Micro H2 Meter Service Manual
Contents
1. converter with a transfer factor of 47 mV uA and a roll off frequency of 3 4 Hz R29 is connected from the inverting terminal of IC6 to the 1 26 volt supply This produces a positive bias on the output of approximately 20mV The sensitivity of the fuel cell is 0 03 0 01 uA producing a nominal 1 4 mV ppm at the output of IC6 The output of IC6 is filtered at 6 5 Hz by R9 and C11 and applied to the input of IC3 B IC3 B is in a non inverting amplifier configuration with a gain of 4 giving 5 6mV ppm at its output The output of IC3 B is connected to channel 0 of the A D converter A D converter 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 CEL 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 Channel 3 is used to monitor the PP3 battery BAT1 through the potential divider R13 and R14 When this battery falls below 6 6 vo2. 1 L 4 DISPLRY py UPP 39 OSC REB R18 B5 NC 3 38 795 H2 FUEL CELL 17 4 R2 PAG PD 16 5 36 R27 F2 PPS TCMP SOUNDER 15 6 35 3 TR2 62 PRA SS 14 7 34 5U 25 2 2 SEK ka 02 PR2 MOSI 27 9 32 E2 PAL MISO ZS 82 pra 1 31 1 1 5 6 29 33 36 38 40 5 5 ego 11 32 25 12 29 R25 1 PCO 32 13 28 TRL 3 03 PB2 i 27 Pel 3e 23 c PEZ 53 be R28 19 3 ES 24 11 83 6 5 PCS 12 23 PB 15 pp Pte USS 21 PCT 4 7 8 18 84 85 37 89 NC pu d R11 4 TP 21 21 t R9 20 01 5V C10 SU F1 CHO VDD 8 3 MED CH 2 ttk TS 22 01 CH2 5 1 9 5 oU 16 1 3 53101 CH3 2 17 DIN T R7 2 24 Et CH4 15 L SSTRB 4 HER 2 3 BLON CHS c 15 0007 Tcu 7 14 DGND au CH 1 POND TP RB AGND REFADJ 1e UREF N C 18 11 C14 SHDN Wie Br C18 SU DATE DRAWING No 944 09
3. 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 15 UNUSED INPUTS NC CONNECTED TO 4 1C2cC gt BU OR SU QU a Le un TR Ls Ut SWI f rs LRL R16 Z RIS 1 4 C5 R17 o p 5U f RI IC3 R Ste 4 c2 STAR POINT amp T R14 PESE FOR AGND R18 1 2 8 R21 A 2 11 15 a 12 eot R19 D2 aN R22 R23 8 R12 R1 18 9 1 v C12 NC 102 B gt Qu 5U 5u SK1 9 COUNTER 1 5 8 ee P 2 g BAT1 R15 T Iti sk2 R2 R3 ICE S TE RES UDD REFERENCE R24 Jag ri 40 956
4. OR 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 47K 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 WATT 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 SURFACE MOUNT RESISTOR 0 125 WATT 5 SIZE 1206 ZERO OHM LINK NOT USED 10K WATT 5 RESISTOR 1MEG WATT 5 RESISTOR 1MEG WATT 5 RESISTOR 1MEG WATT 5 RESISTOR 100K WATT 5 RESISTOR 10K WATT 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 14 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
5. Pd EM Contents page Safety Precaution 2 Important safeguards 2 Looking after your ARK LAY Micro H meter 2 ue d Introduction 2 SUE Before you begin 2 Micro meter system Overview 3 sensor 4 H2 PPM 9 9 Micro H meter COFO je exploded view 5 Disassembling the Micro H meter for servicing 6 Replacing the service Parts of the Micro H5 6 Reassembling the Micro meter 7 Calibrating the Micro meter 8 eo BC OPO Circuit description 9 1 Specifications 12 E n Technical support 13 Parts List 14 Circuit Diagram 17 Micro Meter Service Manual 044 11 Iss 1 1 September 1998 Micro 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 044 11 Version 1 1 September 1998 All other products are trademarks or registered trademarks of their respectiv
6. dvice 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 Micro H Meter Before You Begin Before you begin the servicing operation please read the section on Circuit description very carefully Micro Meter system overview The Micro Medical Micro H gt meter consists of a hand held microcomputer unit 1 incorporating a H gt sensor and is supplied with a mouthpiece adapter with integral one way valve 2 face mask adapter 6 and 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 EE OOOO OOOO OOOOOOOOO 900080000 Oooog Fig 1 The sensor is an electrochemical fuel cell type 7 supplied by City Technology Ltd It works through the reaction of hydrogen at one electrode and oxygen from ambient air at the other This reaction generates an electrical current proportional to the concentration of H exposed to the sensing surface of the fuel cell The subject breathes onto the sensor through the mouth
7. e 200ppm hydrogen 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 Slide the switch on the Micro H meter to the H2 PPM position and wait for the display to read zero 4 Supply a flow of Hydrogen in Nitrogen at a rate of approximately 0 25 l min for 70 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 programmable OTP microcontroller MC68HC705C9ACP IC1 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
8. e 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 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 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 H Meter Avoid exposing the Micro Meter to direct sunlight o Avoid operating the Micro H gt Meter in dusty conditions or near to heating appliances or radiators o Do not keep the Micro H 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 H gt Meter It is a process which is relatively straightforward but must be carried out in a logical sequence Our a
