Novametrix 101 User manual
HAND-HELD RESPIRATORY
MECHANICS MONITOR
Service Manual
Model 101
April 17, 2000
Catalog No. 6800-90-01
Novametrix Medical Systems Inc.
PO Box 690
5 Technology Drive
Wallingford, Connecticut, U.S.A. 06492
Revision History
Revision History
22-May-98 Release
17-Apr-00 Revision 01, R-N746
Rev. 01
Model 101 Service Manual
iii
[This page intentionally blank.]
Revision History
iv
Model 101 Service Manual
Rev. 01
Table of Contents
y
Safety ..................................................................................................... 1
Introduction ...........................................................................................3
Keypad Controls and Indicators ........................................................................4
S
mbols ............................................................................................................. 4
Theory of Operati on ............................ .......... ........... .......... ........... .......5
Main Board ........................................................................................................5
Power Su pply ................. ..................... .................... ..................... ........... ....................5
Reference Voltages .............................. ................ .. ................ ................ ................ .....5
Battery Charger ...........................................................................................................5
On/Off Co n tr ol .. ... ........... ............ .................... ..................... .................... ............ ........6
Digital Control and Microprocessor ...................................... .. .. ................. .. .. .. ............6
Serial Communication .................................................................................................7
Audio ...........................................................................................................................7
Interface ......................................................................................................................8
Analog Control Signals ................................................................................................8
Sensor Identification ....................................................................................................8
Flow Zeroing ...............................................................................................................8
Flow Circuitry ..............................................................................................................9
Baromet ric a nd A ir w a y P re s s u re .... .. ..................... ..................... .................... ...........10
Interface Board ................................................................................................11
Key panel Interface . .................................................................................................. 11
Display interface ........................................................................................................11
LED control ...............................................................................................................11
Power Su pplies ....................... ..................... ..................... .................... ............ ........11
Functional Tes ts ................... ........... ............................. .......... ........... .13
Equipment Required ........................................................................................13
Procedure ........................................................................................................ 13
Accuracy Tests ............................................ .. .. ....... .. .. .... .. .. .. ....... .. .... .15
Equipment Required ........................................................................................15
Procedure ........................................................................................................ 15
Electrical Tests ...................................................................................17
Equipment Required ........................................................................................17
Rev. 01
Model 101 Service Manual
v
Table of Contents
g
y
Procedure ........................................................................................................ 17
Power Supp lies ........ ............ .................... ..................... .................... ............ ............17
Airway Pre s s u re Ca l ib ra tion . .. .. ..................... .................... ..................... ........... ........18
Differen t ia l P re s s ur e Calibration ............ .. ..................... ........... ..................... ........... . 19
Barometric Pressure Calibration .....................................................................19
Maintenance ........................................................................................21
General ...........................................................................................................21
Maintenance Schedules .................................................................................. 21
Cleanin
Batter
Battery Installation .................................................................................................... 23
External B a ttery Char ger ........... ... .. ..................... .................... ............ .................... . 23
Features Connector .............. .. .................. .. ............... .. .................. .................. .. .......23
and Sterilization ................................................................................22
and AC Operation ............................................................................... 22
Assembly Exchanges ...................................................................................... 24
Disassembling the Monitor ........................................................................................ 24
Reassembling the monitor ........................................................................................ 26
Accessories ......................................................................................... 27
Parts Lists ............................................................................................29
6800-00 Final Assembly, Model 101 ............ .................. .................. .................. .......29
6800-01 Main Assembly, Model 101 ................ .. ................................................... .. ..29
2740-01 01 Main Board Assy, Model 101 ........................ .................. .......................30
2740-17 01 Main Board Subassy, Model 101 ......................................................... ..30
2739-01 00 Battery & Comm Interface Board Assy ..................................................32
2741-01 00 Interface Boa rd Assy, Model 101 .............................. .. .............. .............32
6935-48 00 Test Fixture, Flow Leak Test ................................................................. 33
Drawings and Sche matics ................... ........... .......... ........... .......... ....35
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Model 101 Service Manual
Rev. 01
Guarantee
Equipment manufactured or distributed by Novametrix Medical Systems Inc., is fully guaranteed,
covering materials and workmanship, for a period of one year from the date of shipment, except for
certain dispo sable pr oducts and products wit h stated gu arantees other than one year. Novametrix r eserve s
the right to per form gu ara ntee s ervi ce(s) at it s f actor y, at an authorized rep air s tati on, o r at t he cus tome r’s
installation.
