Note: Descriptions are shown in the official language in which they were submitted.
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IMPROVEMENTS RELATING TO HAND HELD ANALYTICAL DEVICES
Field of the Invention
[0001] The present invention is related to an improved handheld analytical
device and,
more particularly, to an improved handheld analytical device which
incorporates a static
discharge element.
Background of the Invention
[0002] Handheld meters that are used for analysis of clinical samples, for
example blood,
interstitial fluid, urine, at the bedside, in the doctor's clinic or for home
use, can be
adversely affected by electrostatic discharge. Such meters, which are often
based on the
principles of electrochemical detection, typically make use of disposable test
sensors. Test
sensors are inserted through a small aperture in the case of the meter,
wherein they make
contact with a port. The port contains a series of connectors that make
electrical contact
with the test sensor. Proper contact is required for the correct operation of
the analytical
system. Typical measurements that may be made using such technology include
glucose,
HbAlc, ketones, and hematocrit.
(0003] Static electricity will build up in the body of a human ~.valking
around a room with
a floor covering of man-made fiber, for example nylon carpet or vinyl floor
covering;
similarly sitting on a stool or chair of man-made materials can also lead to
the build up of
static within the human body. It is not uncommon for static charge exceeding
30kV to be
developed, depending upon the temperature and relative humidity of the
environment.
Static will discharge from a body when it approaches or contacts material of
differing
potential, or is connected to ground. Static discharge will typically follow
the easiest route
to ground, thus for example; lightning is conducted to ground through a
pointed lightning
conductor attached to a building in preference to discharge through the
building itself. As
a general rule, static charge of 1kV will discharge across an air gap of lmm,
thus a 30kV
charge could potentially bridge a gap of 30mm.
[0004] When someone that has developed a high static charge uses a handheld
meter as
described above there is a significant risk that discharge of static into the
meter could
occur, particularly when the user inserts a test sensor. The connector within
the port of the
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meter where test sensors are inserted is vulnerable to static discharge. More
specifically,
the circuits and components of the meter that are electrically joined to the
connector of the
port can be physically damaged if they are exposed to static discharge.
Therefore there is a
need to alleviate this problem.
[0005] The discharge of static to a meter, or more specifically the port of
the meter, could
occur under several circumstances, for example: i) a user who has developed a
high static
charge picks up a meter that has been kept in a bag or cupboard, i.e. the
meter is at a
different potential charge to the user; ii) a user who has carried a meter in
their pocket
hands it to another individual, for example a health care professional, who
has a different
potential charge; iii) the meter comes in contact with an object of different
charge such
that the gap between them is in the range for static discharge to occur. Under
each of these
circumstances and possibly others the discharge of static to the connector in
the meter
could lead to physical damage of the critical circuits and components. Since a
malfunctioning meter can be the result of electrostatic discharge (ESD) there
is a need to
alleviate such effects.
[0006] Methods that are currently in use to alleviate the damaging effects of
ESD on
sensitive circuits and components on a printed circuit board (PCB) involve the
incorporation of surge protection devices, which are costly and relatively
complex
components. The use of such components, which are based on integrated circuit
designs,
adds an additional level of complexity to the circuitry into which they are
incorporated.
There is thus a requirement for further additional testing to validate the
integrity of the of
the PCB assembly. It must he shown that all of the electrical connections on
the PCB have
been correctly formed, free from short circuits or other defects. Thus the
development of
alternative methods and means to alleviate the effects of ESD that can be
incorporated
more readily into a PCB layout are required.
Summary of the Invention
[000.7] The present invention is directed to a meter for the detection of
glucose, the meter
including an opening adapted to receive glucose monitoring strips, the meter
comprising a
conductive pad at the opening arranged such that the strip contacts the pad
when the strip
is inserted into the meter and a plurality of conductive spikes connected to
the pad and
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arranged to contact the strip as it is inserted into the meter to discharge
any static
electricity resulting from the insertion of the strip into the meter. The
present invention is
further directed to a meter wherein the conductive spikes include a plurality
of pointed
ends positioned at the opening. The present invention is further directed to a
meter
wherein the conductive spikes are connected to an electrical ground. The
present invention
is fiu-ther directed to a meter wherein the meter includes a battery and the
conductive
spikes are connected to the battery. A meter according to Claim 4 wherein the
battery
includes a negative terminal and the conductive spikes are connected to the
negative
terminal of the battery.
Description of the Figures
(0008] The invention will now be described, by way of example only, with
reference to
the following figures.
[0009] Figure 1 is a perspective view of the inside of a meter showing a prior
art strip port
connector such as that provided in an Ultra or Fast Take meter available from
LifeScan
Inc., Milpitas, CA, USA. The strip port connector is enlarged in the insert
for clarity.
[0010] Figure 2 is a perspective view of the inside of a meter according to
one
embodiment of the invention showing a printed circuit board with a strip port
connector
incorporating an antistatic bar. The strip port connector is enlarged in the
insert to show
the relationship between the strip port connector and the antistatic bar in
this embodiment.
[0011] Figure 3 is a schematic cross section of a meter according to one
embodiment of
the invention with a strip port connector mounted on a printed circuit board
(PCB) with no
strip present.
