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Service Manual - Frank`s Hospital Workshop

1. 10K Figure 9 35 Main Schematic Diagram 9 53 BATTERY INPUT i POWER SUPPLY 017 n TE me FS Ge TE mw M SRO RN 52 D2 CR24 1UF DRN TP2 R100 5199560 swe GND 22UF 20 ous 14 22UF E ar reso MAIN geo a S loe ce R79 SET2 VREF GND RAW12V JP18 cue oe RST2 22UF 2 PR HEADI AUF 22UF 50 PR HEAD V PR STROBE PR TACH MURS110 PR PRESENT FB vsw VC MES PWR DOWN Tur n DISP PHASE Ee ND POL DRIVERS UH vec CHECK BATTERY DISP DL R127 Rn 14K SUI 150K DISP PHASE BAT BIN RAWI2V TEST 1K C126 1 Wi 100 RAW 5V O1UF t TALIQ COLD SWITCH oO 014 MMBTS401L DISP_DATA PR_PRESENT DISP EX IN INPUT PORT MMBTS551L U3eB ah Aba 9 GO BTN PR HEAD 13
2. 9 45 Figure 9 31 Printer Interface Circuit eerie eese esee sees ense 9 47 Figure 9 33 N 20 SpO Analog Block Diagram 9 49 Figure 9 34 CPU Circuit 55568 9 9 51 Figure 9 35 N 20 Main PCB Schematic Diagram ssccsssssssesscesssssescssesesssssscesscesscesssssessossnessessosseses 9 53 Figure 9 36 N 20 Auxiliary PCB Schematic Diagram esee esset ente testen teneas sees tosta sone ta an 9 55 Figure 9 37 N 20 Flex Circuit Schematic 1 9 57 TABLES Table 4 1 Microprocessor Error 4 7 Table 8 E S fsOEFs icti eti civi iD eae abe ep bdo paa e RUD 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 1 2 1 3 Manual Overview This manual contains service information for the Nellcor portable pulse oximeter models N 20 N 20P that is necessary to maintain and repair the N 20 N 20P by qualified service personnel Note that models d
3. 9 17 Figure 9 18 Input Port Cirit sssrini 00000 9 18 Figure 9 20 Real Time Clock Circuit 020100000000 0 eese 9 19 Figure 9 21 Audio Output Circuit tosta tasto sens 9 20 Figure 9 6 Display Control Block Diagram 4 eere esee statu sees tuse tates suse tasse 9 20 Figure 9 23 User Controls Circuit enses testen tene tn eta sns tasses suse tosta stesso 9 22 Figure 9 26 Analog Reference Voltage 11 2 1 1 1 seen seen ettet 9 25 Figure 9 27 Ambient Light Circuit Lease eee testen sene sens tasse tan 9 25 Figure 9 28 Ambient Temperature tosta tosta sensns tasso senses snae 9 26 Figure 9 29 Battery Voltage 224 9 2 44 0114 0 00 00 00000000 0 0400000 0000000 sesta sees snae tatus eta an 9 26 Figure 9 30 Battery Type Circuit stesso
4. 1 1 1 3 Description of N 20 Portable Pulse Oximeter esee 1 1 2 Routine Maintenance aset tituli dide 2 1 2 1 DIA EI 2 1 2 2 emm m 2 1 2 3 Periodic Safety and Functional Checks 2 1 2 4 Battery is S wr e d E eR d e am 2 1 3 Performance etin icai as coed epbope esintaas c 3 1 3 1 Introduction ARE 3 1 3 2 Required Malerials t Rn AN en rete 3 1 3 3 Performance Tests 3 1 4 LroubleshO0flllg 4 1 4 1 How to Use this Sections 4 1 4 2 Who Should Perform Repairs ueteres eere 4 1 4 3 Replacement Level SUPPOrted 4 1 4 4 Obtaining Replacement 4 1 4 5 Troubleshooting Guide netten 4 2 4 6 Service Procedures 4 4 4 7 EOT CODES 4 7 5 5 1 5 1 TUT ODUCTION 5 1 5 2 Required 5 1 6 Parts cec 6 1 6 1 N 20 N 20P Spare Parts 6 1 7 J
5. sete seta stats tone setas eta seta sete sete 9 4 Figure 9 6 Display Control Block Diagram 2 2 1 seta stats toss setas stans ease ease ease tasto ao 9 5 5 Figure 9 7 Printer Control Block 0 2 9 5 Figure 9 11 Variable Gain 2 9 9 Figure 9 12 Filtering Circuit cccccissssccssecsscvesessosssosscessessssnosevsessiscsassesseasevascesseasdessensconssessessssseasosesenssexssuasodncanses 9 10 Figure 9 4 Digital Circuitry Block 1 ette sete seines toss tone 9 12 Figure 9 14 N 20 Hardware Block Diagram ceres eese eese esee ee ette setas 9 14 Figure 9 15 Address Demultiplexing 1 1 9 15 Figure 9 16 Address Decoding 44 2041 1 00 0 eee esee eee een stessa 9 16 Figure 9 17 CPU Memory 1 1 1 0 1 seta seta
6. 92 D 8115 17 ON OFF 17101765 ADS 15 Gg pe DD ETN Y 243904 2 1 TOIA ADV BIN ADS xg Ere PR HOME MMBTSS51L 13 32 9 RICO 08 R95 015 182 1 7450573 vec PR HEAD 3 AD14 oscouT 028 17101706 AD13 voc VPRN ADIP ADI TO PRINTER GND 519530 TP35 TP36 TEST JEST TEST 010 OUT LSB PR TACH ADS uie C127 wo mo e nee ara m m 181 3 voo E Ai e He sor m HE 9 HE fos He Hi b m 31 400 PR MEAS ADS EXOUTEN 4 7480574 ADS 15 R132 150K AD2 16 ADI 17 ADO EX OUT MSB U17 ATIT BEEPER 18 19 EXINEN ADS z D1 Qt ADS i D2 02 EXOUTEN 2010 1 20 03 ADT ADIZ 5 05 05 2013 7 06 06 511 N 20 ADIS car OSCIN EXOUTEN 11 MAIN PCB PR STROBE 1 7480574 PR PRESENT GND 510550 REAL TIME CLOCK OFF ADV 20 029
7. Figure 5 4 Printer and Flex Circuit Installation Remove the printer button retaining plate 37 by sliding it away from the case assembly 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 Remove the printer button strip 7 from the printer flex circuit Remove the printer flex circuit insulator 24 Remove printer hold down bracket 4 from the back cover by removing the Phillips screw 32 Press the printer hold down bracket into the back cover and remove the printer 5 5 6 6 1 5 5 6 1 N 20 N 20P Spare Parts N 20 N 20P Spare Parts To order replacement parts contact Nellcor 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 SWI Battery switch auxiliary PCB 630106 2 BTI Battery holder auxiliary PCB 901582 3 Battery lithium auxiliary 640112 4 Bracket printer hold down 023133 5 Button battery check 023301 6 S2 Button measure 022948 Button measure European version 026386 7 Buttons printer strip 022947 Buttons printer strip European version 026387 9 Connector shield DB 9 023467 10 P1 Connector DB 9 463103 11 JP1
8. voc vec AUX PCB DIGITAL SECTION p MM p sw d Qs 221 MMBTAt3L Te 4 s Ed miso 9 GO BUTTON PN d VREF 124 0125 R joo a PR STROBE ds C122 C23 LTC201 PR TACH TANT Ut1A TP75 46 ACROSS 035 ACROSS Utt REDLEDAV R160 67 SUPPLY 3 171097 me 9 4 31 1K DOWN d i SHIP ust pu 57 1 44 PR HEADI DISP PHASE d A EE VREF 201 23 A m v T ANGND T2RSTP2 4 aE DISP_POL EX m JRLED AV s P2ST2D o q 1 RS pu FEDAC 2 1 dmi 0 PER cas 2 2 Sur gt w R67 sek AA od S emer TALIQ PS CTRL RAWIQV 0 9 13 TANT 5 7 MUF Ps4 17 4004 PR STROBE R137 ACROSS UB VOLT 8 Prone 28 10K 0 4 14 90 SUPPLY 170201 ai 0 PRTACH IE rire VREF z 1 GND 14 t _ wc 16 13 sj 7 2 and C26 car 9r AMO 32 PRESENT DISP POL 4 ATUF Pss 52 9 0 31 voc 7 x co ALEADT wa ed SL iu 2 4
9. xi vo x2 RST 0512075 ELDRIVE TP76 14 RTC 100 12 DIGITAL IC S BYPASS CAPS oer NEST VBAT P P87 1A TEST vec jede dec tee 1 AUF AUF 1UF I 1UF I 1UF 9 RST A c15 1UF vi C49 22UF R163 32 768KHz 332K Figure 9 36 Auxiliary PCB Schematic Diagram 9 55 N 20 POWER SUPPLY BOARD JP9 22 HDR 0 01uF I a T OOOO DONAN JP10 z EET SEIKO zl HEADER 6 102 16 DOT4 de 14 DOT2 d 5 12 DOTO d 1 zal PR MOTOR 3300UF ON OFF BUTTON R1 51 C4 0 01uF SI9956DY ADVANCE BUTTON R2 S2 cU camen e DD 1K C5 0 01uF DAY DATE BUTTON R3 53 C 1 Figure 9 37 N 20 Flex Circuit Schematic Diagram 9 57
10. 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 4 6 4 4 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 only Printer paper advances but instrument does not print N 20P Cause Action The thermal paper may be improperly loaded characters can be printed on only one side of the thermal paper roll Ensure that the thermal paper i
