Nellcor N-20, N-20P, N-20PA User manual

Service Manual

N-20/N-20P Portable Pulse Oximeter

Caution: Federal law (U.S.A.) restricts this device to sale by or on the order of a physician.

To contact Mallinckrodt’s representative: In the United States, call 1.800.635.5267 or 314.654.2000; outside the United States, call

your local Mallinckrodt representative.

0123

Mallinckrodt Inc. 675 McDonnell Boulevard P.O. Box 5840 St. Louis, MO 63134 USA Tel 314.654.2000 Toll Free 1.800.635.5267

Mallinckrodt Europe BV Hambakenwetering 1 5231 DD's-Hertogenbosch The Netherlands Tel +31.73.6485200

Nellcor Puritan Bennett Inc. 4280 Hacienda Drive Pleasanton, CA 94588 USA

Nellcor Puritan Bennett Inc. is a wholly owned subsidiary of Mallinckrodt Inc. Nellcor, Nellcor Puritan Bennett, Durasensor, Oxisensor II, Oxinet, Dura-Y, Oxiband, and Oxicliq are trademarks of Mallinckrodt, Inc.

To obtain information about a warranty, if any, for this product, contact Mallinckrodt's Technical Services Department, or your local Mallinckrodt representative.

Purchase of this instrument confers no expressed or implied license under any Mallinckrodt patent to use the instrument with any sensor that is not manufactured or licensed by Mallinckrodt.

Covered by one or more of the following U.S. Patents and foreign equivalents: 4,621,643; 4,700,708; and 4,770,179.

CONTENTS

1 Introduction.................................................................................................................................................... 1-1

1.1 Manual Overview ........................................................................................................................................ 1-1

1.2 Warnings and Cautions............................................................................................................................... 1-1

1.3 Description of N-20 Portable Pulse Oximeter ............................................................................................ 1-1

2 Routine Maintenance ..................................................................................................................................... 2-1

2.1 Overview...................................................................................................................................................... 2-1

2.2 Cleaning ...................................................................................................................................................... 2-1

2.3 Periodic Safety and Functional Checks ...................................................................................................... 2-1

2.4 Battery......................................................................................................................................................... 2-1

3 Performance Verification .............................................................................................................................. 3-1

3.1 Introduction................................................................................................................................................. 3-1

3.2 Required Materials...................................................................................................................................... 3-1

3.3 Performance Tests....................................................................................................................................... 3-1

4 Troubleshooting ............................................................................................................................................. 4-1

4.1 How to Use this Section............................................................................................................................... 4-1

4.2 Who Should Perform Repairs...................................................................................................................... 4-1

4.3 Replacement Level Supported ..................................................................................................................... 4-1

4.4 Obtaining Replacement Parts ..................................................................................................................... 4-1

4.5 Troubleshooting Guide................................................................................................................................ 4-1

4.6 Service Procedures...................................................................................................................................... 4-5

4.7 Error Codes................................................................................................................................................. 4-7

5 Disassembly Guide ......................................................................................................................................... 5-1

5.1 Introduction................................................................................................................................................. 5-1

5.2 Required Equipment/Tools.......................................................................................................................... 5-1

6 Spare Parts ..................................................................................................................................................... 6-1

6.1 N-20/N-20P Spare Parts ............................................................................................................................. 6-1

7 Packing for Shipment..................................................................................................................................... 7-1

7.1 General Instructions.................................................................................................................................... 7-1

7.2 Repacking in Original Carton..................................................................................................................... 7-1

iii

CONTENTS

8 Specifications .................................................................................................................................................. 8-1

8.1 Readout ....................................................................................................................................................... 8-1

8.2 Controls....................................................................................................................................................... 8-1

8.3 Operating Modes......................................................................................................................................... 8-1

8.4 Printer Output ............................................................................................................................................. 8-2

8.5 N-20/N-20P Performance............................................................................................................................ 8-2

8.6 Sensor Types................................................................................................................................................ 8-3

8.7 Electrical Specifications.............................................................................................................................. 8-3

8.8 Environmental Specifications...................................................................................................................... 8-4

8.9 Physical Specifications................................................................................................................................ 8-4

9 Technical Supplement.................................................................................................................................... 9-1

9.1 Overview...................................................................................................................................................... 9-1

9.2 Functional versus Fractional Saturation .................................................................................................... 9-1

9.3 Measured versus Calculated Saturation ..................................................................................................... 9-1

9.4 Circuit Analysis........................................................................................................................................... 9-2

9.5 Functional Overview................................................................................................................................... 9-2

9.6 SpO2 Analog Circuitry Block Diagram (Figure 9-3).................................................................................. 9-3

9.7 Definition of Terms...................................................................................................................................... 9-5

9.8 Overall Block Diagram ............................................................................................................................... 9-6

9.9 SpO2 Analog Circuitry................................................................................................................................ 9-7

9.10 Digital Circuitry ................................................................................................................................... 9-12

9.11 Support Illustrations............................................................................................................................. 9-30

FIGURES

Page Number

Figure 5-1: Sensor Lock, and Printer, Paper, and Battery Access Doors...........................................................5-2

Figure 5-2: N-20 Covers with the PCB and Display Assembly............................................................................ 5-3

Figure 5-3: Main, Auxiliary, and Display PCB Assembly.................................................................................... 5-4

Figure 5-4: Printer and Flex Circuit Installation.................................................................................................. 5-5

Figure 9-1: Oxyhemoglobin Dissociation Curve .................................................................................................. 9-2

Figure 9-2: Overall Block Diagram........................................................................................................................ 9-3

Figure 9-3: SpO2 Analog Circuitry Block Diagram............................................................................................. 9-3

Figure 9-4: Digital Circuitry Block Diagram........................................................................................................ 9-4

Figure 9-5: Power Supply Block Diagram............................................................................................................ 9-4

Figure 9-6: Display Control Block Diagram ........................................................................................................ 9-5

Figure 9-7: Printer Control Block Diagram......................................................................................................... 9-5

Figure 9-11: Variable Gain Circuit.................................................................................................................... 9-10

Figure 9-12: Filtering Circuit .............................................................................................................................. 9-11

Figure 9-4: Digital Circuitry Block Diagram...................................................................................................... 9-12

Figure 9-14: N-20 Hardware Block Diagram..................................................................................................... 9-14

CONTENTS

Figure 9-15: Address Demultiplexing Circuit .................................................................................................... 9-15

Figure 9-16: Address Decoding Circuit .............................................................................................................. 9-16

Figure 9-17: CPU Memory Circuit ..................................................................................................................... 9-17

Figure 9-18: Input Port Circuit ........................................................................................................................... 9-18

Figure 9-20: Real-Time Clock Circuit ................................................................................................................ 9-19

Figure 9-21: Audio Output Circuit ..................................................................................................................... 9-20

Figure 9-6: Display Control Block Diagram ...................................................................................................... 9-20

Figure 9-23: User Controls Circuit ..................................................................................................................... 9-22

Figure 9-26: Analog Reference Voltage Circuit................................................................................................. 9-25

Figure 9-27: Ambient Light Circuit.................................................................................................................... 9-25

Figure 9-28: Ambient Temperature Circuit ....................................................................................................... 9-26

Figure 9-29: Battery Voltage Circuit .................................................................................................................. 9-26

Figure 9-30: Battery Type Circuit....................................................................................................................... 9-26

Figure 9-32: Printer Flex Circuit ........................................................................................................................ 9-28

Figure 9-8: LED Drive Circuit ........................................................................................................................... 9-30

Figure 9-9: Differential Synchronous Demodulation Circuit .......................................................................... 9-30

Figure 9-10 N-20 HSO Timing Diagram............................................................................................................ 9-30

Figure 9-13: AC Variable Gain Control Circuits .............................................................................................. 9-30

Figure 9-19: Output Port Circuit ........................................................................................................................ 9-30

Figure 9-22: Display Control Circuit.................................................................................................................. 9-30

Figure 9-24: Power Supply Circuit ..................................................................................................................... 9-30

Figure 9-25: Power Control Circuit.................................................................................................................... 9-30

Figure 9-31: Printer Interface Circuit ................................................................................................................ 9-30

Figure 9-33: N-20 SpO2 Analog Block Diagram................................................................................................ 9-30

Figure 9-34: CPU Circuit..................................................................................................................................... 9-30

Figure 9-35: N-20 Main PCB Schematic Diagram............................................................................................. 9-30

Figure 9-36: N-20 Auxiliary PCB Schematic Diagram...................................................................................... 9-30

Figure 9-37: N-20 Flex Circuit Schematic Diagram .......................................................................................... 9-30

TABLES

Table 4-1: Microprocessor Error Codes............................................................................................................... 4-7

Table 8-1: Sensors................................................................................................................................................... 8-3

1 INTRODUCTION

1.1 Manual Overview

1.2 Warnings and Cautions

1.3 Description of the N-20 Portable Pulse Oximeter

1.1 Manual Overview

This manual contains service information for the Nellcor N-20/N-20P, that is necessary to maintain and repair the N-20/N-20P by qualified service personnel. Note that models designated for sale in Europe differ from models designated for sale in the USA only in that the user control buttons and display use icons rather than alphabetical characters, and that the product labels reflect the appropriate European certifications and company addresses.

1.2 Warnings and Cautions

"WARNING" is used to call attention to procedures that could result in an error in calibration or performance, and/or precautions that are important to ensure the safety of both service personnel and patients.

"CAUTION" is used to call attention to procedures that should be carefully followed to prevent damage to the instrument.

1.3 Description of N-20 Portable Pulse Oximeter

portable pulse oximeter, models

The Nellcor portable pulse oximeters model N-20 (without printer) and N-20P (with printer) provide noninvasive and continuous information about the percent of oxygen that is combined with hemoglobin (SpO

) and pulse rate. A pulse amplitude indicator provides a qualitative indication of

pulse activity and patient perfusion. These instruments can be operated in either spot-check mode (single-measurement), or extended-measurement mode (30 minutes of data). Patients are connected to the instrument by a Nellcor oximeter sensor. The sensor LEDs are driven by the SpO

analog section,

which also conditions the incoming signals, and provides CPU adjustable gains stages. The CPU measures the sensor's analog outputs, continually controls the gain stages, and calculates SpO

The N-20/N-20P is automatically calibrated each time it is switched on, and whenever a new sensor is connected; it sets sensor-specific calibration coefficients by reading a calibration resistor in the sensor. Also, the intensity of the sensor's light sources is adjusted automatically to compensate for differences in tissue thickness and skin color.

Standard user controls consist of a Measure button and a Check-Battery button. The Measure button signals the power control circuit to switch on the power supply. The power supply then provides regulated power to the unit. Once power is on, the CPU reads both the Measure and Check-Battery buttons for user commands.

The N-20P printer provides a hard copy of acquired patient measurements. The printer circuit includes three user control buttons: ON (on/off), ADV (advance), and D/D (day/date). In addition, an ambient temperature sensor is used with the battery voltage input to control printout quality.

1-1

2 ROUTINE MAINTENANCE

2.1 Overview

2.2 Cleaning

2.3 Periodic Safety and Functional Checks

2.4 Battery

2.1 Overview

The N-20/N-20P requires no routine maintenance, routine service, or calibration. If service is necessary, contact qualified service personnel or Mallinckrodt’s representative. Use only Mallinckrodt-approved test equipment when running a performance test on the N-20/N-20P. The user's institution and/or local or national agencies may require testing.

2.2 Cleaning

Dampen a cloth with a commercial, nonabrasive cleaner, and lightly wipe the surfaces of the N-20/N-20P. Do not spray or pour liquid on the instrument or accessories. Do not allow liquid to contact connectors, switches, or openings in the chassis.

2.3 Periodic Safety and Functional Checks

The following checks should be performed at least every 2 years by a qualified service technician.

Inspect the exterior of the N-20/N-20P for damage.

Inspect safety labels for legibility. If the labels are not legible, contact Mallinckrodt Technical Services Department or your local Mallinckrodt representative.

2.4 Battery

When the N-20/N-20P is going to be stored for 3 months or more, remove the battery prior to storage. To replace or remove the battery, refer to Section 5, Disassembly Guide.

2-1

3 PERFORMANCE VERIFICATION

3.1 Introduction

3.2 Required Materials

3.3 Performance Tests

Caution: Adhere to all testing instructions; failure to do so may damage the N-20/N-20P.

3.1 Introduction

This section describes performance verification for the N-20 and N-20P pulse oximeters (hereafter called the “monitor”), following repairs. The N-20/N-20P are powered by alkaline batteries. The N-20/N-20P design includes built-in electrical insulation; no ground resistance or electromagnetic leakage testing is required.

The tests can be performed without removing the monitor cover. If the monitor fails to perform as specified in any test, repairs must correct the discrepancy before the monitor is returned to the user.

3.2 Required Materials

Durasensor Nellcor DS-100A

Tester, Pulse Oximeter Nellcor SRC-2

3.3 Performance Tests

The N-20/N-20P will operate in conjunction with the Nellcor® pulse oximetry tester, model SRC-2, to test instrument performance. The SRC-2 plugs into the DB-9 sensor connector and uses the instrument's power supply and diagnostic software to test the display and the operation of the instrument. Refer to the operator's manuals for the SRC-2 for details on performance testing with the SRC-2.

Other tests, which are outlined below, include the display backlight test, the low battery indicator test, the power-up self-test, and the thermal printer test (printer test applies only to N-20P).

3.3.1 Backlight Test

The electroluminescent backlight illuminates the display in three sections: (1) the main section, i.e., the Oxygen Saturation and Pulse Rate display fields, and the 14-segment pulse rate amplitude indicator; (2) the Low Battery indicator, and (3) Pulse Search indicators each have their own backlight. All backlights flash once during Power-On Self-Test.

The ambient light detector is located underneath a small circular window in the top right corner of the N-20/N-20P display. Under low light conditions, the main section backlight is switched on. If a Low Battery and Pulse Search indicator are lit, the monitor’s backlight is also lit.

To test for proper operation of the display backlight, observe the N-20/N-20P in a darkened room. If any backlight section is not working correctly, contact Mallinckrodt's Technical Services Department or Mallinckrodt's local representative for assistance.

3.3.2 Battery Performance

This test is provided to verify that the monitor will operate for the period specified.

The monitor is specified to operate on battery power as follows:

3-1

Performance Verification

N-20 (no printer) 37 hours with Alkaline batteries.

N-20/P (with printer) 32 hours with Alkaline batteries.

This test requires a new set of batteries. The new batteries must be installed after the test.

Connect the Nellcor SRC-2 pulse oximeter tester to the monitor. Set the switches on the SRC-2 as follows:

Switch Setting

RATE 38

LIGHT LOW

MODULATION LOW

RCAL/MODE RCAL 63/LOCAL Momentarily press the MEASURE button, and verify the following power-up sequence:

All indicators—OXYGEN SATURATION, PULSE RATE, PULSE SEARCH, LOW BATTERY, and the PULSE BARS—light for a few seconds. Verify the OXYGEN SATURATION, and PULSE RATE displays indicate "888.” The OXYGEN SATURATION display momentarily indicates the monitor 3-digit software version. The other displays are not lit. Software versions may vary depending on the type of monitor and the date of manufacture.

The N-20P will display printer status immediately after displaying the software version. The OXYGEN SATURATION display will indicate “Pr”and the PULSE RATE display will indicate either “On” or “OFF.”

The OXYGEN SATURATION display momentarily indicates the letters ”tSt” and the monitor sounds a single tone. The other displays are not lit. “tSt” verifies that the monitor recognizes that a tester is connected.

The OXYGEN SATURATION and PULSE RATE displays indicate “0,” the PULSE SEARCH indicator is flashing, and the PULSE BAR will start to register the simulated pulse.

After a few beats a pulse tone will be heard, and the PULSE SEARCH indicator will turn off. The OXYGEN SATURATION display indicates between 79 and 83, and the PULSE RATE display indicates between 37 and 39.

The monitor must operate for at least 37 hours if the printer is not turned on.

Verify that the LOW BATTERY indicator lights steadily sometime after 30 hours of operation.

Verify that the monitor turns off approximately 1 hour after the LOW BATTERY indicator starts flashing.

Allow the monitor to continue operation until power-down due to low battery.

3.3.3 Power-Up Performance

Monitors with the same software must demonstrate identical startup routines. The power-up tests verify the self-test function.

When an N-20/N-20P is switched on, a sequence of diagnostic tests is run that examines the instrument electronics and display functions. This power-on self-test consists of the following events:

3-2

Immediately after power is switched on, the instrument simultaneously:

Displays the number "8" in all six Oxygen Saturation and Pulse Rate display field segments;

•

Illuminates all 14 pulse rate amplitude indicator segments;

•

• Illuminates the Pulse Search and Low Battery indicators; and

Illuminates the display backlight.

•

During the next few seconds, the instrument:

Switches off the display backlight;

•

• Displays three digits in the Oxygen Saturation display field representing the software version (for

example, 123 is software version 1.2.3).

• Only the N-20P displays the printer status in the display fields; that is, either "Pr On" or "Pr OFF."

If a sensor is attached to the instrument, a zero ("0") appears in first position of the display fields. The Pulse Search indicator flashes; if no sensor is attached to the instrument, horizontal dashes appear in all six Oxygen Saturation and Pulse Rate display fields, and the Pulse Search indicator flashes.

After approximately 1 minute, a short beep occurs and the instrument automatically switches off.

If at any time during the test sequence "Err" followed by a code number is displayed, make a note of the error code and refer to Section 4.7, Error Codes, for a description.

3.3.3.1 How To Run the Self-Test

Place a new set of batteries in the monitor.

Do not connect a sensor or SRC-2 to the monitor.

Momentarily press the MEASURE button, verify the following power-up sequence:

Performance Verification

All indicators—OXYGEN SATURATION, PULSE RATE, PULSE SEARCH, LOW BATTERY, and the PULSE BARS—light for a few seconds. Verify that the OXYGEN SATURATION and PULSE RATE displays indicate "888."

The OXYGEN SATURATION display momentarily indicates the monitor 3-digit software version. The other displays are not lit.

Software versions may vary depending on the type of monitor and the date of manufacture.

The N-20P will display printer status immediately after it displays software version. The OXYGEN SATURATION display will indicate “Pr” and the PULSE RATE display will indicate either “On”or “OFF.”

OXYGEN SATURATION and PULSE RATE display dashes (– – –) in each window, the monitor sounds a single tone, and the PULSE SEARCH indicator is flashing. The other displays are not lit.

Verify that the monitor automatically turns off after 60 seconds.

If the Measure button was held down for more than 3 seconds (extended mode), the monitor will not turn off after 60 seconds but will operate for approximately 3 minutes before automatically turning off.

3.3.4 Printer Test

The following procedure applies to the N-20P only.

