Micromedical Micro User manual

Micro/Micro Plus
Service Manual
051-07 Iss. 1.0September 1998
Contents page
SafetyPrecaution 3
Important safeguards 3
Looking after your
Micro/Micro Plus 3
Introduction 3
Before you begin 3
Micro/Micro Plus
systemOverview 4
Micro Medical
Digital Volume
Transducer 5
Cleaning the Micro
Medical Digital
Volume Transducer 6
Micro/Micro Plus
exploded view 7
Disassembling the
Micro/Micro Plus for
Circuit Investigation 8
Reassembling the
Micro/Micro Plus 9
Circuit description 10
Technical Data 12
Technicalsupport 13
Parts List 14
Circuit Diagram 15

2
Micro/Micro Plus
Service Manual
Information in this document is subject to change without noticeand does notrepresent a
commitment on the part ofMicro Medical Limited. Onlythe parts supplied byMicro Medical
Limited shouldbe used to complete theservice operation described in this manual. Ifin any
wayyou feel unsure about the successful completion of the service operation you should
contact Micro Medical Limited or its appointed agentin your countryor region and arrange the
despatch ofthe product toa Micro Medical Limited Service Centre.
Copyright 1998 byMicro Medical Limited All rights reserved
Drawing no. 051-
Version 1.0
September 1998
All other products are trademarks or registered trademarks oftheir respectiveowners.

3
SafetyPrecaution
The servicing ofthis device is intended to be carried out byaproperly
trained and competent electronicsengineer, or experienced inthe
maintenance and servicing ofmedical devices. Read this manual
thoroughlybefore proceeding with the service. Ifinanydoubt please
contactthe service centre at Micro Medical Limited ortheir accredited
agent in your countryor region.
ImportantSafeguards
oRead all ofthe instructions.
oKeep the instructions in a safe place for later use.
oFollowall warnings and instructions marked on the product.
oWhen replacement parts are required, be sureto usereplacement parts
specified byMicro Medical that havethe same characteristics asthe
original parts. Unauthorised substitutions mayresult in fire, electric or
other hazards.
oDo not place on an unstable table.
oThe productshouldbe operated onlyfrom the type ofpower source
indicated on the label.
Looking after your Micro/Micro PlusSpirometer
oAvoid exposing the Micro/Micro Plus Spirometer to direct sunlight.
oAvoid operating the spirometer in dustyconditions or near to heating
appliances or radiators.
oDo not keep the spirometer in adamp placeor expose it to extreme
temperatures.
oDo not direct the transducer holder towards astrong light source whilst
operating the spirometer.
Introduction
This service manual provides you with information tocarryout the
servicingoperation of the Micro/Micro PlusSpirometer. should the unit
become faultyIt is aprocess, which is relativelystraightforward but must
be carried out in alogical sequence. Our advice is to familiarise yourself
with the contents of this manual before attempting to carryout the
procedure ofreplacing the parts supplied in the service kit for the
Micro/Micro Plus Spirometer.
Before You Begin
Before you begin the servicing operation, please read the section on
Circuit description very carefully:

4
Micro/Micro Plus system overview.
The Micro Medical Micro/Micro Plus Spirometer consists ofa hand held
microcomputer unit (2)incorporating a Micro Medical digital volume
transducer (1).
1. Micro Medical Digital Volume Transducer.
2. Micro microcomputer unit.
3. Lung Function Calculator.
4. PP3 Alkaline battery(BAT2).
Micro
Medical

5
Micro Medical Digital Volume Transducer
The Micro Medical digital volume transducer consists of an acrylic tube
with a vane (3) positioned between a stator (1) and a crossbar (2). The low
inertia vane is attached to a stainless steel pivot (5) which is free to rotate on
two jewelled bearings (4) mounted at the centre ofthe stator plate and cross
bar. Asair is passed through the transducer a vortexis created bythe stator,
which causes the vane to rotate. The numberofrotationsis proportional to
the volume of air passed through the transducer and the frequencyofrotation
is proportional to the flowrate. The transducer passesthrough the PCB,
which contains a light emitting diode (LED) and phototransistor. The LED
produces an infrared beam, which is interrupted bythe vane twice per
revolution. This interruption is sensed bythe phototransistor giving a square
wave output on the collector.
There is no routine maintenance required for the transducer other than
cleaning.
EMITTER 2
DETECTOR
INFRA RED
434
5
1
INFRA RED
VOLUME PROPORTIONAL TO THE NUMBER OF PULSES
FLOW PROPORTIONAL TO THE PULSE FREQUENCY
Flow
=
Volume = k X No. of
pulses
k/pulse
period

