Datex-Ohmeda 90217 ABP User manual

Ambulatory Blood Pressure

Monitor

90217

Service Manual

070-0502-00 Rev. E

Copyright 2003 Datex-Ohmeda, Inc.

C

All rights reserved. Contents of this publication may not be reproduced in any form without the written permission of Datex-Ohmeda,
Inc. Products of Spacelabs Medical, a Division of Instrumentarium, Datex-Ohmeda, Inc. (“Spacelabs Medical”) are covered by U.S.
and foreign patents and/or pending patents. Printed in U.S.A. Specifications and price change privileges are reserved.

Spacelabs Medical considers itself responsible for the effects on safety, reliability and performance of the equipment only if:

• assembly operations, re-adjustments, modifications or repairs are carried out by persons authorized by Spacelabs
Medical, and

• the electrical installation of the relevant room complies with the requirements of the standard in force, and

• the equipment is used in accordance with the operations manual.

Spacelabs Medical will make available, on request, such circuit diagrams, component part lists, descriptions, calibration instructions
or other information which will assist appropriately qualified technical personnel to repair those parts of the equipment which are
classified by Spacelabs Medical as field repairable.

Spacelabs Medical is committed to providing comprehensive customer support beginning with your initial inquiry through purchase,
training, and service for the life of your Spacelabs Medical equipment.

CORPORATE OFFICES

U.S.A.

Spacelabs Medical
5150 220th Ave SE
Issaquah, WA 98029
Telephone: [phone]
Telephone: [phone]
Fax: [phone]

AUSTRALIA

Datex-Ohmeda Pty Ltd
Unit 1, 149 Arthur Street
Locked Bag 356
Homebush, NSW 2140
Telephone: [phone]
Fax: [phone]

AUSTRIA & BELGIUM

Meda n.v.
Oeyvaersbosch 12
B-2630 Aartselaar
Belgium
Telephone: [phone]
Fax: [phone]

CANADA

Datex-Ohmeda Inc.
1093 Meyerside Drive, Unit 2
Mississauga, Ontario L5T 1J6
Telephone: [phone]
Fax: [phone]

CHINA

Datex-Ohmeda Pte Ltd
Shanghai Representative Office
Room 2509 Lippo Plaza
No. 222 Huaihai Road (M)
Shanghai 200021
Telephone: [phone]
Fax: [phone]

FRANCE

Spacelabs Medical
ZAC de Sans-Souci
1211 Chemin de la Bruyére
69760 Limonest
Telephone: [phone]
Fax: [phone]

GERMANY

Datex-Ohmeda GmbH
Dr. -Alfred-Herrhausen-Allee 24
D-47228 Duisburg
Telephone: [phone]
Fax: [phone]

HONG KONG

Spacelabs Medical Limited
Suite 901 Tower 1
China Hong Kong City
33 Canton Road, Tsimshatsui
Kowloon
Telephone: [phone]
Fax: [phone]

INDIA

Datex-Ohmeda India Pvt. Ltd.
International Trade Tower
S 3 Level, Block E
Nehru Place
New Delhi 110019
Telephone: [phone]
Fax: [phone]

ITALY

Datex-Ohmeda S.p.A.
Via Cassanese, 100
20090 Segrate (MI)
Telephone: [phone]
Fax: [phone]

SPAIN

Datex-Ohmeda SL
Manuel Tovar, 26
28034 Madrid
Telephone: [phone]
Fax: [phone]

TAI WAN

Datex-Ohmeda Pte Ltd
Taiwan Representative Office
2/FI No. 85 Sec. 2
Chien-Kuo N. RD.
Telephone: [phone]
Fax: [phone]

THE NETHERLANDS

Datex-Ohmeda B.V.
De Wel 18 3871 MV
Hoevelaken
Telephone: [phone]
Fax: [phone]

Authorized EC Representative
UNITED KINGDOM

Datex-Ohmeda Ltd
71 Great North Road, Hatfield
Herts AL9 5EN
Telephone: [phone]
Fax: [phone]

AUTION:

• US Federal law restricts the devices documented herein to sale by, or on the order of, a
physician.