11. HSO 2 SAMPRED HSO 0 IR RED P1 1 uS 105 6 158 4 177 6 283 2 336 0 337 2 443 2 496 0 515 2 620 8 673 6 State Time 66 99 111 177 210 211 277 310 322 388 421 Figure 9 10 N 20 HSO Timing Diagram 9 35 LTC201 LTC201 5 U11B 2 16 1 REDLED AV 1 From U2 pin 3 4 1 5 7 4 3 U7A 1 RED 2 LMC6044 C9 015UF V7 9 11 LTC201 q 10 34 8K VREF R22 O 12 1 10 07 8 R41 9 15K LMC6044 8 6 U11D LMC6044 LTC201 4 T C32 VREF R31 12 1K BUS TO CPU LMC6044 R5 Q 15K TP86 Figure 9 13 AC Variable Gain Control Circuit 9 37 123 EX_OUT LSB 018 19 DISP DATA 18 DISP CLK 17 16 RST 15 PR MOTOR PR MEAS BEEP 1 19 DOT6 18 PR DOT5 17 PR DOT4 14 DOT 18 PR DOTO EXOUTEN PR STROBE 74HC574 vec O 150K 150K Figure 9 19 Output Port Circuit 9 39 DISP POL DISP DL DISP DATA DISP DISPLAY DRIVERS U19 OSCIN OSCOUT GND O26 O28 BP SI9530 U20 DOUT si OSCIN OSCOUT SI9530 O17 O18 O19 O20 021 022 023 024 025 026 027 028 029 030 O31 032 12 es esq 48 9 39
12. 20 pin headers Auxiliary Power supply Display Printer interface Flex backlight Display control connectors Batteries Audio beeper Check battery button Printer N 20P only Figure 9 2 Overall Block Diagram SpO Analog Circuitry Block Diagram Figure 9 3 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 2 3 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 Input signal conditioning where sensor output current is converted to voltage Signal gain where the separated LED signals are amplified so their current levels are within the A D converter s acceptable range and AC ranging where DC offset is eliminated from each LED signal Input signal Signal gain AC Ranging conditioning photocurrent to voltage variable gain offset conversion filtered for substraction demutiplexed each LED additional gain to 2 channels channel and filtering Main PCB Main PCB Main PCB Microprocessor Main PCB Main PCB Control LED drivers red amp IR To digital section Figure 9 3 Analog Circuitry Block Diagram 9 3 Technical Suppl
13. 9 en Pene vaar D R17 TP49 ans 5 DISP LATCH DISP DL 19 332K sl 100K 2 2 2 S 7 ux une mos Reo E His 10k C SOT 182K 047UF 22 ADS INST raum 525 nm 2 Raven NMI 332K 2 me 5 10 Abt 56 18 XD uc 1 511K 75 cis 56 LTC201 1 C22 120F T REAL RST 18 BEAD 9 d ET R12 a RESET ved 1 4 ADI 5 es 2 0 e 0 m 2 SERIAL DATA SENSOR ve KNA 17 BEAD 9 E 7 WX ux m THOR PORT NPUT 055 LED DRIVE id m PW 1 21 TO0PF 5 5 100 d MMBTASG xi 55 IRAC 1 8 3 32K C30 uno e Q 4 LTC201 EIS Tur am TPO Abie ds 7 met RESET GENERATION ma VREF O1UF 332K m 1 TE AD13 06 cao ZERO ADDRESS DEMUX voc voc ds i 2 AD12 4 Or 401 3 5 R72 0220 as TP Soot D m 7 Pa fa wd 100K 11 4 402K Ap 5 lp A 010 22K 204775 bsg TP ds ser am x e R5 25 RST 4 12 A TER R56 ADB dis R47 E A 022 CR10 5 PHOTO Ait 158k i 1 4 ADT ds Q A ADS TO CENTER MT
14. 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 8 2 8 2 1 8 2 2 8 3 8 3 1 8 3 2 Readout Display shows SpO saturation of arterial hemoglobin oxygen pulse rate and pulse amplitude also included are a Pulse Search and Low Battery indicator and an electroluminescent backlight Controls 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 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 ON button switches the printer on and off D D sets display date and time ADV advances paper and increments time and date Operating Modes Spot Check Mode Pressing the instrument Measure button once for less than 2 seconds starts the spot check mode Spot check mode computes SpO averaged over five valid pulses and displays SpO and pulse rate at the end of the measurement interval If the printer is activated the printout shows the displayed SpO and pulse rate Extended Mode Extended mode is started by holding down the instrument Measure butt
15. 39 35 37 36 35 34 3 35 29 32 12 4 jc v4 34 33 30 HDR 32 JP5 EL DRIVE HDR 7 70V DISP PHASE o R93 182 70V 1 9 TALIQ COLD SWITCH Q14 MMBT5401L C87 VDISP n 390PF 10K 12 55511 H R115 390PF 021 55511 R95 182 196 DISPLAY PS CTRL DISP POL DISP DL 74HC74 Figure 9 22 Display Control Circuit 9 41 BATTERY INPUT GND TO CENTER MOUNTING HOLE VBAT TP1 BATT PLUS 5 G2 52 Gt 51 SI9956DY CR24 TRANZORB 10V POWER SUPPLY Q17 C116 C T 73 22UF AUF ILIM VIN swi sw2 SRC SRC GATE SI9405DY LT1173 C119 m 22UF 130T3 RAW 5V O RAW10V V osc VREF VOUT LT1054CS C90 130T3 2N3906 RAW12V 2N3904 CR31 gt MURS110 CR30 MURS110 2 11172 CR16 gt MURS110 CR25 5367 43V 10 5W Figure 9 24 Power Supply Circuit 9 43 171046 20 MAIN
16. 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 certify that the monitor listed in this form has successfully passed all of these tests Technician Date 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 4 1 4 2 4 3 4 4 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 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
17. ROM Therefore the EPROM is disabled for the range DCOO FFFF and enabled for the 55 Kbyte address range of Oh 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 8K X 8 SRAM 014 TP43 64K X 16 EPROM U15 27C1024L Figure 9 17 CPU Memory Circuit The memory system external to the CPU consists of an 8 x8 static RAM 014 and a 64 x16 015 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 x8 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 EPROM During 16 bit wide bus accesses the CPU uses address line for low high byte selection and address line 0 is not used as a normal address line The CPU can address only 64K x8 bytes or 32K x16 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 GO BTN U16 ADO 19 ai Di 18 Q2 2 D3 ON OFF BTN os uere 06 06 07 07 Q8 EXINEN
18. Ree aee tee 9 5 9 6 OveralEBlockDiagram 5 ada nme AAR A Ee 9 6 9 9 SPO Analog CIECUlITY i iue Ree eene pee Re e DE DE d Ced Pone 9 7 910 Digital Circllry sicat 9 11 Support EP Ea pee d be re tes 9 30 FIGURES Page Number Figure 5 1 Sensor Lock and Printer Paper and Battery Access 5 2 Figure 5 2 N 20 Covers with the and Display Assembly 5 3 Figure 5 3 Main Auxiliary and Display PCB Assembly 0 2 4 4 0 10 0 0 1001 000 5 4 Figure 5 4 Printer and Flex Circuit Installation eese eee eese eese 5 5 Figure 9 1 Oxyhemoglobin Dissociation Curve 4 crecer eee eese teens enne seta setate 9 2 Figure 9 2 Overall Block Diagram 4 eee esee esee ee seta sete sete senes ease ease 9 3 Figure 9 3 SpO2 Analog Circuitry Block Diagram eee e eee ee eese entes eee en sins tn stets tasses ense ea sse ta suus 9 3 Figure 9 4 Digital Circuitry Block Diagram 4 esee eee ee stata stesso seta sene tasses suse tatnen 9 4 Figure 9 5 Power Supply Block Diagram 1 0 00
19. blocks and insulating materials for the replacement connector Install ferrite blocks between plastic lead spacer on the connector and the PCB Insulate connector pin numbers 2 3 and 5 with Teflon tubing and insert inside ferrite block Add insulating material between each end of ferrite block and PCB and secure with Loctite glue 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 S MA EO 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 i
