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SERVICE MANUAL
NPB-40 Handheld Pulse Oximeter

Caution: Federal law (U.S.) restricts this device to sale by or on the order of a physician. To contact Nellcor Puritan Bennett's representative: In the United States, call 1-800-635-5267 or 925-463-4000; outside of the United States, call your local Nellcor Puritan Bennett representative.

012 3

© 2001 Nellcor Puritan Bennett, Inc. All rights reserved.

036048D-0601

Nellcor Puritan Bennett Inc. 4280 Hacienda Drive Pleasanton, CA 94588 USA Telephone Toll Free 1.800.NELLCOR Tyco Healthcare UK LTD Fareham Road Gosport PO13 0AS U.K. Tel: +44.1329.224000

To obtain information about a warranty, if any, for this product, contact Nellcor Puritan Bennett Technical Services Department, or your local Nellcor Puritan Bennett representative. Notice: Purchase of this instrument confers no express or implied license under any Nellcor Puritan Bennett patent to use the instrument with any sensor that is not manufactured or licensed by Nellcor Puritan Bennett. Oxisensor II is a trademark of Nellcor Puritan Bennett, Inc. Covered by one or more of the following U.S. Patents and foreign equivalents: 4,621,643; 4,653,498; 4,700,708; 4,770,179; 4,869,254; 4,928,692; 4,934,372; 5,078,136; 5,351,685; 5,368,026; and Re. 35,122.

TABLE OF CONTENTS
List of Figures List of Tables

Section 1: Introduction................................................................................. 1.1 Manual Overview............................................................................ 1.2 Equipment Description ................................................................... Section 2: Routine Maintenance ................................................................ 2.1 Maintenance Overview ................................................................... 2.2 Battery Maintenance ...................................................................... 2.2.1 Battery Replacement ......................................................... 2.2.2 Battery Disposal ................................................................ 2.3 Cleaning ............................................................................................ Section 3: Performance Verification .......................................................... 3.1 Performance Verification ................................................................... Section 4: Troubleshooting ......................................................................... 4.1 Introduction..................................................................................... 4.2 Who Should Perform Repairs......................................................... 4.3 Repair Level Supported.................................................................. 4.4 How to Use This Section ................................................................ 4.5 Obtaining Replacement Parts ........................................................ 4.6 Troubleshooting Guide ................................................................... Section 5: Disassembly Guide .................................................................... 5.1 Introduction..................................................................................... 5.2 System Disassembly and Reassembly .......................................... Section 6: Spare Parts.................................................................................. 6.1 Introduction..................................................................................... Section 7: Packing for Shipment................................................................. 7.1 General Instructions........................................................................ 7.2 Packing NPB-40 in Original Carton ................................................ 7.3 Packing in a Different Carton ......................................................... Section 8: Specifications ............................................................................. 8.1 Performance ................................................................................... 8.2 Electrical ......................................................................................... 8.3 Environmental................................................................................. 8.4 Physical ......................................................................................... Technical Supplement.................................................................................. S1 Introduction..................................................................................... S2 Pulse Oximetry Principles of Operation .......................................... S2.1 Overview ........................................................................... S2.2 Functional Versus Fractional Saturation............................ S2.3 Measured versus Calculated Saturation............................ S3 Circuit Analysis ............................................................................... S3.1 Overall Unit Block Diagram Analysis ................................. S3.2 CPU PCB Theory of Operation.......................................... S3.3 LCD PCB Theory of Operation .......................................... S4 Schematic Diagrams ......................................................................

1-1 1-1 1-1 2-1 2-1 2-1 2-1 2-2 2-2 3-1 3-1 4-1 4-1 4-1 4-1 4-1 4-1 4-2 5-1 5-1 5-1 6-1 6-1 7-1 7-1 7-1 7-1 8-1 8-1 8-2 8-2 8-3 S-1 S-1 S-1 S-1 S-1 S-2 S-2 S-3 S-5 S-11 S-17

iii

Table of Contents

LIST OF FIGURES 1-1 1-2 2-1 3-1 3-2 3-3 3-4 4-1 5-1 5-2 5-3 5-4 6-1 7-1 S2-1 S3-1 S3-2 S3-3 S4-1 S4-2 S4-3 S4-4 S4-5 LIST OF TABLES 4-1 4-2 Troubleshooting Guide .................................................................. NPB-40 Error Codes ..................................................................... 4-2 4-5 NPB-40 Handheld Pulse Oximeter ................................................ NPB-40 Front Panel....................................................................... NPB-40 Battery Installation ........................................................... NPB-40 Self-Test Front Panel Display .......................................... Printer Interface Setup................................................................... Typical Average Data Print Out ..................................................... Typical Data Print Out ................................................................... Typical Error Code Display ............................................................ Opening the NPB-40 Case ............................................................ Top Case Removal ........................................................................ Unlocking CPU PCB Connector J3 ............................................... Separating LCD PCB from CPU PCB............................................ NPB-40 Expanded View ................................................................ Repacking the NPB-40 .................................................................. Oxyhemoglobin Dissociation Curve .............................................. NPB-40 Block Diagram ................................................................. CPU PCB Block Diagram .............................................................. LCD PCB Block Diagram............................................................... CPU PCB Parts Locator Diagram.................................................. LCD PCB Parts Locator Diagram .................................................. CPU PCB Schematic Diagram ...................................................... LCD PCB Schematic Diagram....................................................... Front Panel Keypad Schematic Diagram ...................................... 1-1 1-2 2-2 3-1 3-3 3-4 3-5 4-2 5-2 5-2 5-3 5-3 6-2 7-2 S-2 S-4 S-6 S-12 FO-1 FO-2 FO-3 FO-4 FO-5

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SECTION 1: INTRODUCTION
1.1 1.2 Manual Overview Equipment Description

1.1

MANUAL OVERVIEW This manual contains information for servicing the NPB-40 handheld pulse oximeter. Only qualified service personnel should service this product. Before servicing the NPB-40, read the operator's manual carefully for a thorough understanding of how to operate the NPB-40.

1.2

EQUIPMENT DESCRIPTION The Nellcor Puritan Bennett NPB-40 handheld pulse oximeter is used for noninvasive spot-check measurement of functional oxygen saturation of arterial hemoglobin (SpO2 ) and pulse rate (measured by the SpO2 sensor). The NPB-40 is for attended monitoring only, and must be used in the continuous presence of a qualified healthcare provider. The NPB-40 can be used on adult, pediatric, and neonatal patients. It can be used in mobile environments when protected from excessive moisture such as direct rainfall. The NPB-40 is powered by four "AA" cell alkaline batteries. An external Hewlett-Packard HP82240B printer can be used with the NPB-40 to printout readings stored in the NPB-40 memory. This printer is available from Nellcor Puritan Bennett. The NPB-40 handheld pulse oximeter is illustrated in Figure 1-1.