The SRC-2 must be used to test the operation of the N-20P printer and the printer's user-control buttons. When an SRC-2 is plugged into the DB-9 connector, the N-20P does not respond to button presses during Power-On Self-Test; however, it does acknowledge any button press after the self-test with an immediate beep and the following display codes:

Button Press Display

Measure 9O battery check bAt

3-3

Performance Verification

ON On ADV Ad D/D dd

combinations Err

1. Press the Measure button: "9O" appears in the Oxygen Saturation display.

2. Press the Battery-Check button: "bAt" appears in the Oxygen Saturation display.

3. Press the printer ON button: "On" appears in the Oxygen Saturation display. A

printer test pattern prints out; the following is an approximate example of the test pattern:

Examine the test pattern to verify that all dots print with a uniform darkness. Overall printout darkness can be adjusted; to adjust printer darkness, see paragraph 4.6.7. If printout darkness is either irregular or dots are missing, contact Mallinckrodt's Technical Services Department or Mallinckrodt's local representative for assistance.

1. Press the printer ADV button. “Ad” appears in the Oxygen Saturation display. Paper advances

one line for each button press.

2. Press the printer D/D button: "dd" appears in the Oxygen Saturation display.

3. End SRC-2 printer test.

3.3.5 Hardware and Software Tests

Hardware and software tests include the following:

Operation with a Pulse Oximeter Tester

Normal Operation

3.3.5.1 Pulse Oximeter Tester

1. Connect the Nellcor SRC-2 pulse oximeter tester to the monitor.

2. Set the switches on the SRC-2 as follows:

Switch Setting

RATE 38

LIGHT LOW

MODULATION LOW

RCAL/MODE RCAL 63/LOCAL

3-4

3. Momentarily press the MEASURE button, and verify the following power-up sequence:

Performance Verification

4. All indicators—OXYGEN SATURATION, PULSE RATE, PULSE SEARCH, LOW

BATTERY, and the PULSE BARS—light for a few seconds. Verify that the OXYGEN SATURATION and PULSE RATE displays indicate "888.”

5. The OXYGEN SATURATION display momentarily indicates the monitor 3 digit software

version. The other displays are not lit.

6. Software versions may vary depending on the type of monitor and the date of manufacture.

The N-20P will display printer status immediately after software version display. The OXYGEN SATURATION display will indicate “Pr,” and the PULSE RATE display will indicate either “On” or “OFF.”

The OXYGEN SATURATION and PULSE RATE displays indicate “0,” the PULSE SEARCH indicator is flashing, and the PULSE BAR will start to register the simulated pulse.

After a few beats a pulse tone will be heard, and the PULSE SEARCH indicator will turn off. The OXYGEN SATURATION display indicates between 79 and 83 and the PULSE RATE display indicates between 37 and 39.

3.3.6.2 Normal Operation

These tests are an overall qualitative check of the system and require connecting a live subject to the monitor:

Connect a DS-100A Sensor to monitor. Place the DS-100A Sensor on the subject as recommended in the monitor Operator's Manual. Press the Measure button for at least 5 seconds to turn on the monitor. The monitor should stabilize on the subject's physiological signal in about 10 to 15 seconds. Verify that the saturation value and pulse rate are acceptable.

3-5

Performance Verification

TEST RESULTS

Model: N-20 Serial:_____________________________

Date:___________Customer Name:________________________________

Description Pass Fail

Performance Tests _____ ____

Backlight Test _____ ____

Battery Performance _____ ____

Testing the Low Battery Indicator _____ ____

Power-Up Performance _____ ____

How to Run the Self-Test _____ ____

Printer Test _____ ____

Pulse Oximeter Test _____ ____

Normal Operation _____ ____

I certify that the monitor listed in this form has successfully passed all of these tests.

Technician:_________________________________________________Date:____________

I certify that the above signed technician has performed the tests listed on this form and the monitor performs satisfactorily.

Support Center Manager:___________________________________________________Date:____________

3-6

4 TROUBLESHOOTING

4.1 How to Use This Section

4.2 Who Should Perform Repairs

4.3 Replacement Level Supported

4.4 Obtaining Replacement Parts

4.5 Troubleshooting Guide

4.6 Service Procedures

4.7 Error Codes

WARNING: Disassembly of the instrument exposes hazardous voltages. To avoid injury or instrument damage, disassembly or maintenance must be attempted only by qualified service personnel.

4.1 How to Use this Section

This section explains how to identify and correct monitor difficulties and provides procedures for common service-related activities, such as battery replacement, clearing paper jams, and adjusting printer darkness.

Use this section in conjunction with Section 3, To remove and replace a part you suspect is defective, follow the instructions in Section 5, Disassembly Guide. The functional circuit analysis, located in the Technical Supplement at the end of this manual, offers information on how the device functions, as well as part locator diagrams and detailed schematic diagrams.

4.2 Who Should Perform Repairs

Only qualified service personnel should open the device housing, remove and replace components, or make adjustments. If your medical facility does not have qualified service personnel, contact Mallinckrodt Technical Services.

4.3 Replacement Level Supported

The replacement level supported for this product is to the printed circuit board (PCB) and major subassembly level. Once you isolate a suspected PCB, replace the PCB with a known good PCB. Check to see that the trouble symptom disappears and the device passes all performance tests. If the trouble symptom persists, swap the replacement PCB and the suspected malfunctioning PCB (the original PCB that was installed when you started troubleshooting) and continue troubleshooting as directed.

4.4 Obtaining Replacement Parts

Mallinckrodt Technical Services provides technical assistance information and replacement parts. To obtain replacement parts, contact Mallinckrodt. Refer to parts by the part names and part numbers listed in Section 6,

Spare Parts

Performance Verification

, and Section 6,

Spare Parts

4.5 Troubleshooting Guide

This section discusses potential symptoms, possible causes, and actions for their resolution. Should this troubleshooting guide fail to address the symptoms evident in a particular N-20/N-20P, please

4-1

Troubleshooting

contact Mallinckrodt's Technical Services Department or a local Mallinckrodt representative for assistance.

If the N-20/N-20P does not perform as expected:

Check for proper sensor placement.

•

• Depending on concentration, indocyanine green, methylene blue, and other intravascular dyes

may affect the accuracy of a measurement.

• These instruments are calibrated to read oxygen saturation of functional arterial hemoglobin

(saturation of hemoglobin functionally capable of transporting oxygen in the arteries), and significant levels of dysfunctional hemoglobins such as carboxyhemoglobin or methemoglobin may affect the accuracy of a measurement.

If the electronics and/or display functions require testing, refer to Section 3,

Battery access door may not be properly latched. Check access door and ensure it is properly

Batteries may be discharged. Exchange them for a new set.

Batteries may be incorrectly installed. Ensure that batteries are oriented according

Batteries may not be making proper electrical contact. Inspect contacts for deformity; clean contacts

Fuse F1 on the auxiliary PCB may be open. See paragraph 4.6.5, Fuse Replacement.

Dust may have accumulated under Measure button causing loss of electrical contact.

Performance Verification

Symptom 1: No response to Measure button.

Cause Action

latched.

to the polarity indicator.

to remove oxidization.

Clean contact points under Measure button (see Section 5.3,

N-20 Disassembly Guide).

4-2

Troubleshooting

Symptom 2: Pulse Search indicator appears for more than 5-10

seconds.

Cause Action

Sensor may be improperly positioned. Ensure the sensor is correctly applied (see

sensor directions for use).

Incorrect sensor may be in use. See sensor directions for use to ensure that

the patient's weight and sensor application is correct. Test the sensor on another person to verify proper operation.

Perfusion may be too low. Check patient status. Test the instrument on

someone else, or try another type of sensor. The N-20/N-20P will not make a measurement if perfusion is inadequate.

Foreign material on the sensor LEDs or photodetector may be affecting performance.

Patient motion may be interfering with the instrument's ability to find a pulse pattern.

Environmental motion may be interfering with the instrument's ability to track a pulse

The sensor may be too tight, there may be excessive illumination (e.g., a surgical or bilirubin lamp or direct sunlight), or the sensor may be placed on an extremity with a blood pressure cuff, arterial catheter, or intravascular line.

The DB-9 sensor connector on the N-20/N-20P may be broken.

Clean the test area and ensure that nothing blocks the sensor site.

If possible, ask the patient to remain still. Verify that the sensor is securely applied and replace it if necessary, move it to a new site, or use a sensor that tolerates patient movement, such as an appropriate adhesive sensor.

Replace the DB-9 connector (Section 4.6.6).

Symptom 3: Pulse Search indicator appears after successful

measurements have been made.

Cause Action

Patient perfusion may be too low. Check patient status. Test the instrument on

someone else, or try another type of sensor. The N-20/N-20P will not make a measurement if perfusion is inadequate.

Patient motion may be interfering with the instrument's ability to find a pulse pattern.

Environmental motion may be interfering with the instrument's ability to track a pulse.

Symptom 4: Dashes (– – –) appear in the display.

Cause Action

The sensor is not connected to the instrument. Check all sensor connections; try substituting

another sensor. Check all extension cables. If an extension cable is in use, remove it and plug the sensor directly into the instrument.

Symptom 5: Pr Err is displayed during the Power-On Self-Test (N-20P only).

4-3

Troubleshooting

Cause Action

The printer is not operational, but the N-20P continues to obtain patient measurements.

Check to see if the paper is jammed. Examine the print head and ensure that it has returned to the home position.

Symptom 6: Err followed by a number appears on the display.

Cause Action

See Section 4.7 for error codes. Record the number that is displayed.

Symptom 7: Time or date is incorrect (N-20P only).

Cause Action

The real-time clock (RTC) battery may be exhausted. Replace the RTC battery (see Section 4.6.4).

Reset the time and date (see Section 4.6.3).

Symptom 8: Printer fails to operate (N-20P only).

Cause Action

Fuse F2 on the auxiliary PCB may be open. See paragraph 4.6.5 for information about

fuses.

Symptom 9: Printer paper advances but instrument does not print (N-20P only).

The thermal paper may be improperly loaded; characters can be printed on only one side of the thermal paper roll.

Symptom 10: Paper mechanism jams (N-20P only).

Note: If a printer paper jam is detected during Power-On Self-Test, Pr Err may appear on the display.

4.6 Service Procedures

Cause Action

Ensure that the thermal paper is properly loaded; if needed, remove the roll of printer paper and reload the printer paper.

Cause Action

Switch off the N-20P. Then check to see if the print head is at the home position; if so, attempt to pull the paper out by pulling gently—do not force it.

If the print head is not at the home position, and the paper cannot be easily pulled out from the printer, then the printer may need to be disassembled to remove the paper jam (see Sections 5.3,

Procedure, Printer Paper).

N-20 Disassembly

and 4.6.2,

Loading/Clearing

4-4

The following service procedures are most likely to be encountered by the service technician. The PCB designation for a component appears in parentheses, for example, (BT1) or (U15).

4.6.1 Installing Batteries

1. Remove the battery cover access door by pressing the battery compartment access door latch.

Install four alkaline "C" cell batteries. Be sure to observe the polarity indicator sticker.

3. Replace the battery cover access door.

4.6.2 Loading/Clearing Printer Paper

The N-20P uses a thermal paper that can show printed characters on one side only. Make sure that the paper roll is correctly installed; always refer to the graphical instruction label found on the paper roll.

1. Press down and outward on the top of the paper compartment door to remove it.

2. Feed the paper into the paper compartment slot; refer to the graphic label for orientation.

3. Press and hold the ADV button until the end of the paper appears at the paper exit slot.

4. Replace the paper compartment door.

If the paper jams either during the loading process or during printing, proceed as follows:

1. Remove both the paper door and the printer-head access cover.

2. Firmly grab and pull the paper roll backward—out and away from the print head—observe

the access to the print head to determine whether or not the paper escaped from the jammed position.

3. If paper remains jammed between the print head and printer, press the ADV button; the

jammed paper may work its way out. If the paper remains jammed, and the printer drive does not advance the paper, manually advance the drive gear on the side of the printer to free the paper.

4. If these attempts fail to free the jammed paper, remove the printer from the unit to gain full

access (see paragraph 5.3, N-20 Disassembly Procedure).

Troubleshooting

4.6.3 Setting Date and Time

The following procedure applies to the N-20P only.

The following code letters and numbers appear in both Oxygen Saturation and Pulse Rate display fields. The symbol "xx" represents information in the Oxygen Saturation display field and "yy" represents information in the Pulse Rate display field.

Begin this procedure by first removing any sensor from the instrument.

Turn on the monitor without the sensor connected. Switch on the N-20P and allow the unit to run the Power-On Self-Test.

2. When dashes appear in the Oxygen Saturation and Pulse Rate displays, press the D/D

(day/date) button once. At this point, the Oxygen Saturation display field shows "txx", with "t" representing time; "xx" representing hours, and "yy" representing minutes. Note that "xx" (hours) is flashing.

Press the ADV (advance) button repeatedly until the correct hour is displayed. Press the D/D button once. Note that "yy" (minutes) is now flashing.

5. Press the ADV button repeatedly until the correct minute is displayed.

6. At this point, the Oxygen Saturation display field shows "dxx", with "d" representing date;

"xx" representing the month, and "yy" representing the date. Note that "xx" (month) is flashing.

Press the ADV button repeatedly until the correct month is displayed.

8. Press the D/D button once. Note that "yy" (date) is flashing.

9. Press the ADV button repeatedly until the correct date is displayed.

10. Press the D/D button. At this point, the Oxygen Saturation display field shows "Yxx", with

"Y" representing "year.” Note that "xx" (year number) is flashing.

11.

12.

Press the ADV button repeatedly until the correct year number is displayed. Press the D/D button once. The N-20P turns itself off within 5 seconds.

4-5

Troubleshooting

13. Date and time are now correct. Check by switching on the N-20P with the printer enabled.

After the N-20P executes its Power-On Self-Test, the printer prints the spot check mode header with the correct date and time.

4.6.4 Replacing the Real-Time Clock (RTC) Battery

The socket for the RTC battery (BT1) is located on the auxiliary PCB at grid location 5D. Typical life of the clock battery is 5 years.

1. Disassemble the N-20 (see Section 5.3, N-20, Disassembly Procedure).

2. Using a thin flathead screwdriver, gently pry the RTC battery from its socket.

Insert a new battery into the socket, observing the polarity indication (socket's clip and battery's flat side are positive).

4. Reassemble the unit.

5. Reset the clock (see paragraph 4.6.3, Setting Date and Time).

4.6.5 Replacing Fuses

Two fuses (F1 and F2) are located on the auxiliary PCB. Fuse F1 may open to protect the CPU and its associated components from damage if the power supply malfunctions. Fuse F2 may open to protect the printer from damage due to excessive voltage if the printer head jams or has been physically damaged. Refer to the auxiliary PCB schematic for the locations of F1 and F2.

4.6.6 Replacing the DB-9 Connector

1. Disassemble the N-20 (see Section 5.2); the connector is on the main PCB at grid location 3A.

2. Using a low-power soldering iron, unsolder the connector from the PCB and remove it. Save all

Teflon tubing, ferrite blocks, and insulating materials for the replacement connector.

3. Install ferrite blocks between plastic lead spacer on the connector and the PCB.

4. Insulate connector pin numbers 2, 3, and 5 with Teflon tubing, and insert inside ferrite block.

5. Add insulating material between each end of ferrite block and PCB, and secure with Loctite glue.

6. Solder new connector to PCB and visually check PCB for stray drops of solder before

reassembling.

7. Switch on the N-20/N-20P and test the connector with a patient sensor.

4.6.7 Adjusting Printer Darkness

Caution: Adjust the printer darkness setting until the lightest legible print is visible.

Setting the print darker than this could reduce the life of the printer-head. Although the N-20P is designed to automatically compensate for conditions that might influence the quality of the printout, the user may want to adjust the print darkness. The normal darkness setting is set at the factory; this setting maximizes both readability and life of the printer-head.

1. Switch on the N-20P in spot check mode. (Depressing the instrument Measure button once starts

Spot-check mode.)

2. Simultaneously press and hold the ADV and ON buttons for 2 seconds. If these buttons are not

pressed at the same time, two audible beeps will sound and the N-20P either advances the paper or switches off, depending on which button press is first sensed. If the buttons are pressed at the same time, a single audible beep will sound, Pr SEt is displayed, and the printer prints one of the following 6 lines:

4-6

PRINTING LIGHTER (10% lighter than normal darkness) PRINTING LIGHT (5% lighter than normal) PRINTING NORMAL (normal darkness) PRINTING DARK (5% darker than normal) PRINTING DARKER (10% darker than normal) PRINTING DARKEST (15% darker than normal)

Note: The parenthetic line description is not printed, and button presses are ignored whenever the printer is printing.

1. Press the ADV button to change the darkness setting. The printer prints a line with each button

press, and the setting increments from lighter to darkest and then wraps back to lighter.

2. Allow the N-20P to switch off (about 30 seconds). The last print darkness setting is remembered when the N-20P is switched back on. Test this by repeating the procedure and skipping step 3.

4.7 Error Codes

If a failure is detected during the Power-On Self-Test or during any performance test, the error message (Err) appears in the Oxygen Saturation display and a 3-digit error code number appears in the Pulse Rate display.

If an error message appears, find its category (the first digit of the error code represents the category) and record the error code number. Match the number to the description in the following table, and contact Mallinckrodt's Technical Services Department or Mallinckrodt's local representative for assistance.

Internal tests are performed in the order of the table listing. The first error condition encountered is the one displayed.

4.7.1 Category 1 — Microprocessor Errors

Troubleshooting

Table 4-1: Microprocessor Error Codes

Errors in the CPU (main PCB). Likely action is replacement of the CPU.

101 Error in internal RAM registers test

102 Error in zero register test

103 Error in register contents clearing test

104 Error in register contents increment test

105 Error in register contents decrement test

106–109 Errors in logical operations test

110 Error in exchange test

111 Error in timer tests

112 Error in window select register test

113, 114 Errors in stack manipulation test

115–117 Errors in CPU flags test

118 Error in interrupt pending register test

119 Error in program counter test

120 Error in CPU serial port test

121 Error in pulse width modulation register test

122 Error in A/D register test

123 Error in addressing modes test

124 Error in high speed input register test

125 Error in content addressable memory test

126–129 Errors in arithmetic operations test

4.7.2 Category 2 — RAM Memory Errors

Errors in RAM memory (main PCB). Likely action is replacement of the main PCB.

4-7

Troubleshooting

201–203 Errors in external RAM test

4.7.3 Category 3 — PROM Errors

Errors in PROM memory (main PCB). Likely action is replacement of the PROM.

301 Error in PROM test

4.7.4 Category 4 — I/O Port Errors

Errors in the CPU's internal I/O port (main PCB). Likely action is replacement of either the CPU or the main PCB.