6
Cleaning the Digital Volume Transducer
The transducer requires no routine maintenance or servicing. However if you
wish to sterilise or clean the transducer it maybe removed bythe following
procedure.
1. Remove the transducer bygentlypulling from the main bodywith a
twisting action.
2. The transducer maynowbe immersed in warm soapywater for routine
cleaning or immersed in a cold sterilising solution e.g. Alkacide for a period
not exceeding 15 minutes. (Alcohol and chloride solutions should be
avoided.)
3. After cleaning or sterilising, the transducer should be rinsed in distilled
water and dried.
4. Reassemble the transducer into the Micro/Micro Plus Spirometer.
Alkacide is available from Micro Medical in convenient 250ml plastic
bottles (Cat No. SSC1000)

7
Micro/Micro Plus Spirometer exploded view(fig 1)
1. Bottom Moulding 2. Top Moulding
3. PCB Assembly 4. Turbine sleeve
5. Coated O ring 6. O ring capture ring
7. Polycarbonate window 8. 2 xScrews
Item8
Item1
Item8
Item2
Item6
Item3
Item7
Item4Item5

8
Disassembling the Micro/MicroPlus for CircuitInvestigation.
If the Micro/Micro Plus Spirometer becomesfaultythen the following
procedure is needed to investigate the fault.
1 Remove the digital volume transducer from the microcomputer unit by
gentlypulling the transducer from the microcomputer unit with a twisting
action.
2 Turn the unit face down and slide back the batterycover.
3 Remove the batteryand place to one side.
4 Remove the 2 screws on the bottom moulding.
5 Turn the Micro/Micro Plus face up and ease the top moulding from the
bottom and turn the top moulding over so as the unit is in two halves.
6 Remove the PCB from the bottom moulding and put the bottom
moulding to one side.
7 The Micro/Micro Plus is nowreadyfor fault finding

9
Reassembling the Micro/Micro Plus
1. Place the PCB into the bottom moulding and wire batterylead as as
shown in fig 2.
2. Replace items 4, 5 and 6 (Fig1) into the bottom moulding.
3. Position top moulding on top ofbottom moulding and push together
(ensure that the batteryleads are not trapped).
4. Turn unit face down and replace the 2 screws.
5. Replace the PP3 batteryensuring correct polarity.
6. Replace the batterycover.
7. Turn the unit face up and refit transducer into the microcomputer unit.
8. The unit is nowreadyfor operation.
Fig 2

10
Circuit description
The circuit is based on the Motorolaone time programmable (OTP)
microcontroller MC68HC705C9ACFN (IC1) operating at aclock frequency
of1MHz.This processor contains 7Kbytes ofEPROM, 176 Bytes of
RAM, programmable output latches, and a serial peripheral interface (SPI).
The processor monitors pulses from the transducer, calculates the
spirometrymeasurements, and directlydrives the LCD displayaccording
to the position of the slide switch. The state ofthe batteryis also
monitored and awarning is displayed when necessary.Calibration
information is stored in a 256 bit serial EEPROM, IC5, and communicates
with the microcontroller via the SPI.
Reset
The reset circuit consists ofasingle chipreset (IC7) which holds the reset
line lowfor 350ms after the 5volt supplyhasreached the threshold
voltage of4.5 volts. The reset signalis then applied to the microprocessor
(IC1),
Power Supply
The unit is powered an alkaline 9volt PP3 battery(BAT1) and switched by
IC3 which is arranged in abi-stable configuration. When the unit is turned
on via the slide switch a momentarypulse appears on pin 1ofIC3 bythe
action ofR8, R9 and C10. This pulse toggles the bi-stable circuit so that
pin 11 ofIC3will go lowturning transistor TR4on and supplying 9volts to
the lowdrop out regulator (IC4). When the unit is turned off pin 13 ofIC3
is pulled lowreversing the bi-stable action and turning TR4off. If the unit
is lefton without use for 6minutes then pin 31 ofIC1 is driven high under
software control turning on TR5 which will turn the unit offvia the bi-stable
circuit.
Batterymonitoring
The terminal voltage ofthe batteryis monitored bythe action ofR4, R5,
R6, and TR2. The emitter of TR2 is held at 5 volts and the base voltage is
derived from the battery through the potential divider formed byR4 and
R5. When the batteryvoltage falls to approximately6volts, the voltage on
the base ofTR2 is 4.4 volts and the transistor turns on. The collector will
rise to about 4.6 voltsand this is monitored bythe processor on pin 13
(PB0) when the unit is switched on. When alowbatterycondition is
detected the processor signals to the user that the batteryis lowby
flashing the letters bat three times on the displayaccompanied byan
audible warning.