Figure 1-1: NPB-40 Handheld Pulse Oximeter The NPB-40 is operated using a four-key keypad and an LCD display on the front panel as shown in Figure 1-2. Refer to the NPB-40 operator's manual for complete operating instructions.

1-1

Section 1: Introduction
1 2 3 4 5 6 7 8 9 10 11 12 13 Pulse Amplitude indicator Pulse Rate display Pulse Search display Low Battery indicator Sensor disconnect indicator Power On/Off key Display Light/Beep On/Off key Store Data/Print key Shift key Store Data icon Shift icon Print icon SpO2% display

1 13 12 11 10 9 8 2 3 4 5 6 7

Figure 1-2: NPB-40 Front Panel

1-2

SECTION 2: ROUTINE MAINTENANCE
2.1 2.2 2.3 Maintenance Overview Battery Maintenance Cleaning

2.1

MAINTENANCE OVERVIEW The NPB-40 requires no routine service or calibration. The performance verification tests in Section 3, Performance Verification, may be used following repairs or during routine maintenance (if required by your local institution).

2.2

BATTERY MAINTENANCE Warning: The NPB-40 uses four "AA" cell alkaline batteries for operation. If batteries are not replaced when recommended or are not disposed of properly, serious personal injury or damage to the NPB-40 could result. Caution: When inserting the positive end of each battery, exercise caution to not damage the small coiled spring contact. Nellcor Puritan Bennett recommends that you comply with the following guidelines for battery replacement and battery disposal as a minimum.

2.2.1

Battery Replacement Caution: The NPB-40 could be damaged by batteries that are left unused in the unit and begin to leak. Never store the NPB-40 with the batteries installed for a prolonged period of time. NPB-40 batteries should be replaced whenever a low battery indication is observed on the unit. Remove the batteries if you will be storing the NPB-40 for longer than one month. Refer Figure 2-1 for replacing the batteries. Note: For easier battery installation, insert the negative end of the battery first when installing each battery.

2-1

Section 2: Routine Maintenance

Figure 2-1: NPB-40 Battery Installation 2.2.2 Battery Disposal When NPB-40 batteries have been replaced, dispose of the old batteries. Always follow local ordinances when disposing of the NPB-40 batteries. Warning: Never dispose of NPB-40 batteries by burning. The batteries could explode in fire and cause serious personal injury. 2.3 CLEANING Caution: Do not immerse the NPB-40 or accessories in liquid or use caustic or abrasive cleaners. To clean the NPB-40, dampen a soft cloth with a commercial nonabrasive cleaner and wipe the unit with the cloth.

2-2

SECTION 3: PERFORMANCE VERIFICATION
3.1 Performance Verification

3.1

PERFORMANCE VERIFICATION The performance of the NPB-40 can be verified using the following procedure. Before performing this procedure, the NPB-40 must have fresh batteries installed. If any of the required observations cannot be obtained, do not return the NPB-40 to service before referring to Section 4, Troubleshooting. You will need an SRC-2 pulse oximeter tester to perform this procedure. If the performance of the printing function will be verified, you will need an HP82240B printer. The NPB-40 is to be turned off and any sensors disconnected before performing this procedure. 1. 2. Press the On/Off key on the front panel keypad. The NPB-40 will perform a self-test. Verify that all display segments are lit during the self-test as shown in Figure 3-1. Also verify that a low pitched audio tone is heard at the end of the self test. Also verify that you then hear a high, a low, and a high pitch error tone indicating that a sensor is not connected. Verify that dashes are shown on the display and the SENSOR DISCONNECT indicator is flashing.

Figure 3-1: NPB-40 Self-Test Front Panel Display 3. 4. Wait for 20 to 40 seconds. Verify that two triple beeps are heard. Verify that the NPB-40 then shuts itself off. Connect an SRC-2 pulse oximeter tester to the NPB-40 sensor connector. Note: If the SRC-2 is connected directly to the NPB-40 sensor connector, its controls will be facing the opposite direction of the NPB-40 controls. Connecting the SRC-2 through a sensor extension cable, such as the Nellcor Puritan Bennett model EC4 or EC-8, will make it easier to perform this procedure.

3-1

Section 3: Performance Verification

Set the SRC-2 controls as follows: RATE LIGHT MODULATION LOCAL/REMOTE/RCAL 5. 6. 112 HIGH 1 HIGH LOCAL

Press the On/Off key on the NPB-40 front panel keypad. When the self-test is complete, verify that the PULSE SEARCH indicator illuminates momentarily and verify that the NPB-40 is displaying a pulse rate of 112 (±3 bpm), that the pulse amplitude indicator is displaying properly, that the SpO 2% indicator is displaying 81 (±2 %), that a pulse beep can be heard, and that the PULSE SEARCH indicator is off. Set the following SRC-2 controls as indicated: RATE LIGHT MODULATION 38 HIGH 2 LOW

7.

Wait 30 seconds and verify that the NPB-40 is displaying a pulse rate of 38 (±3 bpm), that the pulse amplitude indicator is displaying properly, that the SpO 2% indicator is displaying 81 (±2 %), that a pulse beep can be heard, and that the PULSE SEARCH indicator is off. 8. Set the following SRC-2 controls as indicated: RATE LIGHT 201 LOW

Wait 30 seconds and verify that the NPB-40 is displaying a pulse rate of 201 (±3 bpm), that the pulse amplitude indicator is displaying properly, that the SpO 2% indicator is displaying 81 (±2 %), that a pulse beep can be heard, and that the PULSE SEARCH indicator is off. 9. Set the following SRC-2 control as indicated: MODULATION HIGH

Wait 30 seconds and verify that the NPB-40 is displaying a pulse rate of 201 (±3 bpm), that the pulse amplitude indicator is displaying properly, that the SpO 2% indicator is displaying 81 (±2 %), that a pulse beep can be heard, and that the PULSE SEARCH indicator is off. 10. Press the Shift key followed by the Display Light/Beep On/Off key. Verify that the SHIFT indicator illuminates when the Shift key is pressed then verify that the pulse beep stops and the SHIFT indicator extinguishes when the Display Light/Beep On/Off key is pressed. Press the Shift key followed by the Display Light/Beep On/Off key and verify that the pulse beep can be heard again at a low level.

11.

3-2

Section 3: Performance Verification

12. 13.