Novametrix’ obligations under this guarantee are limited to repairs, or at Novametrix’ option,
replacement of any defective parts of our equipment, except fuses, b atteries, and calibration gasses,
without charge, if said defects occur during normal service.
Claims fo r damage s durin g shipme nt must be filed pro mptly wi th the tr ansportati on compa ny. All
correspond ence co ncerning the equ ip ment must specify bot h t he model name and number, an d t he serial
number as it appears on the equipment.
Improper use, mishandling, tampering with, or operation of the equipment without following specific
operating instructions will void this guarantee and release Novametrix from any further guarantee
obligations.
Service Department
For factory repair service, call toll free
1-800-243-3444
In Connecticut, call Col lect (2 03) 265-7701
(203) 284-0753
FAX
http://www.novametrix.com
techline@novametrix.com
Email
Caution:
license d medical practitioner.
Copyright 1998, 2000 Novametrix Medical Systems Inc. This document contains information which
is proprietary and the property of Novametrix Medical Systems Inc., and may not be reproduced, stored
in a retrieval system, translated, transcribed, or transmitted, in any form, or by any means, without prior
explicit written pe rmissio n from Novametrix Medical Systems Inc.
Federal (U.S.A.) law restricts this device to sale, distribution, or use by or on the order of a
Declaration of Conformity with European Union Directive
The Authorized Representative for Novametrix equipment is:
D.R.M. Green
European Compliance Services Limited
Oakdene House
Oak Road
Watchfield
Swindon, Wilts SN6 8TD
Rev. 01 Model 101 Service Manual
vii
Guarantee
Service Policy
Novametrix Medical Systems Inc. provides 24-hour a day access to technical support through its
Technical Suppo rt Depa rtment in Wallingford, C onnecti cut, and company S ervice Re presen tatives
located throug hout th e United Sta tes. (Outside the U.S., prim ary technica l suppor t is handled t hrough ou r
qualified international sales and service distributors.)
Novamet ri x wil l provide Warranty Service suppor t wi thi n 48 ho urs of receiv in g a re quest for assistanc e.
Contact the Technical Support Department by telephone toll free at 800- 243 -3444, or 203-265-7701; by
facsimile at 203-284-0753; or, by e-mail at techline@novametrix.com. After hours telephone support
requests (before 8:00 AM and after 5:00 PM Eastern Time) will be responded to promptly by the
Technical Support on-call staff. After hours facsimile and e-mail requests will be answered the next
busines s day. It is suggested tha t an y perso n cal ling in for techni cal su pport h a ve t he equi pmen t a va ilabl e
for product identification and preliminary troubleshooting.
Novamet ri x reserves the right to repair or replace any product found to be defective during the warr ant y
period. Repair may be provided in the form of replacement exchange parts or accessories, on-site
technical repair assistance or complete system exchanges. Repairs provided due to product abuse or
misuse will be considered “non-warranty” and invoiced at the prevailing se rvice rate. Repl aced or
exchanged materials are expected to be returned to Novametrix within 10 days in order to avoid
(additional) charges. Return materials should be cleaned as necessary and sent directly to Novametrix
using the r et urn paperwork an d shipping label ( s) provided. (Transferri ng r et u rn m at eri al s t o a local sale s
or dealer representatives does not absolve you of your return responsibility.)
Novametrix manufactures equipment that is generally field serviceable. When repair parts are provided,
the recipient can call Technical Support for parts replacement assistance and repair assurance. In the
event a replacement part requires increased technical ca pability, Technical Support may request
Biomedical assistance, provide on-site technical suppo rt or complete replaceme nt equipment. If the
customer requires the return of their original product, the exchange material will be considered “loaner
material” and exchanged again after the customer equipment is repaired.
Novametrix promotes customer part icipation in w arranty repairs, should they beco me necessary. A
longer useful product life, and quicker, more cost-effective maintenance and repair cycles—both during
and after the warranty period, are benefits of a smooth transition into self-maintenance. The Technical
Support Department can provide technical product support at a level appropriate to your protocol and
budget requirements.