(0012j Figure 4 is a schematic cross section of the meter of figure 3, showing
a strip
approaching the port of the meter.
[0013] Figure 5 is a schematic cross section of the meter of figure 3, showing
the strip
approaching and entering the meter so as to touch the edge of the spring pin.
[0014] Figure 6 is a schematic perspective view of the meter of figure 3,
showing three
individual spring pins, when no strip is present, along with the antistatic
bar near the front
edge of the PCB, which is the first point of electrical contact for an
incoming strip.
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[0015] Figure 7 is a schematic perspective view of the meter of figure 3, with
a sensor
strip fully inserted, showing three spring pins touching separate contact pads
on the strip.
[0016] Figures 8A and 8C SNOW top and bottom plan views of the strip port
connector, and
Figures 8B and 8D show cross sections through the strip port connector that
indicate the
location and profile of the spring pins.
[0017] Figure 9 shows a plan drawing of the top of a printed circuit board,
which indicates
the location of the antistatic bar according to one embodiment of the
invention and the
contact points that are used to attach the strip port connector.
[0018] Figure 10 shows a plan drawing of the bottom of the printed circuit
board, which
indicates the location of the antistatic bar according to one embodiment of
the invention
and the contact point for the negative battery terminal.
[0019] Figure 11 shows a cross section of the printed circuit board shown in
Figures 10
through line C-C and highlights the antistatic bar on each surface connected
through the
board by a via hole. The negative of the battery terminal is also shown,
connected to the
antistatic bar by a conductive track.
[0020] Figure 12 shows a plan drawing of the upper surface of a printed
circuit board
according to a fourth embodiment of the invention.
[0021] Figure 13 shows a plan drawing of the Lower surface of a printed
circuit board
according to a fourth embodiment of the invention.
[0022] Figure 14 shows a plan drawing of the printed circuit board of Figure
12 showing a
strip port connector in place, indicating the relationship between the case of
the meter in
proximity of the strip port and the PCB.
[0023] Figure 15 shows a cross section taken through Figure 14 through line D-
D and
shows the relation ship between the PCB and the case of the meter.
[0024] Figure 16 shows a set of alternative embodiments of the antistatic bar.
Detailed Description of the Invention
[0025] Figure 1 is a perspective view of the inside of a prior art meter,
showing a
connector that is , used to make electrical contact with a disposable test
sensor for
measuring an analyte or indicator such as glucose mounted on a printed circuit
board 2.
One example of such a meter is an Ultra or Fast Take meter available from
LifeScan Inc.,
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Milpitas, CA, USA. The figure includes an expanded view of the connector for
clarity. A
number of electronic circuits and components (not shown) are assembled on the
surface of
printed circuit board 2 to form a working meter. The circuits terminate at the
connector 6
into which test sensors such as disposable test strips (not shown) are
inserted in
preparation for making a measurement of a clinical sample. The connector 6 has
five
individual spring pin contacts 8, I0, 12, 14 and 16, that make electrical
contact with
individual conductive connection pads on a test sensor (not shown) and in so
doing forms
a complete analytical system.
(0026] The individual spring pins or connectors 8, 10, 12, 14 and 16, which
are resiliently
biased towards the printed circuit board (PCB) 2, are held within a support 4
that is
physically mounted on the surface of PCB 2. In the absence of a test sensor
there is
usually a small air gap, typically less than lmm, between the ends of spring
pins 8, 10, 12,
14 and 16 and the surface of PCB 2. The purpose of this air gap is to ensure
that spring
connectors 8, 10, 12, I4 and 16 are not under stress at the point of
manufacture. If the
stress experienced by the spring pins 8, 10, 12, 14 and 16 is not controlled
at manufacture
it could lead to premature failure of the component and hence the meter.
[0027] The spring pins 8, 10, 12, 14 and 16 are fixed within support 4 mounted
on PCB 2
and form what is termed a strip port connector (SPC) 6. A groove in support 4
provides a
channel 18 on the surface of PCB 2 that allows for guided insertion of a test
sensor (not
shown), such that it makes electrical contact with spring pins 8, I0, 12, 14
and 16. More
specifically electrical contact is made between individual spring pins 8, 10,
12, 14 and 16
and distinct conductive contact pads on the test sensor that allow a
measurement to be
made on the strip by the meter. A conductive pad 17 is provided part way
between SPC 6
and the edge 15 of PCB 2. Pad 17 has two portions on the upper surface of PCB
2 spaced
apart to allow a strip to be inserted into channel 18 without traveling over
the conductive
pad 17. A further part of pad I7 is provided as a continuous bar on the
underside of PCB
2, shown by the dotted box in the figure.
[0028] Figure 2 is a perspective view of the inside of a meter according to
one
embodiment of the present invention, which has been modified to include a
conductive bar
26. The figure shows one possible geometrical relationship between conductive
or
antistatic bar 26 and SPC 6 mounted on PCB 2. SPC 6 is used to make electrical
contact
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with a strip 32 (shown in Figure 7). The figure includes an enlarged view of
SPC 6 for
clarity.