Press the Shift key followed by the Display Light/Beep On/Off key and verify that the pulse beep can again be heard again at a higher level. Press and release the Display Light/Beep On/Off key on the front panel keypad and verify that the LCD backlight comes on, remains on and the LCD is adequately illuminated. Press the Display Light/Beep On/Off key on the front panel keypad and verify that the LCD backlight is off. Set the following SRC-2 control as indicated: LOCAL/REMOTE/RCAL REMOTE

14. 15.

16.

On the NPB-40, verify that the PULSE SEARCH indicator illuminates after a few seconds and that the number "0" is displayed in the SpO 2% and pulse rate displays. Set the following SRC-2 control as indicated: LOCAL/REMOTE/RCAL LOCAL

17.

18.

On the NPB-40, verify that the PULSE SEARCH indicator illuminates momentarily and verify that the NPB-40 is displaying a pulse rate of 201 (±3 bpm), that the pulse amplitude indicator is displaying properly, that the SpO 2% indicator is displaying 79 to 83, that a pulse beep can be heard, and that the PULSE SEARCH indicator is off. Note: If an HP82240B printer is not available, skip steps 19 through 27 and proceed to step 28.

19. 20.

Refer to the printer operator's manual as needed. Verify that paper is properly installed in the printer and turn the printer on. Align the NPB-40 with the printer as shown in Figure 3-2.

0°­ 5° 0°­ 5° 1"­ 2" (2.5 ­ 5.1 cm.)

Figure 3-2: Printer Interface Setup

3-3

Section 3: Performance Verification

21.

On the NPB-40, press the Shift key followed by the Store Data/Print key on the front panel keypad. Note: In the following steps, printed SpO2% values will be 79 to 83 and pulse rate values will be 201, ±3 bpm. Figures 3-3 and 3-4 are examples of typical print outs. The NPB-40 will not display pulse or SpO2% values while printing.

22.

Verify that the PRINT icon is illuminated on the NPB-40 display, that the printer begins printing and that the printer prints out a summary report similar to that shown in Figure 3-3.

Figure 3-3: Typical Average Data Print Out 23. With the SRC-2 connected to the NPB-40 and still set up as in step 18, press only the Store Data/Print key on the front panel keypad and verify that the LCD display indicates "1-Id" and the STORE DATA icon illuminates. Press only the Store Data/Print key on the front panel keypad and verify that the LCD display indicates "2-Id" and the STORE DATA icon illuminates. Press only the Store Data/Print key on the front panel keypad and verify that the LCD display indicates "3-Id" and the STORE DATA icon illuminates. Align the NPB-40 with the printer as shown in Figure 3-2 and press the Shift key on the NPB-40 front panel keypad, followed by the Store Data/Print key. Verify that the PRINT icon is illuminated on the NPB-40 display, that the printer begins printing and that the printer prints out data similar to that shown in Figure 3-4. As data stored in steps 24, 25, and 26 is printed out, the NPB-40 display will indicate "1-Id", "2-Id", and "3-Id", respectively.

24.

25.

26.

27.

3-4

Section 3: Performance Verification

Figure 3-4: Typical Data Print Out 28. 29. Press the On/Off key on the front panel keypad. Verify that the NPB-40 shuts off.

3-5

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SECTION 4: TROUBLESHOOTING
4.1 4.2 4.3 4.4 4.5 4.6 Introduction Who Should Perform Repairs Repair Level Supported How to Use This Section Obtaining Replacement Parts Troubleshooting Guide

4.1

INTRODUCTION This section provides information for troubleshooting the NPB-40 and helping you to isolate a failure to the front panel keypad, the CPU PCB, or the LCD PCB. A troubleshooting guide is provided in Paragraph 4.6, "Troubleshooting Guide" that lists possible difficulties, along with probable causes, and recommended actions to correct each difficulty. The Technical Supplement at the end of this manual provides information on how the components of the NPB-40 function.

4.2

WHO SHOULD PERFORM REPAIRS Only qualified service personnel should remove and replace components of the NPB-40. Repairs to the NPB-40 are limited to the repair level identified in Paragraph 4.3, "Repair Level Supported." If your facility does not have qualified service personnel, contact the Nellcor Puritan Bennett Technical Services Department or your local Nellcor Puritan Bennett representative.

4.3

REPAIR LEVEL SUPPORTED Besides the batteries, the NPB-40 has five replaceable components, the case top with the front panel keypad, the case bottom, the CPU PCB, the LCD PCB, and the battery compartment door.

4.4

HOW TO USE THIS SECTION Failures of the case bottom, the battery compartment door, and the case top, not including the front panel keypad, are determined by visually inspecting these components for cracks or deformations and for mechanical failures such as the screw holes stripping out in the case top. The case top and the front panel keypad are replaced together. Use the troubleshooting guide provided in Paragraph 4.6, "Troubleshooting Guide" to isolate failure to the front panel keypad, the CPU PCB, or the LCD PCB. Once a failure has been isolated, refer to Section 5, Disassembly Guide for instructions for removing and replacing a component of the NPB-40.

4.5

OBTAINING REPLACEMENT PARTS Nellcor Puritan Bennett Technical Services Department provides technical assistance information and replacement parts. To obtain replacement parts, contact the Nellcor Puritan Bennett Technical Services Department or your local Nellcor Puritan Bennett representative. Refer to parts by the part names and part numbers listed in Section 6, Spare Parts.

4-1

Section 4: Troubleshooting

4.6

TROUBLESHOOTING GUIDE If you encounter a problem that cannot be resolved through a visual inspection, refer to Table 4-1 which provides a list of symptoms, probable causes, and recommended actions to take to correct the problem. It is recommended that corrective actions be performed in the order presented. For a symptom that is not listed in Table 4-1, contact the Nellcor Puritan Bennett Technical Services Department or your local Nellcor Puritan Bennett representative. If an error code is shown on the front panel LCD display, as shown in Figure 4-1, turn the NPB-40 off and back on again. If the error code still persists, refer to Table 4-2 for the indicated failure and corrective action.

Figure 4-1: Typical Error Code Display Once you have performed the recommended action, reassemble the NPB-40, refer to Section 3, Performance Verification, and conduct a performance verification before returning the NPB-40 to service. If the symptom persists, continue troubleshooting. Table 4-1: Troubleshooting Guide Symptom The unit does not turn on when the On/Off key is pressed. Probable Cause The batteries are missing. The batteries are installed incorrectly or are backwards. The batteries are at or near a voltage too low for the NPB-40 to operate. Corrective Action Open the battery compartment and if batteries are missing, install new batteries. Open the battery compartment and if batteries are not installed correctly, remove and reinstall the batteries. Install new batteries.