Contents

Chapter Page

Introduction

Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1-1

User Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1-2

Display. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1-2

Programming Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1-3

Setup

Installing the Batteries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-1

Initializing the Monitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-2

Operational Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-7

Theory

Pressure Amplifier. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-1

Oscillometric Amplifier. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-2

90217 Block Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-4

Digital Circuitry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-5

Unit Power. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-6

Software Flow Chart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-8

Maintenance

Cleaning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-1

Calibration Check . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-3

Calibration Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-4

Operational Verification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-10

Manifold Kit - P/N 050-0110-00 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-13

Disassembly Procedures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-14

Troubleshooting

Monitor Event Codes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-1

Base Station Report Event Codes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-3

Problem Solving Checklist. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-5

Parts

90217 Field Replaceable Parts Lists. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6-1

Drawings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6-3

Symbols

i

Introduction

Contents

Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

User Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Display . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Programming Options. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Overview

The Model 90217 is a small, lightweight battery-powered Ambulatory Blood Pressure (ABP) monitor
that uses the non-invasive Oscillometric method to measure blood pressure and heart rate. This
data is then stored into memory for later transfer to an ABP Analysis System (FT1000A/FT2000A or
equivalent), a PC Interface, a Base Station, or a Report Generator for data analysis, report printing,
and archiving.

The 90217 monitor is housed in a plastic case with a removable battery cover that provides access
to its three AA cells. Inside the monitor are three printed circuit boards: the Main, Power, and Display
boards.

Programming resides in an internal 128k RAM and Microprocessor ROM. Most of the code exists in
the RAM and can be updated via an infrared (IR) serial port located at the rear of the unit. The
internal ROM contains a boot code and other codes for downloading and completing special tasks.

The IR serial port transfers collected data to a report generator and sends setup changes to the ABP

monitor.

A rechargeable lithium battery keeps the RAM and real-time clock backed up during periods when
the AA batteries are removed.

1-1

Ambulatory Blood Pressure Monitor

User Controls

The 90217 ABP monitor provides two user controls: a START/STOP button and Power ON/OFF
switch.

Power ON/OFF Switch

When turned ON, this switch activates the monitor and begins executing the timed blood pressure
program.

START/STOP Button

This front panel control manually starts a blood pressure measurement, stops a measurement
already in progress, or sets special modes of operation (refer to the 90207, 90217 Ambulatory Blood
Pressure Monitors Operations Manual, P/N 070-0137-xx).

Display

The monitor display is a 4-digit LCD that presents the following information (refer to the 90217
Ambulatory Blood Pressure Monitors, Operations Manual (P/N 070-0137-xx) for instructions on
use).

Systolic/Diastolic Pressure and Heart Rate

Patient information appears on the display sequentially with systolic first, diastolic next, and then
heart rate. Each parameter appears for approximately one second. The screen is blanked for one
second and the sequence of readings is re-displayed two more times.

A bar indicator at the left of the display identifies which parameter is currently being displayed. It
appears next to the “sys” for systolic, next to “dia” for diastolic pressure, and next to the heart symbol
for heart rate.

Time of Day

A real-time clock provides the time of day, which appears between measurement cycles and can be
programmed in either a 12- or 24-hour mode.

1-2

Introduction

Cuff Pressure

This pressure can be shown while the monitor is taking a measurement. If cuff pressure is not
selected, “----” appears. Cuff pressure can be enabled or disabled in software.

Event Code

Event codes are 4-digit LCD messages that begin with “EC” or, in some cases, show specific codes
such as “LLL” for a low battery. If enabled, a beep sounds during an event code and the code is
displayed on the monitor. Refer Troubleshooting on page 5-1 for event code information.

Count Down Sequence

Whenever the monitor begins a measurement cycle, it turns its tone ON (if beep is enabled) and
counts down from 5555 to 1111 on the display.

IR Communications

During IR communications, the monitor first displays “9999” on the LCD to indicate that it has
detected a cable connect and has gone into the communication mode. The monitor periodically
attempts to contact a modem. The left two digits on the monitor display indicate the steps in the
communication process. For more information, refer to Base Station via Modem on page 2-3.

Programming Options

These monitor options are user programmed:

Day or Night Modes

Day mode = beeper ON, inflation time approximately 15 seconds

Night mode = beeper OFF, inflation time approximately 20 seconds

Measurement Intervals and Periods

Measurement intervals are selectable from 6 to 120 minutes (in one minute increments) for each
period. It is also possible to not have readings taken during a specified period. Up to 12 periods may
be defined.

Clinical Verification Mode

When set to this mode, the monitor is forced to bleed to 40 mmHg or to one step below diastole
(whichever is lower) for each reading.

Office Check Mode

This mode verifies monitor operation and allows a user to view cuff pressure and blood pressure
results regardless of any previous disabling of the display. During Office Check Mode, the monitor
bleeds an additional pressure step below diastole.

