Dopplex Hand Held Service Manual

Table of Contents

HEALTHCARE

Contents

Page No.

1. General Information...4 1.1 1.2 1.3 1.4 1.5

Introduction...4 Servicing Policy...4 Description...4 Antistatic Handling...5 Construction...5

2. Quality, Reliability and Safety...6 2.1 2.2 2.3 2.4

Safety...6 Maintenance...6 Cautions...6 General Care And Cleaning...7

3. Specifications...8 3.1 3.2 3.3 3.4 3.5 3.6 3.7

Safety...8 Power Supply...8 Enclosure...8 Controls and Indicators...8 Auto Shut Off...9 Outputs...10 Probes...10

4. Technical Classification...11 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 4.10 4.11 4.12 4.13 4.14 4.15 4.16 4.17 4.18 4.19

The Doppler Principle...11 Doppler Audio Processing...11 Fetal Heart Rate Processing, (FD2-P, MD2-P, FD1-P)...11 Bi-directional Signal Processing (MD2-P, SD2-P, RD2...11 Probe Identification...12 Active Noise Reduction...12 Intelligent Auto Shut Off (FD2-P, SD2-P, MD2-P, FD1-P, RD2)...12 Calibration Pulses...12 Waveform Conversion...12 PPG...13 Data Output...13 Microcontroller...13 Standard/Smoothed Mode FHR...13 Manual Mode FHR...13 Audio Dopplex (D920-P, D930-P), Mini Dopplex (D900-P)...14 FD2-P, SD2-P, MD2-P, FD1-P, RD2...15 Obstetric Probe (OP2HS, OP3HS, D920-P, D930-P, FD1-P)...19 Vascular Probe (VP4HS, VP5HS, VP8HS, VP10HS, EZ8)...20 PPG Probe...21

5. Static Precautions...23 5.1 5.2

What Is Static Electricity?...23 Protective Measures...23

6. Servicing Procedures - Control Unit...24 6.1 6.2 6.3 6.4

2

Control Unit Dismantling Procedure...24 PCB Removal...25 Changing Components...25 Control Unit Reassembly...26

7. Probe Head Replacement Procedure...31 7.1 7.2 7.3 7.4 7.5 7.6 7.7 7.8

Equipment Required...31 Preparation - For High Sensitivity Probes... (OP2HS,OP3HS,VP4HS,VP5HS,VP8HS,VP10HS,EZ8)...31 Dismantling Procedure - All Probes except D920-P, D930-P & FD1-P...32 Dismantling Procedure - D920-P, D930-P & FD1-P...32 New Head Fitting and Alignment...33 Reassembly Procedure - All Probes except D920-P, D930-P & FD1-P...38 Reassembly Procedure - D920-P, D930-P & FD1-P...39 Waterproof Inspection & Test Procedure - D920-P, D930-P & FD1-P...41

8. Probe Functional Test Specification...42 8.1 8.2 8.3

Equipment Required...42 Functional Tests - Vascular Probes VP4HS - VP10HS...42 Functional Test - Obstetric Probes OP2HS, OP3HS, D920-P, D930-P, FD1-P . .43

Table of Contents

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9. Fault Finding...44 9.1 9.2 9.3 9.4 9.5 9.6 9.7

LCD - Marks On Display...44 No Sound...44 Unit Dead...44 No Output From Sockets...44 Poor Heart Rate Tracking...44 Poor Sensitivity, Crackling...44 PPG not locking on...44

10. Spare Parts list...45 10.1 10.2 10.3 10.4 10.5 10.6

D900-P Parts List...45 D920-P, D930-P Parts List...47 MD2-P, SD2-P, FD2-P, FD1-P, RD2 Parts List...49 Obstetric and Vascular Probe Parts List...51 D920-P, D930-P, FD1-P Probe Parts List...52 ISP3 Probe Parts List...53