Please contact Technical Support for information on these additional programs and services:
• Focus Series Technical Training Seminars
• Test Equipment and Test Kits
• Service Contract / Parts Insurance Plans
• On-Site Technical Support
•“Demand Services” including
Flat rate parts -exchange
Flat rate return for repair
Time and Material
• Full warranty, discounted replacement sensors
Model 101 Service Manual Rev. 01
viii
Section 1
The VENT✔ Handneld Resp iratory Mecha nics Monitor, Model 10 1, is electrically is olated. Patient
leakage current flowing from the instrument to ground is limited to less than 10 uA.
• Keep the VENT✔ and its accessories clean. Do not operate the VENT✔ when it is wet due to sp ills
or condensation.
• Connect only Novametrix Series 3 Flow Sensors to the VENT✔. For maximum performa nce ; keep
the pressure sensor ports oriented upward, and keep the sensor clear of moisture and secretions by
proper breathing circuit maintenance.
• Connect the sensor first to the VENT✔ and then to the patient breathing cir cuit in order to limi t
circuit volume loss and to avoid excessive moisture build-up in the flow sensor tubing.
• VENT✔ has electrically isolated inputs. Patient leakage current flowing from the instrument to
ground is limit ed to less than 10 µA at 120 V, 60 Hz. Pa tient iso lati on is grea ter t han 1 0 MΩ, 2500V
rms at 60 Hz.
• Where electr omagnetic devic es (i.e., ele ctrocautery) ar e used, patient monitoring may be interrupted
due to electromagnetic interference. Electromagnetic fields up to 3 V/m will not adversely affect
system performance.
• VENT✔ contains no user serviceable parts. Refer servicing to qualified service personnel.
• This product and its accessories which have patient contact are latex free.
For maximum patient and operator safety, observe the following warnings and cautions.
Safety
WARNINGS
!
Indicates a potentially harmful condition that can lead to personal injury.
Explosion Haza rd:
•
instrument in such an environment may present an explosion hazard.
Electrical Sho ck Hazard:
•
monitor or sensor. Refer servicing to qualified service personnel.
Fire Hazard:
•
Use in such an environment may present a fire hazard.
Failure of Operatio n:
•
has been corrected by qualified personnel.
• Do not apply tension to t he sensor tubing whi le connected to a patie nt breathing ci rcuit, as accid ental
extubation may result.
• Do not position the flow sensor’s tubing in any manner that may cause entanglement or
strangulation.
• Use the optional external battery charger in non-patient areas only.
Do NOT use the VENT✔ in the presence of flammable anesthetics. Use of this
Always turn the monitor off befor e c le ani ng i t. Do NOT us e a damaged
The VENT✔ should not be exposed to elevated oxygen levels at elevated pressures.
If the monitor fails to respond as described, do not use it until the situation
Rev. 01
Model 101 Service
Manual
1
Section 1
CAUTIONS
Indicates a condition that may lead to equipment damage or malfunction.
• Federal (U.S.A.) law re stri cts th is devi ce to sal e, dist ribut ion, or us e by or on the order of a licens ed
medical practitioner.
• Electrical Shock Hazard: Always turn the monitor off before cleaning. Do NOT use a damaged
monitor.
• Do NOT use a damaged flow sensor.
• Do NOT immerse the monito r or senso rs in liquids.
• Do NOT sterilize the monitor or the sensors.
• No user serviceable parts inside. Refer servicing to qualified service personnel.
• Operate at temp era tu res between +10° C to +40° C (50-104° F), < 90% relative humidity (non-
condensing).
• Avoid storing the monitor at temp eratures less than -20° C or greater than +55° C (<-4° F or >131°
F).
NOTES
Indicates points of particular interest or emphasis for more efficient or convenient operation.
• The VENT✔ operates with Novametrix Series 3 Flow Sensors only.
• The VENT✔ performs an automatic zero (self calibration) periodically and as needed. During this
time, monitoring is interru pted for le ss than th ree seconds.
• The automatic zero can be manually initiated by simultaneously pressing the DATA and GRAPH
keys. After cha ngi ng th e sensor from Adult to Neon at al ( whil e t he VENT✔ is operation al ), w ai t 30
seconds then perform an automatic zero.
• This product and its accessories which have patient contact are free of latex.
