PC based instrumentation as an economic method for quality assurance-an experience based on development of hydrocephalus shunt test system

Abstract

A PC based system is an attractive alternative to conventional
methods of industrial quality assurance for its high reliability at
lower cost. A custom assembled system with user friendly software is
ideal for industries, especially when the quantity requirement is small.
This concept is illustrated with an example of the development of a PC
based test system for the quality assurance of hydrocephalus shunt-a
neurosurgical implant. During the technology transfer of the device, a
16 channel PC controlled test system has been developed for classifying
the device according to their pressure-flow characteristics. Here, the
speed of the multichannel peristaltic pump is controlled for various
flow rates ranging from 5 ml/hour to 50 ml/hour and the corresponding
pressure drop sensed by the transducer is amplified, digitized and
monitored. Depending on the measured values, the software classifies all
the accepted devices in appropriate ranges and rejects the rest. The
test results are printed out in proper format. All the subsystems and
components used are in modular form and are standard products of leading
manufacturers, enabling the user industry to operate and maintain the
system without the help of the developer

Full text

Page 1

PC BASED INSTRUM[ENTATIQN AS AN ECONOMIC METHOD FOR
QUALITY ASSURANCE - AN EXPERIENCE BASED ON
DEVELOPMENT OF HYDROCEPHALUS SHUNT TEST SYSTEM
Nagesh DS, Sriniva,san Nair SK, Muraleedharan CV & Bhuvaneshwar GS
Biomedical Technology Wing
Sree Chitra Tirunal Institute for Medical Sciences & Technology
Trivandrum-6950 12. INDIA
A BSTR4CT
PC based spstem is an attractive alternative to conventional
methods of industrial quality assurance for its high reliability at
lower cost. A custom assembled system with user friendly software
is ideal for industries, especially when the quantity requirement is
small This concept is illustrated with an example of the development
of a PC based test system for the quality assuramce of hydrocephalus
shunt - a neurowrgical implant.
During the technology transfer of the device, a 16 channel PC
controlled test system has been developed for classifying the device
according to their pressure-flow characteristics.. Here, the speed of
the multichannel peristaltic pump is controlled for various flow rates
ranging from 5 mVhour to 50 mVhour and the corresponding
pressure drop sensed by the transducer is amplified, digitized and
monitored. Depending on the measured values, the software
classifies all the arcepted devices in appropriate ranges and rejects
the rest. The test results are printed out in proper format.
All the subsystems and components used are in modular form
and are standard products of leading manufacturers, enabling
the user industry to operate and maintain the system without the
help of the developer.
KEY WORDS : H)drocephalus shunt (ZUahty assurance, PC Based
m\truinentation, Shunt test sq stern
I VTRCID I YTIO Y
Zero defect production is an essential requirement of a
reliable mdcal device. (mod manufachiring practices with strict
process quality assurance procedures can only result this.
PC based instrumentation systems ar'e efficiently used for
quality assurance. due to its high accurac? . speed and reliabilitv.
Custoh designed and assembled devices are useful when the
number of units required are small.
Such a s!steni has been developed during the technoloa
transfer of II!drocephalus shunt for the industry absorbed the
t ccholo g,
DETK 'E
abuormal condition ofthe brain due to
thc accumulation of the cerebrospinal fluid (CSF) clue to its (i)
o\'cI production. (ii) lon absoiption or (iii) constriction in f l o w
paths. The most common procedure for treating hq droccphalus
in\ 011 ing implanting a h~clrocephalus shunt SJ stcm that drains
CSF from the brain either to thc right atrimn of tlic heart
or more often to tlic peritoneal cm it! [ 21
I Ijtlrcscphalus is ~II
These devices are calibrated according to their pressure - flow
characteristics, into three ranges viz. low pressure, medium
pressure or high pressure(Fig. 1). For implantation, depending on
i'RESSURE (cm water)
,
MEDIUM PRESSURE RANGE
LOW PREESURE RANGE
10
20
30
40
50
60
FLOW ("r)
Figure 1 Range classification of the device
the patient need. shunt falling in onc of these ranges is selected.
TEST "52STELi1
The devices are tested for its pressure-flow characteristics
according to ASTMS0 standard [ 1.41.
During the tecbnolog transfer of the device. a fully automatic
16 channel E ' C controlled test system has been developed to
caw out the elitire process.
The schemtic of the set up is shown in figure (2). 'Ihs
basicall? consists of a \\ell calibrated peristaltic pump. sensors,
amplifier. M 3 - DIA convertors and a PC.
Out of thc 16 channcls. 15 are for pressure monitoring and
one for ternperahire. Each channel consists of a sensor, amplifier
and an AA) convertor. IYA converted output from PC controls
the specd ofthe piimp
Proceedings RC IEEE-EMBS & 14th EIMESI - 1995
1.35
Authorized licensed use limited to: Sree Chitra Tirunal Inst. for Medical Sci. & Tech.. Downloaded on July 25, 2009 at 02:16 from IEEE Xplore. Restrictions apply.