401–409 Errors in I/O port test

4.7.5 Category 5 — Reserved

4.7.6 Category 6 — Clock Errors

Failure of the real-time clock (auxiliary PCB), or timing differences between the CPU’s clock and the real-time clock. Likely action is replacement of the main or auxiliary PCB.

601 Failure of real-time clock

602, 603 Errors in real-time clock

4.7.7 Category 7 — Watchdog-Timer Errors

Error in the watchdog-timer circuit of the CPU (main PCB). Likely action is replacement of the CPU.

701, 702 Errors in watchdog-timer

4.7.8 Category 8 — Printer Errors

Error in the printer (see Section 5.1, Troubleshooting).

If a printer error condition occurs, no error code number will display, rather the display reads Pr Err.

4-8

5 DISASSEMBLY GUIDE

5.1 Introduction

5.2 Required Equipment/Tools

5.3 N-20 Disassembly Procedure

5.4 N-20P Disassembly Procedure

WARNING: Only qualified service personnel must perform repair and testing. Improper repair and/or adjustment may compromise patient safety or the accuracy of the instrument.

5.1 Introduction

The N-20/N-20P can be disassembled down to all major component parts, including:

• PCBs battery

•

• cables

• chassis enclosures

WARNING: Before attempting to open or disassemble the N-20/N-20P, disconnect the power cord.

Caution: Observe ESD (electrostatic discharge) precautions when working within the unit.

Note: Some spare parts have a business reply card attached. When you receive these spare parts, please fill out and return the card.

5.2 Required Equipment/Tools

Screwdriver, Phillips-head, small

•

Screwdriver, Phillips-head, medium

•

Pliers, long nose

•

• Screwdriver, small flathead

• Soldering iron, low-power

Screwdriver, small blade

•

Needle-nose pliers

•

5.2.1 N-20 Disassembly Procedure

Whenever repair or disassembly is required, always wear a ground strap connected to active ground. Before any disassembly or service procedure, switch instrument power off.

5-1

Disassembly Guide

Figure 5-1: Sensor Lock, and Printer, Paper, and Battery Access Doors

1. Remove the battery door (19) and batteries.

2. Remove the sensor lock (34) by lightly pressing in on its ears and pulling out from the sensor shroud.

3. Remove the paper door (20) and paper roll, and the printer door (21).

5-2

5.2.2 Removing the Covers

Disassembly Guide

27 26

Figure 5-2: N-20 Covers with the PCB and Display Assembly

1. Remove screw cap (30), and loosen the captive screw (31), which secures the rear cover (15).

2. Separate the front cover (16) from the rear cover by wedging a thin flathead screw driver between the covers at the base of the instrument and slowly prying them apart.

Note: The covers are hinged at the top end in a different way; do not attempt to separate the covers using this technique at the top of the instrument. Once the covers are separated at the bottom end, lift away the bottom end of the front cover first, allowing the tabs at the top end to act as a hinge.

5-3

Disassembly Guide

5.2.3 Removing the PCBs and Display Assembly

Tab #1

Flex #1

Flex #3

Tab #3

Flex #2

Tab #4

Tab #2

11 12

13 26

Detail B

Detail A

Figure 5-3: Main, Auxiliary, and Display PCB Assembly

1. Remove the Measure button (6) from the main PCB.

2. Remove the entire PCB/Taliq display assembly from the rear cover by tilting opposite the Battery-Check button (5).

3. Raise the locking tabs on the connectors (11, 12, and 13) to release the cable, on the auxiliary PCB (26), and remove the three flex display circuits.

4. Separate the auxiliary PCB from the main PCB (27) by pulling the PCB headers apart at the base.

5. Remove the display assembly (18) from the main PCB by unsoldering the four tabs that are physically bent around the main PCB. These tabs are bent to ensure contact with the ground plane of the main PCB.

6. Using a long-nose plier, remove the display assembly by untwisting the four tabs (see Detail A and B).

5.2.4 N-20P Disassembly Procedure

1. Remove the paper door (20) and any printer paper by firmly grasping the paper roll, and pulling the roll outward from the printer.

2. See paragraphs 5.2.1 and 5.2.2, N-20 Disassembly Procedure, for removal of covers, PCBs, and the display assembly.

5-4

5.2.5 Disassembling the Printer/Flex Circuit Assembly

Disassembly Guide

Figure 5-4: Printer and Flex Circuit Installation

1. Remove the printer button retaining plate (37) by sliding it away from the case assembly.

2. Disconnect the two flex-circuit headers of the printer (29) from the connectors on the printer flex circuit (28) by slowly pulling outward from side to side at alternating ends of the connectors.

3. Remove the printer button strip (7) from the printer flex-circuit.

4. Remove the printer flex-circuit insulator (24).

5. Remove printer hold-down bracket (4) from the back cover by removing the Phillips screw (32).

6. Press the printer hold-down bracket into the back cover and remove the printer.

5-5

6 SPARE PARTS

6.1 N-20/N-20P Spare Parts

To order replacement parts, contact Mallinckrodt's Technical Services Department and order by part number. Item numbers correspond to the callout numbers in the figures.

Item Designator Description P/N

1 SW1 Battery switch (auxiliary PCB) 630106

2 BT1 Battery holder (auxiliary PCB) 901582

3 BT1 Battery, lithium (auxiliary PCB) 640112

4 Bracket, printer, hold-down 023133

5 Button, battery-check 023301

6 S2 Button, measure 022948

7 Buttons, printer, strip 022947

9 Connector shield, DB-9 023467

10 P1 Connector, DB-9 463103

11 JP17, JP18 Connector, pin header 10x2, low profile (auxiliary PCB) 491244

12 JP5 Connector, ZIF, flex, 7-pin (auxiliary PCB) 491242

13 JP9 Connector, ZIF, flex, 22-pin (auxiliary PCB) 491250

14 JP2,3 Connector, ZIF, flex, 32-pin (auxiliary PCB) 491243

15 Cover, rear (non-printer model) 022929

16 Cover, front, with gasket assembly 022921

17 D8 Diode, photo, 8440 (main PCB) 591017

18 Display, Taliq, analog shield assembly 024466

19 Door, battery 022924

20 Door, paper. 022938

21 Door, printer 026338

22 F2 Fuse, micro, 1 amp (auxiliary PCB) 691236

23 F1 Fuse, micro, 1.5 amp (auxiliary PCB) 691239

24 Insulator, printer 026139

25 Nut, keps,SS, 4-40 851101

26 PCB, auxiliary 024472

27 PCB, main 024468

28 Printer flex circuit 024464

29 Printer 024462

30 Screw cap 023451

Button, measure (European version) 026386

Buttons, printer, strip (European version) 026387

Cover, rear (printer model) 026339

Display, Taliq, analog shield assembly (European version) 026765

6-1

Spare Parts

31 Screw, captive 891324

33 Screw, plastite 871031

34 Sensor lock 022943

35 Sensor shroud 022944

36 Spacer 023452

37 Stiffener, printer button 023131

39 BZ1 Transducer, audio, piezo ceramic 691230

Item Designator Description P/N

Screw, Phillips, 4-40 × 1/4

Tape, foam (.88" × .38")

801025

023300

6-2

7 PACKING FOR SHIPMENT

7.1 General Instructions

7.2 Repacking in Original Carton

7.3 Repacking in a Different Carton

Should you need to ship the N-20/N-20P monitor for any reason, follow the instructions in this section.

7.1 General Instructions

Pack the monitor or printer carefully. Failure to follow the instructions in this section may result in loss or damage not covered by the Mallinckrodt warranty. If the original shipping carton is not available, use another suitable carton or call Mallinckrodt Technical Services to obtain a shipping carton.

Prior to shipping the device, contact Mallinckrodt Technical Services for a returned goods authorization (RGA) number. Mark the shipping carton and any shipping forms with the RGA number.

7.2 Repacking in Original Carton

If available, use the original carton and packing materials. Pack the monitor or printer as follows:

Place the monitor, or printer, and, if necessary, accessory items in original packaging. Place in shipping carton and seal carton with packing tape. Label carton with shipping address, return address, and RGA number.

7.3 Repacking in a Different Carton

If the original carton is not available:

1. Place the monitor or printer in plastic bag.

2. Locate a corrugated cardboard shipping carton with at least 200 pounds per square inch (psi) bursting strength.

3. Fill the bottom of the carton with at least 2 inches of packing material.

4. Place the bagged unit on the layer of packing material and fill the box completely with packing material.

5. Seal the carton with packing tape.

6. Label carton with shipping address, return address, and RGA number.

7-1

8 SPECIFICATIONS

8.1 Readout

8.2 Controls

8.3 Operating Modes

8.4 Printer Output

8.5 N-20/N-20P Performance

8.6 Sensor Types

8.7 Electrical Specifications

8.8 Environmental Specifications

8.9 Physical Specifications

8.10 Quality Information

8.1 Readout

Display shows SpO included are a Pulse Search and Low Battery indicator, and an electroluminescent backlight.

8.2 Controls

8.2.1 N-20

The Measure button switches the instrument on and off, and initiates the measurement cycle.

The Battery-Check button is used to check battery condition and switches beeper on and off.

8.2.2 N-20P

The Measure button switches the instrument on, initiates the measurement cycle, and switches instrument off.

The Battery-Check button is used to check battery condition and switches beeper on and off.

button switches the printer on and off.

sets display date and time.

D/D

ADV advances paper and increments time and date.

8.3 Operating Modes

8.3.1 Spot Check Mode

(saturation of arterial hemoglobin oxygen), pulse rate, and pulse amplitude; also

Pressing the instrument Measure button once for less than 2 seconds starts the spot check mode. Spot check mode computes SpO

end of the measurement interval. If the printer is activated, the printout shows the displayed SpO pulse rate.

8.3.2 Extended Mode

Extended mode is started by holding down the instrument Measure button for approximately 3 seconds, plus any time required to complete the power-on self-test. The N-20/N-20P displays updated SpO2 and pulse rate with every pulse (after five valid pulses have been detected). The N-20/N-20P

remains active until 3 minutes after the sensor is removed, or until the instrument is turned off.

averaged over five valid pulses and displays SpO2 and pulse rate at the

and

8-1

Specifications

For the N-20, a 2% or greater decrease in SpO2 is indicated by two brief, low-pitched tones.

The N-20P printout shows SpO2 and pulse rate at 30-second intervals. For the N-20P, a 2% or greater

decrease in SpO2 is indicated by two brief, low-pitched tones and an asterisk (*) on the printout. At

the end of the measurement period, a header and statistical summary values (minimum, maximum, and mean of both pulse rate and oxygen saturation) are printed.

8.4 Printer Output

When activated by the printer

spot check mode), with space provided for writing in patient identification. The thermal paper printout measures roughly 40 mm (1.6 in.) by 100 mm (4.0 in.) in size.

If the N-20P is in spot check mode and the printer is turned on any time during a measurement or after a measurement is taken and before the N-20P powers down, the printer will catch up and print a complete record of the measurements recorded up to the current moment.

8.5 N-20/N-20P Performance

8.5.1 Range

Saturation: 0–100%

Pulse Rate: 20–250 beats per minute (bpm) ± 1 standard deviation

8.5.2 SpO2 Accuracy

Adults: 70–100% ± 2 digits

Neonates: 70–100% ± 3 digits

Pulse Rate: 20 –250 bpm ± 3 digits

8.5.3 Response

In spot check mode, the measurement cycle (from button press to display of data) is five valid pulses.

button, the N-20P output shows date, time, SpO2, and pulse rate (in

In extended mode, the instrument measures for a period of up to 30 minutes and continuously displays updated SpO2 and pulse rate.

70-100%. This variation equals plus or minus one standard deviation (1SD), which encompasses 68% of the population. All accuracy specifications are based on testing the subject monitor on healthy adult volunteers in induced hypoxia studies across the specified range. Adult accuracy is determined with Oxisensor II D-25 sensor. Neonatal accuracy is determined with Oxisensor II N-25 sensor.

8-2

Accuracies are expressed as plus or minus “X” digits (saturation percentage points) between saturations of

This variation equals one SD.

8.6 Sensor Types

Specifications

Table 8-1: Sensors

Sensor Model Patient Size

Oxisensor

Oxibandoxygen transducer (reusable with disposable nonsterile adhesive)

Durasensoroxygen transducer (reusable, nonsterile)

Nellcor reflectance oxygen transducer (reusable, nonsterile) RS-10 >40 kg

Dura-Ymultisite oxygen transducer (reusable, nonsterile)

For use with the Dura-Y sensor:

Ear clip (Reusable, nonsterile)

Pedi-Check pediatric spot-check clip (reusable, nonsterile)

OxiCliqoxygen transducers (sterile, single-use only)



II oxygen transducers (sterile, single-use only)

N-25/N-25LF I-20/I-20LF D-20 D-25/D-25L R-15

OXI-A/N OXI-P/I

DS-100A >40 kg

D-YS

D-YSE

D-YSPD

P N I A

<3 or >40 kg 3 to 20 kg 10 to 50 kg >30 kg >50 kg

<3 or >40 kg 3 to 40 kg

>1 kg

>30 kg

3 to 40 kg

10 to 50 kg <3 or >40 kg 3 to 20 kg >30 kg

8.7 Electrical Specifications

8.7.1 Battery

Type: four 1.5-V alkaline "C" cell batteries

Battery Capacity: typically 37 hours for N-20

typically 32 hours for N-20P

8.7.2 Instrument

Power Requirements: 4–6 VDC, supplied by battery only

Leakage Current: Meets applicable IEC- 601 and AAMI/ANSI standards;

the N-20/N-20P has no power or ground connections

Patient Isolation:No electrical connection to patient (inherently insulated)

8-3

Specifications

8.8 Environmental Specifications

8.8.1 Operating Temperature

Instrument: 0 to 40 °C (32 to 104 °F)

8.8.2 Storage Temperature

-20 to 50 °C (4 to 122 °F)

Humidity: Any humidity/temperature combination without condensation

Altitude: 0 to 6200 meters (0 to 20,000 ft)

8.9 Physical Specifications

Physical specifications are based on product without the protective boot.

8.9.1 Weight (with batteries installed)

N-20: 0.6 kg (1.3 lb)

N-20P: 0.62 kg (1.4 lb)

8.9.2 Dimensions

N-20: 19.0 cm high × 7.6 cm wide × 5.08 cm deep

(7.5 in. × 3.0 in. × 2.0 in.)

N-20P: 19.0 cm high × 7.6 cm wide × 6.35 cm deep

(7.5 in. × 3.0 in. × 2.5 in.)

8.10 Qualifying Information

The Nellcor N-20/N-20P is calibrated to measure arterial hemoglobin oxygen saturation of functional hemoglobin. The specified accuracy of this measurement is based on statistical analysis of arterial blood samples as measured on an IL282 CO-Oximeter.

Indocyanine green, methylene blue, and other intravascular dyes, depending on concentration, may interfere with the accuracy of data obtained from the instrument. Carboxyhemoglobin or other dyshemoglobins may also interfere with the accuracy of the data if present in significant concentration.

8-4

9 TECHNICAL SUPPLEMENT

9.1 Overview

9.2 Functional versus Fractional Saturation

9.3 Measured versus Calculated Saturation

9.4 Circuit Analysis

9.5 Functional Overview

9.6 Definition of Terms

9.7 Overall Block Diagram

9.8 SpO

9.9 Digital Circuitry

9.10 Circuit Illustrations

9.1 Overview

Analog Circuit

The N-20/N-20P is based on the principles of spectrophotometry and optical plethysmography. Optical plethysmography uses light absorption technology to reproduce wave forms produced by pulsatile blood. The changes that occur in the absorption of light due to vascular bed changes are reproduced by the pulse oximeter as plethysmographic wave form.

Spectrophotometry uses various wavelengths of light to qualitatively measure light absorption through given substances. Many times each second, the N-20/N-20P passes red and infrared light into the sensor site and determines absorption. The measurements, which are taken during the arterial pulse, reflect absorption by arterial blood, nonpulsatile blood, and tissue. The measurements that are obtained between arterial pulses reflect absorption by nonpulsatile blood and tissue.

By correcting "during pulse" absorption for "between pulse" absorption, the N-20/N-20P determines red and infrared absorption by pulsatile arterial blood. Because oxyhemoglobin and deoxyhemoglobin differ in red and infrared absorption, this corrected measurement can be used to determine the percent of oxyhemoglobin in arterial blood: SpO

is the ratio of corrected absorption at each wavelength.

9.2 Functional versus Fractional Saturation

The N-20/N-20P measures functional saturation, that is, oxygenated hemoglobin expressed as a percentage of the hemoglobin that is capable of transporting oxygen. It does not detect significant levels of dyshemoglobins. In contrast, some instruments such as the IL282 Co-oximeter measure fractional saturation, that is, oxygenated hemoglobin expressed as a percentage of all measured hemoglobin, including dyshemoglobins.

Consequently, before comparing N-20/N-20P measurements with those obtained by an instrument that measures fractional saturation, measurements must be converted as follows:

functional saturation =

100 - (% carboxyhemoglobin + %methemoglobin)

fractional saturation

9.3 Measured versus Calculated Saturation

When saturation is calculated from a blood gas measurement of the partial pressure of arterial oxygen (PaO2), the calculated value may differ from the N-20/N-20P SpO2 measurement. This is because the

calculated saturation may not have been corrected for the effects of variables that can shift the relationship between PaO2 and saturation.

x100

9-1

Technical Supplement

Figure 9-1 illustrates the effect that variations in pH, temperature, partial pressure of carbon dioxide (PCO2), and concentrations of 2,3-DPG and fetal hemoglobin may have on the oxyhemoglobin

dissociation curve.

100

Saturation (%)

pH Temperature PCO

2,3-DPG

Fetal Hb

PO2(mmHg)

pH Temperature PCO

2,3-DPG

10050

Figure 9-1: Oxyhemoglobin Dissociation Curve

9.4 Circuit Analysis

The following paragraphs discuss the circuits of the N-20/N-20P.

9.5 Functional Overview

This section provides a detailed explanation of N-20/N-20P operation using block diagrams and circuit schematics.