11. Ordering Information...54 11.1

Service Returns...54

Appendix A...55 Special Handling Procedures...55

Appendix B...56 Device History Record Sheet...56

Appendix C...57 Recommended Recorder Specifications...57

Appendix D...58 Test Equipment Specifications...58

Appendix E...59 D920-P, D930-P Probe Cable Wiring Details...59

Appendix F...60 Waveform Output Connector Details SD2-P / MD2-P...60

Appendix G...61 Trace Examples...61

3

General Information

HEALTHCARE

1. General Information Alltho ough eve ery care ha as been ta aken to o ensurre tha at the e info orma atiion in thiis ma anua al is accurrate e, contiinuo ous deve elopme ent ma ay resullt in equiipme ent cha ange es. The e Co ompa any rese erve es the e right to o ma ake suc ch cha ange es wiitho out prrior no otiifiicatiion, and d resulltiing ma anua al ina accurracies ma ay occurr. Thiis ma anua al and d any cha ange es are prrote ecte ed by copyrright.

1.1

Introduction This service manual provides the technical information required for repair and maintenance of the Huntleigh Healthcare Ltd... Mini Dopplex - D900-P Audio Dopplex - D920-P (with fixed waterproof 2MHz probe), D930-P (with fixed waterproof 3MHz probe) Fetal Dopplex II - FD1-P Super Dopplex II - SD2-P Multi Dopplex II - MD2-P Fetal Dopplex - FD1-P (with fixed waterproof 2MHz probe) Rheo Dopplex ... hand held Dopplex range, including the range of OPHS (Obstetric High Sensitivity Probes) and VPHS (Vascular High Sensitivity Probes) interchangeable transducers.

Please note that the Super Dopplex 1, Multi Dopplex 1 and (NTD) probes are not compatible with the D900-P, FD1-P, SD2-P, MD2-P, RD2.

1.2

Servicing Policy Due to the nature of static sensitive surface mount technology specialised equipment and training is required when working on the surface mounted components used within these products. For this reason circuit diagrams are not included in this manual. Block diagrams and fault finding sections are included to make fault finding to leaded component level possible. Units within the warranty period must not be dismantled and should be returned to Huntleigh Healthcare Ltd for repair. Any units returned showing signs of tampering or accidental damage will not be covered under the warranty (refer to user manual for further details).

1.3

4

Description The Dopplex range of products includes the D920-P, D930-P, D900-P, FD2-P (Obstetric Doppler with heart rate display) SD2-P (dedicated vascular Doppler), MD2-P (Bi-directional vascular Doppler), D920-P, D930-P (Mini Dopplex with waterproof probe), FD1-P (Obstetric Doppler with heart rate display and waterproof probe) and RD2 (vascular Dopplex with Photoplethysmographic sensor).

The FD1-P and D920-P have dedicated 2MHz probes that are hard wired via a retractile cable. The D930-P has a dedicated 3MHz probe that is hard wired via a retractile cable.

Miinii Do oppllex (D900-P P)

is primarily a vascular unit with a non-directional waveform output. The Mini Dopplex accepts the obstetric probes, providing audio only output.

Fe eta al Do oppllex II (FD2-P P)

has interchangeable probes accepting the full range of obstetric and vascular probes, although it is primarily a Fetal Dopplex with a heart rate display. Using the vascular probes, only audio signals are available and there is no rate counting facility, or waveform outputs.

Supe er Do oppllex II (SD2-P P)

is a dedicated vascular Doppler with all the vascular functions of the MD2-P, but without the RS232 waveform output.

Mulltii Do oppllex II (MD2-P P)

is a multi-purpose Doppler with bi-directional waveform and stereo headphone outputs. Graphical representation of velocity waveforms is given by the LCD display. The same obstetric features of the FD2-P are incorporated into the MD2-P.

Aud dio Do oppllex (D920-P P D93 30-P P)

are dedicated obstetric Dopplers with fixed waterproof 2MHz (D920-P) and 3MHz (D930-P) probes.

General Information

HEALTHCARE

Aqua a Do oppllex Pllus (FD1-P P) is derived from the FD2-P, but has a hardwired waterproof probe. Rhe eo Do oppllex II(RD2)

has the vascular functions of the MD2-P with the addition of a Photoplethysmographic sensor.

For further details on the controls of the D900-P, D920-P, D930-P, FD2-P, SD2-P, MD2-P, FD1-P and RD2 units, please refer to the user manuals.

