transistor Q27 off which causes the regulator to change its output
to a float charge voltage of approximately 13.2 VDC, which maintains the battery in a
constant state of readiness.

If AC power is lost or is not available, the monitor automatically operates from its
internal battery without interruption. The AC ON indicator is extinguished and a
BATTERY ICON appears on the display, indicating the current power level of the
battery. While on internal DC power, the current state of the battery is monitored by both
software and hardware (IC29, IC28A and IC35A). Should the battery power level get
critically low, the monitor software, which monitors the VBATTADC signal into A/D
Converter IC9 (sheet 2 on schematic), alerts the user. If the monitor is not placed on
AC MAINS power within approximately ten minutes, the software will turn the unit off.
Should the software fail to turn the monitor off, the hardware cutoff, controlled by
comparator IC35A, activates, turning the unit off.

Stable reference voltages for the analog circuitry are derived from IC7 (sheet 1 on
schematic), a precision 2.5V with low drift. Five Volt and 2.5 Volt references are
generated by IC8.

Refer to Table 9.

Theory of Operation

3

Signal Supply Description

VDCIN +10 - +15 VDC Main DC input generated from offline switcher or internal battery

VBATT +10 - +12.5VDC Internal Battery DC input

VBACK +2.5VDC or +5VDC Supply for SRAMs, either VDD or 2.5V to maintain SRAM data

during power down

VHTR +12V or VBATT Supply for the Capnostat Case and Detector heaters and Fan,

regulated at 12V when MAINS power available or from VBATT
when unit is on battery power

DISPVA +12V or VBATT Supply for the EL Display, regulated at 12V when MAINS power

available or from VBATT when unit is on battery power

VDD +5VDC Regulated digital logic supply

VVDD +5VDC Regulated and filtered supply for the valves

CVDD +5VDC Regulated and filtered logic supply for CO

DVDD +5VDC Regulated and filtered logic supply for general analog sub-

systems

ADCVDD +2.14VDC ADC input for monitoring VDD

+VA +14VDC (nominal) Loosely regulated off of the 5VDC feedback line

Table 9: Power Supply Outputs

analog sub-system

2

Rev. 00

Model 7300 Service Manual

19

3 Theory of Operation

Analog Board 2765-01

+VSRC +12VDC Linearly Regulated and filtered positive supply for the Capnostat

Source. Tracks -VSRC to provide a 24V +/- 2.5% differential
voltage across the source

ADCPVSRC+0.85VDC ADC input for monitoring +VSRC

-VSRC -12VDC Linearly Regulated and filtered negative supply for the Capnostat
Source. Tracked by +VSRC to provide a 24V +/- 2.5% differential
voltage across the source

ADCNVSRC+0.75VDC ADC input for monitoring -VSRC

-VA -14VDC (nominal) Loosely regulated off of the 5VDC feedback line

IRAW +7.5VDC (nominal) Loosely regulated off of the 5VDC feedback line, isolated from the

other transformer windings

IVDD +5VDC Linearly Regulated to provide an isolated digital and analog power

source

Table 9: Power Supply Outputs

3.3.6 Logic and Input / Output Signal Control

Refer to sheet 6 on 2764-03 schematic.
Chip selection for the serial peripherals are provided by decoders IC43 and IC46 and

by the inverters IC47, IC45E and IC45F. Latch IC41 is used mainly to control the
system pneumatics, with Latch IC42 providing additional control signals for the
2765-01 Analog Board. Input buffer IC44 allows the digital system to read various
status signals from the Analog Board.

3.4 Analog Board 2765-01

3.4.1 CAPNOSTAT Interface

Refer to sheet 1 on 2765-03 schematic.
A twenty pin connector, J2, interfaces the CAPNOSTAT with the system electronics.

Ferrite filters have been placed on all lines to suppress radiated EMI and reduce
susceptibility from high frequency external sources of interference.

Stable reference voltages for the sensors and analog circuitry are derived from IC1, a
precision 2.5V reference with low drift. Five Volt and 2.5 Volt references for the CO
and Saturation circuits are generated by IC2. Positive and negative supply rails for the
analog circuitry are derived from linear regulators IC6, IC7 and IC50, while regulators
IC3 and IC49 and provide regulated voltage supplies for the CAPNOSTAT itself.