The relationship between these components and their interconnection is illustrated in the overall block diagram (Figure 9-2). The main component circuitry has been divided into the following subsections:

9-2

Technical Supplement

9.6 SpO

Patient sensor

Batteries

4-6 VDC

Main PCB

analog

SpO Microprocessor Memory Display control Sensors: temperature

ambient light battery voltage

20-pin headers

Auxiliary PCB

time

Measure button

Check battery button

PROM

Power supply Printer interface Display control Audio beeper

Realclock

Flex

connectors

Figure 9-2: Overall Block Diagram

Analog Circuitry Block Diagram (Figure 9-3)

Display

backlight

Printer

flex circuit

Printer

N-20P only

Analog circuitry has high signal sensitivity and reduced susceptibility to noise. Its design allows for a wide range of input signal levels and a broad range of pulsatile modulation. The SpO

analog circuit

(Figure 9-3) consists of four subsections:

1. Sensor output/LED control, where the CPU controls the gain of both LEDs so that signals received at the input amplifier are in its acceptable dynamic range

2. Input signal conditioning, where sensor output current is converted to voltage

3. Signal gain, where the separated LED signals are amplified so their current levels are within the A/D converter's acceptable range; and

4. AC ranging, where DC offset is eliminated from each LED signal.

Patient sensor

LEDs

Input signal conditioning photocurrent

to voltage

conversion demutiplexed to 2 channels

Main PCB

LED drivers

(red & IR)

Main PCB

Signal gain

variable gain,

filtered for

each LED

channel

Main PCB

Control

AC Ranging

offset

substraction;

additional gain

and filtering

Main PCB

Microprocessor

Main PCB

To digital section

Figure 9-3: SpO2 Analog Circuitry Block Diagram

9-3

Technical Supplement

9.6.1 Digital Circuitry Block Diagram (Figure 9-4)

Figure 9-4

shows the N-20/N-20P hardware and circuits, which include the CPU and system memory, the power supply and power control circuitry, user controls, display and ambient light sensors, audio output, thermal printer (N-20P only) and ambient temperature sensor, and the real-time clock.

Measure Check Battery

Power supply

To analog section

& control

CPU

Main PCB

Memory

software

N-20/N-20P Control buttons

AUX PCB

Real-time

clock

AUX PCB

Ambient

light sensor

Ambient

temp. sensor

Figure 9-4: Digital Circuitry Block Diagram

9.6.2 Power Supply Block Diagram (Figure 9-5)

Main PCB

AUX PCB

Display drivers

Audio beeper

Printer

ON ADV D/D

Display

AUX PCB

(N-20 only)

Printer Control button

Power supply circuitry (Figure 9-5) is located on the auxiliary PCB and consists of four subsections:

1. Four "C" size batteries that provide 4-6 VDC

2. Power control circuitry that senses a press of the Measure button and switches power on

3. Power shutoff circuit that controls power to all circuits except the power control circuit

4. Power supply circuits include a regulated power supply at 5 VDC, unregulated power supplies of

-5 VDC, 10 VDC, and 12 VDC, and a high voltage power supply of 70 VDC.

Measure

Disposable

batteries

4-6 VDC

button

Power control circuits

AUX PCB

Power shutoff circuits

(fuse,

EMI protect, ESD protect)

Power supply

circuits

-5

VDC

SpO2 Analog section

(main board)

+10 VDC

+12 VDC

+5 VDC

+70 VDC

Main PCB

Microprocessor

Display drivers

AUX PCB

Display backlight

Figure 9-5: Power Supply Block Diagram

9-4

9.6.3 Display Control Block Diagram (Figure 9-6)

The N-20/N-20P display is controlled by the display control circuitry (see Figure 9-6). A sensor is used to measure ambient light. During low light conditions, the display backlight, an electroluminescent device, is automatically switched on.

Main PCB

Microprocessor

Main PCB

Control

conditioning

circuit

(generates

timing

signals)

AUX PCB

Display driver

(1)

Display driver

(2)

Technical Supplement

Display

AUX PCB

High voltage

control circuit

(enables +70 VDC to display)

Figure 9-6: Display Control Block Diagram

9.6.4 Printer Control Block Diagram (Figure 9-7)

Printer circuitry (Figure 9-7) is divided into two subsections: the printer interface and the printer flex circuit. The printer interface circuitry is present on all models, but is disabled by software in the N-20. The printer flex circuit is added when a printer is present.

Main PCB

Microprocessor

AUX PCB

Printer

interface

Printer

flex

circuit

(N-20P only)

PCB

On ADV

70 volts

D/D

User push buttons

N-20 only

Display

backlight

Printer

(N-20 only)

Figure 9-7: Printer Control Block Diagram

9.7 Definition of Terms

9.7.1 Analog to Digital (A/D) converter

The CPU has a 10-bit A/D converter on board. Up to eight different analog inputs can be provided to the A/D for measurement.

9.7.2 Central Processing Unit (CPU)

An Intel 80C196KC 16-bit microcontroller. The CPU sends and receives control signals to the SpO analog section, display, and optional printer.

9-5

Technical Supplement

9.7.3 Content Addressable Memory (CAM)

The CPU controls the HSO lines with the CAM. CAM is software controlled and programmed with events scheduled relative to one of two internal timers.

9.7.4 High Speed Outputs (HSO)

The 6 HSO lines control most of the timing of the LED signal pulse and the demodulation of the received signal.

9.7.5 Input and Output (I/O)

Input and Output (I/O) are digital lines that are used by the CPU to read in data and output data.

9.7.6 Light-Emitting Diodes (LEDs)

Two LEDs are used in Nellcor oximetry sensors. Light is transmitted through body tissue and received by a photodetector circuit that converts it to photocurrent. The two wavelengths, which are used for calculation of pulse rate and oxygen saturation in blood, are transmitted at the following frequencies:

• infrared (IR) light at approximately 915 microns

• red light at approximately 660 microns

9.7.7 Pulse Width Modulation (PWM)

The three 8-bit PWM outputs can be software controlled; their duty cycle can be changed from 0-255/256 of the total pulse duration. PWM frequency is the crystal frequency of the CPU, which is 10 MHz divided by 1024. The PWMs control the gains within the analog circuit.

9.7.8 RCal

Sensor RCal value is a resistance value specific to an individual sensor. This value is used by the software during oxygen saturation computations to maximize accuracy.

9.7.9 Real-Time Clock (RTC)

The RTC is used with the optional printer to track time and date for printouts.

9.8 Overall Block Diagram

Exclusive of covers, buttons, and external connectors, the N-20/N-20P consists of three main components: the main PCB, the auxiliary PCB, and the display assembly and analog shield.

9.8.1 Main PCB

Contains the SpO2 analog circuitry; the CPU; support memory circuits; sensor circuits for ambient

light, temperature, and battery voltage; the check battery circuit; a serial data port; and some display control circuits.

9.8.2 Auxiliary PCB

9-6

Contains the power supply circuitry; the display driver circuits; the real-time clock; the interface circuitry for the printer flex circuit board (which is not used unless a printer is present); and audio output hardware.

9.8.3 Display and Analog Shield Assembly

This assembly connects to the main PCB by flex circuits. A metal shield shrouds the SpO2 analog circuits on the main PCB to protect them from EMI. An integrated electroluminescent backlight

illuminates the display under low light conditions.

The N-20P has an additional printer control board (printer flex circuit) and printer hardware. The following block diagram shows the relationship between these components.

Technical Supplement

9.9 SpO

Analog Circuitry

This subsection describes the SpO and reduced susceptibility to noise. Its design allows for a wide range of input signal levels and a

broad range of pulsatile modulation. The SpO subsections:

9.9.1 Sensor Output/LED Control

The CPU controls the gain of both LEDs so that signals received at the input amplifier are within an acceptable dynamic range. Signal channel gain may also need to be increased. The CPU uses PWM lines to control LED current level or to amplify the signal channel.

9.9.2 Input Conditioning

Sensor output current is converted to voltage. A demodulation circuit minimizes the effects of other light sources and stray frequency inputs. Because the IR and RED signals are at different current levels, the two LED signals are demultiplexed and separately amplified, so they can be compared with each other. Two circuits handle the demultiplexing by alternately selecting LED signals using switches. Filters then remove noise and smooth the signals before sending them to the amplifiers.

9.9.3 Signal Gain

The separated LED signals are amplified so that their current levels are within the A/D converter's acceptable range. The signals are filtered to improve the signal-to-noise ratio, and clamped to a reference voltage.

analog hardware. The analog circuitry has high signal sensitivity

analog block diagram (Figure 9-3) consists of four

9.9.4 AC Ranging

DC offset is eliminated from each LED signal. An analog switch sets the mean signal value to the mean of the A/D converter range, and the AC modulation is superimposed on that DC level. Then, each AC signal is amplified and filtered to eliminate residual effects of the PWM modulations. Finally, these two signals are input to the CPU A/D converter.

The relationship between these subsections is shown in the following block diagram.

9.9.5 Sensor Output/LED Control

The SpO2 analog circuitry provides control of the red and IR LEDs such that the received signals are within the dynamic range of the input amplifier. Because excessive current to the LEDs will induce changes in their spectral output, it is sometimes necessary to increase the received signal channel gain. To that point, the CPU controls both the current to the LEDs, and the amplification in the signal channel.

At initialization of transmission, the LEDs' intensity level is based on previous running conditions, and the transmission intensity is adjusted until the received signals match the range of the A/D converter.

9-7

Technical Supplement

If the LEDs reach maximum output without the necessary signal strength, the PWMs will increase the channel gain. The PWM lines will select either a change in the LED current or signal gain, but will not do both simultaneously.

The LED circuit switches between red and IR transmission and disables both for a time between transmissions in order to provide a no-transmission reference. To prevent excessive heat build-up and prolong battery life, each LED is on for only a small portion of the duty cycle. Also, the frequency of switching is well above that of motion artifact and not a harmonic of known AC transmissions. The LED switching frequency is 1.485 kHz. The IR transmission alone, and the red transmission alone will each be on for about one-fifth of the duty cycle; this cycle is controlled by the HSOs of the CPU.

9.9.5.1 LED Drive Circuit

The LED drive circuit is illustrated in

The IR and red LEDs are separately controlled with their drives’ currents multiplexed over two shared wires. Current to the IR LED is in the range of 4.3-50.0 mA; and, current to the red LED is in the range of 6.5-75.0 mA. Currents are limited to less than 100 mA for two reasons: (1) slight excess current can potentially change the emission characteristics of the LEDs, and (2) large excess current could create excessive heat at the sensor site.

The IR/red LED transmission signal (HSO1 of the CPU) is fed into the select inputs of the triple single-pole-double-throw (SPDT) analog multiplexing switch U10, causing either the IR or the red LED transmission to be enabled.

PWM1, which is filtered by the network of R44, C37, R52, and C38, is input to the LED drive circuit switch U10, and controls the magnitude of the IR LED current supply.

PWM2, which is filtered by the network of R43, C36, R53, and C39, is also input to U10, and controls the red LED current magnitude.

Two NPN transistors (Q1 and Q2) act as current sources for the IR and red LED outputs. Two PNP transistors (Q3 and Q4) act as switches between the IR and red LED output lines. Transistor Q5 acts as an LED drive current limiter; it clamps output of the current regulator circuit to the required level. If any resistor in the LED drive circuit fails, current to the LED will still be limited to a safe level.

The RSENS line senses the RCal value and enables the CPU to make the proper calculations based on the type of sensor being used.

9.9.6 Input Conditioning

Figure 9-8

(at the end of this section).

Input to the SpO2 analog circuit is the current output of the sensor photodiode. In order to condition the signal current, it is necessary to convert the current to voltage.

A differential synchronous demodulation circuit is used to reduce the effects of other light sources and stray frequency inputs to the system. Because the IR and red signals are absorbed differently by body tissue, their received signal intensities are at different levels. Therefore, the IR and red signals must be demodulated and then amplified separately in order to compare them to each other. Demultiplexing is accomplished by means of two circuits that alternately select the IR and red signal. Two switches that are coordinated with the IR and red transmissions control selection of the circuits. A filter with a large time constant follows to smooth the signal and remove noise before amplification.

9.9.6.1 Differential Synchronous Demodulation Circuit

The differential synchronous demodulation circuit is illustrated in Figure 9-9 (at the end of this section).

9-8

Technical Supplement

Before the current from the photodetector is converted to voltage, any high frequency noise is filtered by C40 and R17. The op-amp U1A is used in parallel with the current-to-voltage converter U1D to cancel any DC voltage, effectively AC coupling the output of U1D. The average value of the SpO

analog reference voltage (VREF) of U1D, 5 V, is measured at pin 14 of test point 49.

The same line that controls the on/off pulsing of the LEDs controls U6D, a single-pole-single-throw (SPST) analog switch. When either of the LEDs are on (the line is low and the switch is closed), U35 is used as a non-inverting amplifier. When the LEDs are both off, U35 is used as an inverting amplifier. The signal at the output of amplifier U35 is then demultiplexed.

The CPU HSO lines SAMPRED and SAMPIR, which are both active low, control SPST analog switches U6A and U6B, respectively. Switch U6A is closed to sample the red signal; switch U6B is closed to sample the IR signal. The sampling rate for both switches is 10 kHz. Switching is coordinated with the LED transmission so that the IR and red signals are each sampled twice per cycle; that is, once when the LED is off (signal inverted), and once when the LED is on (signal not inverted). The filtering circuit that follows has a long time constant, thereby acting as an averaging circuit.

A simplified N-20 HSO timing diagram is illustrated in Figure 9-10 (at the end of this section).

If the instantaneous average photocurrent (DC offset) is excessive and U1D cannot bring it to VREF, the PHOTOI line to the CPU (HSI0) is activated. This action is an indication of excess ambient light into the photosensor, or the occurrence of excess noise in the input circuit. It also serves as a warning to the instrument that the sensor signal may be contaminated and causes the software to send an error message. After about 3 seconds of continuous photocurrent signal, pulse search annunciation will begin. After about 10 seconds of continuous photocurrent signal, zeros will be displayed.

9.9.7 Signal Gain

The separated IR and red signals are amplified so that their DC values are within the range of the A/D converter. Because the received IR and red signals are typically at different current levels, the signal gain circuits provide independent amplification for each signal as needed. The gain in these circuits is adjusted by means of the PWM lines.

After the IR and red signals are amplified, they are filtered to improve the signal-to-noise ratio and clamped to a reference voltage to prevent the combined AC and DC signal from exceeding an acceptable input voltage from the A/D converter.

9.9.7.1 Variable Gain Circuits

The variable gain circuits are illustrated in Figure 9-11.

9-9

Technical Supplement

VREF

C122

VCC

C35

.1UF

RED

-5V

OFF/ON

U2 VDD

VEE

VSS

X 4053

R26

3.32K C24

.47UF

INH

Z1 Z0

Y1 Y0

X1 X0

C B A

VREF

R25

82.5K

R24

82.5K

.1UF

To LED control

PWM2

VREF

C127 220PF

VREF

IR LED/AV

TP51

TP52

PWM1

RED

9 10 11 6

3 5

1 2

13 12

C34

1NF

C33

1NF

R39

47.5K

Q6 2N3906

2N3906

C126 220PF

U1C

LF444

U1B

LF444

The two variable gain circuits are functionally equivalent. The gain of each circuit is contingent upon the signals received level and is controlled to bring each signal to approximately 3.5 V. Each circuit uses an amplifier and one switch in the triple SPDT analog multiplexing unit U2.

The gain in each of the circuits is accomplished by means of a feedback loop, which includes one of the SPDT switches in U2. The PWMs control whether the feedback loop is connected to ground or to the amplifier output. The feedback is then averaged by C33/R25 (red), and C34/R24 (IR). The higher the value of PWM2, the greater the IR gain; the higher the value of PWM1, the greater the red gain.

9.9.7.2 Filtering Circuits

The filtering circuits are illustrated in Figure 9-12.

These circuits consist of two cascaded second-order filters with a break frequency of 10 Hz. Pairs of diodes (D1/D3 and D2/D4), that are located between VREF and ground at the positive inputs of the second amplifiers, maintain the voltage output within the range of the A/D converter.

Figure 9-11: Variable Gain Circuit

9-10

Technical Supplement

RED

R6 100K

R11 100K

C16

.12UF

R7 100K

.068UF

C18

.12UF

R10 100K

.068UF

C15

C17

TP89

C13

.12UF

C19 .12UF

.068UF

C20

VREF

CR1

1N914

CR3 1N914

U4B

OP490SO

1N914

CR2

CR4

TP81

U4D

+12V

-5V

1 3

OP490SO

U4A

OP490SO

TP82

100KR9100K

C14

.068UF

R13

100K

R12

100K

VREF

U4C

OP490SO

TP90

REDDC

IRDC

9.9.8 AC Ranging

In order to measure a specified level of oxygen saturation and to still use a standard-type combined CPU and A/D converter, the DC offset is subtracted from each signal. Because the DC portion of the signal can be on the order of one thousand times the AC modulation, 16 bits of A/D conversion would otherwise be required to accurately compare the IR and red modulations between the combined AC and DC signals. The DC offsets are subtracted by using an analog switch to set the mean signal value to the mean of the range of the A/D converter whenever necessary. The AC modulation is then superimposed upon that DC level. This is also known as AC ranging.

Each AC signal is subsequently amplified such that its peak-to-peak values span one-fifth of the range of the A/D converter. The amplified AC signals are then filtered to remove the residual effects of the PWM modulations and, finally, are input to the CPU. The combined AC and DC signals for both IR and red signals are separately input to the A/D converter.

9.9.8.1 Offset Subtraction Circuits

The AC variable gain control circuit is illustrated in Figure 9-13 (at the end of this section). Voltage dividers R22 and R41 (red), and R31 and R5 (IR), which are located between VREF and ground, establish a baseline voltage of 2.75 V at the input of the unity gain amplifiers U7C (red) and U7D (IR).

Figure 9-12: Filtering Circuit

9-11

Technical Supplement

Whenever SPST analog switches U11A and U11D are closed by HSO0 (active low), the DC portions of the IR and red signals create a charge, which is stored on C29 and C89, respectively. These capacitors hold this charge even after the switches are opened and the resulting voltage is subtracted from the combined signal— leaving only the AC modulation output. This AC signal is superimposed on the baseline voltage output by U7C and U7D. The IRDC and REDDC are then filtered and input to the CPU, and can be measured at TP58 and TP54, respectively.

9.9.8.2 AC Variable Gain Control Circuits

The AC variable gain control circuit is illustrated in Figure 9-13 (at the end of this section).

The AC modulations are amplified by U7A (red) and U7B (IR) and superimposed on the baseline voltages present at the output of U7D (IR) and U7C (red). The amplification is handled by means of the SPDT analog multiplexing switch U3 within the feedback loop, which increases gain as PWM0 is increased. The IRAC and REDAC are then filtered and input to the CPU, and can be measured at TP55 and TP59, respectively.

9.10 Digital Circuitry

The digital hardware and related circuitry, which is illustrated in the following block diagram (Figure 9-4), includes the following subsystems:

Measure Check Battery

To analog section

9.10.1 CPU

A 16-bit microcontroller that includes a serial port, watchdog timer, A/D converter with an 8-input analog multiplexer, 3-pulse width modulators, and a high-speed I/O subsystem.

9.10.2 System Memory

Power supply

& control

CPU

Main PCB

Memory

software

Real-time

clock

N-20/N-20P Control buttons

AUX PCB

Ambient

light sensor

Ambient

temp. sensor

Figure 9-4: Digital Circuitry Block Diagram

Main PCB

AUX PCB

Display drivers

Audio beeper

Printer

ON ADV D/D

Display

AUX PCB

(N-20 only)

Printer Control button

9-12

External to the CPU and consists of an 8K × 8 static RAM and a 64K × 16 EPROM.

