Micro Medical Mouth Pressure Meter Service Manual

Contents page

Introduction 3
Operation 3

Mouth Pressure
Meter Layout 4

Sealing Strip Position 5
Cleaning and

Maintaining the Mouth
Pressure Meter 5

Disassembling the
Mouth Pressure Meter 6

Reassembling the
Mouth Pressure Meter 6

Circuit Description 7
Parts List 8
Technical Support 10
Circuit Diagram 11

Mouth Pressure Meter
Service Manual

027-11 Iss. 1.0 September 1998

Mouth Pressure 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. 027-11
Version 1.0
September 1998
All other products are trademarks or registered trademarks of their respective owners.

2

Introduction

The Micro Medical mouth pressure meter comprises of a hand held
electronics unit that incorporates a removable Micro Medical mouthpiece
holder/insert.

The unit is designed for the rapid assessment of inspiratory and expiratory
respiratory muscle strength. The result of each measurement is presented
in units of cmH2O on the Liquid Crystal Display screen on the face of the
meter.

Measuring the mouth pressure created during a maximum effort against a
closed airway indirectly assesses the strength of the inspiratory or
expiratory muscles. The manoeuvre is therefore effectively isometric.

Operation

The Micro Medical Mouth Pressure Meter has been designed for easy
operation and after fitting the battery and flanged rubber mouthpiece, the
Mouth Pressure Meter is ready for use.

To measure the maximum expiratory pressure (Pemax), slide the switch
on the face of the meter from the “OFF” position to the expiratory position
(exp cms), and wait for the display to zero. Instruct the subject to inhale to
TLC (Total Lung Capacity) and then, before exhaling, to insert the
mouthpiece into the mouth ensuring that the flange is positioned over the
gums and inside of the lips and that the “bite blocks” are between the
teeth. For an accurate measurement it is important that there are no leaks
in the system. When the mouthpiece is correctly positioned, instruct the
subject to exhale with as much effort as is possible against the resistance.
A small controlled leak in the system will prevent the generation of
excessively high mouth pressures.

Before repeating the measurement or before performing an inspiratory
manoeuvre, the instrument must be reset by sliding the switch to the “OFF”
position.

To measure the maximum inspiratory pressure (PImax), slide the switch
on the face of the meter from the “OFF” position into the inspiratory
position (ins cms), and wait for the display to zero. Instruct the subject t
exhale to RV (Residual Volume), and then to insert the mouthpiece
according to the above procedure. Instruct the subject to breathe in with
maximum effort against the resistance.

It is important that the maximum effort is sustained for at least one second
for each inspiratory and expiratory measurement.

The Mouth Pressure Meter is switched “OFF” by moving the switch
downwards to the “OFF” position then the display will be blank.

3

Mouth Pressure Meter Layout

1. Mouth Pressure Meter PCB

2. Top Moulding

3. Bottom Moulding

4. Turbine sleeve

5. Retaining ring

6. Coated O ring

7. Mouthpiece Holder

8. Acrylic tube

9. Blanking plate

10. 13mm of EMPD sealing strip with 4mm diameter central hole

11. Countersunk screws

12. M2.5 x 10mm Pan head screw

7

6

8
9

12

10

2

4

1

5
6

3

11

11

4

Sealing strip position

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1

Locating Pip

Cleaning and maintaining the Mouth Pressure Meter

The Micro Medical Mouth Pressure Meter requires no routine maintenance
or servicing.

The transducer assembly may be removed from the instrument for
cleaning by gently twisting the mouthpiece holder and, at the same time
pulling the assembly from the body of the meter.

The assembly may be immersed in a solution of warm soapy water or a
proprietary disinfecting solution. If sterilisation is required, a cold solution
such as Alkacide is recommended. This must be used according to the
manufacturers instructions to achieve the required degree of sterilisation.
Do not autoclave the transducer and avoid the use of alcohol or chlorine
based solutions. After cleaning/sterilisation, rinse the assembly in distilled
water, dry thoroughly and reassemble.

Should insertion of the transducer into the holder become difficult, the
application of a small amount of silicone grease to the ‘O’ ring, located
within the holder, will facilitate replacement of the assembly.

Calibration is factory set and should remain constant throughout the
lifetime of the device. However the Mouth Pressure Meter can be
calibrated if in doubt by the Micro Medical Service Centre.

5

Disassembling the Mouth Pressure Meter.