• The C
• To determine the VENT✔ software version, turn the monitor on. During the self test performed at
power up, the softwar e lev el is sho wn on the thir d line as “main-101-xx”, where “xx” is the software
version.
• Some VENT✔ monitors were produced with the statement “Use only Novamet rix approved devic es,
13 VDC, 1A” located on the label at the Flow Sensor Input Connector. This erroneous statement
does NOT apply to the VENT✔ monitor and should be ignored.
/C Compliance Ratio (neonatal) parameter is not supported.
20
2
Model 101 Service
Manual Rev. 01
Section 2
The VENT✔ Handheld Respiratory Mechanics Monitor, Model 101 is shown below.
Keypad &
Display
Introduction
Connect Series 3
Flow Sensor
t
n
e
i
t
a
P
o
T
r
o
t
a
l
i
t
n
e
V
o
Neonatal Pediatric/Adult
Sensor
#6718/6720
T
Sensor
#6717
Features
Quick Guide
Rev. 01
Connector
Battery Access
Compartment
Model 101 Service
Manual
3
Section 2
g
g
g
g
g
g
Keypad Controls and Indicators
2.1 Keypad Controls and Indicators
1
2
3
4
POWER GRAPH DATA
A
# Key Action Function
POWER
1 Press Turns
GRAPH
2Press
DATA
3Press
Press Turns displ ay backlight on/off.
4
Press &
Hold
A None
VENT
Display Graph Screens.
Additional presses caus es
h available Graph Screens.
throu
Display Data Screens.
Additional presses caus es
h available Data Screens.
throu
Adjusts contrast/viewin
(1 step/sec.)
Illuminated if powered from battery
Green; battery char
Yellow flash in
Red flashin
NEO
B
✔ on/off.
✔ to sequence
VENT
✔ to sequence
VENT
angle of display
ed
slowly; capacity getting low
quickly; exhausted in 10-15 min.
4
Model 101 Service
NEO
B None Illuminates when a Neonatal sensor is connected.
2.2
Symbols
Symbol Description
Patient Iso lation
Identifies patient isolation connection as type BF.
!
Manual Rev. 01
Attention
Consult manual for detailed information.
Section 3
3.1 Main Board
3.1.1 Power Supply
Refer to page 4 of the schematic 2740-03. An external power source can be connected to J403 to power
the monitor and charge a rechargeable battery (only Novametrix approved rechargeable batteries and
chargers should be used with the model 101). The internal battery connects to the cathode of D11, fuse
F1 provides overload protection. Since the monitor has the possibility of being powered by the internal
battery or an external charger, diodes D4 and D11 isolate each of these sources from one another.
3.1.2 Reference Voltages
Refer to page 5 of the 2740-03 schematic. A 2.5 volt reference (AVCC_2) is generated by U10 and
buffered by U1A. This voltage is amplified by U1B and Q1 and supplies a 5 volt line (AVCC). The 2.5
volt reference is divided down by resistors R6 and R7, buffered by U2B to supply a 1.5 volt reference
(A_1_5V). A neg ative 2.5 volt reference (NEG_AVCC_2) is gene ra ted by U9B and Q9 which are set up
as a unity gain inverting amplifier fed by the 2.5 volt reference (AVCC_2).
Theory of Operation
3.1.3 Battery Charger
Refer to page 9 of the 2740-03 schematic. The internal NiMH battery will charge when the monitor is
connected to the DC wall mount adapter or installed in the cradle option. Battery charging is controlled
by U11, a frequency modulated fast charge controller. U11 monitors temperatu re, voltage, and time
throughout the charging proc ess to safely and effectively charge the internal batte ry. The charger is
configured to terminate charging using the ∆T/∆t (delta temperature/delta time) method of charge
termination. Charging is ma in ta ined at the C/4 (600mA) rate whi le cu rr ent t o the battery i s controlled by
Q11, Q2 , Q1 2, a nd th e MO D ou tpu t of U11. Q2 pr ovid es b ase drive fo r Q11 whi le Q 12 se rves t o sh ut
Q11 off very quickly on a cycle by cycle basis allowing the large currents required for charging to pass
through Q11 which is a surface mount SOT-23 package capable of 500mW power dissipation.