9.10.3 Real-Time Clock (RTC)

The RTC keeps track of date and time, which is printed on each printout. The RTC is powered by a lithium battery designed to last up to 5 years before needing replacement.

9.10.4 Audio Output

A piezoelectric ceramic beeper is used for audio output.

9.10.5 Display Control

A high-visibility display provides oxygen saturation and pulse rate values. An ambient light sensor responds to low-light conditions and turns on the display backlight.

9.10.6 User Controls

A Measure button and a Battery-Check button. The Measure button signals the power control circuit to switch on the power supply. Press and hold the Battery-Check button to display a percentage of useful life remaining in the batteries.

9.10.7 Power Supply/Power Control Circuitry

The N-20/N-20P receives power from 4 "C" cell batteries. The power control circuitry discontinues power to the unit when the batteries are no longer reliable.

Technical Supplement

9.10.8 Thermal Printer (N-20P only)

Generates a hard copy of oxygen saturation and pulse rate values. A sensor monitors ambient temperature and adjusts printer output to ensure consistent print quality.

9.10.9 CPU

The CPU circuit is illustrated in Figure 9-14.

The Intel 80C196KC CPU is a 16-bit microcontroller with built-in peripherals including: a serial port, watchdog timer, A/D converter with an 8-input analog multiplexer, three pulse width modulators, two 16-bit counter/timers, up to 48 I/O lines, and a high-speed I/O subsystem.

The CPU is capable of running up to 16 MHz, but it is run at 10 MHz for decreased power consumption. All unused inputs are tied to either Vcc or ground through resistors—this prevents unused inputs floating to any voltage and causing excess power drain. The READY input pin is tied high, thereby disabling wait-state generation; all bus accesses are zero-wait state. The EA pin is tied low to enable addressing of the external EPROM.

When the power supply is first switched on by the power control circuit, the reset generation circuit holds the CPU RESET pin low for at least 20 ms, then allows the internal pull-up resistor to bring it high; this assures a good CPU reset.

An internal watchdog timer is enabled and runs continuously. The watchdog timer provides a means of recovering from a software upset caused by ESD, EMI, etc. If the software does not clear the timer at least every 64K state-times (13.1 ms), the CPU will drive RESET low, resetting the entire unit. The reset output by the CPU is only 16 state-times long (3.2 µs). Q22 provides isolation from C65 so the CPU can drive a good reset to the display control circuit.

9-13

Technical Supplement

Patient

Sensor

Analog

Reference

Voltage

Serial

Interface

SpO2

Analog

Section

AD Bus

Output

Port

Enables

Control Analog

Input

Port

Ambient

Light

Address

Decoding

CPU

AD BusControl

Address

Demultiplexing

CPU

Memory

Battery

Voltage

Address

Temperature

Analog

Power

Off

Power On

Standard

Supply

Ambient

Battery

Power

Control

Power

Control

Power Supply

User

Digital I/O

Battery

Type

Lithium

Battery

External to Board

BUSSES SIGNALS

Output Port

Real Time

Clock and

Non-Volatile

Memory

Input Port

Audio

Output

Display

Control

User

Display

Digital I/O

Printer

Interface

Power Control

User

Controls

Optional Printer

Flex Circuit with

User Controls

Figure 9-14: N-20 Hardware Block Diagram

The CPU has the ability to dynamically switch the data bus width—based on the BUSWIDTH input pin. A low on BUSWIDTH tells the CPU to access memory only 8 bits at a time. When accessing the static RAM, BUSWIDTH is low, automatically reading the 8-bit wide RAM. Since BUSWIDTH is connected to the active low RAM enable line (RAMEN), all other memory and mapped I/O are read or written 16 bits at a time.

analog section includes AC and DC

The CPU measures eight analog inputs. Input from the SpO

signals for the oximeter sensor red and infrared channels, and the sensor calibration resistor RSENS. Light, temperature, and battery voltage are also measured.

9-14

The N-20 CPU is configured as follows:

• Decoded AD0 and BHE generate separate WR write strobes for the low and high bytes of a word.

The signal WR (pin WRL) is the low-byte write strobe.

• A standard address latch enable (ALE) is generated and used.

HSO pins 4 and 5 are configured as outputs. The HSO is used to generate stable timing control

•

signals to the SpO2 analog section, display, and printer.

• The timer-2 external control pins T2CLK, T2RST, T2U-D, and T2CAPT are disabled via

software and used as standard I/O.

• The HOLD, HLDA, and BREQ bus accessing is disabled via software and the pins are used as

standard I/O.

• Pins HSI0 and EXTINT are configured for interrupt input. The CPU receives 2 external

interrupts (signals PR_TACH and PHOTOI).

• RXD and TXD are configured as a standard asynchronous serial transmitter and receiver for the

serial interface. PWM0, PWM1, and PWM2 pins are configured as pulse width modulator outputs. They are used

•

to control gains within the SpO2 analog section.

9.10.9.1 Address Demultiplexing

The address demultiplexing circuit is illustrated in Figure 9-15.

Technical Supplement

U13 and U33 are transparent latches that latch the address portion of the AD bus data on the falling edge of ALE; the outputs are always enabled. The outputs of U13 and U33 are always the address portion of the AD bus.

ADDRESS DEMUX

AD0 AD1 AD2 AD3 AD4 AD5 AD6 AD7

ALE

TP39

AD8 AD9 AD10 AD11 AD12 AD13 AD14 AD15

ALE

TP40

2 3 4 5 6 7 8 9

R108 10K

2 3 4 5 6 7 8 9

R109 10K

U13 D1

D2 D3 D4 D5 D6 D7 D8

C OC

74HC573

U33 D1

D2 D3 D4 D5 D6 D7 D8

C OC

74HC573

Q1 Q2 Q3 Q4 Q5 Q6 Q7 Q8

A10

A11

A12

A13

A14

A15

Figure 9-15: Address Demultiplexing Circuit

9-15

Technical Supplement

9.10.9.2 Address Decoding

The address decoding circuit is illustrated in Figure 9-16.

ADDRESS DECODING

WR RD

A10

A12 A13 A14 A15

U30B

A14

A15

A11

74HC10

1 2 3

6 4 5

TP71

U28

A B C

G1 G2A G2B

74HC138

10K

R134

EXINEN

EXOUTEN

Y4 Y5 Y6 Y7

1 2

9 10 11

10 9 7

U30A

74HC10

U30C

74HC10

DC00-DFFF

E000-FFFF

RAMEN

0000-DBFF

ROMEN

TO: N-20 AUX PCB

TP74

20 20 HDR

VCC

Figure 9-16: Address Decoding Circuit

The CPU has a 64 Kbyte address range of 0-FFFF. RAM, EPROM, and I/O ports share this space. The address decoding circuit splits up this space and output enable lines to the RAM, EPROM, and I/O ports.

U30A generates the static RAMs active low enable signal, RAMEN. When address lines A13, A14, A15 are all high, U30As output goes low, enabling the RAM. This occurs for the 8K address range of E000-FFFF.

U30B and U28 are used to generate the input port and output port active low enable signals EXINEN and EXOUTEN. When address lines A15, A14, A11, and A10 are high, and A13 is low, U28 becomes enabled. With U28 enabled, one of the 8 outputs is set low. The output to go low is selected by pins A, B, and C. They form a 3-bit binary number with pin C being the most significant bit. So when address line A12 is high, WR active (low), and RD inactive (high), a binary 5 is produced on pins A, B, and C, forcing output Y5 (EXOUTEN) low. This enables the output port for writing. When address line A12 is high, WR inactive, and RD active, a binary 3 is produced on pins A, B, and C, forcing output Y3 (EXINEN) low. Note that in both previous conditions, A15, A14, A12, A11, and A10 are high and A13 is low.

The input port and the output port both share the same 1 Kbyte address space of DC00-DFFF. When data are written to that address, the output port enable signal EXOUTEN is activated. But when data are read from the same address, EXINEN is activated. Because the CPU is configured to use a 16-bit bus, except for RAM, any even address in the DC00-DFF range could be used for external port access. In other words, reading or writing address DC00, DC02, DC04, etc., will all produce the same

9-16

results. Due to the CPU configuration, the write strobe WR (WRL pin) is only active for low-byte writes; therefore, both bytes of the external output port must be written to at the same time. The upper byte of the output port cannot be written to alone, no write strobe and, therefore, no EXOUTEN signal will be generated.

U30C generates the EPROMs active low enable signal, ROMEN. The active low signals RAMEN and EXINEN are basically used as EPROM disable signals. When RAMEN or EXINEN or test point TP71 are low, the output of U30C, ROMEN, is forced high, disabling the ROM. Therefore, the EPROM is disabled for the range DC00-FFFF and enabled for the 55 Kbyte address range of 0h-DBFF. TP71 is used during board testing to disable the EPROM.

9.10.10 CPU Memory

The CPU memory circuit is illustrated in Figure 9-17.

RAMEN

WR RD

A0 A1 A2 A3 A4 A5 A6 A7 A8 A9 A10 A11 A12

8K X 8 SRAM

U14

A10

A11

A12

CS1

CS2

Technical Supplement

AD0

12 13 15 16 17 18 19

VCC

R133 10K

AD1 AD2 AD3 AD4 AD5 AD6 AD7

D1 D2 D3 D4 D5 D6 D7

TP43

64K X 16 EPROM

ROMEN

VCC VCC

A1 A2 A3 A4 A5 A6 A7 A8 A9 A10 A11 A12 A13 A14 A15

A10

A11

A12

A13

A14

A15

VPP

PGM 27C1024L

U15

O10 O11 O12 O13 O14 O15

O0 O1 O2 O3 O4 O5 O6 O7 O8 O9

AD0

AD1

AD2

AD3

AD4

AD5

AD6

AD7

AD8

AD9

AD10 AD11

AD12

7 6

AD13 AD14

AD15

Figure 9-17: CPU Memory Circuit

The memory system external to the CPU consists of an 8 K × 8 static RAM (U14) and a 64 K × 16 EPROM (U15). The EPROM is 16 bits wide to enhance CPU performance. Because RAM is infrequently accessed, it is only 8 bits wide.

9-17

Technical Supplement

U14 is a standard 8K × 8 static RAM. Test point TP 43 is used during testing to disable the output.

The program that the CPU runs is stored in U15. U15 is a 16-bit wide output, one-time programmable (OTP) EPROM. During 16-bit wide bus accesses, the CPU uses address line A0 for low/high byte

selection, and address line A0 is not used as a normal address line. The CPU can address only 64K × 8 bytes or 32K × 16 bytes. Pin A15 of U15 is tied low, always selecting the lower half of the EPROM.

Signal ROMEN is then used to enable the EPROM for the proper memory area.

9.10.10.1 Input Port

The input port circuit is illustrated in Figure 9-18.

EX_IN INPUT PORT

AD0 AD1 AD2 AD3 AD4 AD5 AD6 AD7

EXINEN 74HC573

19 18 17 16 15 14 13 12

U16

Q1 2D1 Q2 3D2 Q3 4D3 Q4 5D4 Q5 6D5 Q6 7D6 Q7 8D7 Q8 9D8

GO_BTN

ON_OFF_BTN DD_BTN ADV_BTN PR_HOME BAT_TYPE RTC_IO

VCC

U16 is the input port external to the CPU. The logic levels on the inputs (pins D1-D8) are output to the CPU via the AD bus while EXINEN is strobed low. All of the user control buttons are input via U16. Also, the battery type is sensed via U16; a high on signal BAT_TYPE signifies to the CPU that rechargeable batteries are being used. If the optional printer head is in the home position, PR_HOME will be a logic high.

Pin D8 (RTC_IO) and an output bit of the external output port are connected. They work as a pair to create a bidirectional bit for communicating with the RTC (see Section 3.5.3, Real-Time Clock and Non-Volatile Memory).

9.10.10.2 Output Port

The output port circuit is illustrated in Figure 9-19 (at the end of this section).

The output port external to the CPU consists of 2 octal D latches , U18 and U17; they function as a single 16-bit output port. U18 is the lower byte (LSB) and U17 is the upper byte (MSB). The output of U18 is always enabled. The output bits of U18 control: audio output, optional printer, RTC, and display.

The signal PR_STROBE controls U17s output drivers. Under normal operation, the outputs are tristated and resistors R148-R154 pull the outputs low. PR_STROBE is driven low to turn on the output drivers of U17. Signals PR_DOT0-PR_DOT6 (pins Q1-Q7) drive the 7 print dots of the optional printer. PR_STROBE pulses all 7 of the dot lines for a specific time period (see also "Printer Interface"). When the CPU is first powered on, PR_STROBE is in a tristate condition. R123 assures that U17 does not accidentally turn on the printer head dots until required to. Pin Q8 (RTC_IO) and an input bit of the external input port are connected. They work as a pair to create a bidirectional bit for communicating with the RTC (see also "Real-Time Clock and Non-Volatile Memory").

Figure 9-18: Input Port Circuit

9-18

Both bytes of external output port (i.e., U18 and U17) must be written to at the same time. The upper byte of the output port (U17) cannot be written to independently (see also "Address Decoding").

9.10.11 Real-Time Clock (RTC) and Non-Volatile Memory

The real-time clock circuit is illustrated in Figure 9-20.

The RTC has two functions: (1) it provides non-volatile memory that is used to remember whether the printer should be enabled at power on, and (2) to keep track of time and date for the N-20P printer. The N-20 does not require or use the RTC; it is disabled via software.

VCC

REAL TIME CLOCK

CR22 1N914

Technical Supplement

TP86 TEST

TP76

TEST

C114

.1uF

CR23

1N914

R163

3.32K

BT1 3V

32.768KHz

U29

VCC

GND

DS1202S

SCLK

I/O

RST

RTC_CLK

RTC_IO

RTC_RST

TP85 TEST

TP87 TEST

Figure 9-20: Real-Time Clock Circuit

The RTC chip U29 uses a 3-wire synchronous serial interface to communicate with the CPU. The CPU brings signal RTC_RST high to activate communication with the RTC. RTC_CLK clocks data into and out of the RTC chip. RTC_IO is the bidirectional communication data bit. The CPU drives RTC_IO when writing data and commands to the RTC. The CPU tristates RTC_IO and then reads data back on it from the RTC.

Crystal Y1 provides an accurate 32.768 KHz clock input whenever the time keeping circuitry of U29 is activated. The CPU enables the timekeeping function only when an optional printer is installed. If no printer is installed, the CPU switches off timekeeping, thereby extending battery life. Also, with no printer installed, the RTC clock is used only during diagnostic testing to verify the CPU clock timing.

The lithium battery BT1 and diodes CR22 and CR23 provide the power switch over and constant power needed to keep the time and RAM data while the unit is not in use. Whenever the unit is powered on, Vcc is at 5 V and U29 is powered via CR22. CR 23 is reverse biased because BT1 at 3 V is at a lower potential than Vcc. Whenever the unit is powered off, the potential between Vcc and switched ground is 0 V, CR23 is forward biased, and U29 is powered by BT1. CR22 is reverse biased, isolating BT1 from Vcc. This circuit design allows BT1 life of up to 5 years, typically, without the unit being powered on.

U29 holds 24 bytes of RAM, which is used for non-volatile storage of CPU data.

9.10.12 Audio Output

The audio output circuit is illustrated in Figure 9-21.

9-19

Technical Supplement

BEEP_1 BEEP_2

BZ1, a piezo ceramic sounder, is the audio output device. Due to its low drive current of 2 mA maximum, no drive circuitry is needed, and the audio output device is driven directly from the external output port. It is differentially driven with 2 square waves 180 degrees out of phase. The drive frequency is approximately 1480 Hz or 740 Hz and is generated by the CPU. BZ1 is differentially driven to obtain maximum audible volume.

9.10.13 Display Control Circuitry

The display control circuit is illustrated in Figure 9-22, at the end of this section.

The Taliq display is controlled by the display control circuitry. A photosensor measures ambient light and automatically switches on the electroluminescent display backlight during low light conditions. The display control circuitry is divided into the following subsections:

9.10.13.1 Control Conditioning Circuit

The control conditioning circuit, located on the main PCB (Figure 9-6), processes signals generated by the CPU to produce timing signals for the display drivers.

TP75 TEST

BZ1

AT17

BEEPER

TP74

TEST

Figure 9-21: Audio Output Circuit

9.10.13.2 Display Driver ICs

The display driver ICs are located on the auxiliary PCB (Figure 9-6). Each of the two display driver ICs have 32 high-voltage outputs that enable individual segments of the display to be turned on or off.

9.10.13.3 High Voltage Control Circuit

The high voltage control circuit is located on the auxiliary PCB (Figure 9-6). The high voltage control circuit allows the CPU to switch on or off the display's high voltage input.

Main PCB

Microprocessor

Main PCB

Control

conditioning

circuit

(generates

timing

signals)

AUX PCB

High voltage

control circuit

(enables +70 VDC to display)

AUX PCB

Display driver

(1)

Display driver

(2)

70 volts

Figure 9-6: Display Control Block Diagram

Display

backlight

9-20

9.10.13.4 Control Conditioning Circuit

The CPU generates a 400-µs low-pulse train at a 160 Hz rate on signal DISP_PHASE. Half of U34 takes DISP_PHASE as an input and creates DISP_POL as an 80 Hz 50% duty cycle square wave. A CPU reset initializes DISP_POL low when any CPU reset occurs so the software knows the initial state. The other half of U34 is used to synchronize the rising edge of the DISP_DL with the rising edge of DISP_POL. The CPU brings DISP_LATCH signal high before the rising edge of DISP_PHASE; this allows the high to be clocked out to DISP_DL on the rising edge of DISP_PHASE. About 100 µs after the rising edge of DISP_PHASE, the CPU brings DISP_LATCH low, asynchronously resetting DISP_DL low.

9.10.13.5 Display Driver Control Circuits

U19 and U20 are the display segment driver chips. Each chip has 32 high-voltage outputs and a display common marked BP (backplane). The display data are input to U19 and U20 by the CPU via a serial shift register input. U19 and U20 are daisy-chained together, forming a 64-bit serial shift register. Display data are loaded and shifted down via the DISP_DATA and DISP_CLK signals. When all 64 bits of the shift register are loaded, a high pulse on DISP_DL updates the display, all 64 bits at the same time. The display is clocked with an 80 Hz 50% duty cycle waveform by signal DISP_POL. The display cannot be driven by DC voltages or display damage will result. Display segments are illuminated by creating a 180-degree phase shift between the segment pin and the BP common pin. Segments are left dark by making the waveform on the segment pin be in phase with the BP pin. The display has an electroluminescent (EL) backlight, and is driven the same as the display segments. Connectors JP2, JP3, and JP5 connect the display and EL backlight to the drive electronics.

