MicroLoop MK8 Service Manual

105-45 Issue. 1.0 August 2007

Micro Medical

Micro

Medical

Contents

MicroLoop - System Overview

MicroLoop MK8 System

The Micro Medical MicroLoop is a data recording spirometer consisting of a hand held microcomputer unit incorporating a high resolution, colour touch screen, USB interface and transducer ports.

Supplied with the microcomputer is a Cradle base unit, Bi-directional transducer, disposable mouthpieces, mains adapter, nose clip and USB cables.

The MicroLoop is powered by internal Nickel Metal Hydride cells or by the mains adapter supplied, either connected to the cradle or directly to the MicroLoop unit.

When testing a subject, the Bi-directional transducer is plugged into the microcomputer unit. The Bi-directional transducer is used to measure the subjects expired flow and volume in accordance with the operating manual.

CRADLE BIDIRECTIONAL TRANSDUCER PSU

Figure 1 MicroLoop System Components

Bidirectional Transducer

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 that 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 that 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 that contains a pair of light emitting diodes (LED's) and phototransistors. The transducer is fixed to the mouthpiece holder that pushes into the main body and is captured by an "O" ring seal. The LED's produce infrared 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. The square waves are detected by a microprocessor that measures the period of each pulse and transmits that information to the main unit via a high-speed asynchronous serial link.

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

Rotating vane Infra red emitter Swirl plate Jewelled bearing Infra red detector Volume = k X No. of pulses Volume proportional to the number of pulses Flow proportional to the puse frequency

MicroLoop Mk8 Repair

Disassembling the MicroLoop Mk8 for Repairs

1. Disconnect the mains power supply

2. Place the MicroLoop Mk8 face down on a soft surface. Remove the four screws in the lower moulding. Put the screws to one side.

3. Turn the unit face up before easing the upper and lower mouldings apart.

4. Taking all precautions against static damage, lift the MicroLoop PCB and display out of the bottom moulding and place on an antistatic work surface. Note that the battery is secured to the bottom moulding by an adhesive pad.

5. Reconnect the power supply to the MicroLoop Mk8 charging socket

6. The MicroLoop is now ready for fault finding.

Reassembling the MicroLoop after repairs

1. Disconnect all mains power supplies.

2. Place the MicroLoop PCB and display assembly into the MicroLoop bottom moulding.

3. Insert the top and bottom end panels into the bottom moulding. It may be necessary to lift the PCB slightly in order to fit the