(Continued on next page)

4-2

Section 4: Troubleshooting

Table 4-1: Troubleshooting Guide (Continued) Symptom The unit does not turn on when the On/Off key is pressed. (continued) Probable Cause The sensor is defective. Corrective Action Replace the sensor.

The front panel keypad is defective.

Flex circuit between front panel and CPU PCB is disconnected. A CPU PCB component has failed.

One or more keys on the front panel keypad does not work.

The front panel keypad is defective.

Flex circuit between front panel and CPU PCB is disconnected. A CPU PCB component has failed. (Continued on next page)

Open the NPB-40, disconnect the case top from J3 on the CPU PCB and connect an ohmmeter between the flex circuit conductor for J3, pin 5 and the conductor for J3, pin 3. Observe a short when the On/Off key is pressed and an open when not pressed. If incorrect, replace case top. If all keys function correctly, replace CPU PCB. Caution: Unlock J3 before attempting to remove flex circuit conductor. Inspect the flex circuit between the front panel and the CPU PCB and reconnect if loose. Inspect the CPU PCB components and circuit board for cracking, burning, or damage, and replace the CPU PCB if any are found. If any failed components are observed, replace CPU PCB. Replace the CPU PCB with a known good PCB. Open the NPB-40, disconnect the case top from J3 on the CPU PCB and connect an ohmmeter lead to the flex circuit conductor for J3, pin 3. Refer to the front panel schematic diagram and individually connect the other ohmmeter lead to each conductor for the other keys. Observe a short when the key is pressed and an open when not pressed. If incorrect, replace case top. If correct, replace the CPU PCB. Caution: Unlock J3 before attempting to remove flex circuit conductor. Inspect the flex circuit between the front panel and the CPU PCB and reconnect if loose. Inspect the CPU PCB components and circuit board for cracking, burning, or damage and replace the CPU PCB if any are found.

4-3

Section 4: Troubleshooting

Table 4-1: Troubleshooting Guide (Continued) Symptom One or more keys on the front panel keypad does not work. (Continued) One or more display segments does not work. Probable Cause CPU PCB has failed. Corrective Action Replace the CPU PCB with a known good PCB. Inspect the LCD PCB components and circuit board for cracking, burning, or damage and replace the LCD PCB if any are found. Inspect the flex circuit between the LCD and the LCD PCB has come loose and replace the LCD PCB if loose. Replace the LCD PCB with a known good PCB. Turn the beeper back on.

An LCD PCB component has failed. Flex circuit between LCD and LCD PCB has come loose.

Beeper does not beep for pulse indication or no sound can be heard from the beeper.

The beeper has been turned off or its volume is turned down too low to hear. The holes for the beeper on the back of the NPB-40 are blocked. The external output port on the CPU PCB has failed. The beeper on the LCD PCB has failed The SpO2 sensor is not connected properly.

Clear the holes for the beeper on the back of the NPB-40. Replace the CPU PCB with a known good PCB. Replace the LCD PCB with a known good PCB. Connect the SpO2 sensor to the NPB-40. Replace the SpO2 sensor with a known good SpO2 sensor. Replace the LCD PCB with a known good PCB. Replace the CPU PCB with a known good PCB. See "One or more keys on the front panel keypad does not work," above. Replace the LCD PCB with a known good PCB. Install new batteries.

Pulse rate or SpO2 value is not displayed and the unit is on.

The SpO2 sensor has failed. A component on the LCD PCB has failed. A component on the CPU PCB has failed. LCD backlight does The Display Light not come on when key on the front the Display Light panel keypad is key is pressed. defective. The backlight LEDs on the LCD PCB have failed. The unit shuts off The batteries are at when the LCD or near a voltage too backlight is turned low for the NPB-40 to on. operate.

4-4

Section 4: Troubleshooting

Table 4-1: Troubleshooting Guide (Continued) Symptom Printer will not print. Probable Cause The printer is turned off. The Store Data key on the front panel keypad is defective. The printer batteries are at or near a voltage too low for it to operate. The NPB-40 and printer are not properly aligned. A component on the LCD PCB has failed. A component on the CPU PCB has failed. The printer is defective. Corrective Action Turn on the printer. See One or more keys on the front panel keypad does not work, above. Install new batteries in the printer. Refer to the operator's manual for instructions for aligning the NPB-40 with the printer. Replace the LCD PCB with a known good PCB. Replace the CPU PCB with a known good PCB. Attempt to print using another known good NPB-40. If the printer still does not print, troubleshoot the printer

Table 4-2: NPB-40 Error Codes Error Code 100EEE Failure Indicated Failure in the microprocessor analog-to-digital converter on the CPU PCB. Failure of the microprocessor on the CPU PCB. Failure of the RAM on the CPU PCB. Failure of the ROM on the CPU PCB. Failure in the microprocessor I/O ports on the CPU PCB. Failure of the watchdog circuit on the CPU PCB. Failure of the memory on the CPU PCB when storing an event or when printing. Corrective Action 1. Replace the sensor. 2. Replace the CPU PCB with a known good PCB. Replace the CPU PCB with a known good PCB. Replace the CPU PCB with a known good PCB. Replace the CPU PCB with a known good PCB. Replace the CPU PCB with a known good PCB. Replace the CPU PCB with a known good PCB. Replace the CPU PCB with a known good PCB.

150EEE 151EEE 152EEE 153EEE

154EEE 155EEE

4-5

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SECTION 5: DISASSEMBLY GUIDE
5.1 5.2 Introduction System Disassembly and Reassembly

5.1

INTRODUCTION The NPB-40 can be disassembled into five assemblies: · · · · · Note: Case top/front panel keypad Case bottom CPU PCB LCD PCB Battery compartment door Some spare parts you receive will have a business reply card attached. When you receive these spare parts, please fill out and return the business reply card.

The only tool you will need to disassemble or reassemble the NPB-40 is a Number 1 (medium) Phillips-head screwdriver. Caution: Observe ESD (electrostatic discharge) precautions when disassembling and reassembling the NPB-40 and when handling any of the components of the NPB-40. 5.2 SYSTEM DISASSEMBLY AND REASSEMBLY Use the following procedure to disassemble the NPB-40. Reassemble the monitor in reverse order and, if the unit is to be returned to service, install batteries when reassembly is complete and replace the battery compartment door. Nellcor Puritan Bennett recommends that you follow this disassembly procedure in the order presented. Note: 1. 2. Before you begin to disassemble the NPB-40, remove the battery compartment door and remove the batteries. Place the NPB-40 on a nonabrasive surface so that the back of the unit is up and the bottom of the unit is closest to you. Remove the four screws holding the case together as indicated in Figure 5-1. Note: The two screws at the top of the NPB-40 are longer than those at the bottom. When reassembling the unit, be sure to install the longer screws at the top and the shorter screws at the bottom.