1.4

Antistatic Handling Due to the nature of the components used within the D900-P, D920-P, D930-P, FD2-P, SD2-P, MD2-P, FD1-P, RD2 units special precautions must be taken to avoid damage to the CMOS and microcontroller based circuitry. Static damage may not be immediately evident but could cause premature failure. This series of units must only be dismantled and serviced within a specialised handling area (SHA) as defined by CECC00015 (published by CENELEC) to avoid damage to the assemblies.

1.5

Construction The control unit comprises a single PCB on which all circuitry and electro-mechanical components are mounted directly except for the loudspeaker which is attached by flying leads. A hard wired cable provides the connection to the probe. The PCB has surface mounted components on both sides. All leaded and electro-mechanical components are on one side. All electro-mechanical and through hole components on the control PCB are serviceable using standard tools and soldering techniques, provided that anti-static precautions are always observed. The case of the control unit is moulded in ABS polycarbonate alloy, and comprises two halves. The loudspeaker, on/off switch and display are on the front of the unit.

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Safety Aspects

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2. Safety Aspects 2.1

Safety The e D900-P P, D920-P P, D93 30-P P, FD2-P P, SD2-P P, MD2-P P, FD1-P P, RD2, Do oppllers and d the eir prrobes are desiigne ed to o hiigh sta and dards of pe erfo orma anc ce, reliability and d sa afe ety. Che ecks sho oulld alwa ays be ma ade afte er carryiing out any repa airs or disma antlling of the e equiipme ent.

2.2

Maintenance Regular inspections must be made to check the integrity of the unit, and to ensure that the cable is not showing any signs of wear or is noisy when flexed. For functional testing of specific product features, refer to the user manual. If you require any assistance with safety testing your Dopplex equipment, contact Huntleigh Healthcare Ltd or your supplier directly. For the U.K. refer to the Health Equipment Information Document No 95 - Code Of Practice For Acceptance Testing Of Medical Equipment. The following safety summary should be read before operating or carrying out any of the procedures described in this manual.

2.3

Cautions Do not use the D900-P, D920-P D930-P, FD2-P, SD2-P, MD2-P, FD1-P, RD2 units in the presence of flammable gases such as anaesthetic agents. This product is not designed for sterile use. Do not use in the sterile field unless additional barrier precautions are taken. Do not

6

-

immerse in any liquid (except probe on D920-P, D930-P/FD1-P.

-

use solvent cleaners.

-

use high temperature sterilising processes (such as autoclaving).

-

use E-beam or gamma radiation sterilisation.

2.4

General Care And Cleaning Ha and dling

The control unit and the body of the probe are robust and require no special handling. However, the ultrasound probes have delicate faceplates and must be handled with care. Do not apply excess pressure directly to the probe faceplate. Take great care not to drop or knock the probe, stress the PPG sensor cable or scratch the sensor face.

Ma ainte ena anc ce

Other than normal cleaning and replacement of batteries the Dopplex units do not require maintenance.

Sto orage e

If your Dopplex unit is to be stored for a long period of time the battery should be removed.

Clleaniing

Excess gel should always be wiped off after use before parking the ultrasound probes.

Safety Aspects

HEALTHCARE

The probes and main unit can be cleaned with a damp cloth impregnated with a mild detergent, but take great care not to allow any water or other fluid to seep into either unit. To assist in disinfection, a soft cloth dampened with a solution of sodium hypochlorite 1000ppm may be used, and the units wiped dry. Alternatively, alcohol saturated swabs can be used on the faceplate and nosecone area of the ultrasound probes and on the PPG sensor. Please be sure to check your local control of infection policies, or any equipment cleaning procedures.

Ca autiion

Phenolic, or antiseptic solutions such as Steriscol or Hibiscrub should never be used on any part of the system, as these chemicals will damage the case material.

Co ouplling Ge el

The use of water based gel supplied by Huntleigh Healthcare is strongly recommended. Oil based gels can damage the probe and must not be used. The use of oil based gels will invalidate your warranty.