Technical Supplement

9.10.13.6 High Voltage Control Circuit

The cold switch circuit performs two basic functions: (1) it allows the CPU to enable and disable the display high voltage VDISP, and (2) it slows the edge slew rate of the segment drivers as it switches the high voltage. When the signal DISP_PHASE is low, Q14 is disabled, pulling VDISP low. Whenever the CPU is powered on, DISP_PHASE is tristated. The base emitter junction of Q12 pulls DISP_PHASE low, disabling the high voltage. This assures that the high voltage is only enabled to the display when controlled by the CPU.

The Taliq display is similar to an LCD in that the load of a segment is mainly capacitive. A cold switch circuit provides a current-limited 70 V to VDISP. R93, R95, Q21, and Q14 do the on/off switching and current limiting. As the driver chips' output waveforms and DISP_PHASE change states, the capacitive loads of the display cause VDISP to current limit until the capacitance is fully charged. This constant output current is integrated into the display capacitive loads, causing a highly linear rising and falling voltage ramp on VDISP. Because the high voltage to the drive chips (VDISP) is ramped, the outputs of the driver chips U19 and U20 are also ramped at the same controlled rate. This design is used to reduce current spikes on the 70 V power supply, and, in addition, reduces the EMI generated by the display due to the lower slew rates of the high voltage switching signals.

9.10.14 Standard User Controls

The user controls circuit is illustrated in Figure 9-23.

9-21

Technical Supplement

TO: N-20 MAIN PCB

JP18

GO_SW

CHECK BATTERY

TP88

TEST

SW1

R74

VCC

R102

15K

R79

3.32K

L11

VCC

R71

L12

C126

100PF

150K

C64 .01UF

BAT_BTN

C123

100PF

GO_BTN

TP72

TEST

TP71 TEST

TP81

TEST

VCON

R78 150K

C66 .01UF

GO BTN

To U21

pin 4

R80

221

MEASURE

BUTTON

Figure 9-23: User Controls Circuit

The standard user controls consist of two momentary push-button switches (measure and check-battery). The Measure button is an elastomeric contact switch, and the Check-Battery button is a mechanical momentary switch.

The CPU input lines BAT_BTN and GO_BTN are normally pulled to the high state by R71 and R78. Whenever a button is depressed, the CPU input line is pulled low through R74 and R80. The switch contacts are debounced with C64 and C66. L11, L12, C126, and C123 provide a current path for ESD protection.

In addition to being read by the CPU, the Measure button also activates the power supply via the power control circuit. Note that the Measure button has circuitry on both the main PCB as well as the auxiliary PCB.

9.10.15 Power Supply/Power Control Circuitry

GO_SW

TO: N-20 AUX PCB

JP8 1

9-22

Power supply circuitry is located on the auxiliary PCB and consists of the following subsections:

• Batteries—Four 1.5-V alkaline "C" size batteries provide 4-6 VDC power.

• Power control circuitry—Power control circuitry is connected to the batteries. It senses any

press of the Measure button and switches on the power supplies. Reverse current limiting protects the N-20/N-20P from damage if batteries are inserted incorrectly.

• Power shutoff circuit—This circuit controls power to all circuits except the power control circuit.

In addition, a fuse protects the power supply from excessive current draw. The power supply is also protected against electrostatic discharge and electromagnetic interference.

Power supply circuits consists of the following power supplies:

•

Regulated power supply: Power supplied by the batteries is regulated at 5 VDC. All of the digital circuitry and some of the SpO2 analog circuitry use this supply.

Unregulated power supplies: 5 VDC is converted by a switched capacitor network into unregulated power supplies of –5 VDC, 10 VDC, and 12 VDC, all of which are used in the SpO2 analog circuits.

High voltage power supply: A voltage regulator/doubler converts battery power to 70 VDC; the display drivers as well as the display backlight need this increase in power.

The power supply circuit is illustrated in Figure 9-24, at the end of this section.

9.10.15.1 Power Control Circuitry

Technical Supplement

The power control circuit is illustrated in Figure 9-25, at the end of this section.

The power control circuit consists of U21 and its associated components. U21 is a D flip/flop with asynchronous preset and clear; only the preset and clear are used.

Power is applied to U21 via CR11 whenever batteries are installed. CR11 provides protection for U21 if the batteries are installed with reverse polarity. This error condition will reverse bias CR11, thereby disabling current flow to U21.

The much larger RC time constant of R110, C67 compared to R78, C66 guarantees that the unit will not be accidentally powered on when batteries are first installed.

Whenever the Measure button is pressed, a low on GO_SW sets the output signal PWR_ON high. This condition connects switched and battery grounds, enables the power supplies, and switches on the unit. Whenever the CPU determines that the power should be switched off, it forces PWR_DOWN low. This action clears output PWR_ON to a logic low, disconnecting ground, and switching off the power supplies (see also Power Supply).

R79 and R81 provide current limit protection to U21 inputs. They also limit the current that will flow through U21 inputs to the CPU when the batteries are installed backwards. In the reverse battery error condition, massive current can flow from the inputs of U21 through the input protection diodes and/or substrate inside the CPUs integrated circuit. These resistors limit that current path to safe levels.

9.10.15.2 Power Shutoff Circuit

Refer to Figure 9-24, "Power Supply Circuit" (at the end of this section).

Fuse F1 protects the unit from excessive current draw. CR24 protects against large voltage transients caused by ESD, EMI, etc.

Q15 is a dual-channel FET; the drain of Q15 part 2 (pin D2) is connected to battery ground; the gate (G2) is connected to battery plus; and R155 applies a bias to the source (S2) so it will switch on when a positive voltage is applied to G2. When batteries are correctly installed, Q15 part 2 is switched on

9-23

Technical Supplement

and conducts. If batteries are installed backward, Q15 part 2 switches off and disables current flow. This protects the units power supply circuitry from an accidental reversal of battery potential.

Q15 part 1 controls the power supplies. When a logic high is placed on the gate (pin G1) signal, PWR_ON battery ground is connected to the circuit and switched to ground via Q15 parts 1 and 2. When the power control circuitry pulls PWR_ON low, switched ground switches to a high impedance state. This action switches off the power supply and, therefore the unit, except for the power control circuit.

9.10.15.3 Vcc Power Supply

Refer to Figure 9-24, "Power Supply Circuit,” at the end of this section.

The Vcc power supply is a switched inductor voltage regulator operating in boost mode (U22). The power input is provided by the batteries (VBAT). NFET (Q17) operates as a linear post regulator. The 1 M resistor (R77) operates as a static bleed device across the switched regulator when the regulator is switched down. The regulated output is Vcc (5 V ± 5%).

9.10.15.4 Raw Power Supplies

Refer to Figure 9-24, "Power Supply Circuit,” at the end of this section.

The input to the raw power supplies is Vcc, which is a switched-capacitor voltage converter operating in separate multiply and invert modes in conjunction with supporting circuitry. U23 inverts Vcc and outputs raw –5 V. Raw 10 V is derived by voltage doubling Vcc with CR14, CR19, CR20, and CR78. Raw 12 V is derived by voltage tripling Vcc with CR15, Q8, Q9, C96, C81, R119, and R120.

The raw power supplies are used as bias supplies for the SpO2 analog section and are not tightly regulated. The normal operating range of the raw power supplies are:

raw –5.0 V = –6.0 V to –4.0 V

raw 10.0 V = 7.5 V to 11.0 V

raw 12.0 V = 12.0 V to 15.0 V

9.10.15.5 High Voltage Supply

Refer to Figure 9-24, "Power Supply Circuit,” at the end of this section.

The input power for the high voltage supply is provided by the batteries (VBAT). The high voltage supply is a switched-inductor voltage regulator (U26) that operates in conjunction with a capacitive voltage doubler to output 72 VDC ± 5%. To protect against a runaway voltage condition, CR25 clamps U26's output to a safe level.

9.10.16 Analog Reference Voltage

The analog reference voltage circuit is illustrated in Figure 9-26.

9-24

RAW10V

R123 182

C95 22UF

2 4

R161

10K

VREF

U32

VIN GND

LT1021

2N3904

Q24

VOUT

TRIM

Q23 2N3904

TP60

6 5

+5.7

VREF

0.1UF

Technical Supplement

R124 1

TP70

GND

C12 22UF

RAW12V

RAW-5V

U32 provides an accurate, regulated voltage that is used as the reference voltage for the A/D inside the CPU. Filtering is provided by C6, C12, and R124. The voltage output VREF is 5 V.

9.10.17 Ambient Light

The ambient light circuit is illustrated in Figure 9-27.

R121

221

R122

221

C80

0.1UF

C94

0.1UF

+12V

-5V

C91 22UF

C93 22UF

TP61

TP62

Figure 9-26: Analog Reference Voltage Circuit

LIGHT SENSOR

VCC

D8 VTB8442B

VCC

Diode D8 is a photodiode that is used to measure ambient light. Q8, R68, and R136 provide current gain for D8 photocurrent. The amplified photocurrent flowing through R136 creates a voltage drop, which is measured by the CPU. The CPU continually monitors the light source output at AMB_LIGHT (TP72). Under low ambient light conditions, the CPU automatically switches on the display backlight.

9.10.18 Ambient Temperature

The ambient temperature circuit is illustrated in Figure 9-28.

R68

2.2M

Q8 MMBTA13L

R136

33.2K

C63 .01UF

Ambient Light

TP72

Figure 9-27: Ambient Light Circuit

9-25

Technical Supplement

Figure 9-28: Ambient Temperature Circuit

U5 is a precision-temperature sensor. It outputs (PR_TEMP) a voltage proportional to the ambient temperature, which is 10 mV per degree centigrade. For example, at a room temperature of 25 °C, the U5 output would be 250 mV. U5 is used whenever an optional printer is installed. Because the printer is a thermal printer, ambient temperature must be compensated for.

9.10.19 Battery Voltage

The battery voltage circuit is illustrated in Figure 9-29.

TEMP SENSOR

VCC

TEMP

GND

LM35

BATTERY VOLTAGE SENSE

VBAT

R69

15.8K 1% BAT_VOLT

R70

47.5K 1%

PR_TEMP

TP73

C62 .01UF

C115

0.1uF

The analog input voltage range of the CPU is 0-5 VDC. Because the battery voltage may be as high as 6.2 V, R69 and R70 form a voltage divider to decrease the measured battery voltage to a usable level. The gain is 0.75; thus, if the battery voltage was 6 V, then the voltage of BAT_VOLT would be

6 × 0.75 which equals 4.5 V.

The software has the ability to determine when battery power is too low. If the software determines that the battery voltage is too low to provide accurate information, the software generates an audible signal and automatically switches the unit off. If an optional printer is installed, the battery voltage data are used to compensate for battery voltage changes that can affect printout quality.

9.10.20 Battery Type

The battery type circuit is illustrated in Figure 9-30.

VRECHARGE

N-20 AUX PCB

TP2

TEST

R100

15K

Figure 9-29: Battery Voltage Circuit

VCC

CR27 1N914

R101 150K

Figure 9-30: Battery Type Circuit

BAT_TYPE

9-26

The unit can operate with either disposable or rechargeable batteries. Battery type input is digital; a high input informs the CPU that rechargeable batteries are in use. If rechargeable batteries are used,

the battery and the VRECHARGE terminals are mechanically connected. This applies the battery voltage to VRECHARGE, pulling BAT_TYPE high. R100 and CR27 are a current-limiting resistor and a voltage-clamping diode that are used to protect the input port from excessive battery voltage. If disposable batteries are used, VRECHARGE is electrically isolated, which allows R101 to pull BAT_TYPE input low.

The nominal voltages and voltage discharge curves are significantly different between rechargeable and disposable batteries. In order for the CPU to predict how much "battery life" remains, the nominal voltage and discharge curves must be known; the BAT_TYPE signal provides that information.

9.10.21 Printer Control

Printer circuitry is divided into two subsections: the printer interface and the printer flex circuit. Printer interface circuitry is present on both models, but is disabled by software in the N-20.

• Printer interface circuit (auxiliary PCB)—This circuit detects the presence of the flex circuit,

and supplies power to the print heads and paper-advance motor. Noise generated by the printer motor is filtered. The circuitry is protected from excessive battery currents by a fuse. The printer interface circuit is illustrated in Figure 9-31 (at the end of this section).

• Printer flex circuit (N-20P only)—The printer flex circuit is added when the printer is present.

The printer generates a timing signal that is read by the CPU and sent to the flex circuit. This circuit signals the CPU that a printer is present by connecting one CPU input to ground. Power and power control signals from the auxiliary PCB generate an output load for a resistor array; heat from this process produces a dot matrix pattern on thermal paper. The printer flex circuit is illustrated in Figure 9-32.

Technical Supplement

9-27

Technical Supplement

TO N-20 AUX BOARD

JP9

22 HDR

VPRN

DOT4

PR_DOT6

PR_DOT5

PR_DOT4

PR_DOT3

PR_DOT2

PR_DOT1

PR_DOT0

PR_MOTOR

PWR_ON

PR_PRESENT

ON_OFF

ADV

SEIKO

MTP102-16

PRINTER

JP10

M+

M-

3 4

5 6

HEADER 6

INM

IN0

IN1

IN2

IN3

IN4

IN5

IN6

VCC LB1256

3300UF

SI9956DY

OUTM

OUT0 OUT1 OUT2 OUT3 OUT4 OUT5 OUT6

GND

11 18 17 16 15 14 13 12

0.01uF

DOT6DOT6 DOT5 DOT4 DOT3 DOT2 DOT1 DOT0

ADVANCE BUTTON

DAY/DATE BUTTON

JP11 8

7 6 5 4 3 2 1

HEADER 8

ON OFF BUTTON

User control is provided by momentary push buttons: ON (on/off), ADV (advance), and D/D (day/date). ON enables or disables the printer, sets date, time, and other clock parameters.

When a low battery voltage condition is present, the N-20 adjusts power to the printer's head; however, a weak battery voltage condition causes the printer to shut off, thereby allowing the N-20P to continue to display oxygen saturation and pulse rate readings until the batteries are exhausted. An ambient temperature sensor adjusts printout quality to compensate for environmental conditions.

9.10.22 Printer Interface Circuit

The printer interface circuit is illustrated in Figure 9-31, at the end of this section.

9-28

Figure 9-32: Printer Flex Circuit

controls the advance of printer paper, and

ADV

D/D

Technical Supplement

The N-20 is configured in two ways, with printer and without printer. The following is a description of the printer interface circuitry found on all N-20 auxiliary PCBs. The printer interface circuitry is there regardless of the unit configuration; however, if the optional printer is not installed, this circuitry serves no function.

The CPU reads the PR_PRESENT signal to determine if a printer is installed. With PR_PRESENT left floating, it is pulled high by the weak pull-up resistor inside the CPU. If a printer is installed, PR_PRESENT is connected to switched ground, which causes a low input to the CPU. The optional printer circuit is protected from excessive battery currents by fuse F2. CR28 is used to block noise generated by the printer motor being injected onto the batteries.

The N-20 printer is a 16-character–wide thermal dot matrix printer, which generates a CPU interrupt for every dot column. The thermal energy given to the print head is controlled by the pulse width of the active high signals PR_DOTx. In order to provide consistent print quality, the ambient temperature, print drive voltage, and print head resistance must be measured and accounted for.

Inside the print head are seven resistors that heat up when power is applied, and in turn create dark dots on the thermal paper. One lead of the print-head resistors is connected to the printer supply voltage VPRN; the other lead is connected to the driver chip (see Optional Printer Flex Circuit with User Controls). One of the print dot resistor leads (DOT4) is also fed back to the printer interface circuitry. The DOT4 signal is a print dot resistor with a range of 11–16 ohms, which is connected to VPRN.

The print head resistance is measured by U36. A two-level resistor bridge is formed by R143, R144, R145, R146, and head resistor DOT4. The resistor bridge is switched on when PR_MEAS is pulled high, pulling TP77 low and biasing the resistor bridge. The logic outputs of PR_HEAD1 and PR_HEAD2 are read in by the CPU to determine which of the three head resistance categories this particular head is R156, ensuring that Q20 does not switch on when the batteries are installed backward. Due to the large current draw of the resistor bridge and the fact that the head resistance does not change significantly over time, the head resistance is measured only once at every power-on.

The CPU starts the printer motor running by setting PR_MOTOR high. A single motor drives both the print head and paper-advance mechanisms. The printer provides a printer timing generator (TG) signal, which is an AC waveform of about 4 Vpp. Q19, R106, R142, and CR29 convert the AC waveform to a CMOS level square wave; this signal (PR_TACH) is then used as a CPU interrupt line. An interrupt routine services the printer, thereby producing the required dot patterns to create the characters. C127 is used to filter noise.

The position of the print head is sensed by the signal PR_HOME. Whenever the print head is not in the home position, a switch in the printer closes, shorting PR_HOME to switched ground. Whenever the print head is in the home position, the switch opens, allowing R118 to pull PR_HOME high.

The print head dot pattern and pulse width are controlled by the CPU. The proper printer dot values are loaded into the output port, then the proper pulse width is loaded into the CPU CAM for PR_STROBE. The signal PR_STROBE enables the outputs for the specified pulse width. When the PR_DOTX lines are high, a dot will be printed.

9.10.23 Printer Flex Circuit and User Controls

The printer flex circuit is illustrated in Figure 9-32.

The thermal printer is plugged in via connectors JP10 and JP11. The PR_PRESENT signal is connected to switched ground to tell the CPU that a printer is installed. U1 is a Darlington pair driver chip that is used to drive the printer dots and motor. When an input is high, the output is shorted to ground, driving the output load.

9-29

Technical Supplement

Constant power (VPRN) and a power control line (PWR_ON) are provided by the auxiliary PCB. Q1 is used as a power control FET. Both halves are used in parallel to reduce the on resistance. When PWR_ON is high, the sources (S1, S2) short to the drains (D1, D2), connecting ground to U1 and C3. PWR_ON also controls the regulated power supplies; thus, Q1 and the power supplies are both enabled and disabled at the same time.

The large bulk capacitor C3 is required due to the large current spikes that are required by the printer and the large internal series resistance of disposable batteries. Bulk capacitance is required to lessen the drop in battery voltage caused by the current spikes.

The N-20P has three additional user-control buttons. L8, L9, L10, C120, C121, and C122 provide ESD protection. R103, R104, and R105 provide pull-ups when the user buttons are open. These pull-up resistors are in the printer interface circuit to ensure that the buttons (ON, ADV, and D/D) are never left floating, regardless of whether an optional printer flex circuit is installed or not.

The optional user controls consist of three momentary push-button elastomeric contact switches. Pull-up resistors are provided by the printer interface circuitry. R1, R2, and R3 help protect the input port by providing some current-limiting capability. C4, C5, and C6 debounce the switch contacts.

