Micro Medical ML3500 Service Manual

Microlab ML3500 ­ServiceManual

050-13 Iss. 1.0 June 2000

Contents

Exploded Isometric View............................................................................................3

System Overview.........................................................................................................4

Figure 1 .......................................................................................................................4

Transducer...................................................................................................................5

Figure 2 .......................................................................................................................5

Disassembling the MicroLab for Repairs..................................................................6

Reassembling the Microlab after repairs………………………………………………...6
Circuit Description

Circuit Overview ............................................................................................................. 7

Processor Control Section......................................................................................................................7

Address Bus............................................................................................................................................7

Ram Address Lines.................................................................................................................................7

Reset.......................................................................................................................................................7

Keypad....................................................................................................................................................7

Real Time Clock......................................................................................................................................8

Display.............................................................................................................................................8

Serial Interface........................................................................................................................................8

Battery Monitoring...................................................................................................................................8

Printer Driver...........................................................................................................................................8

Power Supply..........................................................................................................................................9

Printer Mechanism..................................................................................................................................9

Transducer Interface...............................................................................................................................9

Parts List....................................................................................................................10

Technical Support.....................................................................................................13

Fault Analysis............................................................................................................14

Circuit Diagrams........................................................................................................15

Circuit overview.....................................................................................................................................15

Processor Section.................................................................................................................................16

Power supply…………………………………………………………………………………………………...17
Printer Driver……………………………………………………………………………………………………18
PCB layer 1……………………………………………………………………………………………………..19
PCB layer 2……………………………………………………………………………………………………..20

2

Exploded Isometric View

Exploded Isometric View

Top
moulding

Printer
mechanism

Contrast
thumbwheel

Bottom
moulding

Screw

3

MicroLab - System Overview (Fig. 1)

The Micro Medical MicroLab is a data recording spirometer consisting of a microcomputer unit

(1) incorporating an LCD graphic display, data entry keypad, RS232 serial interface and all associated
circuitry. This is supplied with a digital volume transducer (2), disposable mouthpieces, transducer
holder (3) and mains adapter (4). The MicroLab is powered by internal rechargeable Nickel Cadmium
cells or by the mains adapter supplied (4).
When testing a subject the transducer is inserted into the holder which is plugged into the
microcomputer unit. The digital volume transducer is used to measure the subjects expired flow and
volume in accordance with the operating manual.

micro

lab

31 2
64 5

1

3

Micro

Medical

2

97 8

Del

0

4

Fig. 1

4

Transducer (Fig. 2)

The Micro Medical digital volume transducer consists of an acrylic tube with a vane positioned

between two swirl plates. The low inertia vane is attached to a stainless steel pivot which is free to
rotate on two jewelled bearings mounted at the centre of the swirl plates. As air is passed through the
transducer a vortex is created by the swirl plates which causes the vane to rotate in a direction
dependant upon the direction of air flow. The number of rotations is proportional to the volume of air
passed through the transducer and the frequency of rotation is proportional to the flow rate. The
transducer housing consists of a main body which contains a pair of light emitting diodes (LED’s) and
phototransistors. The transducer is fixed to the mouthpiece holder which pushes into the main body
and is captured by an “O” ring seal. The LED’s produce infra red beams which are interrupted by the
vane twice per revolution. This interruption is sensed by the phototransistors. The output from the
collector of each phototransistor will be a square wave with a phase difference between the two of +
or - 90 degrees depending upon the direction of flow.
There is no routine maintenance required for the transducer other than cleaning according to
the instructions in the operating manual.

Micro Medical Digital Volume Transducer

Volume proportional to the number of pulses
Flow proportional to the puse frequency

Rotating

vane

Volume = k X No. of pulses

Infra red

emitter

Infra red
detector

Swirl
plate

Flow = k / pulse period

Jewelled

bearing

5