T empera ture is moni tored usi ng the batt ery’s internal th ermistor , R115, R11 6, and R118. Resis tors R115,
R116, and R118 set the ∆T/∆t charge termination parameter to 1ºC per minute. R39 and R106 set the
maximum temperature for charge termination (a safety override) to 45ºC. Battery charging is initiated in
one of two w ays . Ei t her by ap ply ing 13 VDC t o +VCHG, therefore prov idi ng power (BVDD) to U11, o r
by inserti ng a r ech arg eab le batt er y in t o the ba tter y co mp ar tme nt (p r ovi ded exte rna l p ower is availa ble ).
Resistors R34 and R36 set up a divider which determines whether the installed battery is within the
correct voltage range for charging. BVDD is regulated by D1, a 5.1V zener diode while R35 keeps D1
Rev. 01
Model 101 Service
Manual
5
Section 3
Main Board
operating in the knee region and C68 and C69 provide filtering. Over current protection is provided by
F2, a 1A slo-blo replaceable fuse. Reverse leakage protection is provided by D2 and D7 which prevents
the battery from trying to power BVDD and +VCHG in the battery operation state.
3.1.4 On/Off Control
Refer to page 4 of the 2740-03 schematic. When the power key is pressed the cathode of D3 is brought
to ground, br ing ing t he anode lo w, this biases Q3 B on and allows VDCI N t o p o w e r the unit. Pressing the
power key again will signal the processor that the unit must power down. The processor will assert the
POWER_HOLD line (low) to bias Q4 off, this will turn Q3B off and power the unit down.
The voltage level of the battery (or power source) is monitored by U13A. If the VSWDC level drops
below a certain thres hol d then comparator U13A will go l o w, this will pu ll the POWER_H OL D l ine low
through D19 and shut the monitor down.
3.1.5 Digital Control and Microprocessor
Refer to page 1 of t he 2740-03 schemat ic. Th e syst em i s contro ll ed by mi cropr ocesso r U18. Ei ght a nalog
channels are monit o r ed and proc essed and sev er al digi tal lines are genera ted for vario us ope ra ti ons. The
analog channels are monitored and converted to digital information by the microprocessor. These
channels are listed below:
ANALOG
CHANNEL
ACH_0 Airway flow channel X1
ACH_1 Airway flow channel X10
ACH_2 Airway flow channel X100
ACH_3 Airway flow channel X1000
AWPRESS Airway pressure zero
ABPRESS Barometric pressure
F5V CPU power plane measurement
VBATTADC Battery voltage measurement
The digital lines are listed below:
DIGITAL LINES DESCRIPTION
8255_CS Chip select for programmable peripheral interface, U22
DAC_SDI Serial data input line for U8 and U25
DAC_LD Load assert line for U8
DESCRIPTION
6
Model 101 Service
DAC_CLK Clock signal for U8
OCDRV_0 Drive signal for opto isolator 1
OCDRV_1 Drive signal for opto isolator 2
Manual Rev. 01
Main Board
Section 3
OCDRV_2 Drive signal for opto isolator 3
POWER_HOLD Signal line asserted low for powering down the monitor
VLV_CNTL Valve control line used for zeroing pressure sensors
CLKOUT 1/2 of the system clock output (6MHz)
MPU_TXD Serial communic ation tran smit line
MPU_RXD Serial communication receive line
750KHz Clock input signal for audio output pulse width modulated signal
EE_OUT Erasable EPROM data output signal
LED_PWM Clock output signal for display back light
EE_CS Erasable EPROM chip select
COMMPWR Enable/sleep control for RS232 Transceiver, U17
AUD_CLK Audio drive output signal
ALE Address line enable (A0-A7)
INST Control line for R AM and ROM a ccess
WR Write enable
RD Read enable
Crystal Y1 sets the operating fre quency at 12MHz. System softw are is stored in U21, a flash ROM
device, and system RAM in U19. Decoding for the RAM and ROM is handled by U27, U28 and U20.
Address lin es A0-A 7 are s hared wi th dat a line s D0- D7, U15 d ecodes the dat a line s as add ress l ines w hen
needed through the ALE line.
The digital supply is monitored by U26, if the voltage drops below a certain threshold then the SRST*
signal will reset the system. The SRST* line will also bias Q8 off, this will assert the RESET line that
will reset other chips on the board at the same time that the microprocessor is reset.