9.11 Support Illustrations

These illustrations, at the end of this section, support the descriptions within this manual.

Figure 9-8: LED Drive Circuit

Figure 9-9: Differential Synchronous Demodulation Circuit

Figure 9-10 N-20 HSO Timing Diagram

Figure 9-13: AC Variable Gain Control Circuits

Figure 9-19: Output Port Circuit

Figure 9-22: Display Control Circuit

Figure 9-24: Power Supply Circuit

Figure 9-25: Power Control Circuit

Figure 9-31: Printer Interface Circuit

Figure 9-33: N-20 SpO

Analog Block Diagram

Figure 9-34: CPU Circuit

Figure 9-35: N-20 Main PCB Schematic Diagram

9-30

Figure 9-36: N-20 Auxiliary PCB Schematic Diagram

Figure 9-37: N-20 Flex Circuit Schematic Diagram

SENSOR INPUT

5 9 4 8 3

L3 7 2 6 1

DB9F

TP47

TO CENTER MTG. HOLE

C119

100PF

VCC

C55

TP50

R46 10K

MMBTA56

Q2 MMBTA06

TP45

TP48

C118

100PF

.1UF

MMBTA56

TP46

R64

10K

R54

6.8

VREF

C116

100PF

VREF

C117

100PF

R18

6.04K

RSENS

C5 .01UF

LED DRIVE

MMBTA06

R51

22.1K

R45 10K

R47 10K

R48 10K

12 13

11 10

C53

.1UF

U9A

VCC

U10

X0 X1

INH A B

4053

VSS

VEE

VDD

Q5 2N3904

7 LT1013

VCC

TP77

C60

4.7PF

R53

100K

C39

.022UF

R52 100K

C38

R135

3.74K

C36 .1UF

R42 280K

TP83

R43 20K

C37 .1UF

22PFC123

PWM2 PWM1

R50 182K

TP84

R44 20K

PHOTOI

IR/RED

R49

100K R162

100K

CR12

IR/RED

OFF/ON

1N914

CR18

LED DIS

1N914

RSENS

Figure 9-8

LED Drive Circuit

9-31

15.8K

R56

LT1013

U9B

PHOTOI

VREF

40.2K

R57

TP44

SENSOR INPUT

DB9F

LF444

U1A

182K

390PF

C40

3.32K

R58

3.32K

R17

VREF

LF444

U1D

TP49

.047UF

C22

.047UF

C59

511K

R157

280K

R19

VREF

18PF

-5V LTC201

U6B

14 15

LTC201

U6A

3 2

+12V

.1%

88.7K

R159

LT1097

U35

481

-5V

+12V

LTC201

U6D

7 6

.1%

88.7K

R158

2.0K

R63

51.1K

R160

R23

VREF

TP79

TP78

LTC201

U6C

VREF

3.32K

R27

3.32K

R26

.47UF

C25

.47UF

C24

82.5K

VREF

SAMPRED

SAMPIR

OFF/ON

RED

Figure 9-9

Differential Synchronous Demodulation Circuit

9-33

OFF/ON (HSO.1)

/SAMPIR

(HSO.2)

/SAMPRED

(HSO.0)

IR/RED

(P1.1)