20. 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 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 Nellcor Technical Services Department or your local Nellcor representative 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 3 2 3 3 3 3 1 3 3 2 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 disc
21. 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 3 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 5 2 44 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 Disassembly Guide 5 2 5 Disassembling the Printer Flex Circuit Assembly pou NAP w 29
22. is the bidirectional communication data bit The CPU drives IO when writing data and commands to the The CPU tristates 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 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 029 is powered by BT1 CR22 is reverse biased isolating BT1 from Vcc This circuit design allows 1 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 TP75 TEST TEST AT17 BEEPER Figure 9 21 Audio Outp
23. 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 The relationship between these subsections is shown in the following block diagram Sensor Output LED Control The 5 2 analog circuitry provides control of the red and IR LEDs such that the received signals 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 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 tran
24. 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 is also fed back to the printer interface circuitry The DOTA signal is a print dot resistor with a range of 11 16 ohms which is connected to VPRN 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 MEAS is pulled high pulling TP77 low and biasing the resistor bridge The logic outputs of PR HEADI and 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 15 measured only once at every power on The CPU starts the printer motor running by setting MOTOR high A single motor drives both the print head and paper advance mechanisms The printer provides a printer timing gen
25. 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 HSIO 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 Signal Gain 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
26. 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 e 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 9 27 Technical Supplement SEIKO MTP102 16 PRINTER TO N 20 AUX BOARD VPRN 8 18 DOTS ds PR_DOTS DOT4 ds 15 DOT3 4 PR DOT4 14 DOT2 das 13 de PR DOT3 12 DOTO HEADER 8 LB1256 3300UF ON OFF BUTTON 51 SI9956DY 0 01uF Figure 9 32 Printer Flex Circuit User control is provided by momentary push buttons ON on off ADV advance and D D day date ON enables or disables the printer ADV controls the advance of printer paper and D D 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 allow
27. 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 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 Technical Supplement 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 N 20 does not require or use the it is disabled via software veo REAL TIME CLOCK CR22 TP86 TEST RTC CLK O 85 RTC IO TEST TP87 TEST RTC RST 0512025 32 768 2 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 high to activate communication with the RTC CLK clocks data into and out of the RTC chip RTC IO
28. which are used in SpO 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 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 low on SW sets the output signal ON high This condition connects switched and battery grounds enables the power supplies and switches the unit Whenever the CPU determines that the power should be switched off it forces DOWN low This action clears output PWR ON to a logic low disconnecting ground and switching off the power supplies see also Power Supply 79 and R81 provide current limit prote
29. will indicate either 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 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 Immediately after power is switched on the instrument simultaneously Displays the number 8 in all six Oxygen Saturation and Puls
30. 14 TP82 1 914 Vay D 0 49050 R12 100K C17 1 0680 3 5V VREF C4 Figure 9 12 Filtering Circuit 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 9 9 8 1 9 9 8 2 9 10 Technical Supplement 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 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 volt
31. 50 beats per minute bpm 1 standard deviation SpO Accuracy Adults 70 100 2 digits Neonates 70 100 3 digits 2 Pulse Rate 20 250bpm 3 digits 2 Response In spot check mode the measurement cycle from button press to display of data is five valid pulses In extended mode the instrument measures for a period of up to 30 minutes and continuously displays updated SpO gt and pulse rate Accuracies are expressed as plus or minus digits saturation percentage points between saturations of 70 100 This variation equals plus or minus one standard deviation 15 which encompasses 68 of the population 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 This variation equals one SD 8 6 8 7 8 7 1 8 7 2 8 8 8 8 1 Sensor Types Table 8 1 Sensors Specifications Oxiband oxygen transducer reusable with disposable OXI A N nonsterile adhesive OXI P I Sensor Model Patient Size Oxisensor II oxygen transducers sterile single use only aL rand 2 kg D 20 10 to 50 kg D 25 D 25L gt 30 kg R 15 gt 50 kg 3 gt 40 kg 3to 40 kg Durasensor oxygen transducer reusable nonsterile DS 100A gt 40 kg Nellcor reflectance oxygen transduc
32. 7 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 2 3 Connector ZIF flex 32 pin auxiliary 491243 15 Cover rear non printer model 022929 Cover rear printer model 026339 16 Cover front with gasket assembly 022921 17 D8 Diode photo 8440 main PCB 591017 18 Display Taliq analog shield assembly 024466 Display Taliq analog shield assembly European version 026765 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 6 1 Spare Parts Item Designator Description P N 31 Screw captive 891324 32 Screw Phillips 4 40 x1 4 801025 33 Screw plastite 871031 34 Sensor lock 022943 35 Sensor shroud 022944 36 Spacer 023452 37 Stiffener printer button 023131 38 Tape foam 88 x 38 023300 39 71 Transducer audio piezo ceramic 691230 6 2 7 PACKING FOR SHIPMENT 7 1 General Instructions 7 2 Repacking in Original Carton 7 3 Repacking in a Different Carton 7 1 7 2 7 3 Should you need to ship the N 20 N 20P monitor for any rea
33. 74HC573 Figure 9 18 Input Port Circuit 016 the input port external to the CPU logic levels on the inputs pins D1 D8 are output to the CPU via the AD bus while EXINEN is strobed low of the user control buttons are input via U16 Also the battery type is sensed 016 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 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 9 18 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 DOTO PR pins Q1 Q7 drive the 7 print dots of the optional printer PR STROBE pulses all 7 of the dot lines for a specific