WARNING :

Thiis prroduc ct is no ot desiigne ed fo or ste erile use e. Fo or und derwa ate er use e whe ere conta amiina atiion or cross conta amiina atiion ma ay occurr, e.e e. durring labourr and d delive ery, additiiona al barrier prrecautiions must be ta aken.

7

Specifications

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3. Specifications 3.1

Safety Type of prottecttion againstt electtric sh hock k.

3.2

Degree of prottecttion againstt electtric sh hock k

Type B applied part

Mod de of operattion.

Continuous

Degree of prottecttion againstt watter ingress

IPX0

Degree of Safety in Presence of Flammable Gases:

Not suitable for use in the presence of flammable gases.

Power Supply

Ba atte ery Type e

3.3

3.4

Class 1 (when operated via the supplied PSU) / internally powered.

9 Volt alkaline manganese 6LF22, 6LR61 or equivalent (e.g.MN1604).

Enclosure Ca ase e Ma ate erial

Injection moulded ABS Polycarbonate Alloy.

Diime ensiions (mm) (He eight x Wiidth x De epth)

140 x 74 x 27

We eight

295 gms (including probe and battery)

Controls and Indicators LCD Diispllay

Custom reflective liquid crystal display

3 x 7 se egme ent displlay**

Displays fetal heart rate and probe frequency ** Available on RD2, FD2-P, SD2-P, MD2-P and FD1-P only.

8

Symbol

Description Indicates Standard FHR Mode Selected (FD1-P, FD2-P, MD2-P only).

Indicates Smoothed FHR Mode Selected (FD1-P, FD2-P, MD2-P only).

Indicates Manual FHR Mode Selected (FD1-P, FD2-P, MD2-P only).

Specifications

HEALTHCARE

Represents Bi-directional blood flow velocity. RD2, in PPG mode indicates size of signal from sensor. (MD2-P, SD2-P and RD2 only). Indicates RS232 communication enabled. This flashes when communication is in progress. (FD2-P, MD2-P only). Audio/Mini- indicates power on. FD2-P/SD2-P/RD2/MD2-P- indicates power on with probe not connected. Indicates battery low and requires replacement.

RT indicates Venous Refilling Time (RD2 only).

VP indicates Venous Pump Power (RD2 only).

Shows when blood flow waveforms are inverted (RD2 only).

3.5

Probe Alignment

Arrow on socket of probe and on barrel of plug

On/Off Button

Front panel push-on / push-off

Mode Buttons

Refer to User Manual

Auto Shut Off FD2-P P, SD2-P P, MD2-P P, FD1-P P, RD2

If no signal detected for 3 minutes within a 10 minute time out.

D900,D920, D93 30

Fixed 5 minute time out.

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Specifications

HEALTHCARE

3.6

Outputs Audio Output Po owe er

500mW rms into 8 internal speaker 25mW rms max (32 headphones)

D920-P P, D93 30-P P, D900P,FD2-P P, FD1-P P, RD2

3.5mm stereo socket on top panel (mono output).

MD2-P P, RD2, SD2-P P

3.5mm stereo socket on top panel (stereo output).

Data Output Port FD2-P P, MD2-P P, RD2

WARNING:

Sub-miniature 8 pin DIN socket.

The e Do oppllex uniits must onlly be conne ecte ed to o equiipme ent whiich compllies wiith inte erna atiiona al sa afe ety sta and dards suc ch as IEC601-1 1, IEC950, UL54 44 or IEC65, and d whe ere the e syste em is confiigurred to o me eet IEC601-1 1-1 1.

Waveform Socket No on-d directiiona al (Miinii Do oppllex)

3.5mm mono socket. Fixed f/V 0.5V/kHz.

Bii-d directiiona al (MD2-P P, RD2)

Sub-miniature 8 pin DIN socket, 3.5V Full scale. Variable f/V depending on gain setting - refer to user manual.

Cal Signal

3.7

10

Miinii Do oppllex

0kHz, 1kHz, 2kHz, 0kHz stepped pulse.

MD2-P P, RD2

Stepped pulse sequence at 0.05% and 0.1% of probe frequency. Zero baseline at start and end of sequence (available on x1 gain setting only).