If the Mouth Pressure Meter becomes faulty then the following procedure is
needed to investigate the fault.

1. Remove the mouthpiece holder from the main unit by gently pulling the
mouth piece holder from the unit with a twisting action.

2. Turn the unit face down and slide back the battery cover.

3. Remove the battery and place to one side.

4. Remove the 2 screws from the bottom moulding (Item 11) and put to
one side.

5. Turn the unit face up and ease the top moulding from the bottom
moulding and turn the top moulding to reveal as shown below.

6. Remove the PCB from the bottom moulding and put the bottom
moulding to one side.

7. The Mouth Pressure Meter is now ready for fault finding.

Reassembling the Mouth Pressure Meter

1. Place the PCB into the bottom moulding and wire the battery lead as
shown below.

2. Replace items 4,5 and 6 into the bottom moulding as shown in the
Mouth Pressure Meter layout drawing.

3. Position the top moulding on top of the bottom moulding and push
together. (ensure that the battery leads are not trapped).

4. Turn the unit face down and secure the unit with the retained screws.

5. Refit the PP3 battery ensuring correct polarity.

6. Slide on the battery cover.

7. Turn the unit face up and refit the mouthpiece holder.

8. The Mouth Pressure Meter is now ready for operation.

6

Circuit Description

Power Supply and battery monitoring

The Mouth pressure meter is powered by a PP3 9V Alkaline battery and is
monitored by a battery-low detection circuit consisting of R17, R18, TR1
and ZD1. R17 and R18 form a potential divider across the battery and the
voltage obtained is applied to the emitter of TR1. The base of TR1 is held
at 1.26 volts by ZD1 and TR1 turns on the emitter voltage falls to
approximately 0.7 volts. The collector is held high by R19 and will fall
when TR1 turns on at a battery voltage of 7.5 volts. The battery low
indicator on the display is normally connected to the back plane (BP)
through the analogue switch, IC8C, and is not displayed. The collector of
TR1 controls the switch and when the battery is low, the connection to the
back plane is broken. In this case, the indicator is turned on by the
connection to the inverse of the back plane through R22.

Pressure Sensor Conditioning Circuit

The mouth pressure meter consists of an internally temperature
compensated solid state pressure transducer (PT1). The transducer is
driven with an 840µA constant current source consisting of R4, R5, ZD1
and IC5A. The differential signal from the pressure transducer is amplified
by IC1, IC2 and IC5B, set up in an instrumentation configuration, and
referenced to COM. COM is a reference level output of IC6 set to 2.8 volts
below the positive supply. The signal is then inverted by IC5C. The non­inverted signal from IC5B is used when an inspiratory pressure
measurement is selected and the inverted signal, from IC5C, is used when
an expiratory measurement is required. The selected signal is low pass
filtered at 0.7Hz by C10 and R14 or R15.

Reset

When the unit is first switched on, a bi-stable circuit formed by IC9A and B
is set such that the output of IC9C is low. This output is connected to the
analogue switches, IC8A and B. IC8A is used to discharge the peak
detector holding capacitor, C1, and IC8B is used to disconnect the input to
the A.D converter, IC6. The bi-stable circuit is reset by IC7A when the
signal from IC5B or C rises to 18mV above COM. This level is set by the
potential divider formed by R27 and R28.

7

Peak detector

The signal from IC5B or C is the passed through a peak detector formed
by IC3, D2, R10 and C1. As the pressure signal rises the input on the
non-inverting input to IC3 is above the voltage held on the storage
capacitor, C1, and the output will go high to charge the capacitor through
D2. When the signal falls below the stored voltage then the output of IC3
will drop and the voltage on the storage capacitor will be held. At this time
the output of IC7B will go high, causing pin 1 of IC6 to go high shortly
afterwards. Pin 1 of IC6 is the HOLD input that freezes the display. This
ensures that the reading will remain stable on the display indefinitely,
regardless of any small drift on the storage capacitor.

A/D Convertor

IC6 is a 3½ digit analogue to digital converter with built-in LCD driver. The
display consists of a liquid crystal sandwiched between transparent
electrodes, representing each segment, and a back plane. The back plane
is supplied with a square wave voltage with a nominal frequency of 60Hz
generated on pin 21 of IC6. Each segment is connected to a pin on IC6
and is active when a voltage in anti-phase to the back plane is applied and
in-active when the segment voltage is in phase with the back plane. The
input to the A/D converter is on pin 31 of IC6 and is compared to the
reference input, pin 36. The reference input voltage is derived from the
potential divider formed by R23 and R24, which sets the sensitivity of the
A/D converter.