3.4.2 CO2 Input Signal Path

Refer to sheet 2 on 2765-03 schematic.
The signals from the sensor CO2DATAIN (CO

Signal) have similar signal paths. The CO2DATAIN passes through a high pass filter
with a gain of 7.65 consisting of C60, R68 and buffer amplifier IC15B. The signal is fed
to a Butterworth low pass filter IC15A and associated components. This filter has a
gain of 2 with a corner frequency of 1.5 kHz. The output from the low pass filter is fed
to a 12-bit Digital to Analog converter IC14. The signal, CO2DFB comes into the
feedback pin of the DAC, which acts as a programmable gain stage. Here, under

NICO

Data) and CO2REFIN (Reference

2

2

20

Model 7300 Service Manual

Rev. 00

Analog Board 2765-01

Theory of Operation

3

processor control, the signal's gain is adjusted to an acceptable level for conversion.
The gain setting is adjusted using the digitized signal out of A/D Converter IC4 (sheet
1 on schematic) as part of the feedback loop. Similarly, CO2REFIN is conditioned by
high pass filter IC16B with a gain of 3.5 and low pass filter IC16A with a gain of 2. The
equivalent fixed gains for the two input signals are not equal in order to compensate for
differences in the output signal levels of the infra-red detectors in the CAPNOSTAT.

The output from DAC IC14 corresponding to signal CO2DATAIN is buffered by IC12A
and AC coupled through C49 to IC11A. The CO2DATA signal received from the
CAPNOSTAT is AC coupled prior to the high pass filter to remove any DC bias by C60.
Prior to sampling a CO

signal, the CO2AZ (Auto Zero) pulse turns Q1 on causing any

2

residual charge on C49 to discharge to ground. At the start of the source pulse, the
CO2AZ pulse goes Low and the CO

signal from the sensor is acquired. The signal is

2

buffered by IC11A before appearing at the input of the sample and hold amplifier,
IC13A. Near the end of the source pulse, the CO2SSH (CO

Sample and Hold) goes

2

Low and the peak signal is acquired on the internal sample and hold capacitor.
CO2SSH returns high at the end of the cycle, and the CO

signal on the sample

2

capacitor is held at the peak value. The signal then passes through a low pass filter and
resistive divider network consisting of R51, R53 and C51 before being converted by the
A/D Converter IC4 into digital data and analyzed by the processor. The signal CO2REF
follows an identical zeroing and acquisition path.

3.4.3 CO2 Case and Detector Heater Regulation

Refer to sheet 2 on 2765-03 schematic.
For the purpose of describing the regulation loop, the case heater circuitry will be

considered. The detector and case heater circuitry are identical.
Inside the CAPNOSTAT, a sensing thermistor is thermally connected to the heater

module. Initially, the CAPNOSTAT is at ambient temperature and the resistance of the
thermistor is large. A small current flows through the signal path CASETHERM and
only a small voltage is developed across R47. The microprocessor programs the TPU
to allow an initial maximum duty cycle of 70% to power the PWM heater circuitry. This
causes the heater control MOSFET on the NICO 2764-01 Power Board to be pulsed
on and off with a duty cycle that is under direct control of the program software. As the
heater warms up the case, the thermistor's resistance decreases, raising the voltage
appearing at the input of the control loop. As described below, the MPU looks at this
output voltage and decreases the duty cycle of the PWM control circuitry, gradually
reducing the power output into the heater. When the desired temperature set point is
reached, a balance is struck between the energy delivered into the system and the heat
flow out of the system.

The case thermistor is sensed by amplifier IC9B. The difference between the signal at
the non-inverting input and the reference appearing at the inverting terminal generates
an error voltage proportional to the sensed temperature at the amplifier's output:

eo (V) = [83.133V / (Rth+3.32K)] - 10.2V where eo = amplifier output voltage

Tem p (qC) = 4.1288 (qC/V) * e

This error voltage is low pass filtered by amplifier IC8B, sent to the ADC and processed
by the CPU to regulate the output pulses from the TPU. The error voltage out of
amplifier IC9B also appears at the temperature watchdog comparator IC10A. If the

V + 41.7321qC

o (T)

where eo = amplifier output voltage at

= resistance of the thermistor

R

th

= 4.36933K at 45qC

temperature T

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3 Theory of Operation

3.4.4 Flow Zeroing and Patient Line Purging

Analog Board 2765-01

error voltage reaches approximately 56 degrees Celsius, the comparator trips, causing
the output to go Low and turning off the heater supply on the Power Board.

