Micro CO Meter Service Manual
Contents
1. UNUSED INPUTS TT ye CONNECTED TO OR 9 R20 TR3 L U 3 R16 515 104 gt cs R17 su STAR POINT R14 FOR AGND he R18 4 nu I c6 c7 R19 s R12 Pl NC SU Gu SKT COUNTER gt weie ic 55 NS ZE I S TP 2 p BATI R15 c3 au el 7 Hac R3 Re K ji leze RES upp REFERENCE zza IRQ L 10 osc1 raat oe DISPLAY oS OPP 22 39 Posee ct a SL R1B s 20 4 NC PATI 3 58 TCAP Ey CO FUEL CELL PRE POT z za PAS G TCH SOUNDER Paa 5 55 a s PAB 3 SCK 7 PR2 o 3 MOSI PAI 31 miso Aoa 5 PRO Se ERGI 1 5 6 29 33 36 11 30 SENSING SK3 FEB 8 RS PBI a 28 TRL 27 cist 15 26 RG PEAT 15 25 PBS 24 au 23 22 21 4 7 8 13 34 35 37 39 NC au TP a B1 21 sy R9 fa Fl CHO 3 i G1 CHL 1g 2 22 51 cH2 ice 23 D1 CRS 4 R7 2 24 EF 5 2 3 BLOW g c11 TP 8 58 AGNO ja NC 10 11 GIA DRAWN TITLE ISSUE DATE DESCRIPTION OF MOD DATE DESCRIPTION OF MOD CPL MICRO CO METER DATE DRAWING No a 15 9 38 031 2082. N SS Safety Precaution 2 Important safeguards 2 Looking after your f f 7 Micro CO meter 2 NZ a Introduction 2 a Before you begin 2 Micro CO meter system Overview 3 COHb CO sensor 3 Micro CO meter Sa jJ exploded view 6 Disassembling the Micro CO meter for Servicing 7 Replacing the service parts of the Micro CO 7 Reassembling the Micro CO meter 8 Calibrating the Micro CO meter 9 i Circuit description 10 Specifications 13 Technical support 14 fea Parts List 15 C Circuit Diagram 17 Micro CO Meter Service Manual 037 16 Iss 1 2 September 1998 Micro CO Meter Service Manual Information in this document is subject to change without notice and does not represent a commitment on the part of Micro Medical Limited Only the parts supplied by Micro Medical Limited should be used to complete the service operation described in this manual If in any way you feel unsure about the successful completion of the service operation you should contact Micro Medical Limited or its appointed agent in your country or region and arrange the despatch of the product to a Micro Medical Limited Service Centre Copyright 1998 by Micro Medical Limited All rights reserved Drawing no 037 16 Version 1 2 September 1998 All other products are trademarks or registered trademarks of their respective owners Safety Precautio
3. The A D converter is a 10 bit 8 channel serial interface low powered device with an integral voltage reference of 4 096 volts Channel 0 is used to monitor the output of the fuel cell Channel 1 monitors the lithium battery BAT2 from the output of the buffer amplifier IC3 A R16 between BAT2 and the inverting amplifier prevents the battery from discharging through the op amp when the supply is switched off The battery has an end point of 3 volts and when this level is reached the message CELL will be displayed When this happens follow the procedure outlined in Servicing Channel 2 measures the setting on the calibration potentiometer VR2 which can be adjusted between 0 volts and Vref 11 Channel 3 is used to monitor the PP3 battery BAT1 through the potential divider R13 and R14 When this battery falls below 6 6 volts a battery low warning is temporarily indicated on the display upon switch on When the battery falls below 6 1 volts the message is displayed permanently and the unit cannot be used Reset Circuit This consists of the dedicated reset controller IC7 This device holds the reset low whilst the supply voltage is below 4 5 volts and takes the reset high after a period of 350msec once the supply has stabilised Display The display is a custom 3 2 digit low power LCD The seven segments of the three digits the decimal point the backplane and the blow legend are driven directly by ports A B and C of the micro