8

Parts List

Designation Description

IC1
IC2
IC3
IC4
IC5
IC6
IC7
IC8
IC9

R1 10K OHM RESISTOR 1% METAL FILM
R2 1K5 OHM RESISTOR 1% METAL FILM
R3 10K OHM RESISTOR 1% METAL FILM
R4 1K5 OHM RESISTOR 1% METAL FILM
R5 8K2 OHM RESISTOR 1% METAL FILM
R6 4K7 OHM RESISTOR 1% METAL FILM
R7 10K OHM RESISTOR 1% METAL FILM
R8 10K OHM RESISTOR 1% METAL FILM

R9 10K OHM RESISTOR 1% METAL FILM
R10 10K OHM RESISTOR 1% METAL FILM
R11 10K OHM RESISTOR 1% METAL FILM
R12 10K OHM RESISTOR 1% METAL FILM
R13 10K OHM RESISTOR 1% METAL FILM
R14 220K OHM RESISTOR 1% METAL FILM
R15 220K OHM RESISTOR 1% METAL FILM
R16 1K OHM RESISTOR 1% METAL FILM
R17 1K OHM RESISTOR 1% METAL FILM
R18 10K OHM RESISTOR 1% METAL FILM
R19 100K OHM RESISTOR 1% METAL FILM
R20 100K OHM RESISTOR 1% METAL FILM
R21 1M OHM RESISTOR 1% METAL FILM
R22 100K OHM RESISTOR 1% METAL FILM
R23 22K OHM RESISTOR 1% METAL FILM
R24 12K OHM RESISTOR 1% METAL FILM
R25 470K OHM RESISTOR 1% METAL FILM
R26 10K OHM RESISTOR 1% METAL FILM
R27 30 OHM RESISTOR 1% METAL FILM
R28 4.7K OHM RESISTOR 1% METAL FILM
R29 47K OHM RESISTOR 1% METAL FILM

C1 470nF POLYPROPYLENE 0.2" PITCH CAPACITOR

C2 100pF CERAMIC 0.1" PITCH CAPACITOR

C3 220nF POLYESTER 0.2" PITCH CAPACITOR

C4 47nF POLYESTER 0.2" PITCH CAPACITOR

C5 100nF POLYESTER 0.2" PITCH CAPACITOR

C6 10nF CERAMIC 0.1" PITCH CAPACITOR

C7 4.7uF ELECTROLYTIC 0.1" PITCH CAPACITOR

C8 4.7uF ELECTROLYTIC 0.1" PITCH CAPACITOR

C9 47uF ELECTROLYTIC 0.2" PITCH CAPACITOR
C10 1uF MULTI-LAYER CERAMIC 0.2" PITCH CAPACITOR

CDT(x2) 100uF TANTALUM 0.2" PITCH CAPACITOR

RN1 100K 5 WAY RESISTOR NETWORK 6 PINS
RN2 100K 5 WAY RESISTOR NETWORK 6 PINS
VR1 10K 25 TURN POTENTIOMETER

(MC33171P) CMOS OP-AMP
(MC33171P) CMOS OP-AMP
(CA5160E) CMOS OP-AMP
(CA5160E) CMOS OP-AMP
(LM124) QUAD LOW POWER, SINGLE SUPPLY OP-AMP
(ICL7116CPL) 3 DIGIT A/D CONVERTER
(LM393) DUAL COMPARATOR
(4066) QUAD CMOS SWITCH
(4093) QUAD NAND GATE

9

VR2 20K 25 TURN POTENTIOMETER
VR3 NOT USED

D2 (OA202) SILICON DIODE

D3 (OA202) SILICON DIODE

D4 (OA202) SILICON DIODE

ZD1 (REF12Z) 1.26 VOLT BAND GAP REFERENCE

T1 BC182LB) NPN TRANSISTOR

SW1 (SLF2300) DOUBLE POLE 3 POSITION SLIDE SWITCH

10

Technical Support

Great Britain and World Headquarters
Micro Medical Ltd.

PO Box 6
Rochester
Kent ME1 2AZ

Telephone [phone]
Fax [phone]
Web Site http://www.micromedical.com.uk
Email [e-mail]

Contact Micro Medical Ltd. for the local agent in your region or country for local service.

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