3.1.6 Serial Communication
Refer to page 2 of the 2740-03 schematic. Serial communication is handled by U17, the transmit
(MPU_TXD) and receive (MPU_RXD) lines are converted into RS232 levels by U17. Diodes D13 and
D14 are for prot ectio n on the p roc essor side of U17. Ca pac itors C62- C65 are u sed b y U17 for genera ting
the requir ed voltages fo r the RS23 2 levels. L1 and L 2 are hig h frequency filte rs for imm unity and
susceptibility. The RS232 signals appear at the rear connector of the unit and at J401 (circuit board
mounted header connector). The COMMPWR line from the microprocessor enables U17 when high,
when set low U17 is put in sleep mode to conserve power.
Rev. 01
3.1.7 Audio
Refer to page 2 of the 2740-03 sch emat ic. Audibl e tones ar e genera ted by LS1 when dri v en by Q13. The
AUD_CLK line from the microprocessor biases Q13 on and off creating the desired tone output from
LS1. A 750KHz clock signal is generated by U31 from the 6MHz system clock. This clock input is
Model 101 Service
Manual
7
Section 3
Main Board
required by the p rocessor for generati ng the aud io tones of A UD_CL K. The RESET line on U31 pr ev ents
any audio from inadvertently being generated by disabling the chip during power up and power down.
Audio is used for low battery only. There are no other alert outputs in this monitor.
3.1.8 Interface
Refer to page 3 of the 2740-03 schematic. The microprocessor interfaces to the display, key panel, and
LED’s on the 2741 board through U22. U22 also interfaces to the optical isolators (located on the 2740
board), which determine which type of flow sensor is installed (adult, neonatal, or neonatal/CO2). The
microproces sor comm unicates to U22 via t he A0, A1 add ress line s, D0-D7 dat a lines , 8255 _CS, RD and
WR lines. The PA0-PA7 lines are a b u ffered data b us whi ch go to the 2741 boar d wher e t he y are used as
latched I/O. The PB5-PB7 lines decode the appropriate latch on the 2741 board for display and LED
indicator output and key-panel input and the PC5-PC7 lines drive the opto isolators on the 2740 board.
3.1.9 Analog Control Signals
Refer to page 5 of the 2740-03 schematic. The serial to DAC (digital to analog converter) U8 contains
four independent DACs for control signals in the system. A 1.5 volt reference (A_1_5V) is used as the
reference input to all four DACs via U12A, an amplifier with a gain of 2. The clock (DAC_CLK), load
(DAC_LD) and data (DAC_SDI) lines are directly controlled by the microprocessor.
DAC_A and DAC_B’s out puts a re used f or gai n cont rol i n t he fl o w meas uring circu itry. DA C_C’s output
is used for offset adjustments in the airway pressure measuring circuitry. DAC_D controls the VDISP
voltage through U9A and Q10, this varies the contrast on the monitor’s display.
3.1.10 Sensor Identification
Refer to page 8 of the 2740-03 schem atic. When a flow sensor is plugged into the monitor it is
automat ically ident ified by means of a reflective/non -reflective lab el that is read b y the monitor ’s
circuitry. Three opto isolators are used to emit a light and measure any reflection from the label. There
are three bands that can r ef le ct or a bsorb light, this enables eig ht dis ti nct possibilities . The opto isolator s
are driv en by OCDR V_0 th rough OCDRV_2 which drive Q5-Q7 respec tiv ely . If an opto isolat or recei ves
a reflec ti on then the tran si st or portion will conduct and t ri gg er a comparator o u tp ut (U13) to go l ow . T he
outputs OCRD-0, OCRD_1 and OCRD_2 will be read by U22 and allow the processor to determine the
type of flow sensor connected.
3.1.11 Flow Zeroing
Reference p age 3 of the 2740-0 3 schematic. The zero process begin s when the CPU brings the
VL V_CNTL li ne high, this biases Q3A on ener gizing v alv es V1 and V2. This disc onnects the diff erential
pressure transducer U29 (via V1 and V2) and the absolute pressure transducer U30 (via V2) from the
8
Model 101 Service
Manual Rev. 01
Main Board
Section 3
patient airway, and opens all pressur e transducer ports to atmosphere. Diod es D16 and D17 ar e for
protection against back EMF from the valves coils.