(0029] Conductive pad 26 is located directly in front of SPC 6 on the surface
of PCB 2
with one or more (here three) individual, conductive, spike-shaped pads 68
distributed
across the gap in front of strip channel 18. Spikes 68 point in the direction
of edge 15 of
PCB 2, i.e. towards the direction from which a strip would approach SPC 6.
Conductive
pad 26 has, in this example embodiment, a common rail 64 located at the rear
of the pad
between the spikes 68 and SPC 6. Also, in this example embodiment there is one
identical
conductive pad (not shown) on the underside of PCB 2 directly beneath
antistatic bar 26.
Conductive vias (not shown) are provided between the conductive pads 26 on the
two
surfaces of the PCB at end pads 70. In this embodiment conductive pad 26 is
opposite but
not touching edge 15 of PCB 2. In addition, two parts to pad 26 are provided,
each on one
of the upper and lower surfaces of PCB 2. The two parts may be identical or
similar, for
example each may have the same or different numbers and geometry of spikes 68.
Spikes
68 are closer to the entrance port of the meter (shown as item 28 in Figure 3
for example)
than pins 10, 12 and 14. Therefore when a highly charged item is brought close
to the port,
charge will be induced primarily at the sharp corners of conductive pad 26 and
in
particular at the acute angled corners of sharp spikes 68, instead of pins 10,
I2 and 14.
Both conductive bars 26 on the top and bottom of PCB 2 including spikes 68 are
connected to the ground of the PCB. This helps to divert any spark that may
enter the
meter to PCB ground.
[0030] Conductive pad 26 is an integral part of PCB 2 and can be printed
alongside other
PCB conductive tracks and pads. As such conductive pad 26 requires no
additional
components to be applied to the PCB during assembly. Therefore the manufacture
and
validation of the assembled PCB is simplified when compared with the use of
surge
protection components as described above.
[0031] The meter is based upon a central processing unit (CPU), along with
associated
memory chips, and other components, electrically joined together by conductive
tracks on
the surface of PCB 2. The correct operation of the meter is dependant upon the
CPU being
constantly under power, which is necessary to maintain the real-time clock
function. When
the meter, or more specifically the CPU, is in a power saving mode, i.e. when
it is not
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being used to make a measurement of test sample, spring pins 8, 10, 12, 14 and
16 axe
vulnerable to electrostatic discharge (ESD) from charged objects that come
sufficiently
close for a spark to jump from the object to the pins. Indeed, ESD can occur
at any time
when an object at one potential e.g. a finger, strip or something else, is
brought up to a
meter sitting at a different potential. Equally, the meter is at risk when
under power in the
absence of a strip, which can be the case when a user is making use of in
built data
management facilities of the meter. There is also a risk of ESD damage when a
test sensor
is present in the meter during use. A user, having inserted a test sensor,
places the meter
on a table, for example. The user may then move or walk about the room, during
which
time they may develop a significant static charge. When applying a blood
sample to the
test sensor, ESD could therefore occur.
[0032] As described above, a person can develop static charge in excess of
30kV. If a
meter were to be used by such a person it could therefore experience ESD up to
and
exceeding 30kV, which would imply a discharge gap in excess of 30mm. The
circuits and
components of the meter are vulnerable to ESD especially when the meter is
being
handled by a user or health care professional prior to making a measurement.
The
discharge of static into the meter conducted by spring pins 8, 10, I2, 14 and
16 can lead to
physical damage of the circuits and components of the meter. Thus, following
an ESD
event the meter may no longer function correctly.
[0033] Spring pins 8 and 16 are used to control whether the meter is in power
saving
mode or is ready to make a measurement. The meter never completely switches
off. When
there is no test sensor present within the meter it enters power saving mode
to conserve
battery life; because of an onboard real-time clock the meter can never
completely switch
off. In this embodiment of the invention when a conductive track is introduced
between
pins 8 and 16 the meter is brought out of power saving mode in readiness for
making a
measurement, as described in patent number WO 01/67099 AI (Attorney Docket
Number:
DDI-008 PCT), the contents of which are incorporated herein. Spring pins 10,
12 and 14
are involved with the measurement aspect of the meter; each makes contact with
a specific
electrode pad on the test sensor thereby completing the analytical system,
thus enabling
measurements of test sample to be made.
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[0034] Figure 3 is a schematic cross section of a meter 20 with SPC 6 mounted
on PCB 2
when no strip is present . The meter 20 has an external case 22 which houses
and supports
PCB 2 upon which SPC 6 is mounted along with additional circuits and
components (not
shown) required for functional operation of meter 20. A small hole or strip
port 28 is
provided in the case of meter 20 to allow for insertion of a test sensor (not
shown). Strip
port 28 is adjacent to SPC 6 mounted on PCB 2, such that when a test sensor
(not shown)
is inserted through the strip port 28 it engages with SPC 6. SPC 6 comprises a
support 4
that is physically attached to the surface of PCB 2 and a series of spring
pins 24 that are
resiliently biased towards PCB 2. In this second embodiment of the invention a
conductive
pad 26 is provided on the top of PCB 2 immediately adjacent to edge 15 that is
closest to
strip port 28. A conductive track on the surface of PCB 2 (not shown) joins
conductive
pad 26 to PCB ground, which is represented by a negative terminal of the
system battery.