Probes D900-P P, FD2-P P, SD2-P P, MD2-P P, RD2 (iin additiion to o PPG)

OP2HS, OP3HS Obstetric Probes VP4HS, VP5HS, VP8HS, VP10HS, EZ8 Vascular Probes

D920-P P, FD1-P P

Fixed 2Mhz obstetric waterproof probes.

D93 30-P P

Fixed 3Mhz obstetric waterproof probe.

4. Technical Description 4.1

The Doppler Principle The Dopplex Range all use a technique based on the Doppler principle for non-invasively monitoring movement within the body. The Doppler principle states that if a signal is transmitted at a fixed frequency and is reflected by a moving body, the frequency of the received signal will be shifted. An increase in frequency results if the reflector is moving towards the transmitter/receiver, and a decrease results if moving away from the transmitter/receiver. The amount of frequency shift is proportional to the velocity of the reflector relative to the transmitter/receiver. In the Dopplex range, a fixed frequency ultrasonic signal is transmitted from the probe into the body. This is reflected from, for example, moving blood cells. The signal is reflected from these cells and is received by the probe. Due to the movement of the blood cells, a frequency shift results, which is proportional to the blood flow velocity. The Doppler shift is also affected by the angle between the probe and the direction of flow. The Doppler shift is greatest when the flow is directly towards, or away from, the probe.

4.2

Technical Description

HEALTHCARE

Doppler Audio Processing The pocket Dopplex probe contains a transmitter and receiver. In use, the probe sends out a continuous ultrasonic signal (carrier), generated by the piezo-ceramic transmitter crystal, in the frequency range 2 to 10 MHz (depending on probe). This signal is scattered by blood cells or any other "interface" such as skin, muscle layers, organs, walls of vessels etc. A small proportion of the scattered signal will be reflected back and detected by the receiver. By demodulating the received signal (removing the high frequency carrier) the Doppler shifted component (i.e. the difference between the transmitted and received signals) can be produced. With typical target velocities found in the human body, this Doppler shift signal falls within the audio frequency range. It can therefore simply be amplified and heard through a loudspeaker. It is important to remember that the sound you hear is an artificial sound, the frequency (pitch) of which is proportional to the velocity of the moving target. It is not the real sound made by blood rushing through an artery or vein, or movement of the fetal heart.

4.3

Fetal Heart Rate Processing, (FD2-P, MD2-P, FD1-P) In addition to providing this Doppler sound, the circuitry in the FHR signal conditioning section generates an amplitude envelope of the Doppler audio signal. Using auto-correlation, this signal is further processed by the microcontroller to calculate FHR.

4.4

Bi-directional Signal Processing (MD2-P, SD2-P, RD2) To achieve bi-directional flow indication, the Doppler signal must be further processed to separate forward and reverse components. Components of the Doppler signal produced by positive frequency shift represent flow towards the probe, referred to as forward flow. Components of the Doppler signal produced by negative frequency shift represent flow away from the probe, referred to as reverse flow. The circuitry achieves this separation in the vascular signal processing section producing two frequency envelopes using zero crosser techniques. This signal is presented at the waveform output (MD2-P, RD2). The microcontroller also receives these bi-directional signals and displays them on the LCD bargraph to give a visual indication of blood flow velocity and direction.

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Technical Description

HEALTHCARE

4.5

Probe Identification Probe identification is utilised on the D900-P, FD2-P, SD2-P, MD2-P and RD2 Doppler units. This is to allow the control unit to identify which probe has been fitted. Fitting an obstetric probe will disable the waveform output(s). The FD2-P/SD2-P/MD2-P/RD2, with an obstetric probe connected, will display the probe frequency whenever the probe is changed. The FD2-P/SD2-P/MD2-P/RD2, with a vascular probe connected, will give a continuous indication of probe frequency. In the SD2-P, MD2-P and RD2 the frequency to voltage conversion factor is changed according to the frequency of the connected probe and the gain setting, effectively rescaling the output.