AIRWAY PRESSURE
TRANSDUCER
VALVE 2
VALVE 1
PNEUMATIC TUBING
BAROMETRIC PRESSURE
TRANSDUCER
The pressure t ransducer s are “zeroed” by adj usting th e amplif ied and condit ioned pres sure output signals
so that each reading reads approxim ately mid-scal e (512 coun ts) using a s uccessive approxim ation
algorithm. With a reference v oltag e of 5.0 Volts, e ach count retu rne d by the 10-bit ADC is equa l to 4.8 83
mV. Centering the no flow (ambient) signal to the ADC's mid-scale allows the sensor to report both
positi ve and negati v e airw ay pressu res. U8 , a Digit al to A nalog Con ver ter (DA C) provid es the adjustmen t
under microprocessor control. The DAC maintains each adjustment voltage obtained during the zeroing
process until a new zero cycle is initiated.
The patient ai rway pressure t ran sduc er is "zeroed" fir st by adjusting the UB_DAC_A output of the DAC
until the Airway Pressure signal reads mid-scale. The barometric (ambient) pressure as sensed by the
processor is recorded after the airway pressure zero is completed. Next the flow channels are zeroed. A
non-inverting summing amplifier U6A combines two of the DAC's outputs and a constant voltage from
AVCC equal to the mid-scale of the ADC. The output voltage produced by the summer is fed into U14,
a monolithic instrumentation amplifier, which takes the differential output of the pressure transducer,
U29, and adds an of fset equal to the re feren ce v oltag e input . D A C output s UB_D A C_ A and UB_D A C _B
serve to provide the flow channels with a fine and a course adjustment. The result from each channel is
stored in SRAM and used as an offset in the flow calculations. Valves V1 and V2 are then de-energized,
reconnecting the pressure transducers with the patient airway.
Rev. 01
3.1.12 Flow Circuitry
Reference page 6 of the 2740-03 schematic. Differential Pressure Transducer, U29, is a silicon-based,
piezoresistive bridge with four active elements. When pressure is applied between transducer ports P1
and P2, a di f feren tial outpu t v olta ge prop orti onal t o the appli ed pr ess ure is pro duced. The ful l-sc ale i nput
pressure range for the transducer is 0 to 4 inches of water (P1>P2) . By sett i ng the 0 differenti al pres sur e
(no-flow) point to mid-scale (during the zeroing process described earlier), negative pressure readings
(P2>P1) are also available. The transducer is temperature compensated at 25 degrees Celsius and
designed to be driven by a constant current source (U6B).
In the no rmal system operating mode, al l valves are de -energized . Transducer p orts P1 and P2 are
connected to the patient airway. As air flows through the flow sensor, a pressure difference between P1
and P2 is created. This signal is dependent on both the magnitude and the direction on the air flow. The
greater the flo w vol ume, the lar ger the press ure dif f erenc e creat ed betw een the tw o trans duce r ports . The
transducer senses an inspired flow as a positive pressure difference (P1>P2), while an expiratory flow is
Model 101 Service
Manual
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Section 3
Main Board
seen as a ne gative pressure (P2>P1) . With a source vo lt age of approximately 5.0V, the s ensor transform s
this pressure difference into an electrical signal with a nominal absolute magnitude of 50 mV Full-scale
Output. This signal is conditioned and amplified by U14, which is a monolithic Instrumentation
Amplifie r (IA) . The flo w IA U14 als o of fset s th e signa l to the mid-rang e of the ADC obt ained du ring t he
zeroing p rocess. A positive p ressure difference (inspira tory flow) c reates a signal a bove the offs et
(approximately 1.25 to 2.5V). A negative pressure difference (expiratory flow) becomes a 1.25 to 0V
signal. The nom inal ga in of U14 i s set by f ix ed res istor R59 and va riabl e res istor VR1. T he o utput for t he
transducer is adjusted using VR1 and a known pressure input as a calibration reference. With an input
differential pressure of 10 inH
O, the gain of the amplifier is set to give an ADC count of 3498.