[0035] The PCB 2, upon which the components and circuits of meter 20 are
assembled, is
prepared according to the standard procedures and practices for manufacturing
such a
component. The copper layers on each surface of the PCB 2 are etched to reveal
the
conductive tracks that define the meter circuit and join the individual
components that are
required for meter operation. It is common for some areas of copper that are
revealed on
the PCB during the etching process to be coated by a layer of gold using the
process of
electroplating. The process of gold coating, which provides an inert
conductive layer, is
generally used when an area of the PCB is designed as a contact point for an
external
component, for example a strip, where a clean electrical bridge is required.
In the present
invention an additional area of copper track is preserved on the upper and
optionally the
lower surfaces of PCB 2 to provide conductive bar 26 at a location closest to
strip port 28
of meter 20. This area of copper is coated with a layer of gold that is
typically .04 to 1 p,m
thick to form bar 26. The gold-coated area 26 is connected to PCB ground. PCB
ground is
effectively the negative terminal of the system battery.
[0036] Because antistatic bar 26, which is directly connected to PCB ground,
is in close
proximity of strip port 28, it will effectively attract and trap most stray
static that
discharges into strip port 28 and conduct it to PCB ground. In so doing,
antistatic bar 26
can allay potential damage to the static sensitive circuits and components of
PCB 2.
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(0037] Figure 4 is a schematic cross section of the meter 20 of Figure 3,
showing a test
sensor herein referred to as a strip 32, approaching strip port 28 of meter 20
. Arrow 30
indicates the direction of movement of strip 32 towards strip port 28. Strip
32 comprises a
base material 36 onto which are screen-printed a series of conductive tracks
(not shown)
that connect electrode pads 34 to sample application area 38. The base 36 of
strip 32 can
be formed using, but is not limited to for example, ploybutylene teraphthalate
available as
Valox FR-1 from General Electric Structured Products, GEC, Pittsfield, MA,
USA, or
polyethylene teraphthalate available as Melinex ST328 from DuPont Teijin
Films,
Hopewell, VA, USA. Such polymeric materials are well known for their electric
insulation
properties and provide a suitable substrate to receive screen-printed
conductive tracks.
[003] Sample application area 38 provides a defined area on strip 32 to which
test sample
such as blood, urine or interstitial fluid can be applied. Electrode pads 34
are in electrical
contact with a series of electrodes beneath sample application area 38. The
electrodes
beneath sample application area 38 typically comprise a "working" electrode,
at which the
relevant measurement is made and a "counter/reference" electrode, which
completes the
circuit and is required for functional operation of strip 32, as described in
patent number
US5,708,247 (Attorney Docket Number: DDI-002 USA). The presence of sample
application area 3 8 over the working and counter/reference electrodes defines
a specif c
dimensional area such that all strips manufactured according to a given design
yield the
same response, within acceptable error limits, when used to analyze a
predefined sample
solution, for example a control standard.
[0039] Strip 32, which is typically disposable, is designed to make a single
measurement
of a clinical sample, e.g. blood, interstitial fluid or urine. Strips can be
used to assay for
the presence of several key indicators that are regularly used in the
management of
patients at the bedside or in the doctor's surgery or for self monitoring in
the home.
Examples of such indicators include, but are not limited to, glucose, lactate,
ketones,
HbAlc or hematocrit.
[0040] A range of strips are available for the measurement of blood glucose;
for example,
the One Touch Ultra strip from LifeScan Inc., Milpitas, CA, USA; the Optimum
Test strip
from Medisense, Abingdon, Oxon, UK; Ascensia Glucodisc from Bayer Plc,
Newbury,
Berks, UK.
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[0041] The conductive tracks (not shown) on the surface of strip 32 that join
electrode
pads 34 to sample application area 38 are close enough to the end or sides of
strip 32 such
that a user handling the strip could make electrical contact with the
conductive tracks.
Thus it is possible for a user holding strip 32 to discharge static
electricity through the
strip to a conductive object, for example the circuits and components of meter
20.
However, it is more likely that ESD can occur to the meter 20 from a user who
has been
separate from the meter for a time, such that there is a potential difference
between the
user and the meter. In particular, ESD from a finger of a user to SPC 6 can
occur, for
example, when the user moves to pick up the meter 20 from a table.
[0042] In the case of the prior art, as depicted in Figure 1, spring pins 10,
12 and 14
conducted ESD power from the user to the circuits and components of meter 20,
leading to
damage of critical system components and ultimately failure of meter 20. The
presence of
antistatic bar 26 in the present embodiment of the invention is intended to
divert ESD
from the user away from spring pins 24 to PCB ground, thus alleviating
potential damage
of the critical system components. This is because a strip, finger or other
object
approaching port 28 "sees" bar 26 before it "sees" pins 24. Also bar 26 is as
close as
possible to port 28, by being at the very end of PCB 2, in other words
immediately
adjacent edge 15. Furthermore, the shape of the antistatic bar 26 is such that
a charge
density will build up around the points and thereby attract any ESD power.