34. 8 10 Qualifying Information 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 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 Analog Circuit 9 9 Digital Circuitry 9 10 Circuit Illustrations 9 1 9 2 9 3 Overview 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 sit
35. 9 ADO 60 VREF ANGND 0 ACH1 P0 1 ACH2 P0 2 ACH3 P0 3 ACH4 P0 4 5 5 6 0 7 2 2 GND VPP ALE ADV RD 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 ADO P3 0 80C196KC T2CLK P2 3 T2RST P2 4 P2 6 T2U D P2 7 T2CAPT HSIO HSI1 DISP_PHASE MEET HSOO SAMPRED 10K HSO1 OFF ON HSO2 SAMPIR 35 HSO3 Fe S PWMO E SE PRESEN P1 7 HOLD P1 6 HLDA 31 IRLED AV 4 30 PWR DOWN RST Dg P1 4 PWM2 P1 3 PWM1 P1 2 P1 1 P1 0 PR HEAD2 REDLED AV ZERO PHOTO READY INST BUSWIDTH NMI CLKOUT RXD P2 1 TXD P2 0 RESET GENERATION VCC C65 AUF TP42 R73 15K Q22 CR10 2N3904 ines R156 15K L Figure 9 34 CPU Circuit 9 51 LIGHT SENSOR
36. 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 Power supply circuitry is located on the auxiliary PCB and consists of the following subsections Technical Supplement Batteries Four 1 5 V alkaline 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 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 VDC 10 VDC and 12 all of
37. 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 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 o
38. G HOLE 7 d 12 cua R108 e VRED aneo m dus OFFION u33 4 ADS 2 Lg d 15 60 100K ADS 3 18 29 u32 R124 Nels ADIO 4 De 17 A10 AD2 d 16 R123 2 n162 5 02 08 Fig mAWIV i w H LEDDIS NEST m gt Y d Ye GND co Oe es i 100K 18914 RSENS ADi3 7 06 o AB Teas m 22UF 71027 22UF mee HOS d s ADIS 2 T 15 64 16 9 11 AQ 170 vec TdS Ts N 24 d 20 GND Ree 20 HDR EXC M ME ADDRESS DECODING 3 N 20UF EY 22UF Th AUF AUF R70 7 3 me npe qw SENSE va AUX PCB Y m AN a 15 36 sd THIS E a 10 ON Na oe RAWIOV A5 21 mm O H 22UF TEMP SENSOR LY 138 Q 000 us vec 12 RAMEN 33 o sv R122 RAWSV E 0000 08 20 jur ROMEN NOTES 1 ALL RESISTORS 1 8W 1 UNLESS OTHERWISE SPECIFIED
39. PCB JP18 74HC74 C110 0 1UF PWR_DOWN Figure 9 25 Power Control Circuit 9 45 PR PRESENT PR HEAD1 LT1017CS PR HEAD2 LT1017CS VPRN PR TACH Q20 2N3904 DD BTN ADV BTN ON BTN TO PRINTER PCB TG 2N3904 PR HOME PR MEAS HM DOT4 lt PR DOT6 PR DOT5 PR DOT4 PR DOT3 PR DOT2 PR DOT1 PR DOTO PR MOTOR VPRN PWR ON O O _ _ 121 100 120 100 18 ON OFF Figure 9 31 Printer Interface Circuit 9 47 SAMPIR SAMPRED PWM1 Input Signal DC Conditioning Signal Gain AC Ranging Variable Gain Offset Variable Gain Zeroing and Filter Subtraction and Filter and 5 Current to Voltage Variable Gain Offset Variable Gain Conversion and Filter Subtraction and Filter Sensor 1 QFFON a LED Drive LED DIS PMW1 PWM2 rn 4 Output Figure 9 33 N 20 SpO Analog Block Diagram 9 49 REDDC AD15 AD14 AD12 REDAC 5 IRDC 7 IRAC 4 RSENS 11 AMB LIGHT 10 8 PR TEMP 9 15 45 6 48 AD11 49 ADS 51 AD8 52 53 AD6 54 ADS 55 AD4 56 57 AD2 58 5
40. PackmedforShipient 7 1 lil 5 7 1 General InstFUctlOnsz vss d metet teen aede tds 7 1 7 2 Repacking in Original 7 1 S uote eite eR cie edat epe 8 1 6 1 Readouls ts sU E En I odi ecu Etudier E t eat 8 1 6 2 CONTTOLS os ertt e e o dete etuer s e e eee do 8 1 6 3 AR TAE T 8 1 6 4 Printer Output iiie ttti teet e i t te e pes diee tate etes 8 2 8 5 20 20 nne trenes 8 2 8 6 Sensor ea e euam ae ne eI 8 3 6 7 Electrical Specifications aae ae re ath ea de eee t reste eie ee e deed exte 8 3 8 8 Environmental Specifications 8 3 8 9 Physical Specifications eee eese esee netten tnnt tnter teen rete nnne 8 4 9 Technical Supplement d cen I 9 1 9 1 hd RR RERO YT Ro RU RUE RE BR YO E UTOR 9 1 9 2 Functional versus Fractional Saturation esee eere eene 9 1 9 3 Measured versus Calculated Saturation esse sentent eene 9 1 9 4 CirGUll AhnalysLs es eae eet e 9 2 9 5 Functional QVerview ie ERR RR RR age Wis 9 2 9 6 SpO Analog Circuitry Block Diagram Figure 93 9 3 9 7 Definition of Terms cde ete eee Ee e eene e esate
41. 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 Nellcor s representative In the United States call 1 800 635 5267 or 314 654 2000 outside the United States call your local Nellcor representative C 2001 2003 Nellcor Puritan Bennett Inc All rights reserved 062397E 0703 0123 Tyco Healthcare Group LP Nellcor Puritan Bennett Division 4280 Hacienda Drive Pleasanton CA 94588 USA Toll Free 1 800 NELLCOR Authorized Representative Tyco Healthcare UK LTD 154 Fareham Road Gosport PO13 OAS U K Nellcor Puritan Bennett Inc is an affiliate of Tyco Healthcare Nellcor Nellcor Puritan Bennett Durasensor Oxisensor Oxinet Dura Y Oxiband and Oxicliq are trademarks of Nellcor Puritan Bennett Inc To obtain information about a warranty if any for this product contact Nellcor s Technical Services Department or your local representative Purchase of this instrument confers no expressed 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 Covered by one or more of the following U S Patents and foreign equivalents 4 621 643 4 700 708 and 4 770 179 5 RMR UNG itech bese 1 1 1 1 Manual 1 1 1 2 Warnings and Cautions
42. age of 2 75 V at the input of the unity gain amplifiers U7C red and U7D IR Whenever SPST analog switches U11A and U11D are closed by HSOO 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 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 PWMO is increased The IRAC and REDAC are then filtered and input to the CPU and can be measured at TP55 and TP59 respectively Digital Circuitry The digital hardware and related circuitry which is illustrated in the following block diagram Figure 9 4 includes the following subsystems Technical Supplement 9 10 1 9 10 2 9 10 3 9 10 4 9 10 5 9 10 6 9 10 7 _ Measure N 20 N 20P Contr
43. ation 3 3 5 ADV Ad D D dd combinations Err l 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 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 Nellcor s Technical Services Department or Nellcor s local representative for assistance 1 2 3 Press the printer ADV button appears the Oxygen Saturation display Paper advances one line for each button press Press the printer D D button dd appears in the Oxygen Saturation display End SRC 2 printer test 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 3 4 Switch Setting RATE 38 LIGHT LOW MODULATION LOW RCAL MODE RCAL 63 LOCAL 3 Momentarily press the MEASURE button and verify the following power up sequence Performance Verification 4 All