4.6

Active Noise Reduction Active noise reduction is used to reduce the amount of "hiss" that is present. When a signal is below a set level, the cut off point of the low pass filter is lowered effectively reducing the noise level. When a large signal is detected, the bandwidth is increased to allow the full range of the signal to be heard at the loudspeaker.

4.7

Intelligent Auto Shut Off (FD2, SD2, MD2, FD1, RD2) To increase battery life within the FD2-P, SD2-P, MD2-P, FD1-P and RD2 units, the microcontroller will turn the unit off after 3 minutes of no signal. The unit will also switch off after 10 minutes regardless of signal presence. This function is disabled when it is connected to a Printa which is printing in obstetric or vascular mode (not applicable to SD2-P or FD1-P).

4.8

Calibration Pulses The calibration pulses for the D900-P are of 1 and 2kHz irrespective of probe frequency. The MD2-P and RD2 will output pulses of 0.05% and 0.1% of the frequency of the connected probe. The MD2-P and RD2 have bi-directional calibration pulses to scale both forward and reverse channels. The calibration facility is disabled when using gain settings other than x1.

4.9

Waveform Conversion The D900-P has a fixed waveform conversion factor of 0.5V/kHz, whereas the SD2-P, MD2-P and RD2 have a conversion factor determined by the probe fitted and the gain setting. The use of a variable conversion factor results in the waveform output presenting a voltage that is essentially constant regardless of the frequency of probe fitted for the same velocity signal.

12

4.10 PPG The RD2 incorporates a photoplethysmographic sensor which uses a sensitive infra-red sensor to assess, non-invasively, venous incompetency of the lower limb, in response to a calf muscle exercise. The electronics for the PPG is enclosed within a pod to which the PPG sensor is attached by a lightweight straight cable.

4.11 Data Output The data output feature on the FD2-P and MD2-P allows fetal heart rate data to be sent to the Dopplex Printa in real time. The MD2-P and RD2 units send fetal heart rate data via the data socket to the Dopplex Printa in real time OR vascular data to the Dopplex Reporter/Dopplex Printa. The FD2-P, MD2-P and RD2 will flash the data symbol (

Technical Description

HEALTHCARE

)during information transfer.

The MD2-P and RD2 will output bi directional waveform information in an analogue format via the data socket.

4.12 Microcontrollers The D900-P, D920-P, D930-P, FD2-P, SD2-P, MD2-P, FD1-P and RD2 units use a 4 bit microcontroller to carry out "house keeping" duties, such as driving the LCD display and auto shut-off timer. In addition to the 4 bit microcontroller, the FD2-P, SD2-P, MD2-P, FD1-P and RD2 have a second 8/16 bit microcontroller. This performs FHR processing (including auto-correlation), controls the data output, probe decoding and waveform generation.

4.13 Standard/Smoothed Mode FHR The FD2-P and MD2-P can display FHR in Standard or Smoothed mode. Smoothed mode FHR uses 8 beat averaging while Standard mode FHR uses 4 beats averaging.

4.14 Manual Mode FHR The manual mode on the FD2-P and MD2-P can be used when the heart sound can be heard, but is too weak or noisy for the microcontroller to calculate the heart rate automatically. In this mode, the Dopplex unit operates as a stop watch calibrated in BPM (beats per minute). The stop watch is activated by depressing the "Start/Stop" button, 10 heart beats should then be counted and the button released. The display will then show the average heart rate over the last 10 beats.

13

4.15 Audio Dopplex (D920-P, D930-P), Mini Dopplex (D900-P) Block Diagram

ANR Probe Connector

Technical Description

HEALTHCARE

Soft Limiter

Audio Amplifier Speaker

Supply

Ground Zero * Crossing Detector

Probe * Identification

Waveform * Output

Reset

Microcontroller Battery Low Monitor

Battery

Display

PSU

On/Off Switch

Split rail Generator

* Mini Dopplex Only

Power Supply

14

The power supply regulates the battery voltage and provides 5V dc to the microcontroller and all circuitry apart from the audio power amplifier which is supplied directly from the battery. The power supply is activated by the on/off switch. The supply is firstly turned on by the on/off switch and then the microcontroller takes over and keeps the power supply on, turning the supply off when the auto shut off time has elapsed or when the on/off switch is depressed a second time.