Caution: When reassembling the NPB-40, hand tighten the screws that hold the NPB-40 case together to a maximum of 4 inch-pounds. Over tightening could cause the screws to strip out the screw-holes in the top case, rendering it unusable.

5-1

Section 5: Disassembly Guide
Remove screws

Remove screws

Figure 5-1: Opening the NPB-40 Case 3. 4. While holding the case together, turn the NPB-40 over with the front panel up and the bottom of the unit closest to you. Separate the case top from the bottom case on the right side of the unit and rotate the case top to the left as shown in Figure 5-2.

J3

Figure 5-2: Top Case Removal

5-2

Section 5: Disassembly Guide

Caution: Failure to unlock connector J3 on the CPU PCB before attempting to remove the front panel flex circuit could damage the flex circuit. 5. Unlock connector J3 on the CPU PCB as shown in Figure 5-3 and pull the front panel keypad flex circuit out of J3. Note: When reassembling the NPB-40, be sure to lock J3 after you insert the front panel keypad flex circuit. See Figure 5-3.
Unlock J3 Lock Lock CPU PCB

Figure 5-3: Unlocking CPU PCB Connector J3 Note: The battery connectors (spring assemblies) at the bottom of the CPU PCB are held in slots in the battery compartment. In the next step, observe how these connectors are engaged in these slots when you remove the CPU PCB with the LCD PCB and make sure the battery connectors are inserted back in these slots when you reassemble the NPB-40.

6. 7.

Lift the CPU PCB and the LCD PCB together and remove them from the case bottom. To separate the CPU PCB and the LCD PCB, grasp the CPU PCB in one hand and the LCD PCB in the other. Rotate the ends of the two PCBs as shown in figure 5-4 until the two assemblies separate at the connectors J1 and J2.
J1

LCD PCB CPU PCB

J2

Figure 5-4: Separating LCD PCB from CPU PCB Note: When reassembling the NPB-40, be sure to align all 20 pins of both J1 and J2 on the CPU PCB with all 20 sockets of J1 and J2 on the LCD PCB before pressing the two PCBs together.

5-3

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SECTION 6: SPARE PARTS
6.1 Introduction

6.1

INTRODUCTION Spare parts, along with corresponding Nellcor Puritan Bennett part numbers, are shown below. Figure 6-1 shows the replaceable NPB-40 monitor components with numbered callouts that correspond to item numbers in parentheses in the spare parts list below. In December, 1997, the external plastic parts of the NPB-40 were modified. Plastic parts made after that date are incompatible with parts made before that time. To determine which part number to order, look at the back of the instrument. To the right of center, just above the battery compartment door, there will be either 3 holes or three slots for the speaker. If your instrument has three slots, use part numbers from the "After 12/97" column. If the instrument has three holes, use part numbers from the "Before 12/97" column. Item (1) (2) (3) (4) (5) Case Top/Keypad CPU PCB LCD PCB Case Bottom Battery Compartment Door Part Numbers (Before 12/97) 045691 034311 034835 035097 033880 Part Numbers (After 12/97) 048863 034311 034835 035397 034975

6-1

Section 6: Spare Parts

1

2

3

4

5

Figure 6-1: NPB-40 Expanded View

6-2

SECTION 7: PACKING FOR SHIPMENT
7.1 7.2 7.3 General Instructions Packing NPB-40 in Original Carton Packing in a Different Carton

7.1

GENERAL INSTRUCTIONS To ship an NPB-40 handheld pulse oximeter or one of its components for any reason, follow the instructions in this section. Pack the NPB-40 or component carefully. Failure to follow the instructions in this section may result in loss or damage not covered by any applicable Nellcor Puritan Bennett warranty. If available, use the original carton and packing materials and follow the instructions in "Packing in Original Carton." If the original shipping carton and material are not available, use other suitable shipping materials and container and follow the instructions in "Packing in a Different Carton." Prior to shipping the NPB-40 or component, contact Nellcor Puritan Bennett Technical Services Department or your local Nellcor Puritan Bennett representative for a Returned Goods authorization (RGA) number. Mark the shipping carton and any shipping forms with the RGA number. Caution: Observe ESD (electrostatic discharge) precautions when packing any NPB-40 components.

7.2

PACKING NPB-40 IN ORIGINAL CARTON If the original carton and packing materials are available, repack the NPB-40 as shown in Figure 7-1. Add packing material in the bottom of the carton as needed so the NPB-40 will not be able to move during shipment.

7.3

PACKING IN A DIFFERENT CARTON If the original carton and packing material are not available when shipping an NPB-40 or one of its components: 1. 2. 3. 4. Place the NPB-40 or component in a plastic bag. Locate a corrugated cardboard shipping carton with at least 200 pounds per square inch (psi) bursting strength. Fill the bottom of the carton with at least 2 inches of packing material. Place the bagged NPB-40 or component on the layer of packing material and fill the box completely with packing material such that there is at least 2 inches of packing material around all sides of the item. Seal the carton with packing tape. Label carton with shipping address, return address, and RGA number.

5. 6.

7-1

Section 7: Packing for Shipment

Figure 7-1: Repacking the NPB-40

7-2

SECTION 8: SPECIFICATIONS
8.1 8.2 8.3 8.4 Performance Electrical Environmental Physical

8.1

PERFORMANCE Measurement Range SpO 2 0­100% Pulse Rate 20­250 beats per minute (bpm) Accuracy SpO 2 Adults 70­100% 0­69% Neonates 70­100% 0­69% Note: ± 2 digits unspecified ± 2 digits unspecified

Accuracies are expressed as plus or minus "X" digits (oxygen saturation percentage points) between saturations of 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 sensors. Neonatal accuracy is determined with Oxisensor II N-25 sensors. In addition, the neonatal accuracy specification is adjusted to take into account the theoretical effect of fetal hemoglobin in neonatal blood on oximetry measurements. ± 3 bpm

Pulse Rate 20­250 bpm Note:

Accuracy is expressed as plus or minus 3 bpm across the display range. This variation equals plus or minus one standard deviation (1SD), which encompasses 68% of the population.

8-1

Section 8: Specifications

8.2

ELECTRICAL Instrument Power Requirements 6V, supplied by battery-power only Patient Isolation No electrical connection to patient (inherently insulated) Battery Type Four 1.5V alkaline "AA" size batteries Battery Capacity Typically 19 hours with four new disposable alkaline batteries. Note: Not all brands of off-the-shelf alkaline batteries provide the same battery life.