Refer to sheet 5 on 2765-03 schematic.
The zero process begins when the CPU brings the VALVE1, VALVE2, VALVE3

VALVE4and VALVE6 lines high, energizing valves V1, V2, V3, V4 and V6. This action
disconnects the differential pressure transducer IC18 (via V1 and V2) and the absolute
pressure transducer IC29 (via V2) from the patient airway, shunts the differential
pressure sensor ports (V4), and opens all pressure transducer ports to atmosphere
through V3. Valve V6 switches the pump output from the external
internal patient tubing and flow sensor. The differential pressure transducer is “zeroed”
by capturing the digital output of the 20-bit sigma delta A/D Converter, IC25 (sheet 3
on schematic), during this zero flow condition, and using this value to set the software.
The patient airway pressure transducer is "zeroed" by adjusting the output of the DAC,
IC26 pin 10 (sheet 3 on schematic), until the Airway Pressure signal into the ADC, IC4,
reads mid-scale. The barometric (ambient) pressure, as sensed by IC28 (sheet 3 on
schematic), is recorded after the airway pressure zero is completed. IC30 acts to filter
the signals from the barometric pressure and airway pressure channels. After the result
from each channel is stored in SRAM to be used as an offset in the flow and pressure
calculations, valves V1, V2, V3, V4 and V6 are then de-energized, reconnecting the
pressure transducers with the patient airway.

If patient line purging is enabled by the software, the system turns on the pump by
bringing the PURGE line high after the zero values are recorded. A slight pressure is
allowed to build in the pump tubing line that will aid in flushing out the patient airway
tubing. To purge patient line 1, the CPU brings the VALVE1 and VALVE4 signals high,
energizing Valves V1 and V4. V1 connects the pump with the P1 patient line, flushing
out the patient P1 line while V4 shunts across the differential pressure transducer,
preventing a differential pressure from appearing across the transducer. During
purging, the system is able to monitor the pressure that is present in the selected
patient line by reading the AWPRESS signal. VALVE1 is brought low and V1 is the de­energized, once again isolating the pump from the patient airway and allowing a
pressure head to build once more. The VALVE2 line is then brought high and valve V2
is then energized, flushing out the patient P2 line. After all lines have been flushed out,
V1 and V3 are re-engerized allowing any residual pressure to be vented to
atmosphere. All valves are then de-engerized and the PURGE signal is brought low,
turning the pump off. The purging process is complete and normal patient monitoring
continues.

A hardware watchdog, consisting of IC44A and the surrounding circuitry, limits the
maximum pump-on time, preventing overpressure from building in the patient lines.

NICO

Valve to the

3.4.5 Flow Circuitry

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Model 7300 Service Manual

Refer to sheet 3 on 2765-03 schematic.
Differential Pressure Transducer, IC18, is a silicon based, piezoresistive bridge with

four active elements. When a pressure is applied between transducer ports P1 and P2,
a differential output voltage proportional to the applied pressure is produced. The full­scale output range for the transducer is 0 to 10 inches of water (P1>P2). By setting the
0 differential pressure (no-flow) point to mid-scale (during the zeroing process
described earlier), negative pressure readings (P2>P1) are also available. The
transducer is temperature compensated at 25 degrees Celsius and designed to be
driven by a constant voltage source.

Rev. 00

Analog Board 2765-01

Theory of Operation

In the normal system operating mode, all valves are de-engerized and the pump is
inactive. Transducer ports P1 and P2 are connected to the patient airway. As air flows
through the airway adapter pneumotach, a pressure difference between P1 and P2 is
created. This signal is dependent on both the magnitude and the direction of the airflow.
The greater the flow volume, the larger the pressure difference created between the
two transducer ports. The transducer senses an inspired flow as a positive pressure
difference (P1>P2), while an expiratory flow is seen as a negative pressure (P2>P1).
With a supply voltage of 2.5V, the sensor transforms this pressure difference into an
electrical signal with a nominal absolute magnitude of 23 mV Full-scale Output. This
signal is conditioned and amplified by IC23, which is a monolithic Instrumentation
Amplifier (IA). A positive pressure difference (inspiratory flow) creates a signal above
the no-flow zero baseline obtained during the zeroing process. A negative pressure
difference (expiratory flow) is below the set baseline. The nominal gain of IC23 is set
by fixed resistors R85, R83 and variable resistor VR1. The output for the transducer is
adjusted using VR1 and a known pressure input as a calibration reference. With an
input differential pressure of 20 cmH
count of 412160.