1-3

Ambulatory Blood Pressure Monitor

This mode is enabled for the first five successful blood pressure readings (or attempted readings)
following monitor initialization. Office Check can be disabled by a patient cancel and can be re­enabled after turning the power switch ON and holding the START/STOP button in while the last
digit of the software version number is being displayed.

Blood Pressure/Heart Rate Measurements Displayed

These measurements can be selected to appear or not to appear at the end of a measurement.

Cuff Pressure Displayed

This measurement can be selected to appear or not to appear during the measurement cycle.

1-4

Setup

Contents

Installing the Batteries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Initializing the Monitor. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Operational Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Installing the Batteries

Two types of batteries are used in the 90217 ABP Monitor: three standard AA batteries (Spacelabs
Medical P/N 146-5011-xx) to power the cuff air pump, and one rechargeable lithium battery to
backup the clock and RAM circuits when the AA batteries are removed or are exhausted. This
lithium battery receives its charge from the AA batteries and does not normally require replacement.
Its expected life is at least nine years.

If alkaline batteries are used as the AA batteries, they must be replaced after each patient use.
Nickel cadmium batteries require a full charge before each use.

AA Batteries

To replace the three AA batteries:

1. Switch the monitor’s power switch to OFF.

2. Remove the battery compartment cover plate by sliding it to the right until it can be pulled
free.

2-1

Ambulatory Blood Pressure Monitor

!

3. 3. If present, remove the old AA batteries from the monitor and replace each with a fresh
alkaline battery (or fully charged nickel cadmium), being careful to match polarities where
indicated (+ or -).

• The monitor will not operate if batteries are incorrectly installed.

• If the monitor is going to be stored longer than two weeks, remove the AA
batteries to prevent the possibility of leakage or discharge. Spacelabs Medical is
not responsible for product damage caused by battery leakage. If your unit has
been damaged by a leaky battery, contact the battery manufacturer for any
recoverable repair costs.

4. After correctly inserting the batteries, gently slide the battery cover back into place.

5. Switch the monitor ON and verify that the display appears. If there is no display, switch the
monitor OFF and refer to the Troubleshooting chapter in this manual. When power is first
switched ON, the first four digits of the RAM code revision are displayed for about 1 second,
followed by a blanked display, followed by the last two digits of the revision number.

Initializing the Monitor

The ABP monitor must be initialized prior to use. Initialization specifies the monitoring period, patient
information, time format, measurement interval, monitor tone ON/OFF during selected periods,
event code display, and whether or not to display pressure values. To initialize the monitor, connect
it to one of the following analysis systems.

Local Report Generator

For a direct connection to a Local Report Generator, place the monitor into the chute on the Report
Generator (Model 90239A or equivalent):

Local Report Generator Direct Connect Configuration

Ensure that the monitor lines up

Model
90217

against the side to align IR ports

Local Report
Generator
(90239A)

2-2

Setup

!

PC Interface

For a direct connection to an IBM XT/AT/PS2 (or equivalent) via a Model 90219-02/90219-03 (or
equivalent):

1. Connect the ABP monitor to the 90219 Analysis System.

2. Connect the 90219 Analysis System cable from the monitor to the serial port on the PC:

PC Interface Direct Connect Configuration

Model 90219 Analysis System

90217

cable to serial port

ABP

Monitor

3. Refer to the 90219 Ambulatory Blood Pressure PC Interface/Base Station Operations
Manual (P/N 070-0238-xx) for instructions for operating the Analysis System.

Base Station via Modem

For a modem connection to a remote IBM XT/AT/PS2 (or equivalent) base station:

Modem Connection Configuration

cable to

TO

BASE

STATION

MODEM

• The initialization procedure is provided in the 90219 Ambulatory Blood Pressure
PC Direct/Base Station Operations Manual (P/N 070-0238-xx).

PUBLIC

TELEPHONE

NETWORK

MODEM

serial port

ABP

Monitor

PHONE

1. The 90217 can use one of the following modems for communication:

• Hayes Smartmodem 1200

• Hayes Optima 9600 or equivalent

• Most 2400 baud modems

If the remote site also has 90202 or 90207 monitors, a Hayes Smartmodem 1200 must be used with
those monitors.

2-3

Ambulatory Blood Pressure Monitor

!

!

High Speed modems are setup via software commands.