[0043] Figure 5 is a schematic cross section of the meter of figure 3, showing
strip 32
sliding over conductive bar 26 and touching the edge of spring pin 24 . Charge
from strip
32 is conducted to PCB 2 ground by conductive bar 26 either before and/or
during contact
of strip 32 with SPC 6. Any potential difference between meter 20, or more
specifically
the conductive circuits and components on PCB 2, and the incoming strip 32
will have
been equalized by the point of initial contact between strip 32 and spring
pins 24.
Therefore the risk of ESD damage to the circuits and components of meter 20 as
strip 32 is
pressed into contact with spring pins 24 is greatly reduced compared with the
prior art cf.
Figure 1.
[0044] Figure 6 is a schematic perspective view of the meter of Figure 3,
showing three
individual spring pins 10, 12 and 14 each facing forward in the direction of
strip port 28,
when no strip is present. A conductive bar 26 with three forward facing spike
portions 68
to
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is clearly visible at the front edge 15 of PCB 2. Bar 26 and in particular
spikes 68 are the
first point of electrical contact for any spark that may enter strip port 28.
Thus bar 26 will
act to divert most and in some cases alI incoming static charge to PCB ground
and thus
allay potential damage of the critical system components and circuits. The
relationship
between strip port 28 and SPC 6 is also evident. The support 4 defines the
depth to which
an incoming strip 32 can be inserted into meter 20. Spring pins 8 and 16 can
be seen
behind spring pins 10, 12 and 14. In the case of the prior art meter in Figure
1 the absence
of antistatic bar 26 meant that spring pins 10, 12 and 14 were the first and
sharpest point
of contact for any static that could discharge into meter 20 through strip
port 28.
(0045] Conductive bar 26 has been designed in an attempt to attract static
from all paints
outside strip port 28. The sharp points of the three triangular spikes 68 are
intended to
develop a highly charged electric field in the proximity of the points when
approached by
a charged object at a different potential. In other words, charge is induced
at the point of
the spikes. This provides a means to focus and attract the charge on the
charged object that
may enter strip port 28. Thus, when an oppositely charged body comes in close
proximity
of strip port 28, a spark will jump between the spikes 68 of antistatic bar 26
and the
incoming object, for example the finger of someone picking up a meter 20 that
has been
on a table, discharging the charge safely to PCB ground.
[0046] The unique design as well as the close proximity of conductive bar 26
and in
particular in this embodiment the spikes 68 to the edge 15 of PCB 2 is such
that any highly
charged object that approaches strip port 28 will discharge to it in
preference to spring
pins 10, 12 and 14. Static is thus diverted to PCB ground away from the static
sensitive
components and circuits of meter 20, conducted by bar 26. Thus the risk of
potential
damage of the meter 20 and mare specifically the static sensitive components
is greatly
reduced compared with the prior art. Spikes 68 may have an obtuse,
perpendicular or more
particularly an acute angle at the sharp point. Indeed the spikes may have a
sharp point
and an elongate body before joining rail 64 (as seen in Figures 12, 13 and
14).
[0047] Figure 7 is a schematic perspective view of the meter of Figure 3, with
a strip 32
present in SPC 6, showing spring pins 8, 10, 12, 14 and 16 touching separate
contact pads
on strip 32. In this embodiment of the invention the initial contact between
spring pins 12
and 16 through electrode pad 44 on strip 32 provides a signal to the CPU of
meter 20 that
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brings it out of power saving mode in readiness to make a measurement of test
sample.
The use of spring pins 12 and 16 in this way is an improvement over the prior
art, cf.
Figure 1, wherein the connecting of spring pins 8 and 16 by a unique electrode
pad on
strip 32 was required to bring the CPU out of power saving mode, as described
in patent
number WO 01/67099 Al (Attorney Docket Number: DDI-008 PCT). In the present
invention the use of spring pins 12 and 16 as the mechanism to bring the CPU
out of
power saving mode, instead of spring pins 8 and 16, allowed for simplified
manufacturing
of strip 32. The connection between spring pins 12 and 16 is made by electrode
pad 44 on
test strip 32. The use of electrode pad 44 in this way has virtually no impact
on the
measurement performance of strip 32 or meter 20.
(0048] The connections made between spring pins 12 and 14 and electrode pads
44 and 46
on strip 32 respectively are involved with the functional aspect of meter 20.
Electrode pad
44 is connected to the counter/reference electrode and electrode pad 46 is
connected to the
working electrode beneath sample application area 38 on strip 32. When a test
sample is
applied to sample application area 38 a measurement reaction is initiated and
a signal that
is proportional to the concentration of analyte, for example glucose, is
generated and
displayed as a concentration value on the display of meter 20. Spring pins 8
and 10 of SPC
6 serve no functional purpose in this embodiment of the invention, they exist
because of
the common component usage between different meter systems, cf. the Ultra or
Fast Take
Meters produced by LifeScan Inc., Milpitas, CA, USA, as shown in Figure 1.
Although
spring pins 8 and 10 are electrically connected to PCB 2 at points 56 and 62
respectively,
as shown in Figure 9, no conductive tracks exist on PCB 2 beyond the surface
mounting
points. The risk of ESD damage due to contact with spring pins 8 and 10, and
indeed
spring pin 12 which represents PCB ground, is thus negligible compared with
spring pins
14 and 16, which are electrically connected to the functional circuits and
components of
the meter 20.
