Baby CO Meter Service Manual
Contents
1. Plastic Tubing LO Control Indio valve indicator E Reducing EA Connector for calibration 20 ppm carbon monoxide in air sy The plastic tubing supplied with the gas should be pushed firmly over the reducing connector Slowly turn the control knob anti clockwise until the ball in the flow indicator is between the two marks This will then supply a gas flow of approximately 0 25 l min Apply this flow for 25 seconds and if the meter does not read 20ppm use the calibration tool to push the calibration switch The unit will then beep 3 times store the new calibration value and display the following The gas supply should then be turned off 10 Circuit description Refer to the parts list and circuit diagram The circuit is based on the Hitachi one time programmable OTP microcontroller HD64F3687FP U5 operating at a clock frequency of 14 745MHz This processor contains EPROM RAM and eight 10 bit analogue to digital A D converters The current output signal from the sensor is conditioned using a current to voltage converter and is applied to an A D input of the microcontroller Voltages derived from the external PP3 battery and the internal lithium battery are also connected to the A D converter inputs When the unit is first switched on the microprocess2. Contents page Safety Precaution 2 Important safeguards 2 Looking after your Baby CO meter 2 Introduction 2 Before you begin 2 Baby CO system overview 3 CO sensor 5 Baby CO meter exploded view 6 Disassembling the Baby CO meter for servicing 7 Replacing the internal battery 7 Replacing the fuel cell 7 Reassembling the Baby CO meter 8 Calibrating the Baby CO meter 9 Circuit description 11 Power supply 11 Fuel cell amplifier circuit 12 o ee Reset circuit 12 00000000000 Display 12 56000000000 Sounder 12 000 000 Indicator lights 13 od ae eae RS232 interface 13 000000000 0000000 Specifications 14 Technical support 15 Parts List 16 Circuit Diagram 18 Baby CO Meter Service Manual 113 19 Iss 1 0 Jan 2007 Medical Baby 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 2005 by Micro Medical Limited All rights reserved Drawing no 113 19 Version 1 0 September 2007 All other p
3. D3 D4 D5 DISPLAY TR1 TR2 TR3 TR4 TR5 R1 R2 R3 R4 Description OP90GS Precision micro power surface mount BU4S11 Single NAND gate BU4S11 Single NAND gate LM2931M5 0 Low drop out 5 volt regulator HD64F3687FP Hitachi microcontroller 24LC00 16 Byte surface mount serial EEPROM MAX3221CAE Maxim RS232 transceiver MCP602 1 SN Microchip dual rail to rail OP AMP ZHCS750 Schottky diode 3mm green LED 3mm red LED 3mm yellow LED BAS21 Small signal diode LCD 016 03 3 Digit custom display DTC114EKA NPN transistor FMMT591 PNP transistor DTC114EKA NPN transistor DTC114EKA NPN transistor DTC114EKA NPN transistor 330K Resistor 12K Resistor 1M Resistor 10K Resistor 10K Resistor 1M Resistor 1M Resistor 100K Resistor 10K Resistor 560R Resistor 560R Resistor 820R Resistor 100K Resistor 100K Resistor 100K Resistor 10K Resistor 1M Resistor 10K Resistor 10K Resistor 10K Resistor 27R Resistor 1K Resistor 10K Resistor 180K Resistor 360K Resistor 390K Resistor 1M Resistor 10uF Tantalum capacitor 22pF Ceramic capacitor 0 1uF Ceramic capacitor 1uF Ceramic capacitor 16 C5 C6 C7 C8 c9 C10 C11 C12 C13 C14 C15 C16 C17 C18 C19 C20 C21 TH1 sw1 sw2 BAT2 X1 CO CELL 22pF Ceramic capacitor 0 1uF Ceramic capacitor 0 1uF Ceramic capacitor 0 1uF Ceramic capacitor 0 1uF Ceramic capacitor 1uF Ceramic capacitor 0 1uF Ceramic capacitor 10nF Ceramic capacitor 0 1uF Ceramic capacitor 47uF Electrolytic capaci
4. gt 12 Suspected poisoning Red alarm 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 The cell consists of a working electrode and a counter 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 electrode is far in excess of the amount of gas with which it has to deal Gas diffusing onto the working electrode reacts at the surface of the electrode by oxidation CO reacts at the working 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 202 2H 2e gt 2 H20 Baby CO meter exploded view Item 6 Item 5 Item 4 Item 3 Item 2 Item 1 CH Item 10 lt i Item 9 Item 7 Item 8 Disassembling the Baby CO meter for servicing The Baby 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 r