State Time

-60µS-60µS

µS

0 0

105.666158.499177.6 111

283.2 177

336.0 210

337.2 211

443.2 277

496.0 310

515.2 322

620.8 388

673.6 421

Figure 9-10

N-20 HSO Timing Diagram

9-35

VCC

From U2 pin 3

RED

U11C LTC201

R41 15K

U11D LTC201

C9 .015UF

R22

12.1K

C29 .015UF

R31

12.1K

VREF

TP85

VREF

LMC6044

R28

34.8K

U7C

C32

1NF

+5.7

1 1

R36 100K

U7B

LMC6044

LTC201

U11B

1 4

U7A

LMC6044

C111

.01UF

LTC201

U11A

R66

3.32K

C57 .01UF

R60

3.32K

R40

47.5K

C28 1NF

R30 100K

R67

3.32K

R29

3.32K

R61

3.32K

R33

3.32K

R20

3.32K

12 13

2 1

5 3

6 11 10

C61

.01UF

U3 X0

Y0 Y1

Z0 Z1

INH A B C

4053

R21

3.32K

.1UF

C30

C26

VSS

VEE

VDD

C7 .01UF

C27

C58

.1UF

VCC

REDLED/AV

IRDC

C8 .01UF

C31 .47UF

REDLED/AV

IRLED/AV

REDDC

TP54

REDAC

TP55.47UF

C56 .01UF

PWM1

TP56

TP57

PWM0

TP58

IRAC

TP59

/ZERO

R5 15K

TP86

R37

34.8K

U7D

LMC6044

TP76

BUS TO CPU

Figure 9-13

AC Variable Gain Control Circuit

9-37

VCC

R123 150K

AD0 AD1 AD2 AD3 AD4 AD5 AD6 AD7

EXOUTEN

R132 150K

AD8 AD9 AD10 AD11 AD12 AD13 AD14 AD15

EXOUTEN

PR_STROBE

TP82 TEST

2 3 4 5 6 7 8 9

EX_OUT LSB

U18

D1 D2 D3 D4 D5 D6 D7 D8

CLK OC

74HC574

EX_OUT MSB

U17

CLK OC

74HC574

Q1 Q2 Q3 Q4 Q5 Q6 Q7 Q8

DISP_DATA

DISP_CLK

RTC_CLK

RTC_RST

PR_MOTOR

PR_MEAS

BEEP_1

BEEP_2

PR_DOT6

PR_DOT5

PR_DOT4

PR_DOT3

PR_DOT2

PR_DOT1

PR_DOT0

RTC_IO

R148

150K

R150

150K

R152

150K

R154

150K

R149

150K

R151

150K

R153

150K

Figure 9-19

Output Port Circuit

9-39

DISP_POL

DISP_DL

DISP_DATA

DISP_CLK

VCC

VDISP

TP80

TEST

VCC

U19

VDD

VPP

DIN

CLK

LATCH

POL

DOUT

OSCIN

OSCOUT

GND

SI9530

U20

VDD

VPP

DIN

CLK

LATCH

POL

DOUT

OSCIN

OSCOUT

GND

SI9530

DISPLAY DRIVERS

O10 O11 O12 O13 O14 O15 O16 O17 O18 O19 O20 O21 O22 O23 O24 O25 O26 O27 O28 O29 O30 O31 O32

8 7 6 5 4 3 2 1 44 43 42 41 40 39 38 37 36 35 34 33 32 31 30

JP2 1

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

HDR 32

JP3 1

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

HDR 32

DISP_PHASE

VCC

R114

12.1K

RST

+70V

R113

4.75K

Q12 MMBT5551L

TALIQ COLD SWITCH

R115

475K

DISPLAY PS CTRL

U34

SET1

CLK1

RST1

SET2

CLK2

RST2

VCC

Q13 2N3904

Q1 Q1

Q2 Q2

GND

+70V

R93 182

Q14

VCC

R116 10K

R117

6.19K

DISP_POL

5 6

DISP_DL

9 8

C87

C83

MMBT5401L

390PF

Q21 MMBT5551L

R95 182

VDISP

74HC74

EL DRIVE

JP5

1 2 3 4 5 6 7

HDR 7

Figure 9-22

Display Control Circuit

9-41

BATTERY INPUT

TP3

BATT GND

TEST

TP1

BATT PLUS

TEST

1.5A

R155 10K

Q15

SI9956DY

TO CENTER MOUNTING HOLE

CR24

TRANZORB

10V

VBAT

C73

0.1UF

C116 22UF

C117 22UF

POWER SUPPLY

C74 22UF

120UH

CR13

130T3

R134

150

C75

0.1UF

U22

ILIM

VIN

SW1

SW2

LT1173

C70

22UF

120UH

R77

GND

SET

C119

C118

22UF

U23

C82 22UF

V +

OSC

VREF

VOUT LT1054CS

C90

22UF

FB/SD

CAP +

U26

VIN

VSW

LT1172

GND

CAP -

R82 100K

R83

28.7K

GND

R84 10K

R96

3.32K

0.1UF

Q17

SRC

GATE

SI9405DY

R120

22.1K

C96

2.2UF

R119

C85

DRN DRN DRN DRN

R86

31.6K

2N3906

2N3904

CR16

8 7 6 5

R85 100K

C81

.1UF

C112

1UF 50V

MURS110

CR25

5367A

43V 10%

C76

100PF

MURS110

C71 22UF

C125 22UF

C79 22UF

C92

2.2UF 50V

C95

2.2UF 50V

C72 .1UF

CR19

C78

.47UF CR14 130T3

CR15

130T3

CR20130T3

130T3

CR31

CR30 MURS110

C113

4.7UF 50V

R125 390K 1%

R126 390K 1%

R127 14K 1%

VCC

RAW-5V

RAW10V

RAW12V

TP38 TEST

C124 .1UF 100V

+70V

Figure 9-24

Power Supply Circuit

9-43

Q15

TO: N-20 MAIN PCB

JP18

GO_SW

PWR_DOWN

L11

R102

15K

R79

3.32K

VCC

C123

100PF

GO_BTN

TP72

TEST

TP71 TEST

R78 150K

C66 .01UF

R81

3.32K

VCON

R110 475K

C67

0.1UF

TP73 TEST

LT1046

VCONVCON

10 12 11 13

U21

SET1

CLK1

RST1

SET2 D2 CLK2 RST2

VCC

74HC74

C110

0.1UF

Q1 Q1

Q2 Q2

GND

PWR_ON

5 6

TP83

9 8

TEST

TP84

TEST

JP9

PIN 17

VCON

C68

0.1UF

CR11

1N914

VBAT

GO BTN

Figure 9-25

Power Control Circuit

9-45

PR_PRESENT

ON BTN

DD BTN

ADV BTN

VPRN

PR_HOME

PR_MEAS

PR_HEAD1

PR_HEAD2

PR_TACH

R118

150K

VCC

C127

100pf

R106 150K

R147

3.32K

U36B

LT1017CS

U36A

LT1017CS

R142

150K

Q19

2N3904

R156 1K

VBAT

VPRN

R141 1K

VPRN

1 4

CR29

1N914

CR28

130T3

TP77 TEST

R146

VCC

Q20 2N3904

R104

150K VCC

R105

150K

R143

14.0K

R144

1.24K

R145

60.4K

TP78 TEST

TP79 TEST

TP31 TEST

R103 150K

C115

0.1UF

VPRN

TP23 TEST

C122

100PF

TP24 TEST

TP25 TEST

C121

100PF

TP26 TEST

TP35 TEST

C120

100PF

TP36

TP37

TEST

TP27 TEST

TP29

TEST TP28 TEST

L10

TP30 TEST

PR_PRESENT

ON_OFF

ADV

TP32 TEST

TP33 TEST

VPRN

DOT4

VPRN

PR_DOT6

PR_DOT5

PR_DOT4

PR_DOT3

PR_DOT2

PR_DOT1

PR_DOT0

PR_MOTOR

VPRN

PWR_ON

TP34 TEST

TO PRINTER PCB

JP9 1

22 HDR

Figure 9-31

Printer Interface Circuit

9-47

SAMPIR

SAMPRED

PWM1

Sensor

Input Signal Conditioning Signal Gain AC Ranging

Zeroing

and

Current to

Voltage

Conversion

RED

Inverter

LED Drive

DMUX

RED

Variable Gain

and Filter

Variable Gain

and Filter

RSENS

PWM0, PMW1, PWM2

Offset

Subtraction

Offset

Subtraction

IR/RED

OFF/ON

LED DIS

Output

Variable Gain

and Filter

Variable Gain

and Filter

AC + DC

/ZERO PWM0

REDAC

PWM2

CPU

PWM0 IRAC

AC + DC

/ZERO

Figure 9-33

N-20 SpO2 Analog Block Diagram

9-49

ALE

REDDC REDAC IRDC IRAC

RSENS AMB_LIGHT BAT_VOLT

PR_TEMP PR_TACH

AD15 AD14 AD13 AD12 AD11 AD10 AD9 AD8 AD7 AD6 AD5 AD4 AD3 AD2 AD1 AD0

VREF

VCC

U31

VREF

ANGND

ACH0/P0.0

ACH1/P0.1

ACH2/P0.2

ACH3/P0.3

ACH4/P0.4

ACH5/P0.5

ACH6/P0.6

ACH7/P0.7

EXTINT/P2.2

GND

VPP

ALE/ADV

WRL/WR

WRH/BHE

AD15/P4.7

AD14/P4.6

AD13/P4.5

AD12/P4.4

AD11/P4.3

AD10/P4.2

AD9/P4.1

AD8/P4.0

AD7/P3.7

AD6/P3.6

AD5/P3.5

AD4/P3.4

AD3/P3.3

AD2/P3.2

AD1/P3.1

AD0/P3.0 80C196KC

CPU

T2CLK/P2.3 T2RST/P2.4

P2.6/T2U-D

P2.7/T2CAPT

HSI0

HSI1 HSI2/HSO4 HSI3/HSO5

HSO0 HSO1 HSO2 HSO3

P2.5/PWM0

P1.7/HOLD P1.6/HLDA

P1.5/BREQ P1.4/PWM2 P1.3/PWM1

P1.2 P1.1 P1.0

READY

INST

BUSWIDTH

NMI

CLKOUT RXD/P2.1 TXD/P2.0

RESET

XTAL2 XTAL1

C88

PR_HEAD1 PR_HEAD2

REDLED/AV

33 38

/ZERO

PHOTOI

DISP_PHASE

26 27

PR_STROBE SAMPRED

OFF/ON

SAMPIR

34 35

PWM0

39 32

PR_PRESENT

IRLED/AV

PWR_DOWN PWM2

PWM1

22 21

DISP_LATCH IR/RED

LEDDIS

RAMEN NMI

RXD TXD

10K

R76

RST

VCC

R75 10K

TP4

10K R131 43 63 64 3 65 17 18 2

16 66 67

R137 10K

RST

22PF C89

22PF

10MHz

RESET GENERATION

VCC

TP41

Q22

2N3904

R72 100K

VCC

.1UF

R73RST 15K

R156 15K

C65

TP42

CR10 1N914

Figure 9-34

CPU Circuit

9-51

L-8

DB9F

TO CENTER MTG. HOLE

+12V 1M

-5V

U6C

LTC201

SENSOR INPUT

5 9 4 8 3 7 2 6 1

TP47

100PF

C21 22UF

TANT ACROSS U6 SUPPLY

VREF

L1 L2

C119

VREF

R23

TP44

C116

100PF

RAW10V

RAW12V

RAW-5V

VREF

R63

2.0K

R160

51.1K

C40 390PF

R17

3.32K

182K

R58

3.32K

12 13

VREF

C117 C118

100PF

R18

6.04K

0.1% RSENS

C5 .01UF

R123 182

R121 221

R122

221

R159

88.7K

+12V

.1%

U35

2 -5V 3

LT1097

R158

481

88.7K .1%

-5V

U6D

LTC201

U1D

LF444

18PF

+12V

U1A

3 2

LF444

TP45

TP48

100PF

-5V

C55

.1UF

C95 22UF

.1UF

R157 511K

1 1

VCC

MMBTA56

TP46

R54

6.8

2 4

R161

10K

VREF

+12V

C80 22UF .1UF

-5V

C94 22UF

R64

10K

R19 280K

C22 .047UF

TP50

TP49

.047UF

U32

VIN GND

LT1021

C91

C93

TP78

C59

MMBTA56

2N3904

Q24

VREF

R46 10K

VOUT TRIM

TP61

TP62

+12V

Q2 MMBTA06

Q23 2N3904

C124 .1UF

MMBTA06

TP60

TANT ACROSS U35 SUPPLY

-5V

VCC

C35 .1UF

2 U6A LTC201

1 6

15 U6B LTC201

LED DRIVE

R45 10K

R48 10K

R51

22.1K

VREF

6 5

+5.7

16 7 8

4 15 14

R47 10K

C6 .1UF

OFF/ON

U2 VDD C

VEE VSS

ZYY1

XX0 4053

R26

3.32K

R27

3.32K

R124 1

TP70

LIGHT SENSOR

VCC

SpO2 ANALOG

+12V

C125

.1UF

VREF

R25

82.5K

R24

82.5K

13 2

1 5

3 6

11 10 9

IR/RED

C122

9 10

R39

11 6

47.5K

3 5

1 2

13 12

C34

1NF

C25

.47UF

U10 X0

X1 Y0

Y1 Z0

Z1 INH

A B C

4053

C126 220PF

VREF

C33

2N3906

1NF

U1C

LF444

C127

Q7 220PF

VREF

2N3906

U1B

LF444

R135

3.57K

VREF

14 12

X Y Z

VSS VEE VDD

15 4

8 7 16

Q5 2N3904

TP63

TP64

LT1013

VCC

U9A

C53

.1UF

TP77

C11 22UF

C16

R6 100K

.12UF

.068UF

TP51

TP52 R11 100K

.12UF

100K

.068UF

Q25 2N3906

VCC

1 8

R49

100K R162

100K

U4D

14 100K C15

C18

R10

OP490SO

+12V

U4A

OP490SO

C17

-5V

OFF/ON

C60

4.7PF

R53 100K

C36 .1UF

C39

.022UF

R52 100K

C38

.022UF

C123

CR12

1N914

C52C50 C51 .1UF.1UF.1UF

C13

TP81

.12UF

C14

100K

R12

100K

R42 280K

TP83

R43 20K

C37 .1UF

22PF

VCC

C48 22UF

100K

TP89

CR1 VREF

.068UF

R44 20K

CR18

1N914

CR3 1N914

C19 15K .12UF

U4B

6 5

OP490SO

VREF

1N914

.068UF

C20

1N914 R50 182K

TP84

C49 22UF

-5V

B A

INH

Z1 Z0

Y0 X1

C24

.47UF

VREF

C12 22UF

GND

+12V VCC

C23 22UF

TANT ACROSS U11 SUPPLY-5V

U4C

OP490SO

.015UF

U11C LTC201

VREF

R22

12.1K

R41

TP85

C29

CR2

CR4

.015UF

U11D LTC201

TP90

VREF

R31

12.1K

R5 15K

C106 C107

C105C102

LTC201

U11B

U11A

16.1UF 3

1 4

+5.7

U7A

LMC6044

1 1

R28

34.8K

U7C

LMC6044

R36 100K

C111

U7B

LMC6044

C32

1NF

R37

34.8K 12

TP86

C109C108 .1UF.1UF.1UF.1UF.1UF.1UF

C28 1NF

R30

100K

R60

3.32K

R40

47.5K

R66.01UF

3.32K

C57

U7D

LMC6044

R56

15.8K

TP75

TP88

TP87

R20

3.32K

R67

C61

3.32K

.01UF

R29

3.32K

R61

3.32K.01UF

TP79

R33

3.32K

12 13

2 1

5 3

6 11 10 9

VREF

R57

40.2K

C26

.1UF

U3 X0 X

Y1Y0Z Z0

VSS INH A VEE B C

VDD

R21

3.32K

C30

.1UF

3 4

BATTERY VOLTAGE

SENSE

TEMP SENSOR

VCC

VCC D8 VTB8442B

TP53

14 15 4

8 7 16

TP76

C7 .01UF

C27 .47UF

VCC4053

REDLED/AV

IRDC

C8 .01UF

C31 .47UF

U9B

5 LT1013

TP80

TEMP

REDLED/AV

PWM2 SAMPRED SAMPIR OFF/ON

IRLED/AV

C58

.1UF

PWM0

IR/RED OFF/ON

LEDDIS RSENS

VBAT

REDDC

REDAC

/ZERO

PHOTOI

15.8K BAT_VOLT

47.5K

MMBTA13L

R136

33.2K

TP54

TP55

C56 .01UF

PWM1

TP56

TP57

TP58

IRAC

TP59

R69 1%

R70 1%

PR_TEMP

TP73

R68

2.2M

VCC

GND

LM35

C62 .01UF

C115 .1uF

C63 .01UF

TP72

VREF

REDDC REDAC IRDC IRAC

RSENS AMB_LIGHT BAT_VOLT

PR_TEMP PR_TACH

ALE

AD15 AD14 AD13 AD12 AD11 AD10 AD9 AD8 AD7 AD6 AD5 AD4 AD3 AD2 AD1 AD0

ADDRESS DEMUX

U13

AD0

AD1

D2D1Q2

AD2

AD3

AD4

AD5

AD6 AD7

D8 Q8

ALE

TP39

74HC573 R108 10K

U33

AD8

AD9

AD10

AD11

AD12

AD13

AD14

AD15

ALE

TP40

74HC573

R109 10K

13 12 6 5 7 4 11 10 8 9 15 14

VCC

37 62 61 40 41 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

DIGITAL SECTION

CPU

U31 VREF

ANGND

Q1 Q3D3 D2A2

Q4 Q5 Q6 Q7D7

Q1 Q2 Q3 Q4 Q5 Q6 Q7 Q8

ACH0/P0.0 ACH1/P0.1 ACH2/P0.2 ACH3/P0.3 ACH4/P0.4 ACH5/P0.5 ACH6/P0.6 ACH7/P0.7 EXTINT/P2.2 GND

VPP ALE/ADV RD WRL/WR

19 18 17 16 15 14 13 12 A7

19 18 17 16 15 14 13 12

TP5 TP6 TP7 TP8 TP9 TP10 TP11 TP12 TP13 TP14 TP15 TP16 TP17 TP18 TP19 TP20

TP21 TP22

T2CLK/P2.3 T2RST/P2.4 P2.6/T2U-D

P2.7/T2CAPT

A0 A1 A2 A3 A4 A5 A6

A8 A9 A10 A11 A12 A13 A14 A15

A0 A1 A2 A3 A4 A5 A6 A7 A8 A9 A10 A11 A12 A13 A14 A15

ROMEN RD

HSI0

HSI1 HSI2/HSO4 HSI3/HSO5

HSO0

HSO1

HSO2

HSO3 P2.5/PWM0 P1.7/HOLD P1.6/HLDA P1.5/BREQ P1.4/PWM2 P1.3/PWM1

P1.2

P1.1

P1.0

READY

INST

BUSWIDTH

NMI

CLKOUT RXD/P2.1 TXD/P2.0

EA RESET XTAL2 XTAL1

C88

22PF C89

22PF

8K X 8 SRAM

A0 A1 A2 A3 A4 A5 A6 A7 A8 A9 A10 A11

A12 RAMEN WR

64K X 16 EPROM

A10

A11

A12

A13

A14

A15

ROMEN

VCC VCC

44 42 33 38 24 25 26 27 28 29 34 35 39 32 31 30 23 22 21 20 19

43 63 64 3 65 17 18 2 16 66 67

Y2 10MHz

TP43

10K

10 9 8 7 6 5 4 3 25 24 21 23 2

20 26 27 22

24 25 26 27 28 29

31 32 35 36 37 38 39 40 41

3 22 2 43

PR_HEAD1 PR_HEAD2 REDLED/AV /ZERO PHOTOI

DISP_PHASE PR_STROBE SAMPRED OFF/ON SAMPIR

PWM0 PR_PRESENT IRLED/AV PWR_DOWN PWM2 PWM1 DISP_LATCH IR/RED LEDDIS

R131

RAMEN NMI

RXD TXD

RST

R76 10K

U14

A1A0D1 A3

A4 A5 A6 A7 A8 A9 A10 A11 A12

CS1 CS2 WE OE

U15 A0

A1 A2 A3 A4 A5 A6 A7 A8 A9 A10 A11 A12

A14 A15

CE OE VPP PGM

27C1024L

R80

221

GO BUTTON

TALIQ PS CTRL

R137 10K

U34

SET1

CLK1

RST

VCC

TP4

R75

10K

VCC

TP65

RST1

SET2

CLK2

RST2

VCC 74HC74

DISP_POL

DISP_DL

GND

TP66

TXD RXD

R128

C120

10K

100PF

VCC

BEADL6

BEAD

C121

100PF

RESET GENERATION

VCC

AD0

AD1

AD2

VCC

O5 O6

O10

O11

O12

O13A13

O14

O15

TP41

AD3 AD4 AD5 AD6 AD7

R133 10K

AD0 AD1 AD2 AD3 AD4 AD5 AD6A7 15 30 AD7 AD8

AD9 AD10 AD11 AD12 AD13 AD14 AD15

RST

Q22

2N3904

VCC

C65

R72 100K

.1UF

R73 475K

R156 475K

ADDRESS DECODING

U30B 3 4 6 5

74HC10

TP71

2 3

6 4 5

WR RD

A10

A12 A13 A14 A15

A14 A15 A11

CR10 1N914

U28 A

B C

G1 G2A G2B

74HC138

TP42

15 1

DC00-DFFF

U30A 1 2 13

74HC10

U30C 9 10 11

74HC10

GO_SW

PR_HEAD1 PR_HEAD2 PR_STROBE PR_TACH PR_PRESENT

PWR_DOWN DISP_PHASE DISP_POL DISP_DL

RAW10V RAW12V RAW-5V

VCC

VBAT

JP1

1 2

SERIAL DATA

3 4

4 HDR

AD15 AD14 AD13 AD12 AD11 AD10 AD9 AD8 AD7 AD6 AD5 AD4 AD3 AD2 AD1 AD0

E000-FFFF

RAMEN

0000-DBFF

ROMEN

TO: N-20 AUX PCB

PORT

EXINEN EXOUTEN

TO: N-20 AUX PCB

TP74

JP8 1

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

20 HDR

JP7 1

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

20 HDR

NOTES:

1. ALL RESISTORS 1/8W 1% UNLESS OTHERWISE SPECIFIED.

10K R134

VCC

Figure 9-35

Main PCB Schematic Diagram

9-53

BATTERY INPUT

VRECHARGE

6 3

LT1046

TO: N-20 MAIN PCB

JP18

1 2 3 4 5 6 7 8

9 10 11 12 13 14 15 16 17 18 19 20

20 HDR

JP17

9 10 11 12 13 14 15 16 17 18 19 20

20 HDR

GO_SW

PR_HEAD1 PR_HEAD2 PR_STROBE PR_TACH PR_PRESENT

PWR_DOWN DISP_PHASE DISP_POL DISP_DL

AD15 AD14 AD13 AD12 AD11 AD10 AD9 AD8 AD7 AD6 AD5 AD4 AD3 AD2 AD1 AD0 EXINEN EXOUTEN

RAW10V RAW12V RAW-5V VCC

VBAT

3.32K

L11

100PF

DISP_DATA DISP_CLK

TO: N-20 MAIN PCB

DIGITAL IC'S BYPASS CAPS

C97

C98

.1UF

TP3

BATT GND

TEST

TP1

BATT PLUS

TEST

R100

TP2

15K

TEST

VCC

TP72

R102

TEST

15K

GO_BTN

R79

TP71

C123

TEST

VCC

C99

C100

.1UF

VCC

R101 150K

VCON VCON

R78 150K

C66 .01UF

R81

3.32K

VCC

VDISP

TP80

TEST

27 25 23 22 18 26

20 21

VCC

27 25 23 22 18 26

20 21

VCC

C101 .1UF

1.5A

CR27 1N914

TALIQ DRIVERS

U19 VDD

VPP

DIN CLK LATCH POL DOUT SL

OSCIN OSCOUT

GND SI9530

U20 VDD

VPP

DIN CLK LATCH POL DOUT SL

OSCIN OSCOUT

GND SI9530

C49 22UF

VCON

R155 10K

Q15

SI9956DY

U21

SET1

CLK1

RST1

SET2

CLK2

13 R110 475K

C67 .1UF

RST2

VCC

TP73 TEST

O10

O11

O12

O13

O14

O15

O16

O17

O18

O19

O20

O21

O22

O23

O24

O25

O26

O27

O28

O29

O30

O31

O32

O10

O11

O12

O13

O14

O15

O16

O17

O18

O19

O20

O21

O22

O23

O24

O25

O26

O27

O28

O29

O30

O31

O32

74HC74

C110 .1UF

5 6

7 8

Q1 Q1

Q2 Q2

GND

HDR 32

EL DRIVE

TO CENTER MOUNTING HOLE

TRANZORB

BAT_TYPE

PWR_ON

9 8

CHECK BATTERY

JP2 1

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

JP3 1

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

VCC

TP76 TEST

JP5 1

2 3 4 5 6 7

HDR 7

VBAT

C116

C73

CR24

10V

TP83 TEST

R74

TP88

TEST

SW1

EXOUTEN

CR23

1N914

R163

3.32K

BT1 3V

PR_STROBE

VCC

R123

150K

C114

.1uF

22UF

.1UF

VCON

TP84

TEST

VCC

L12

C126

100PF

EX_IN INPUT PORT

U16

AD0

AD1

AD2 AD3

AD4

AD5

14 13

AD6

AD7

74HC573

EXINEN

EX_OUT LSB

U18

AD0 AD1 AD2 AD3 AD4 AD5 AD6 AD7

R132

AD8 AD9 AD10 AD11 AD12 AD13 AD14 AD15

CLK

OC 74HC574

150K

TP82 TEST

EX_OUT MSB

U17

CLK

OC 74HC574

REAL TIME CLOCK

U29

VCC

GND DS1202S

32.768KHz

C68 .1UF

R71 150K

BAT_BTN

C64 .01UF

D1 2Q1 D2 3Q2 D3 4Q3 D4 5Q4 D5 6Q5 D6 7Q6 D7 8Q7 D8 9Q8

Q1 Q2 Q3 Q4 Q5 Q6 Q7 Q8

SCLK

11 1

19 18 17 16 15 14 13 12

I/O RST

POWER SUPPLY

C74

C117

22UF

JP9 PIN 17

TP81

TEST

GO_BTN

ON_OFF_BTN DD_BTN ADV_BTN PR_HOME BAT_TYPE RTC_IO

VCC

DISP_DATA DISP_CLK RTC_CLK RTC_RST PR_MOTOR PR_MEAS BEEP_1 BEEP_2

PR_DOT6 PR_DOT5 PR_DOT4 PR_DOT3 PR_DOT2 PR_DOT1 PR_DOT0 RTC_IO

TP86 TEST

RTC_CLK

RTC_IO

RTC_RST

120UH

PR_HOME

TEST

TP85 TEST

TP87 TEST

R134 150

PR_TACH

R118 150K

PR_MEAS

1 2 3 4

C75 .1UF

PR_PRESENT

PR_HEAD1

PR_HEAD2

VCC

BZ1

AT17

BEEPER

U22 ILIM

VIN SW1 SW2

LT1173

100pf

120UH

VCC

C127

R77

SET

GND

C118

C70

22UF

14 13 12 11

C82 22UF

U36B

LT1017CS

U36A

LT1017CS

VPRN

R142

R106 150K

150K

Q19

2N3904

R147

3.32K

R156

TP74

TESTTP75

R148

R149

150K

R150

150K

R151

150K

R152

150K

R153

150K

150KR154

150K

VBAT

U23

V + OSC VREF VOUT

LT1054CS

R141 1K

R82

100K

C119

R83

28.7K

22UF

FB/SD CAP +

GND

CAP -

C90

22UF

U26

VIN

VSW

GND

LT1172

11 12

VPRN

1 4

5 4

TP77

TEST

Q17

DRN SRC SRC

GATE SI9405DY

R120

22.1K

2.2UF

R119

22.1K

R144

1.24K

R104 150K

VCC

R105 150K

DRN

R86

31.6K

C96

TP78 TEST

TP79 TEST

R145

60.4K

R103 150K

TP31 TEST

C115 .1UF

R85 100K

C81

.1UF

CR25

5367A

43V 10%

DISP_PHASE

VPRN

C76

100PF

C78

.47UF

C112 1UF 50V

CR30 MURS110

C113

4.7UF 50V

+70V

R113

4.75K

Q12 MMBT5551L

R115

R114

12.1K

TP35 TEST

TP24 TEST

TP23

TP26

TEST

TEST TP25 TEST

C120

C121

C122

100PF

C72 .1UF

475K

TP27 TEST

L8 L9 L10

TALIQ COLD SWITCH

Q13 2N3904

TP37

TP36

TEST

TP29

TEST TP28 TEST

C71 22UF

C125 22UF

C79 22UF

C92

2.2UF 50V

C95

2.2UF 50V

R116 10K

TP30 TEST

PR_PRESENT

ON_OFF ADV DD

TP32 TEST

TP33 TEST

VCC

R117

6.19K

VPRN

TG HM

DOT4

VPRN

PR_DOT6 PR_DOT5 PR_DOT4 PR_DOT3 PR_DOT2 PR_DOT1 PR_DOT0 PR_MOTOR

VPRN

PWR_ON

TP34 TEST

VCC

RAW-5V

RAW10V

RAW12V

TP38 TEST

R125 390K 1%

R126 390K 1%

R127 14K 1%

TO PRINTER PCB

390PF

+70V

C124 .1UF 100V

+70V

R93 182

Q14 MMBT5401L

C87

C83 390PF

Q21 MMBT5551L

R95 182

JP9 1

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22

22 HDR

VDISP

2 3

R84

10K

3 4 5 6

R96

3.32K

C85 .1UF

VPRN

R143

14.0K

R146

Q20 2N3904

VCC

Figure 9-36

Auxiliary PCB Schematic Diagram

9-55

TO N-20 POWER SUPPLY BOARD

JP9

1 2 3 4 5 6 7 8

9 10 11 12 13 14

VPRN

TG HM

DOT4

PR_DOT6 PR_DOT5 PR_DOT4 PR_DOT3 PR_DOT2 PR_DOT1 PR_DOT0 PR_MOTOR

8 1 2 3 4 5 6 7

3300UF

INM IN0 IN1 IN2 IN3 IN4 IN5 IN6

VCC

LB1256

OUTM OUT0 OUT1 OUT2 OUT3 OUT4 OUT5 OUT6

GND

JP10 M+ MTG

11 18 17 16 15 14 13 12

DOT6DOT6 DOT5 DOT4 DOT3 DOT2 DOT1 DOT0

1 2 3 4 5 6

HEADER 6

JP11

8 7 6 5 4 3 2 1

HEADER 8

SEIKO

MTP102-16

PRINTER

15 16 17 18 19 20 21 22

22 HDR

PWR_ON

PR_PRESENT

ON_OFF ADV DD

1 2

3 4

S1 G1

S2 G2

SI9956DY

D1 D1

D2 D2

8 7

6 5

0.01uF

ON OFF BUTTON

ADVANCE BUTTON

DAY/DATE BUTTON

Figure 9-37

N-20 Flex Circuit Schematic Diagram

9-57

Nellcor N-20, N-20P, N-20PA User manual

Specifications and Main Features

Frequently Asked Questions

User Manual

1.1 Manual Overview

1.2 Warnings and Cautions

2.1 Overview

2.2 Cleaning

2.3 Periodic Safety and Functional Checks

2.4 Battery

3.1 Introduction

3.2 Required Materials

3.3 Performance Tests

3.3.1 Backlight Test

3.3.2 Battery Performance

3.3.4 Printer Test

3.3.5 Hardware and Software Tests

4.1 How to Use This Section

4.2 Who Should Perform Repairs

4.3 Replacement Level Supported

4.4 Obtaining Replacement Parts

4.5 Troubleshooting Guide

4.6.1 Installing Batteries

4.6.2 Loading/Clearing Printer Paper

4.6.3 Setting Date and Time

4.6.5 Replacing Fuses

4.6.7 Adjusting Printer Darkness

4.7 Error Codes

4.7.3 Category 3 — PROM Errors

4.7.4 Category 4 — I/O Port Errors

4.7.5 Category 5 — Reserved

4.7.6 Category 6 — Clock Errors

4.7.8 Category 8 — Printer Errors

5.1 Introduction

5.2 Required Equipment/Tools

5.2.1 N-20 Disassembly Procedure

5.2.2 Removing the Covers

5.2.3 Removing the PCBs and Display Assembly

5.2.4 N-20P Disassembly Procedure

5.2.5 Disassembling the Printer/Flex Circuit Assembly

6 SPARE PARTS

6.1 N-20/N-20P Spare Parts

7 PACKING FOR SHIPMENT

7.1 General Instructions

7.2 Repacking in Original Carton

8.1 Readout

8.2 Controls

8.3 Operating Modes

8.3.1 Spot Check Mode

8.3.2 Extended Mode

8.5.1 Range

8.5.2 SpO2 Accuracy

8.5.3 Response

8.6 Sensor Types

8.7 Electrical Specifications

8.7.1 Battery

8.7.2 Instrument

8.8.1 Operating Temperature

8.8.2 Storage Temperature

8.9.1 Weight (with batteries installed)

8.9.2 Dimensions

8.10 Qualifying Information

9.1 Overview

9.2 Functional versus Fractional Saturation

9.3 Measured versus Calculated Saturation

9.4 Circuit Analysis

9.5 Functional Overview

9.7 Definition of Terms

9.7.1 Analog to Digital (A/D) converter

9.7.2 Central Processing Unit (CPU)

9.7.3 Content Addressable Memory (CAM)

9.7.4 High Speed Outputs (HSO)

9.7.5 Input and Output (I/O)

9.7.7 Pulse Width Modulation (PWM)

9.7.8 RCal

9.8 Overall Block Diagram

9.8.1 Main PCB

9.8.2 Auxiliary PCB

9.8.3 Display and Analog Shield Assembly

9.9.1 Sensor Output/LED Control