[0049] Figure 8A shows a plan view from above of support 4, with the
associated spring
pins 8, 10, 12, 14 and 16. The figure shows the relative positions of spring
pins 8, 10, 12,
14 and 16 respectively within support 4. Spring pins 8 and 16 are fixed within
support 4
such that their ends lie beneath spring pins 10 and 14 respectively. Thus when
strip 32 is
inserted into SPC 6 assembled on PCB 2 spring pins 10, 12 and 14 make initial
contact
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with strip 32, followed by spring pins 8 and 16; ESD is therefore more likely
to occur to
spring pins 10, 12 and 14. A means to prevent or greatly reduce the likelihood
of ESD
from a charged object to spring pins 10, 12 and 14 is preferably required.
[0050] Figure 8B shows a cross section taken through Figure 8A along the line
marked A-
A. The cross section A-A shows the shape of spring pins 10, 12 and 14, and
more
specifically represents the forward facing spring pin 12 that makes contact
with electrode
pad 44 on strip 32. Arrow 54 points to the portion of spring pin 12 that makes
direct
electrical contact with electrode pad 44 on strip 32. The profile of spring
pin 12 is such
that when SPC 6 is assembled on the surface of PCB 2 an incoming strip 32 will
cause pin
12 to move upwards away from the surface of PCB 2. The material from which the
spring
pins 8, 10, 12, 14 and 16 are manufactured is uch that when a strip 32 is
present in the
SPC 6, the resilient bias of the spring pins 8, 10, 12, 14 and 16 towards the
surface of the
PCB 2 holds strip 32 in place. When the strip 32 is removed from SPC 6, spring
pins 8,
10, 12, 14 and 16 return to their original position.
[0051] Figure 8C shows a plan view from below of support 4, with the
associated spring
pins 8, 10, I2, 14 and 16: The figure shows the relative positions of spring
pins 8, 10, 12,
14 and 16 respectively within support 4. The dimpled ends of spring pins 8 and
16 that
make contact with strip 32 are evident. The support legs 50, that are used to
attach support
4 to PCB 2, are also shown.
[0052] Figure 8D shows a cross section taken through Figure 8C along the line
marked B-
B. The cross section B-B shows the shape of the spring pins 8 and 16, which
are involved
with the switching on/off of meter 20. Arrow 52 points to the dimple on the
end of spring
pin 16 that makes electrical contact with the surface of strip 32. The spring
pins are
deflected away from the surface of PCB 2 when a strip 32 is inserted into SPC
6. The
profile of spring pins 8 and 16 differs from that of spring pins 10, 12 and 14
because they
experience different mechanical forces when strip 32 is inserted.
[0053] Figure 9, which represents one embodiment of the present invention,
shows a plan
drawing of the top surface of PCB 2, which indicates the location of
conductive bar 26 and
holes 58 that are used to attach SPC 6 to PCB 2. The support legs 50 of
support 4 (see
Figure 8) locate within holes 58 through the surface of PCB 2, wherein they
are fixed.
Spring pins 8 and 16 are electrically bonded to points 56 and 57, whereas
spring pins 10,
13
CA 02549212 2006-06-02
WO 2005/053525 PCT/GB2004/005074
12 and 14 are electrically bonded to points 62, 63 and 65 respectively on PCB
2. Bar 26
comprises a common rail 64 onto which are fused the static attracting spikes
68 and
connection pads 70. There are two holes, referred to as conductive vias that
pass through
the surface of PCB 2 beneath connection pads 70. The via hole is used to make
electrical
connections between copper tracks on each surface of PCB 2, permitting
circuits to
continue from one side of the PCB to the other.
[0054] Figure 10 shows a plan drawing of the bottom surface of PCB 2, which
indicates
the location of bar 26 and the contact pad 74 for the negative battery
terminal. When PCB
2 is assembled within the outer casing of meter 20, the squat spikes 68 of bar
26 are
directly aligned behind strip port 28. Virtually any static entering strip
port 28 will thus be
conducted to PCB 2 ground by antistatic bar 26.
[0055] The integration of antistatic bar 26 as part of the basic conductive
copper track on
the surface of PCB 2 provides a simple and reproducible means to equip PCB 2
with
inherent protection from ESD. It is a technique that can be readily adopted
for the
manufacture of a range of PCB layouts that are to be used in the production of
meters
designed to accept disposable test sensors for the measurement of analytes and
indicators
of clinical significance, for example blood glucose. However, such meters
could equally
be used to measure indicators of environmental or other significance, where
the analyte of
interest can be made in aqueous solution.
[0056] Figure 11 shows a cross section through the PCB shown by line C-C in
Figure 10.
The section highlights the conductive bar 26 and negative 'terminal of the
system battery
74. The bar 26. comprises two portions 26A and 26B, one on each side of PCB 2.
Two vias
84 one or sometimes two between each pair of pads 70 form a connection through
PCB 2,
thus providing an electrical bond between the two halves of bar 26A and 26B
respectively.