8.3

ENVIRONMENTAL Operating Temperature Instrument 0 to 55°C Sensor Within physiologic range for specified accuracy Transport/Storage Temperature (boxed) -40 to 70°C, 15-95% RH Humidity Operating 15-95% noncondensing Storage (unboxed) 15-95% noncondensing over a temperature range of -20° C to 60° C Altitude Operating -1280 ft. to 12,000 ft (-390 m to 3,658 m) [650 to 1060 hPa] Storage -2330 ft. to 15,000 ft. (-457 m to 4,573 m) [572 to 1100 hPa]

8-2

Section 8: Specifications

8.4

PHYSICAL Weight (with batteries installed) 0.3 kg (11 oz.) Size 15.75 cm high x 7.5 cm wide x 3.8 cm deep (6.2 in. high x 2.95 in. wide x 1.5 in. deep) Equipment Classification (IEC 601-1 / CSA 601.1 / UL 2601-1) Type of Protection Internally Powered Degree of Protection Type BF Enclosure Degree Protection Class IPX1 Mode of Operation Continuous

8-3

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TECHNICAL SUPPLEMENT
S1 S2 S3 S4 Introduction Pulse Oximetry Principles of Operation Circuit Analysis Schematic Diagrams

S1

INTRODUCTION This Technical Supplement provides a description of the principles of pulse oximetry, a block diagram level theory of operation discussion, and a schematic level theory of operation discussion. Part locator diagrams and schematic diagrams are located at the end of this section as fold-out drawings. These diagrams can be folded out for review while reading the theory of operation.

S2 S2.1

PULSE OXIMETRY PRINCIPLES OF OPERATION Overview The NPB-40 is based on the principles of spectrophotometry and optical plethysmography. Optical plethysmography uses light absorption technology to reproduce waveforms 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 forms. Spectrophotometry uses various wavelengths of light to qualitatively measure light absorption through given substances. Many times each second, the NPB-40 passes red and infrared light into the sensor site and determines absorption. The measurements that 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 NPB-40 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 2 is the ratio of corrected absorption at each wavelength.

S2.2

Functional Versus Fractional Saturation The NPB-40 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 NPB-40 measurements with those obtained by an instrument that measures fractional saturation, measurements must be converted as follows:
functional fractional 100 saturation = saturation x 100-(% carboxyhemoglobin +%methemoglobin)

S-1

Technical Supplement

S2.3

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 NPB-40 SpO2 measurement. This is because the calculated saturation may not have been corrected for the effects of variables that can shift the relationship between PaO 2 and saturation. Figure S2-1 illustrates the effect that variations in pH, temperature, partial pressure of carbon dioxide (PCO 2), and concentrations of 2,3-DPG and fetal hemoglobin may have on the oxyhemoglobin dissociation curve.
100
pH Temperature PCO2 2,3-DPG Fetal Hb

Saturation (%)

50

pH Temperature PCO2 2,3-DPG

0

50
PO2 (mmHg)

100

Figure S2-1: Oxyhemoglobin Dissociation Curve S3 CIRCUIT ANALYSIS This section provides an explanation of NPB-40 theory of operation using block diagrams and schematic diagrams. The NPB-40 consists of three main functional components described in the following paragraphs: · · · The CPU PCB block diagram (Figure S3-2) and schematic diagram (Figure S4-3). The LCD PCB block diagram (Figure S3-3) and schematic diagram (Figure S4-4). The Front Panel PCB schematic diagram (Figure S4-5).

The relationship between these components and their interconnection is illustrated in the NPB-40 block diagram (Figure S3-1).

S-2

Technical Supplement

The following is a list of terms and definitions used in the following paragraphs. 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. Central Processing Unit (CPU). An Intel 80C196KC 16-bit microprocessor. The CPU sends and receives control signals to the SpO2 analog section, display, and printer infrared LED. 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. Input and Output (I/O). Digital lines that are used by the CPU to read in data and output data. Light Emitting Diodes (LEDs). Two LEDs are used in Nellcor Puritan Bennett 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 915 microns red light at 660 microns

Pulse Width Modulation (PWM). The three 8-bit PWM outputs can be software controlled; their duty cycle can be changed from 0 TO 99.6 percent of the total pulse duration. PWM frequency is the crystal frequency of the CPU (10 MHz) divided by 1024. The PWMs control the gains within the analog circuit. 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. S3.1 Overall Unit Block Diagram Analysis Exclusive of batteries covers, keys, and external connectors, the NPB-40 consists of three main functional components: the front panel keyboard, the CPU PCB, and the LCD PCB as follows. · CPU PCB -- contains the CPU; power supply circuitry; support memory circuits; sensor circuits for battery voltage; a serial data port; LCD backlight control; pulsatile beeper drive circuits; and some display control circuits. LCD PCB -- contains the SpO2 analog circuitry and interface to the external sensor; the power conditioning circuitry; the LCD display and display driver circuits; the interface circuitry for the printer (which is not used unless a printer is present); the LCD backlight; and audio output hardware. Front Panel Keyboard -- contains four membrane switches and a line common to all four switches. This assembly connects to the CPU PCB by a flex circuit.

·

·

Refer to Figure S3-1 for this NPB-40 block diagram. The CPU PCB and the LCD PCB are each described in more detail in later paragraphs.

S-3

Technical Supplement

The NPB-40 is powered by four AA-size replaceable alkaline batteries. A dc voltage in the range of 3.6 to 6 Vdc is provided over the life of these batteries. When the voltage from these batteries drops to a level too low to operate the NPB-40, the unit will shut itself off. At that time, the batteries must be replaced. The front panel keypad contains four keys that provide discrete signals that are monitored by the microprocessor on the CPU PCB. Refer to Figure S4-5 for a schematic diagram of the front panel keypad.
CPU PCB 3.6-6 Vdc Batteries On/off key LCD PCB

Power control and PCB power

Raw power

Power condition and PCB power

Power down Front panel keypad Function keys CPU

Battery voltage sense

Sensor analog signal and control

Analog sensor circuits

Patient sensor input

Printer signal External serial interface LCD enable LCD data External output control External output port Beeper signal