2
The signal out of the flow U14 is ta ken through a two-pole low pass filter U7B with a 31Hz cuto ff
frequency to remove unwanted high frequency electronic noise before it is passed on to the four gain
stages (U4 and U5). The four flow differential gain amplifiers provide signal gains of 1 (ACH_0), 10
(ACH_1) , 100 (A CH_2) a nd 1000 (ACH_3). The gain of 1 amplifier is used to b uf fer the fl o w sign al and
provide sign al conditionin g consiste nt with the ot her channe ls. The x10 , x100 and x10 00 chann els
amplify the flow signal according to the following equation:
V
out
= (V
where A
R
R
-Vrefo/2)(Av) + (Vrefo/2)
flow
is the amplifier gain, Rfb/Rv (1, 10, 100 or 1000)
v
is the feedback resistor (R51,R58, R68, R78)
fb
is the reference resistor (R131,R61, R73, R82)
v
The circuit is designed to amplify the difference between the flow signal into each gain stage and the
reference voltage so the zero point of each stage remains at mid-scale.
The output from each gain stage appears at the microprocessor for conversion into digital information.
An alternate pressure transducer, U29A may be installed in place of U29. The principal of operation is
the same a s d esc ri be d above wi th th e ex ce pti on th at it ’s full scale pressure input range is 0 to 10 inches
of water and it is excited by a constant 5.0 volt (AVCC) reference.
3.1.13 Barometric and Airway Pressure
Refer to page 7 of the 2740-03 schematic. U30 is a piezoresistive differential pressure transducer with
port P2 held at a vacuum (0 psi). It measures the absolute pressure difference at port P1 relative to the
vacuum at port P2. The transducer is calibrated for a full scale output of 0 to 30 psi, has internal
temperature com pensati on and is desig ned to be dri ven by a con stant cur rent source. Resi stor R99 is us ed
to set the current through the sensing bridge by amplifier U7A. Instrumen tation amplifier (IA) U23
conditions thi s sign al to corr espond t o the cur rent ba ro metric pressu re , which is set by adj usti ng VR2 for
span and VR3 for of fset. The nomina l gain of thi s amplif ier is 68.75. The out put signal from U23 appears
as an input to both the 10-bit ADC and a second IA, U24. U24 provides gain adjustment via VR4 and
offsets the output signal from the barometric amplifier to mid-scale during the zeroing state. This is
handled by the AW_DAC line fro m U2 A (pa ge 5 of the 2740-0 3 sc hem a ti c) , the output is then fed to the
low pass filter circuit of U12B. The nominal gain of the airway pressure amplifier is 2.1. This signal
connects t o the P1 ( proxi mal to t he p atien t) si de of t he dif f eren tia l pres sure t ransdu cer dur ing m onito ring
and provides patient airway pressure sensing (AWPRESS).
10
Model 101 Service
Manual Rev. 01
Interface Board
Section 3
3.2 Interface Board
3.2.1 Key panel Interface
Refer to page 1 on 2741-03 schemat ic. The ke y panel ke ys are moni tored by the system thro ugh latch U4.
When any key is depressed the associated pull-up resistor (R9-R13) is brought low and the appropriate
line will appear as a low on the PD0-PD7 line. The latch is read by U22 from the main board (lines PD0PD7) when the 0xF800 line is asserted.
3.2.2 Display interface
Refer to page 1 on 2741-03 schematic. Communication to the display is handled by latches U1 and U2,
these in turn are controlled by U22 on the main board. U1 i s ena bl ed by t he oxF806 line and han dle s the
display data lines DS0-DS7. The remaining control lines are handled through U2 and the 0xF807 line.
3.2.3 LED control
Refer to page 1 on 2741-03 schematic. The LEDs on the front panel display are controlled by latch U2
and the 0xF807 li ne. LEDs D1 an d D2 are bico lor LED s that are con tro lled b y two li nes each . D3and D4
are unicolor LEDs.
3.2.4 Power Supplies
Refer to page 2 on 2741- 03 sch ematic . The VSW DC suppl y from the main b oard i s re gula ted t o a + 5 v olt
supply by U3, a VALVE_SUPPLY supply by U7 and ±12 volt supplies by U5 and U6. U7 is used as a
separate5 volt regulator for the main board valves. The other supplies are connected to the main board
through J2.
Rev. 01
Model 101 Service
Manual
11
Section 3
Interface Board
12
Model 101 Service
Manual Rev. 01
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