A conductive track 40 on the lower surface of PCB 2 connects antistatic bar
26B to the
negative terminal of the system battery 74. Thus any static discharged to
antistatic bar 26
is directed to PCB ground and is diverted away from the critical system
components and
circuits. The inclusion of two conductive areas, 26A and 26B, on each surface
of PCB 2
acts to maximize the chance of trapping stray static, thus minimizing the
potential risk of
ESD to the critical system components. Bar 26 is thus situated to fully cover
strip port 28
with respect to incoming sparks that might discharge from a strip 32 or other
charged
14
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WO 2005/053525 PCT/GB2004/005074
object coming sufficiently close to strip port 28 that ESD might occur from
the object to
the conductive circuits and components of the meter.
(0057] Figure 12 shows a plan drawing according to a fourth embodiment of the
invention
of the uppermost surface of a PCB 2. The figure shows a range of conductive
tracks 100
that are involved with the functional aspect of meter 20, and as such they are
shown for
reference only. When PCB 2 is assembled in case 22, strip port 28 is in direct
contact with
the edge 15 of PCB 2. The spikes 68 of antistatic bar 26, which extend to the
edge of PCB
2, therefore terminate at the opening of strip port 28. They are thus placed
to intercept any
sparks that might bridge into strip port 28 from any charged object that comes
sufficiently
close, for example a strip 32, or the finger of a user. The three sharp spikes
68 of bar 26
are each aligned opposite a spring pin 10, 12 or 14 respectively. Induction of
high density
charge fields at the pointed most ends of spikes 68 will therefore
preferentially induce a
spark to jump to bar 26 through sharp spikes 68 instead of to spring pins 10,
12 or 14.
[0058] Figure 13 shows a plan drawing of the underside of the PCB shown in
Figure 12.
The figure shows a range of conductive tracks 100 that are involved with the
functional
aspect of meter 20. Conductive or antistatic bar 26, which exists on both the
upper and
lower surface of PCB 2, are joined through PCB 2 by two pairs of vias beneath
connection
pads 70. Antistatic bar 26 is connected to the negative terminal 74 of the
system battery by
conductive track 40. The presence of antistatic bar 26 on both surfaces of PCB
2 will
minimize the risk of any spark jumping to other conductive points on PCB 2
that might
lead to damage of the static sensitive components of meter 20.
[0059] Figure 14 shows a plan drawing of the PCB of Figure 12 to which has
been added
a strip port connector 6. The figure also indicates the relative position of
case 22 in the
proximity of SPC 6. In particular the close contact between edge 15 of PCB 2
and strip
port 28 is clear. The alignment of spring pins 10, 12 and 14 behind sharp
spikes 68 of bar
26 can be observed. The ends of spring pins 10, 12 and I4, the profile of
which is shown
in Figure 8B, terminate slightly above common rail 64 of the conductive pad
26, as will be
seen more clearly in Figure 15. Strip port 28 is aligned directly in front of
the spikes 68 of
conductive pad 26. The pointed most ends of sharp spikes 68 touch the
interface between
edge 15 of PCB 2 and case 22 at strip port 28. Thus, with respect to an
incoming strip or
other highly charged item that approaches strip port 28, sharp spikes 68 of
bar 26 are the
CA 02549212 2006-06-02
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first conductive element of meter 20 to be encountered. Therefore it is likely
that spikes 68
will induce a high point charge density and thus attract any sparks that
should discharge
from incoming objects.
[0060] The spring pins 8 and 16 are electrically bonded to points 56 and 57
and spring
pins 10, 12 and 14 are electrically bonded to points 62, 63 and 65
respectively. Point 63 is
connected to PCB ground and point 65 is connected to the CPU. The circuit
formed
between points 63 and 65 when a strip is present in SPC 6 in contact with
spring pins 12
and 14 completes the analytical system.
[0061] Figure 15 shows a cross section taken through line D-D of Figure 14.
Support 4 of
SPC 6 is mounted on PCB 2 such that legs 50 penetrate holes within the PCB.
Spring pin
12 is fixed within support 4 such that it faces towards strip port 28.
Conductive pad 26,
comprising parts 26A and 26B respectively, electrically connected through PCB
2 by via
hole 84, commences at edge 15 of PCB 2 and terminates beneath the tip of
spring pin 12.
There is no direct contact between spring pin 12 and conductive pad 26.
[0062] The case 22 of meter 20 abuts edge 15 of PCB 2 to form strip port 28.
The upper
surface of PCB 2, upon which SPC 6 is mounted, is directly aligned with the
surface of the
case within strip port 28. The air gap between edge 15 of PCB 2 and case 22 is
very small
and virtually negligible. However, it is feasible that a spark could penetrate
the gap. Hence
conductive pad 26 is present on upper and lower surfaces of PCB 2 to attract
incoming
sparks and divert static to PCB ground. Incoming strip 32 will thus pass
smoothly along
the semi-continuous surface of case 22 and pad 26, making initial contact with
spikes 68
of conductive pad 26 before entering SPC 6. Spring pins 8, 10, 12, 14 and 16
are deflected
up, away from PCB 2 when a strip 32 is fully inserted into SPC 6.
[0063] Figure 16 shows a range of alternate embodiments of conductive bar 26.