9. lts 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 10 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 7 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 microprocessor 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 11 Specifications Type Range Resolution Accuracy Sensor Life Response time Operating temperature Operating humidity Operating pressure Pressure coefficient Baseline drift Long term drift Power source Battery life Weight Dimensions Display Storage temperature Storage humidity Mic
10. m moulding Carefully remove the fuel cell Item 4 and disregard Unsolder the lithium battery Item 7 from the PCB and disregard Replacing the Service parts of the Micro H 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 2 Remove the H Cat No CEL4400 sensor from the plastic container 3 Remove the wire shorting link from the reference and shorting pins and carefully insert the H gt 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 Reassembling the Micro meter 1 Place the PCB into the bottom moulding 2 Ensure that the slide switch Item 8 and the switch plate Item 9 are both positioned at the bottom of their travel 3 Ensure that the O ring Item 5 supplied with the fuel cell is in place 4 Place the top moulding on top of the bottom moulding and secure using the two self tapping screws 5 Reconnect the PP3 battery ensuring correct polarity Calibrating the H meter Plastic Tubing Reducing for Calibration Flow Indicator Control Valv
11. o 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 C1 and C2 smooth the input and output of IC4 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 201 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 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 0 Volts This is achieved by applying a voltage to the counter electrode to induce the correct bias voltage The output of IC5 is applied to the counter electrode through R1 and the inverting input is connected to the reference electrode through R2 and R3 The negative feedback action of this circuit ensures that the counter electrode is held at whatever potential is required nominally 56mV to keep the reference electrode at O volts with respect to the sensing electrode The sensing electrode is held at ground potential by R6 to ground and R5 which is connected to the virtual earth point of IC6 IC6 together with the associated passive components forms a filtered current to voltage
12. piece connected mouthpiece adapter or through a face mask if the subject is an infant The instrument then displays the peak value obtained in parts per million ppm The Micro H gt is used in the diagnosis of lactose mal absorbtion a condition which produces increased hydrogen levels in the blood when un absorbed lactose reacts with bacteria in the intestines This increased level of hydrogen is expired and can be measured after ingestion of lactose following a period of fasting H 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 electrode 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 H2 reacts at the sensing electrode according to the equation 2H 42e The counter electrode acts to balance out the reaction at the sensing electrode by reducing oxygen in air
13. ro fuel cell 0 500ppm 1 5 of full scale or 1ppm whichever is greater gt 18 months 70 sec to 90 of reading 0 to 40 C 30 90 continuous 0 99 intermittent atmospheric 10 0 02 signal per mBar Oppm auto zero 296 signal loss per month Single Alkaline 9 volt PP3 gt 30 hours of continuous use 160g 170 x 60 x 26mm 31 2 digit LCD 20 C to 70 C 30 to 90 12 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 local agent in your region or country for local service 13 Parts List Designation IC1 IC2 IC3 IC4 IC5 IC6 IC7 IC8 01 2 201 DISPLAY TR1 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 26V BANDGAP REFERENCE LCD 016 03 32 DIGIT CUSTOM DISPLAY BC182LB NPN TRANSISTOR TO92 A PACKAGE ALTERNATIVE BC182LC BC182LB NPN TRANSIST
14. the H sensor and the voltage from the calibration potentiometer are both continuously monitored and the peak of the calculated hydrogen concentration is displayed 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 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 H2 PPM position one end of R23 is pulled low This transition is differentiated by the action of C12 and R22 so 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 IC4 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 H2 PPM position in order t
15. to water 1 202 2H 2e gt 2H2O A low power circuit powered by an internal 950 mA hr lithium battery is used to maintain the fuel cell in a permanently active state to produce a zero start up time The battery has an operational life greater than the life of the electrochemical fuel cell Micro meter exploded view ITEM 1 ITEM 2 ITEM 5 ITEM 4 ITEM 5 ITEM 6 2 cl Lr H cl ITEM 7 L D ITEM 9 ITEM 8 b Disassembling the Micro H meter for servicing The Micro H gt 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 volts When this happens replace both the fuel cell and the lithium battery by following the procedure below SU xg e es 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 botto
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