4. is requested to breathe in maximally hold the breath for 20 seconds and then to expire fully through the mouthpiece connected to the microcomputer unit with the mouthpiece adapter The microprocessor then records the peak value obtained and displays this on a 372 digit LCD display The value can be displayed either as parts per million ppm concentration in the expired air or as the equivalent percentage carboxyhaemoglobin COHb using the mathematical relationships described by Jarvis et al for concentrations below 90ppm and by Stewart et al for higher concentrations Jarvis MJ Belcher M Vesey C Hutchison DCS Low cost carbon monoxide monitors in smoking assessment Thorax 1986 41 886 887 Stewart RD Stewart RS Stamm W Seleen RP Rapid estimation of carboxyhaemoglobin levels in fire fighters JAMA 1976 235 390 392 CO Sensor The sensor is an electrochemical micro fuel cell using gaseous diffusion barrier technology resulting in a direct response to volume concentration rather than partial pressure as with other fuel cells The fuel cell uses a three electrode design which gives increased selectivity to the measured gas compared with two electrode designs The three electrode cell consists of a sensing electrode a counter electrode and a reference electrode separated by a thin layer of electrolyte The gaseous diffusion barrier limits the flow of gas to the sensing electrode and ensures the electrochemical activity of the elec
5. volts When this happens replace both the fuel cell and the lithium battery by following the procedure below Ale r gt x Turn the unit face down and slide back the battery compartment Remove the PP3 battery Remove the 2 self tapping screws Item 1 and put to one side Lift the top moulding Item 6 from the bottom moulding Item 2 Remove the PCB Item 3 from the bottom moulding Carefully remove the fuel cell Item 4 and disregard Unsolder the lithium battery Item 7 from the PCB and disregard Replacing Service parts of the Micro CO 1 Solder the new battery in place Cat No BAT3700 Take great care not to short circuit the terminations even momentarily as the low internal impedance of lithium batteries will result in a high current consumption and greatly reduced life Remove the CO Cat No MCEL3700 sensor from the plastic container Remove the wire shorting link from the reference and shorting pins and carefully insert the CO cell into the PCB Note The fuel cell must not be left for more than a few minutes without the shorting link before inserting into the PCB or damage to the cell may result The assembled PCB must now be left for two weeks to allow the fuel cell to stabilise at the bias voltage of 220mV After two weeks check that the output of the op amp IC3D is between 180 and 220mV with the unit switched on and no carbon monoxide present on the sensor This can be measured betwee
6. URFACE MOUNT RESISTOR 0 125 WATT 5 SIZE 1206 180K SURFACE MOUNT RESISTOR 0 125 WATT 5 SIZE 1206 820K SURFACE MOUNT RESISTOR 0 125 WATT 5 SIZE 1206 10K WATT 5 RESISTOR 1MEG WATT 5 RESISTOR 1MEG WATT 5 RESISTOR 1MEG WATT 5 RESISTOR 100K WATT 5 RESISTOR 10K 4WATT 5 RESISTOR 10K WATT 5 RESISTOR 10K WATT 5 RESISTOR 10K WATT 5 RESISTOR 1 8MEG SURFACE MOUNT RESISTOR 0 125 WATT 5 SIZE 1206 3266X 100K 100K MULTI TURN POTENTIOMETER 47uF 16 VOLT ELECTROLYTIC CAPACITOR 47uF 16 VOLT ELECTROLYTIC CAPACITOR 47pF CERAMIC CAPACITOR 47pF CERAMIC CAPACITOR 47uF 16 VOLT ELECTROLYTIC CAPACITOR 47uF 16 VOLT ELECTROLYTIC CAPACITOR 0 1uF CERAMIC CAPACITOR 15 C8 c9 C10 C11 C12 C13 C14 C15 C16 SW1 BAT2 X1 1uF MULTILAYER CERAMIC CAPACITOR 0 1uF CERAMIC CAPACITOR 47uF 16 VOLT ELECTROLYTIC CAPACITOR 47uF 16 VOLT ELECTROLYTIC CAPACITOR 0 1uF CERAMIC CAPACITOR 47uF 16 VOLT ELECTROLYTIC CAPACITOR 0 1uF CERAMIC CAPACITOR 100pF CERAMIC CAPACITOR 1nF CERAMIC CAPACITOR SLF2300 DOUBL POLE 3 POSITION SLIDE SWITCH LS14250 SAFT PCB MOUNTED 950mA HOUR LITHIUM CELL 4MHz CERAMIC RESONATOR 16