Printer IR LED drive

LCD

Beeper

Backlight control

LCD backlight

Figure S3-1: NPB-40 Block Diagram

S-4

Technical Supplement

Power from the batteries is controlled and filtered by the power control and PCB power circuits on the CPU PCB. When the On/Off key is pressed on the front panel keypad and the unit is turned off, the power control circuits will turn on the unit. If the unit is on when the On/Off key is pressed, the unit will be turned off. The PCB power circuits provide filtered power for the circuits on the CPU PCB and raw power is passed to the LCD PCB where it is conditioned for the circuits there. A patient sensor connected to the NPB-40 contains a resistance that is a calibration reference for the sensor. The analog sensor circuits on the LCD PCB then measure the signal from a photodiode in the sensor that is different based on the light absorption characteristics of each patient. That signal is processed by the analog sensor circuits and measured by the CPU. The LED drive signals are then adjusted by the CPU to obtain an optimum signal from the photodiode. The CPU provides a drive signal for an IR LED on the LCD PCB. When this IR LED is aligned with a receiving photodiode on an external printer, patient data stored in the NPB-40 can be printed. An external output port on the CPU PCB is controlled by the CPU and sends drive signals to the beeper and LCD backlight and display data to the LCD. An external serial data interface, used during testing in manufacturing only, is also controlled by the CPU. This interface is only accessible with a special test fixture. S3.2 CPU PCB Theory of Operation Refer to Figure S3-2 for the CPU PCB block diagram and to Figure S4-3 for the CPU PCB schematic diagram in the following description. The CPU PCB hardware and related circuitry, which is illustrated in the following block diagram, includes the following subsystems: · CPU -- A 16-bit microprocessor 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. System memory -- External to the CPU and consists of an 8K x 8 static RAM and a 64K x 16 EPROM. Display control -- The CPU provides drive and control signals for the LCD driver and display on the LCD PCB. Audio output drive-- Drives a piezoelectric ceramic beeper on the LCD PCB for audio output. Printer drive-- The CPU provides a printer drive signal that is applied to an IR LED on the LCD PCB. Power supply/Power control circuitry -- The NPB-40 receives power from 4 "AA" cell batteries. The power control circuitry discontinues power to the unit when the batteries are no longer reliable.

· · · · ·

S-5

Technical Supplement
From batteries 3.6-6 Vdc From front panel keypad On/off key To LCD PCB Battery power Battery power feedback Power switch circuit Power shut off control Shift key Raw +10 Vdc Power supply circuit Raw -5 Vdc

Power on VCC (+5 Vdc) To CPU PCB circuits

Battery voltage sense RD/WR RAM AD 0-7

ADDR 0-12

Display light/ beep on/off key Store data/ print key WR

RAM enable

ADDR 9-15 EPROM enable

Address decoding

AD 0-15 ALE Microprocessor Address latch

ADDR 1-15

RD AD 0-15 AD 0-7 External output enable

EPROM

WD RST VCC monitor and watchdog reset circuit

To/from LCD PCB Beeper drive External output port LCD light enable LCD CLK, DATA, CE LCD enable Printer LED signal Beeper LCD backlight LCD driver Printer interface V ref

10MHz clock circuit

Analog sensor voltage reference Analog sensor signal Analog circuit control signal

Sensor circuits

Figure S3-2: CPU PCB Block Diagram

S-6

Technical Supplement

S3.2.1 CPU The Intel 80C196KC CPU is a 16-bit microprocessor 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 watchdog reset 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). 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-L), all other memory and mapped I/O are read or written 16 bits at a time. Eight analog inputs are measured by the CPU. Input from the SpO2 analog section on the LCD PCB includes AC and DC signals for the oximeter sensor red and infrared channels, and the sensor calibration resistor RSENS. The battery voltage and reference voltage from the LCD PCB are also measured. The 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. HSO4 and HSO5 are configured as outputs. The HSO is used to generate stable timing control signals to the SpO2 analog section, display, and printer driver. External control pins: P2.2, P2.3, and P2.4 are configured to monitor front panel keyboard keys Store Data/Print, Display Light/Beep On/Off, and Shift keys, respectively. Pins HSI0 is configured for interrupt input. The CPU receives one external interrupt (signal PHOTOI).

· ·

·

·

S-7

Technical Supplement

· ·

P2.0 and P2.1 are configured as a standard asynchronous serial transmitter and receiver for a factory serial interface. P2.5, P1.3, and P1.4 are configured as pulse width modulator outputs. They are used with outputs from P1.6 and P2.6 to control gains within the SpO 2 analog section.

S3.2.1.1 Address Demultiplexing U10 and U11 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 U10 and U11 are always the address portion of the AD bus. S3.2.1.2 Address Decoding 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 external output ports. When address lines A13, A14, A15 are all high, the output of U7C goes low, enabling the RAM and generates the active low enable signal RAMEN-L. This occurs for the 8K address range of E000-FFFF. U8 is used to generate the output port active low enable signal EXOUTEN-L. When address lines A15, A14, A11, and A10 are high, and A13 is low, U8 becomes enabled. With U8 enabled, the Y3 output 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 3 is produced on pins A, B, and C, forcing output Y3 (EXOUTEN-L) low. This enables the output port for writing. Note that in this condition, A15, A14, A12, A11, and A10 are high and A13 is low. The output port uses the address space of DE00-DFFF. When data is written to that address, the output port enable signal EXOUTEN-L is activated. Because the CPU is configured to use a 16-bit bus, except for RAM, any even address in the DE00-DFFF range could be used for external port access. In other words, reading or writing address DF00, DE02, DE04, etc., will all produce the same results. U7A generates the EPROMs active low enable signal, ROMEN-L. The active low signals RAMEN-L and EXOUTEN-L are basically used as EPROM disable signals. When RAMEN-L or EXOUTEN-L or the Y3 output of U8 are low, the output of U7A, ROMEN-L, is forced high, disabling the ROM. Therefore, the EPROM is disabled for the range DE00-FFFF and enabled for the address range of 0-DFFF. S3.2.2 CPU Memory The memory system external to the CPU consists of an 8 K x 8 static RAM (U12) and a 64 K x 16 EPROM (U5). The EPROM is 16 bits wide to enhance CPU performance. Because RAM is infrequently accessed, it is only 8 bits wide. U12 is a standard 8K x 8 static RAM.

S-8

Technical Supplement

The program that the CPU runs is stored in U5. U5 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 is not used as a normal address line. The CPU can only address 64K x 8 bytes or 32K x 16 bytes. Pin A15 of U5 is tied low, always selecting the lower half of the EPROM. Signal ROMEN-L is then used to enable the EPROM for the proper memory area. The output port external to the CPU consists of an octal D latch, U9. The output of U9 is always enabled. The output bits of U9 control the beeper output, the LCD backlight, and the LCD display drive signals. S3.2.3 Standard User Controls The standard user controls consist of four momentary push-button switches on the front panel keypad. These keys are metal dome membrane contact switches. The front panel switches Store Data/Print, Display Light/Beep On/Off, and Shift are connected to the microprocessor, U4, input lines P2.2, P2.3, and P2.4 and are normally pulled to the high state by R10, R8, and R18. Whenever one of these keys is pressed, the U4 input line is pulled low. The switch contacts are debounced in software. The fourth front panel switch, On/Off, is connected to the power switch described Power Supply/Power Control Circuitry. S3.2.4 Power Supply/Power Control Circuitry The power supply and power control circuitry consists of the following primary elements. · · Batteries -- Four 1.5 V alkaline "AA" size batteries provide 3.6-6 Vdc power. Power entry circuit -- Components protect the NPB-40 from damage if batteries are inserted incorrectly and provide reverse current limiting and over-voltage or spike protection. In addition, a self-resetting fuse protects the power supply from excessive current draw. The power supply is also protected against electrostatic discharge and electromagnetic interference. Power switch circuitry -- This circuit controls power applied to the power supply circuits. Power control circuitry is connected to the batteries. It senses any press of the front panel keypad On/Off key and switches the power supply circuit on or off. A control signal to this circuit from the CPU will also shut off the NPB-40 when battery voltage drops to an unusable level. Power supply circuits --consist of a power generation circuit that provides +10Vdc, +5Vdc, and -5Vdc.