44. ation When saturation is calculated from a blood gas measurement of the partial pressure of arterial oxygen PaO the calculated value may differ from the N 20 N 20P measurement This is because the calculated saturation may not have been corrected for the effects of variables that can shift the relationship between PaO and saturation 9 1 Technical Supplement 9 4 9 5 9 2 Figure 9 1 illustrates the effect that variations in pH temperature partial pressure of carbon dioxide PCO and concentrations of 2 3 DPG and fetal hemoglobin may have on the oxyhemoglobin dissociation curve pH Temperature PCO2 d 2 3 DPG Fetal Hb 100 pH 9 50 Temperature S 1 2 5 t 2 3 DPG b d N 50 100 mmHg Figure 9 1 Oxyhemoglobin Dissociation Curve Circuit Analysis The following paragraphs discuss the circuits of the N 20 N 20P 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 6 Technical Supplement Patient Main PCB SpOe analog Microprocessor Memory Display control Sensors temperature ambient light battery voltage Measure button
45. 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 2 2 2 3 2 4 Overview N 20 N 20P requires no routine maintenance routine service or calibration If service is necessary contact qualified service personnel or Nellcor s representative Use only Nellcor 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 Cleaning Dampen a cloth with a
46. battery type circuit is illustrated in Figure 9 30 2 0 Figure 9 30 Battery Type Circuit unit can operate with either disposable or rechargeable batteries Battery type input 15 digital a high input informs the CPU that rechargeable batteries are in use If rechargeable batteries are used 9 26 Technical Supplement 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 e 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
47. block diagram shows the relationship between these components 9 9 9 9 1 9 9 2 9 9 3 9 9 4 9 9 5 Technical Supplement SpO Analog Circuitry This subsection describes the SpO 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 analog block diagram Figure 9 3 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 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 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
48. ction label found on the paper roll 1 Press down and outward on the top of the paper compartment door to remove it 2 Feed 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 Setting Date and Time 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 th
49. ction 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 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 9 23 Technical Supplement Q15 part 1 controls the power supplies When a logic high is placed on the gate pin G1 signal PWR battery ground is connected to the circuit and switched to ground 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
50. e 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 3 3 3 1 3 3 4 Performance Verification 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 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 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 All indicators BC OX YGEN SATURATION PULSE RATE PULSE SEARCH LOW BATTERY and the PULSE BARS light for a f
51. e 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 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 saturation x100 7 100 96 carboxyhemoglobin methemoglobin Measured versus Calculated Satur
52. ement 9 6 1 9 6 2 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 N 20 N 20P Control buttons Check Battery amp control PCB Ambient Main light sensor PCB AUX PCB CPU Display Display Main PCB drivers Memory lt 4 Audio beeper AUX PCB amp software To analog section Real time AUX Ambient Main Printer Control button Figure 9 4 Digital Circuitry Block Diagram r Power supply AUX Power Supply Block Diagram Figure 9 5 Power supply circuitry Figure 9 5 is located on the auxiliary PCB and consists of four subsections 1 2 3 4 Four size batteries that provide 4 6 VDC Power control circuitry that senses a press of the Measure button and switches power on Power shutoff circuit that controls power to all circuits except the power control circuit 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 button AUX PCB Main PCB shutoff Power circuits Power control fuse supply circuits EMI protect circuits AUX PCB ESD pro
53. er reusable nonsterile RS 10 gt 40 kg Dura Y multisite oxygen transducer reusable nonsterile D YS gt 1 kg For use with the Dura Y sensor Ear clip Reusable nonsterile D YSE gt 30 kg Pedi Check Pediatric spot check clip reusable nonsterile D YSPD 3 to 40 kg OxiCliq oxygen transducers sterile single use only x p TE 3to 20 kg A gt 30 kg Electrical Specifications Battery Type four 1 5 V alkaline C cell batteries Battery Capacity typically 37 hours for N 20 typically 32 hours for N 20P 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 Environmental Specifications Operating Temperature Instrument 0 to 40 C 32 to 104 F 8 3 Specifications 8 8 2 8 9 8 9 1 8 9 2 Storage Temperature 20 to 50 4 to 122 F Humidity Any humidity temperature combination without condensation Altitude 6200 meters 0 to 20 000 ft Physical Specifications Physical specifications are based on product without the protective boot Weight with batteries installed N 20 0 6 kg 1 3 Ib N 20P 0 62 kg 1 4 Ib Dimensions N 20 19 0 cm high 7 6 cm wide x5 08 cm deep 7 5 in x3 0 in 2 0 in N 20P 19 0 cm high 7 6 cm wide x6 35 cm deep 7 5 in x3 0 in 2 5 in
54. erator 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 TACH is then used as 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 DOTX lines are high a dot will be printed 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 Constant power VPRN and a power control line PWR ON are provided by
55. esignated 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 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 Description of N 20 Portable Pulse Oximeter 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 sensor s analog outputs continually controls the gain stages and calculates SpO The N 20 N 20P is
56. ew 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 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 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 90 battery check bAt ON On 3 3 Performance Verific
57. g 4 6 4 4 6 5 4 6 6 4 6 7 4 6 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 Replacing the Real Time Clock RTC Battery The socket for the battery 1 is located on the auxiliary 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 3 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 X Reset the clock see paragraph 4 6 3 Setting Date and Time 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 Replacing the DB 9 Connector 1 Disassemble the N 20 see Section 5 2 the connector is on the main PCB at grid location 2 Using a low power soldering iron unsolder the connector from the PCB and remove it Save all Teflon tubing ferrite
58. gnitude of the IR LED current supply PWM2 which is filtered by the network of R43 C36 R53 and C39 is also input to 010 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 Input Conditioning 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 con