7. ammable OTP microcontroller MC68HC705C9ACP 161 operating at a clock frequency of 1 MHz This processor contains 7 Kbytes of EPROM 176 Bytes of RAM programmable output latches and a serial peripheral interface SPI The current output signal from the sensor is conditioned using a current to voltage converter and is applied to a 8 channel analogue to digital A D converter connected to a microprocessor The calibration potentiometer is also connected to the A D converter When the unit is first switched on the microprocessor records the baseline reading from the A D and uses this value to auto zero the instrument The signal from the CO sensor and the voltage from the calibration potentiometer are both continuously monitored and the peak of the calculated carbon monoxide concentration is displayed Power Supply The unit has two separate supplies The main supply is provided by the externally accessible alkaline 9 volt PP3 battery BAT 1 The instrument may be switched on and off with the slide switch and may also be switched off by a signal from the processor This is done if the unit is left on without use for a period of 5 minutes in order to conserve battery power The supply is controlled by gates A and B of IC2 arranged in a bi stable configuration and powered continuously from BAT1 When the slide switch is moved to the CO PPM position one end of R23 is pulled low This transition is differentiated by the action of C12 and R22 s
8. e contents of this manual before attempting to carry out the procedure of replacing the parts supplied in the sensor replacement kit for the Micro CO Meter Before You Begin Before you begin the servicing operation please read the section on Circuit description very carefully Micro CO Meter system overview The Micro Medical Micro CO meter consists of a hand held microcomputer unit 1 incorporating a CO sensor and is supplied with a mouthpiece adapter with integral one way valve 2 together with disposable cardboard mouthpieces 5 The microcomputer unit is powered by a single alkaline PP3 battery 4 and is supplied with a reducing connector for calibration 3 C The CO sensor is an electrochemical fuel cell and works through the reaction of carbon monoxide at one electrode and oxygen from ambient air at the other This reaction generates an electrical current proportional to the concentration of CO exposed to the sensing surface of the fuel cell The current output signal from the sensor is conditioned using a current to voltage converter and is applied to an analogue to digital A D converter inputs of the microprocessor When the unit is first switched on the microprocessor records the baseline reading on the A D input and uses this value to auto zero the instrument The subject
9. l agent in your region or country for local service 14 Parts List Designation IC1 IC2 IC3 IC4 IC5 IC6 IC7 IC8 D1 D2 ZD1 DISPLAY TR2 TR3 R1 R2 R3 R4 R5 R6 R7 Description MC68HC705C9ACP MOTOROLA OTP MICROCONTROLLER 4093 QUAD 2 INPUT NAND GATE TL27L2CP DUAL LOW POWER OP AMP LM2931AZ5 LOW DROP OUT LOW POWER 5 VOLT REGULATOR OP90GS PRECISION MICRO POWER OP AMP OP90GS PRECISION MICRO POWER OP AMP DS1233 10 DALLAS ECONO RESET MAX186DCAP 12 BIT SSOP SERIAL D A OR MAX192BCAP 10 BIT A D 1N4148 GENERAL PURPOSE DIODE BAT42 GENERAL PURPOSE SCHOTTKY DIODE TCO4BCZM 1 26 BANDGAP REFERENCE LCD 016 03 31 2 DIGIT CUSTOM DISPLAY BC182LB NPN TRANSISTOR TO92 A PACKAGE ALTERNATIVE BC182LC BC182LB NPN TRANSISTOR TO92 A PACKAGE ALTERNATIVE BC182LC ZTX751 PNP TRANSISTOR E LINE PACKAGE 1K SURFACE MOUNT RESISTOR 0 125 WATT 5 SIZE 1206 10K SURFACE MOUNT RESISTOR 0 125 WATT 5 SIZE 1206 10K SURFACE MOUNT RESISTOR 0 125 WATT 5 SIZE 1206 15K SURFACE MOUNT RESISTOR 0 125 WATT 5 SIZE 1206 10 OHM SURFACE MOUNT RESISTOR 0 125 WATT 5 SIZE 1206 1K SURFACE MOUNT RESISTOR 0 125 WATT 5 SIZE 1206 10K WATT 5 RESISTOR 3 3K WATT 5 RESISTOR 22K WATT 5 RESISTOR 100K SURFACE MOUNT RESISTOR 0 125 WATT 5 SIZE 1206 10 OHM WATT 5 RESISTOR 4 7M YWATT 5 RESISTOR 100K WATT 5 RESISTOR 100K WATT 5 RESISTOR 100K WATT 5 RESISTOR 1M SURFACE MOUNT RESISTOR 0 125 WATT 5 SIZE 1206 100K S