The Hayes Smartmodem 1200 which attaches to the monitor must be setup as follows:

Switch #

1down

2up

3down

4down

5down

6up

7up

8down

9up

10 up

2. Connect the serial port cable (P/N 012-0096-00) between the monitor and the modem.

• If call waiting or call forwarding are options on the telephone used to transfer data,
ensure that both are deactivated or modem communications may be interrupted.
In addition, telephone systems such as CBX or PBX can cause interference with
the modem, or the modem can cause interference with the switching system.

To initialize the monitor for a remote connection:

1. Contact the base station by telephone (for remote operation only).

2. Ask the base station operator to initialize the monitor. Give the following information to the
operator:

Setting at Monitor

Site

• Patient's name.

• Patient ID number.

• If the monitor display is to be active or inactive.

• Time of day (12- or 24-hour format).

• If measurements are to be displayed (systolic/diastolic and heart rate).

• Multiple or single cycle times. If using a single cycle for the 24-hour monitoring period,

indicate the cycle interval and whether the tone is ON or OFF. For multiple cycle time,
specify each cycle interval and whether the tone is ON or OFF for each cycle.

• Any other information the base station operator may request.

3. The base station operator enters the patient information in the computer.

4. Prepare the monitor to receive the patient data from the base station.

• Switch the modem ON.

• When instructed by the base station operator, switch the ABP monitor ON.

• The modem link must be established within 45 seconds for the 90217. If this does
not happen, switch the monitor OFF and return to step 1.

2-4

5. When the information transfer is complete, the ABP monitor beeps and voice

!

communication is restored.

• Switch the monitor OFF and disconnect it from the modem.

• If there is a direct connection between the monitor and the base station, switch the
monitor OFF and disconnect it from the ABP data interface unit.

To transfer readings from the monitor to the base station:

1. Contact the base station by telephone (for remote operation only).

2. Ask the base station operator to read the monitor. Give the following information to the
operator:

• Patient's name.

• Patient ID number.

• Any other information that the base station operator may request.

3. The base station operator enters the patient information into the computer. (If the monitor is
in a remote location, the operator must turn power to the base station modem ON.)

4. Prepare the monitor to transfer data to the base station.

• Switch the modem ON.

• When instructed by the base station operator, switch the ABP monitor ON (for remote

operation only).

Setup

• The modem link must be established within 45 seconds for the 90217. If this does
not happen, switch the monitor OFF and return to step 1.

5. When the information transfer is complete, the ABP monitor beeps and voice
communication is restored.

• Switch the monitor OFF and disconnect it from the modem.

Modem Indicator Lights

When the monitor is switched ON, the modem’s RD (receive data) and SD (send data) lights flash
for several seconds. The OH (on hook) indicator is lit when the monitor starts communicating with
the remote modem. When both modems connect, the CD (carrier detect) is lit. The SD and RD lights
flash as data is being transferred.

After the transmission is complete and the monitor is turned OFF, the HS, TR and MR indicators will
always remain lit at the local modem.

2-5

Ambulatory Blood Pressure Monitor

!

90217 Modem Connection Status Indications

The left-most digit of the 90217 display shows the various stages of the modem connection process:

1 Sending modem identify query.

2 Waiting for response to identify query.

3 Sending modem reset commands.

4 Sending modem setup commands.

5 Send off-hook command.

6 Waiting for contact.

7 Contact established.

9 Not attempting to contact modem.

Once contact has been established, the second digit from the left on the 90217 display indicates the
baud rate of the connection. On high speed modems, the indicated speed refers to the connection
between the ABP monitor and the modem. The two modems may be communicating at some speed
other than that at which the modem is communicating with the monitor.

The baud rate codes are as follows:

0 1200

1 not used

2 2400

3 4800

4 9600

5 19.2 k

6 38.4 k

Setup Test

• Verify that all cable connections are installed correctly and are connected
securely.

Switch the ABP monitor ON. It initially displays “9999”. When the monitor is being read or initialized,
these digits change to indicate that communication is taking place between the monitor and the
analysis system. When communication is complete, the digits stop changing.

The right-most digit indicates that a message has been sent from the monitor to the base station.
The second digit from the right indicates that a non-garbled message has been received by the
monitor. A common failure mode is with only the right digit spinning. This indicates garbled
messages are being received and an “I don’t understand” response is being transmitted by the
monitor.

2-6

Setup

!

Operational Tests

Conduct the following procedures to verify proper operation of the Model 90217 ABP Monitor.

