Micro Medical MicroLoop Service Manual

MicroLoop ­ServiceManual

047-11 Iss. 1.0 March 1998

Contents

System Overview.........................................................................................................3

Figure 1 .......................................................................................................................3

Transducer...................................................................................................................4

Figure 2 .......................................................................................................................4

Disassembling the Microloop for Circuit Investigation ...........................................5

Circuit Description

Circuit Overview ............................................................................................................. 6

Processor Control Section......................................................................................................................6

Address Bus............................................................................................................................................6

Ram Address Lines.................................................................................................................................6

Reset.......................................................................................................................................................6

Keypad....................................................................................................................................................6

Real Time Clock......................................................................................................................................7

Display.....................................................................................................................................................7

Serial Interface........................................................................................................................................7

Battery Monitoring...................................................................................................................................7

Power Supply..........................................................................................................................................7

Transducer Interface...............................................................................................................................8

Parts List......................................................................................................................9

Technical Support.....................................................................................................11

Fault Analysis............................................................................................................12

Circuit Diagram..........................................................................................................13

2

MicroLoop - System Overview (Fig. 1)

The Micro Medical MicroLoop 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 MicroLoop 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.

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MicroLoop

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Fig. 1

3

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 airflow. 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

4

Disassembling the Microloop for Circuit Investigation

1. Disconnect all mains power supplies

2. Remove the rear adhesive label and disregard.

We recommend that you use a Philip Number Zero screwdriver for the following
instruction.

3. Place the Microloop face down to remove the two screws in the lower moulding, and put the
screws to one side.

4. Turn the unit face up and ease the upper and lower mouldings apart by lifting the top moulding at
an angle as illustrated in the diagram below until it becomes loose.

5. Ease the LCD display printed circuit board out of its plastic supports and rest inside of upper
moulding.

6. Reconnect mains power supply

7. The Microloop is now ready for Circuit Investigation.

If you are not familiar with the operation of the Microloop please read the following section
in this manual ‘Circuit Description’ and use the Circuit diagrams at the back of this manual.

Top moulding

Locating
lugs

Battery pack

Display

2 off screws

Bottom moulding

5