5. acing fuel cell of the Baby CO 1 Remove the CO sensor Cat No CEL7300 from the plastic container 2 Carefully insert the CO cell into the PCB with the correct orientation Reassembling the Baby CO meter 1 2 3 Place the PCB into the bottom moulding Tuck the battery strap between the battery and the side wall of the bottom moulding away from the slide switch Ensure that the slide switch Item 9 and the switch plate on the top moulding item10 are both positioned at the bottom of their travel Ensure that the rubber gasket Item 5 is in place in the top moulding Place the top moulding on top of the bottom moulding ensuring the rubber gasket fits over the cell correctly and secure using the two self tapping screws Reconnect the PP3 battery ensuring correct polarity Calibrating the CO meter Calibration will remain stable to within 2 over one month and typically to within 10 over 6 months Micro Medical supplies calibration gas 20ppm CO in air and recommends that the unit is recalibrated on a 6 monthly basis See page 13 for calibration accessories To carry out the calibration locate the calibration switch on the right hand side of the instrument as shown below Calibration Switch Push the slide switch to the CO PPM position and wait for the unit to display zero Screw the control valve firmly onto the cylinder and connect the gas supply as shown below
6. digital A D converter 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 is requested to breathe in maximally hold the breath for 10 seconds and then to expire fully through the mouthpiece connected to the microcomputer unit with the mouthpiece adapter As an aid to timing the breath holding period a countdown from 10 to 0 is displayed after the unit is turned on The microprocessor then records the peak value obtained and displays this on a 3 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 As a quick guide to the estimated smoking level red amber and green indicator lights are provided The following levels of CO activate these lights CO ppm COHb Cigarette consumption Indicator 0 5 0 0 8 Non smoker Green 6 10 1 1 6 Light smoker Amber 11 72 1 8 12 Heavy smoker Red gt 72
7. electrode proportional to the concentration of target gas at the sensing surface This current is converted to a voltage by the action of U1 and the associated passive components at a nominal transfer factor of 387mMV uA This signal is further amplified by USA with a gain of 2 08 and applied the A D input of the microcontroller pin 44 after being filtered by the action of R8 and C4 The sensitivity of the CO fuel cell is 0 045 0 015uA giving a nominal amplified output of 36mV ppm CO Reset Circuit This microcontroller has internal reset circuitry that requires C12 and D5 for proper operation Display The display is a custom 3 digit low power LCD The segments and backplane are driven directly by microcontroller The backplane is driven by a square wave of nominally 60Hz The individual segments are driven by a similar square wave that 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 pins 24 and 25 of U5 12 Indicator lights The three indicator LED s are driven from pins 51 52 and 53 of the microcontroller through transistors TR3 TR4 and TR5 RS232 interface The transmit and receive ports for RS232 transmission are on pins 46 and 45 respectively of the microcontroller The transmission is converted from logic to RS232 levels by the U7 13 Specifications Type Range Resolution Gree
8. eplacing 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 bt2 will be displayed when the voltage falls below 3 volts The fuel cell exhibits a gradual loss of sensitivity with time and has effectively expired when the unit can no longer be calibrated When either the fuel cell or the lithium battery has expired replace by following the procedure below 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 1 2 3 4 Liftthe top moulding Item 6 from the bottom moulding Item 2 5 Remove the PCB Item 3 from the bottom moulding 6 If the fuel cell Item 4 is exhausted carefully remove by gently pulling away from the PCB 7 Ifthe battery Item 8 has expired then note the orientation and remove from the PCB mounted clips by pulling on the battery strap Item 7 directly away from the PCB Put the battery strap to one side and discard the battery Replacing internal battery of the Baby CO 1 Place the battery strap over the new battery Cat No BAT5900 and push into the PCB mounted clips ensuring the correct orientation 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 Repl
9. his happens the slide switch must be pushed to the off position and then to the CO PPM position in order to initiate another pulse through C15 to turn the unit back on again The output of the 5 volt regulator supplies the processor and associated circuitry C13 and C14 smooth the input and output of U4 BAT1 is monitored by an A D input of the microcontroller pin 62 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 11 The secondary power supply is provided by a single 3 6 volt lithium cell BAT2 used to permanently power the fuel cell amplifier circuit consisting of the op amp U1 and associated passive circuitry The amplifier circuit draws less than 11uA from the 1000mA Hr lithium battery giving a nominal operational life of greater than 10 years BAT2 is buffered by U8B and monitored by an A D input of the microcontroller pin 63 R27 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 bt2 will be displayed When this happens follow the procedure outlined in Servicing Fuel cell amplifier circuit The fuel cell provides an output current from the counter