The signal out of the flow IA is taken through a two-pole low pass filter IC22A with a 31
Hz cutoff frequency to remove unwanted high frequency electronic noise. It is then
passed on to the 20-bit sigma delta ADC, where it is transformed from an analog
voltage into a digital code for processing by the CPU, located on the 2763-01 Digital
Board.

O, the gain of the amplifier is set to give an ADC

2

3

3.4.6 Barometric and Airway Pressure

Refer to sheet 3 on 2765-03 schematic.
IC29 is a piezoresistive differential pressure transducer with port P2 held at zero psi. It

measures the absolute pressure difference at port P1 relative to the vacuum at port P2.
The transducer is calibrated for a full scale output of 0 to 15 psi, has internal
temperature compensation, and is designed to be driven by a constant voltage source.
Instrumentation amplifier (IA) IC28 conditions this signal to correspond to the current
barometric pressure, which is set by adjusting VR3. The nominal gain of this amplifier
is 67, which corresponds to a 12-bit ADC count of 4012 at 760 mmHg. The output
signal from IC28 is low pass filtered by IC30B and appears as an input to both the 12­bit ADC and a second IA, IC27. IC27 provides gain adjustment via VR2 and offsets the
output signal from the barometric amplifier to mid-scale during the zeroing state. The
nominal gain of the airway pressure amplifier is 5. This signal connects to the P1
(proximal to the patient) side of the differential pressure transducer during monitoring
and provides patient airway pressure sensing.

3.4.7 Patient Airway Adapter Type Sensing

Refer to sheet 5 on 2765-03 schematic.
Given a specific flow sensor type (i.e., Adult), the physical characteristics of the sensor

will be consistent from one adapter to another. However, due to the differences in the
physical size and geometry of the various flow sensor types, each type (i.e., Adult,
Adult Combo) requires different coefficients be used in the calculation of flow. Each flow
sensor type has a unique 4-bit code associated with it. This pattern molded into the
connector body can be optically reflective or non-reflective and is read by the system.
A pulse is generated by the CPU that turns on the LED component of a opto-coupler
mounted directly beneath each pattern segment. If the pattern segment associated with
that opto-coupler is reflective, the LED's light will cause its photodetector mate to be
turned on, which generates a signal that is sensed by the system and relayed back to
the CPU. If the segment is non-reflective, no signal is returned to the sensing circuitry.

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3 Theory of Operation

3.4.8 NICO Sensor Rebreathing Valve Control

3.4.9 Saturation Input Signal Path and Signal Conversion

Analog Board 2765-01

A four-bit code can generate 16 unique pattern combinations. One code condition, all
zeros (no reflection), is reserved for detecting when the sensor unplugged. The circuitry
to decode the flow sensor type consists chiefly of connector J5 and comparator IC40.

Refer to sheets 3 and 5 on 2765-03 schematic.
To initiate a

rebreathing mode, valve V5 is energized, which switches the tubing to the external
valve from atmosphere to the pump. The pump is turned on, causing the diaphragm in
the
by pressure transducer IC32 and IA IC31. When adequate pressure to switch the valve
is reached, the pump turns off and the software continues to monitor the airline
pressure to ensure pressure is maintained. Valve V6 has a time-out watchdog, IC44B,
to ensure that software control over the external

Refer to sheet 4 on 2765-03 schematic.
On power up, the system performs a self-calibration cycle to establish the level of

background circuit offset. Calibration is performed by coordinating the control signals
SPO2CAL, SPO2SC1, ASAMPL, RSAMPL, ISAMPL, SIGNDL and INSIGL. Once the
system baseline has been acquired, the Red and Infrared ADCs, IC33 and IC37, adjust
their output to compensate for any system offsets found. Since the LED drives are
staggered, a single detector is used to multiplex the individual signals on a common
signal input line. Amplifier IC36B performs a current to voltage conversion on the input
signal, and analog switch IC35 steers the signal to the proper 20-bit ADC based upon
the LED channel (Red or Infrared) that is currently active. A sample and hold circuit for
each channel made up of IC35 and IC34 transform the pulsed input signal into a
constant voltage level for signal conversion. The main timing signal generation for
saturation signal acquisition is generated by the TPU. Amplifier IC38A generates an
analog signal, SPO2PROB, that varies with the saturation probe type. SPO2PROB is
converted to digital form by ADC IC9 on the

valve to switch to rebreathing mode. The pressure in the airline is monitored

NICO

cycle and switch the external

NICO

Valve from non-rebreathing to

NICO

valve is maintained.

NICO

2763-01 Digital Board Schematic.

NICO

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Model 7300 Service Manual

Rev. 00