Power On Reset Resets the microcontroller whenever the unit is switched on.

Probe Identification (D900-P) The probe identification feature is used to disable the waveform output whenever an obstetric probe is being used. The probe identification detects the DC level on the output from the probe thus determining the type of probe fitted.

Battery Monitor The battery monitor circuit enables the microcontroller to assess the battery voltage by comparing this to a reference voltage.

Technical Description

HEALTHCARE

Active Noise Reduction (ANR) Active noise reduction is a technique used to reduce the amount of noise or "hiss" depending on signal level. When a large signal has been detected the cut off point of the filter is moved so that there is no reduction in high frequency content of the signal. When the signal level is low, or no longer present the filter is switched in to reduce the high frequency hiss.

Soft Limiter The soft limiter reduces the level of any harsh overload signals that may occur, for example, when the probe is moved.

Audio Power Amplifier The audio power amplifier drives the loudspeaker or headphones. The input level is set by the volume control. The output signal is fed to the loudspeaker, via the switched headphone socket. On start up there is a delay in the supply of power to the audio amplifier. This allows the circuit to stabilise.

Zero Crossing Detector (D900-P) A zero crossing detector converts the Doppler signal to a corresponding pulse train. This is then fed to the microcontroller which outputs a pulse position modulated signal which is low pass filtered to produce the waveform output voltage.

Split Rail Generator The split rail generator is necessary to bias the amplifiers correctly to allow linear operation. The split rail generator supplies a +2.5V dc reference so that the maximum output swing from the amplifiers can be achieved.

15

4.16 FD2-P, SD2-P, MD2-P, FD1-P, RD2 Block Diagram All Pass Network ANR Sense

Soft Limiter

ANR

Stereo* Power Amplifier

Flow* Separation

All Pass* Network

Soft* Limiter

ANR*

Probe Connector

Technical Description

HEALTHCARE

FHR^^ Signal Cond.

Tare^

Automatic Gain ^^ Control

Zero* Crossers

Gain^

Supply Probe Identification Ground Mode/ Function Buttons

Slave Microcontroller

Master Microcontroller

Battery Monitor

Data+ Output

Display

Battery

PSU

Split Rail Generator

Reset

Analogue* Waveform Outputs

On/Off Switch * MD2, SD2, RD2 Only + Not fitted on SD2, FD1-P P ^ Fitted on RD2 ^^ Not fitted on RD2, SD2 or FD2

16

Power Supply The power supply regulates the battery voltage and provides +5Vdc to the microcontroller and all circuitry apart from the audio power amplifier which is supplied directly from the battery. The power supply is activated by the on/off switch. The supply is firstly turned on by the on/off switch and then the microcontroller takes over and keeps the power supply on, turning the supply off when the auto shut off time has elapsed or the on/off switch is depressed a second time.

Power On Reset This resets the master microcontroller whenever the unit is switched on. The slave microcontroller is reset by the master microcontroller.

Probe Identification

Technical Description

HEALTHCARE

The probe identification feature is used to automatically select the operating mode, depending on the probe type and in the SD2-P, MD2-P and RD2, to automatically scale the waveform output. The probe identification circuit detects the DC level on the output from the probe thus determining the type of probe fitted.

Battery Monitor The battery monitor circuit enables the microcontroller to assess the battery voltage by comparing this to a reference voltage.

Active Noise Reduction (ANR) Active noise reduction is a technique used to reduce the amount of noise or "hiss" depending on signal level. When a large signal has been detected the cut off point of the filter is moved so that there is no reduction in high frequency content of the signal. When the signal level is low, or no longer present the filter is switched in to reduce the high frequency hiss.

Active Noise Reduction Sensing The active noise reduction system relies on the control signal from the sensing circuitry. The filter response is dependent on the control signal level.

Soft Limiter The soft limiter reduces the level of any harsh overload signals that may occur, for example, when the probe is moved.

Audio Power Amplifier The audio power amplifier drives the loudspeaker or headphones. The input level is set by the volume control. The output signal is fed to the loudspeaker, via the switched headphone socket. On start up there is a delay in the supply of power to the audio amplifier. This allows the circuit to stabilise.