10. n The servicing of this device is intended to be carried out by a properly trained and competent electronics engineer or experienced in the maintenance and servicing of medical devices Read this manual thoroughly before proceeding with the service If in any doubt please contact the service centre at Micro Medical Limited or their accredited agent in your country or region Important Safeguards Read all of the instructions Keep the instructions in a safe place for later use Follow all warnings and instructions marked on the product O O O O When replacement parts are required be sure to use replacement parts specified by Micro Medical that have the same characteristics as the original parts Unauthorised substitutions may result in fire electric or other hazards O Do not place on an unstable table o The product should be operated only from the type of power source indicated on the label Looking after your Micro CO Meter o Avoid exposing the Micro CO Meter to direct sunlight o Avoid operating the Micro CO Meter in dusty conditions or near to heating appliances or radiators o Do not keep the Micro CO Meter in a damp place or expose it to extreme temperatures Introduction This service manual provides you with information to carry out the servicing of the Micro CO Meter It is a process which is relatively straightforward but must be carried out in a logical sequence Our advice is to familiarise yourself with th
11. n the two test points adjacent to the slide switch If necessary adjust VR1 to bring the voltage within range Reassembling the Micro CO meter 1 2 3 Place the PCB into the bottom moulding Ensure that the slide switch Item 8 and the switch plate Item 9 are both positioned at the bottom of their travel Ensure that the O ring Item 5 supplied with the fuel cell is in place Place the top moulding on top of the bottom moulding and secure using the two self tapping screws Reconnect the PP3 battery ensuring correct polarity Calibrating the CO meter Plastic Tubing TF Reducing for Calibration Flow Indicator Control Valve 20 400ppm CO in Nitrogen 1 Setup the calibration equipment as shown above 2 Locate the calibration potentiometer positioned in the battery compartment by moving the battery without disconnection 3 Slide the switch on the Micro CO meter to the middle position CO PPM 4 Supply a flow of CO in Nitrogen at a rate of approximately 4 l min for 25 seconds and then turn off the supply 5 Wait until the reading on the LCD display has stabilised 6 Adjust the potentiometer so that the reading on the LCD display is the same as the measured reading on the gas bottle 7 The unit is now ready for operation Circuit description Refer to parts list and to circuit diagram 037 20 The circuit is based on the Motorola one time progr
12. o that a momentary pulse appears on pin 9 of IC3 This pulse will toggle the bi stable circuit so that pin 11 will go low turning transistor TR3 on and supplying 9 volts to the low drop out regulator C4 When the slide switch is returned to the off position pin 13 of IC3 is pulled low the bi stable action is reversed and TR4 will be turned off If the unit is left on without use for 6 minutes then pin 30 of IC1 is driven high under software control turning on TR1 which will also turn the unit off via the bi stable circuit When this happens the slide switch must be pushed to the off and then to the CO PPM position in order to initiate another pulse through C12 to turn the unit back on again The output of the 5 volt regulator supplies the processor and associated circuitry The input and output of IC4 is smoothed by C1 and C2 respectively The secondary power supply is provided by a single 3 6 volt lithium cell used to permanently power the fuel cell conditioning circuit consisting of the op amps IC5 and IC6 and the precision voltage reference ZD1 together with the associated passive circuitry The conditioning circuit draws less than 72uA from the 950 mA Hr lithium battery giving an operational life of 18 months 10 Fuel cell conditioning circuit For correct operation the reference electrode of the fuel cell must be held at a constant bias voltage with respect to the sensing electrode 220mV This is achieved by appl