10. n indicator light Amber indicator light Red indicator light Flashing red light alarm Accuracy Sensitivity drift Sensor Life Response time Hydrogen cross sensitivity Operating temperature Operating pressure Pressure coefficient Relative humidity Non condensing Baseline drift Long term drift Power source Main battery life Internal battery life Weight Dimensions Display Storage temperature Storage humidity Electro chemical fuel cell 0 100ppm 1ppm 0 to 6ppm 0 to 1 COHb 7 to 10ppm 1 1 to 1 6 COHb 11 to 72ppm 1 8 to 12 COHb gt 72ppm gt 12 COHb 5 of full scale of 1ppm whichever is the greater 0 5 C gt 2 to 5 years lt 15 sec to 90 of reading lt 15 15 to 25 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 10 years 180g Including battery 170 x 60 x 26mm 3 digit LCD 20 to 70 deg Celsius 30 to 90 14 Technical Support Great Britain and World Headquarters Micro Medical Ltd PO Box 6 Rochester Kent ME1 2AZ Telephone 44 0 1634 893500 Fax 44 0 1634 893600 Web Site http www micromedical co uk Email support micromedical co uk Contact Micro Medical Ltd for the local agent in your region or country for local service 15 Parts List Designation U1 U2 U3 U4 U5 U6 U7 U8 D1 D2
11. or records the baseline reading from the A D and uses this value to auto zero the instrument The signal from the CO sensor is continuously monitored and the peak of the calculated carbon monoxide concentration is displayed and transmitted through the RS232 driver U7 Power Supply The unit has two separate supplies The externally accessible alkaline 9 volt PP3 battery BAT 1 provides the main supply 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 fora period of 4 minutes in order to conserve battery power The supply is controlled by gates U2 and U3 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 R7 is pulled low This transition is differentiated by the action of C15 and R6 so that a momentary pulse appears on pin 2 of U3 This pulse will toggle the bi stable circuit so that pin 4 of U2 will go low turning transistor TR2 on and supplying 9 volts to the low drop out regulator U4 When the slide switch is returned to the off position pin 1 of U2 is pulled low the bi stable action is reversed and TR2 will be turned off If the unit is left on without use for approximately 4 minutes then pin 44 of U5 is driven high under software control turning on TR1 which will also turn the unit off via the bi stable circuit When t
12. roducts are trademarks or registered trademarks of their respective owners Safety Precaution 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 o Read all of the instructions o Keep the instructions in a safe place for later use o Follow all warnings and instructions marked on the product 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 Baby CO Meter o Avoid exposing the Baby CO Meter to solvents including alcohol and disinfectants o Avoid operating the Baby CO Meter in dusty conditions or near to heating appliances or radiators o Do not keep the Baby 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 Baby CO Meter It is a process which is relati
13. tor 0 1uF Ceramic capacitor 33pF Ceramic capacitor 33pF Ceramic capacitor 1uF Ceramic capacitor 1uF Ceramic capacitor 0 1uF Ceramic capacitor 0 1uF Ceramic capacitor NTC 47K thermistor SLF2300 Double pole 3 position slide switch Push switch SL235 CVHZ Sonnenschein 1A Hr AA Lithium cell 14 745 MHz crystal 1000 ppm CO fuel cell 17 sI 9 s t z A OA O A PLUS LURO Exa 01 1011 a vona Isqun ES OO Te POF i Da GUA Dvr a A 3 It Es gt ls AVOICCEXVIN SS THALA THALA THALA ame s E ITO ANL a ae j 0 a 8 S aL IL aL Ex Ls HT Y wats lan E pe a 7 X o or NI jo ange EWR AR NEON AR TA a ea za Wis AV ISIC aro ae wes WOS wos Cele HOLIMS ATWO an I ond Te f E v v v lt Il AS AS AS EMS mor o avciva TWD A WI 4 ME d 5 Ta lt A 9 ia AE ava DN e 4 e 19 F aro I Str ee 00 sal wn loo AS Moe 97
14. vely straightforward but must be carried out in a logical sequence Our advice is to familiarise yourself with the contents of this manual before attempting to carry out the procedure of replacing the parts supplied in the sensor replacement kit for the Baby CO Meter Before You Begin Before you begin the servicing operation please read the section on Circuit description very carefully Baby CO Meter system overview The Micro Medical Baby 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 00000000000000 000000000000 0000 oO 0 oO O oO oO O oO 000000000 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
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