Equipment Required

• 90219-02 system

• 90219-03 ABP Base Station software

• Type AA alkaline batteries (3)

• Cable, 90217 to PC, P/N 012-0097-xx (greater than -02)

• Setup for air leaks (see Air Leak Test for illustration)

• Analog manometer (optional)

• Stop watch or equivalent

• Battery spring insertion tool, P/N 003-0084-00

Visual Inspection

1. Check the display window and ensure that it is clear (free from scratches, contamination,
etc.) with the words “SYS DIA” appearing on the left side.

2. Verify that the front panel START/STOP button responds with a clear “snap” when
depressed.

3. Inspect inside the battery compartment to ensure that the battery springs are clean and
provide a good electrical contact with the batteries.

4. Install the three AA batteries and verify that the battery door closes and latches properly.

Air Leak Test

1. Connect the test setup illustrated below:

• This figure shows the use of both an analog and digital manometer. Both or either
can be used in these tests. If only one manometer is used, block off the unused
hose.

2-7

Ambulatory Blood Pressure Monitor

!

!

2. Close the squeeze bulb valve.

3. Turn the 90217 ON and press the START/STOP button.

4. Verify the following monitor response:

• Two beeps are sounded.

• The display counts down: 5555, 4444, 3333, 2222, 1111.

• Pumping begins and “_ _ _ _” is displayed (could display the pump pressure, depending
upon how the monitor was initialized).

5. Verify that the system pumps up to 165 mmHg, +/- 8 mmHg, before the pressure begins to
drop in 7 to 9 mmHg steps. Ensure that the pressure does not drift down.

• It may take 3 or 4 steps before the cuff size is learned by the monitor and the
steps fall within this range.

6. Verify that the display reads “EC18”.

7. Open the bulb valve and remove the monitor from the manometer setup.

PC Interface Test

1. Connect the system as illustrated:

2. Power ON all devices.

3. Start the 90219-03 Base Station software (loaded on hard drive).

4. Type: ABP (or ABPPCI) and press the Enter key on the base station.

• If the file name has been changed from ABP, type DIR and press Return to
determine the new name.

2-8

Setup

!

5. Switch the 90217 power switch ON.

6. Press in this order:

Space Bar

1 (ABP communication)

3 (direct connect - skip this step if a PC Interface data key is attached instead of a base

station data key)

2 (read ABP unit)

7. Press any key (wait).

8. Type 8, Enter key, and Y (yes).

• “8” is the name of a dummy file which should be setup on the computer already.

9. Press the END key.

10. Verify that the clinical data appears on the computer screen. The last reading on this screen
is the results of the test done earlier in these procedures.

11. Verify that the date and time are correct and that the event code “EC18” appears.

12. Press the ESC key.

13. Initialize the 90217 by typing:

1 (initialize ABP)

14. Press the END key and use the up arrow key until PATIENT NAME is selected.

15. Type:

TEST and press the Enter key

1234567890 and press the Enter key

NONE and press the END key

16. Verify that the display reads “***MONITOR INITIALIZED***”.

17. Press:

Space Bar

ESC key

ESC key

ESC key

Y key (yes)

18. Remove the 90217 from the system and switch power OFF.

19. Remove one AA battery.

20. Wait one minute and reinstall the battery.

21. Switch 90217 power ON and verify that the time remained correct.

2-9

Theory

Contents

Pressure Amplifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Oscillometric Amplifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

90217 Block Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Digital Circuitry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Unit Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Software Flow Chart. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Pressure Amplifier

The pressure amplifier monitors the voltage produced across the pressure transducer. This voltage
is proportional to the pressure in the arm cuff.

The pressure transducer circuits require temperature compensation to account for changes in
sensitivity. This is accomplished by using a reference current to provide a constant current source
into the bridge. Any change in bridge resistance due to temperature will change the bridge voltage in
an amount that compensates for any change in sensitivity.

Voltage across the transducer is amplified differentially and turned into a single ended voltage that is
amplified, offset and sent to the processor’s A/D converter, the oscillometric amplifier and the
overpressure detector.

Offset Adjust

Both transducer offset and operational amplifier offset are nulled out using a pressure offset
adjustment. Minor variations in the offset are tracked and compensated for in software.

Gain Adjust

Changes in gain are compensated for with a gain adjustment. The voltage gain to the A/D converter
is +15 mv/mmHg, and the voltage is offset by approximately 0.09 volts. This 0.09 volts is inserted to
prevent the A/D converter signal from going negative during drifts in the offsets. The 0.09 volt offset
is subtracted in software.

3-1