Page 2

SIGNAL
CONDrrlONER
i
I
FLOW 1
COmROLLTR
1
DISTILLED
WATER
R i SERVOlR
PR E88U RE
TRANSDUCER
DEVICE
PUMP
Figure 2 Block schematic of test set up
All the subsystems of the system lllie transducers. ampldier.
ARI - D/A card. the mounting cabinet, PC etc.. are in modular
form and are the standard products of leading manufacturers.
Only software has been custom development.
In addition to cost reduction. this also gives the independencq-
to the Industry. At the event of problem arises. If an)-, anybod!-
tem can easily locate the subsystem which
has failed without the help of the developer. Since each of the
subsystems arc interchangeable. spares can be used to replace
the defwtive parts aud the defective one can be send for repair to
the original manufacturer directly [SI.
Test conditions
Testing is carried out under the folloning conditions
leniperature oftest bath : 37 22°C'.
Level of water bath shall remain constant ithin i2rrmi.
Shunt shall be presoaked for suffient time.
Pump speed shall not vaq &5%
The fluid test medium in the source rescn.oir shall be
deaeriated, distilled water at 37 t2"C
resting is carried out at 6 diffcreut flon rates 1 ai? ing fioiii
~mlihonr to 50 mllhour.
~ e s ~ u ~ e m o ~ ~ o r i n ~
signal conditioning board ( PC'1.r) 7702 - L>!iialop Micro
Systems) is supplied to the pressure transduccr. .I hi.
instrumentation amplification adjusted to pile an output d
volts for 500 mn1 ofwater considering the inpiit \.oltagc ol'tlic
A/D card and the max~nuni presslire to be Iiieasiiied All
cables are sheathcd and a low pass liltcr is uicorporatcd to
rcduce interftrence. l'uo numbers of' 8 cliaiincl. 1 ?. hi[
converters are used for AA3 conversion r.3 1
: A 5 volt constant \olta~c siippl! li-otii
5
Proceedings RC IEEE-EMBS fi 14th BMESl - 1995
1.36
Temperature monitoring : The sipal conditioning board
provides the constant current source of lm4 to the PT 100
probe. Amplifier is calibrated to give 5 Volts at 40°C to
achieve maximum sensitivity at the measuring range.
Pump : A highly precise and well calibrated 16 channel roller
pump(1smatec G 78001-20. Cole Parmer -U.S.A) having a
variable flow rate up to 60 mVhour is used for fluid
circulation. The speed of the pump is controlled by external
injection of voltage. Each of the 8 chanuel Ax) card has one
additional D/A output. Thus is used €or controlling the speed
of the pump.
Water bath : A temperature controlled water bath made of
Stamless Steel is used as test bath.
Instrumentation cabinet : All the amplifer modules and
connectors for various for various cables are mounted on a
cabinet(President Sy-stems). All the units are in modular form
for easy maintenance and trouble shooting.
Microcomputer : The PC-AT (C'rompton Cireaves) controls
the whole testing activity through a custom developed
software. The A/D - D/A cards are incorporated in the
additional ISA slots provided in the PC.
Sofhare : Soh-are is custom developed, menu driven and
user hendly. In addition to testing, the software can also
camjout the calibration of transducers and the pump. Periodlc
calibration is advised for the reliability of testing. After each
test. all the accepted devices are classified in appropriate
ranges according to their pressure-flow characteristics and the
rest is rejected. The results are stored as data files and data
analysis aud printing out can be carried at any time. Adequate
\-ariable timing - high at low flow and low at high flow - is
given for deariation. Once the devices are mounted on the
holder. the 1 % hole process of testing is antomatic. minimising
the operator fatigue and errors.
I hc PC controllcd \? \tern dc.c eloped has been put in to usc
1 he modular forrn of construction mahes the 44 3tem economic
and \ci\atde E \en thou& thc q,liteni I\ m\tom designed. duc
io it\ modiilaI appioacb. the senicmg and tiouble \hooting
Laii bc ~ ~ ~ i t d out b.r the mer induztc hclf
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