Any sharp
geometry will act to intensify the electric field around the point, and as
such it can be used
to increase the probability that a spark will jump to that point. Static
electricity is known
to bridge between two~conductive bodies of differing electrical potential when
they come
in close proximity. The purpose of bar 26 is thus to equalize any differences
in potential
between the circuits and components of meter 20 and a user, or other charged,
conductive
objects that come sufficiently close to strip port 28 that a spark could
bridge the gap
between the conductive components of meter 20 and the charged object. In
normal use,
16
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WO 2005/053525 PCT/GB2004/005074
predominantly at the point of strip insertion, meter 20 is most vulnerable to
the effects of
ESD.
[0064] The alternate designs 90 to 98 represent various embodiments of
antistatic bar 26,
each making use of different conductor spikes 68. The example embodiment 26 is
such
that maximum protection of strip port 28 is provided. The individual conductor
spikes 68
are aligned equally across PCB 2 behind strip port 28, and more specifically
opposite and
in some cases in line with spring pins 10, 12 and 14, thereby placing them to
cover the
entire strip port 28. The induction of a high charge density at the pointed
most ends of
spikes 68 serves to attract static and thus cause a spark to jump from the
charged object
approaching strip port 28 and antistatic bar 26 in preference to spring pins
10, 12 or 14.
However, if the number of spikes 68 were to be increased this would have the
effect of
reducing the effective point charge density, thus decreasing the likelihood of
a spark
jumping to bar 26 in preference to spring pins 10, 12, and 14. In an extreme
case bar 26
could exist as a solid rectangular bar in front of SPC 6. However, such a
structure would
not induce the same high point charge density, as for example is the case with
the example
embodiment 26. Therefore, such a structure would not be expected to provide
any
significant protection of meter 20.
Advantages
[0065] The present invention presents a simple, robust means of equipping the
PCB used
in the manufacture of hand held instrumentation designed to measure analytes
of clinical
significance with a means to allay the effects of ESD. For example, during the
measurement of glucose using disposable sensor strips that are inserted into a
meter
through a strip port, it is, possible for static to discharge from a user, via
a strip, to the
sensitive circuits and components of the meter. The addition of a conductive
area at the
front edge of the PCB, which is the primary point of electrical contact with
the PCB, acts
to transfer any stray static quickly and efficiently to PCB ground. In so
doing the
potentially damaging effects of ESD on the meter are thus minimized.
[0066] The inclusion of the antistatic bar, which is formed during initial
processing of the
PCB upon which the meter is based, requires no additional components to be
added. It is a
simple, cost effective means of including antistatic protection to the PCB:
The structure of
the conductive or antistatic bar is such that a common rail joins two
conductive pads, one
17
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WO 2005/053525 PCT/GB2004/005074
at each end. The conductive pads are used to integrate two bars, one on each
surface of the
PCB, connected through the PCB by vias. A series of conductive spikes are
provided on
the common rail pointing towards the strip port, the purpose of which are to
induce high
point charge and thus provide a route for electrostatic discharge. The
presence of a
conductive bar on each surface of the PCB at the interface with the case is
intended to
attract and thus divert any static away from the sensitive components of the
meter to PCB
ground.
[0067] The case of the meter and more specifically the port through which
strips are
inserted has been designed such that when the PCB is assembled within the case
a semi-
continuous path is formed. An incoming strip will initially slide over the
upper surface of
the case at the mouth of the strip port. The strip will then make initial
contact with the
conductive pad and more specifically the sharp spikes of the conductive pad
that lie across
the interface between the PCB and the case. The strip will therefore discharge
any static to
the spikes before it makes contact with the pins within the connector that
contact the
individual electrode pads of the strip. Thus potential damage to the static
sensitive
components and circuits of the meter is allayed.
(0068] It will be recognized that equivalent structures may be substituted for
the structures
illustrated and described herein and that the described embodiment of the
invention is not
the only structure that may be employed to implement the claimed invention. In
addition,
it should be understood that every structure described above has a function
and such
structure can be referred to as a means for performing that function.
[0069] While preferred embodiments of the present invention have been shown
and
described herein, it will be obvious to those skilled in the art that such
embodiments are
provided by way of example only. Numerous variations, changes, and
substitutions will
now occur to hose skilled in the art without departing from the invention. It
should be
understood that various alternatives to the embodiments of the invention
described herein
may be employed in practicing the invention. it is intended that the following
claims
define the scope of the invention and that methods and structures within the
scope of these
claims and their equivalents be covered thereby.
[0070] It will be recognized that equivalent structures may be substituted for
the structures
illustrated and described herein and that the described embodiment of the
invention is not
1~
CA 02549212 2006-06-02
WO 2005/053525 PCT/GB2004/005074
the only structure that may be employed to implement the claimed invention. In
addition,
it should be understood that every structure described above has a function
and such
structure can be referred to as a means for performing that function.
[0071] While preferred embodiments of the present invention have been shown
and
described herein, it will be obvious to those skilled in the art that such
embodiments are
provided by way of example only. Numerous variations, changes, and
substitutions will
now occur to hose skilled in the art without departing from the invention. It
should be
understood that various alternatives to the embodiments of the invention
described herein
may be employed in practicing the invention. It is intended that the following
claims
define the scope of the invention and that methods and structures within the
scope of these
claims and their equivalents be covered thereby.
19