59. indicatorpe OXYGEN SATURATION PULSE 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 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 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
60. ing 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 9 10 23 Technical Supplement 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 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 DOTx In order to provide consistent print quality the ambient
61. is procedure by first removing any sensor from the instrument 1 Turn on the monitor without the sensor connected Switch on 20 and allow 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 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 Press the ADV button repeatedly until the correct minute is displayed At this point the Oxygen Saturation display field shows dxx with d representing date representing the month and representing the date Note that xx month is flashing Press the ADV button repeatedly until the correct month is displayed Press the D D button once Note that yy date is flashing Press the ADV button repeatedly until the correct date is displayed 0 Press the D D button At this point the Oxygen Saturation display field shows with Y representing year Note that xx year number is flashing 11 Press the ADV button repeatedly until the correct year number is displayed 12 Press the D D button once The N 20P turns itself off within 5 seconds SON due 4 5 Troubleshootin
62. isplay s high voltage input Main PCB Main PCB AUX PCB Control Display driver conditioning 1 Microprocessor circuit Display generates timing Display driver signals 2 Display AUX PEB backlight High voltage control circuit 70 volts enables 70 VDC to display Figure 9 6 Display Control Block Diagram Technical Supplement 9 10 13 4 Control Conditioning Circuit The CPU generates a 400 15 low pulse train at a 160 Hz rate on signal DISP PHASE Half of 034 takes DISP PHASE as an input and creates DISP POL an 80 Hz 50 duty cycle square wave 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 us 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 020 are the display segment driver chips Each chip has 32 high voltage outputs and 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
63. its at a time The CPU measures eight analog inputs Input from the SpO analog section includes AC and DC signals for the oximeter sensor red and infrared channels and the sensor calibration resistor RSENS Light temperature and battery voltage are also measured Technical Supplement The N 20 CPU is configured as follows Decoded ADO and 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 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 SpO 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 HOLD HLDA and BREQ bus accessing is disabled via software and the pins are used as standard I O e Pins HSIO and EXTINT are configured for interrupt input The CPU receives 2 external interrupts signals TACH and PHOTOT RXD and TXD are configured as a standard asynchronous serial transmitter and receiver for the serial interface PWMO and PWM pins are configured as pulse width modulator outputs They are used to control gains within the SpO analog section 9 10 9 1 Address Demultiplexing address demultiplexing circuit is illustrated in Figure 9 15 U13 and U33 are transparent la
64. ive low and RD inactive high a binary 5 is produced on pins A B and C forcing output YS 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 range could be used for external port access In other words reading or writing address DC00 DC02 DC04 etc will all produce the same Technical Supplement 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 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
65. m 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 us Q22 provides isolation from C65 so the CPU can drive a good reset to the display control circuit 9 13 Technical Supplement 9 14 Analog Ambient Reference Light Voltage Ambient emperature Battery Voltage Serial Interface Control Control 1 Section Control Address Address Decoding Demultiplexing Enables Standard User Supply Power On Digital 1 0 Input Port lt Output Port T Real Time Lithium Clock and Display Printer Battery Non Volatile Control Interface Memory Power Control pi eire Controls 1 External to Board 1 1 User BUSSES Display Optional Printer ep HEN Flex Circuit with SIGNALS 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 all other memory and mapped 1 are read or written 16 b
66. n an extremity with a blood pressure cuff arterial catheter or intravascular line 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 The DB 9 sensor connector on the N 20 N 20P may be broken 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 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 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 Symptom 4 Dashes appear in the display
67. n 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 019 and 020 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 Technical Supplement GO BTN TO N 20 MAIN PCB ie JP18 CHECK BATTERY R71 150K BAT BTN TO N 20 AUX PCB JP8 GO SW 52 MEASURE BUTTON 1 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 Figure 9 23 User Controls Circuit The CPU input lines 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
68. ncountered is the one displayed 4 7 1 Category 1 Microprocessor Errors 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 gt Category 2 RAM Memory Errors Errors in RAM memory main PCB Likely action is replacement of the main PCB 201 203 Errors in external RAM test Troubleshooting 4 7 3 4 7 4 4 7 5 4 7 6 4 7 7 4 7 8 4 8 Category 3 PROM Errors Errors in PROM memory main PCB Likely action is replacement of the PROM 301 Error in PROM test Category 4 Port Errors E
69. nverter on board Up to eight different analog inputs can be provided to the A D for measurement Central Processing Unit CPU An Intel 80 196 16 bit microcontroller The CPU sends and receives control signals to the analog section display and optional printer 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 5 Technical Supplement 9 7 4 9 7 5 9 7 6 9 7 7 9 7 8 9 7 9 9 8 9 8 1 9 8 2 9 8 3 9 6 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 Input and Output 1 O are 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 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 e infrared IR light at approximately 915 microns e red light at approximately 660 microns 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 cr