17

Technical Description

HEALTHCARE

Zero Crossing Detector (SD2-P, MD2-P, RD2) Two zero crossing detectors convert the Doppler signals to corresponding pulse trains. The pulse trains are then fed to the microcontroller which converts them to pulse width modulated signals which are then filtered to produce the waveform output voltages.

Split Rail Generator The split rail generator is necessary to bias the amplifiers correctly to allow linear operation. The split rail generator supplies a +2.0V dc reference so that the maximum output swing from the amplifiers can be achieved.

Data Output The data control IC is an RS232 interface device enabling the microcontroller to communicate with the Dopplex Printa or a computer. The data/waveform socket presents the data from the microcontroller which represents either bi-directional flow waveforms or fetal heart rate, depending on operating mode.

All Pass Network The All Pass network is used to apply 90° phase shift to one quadrature probe output signal with respect to the other.

Flow Separation The two phase shifted signals are added and subtracted to produce the forward and reverse flow channels.

Stereo Audio Power Amplifier (SD2-P, MD2-P, RD2) The audio power amplifier provides stereo outputs to the headphone socket. These are combined in the internal loudspeaker.

FHR Signal Conditioning The FHR signal conditioning circuit produces an amplitude envelope from which the microcontroller calculates the fetal heart rate when using an obstetric probe.

Gain control The gain of the first amplifier of the FHR signal conditioning circuit is increased or decreased by the microcontroller, to regulate the signal level avoiding overloading the following stages.

Analogue Waveform Outputs

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Pulses representing the frequency envelopes of the Doppler signals are output from the microprocessor to two integrating low-pass filters. The two filter outputs are then fed to the analogue waveform/data output socket.

Gain A small amount of gain is applied to the incoming PPG signal to ensure that the Microcontroller is functioning at its maximum resolution. This signal is multiplexed with data relating to the infra red intensity.

Tare The Tare line from the Microcontroller is sent to the PPG pod, this will reset the DC level at the output from the probe and start the test. This signal is also the control line for the multiplexer.

4.17 Obstetric Probe (OP2HS, OP3HS, D920-P, D930-P, FD1-P)

Technical Description

HEALTHCARE

Block Diagram Probe Head Tx Xtal

Transmitter

Oscillator

Rx Xtal

Demodulator

Amplifier / Filter To Control Unit Probe Coding

Oscillator A ceramic resonator based oscillator circuit provides a reference for the probe receiver and, via the transmitter, the output signal.

Transmitter The output from the oscillator is amplified by a single transistor; the gain of this stage is controlled by a variable resistor. This allows the output voltage to be set according to the impedance of the probe head, thus setting the output power level.

Demodulator The demodulator effectively removes the carrier (transmitter frequency), which leaves us with a Doppler shifted signal. The demodulator stage requires a reference signal from the transmitter stage.

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Technical Description

HEALTHCARE

Amplifier/Filter The amplifier/filter amplifies the signal from the demodulator stage and removes unwanted noise. The probe has a filter response tailored to maximise the output signal and minimise noise and overload.

Probe Coding This superimposes a DC level (depending on probe frequency) onto the output signal.

4.18 Vascular Probe (VP4HS, VP5HS, VP8HS, VP10HS, EZ8) Block Diagram Probe Head Tx Xtal

Transmit Amplifier

Johnson Counter

Demodulator Rx Xtal

Oscillator

Amplifier / Filter

Receive Amplifier

To Control Unit Demodulator

Amplifier / Filter Probe Coding

Oscillator A crystal oscillator provides references for the probe demodulator and output signal. The oscillator frequency is four times that of the probe ultrasonic output.

Johnson Counter The Johnson Counter provides two outputs, which are 90° phase shifted with respect to each other. It also divides the oscillator signal frequency by four.

Transmitter The output from the oscillator is amplified by a single transistor; the gain of this stage is controlled by a variable resistor. This allows the output voltage to be set according to the impedance.

Receive Amplifier 20

The received signal is amplified by two FETs (Cascode amplifier) providing the demodulators with a suitable signal.