·

·

S-9

Technical Supplement

S3.2.4.1 Power Entry Circuitry Self-resetting fuse R22 protects the NPB-40 and will open when current in excess of 0.75 Amps is drawn by the unit. R22 will close when the condition causing excessive current has been eliminated. CR7 provides reverse current protection and limits negative voltages (batteries reversed) to safe levels. In either of these conditions, CR7 will conduct and cause fuse R22 to open. CR5 protects against large voltage transients caused by ESD, EMI, etc. and will pass these undesirable transients to ground. S3.2.4.2 Power Supply Feedback Circuitry The power supply feedback circuit consists of Q1 and its associated components. When batteries are installed and the NPB-40 is turned off, the battery voltage (VBAT) is applied through resistor R2 at the collector of Q1 providing a logic 1 level voltage to the D input of flip-flop U1B in the power switch circuit. When the NPB-40 is turned off, VCC is at 0 volts and Q1 is turned off. When the NPB-40 is turned on (See "Power Switch Circuitry"), the VCC potential is applied to the base of Q1, which turns it on. The voltage at the D input of U1B then drops to a low voltage to provide a logic 0. S3.2.4.3 Power Switch Circuitry The power control circuit consists of U1B and its associated components. U1B is a D flip/flop with asynchronous preset and clear; only the clear is used. Battery voltage is applied to U1B whenever batteries are installed. The NPB40 is turned on and off by pressing the On/Off key on the front panel keypad. The BTN PWR line is normally pulled up to the battery voltage by R3. When battery voltage is at an acceptable level and the On/Off key on the front panel keypad is pressed, the BTN PWR line is grounded and the resultant highgoing pulse from U2A toggles the CLK input of U1B and the high D input logic level is transferred to the Q output. The logic state of the D input is controlled by the power supply feedback circuitry (See "Power Supply Feedback Circuitry"). When the NPB-40 is off the D input of U1B is high. Pressing the front panel On/Off key sets the Q output and the PWR ON signal high. This enables the power supply circuits, which then generate the operating voltages for the NPB-40. The Q-not output of U1B is applied to U4 analog to digital converter input P0.6 through a battery voltage sensing circuit consisting of U2B, R14, R17, and C14. When the battery voltage drops below 3.6 Vdc, as measured by U4, the PWR DOWN line at U4 output HSO3 goes high and turns on Q2, which clears flip-flop U1B and the PWR ON signal at the Q output goes low and turns off the power supply circuits. When the NPB-40 is turned on, the D input of U1B is low (See "Power Supply Feedback Circuitry"). When On/Off key on the front panel keypad is pressed, the BTN PWR line is grounded and the resultant high going pulse from U2A toggles the CLK input of U1B and the low D input logic level is transferred to the Q output. This sets the Q output and the PWR ON signal low, which turns off the power supply circuits.

S-10

Technical Supplement

S3.2.4.4 Power Supply Circuits When the PWR ON signal at the S/S input of U3 is high, U3 generates a square wave signal that drives the primary winding of transformer T1. The three secondary windings of T1 are rectified and filtered to provide RAW+10V, VCC (+5Vdc), and RAW-5V. The VCC signal is resistor divided by R9 and R12 for a feedback voltage that U3 must see to continue operating. VCC is used on the CPU and the LCD PCBs for operating circuit power. RAW+10V and RAW-5V are supplied to the LCD PCB for backlight power and for power conditioning for the SpO 2 analog circuits. S3.2.5 Serial Interface The serial interface is only used for factory test purposes, and is not at the RS-232 level, neither is it electrically isolated and, therefore, cannot be used outside of the factory. The serial data port J5 is a TTL level serial interface. RXD and TXD are configured as a standard asynchronous serial transmitter and receiver at 19.2 Kbaud with 1 stop bit, 8 data bits, and no parity. The serial interface can operate in full duplex mode. If no external serial data device is connected, R19 pulls the RXD input high which prevents the input from floating when it is not being used. S3.2.6 Printer Control Microprocessor U4 provides a drive signal (IR OUT) at HSO5 that controls an infrared LED on the LCD PCB which is used to interface with an external printer. S3.2.7 External VCC Monitor and Watchdog Timer The external VCC monitor and watchdog timer circuit consists of U6 and associated components. U6 provides two functions. If the VCC input voltage drops below 4.0 Vdc, U6 will drive the RST-L line low, which resets microprocessor, U4. U6 also periodically receives the WD RST pulse output from U4. If U6 does not receive the WD RST signal at least every 500 ms, it will drive the RST-L line low, which resets U4. S3.3 LCD PCB Theory of Operation Refer to Figure S3-3 for the LCD PCB block diagram and to Figure S4-4 for the LCD PCB schematic diagram in the following description. This subsection describes the SpO 2 analog hardware. The 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 2 analog circuitry consists of four subsections: · 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 Pulse Width Modulation (PWM) lines to control LED current level or to amplify the signal channel. 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.

·

S-11

Technical Supplement

Filters then remove noise and smooth the signals before sending them to the amplifiers. · 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. 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.

·

S-12

Technical Supplement

The relationship between these subsections is shown in the LCD PCB block diagram, Figure S3-3.
To/from CPU PCB Raw +10 Vdc Raw -5 Vdc V ref Printer LED signal LCD clock LCD data LCD enable LCD light enable Beeper drive Analog sensor signal Analog circuit control signals LCD backlight Red channel Beeper IR channel LCD driver LCD Power conditioning +10Vdc -5 Vdc Printer IR LED

LED drive

Sensor D-connector

To/from patient sensor LED drive

RSENS

Photodiode

Figure S3-3: LCD PCB Block Diagram

S3.3.1 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.

S-13

Technical Supplement

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. 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 drive 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 cycl