70. ol buttons Check Battery Power supply AUX amp control PCB Ambient Main light sensor Display Display Main PCB drivers Memory gt Audio beeper AUX PCB amp software To analog section Real time AUX Ambient Main Printer Control button PCB PCB SOLA HUM Figure 9 4 Digital Circuitry Block Diagram 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 System Memory External to the CPU and consists of an 8K 8 static RAM and a 64K x16 EPROM 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 Audio Output A piezoelectric ceramic beeper is used for audio output 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 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 Power Supply Power Control Circuitry N 20 N 20P receives power from 4 C cell batterie
71. on 6 Spare Parts 4 1 Troubleshooting 4 5 4 2 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 contact Nellcor s Technical Services Department or a local Nellcor 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 Performance Verification Symptom 1 No response to Measure button Cause Action Battery access door may not be properly latched Check access door and ensure it is properly latched Batteries may be discharged Exchange them for a new set Batteries may be incorrectly installed Ensure that batteries are oriented according to the polarity indicator Batteries may not be making proper electrical contact Ins
72. on for approximately 3 seconds plus any time required to complete the power on self test The N 20 N 20P displays updated SpO 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 8 1 Specifications 8 4 8 5 8 5 1 8 5 2 8 5 3 For the N 20 a 2 or greater decrease in SpO is indicated by two brief low pitched tones The N 20P printout shows SpO and pulse rate at 30 second intervals For the N 20P a 2 or greater decrease in SpO 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 Printer Output When activated by the printer ON button the N 20P output shows date time SpO and pulse rate in 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 N 20 N 20P Performance Range Saturation 0 100 Pulse Rate 20 2
73. paper jams and adjusting printer darkness Use this section in conjunction with Section 3 Performance Verification and Section 6 Spare Parts 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 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 Nellcor Technical Services 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 Obtaining Replacement Parts Nellcor Technical Services provides technical assistance information and replacement parts To obtain replacement parts contact Nellcor Refer to parts by the part names and part numbers listed in Secti
74. pect contacts for deformity clean contacts to remove oxidization 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 Clean contact points under Measure button see Section 5 3 N 20 Disassembly Guide 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 Clean the test area and ensure that nothing blocks the sensor site 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 o
75. 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 20 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 raw 10 0 V 75 to 11 0V raw 12 0 V 12 0V to 15 0V 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 batterie
76. re 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 Figure 9 36 N 20 Auxiliary PCB Schematic Diagram Figure 9 37 N 20 Flex Circuit Schematic Diagram VCC INPUT t LED DRIVE R46 1UF 10K 45 m 54 v 4 56 5 Dk R48 06 10 C39 R51 0220 s 100 TP48 2 5 R18 Q2 F 6 04K MMBTAOG R47 RSENS 10 Q5 TO CENTER HOLE 2N3904 5 DUE 22 5 IR RED IR RED R49 CR12 OFF ON 1908 1 914 162 CR18 LED DIS 109K 1N914 RSENS Figure 9 8 LED Drive Circuit 9 31 SENSOR INPUT o 09 gt R1 LTC201 12 U1D 14 1M C1 LF444 1 1 SAMPRED SAMPIR 1 3 2 LTC201 1 6 14 15 068 LTC201 U9B 5 PHOTOI LT1013 Figure 9 9 Differential Synchronous Demodulation Circuit 9 33 OFF ON HSO 1 SAMPIR
77. repancy before the monitor 15 returned to the user Required Materials Durasensor Nellcor DS 100A Tester Pulse Oximeter Nellcor SRC 2 Performance Tests The N 20 N 20P will operate in conjunction with the Nellcor amp 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 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 obse
78. rrors 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 port test Category 5 Reserved 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 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 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 5 DISASSEMBLY GUIDE 5 1 Introduction 5 2 Required Equipment Tools 5 3 N 20 Disassembly Procedure 5 4 N 20P Disassembly Procedure 5 1 5 2 5 2 1 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 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
79. rve the N 20 N 20P in a darkened room If any backlight section is not working correctly contact Nellcor s Technical Services Department or Nellcor s local representative for assistance 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 3 3 3 3 2 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 indicators OX YGEN 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 the PULSE RATE display
80. s 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 9 10 9 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 CPU The CPU circuit is illustrated in Figure 9 14 The Intel 80 196 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 fro
81. s 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 protect against a runaway voltage condition CR25 clamps U26 s output to a safe level 9 10 16 Analog Reference Voltage 9 24 The analog reference voltage circuit is illustrated in Figure 9 26 Technical Supplement 121 RAW12V 61 221 1 C80 22UF 0 1UF 5V RAW 5V TP62 221 C94 2205 16 Figure 9 26 Analog Reference Voltage Circuit 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 LIGHT SENSOR 08 9 VTB8442B Y Q8 MMBTA13L TP72 R136 33 2K x 63 O1UF Figure 9 27 Ambient Light Circuit 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 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 illustra
82. s displayed and the printer prints one of the following 6 lines 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 Troubleshooting 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 Nellcor s Technical Services Department or Nellcor s local representative for assistance Internal tests are performed in the order of the table listing The first error condition e
83. s properly loaded if needed remove the roll of printer paper and reload the printer paper Symptom 10 Paper mechanism jams N 20P only Cause Action Note If a printer paper jam is detected during Power On Self T est Pr Err may appear on the display 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 N 20 Disassembly Procedure and 4 6 2 Loading Clearing Printer Paper Service Procedures The following service procedures are most likely to be enc ountered by the service technician The designation for a component appears in parentheses for example 1 or U15 4 6 1 4 6 2 4 6 3 Troubleshooting Installing Batteries 1 Remove the battery cover access door by pressing the battery compartment access door latch 2 Install four alkaline C cell batteries Be sure to observe the polarity indicator sticker 3 Replace the battery cover access door 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 instru