13. processor The backplane is driven by a square wave of nominally 60Hz The individual segments are driven by a similar square wave which is in phase with the backplane when the segment is off and 180 degrees out of phase when the segment is on Sounder The sounder is operated by a 1kHz square wave generated by pin 35 of IC1 One connection of the sounder is driven directly by pin 35 and the other by the inverted signal from TR1 This push pull arrangement raises the driving voltage to the sounder and increases the volume 12 Specifications Type Range Resolution Sensor Life Response time Hydrogen cross sensitivity Operating temperature Operating pressure Pressure coefficient Relative humidity Non condensing Baseline drift Long term drift Power source Battery life Weight Dimensions Display Micro fuel cell 0 500ppm 1ppm gt 1 year lt 20 sec to 90 of reading lt 10 0 to 40 C Atmospheric 10 0 02 signal per mBar 15 90 continuous 0 99 intermittent Oppm auto zero lt 2 signal loss per month Single Alkaline 9 volt PP3 gt 30 hours of continuous use 160g 170 x 60 x 26mm 3 digit LCD 13 Technical Support Great Britain and World Headquarters Micro Medical Ltd PO Box 6 Rochester Kent ME1 2AZ Telephone 44 0 1634 360044 Fax 44 0 1634 360055 Web Site http www micromedical com uk Email support micromedical com uk Contact Micro Medical Ltd for the loca
14. trode is far in excess of the amount of gas with which it has to deal Gas diffusing onto the sensing electrode reacts at the surface of the electrode by oxidation CO reacts at the sensing electrode according to the equation CO H20 gt CO 2H 2e The counter electrode acts to balance out the reaction at the sensing electrode by reducing oxygen in air to water V20 2H 2e gt 2 HO The CO fuel cell requires a bias voltage of 220mV to be supplied permanently to the reference electrode The low power circuitry supplying this voltage is powered by an internal 950mA hr lithium cell with an operational life greater than the life of the electrochemical fuel cell Micro CO meter exploded view ITEM 1 ITEM 2 ITEM 3 ITEM 4 ITEM 5 ITEM 6 CE SI ITEM 7 L D ITEM 9 ITEM 8 b Disassembling the Micro CO meter for servicing The Micro CO microcontroller unit comprises of a solid state electronic circuit in a robust ABS housing and does not require any preventative maintenance Routine maintenance consists of replacing the fuel cell and internal lithium battery when they are exhausted The 3 6 volt lithium battery is continuously monitored by the microcontroller and the message CEL will be displayed when the voltage falls below 3
15. ying a voltage to the counter electrode to induce the correct bias voltage The 3 6 volt supply from BAT2 is split by the action of R17 and the low power reference diode ZD1 to give a 2 34 1 26 volt supply with the anode of ZD1 connected to 0 volts The stable 220mV reference is generated by the potential divider formed by R18 and R19 This reference is applied to the non inverting input of IC5 The output of IC5 is applied to the counter electrode through R1 The inverting input of IC5 is connected to the reference electrode through R2 and R3 The negative feedback of this circuit ensures that the counter electrode is held at whatever potential is required nominally 350mV to keep the reference electrode at 220mV with respect to the sensing electrode The sensing electrode is held at 0 volts by the action of R5 and R6 which is connected to the virtual earth point of IC6 Fuel cell amplifier circuit The fuel cell provides an output current from the sensing electrode proportional to the concentration of target gas at the sensing surface This current is converted to a voltage by the action of IC6 and the associated passive components at a transfer factor of 15mV uA This signal is further amplified by IC3 b and applied to IC8 The sensitivity of the CO fuel cell is 0 1 0 02uA giving a nominal output of 1 5mV ppm CO The output of IC6 is filtered at 60Hz by R9 and C11 and applied to the input of IC3 B A D converter
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