84. seta tasses ense 9 26 Figure 9 32 Printer Flex Circuit aeree ee 9 28 Figure 9 8 LED Drive Circuit 9 31 Figure 9 9 Differential Synchronous Demodulation Circuit eere eere 9 33 Figure 9 10 N 20 HSO Timing Diagram 4 42 2 02 01 00 070 66 610 68010 10 816 100000000041 1 0000 000 0 0410 tatus eta an 9 35 Figure 9 13 AC Variable Gain Control Circuits eere eee essen ense enne insta 9 37 Figure 9 19 Output Port Circuit sisisi 9 39 Figure 9 22 Display Control 1 9 41 Figure 9 24 Power Supply Circuit 04 4 0 4 4 assesses soss 9 43 Figure 9 25 Power Control 1 01 11 1
85. smissions 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 7 Technical Supplement 9 9 5 1 9 9 6 9 9 6 1 9 8 LED Drive Circuit The LED drive circuit is illustrated in Figure 9 8 at the end of this section 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 PWMI which is filtered by the network of R44 C37 R52 and C38 is input to the LED drive circuit switch U10 and controls the ma
86. son follow the instructions in this section 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 Nellcor warranty If the original shipping carton is not available use another suitable carton or call Nellcor Technical Services to obtain a shipping carton Prior to shipping the device contact Nellcor Technical Services for a returned goods authorization RGA number Mark the shipping carton and any shipping forms with the RGA number 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 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 Hill 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 Sealthe carton with packing tape 6 Labelcarton with shipping address return address and RGA number 7 1 8 SPECIFICATIONS 8
87. tches 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 U13 74HC573 R108 Figure 9 15 Address Demultiplexing Circuit 9 15 Technical Supplement 9 10 9 2 Address Decoding 9 16 address decoding circuit is illustrated in Figure 9 16 EXINEN 20 HDR ADDRESS DECODING TO N 20 AUX PCB 000 74 10 U30C 0000 DBFF ROMEN O 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 15 are all high U30As output goes low enabling the RAM This occurs for the 8K address range of E000 FFFF U30B and 028 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 act
88. tect Display drivers AUX PCB Display backlight Disposable 4 6 VDC batteries SpO2 Analog section main board Figure 9 5 Power Supply Block Diagram 9 6 3 9 6 4 9 7 9 7 1 9 7 2 9 7 3 Technical Supplement Display Control Block Diagram Figure 9 6 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 Main PCB AUX PCB Control Display driver conditioning 1 Microprocessor circuit Display generates Display backlight timing Display driver signals 2 AUX PCB High voltage control circuit 70 volts enables 470 VDC to display Figure 9 6 Display Control Block Diagram 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 AUX PCB 20 Printer flex Microprocessor Printer circuit interface N 20P only PCB User push buttons Printer N 20 only Figure 9 7 Printer Control Block Diagram Definition of Terms Analog to Digital A D converter The CPU has a 10 bit A D co
89. ted in Figure 9 28 9 25 Technical Supplement TEMP SENSOR Figure 9 28 Ambient Temperature Circuit U5 is a precision temperature sensor It outputs 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 05 output would be 250 mV 05 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 VBAT TP73 R69 15 8K 196 BAT VOLT BATTERY VOLTAGE SENSE R70 47 5K C62 1 O1UF Figure 9 29 Battery Voltage Circuit 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 x0 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
90. the auxiliary PCB 01 is used as a power control FET Both halves are used in parallel to reduce the on resistance When 9 29 Technical Supplement 9 11 PWR ON is high the sources 51 S2 short to the drains D1 D2 connecting ground to U1 and 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 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 Support Illustrations These illustrations at the end of this section support the descriptions within this manual Figu
91. trol selection of the circuits A filter with a large time constant follows to smooth the signal and remove noise before amplification Differential Synchronous Demodulation Circuit The differential synchronous demodulation circuit is illustrated in Figure 9 9 at the end of this section Before the current from the photodetector is converted to voltage any high frequency noise 15 filtered by and R17 The op amp is used in parallel with the current to voltage converter U1D to cancel any DC voltage effectively AC coupling the output of UID The average value of the SpO analog reference voltage VREF of UID 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 9 9 7 9 9 7 1 Technical Supplement coordinated with the LED transmission so that the IR and red signals are each sampled twice per cycle
92. ut Circuit 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 1s 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 is differentially driven to obtain maximum audible volume 9 10 13 Display Control Circuitry The display control circuit 15 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 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 d
93. voltage from the A D converter Variable Gain Circuits The variable gain circuits are illustrated in Figure 9 11 VREF Q C122 AUF To LED control PWM2 PWM1 IR LED AV TP52 Figure 9 11 Variable Gain Circuit 9 9 Technical Supplement 9 9 7 2 9 9 8 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 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 Filtering Circuits 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 U4C E P490S 100K 100K RUSO C14 TP89 T CR1 E OP490SO C15 068UF gt 068UF 1N9
94. 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 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 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 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 Disassembly Guide 5 2 2 Removing the Covers 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
95. ystal frequency of the CPU which is 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 Real Time Clock RTC The is used with the optional printer to track time and date for printouts 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 Main PCB Contains the SpO 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 Auxiliary PCB 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 Display and Analog Shield Assembly This assembly connects to the main PCB by flex circuits A metal shield shrouds the SpO 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

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