Integrated circuit hydrated sensor apparatus

A plastic covered nonconducting substrate with an electrical circuit means is secured to the extent to withstand the presence of liquids in contact with the substrate. The covered substrate can have the substrate with one or more fluid preconditionable electrical components, a housing secured to the substrate to maintain contact of the preconditioning fluid with the electrical component like a sensor, and moisture impervious seals to cover openings in the housing for the disposition of the preconditioning fluid in the housing for contact with the electrical component on the substrate. The housing can have one or more parts and have one or more channels for containing the preconditioning fluid. The electrical component can be an improved electronic wiring board having a thermistor and at least one blood gas sensor supported, in close relation, one to the other, on one side of the board and a heater supported on the other side of the board to provide heat in response to temperature sensed by the thermistor, to at least the region where the thermistor and the blood gas sensor are positioned on the board to control the temperature of the region of the board within a narrow distribution of temperatures.

The present invention is directed to a sensor apparatus having hydrated 
membranes present on a nonconducting substrate that also has present an 
electrical circuitry. More particularly, the present invention is directed 
to the sensor apparatus having hydrated membranes on a ceramic substrate 
that has an integrated circuit produced by such techniques as silk 
screening, thick film and/or thin film processing. 
Also the present invention is related to an improved electronic wiring 
substrate like a wiring board useful for detecting one or more analytes 
and their amounts in fluid samples. 
BACKGROUND OF THE INVENTION 
Numerous methods and apparatus exist in the art for measuring chemical 
components of fluids. For instance, when the fluid is a liquid or liquid 
with a dissolved gas with or without the presence of solids, it may be 
necessary with current technology to transport a sample to a location for 
testing. With centralized testing, the bulky, stationary, elaborate and 
sophisticated equipment performs the analysis on a practically endless 
number of samples. An example of this is the qualitative and/or 
quantitative measurement of constituents or analytes of blood. For 
instance, the measurement of blood gases, usually a measure of the partial 
pressures of oxygen and carbon dioxide, along with the pH from a sample of 
arterial blood gives the state of the acid base balance or the 
effectiveness of both the respiratory and cardiovascular systems of the 
human or vertebrate body. For measuring constituents of blood, the blood 
sample is drawn from the patient and usually, as in the case of blood 
gases, transported to a central location for testing. 
This technique of transporting the sample to stationary measuring equipment 
can lead to problems. Ingenious technology has broached solutions to 
maintain the original composition of the fluid during transportation. 
Elaborate designs for syringes used in taking the blood samples overcame 
some problems that resulted in inaccurate readings of the particular 
chemical constituent being measured. For instance, for determining blood 
gas composition, the problem of air contamination in the collected sample 
was solved by the use of liquid heparin as an anticoagulant. 
Unfortunately, this introduced a sample dilution problem. Subsequent 
development resulted in the use of heparin in the dry state as opposed to 
the liquid state to avoid this dilution. Also, elaborate designs are 
provided for proper mixing of the sample after transportation but before 
testing. Even with these improvements, there are many reports in the 
literature that suggest that the values obtained in the measurement of 
blood gases depend on the type of measuring equipment and the technique 
for sample collection. 
The art also has attempted to develop more portable measuring equipment 
rather than the fairly expensive nonportable equipment that engender the 
elaborate and cumbersome transportation techniques. Devices that are very 
portable could shorten or overcome transporting the sample altogether so 
that a patient's blood gases could be measured at the bedside in a manner 
similar to measuring a patient's temperature. U.S. Pat. Nos. 3,000,805 and 
3,497,442 show two such devices. The former has electrodes located on a 
syringe plunger and the latter has electrodes placed on the syringe well 
to conduct the measurements. The electrodes are the sensing devices for 
the blood gases. In the allowed U.S. patent application Ser. No. 
07/343,234, Applicants' assignee describes and claims a portable blood gas 
sensor which includes electrodes fabricated from a conventional silk 
screening process where the electrodes are screened on to a ceramic 
substance. Typically, these electrodes are used along with an electrolyte 
and analyte permeable membrane that covers the sensor. Some of these 
membranes may be hydratable membranes that can be stored in a dry state 
and hydrated just prior to use. 
It is an object of the present invention to provide a sensor assembly 
apparatus that utilizes at least one hydratable membrane that can be 
useful in portable measuring devices or can be placed in catheter lines or 
actually utilized with stationary equipment where the apparatus allows for 
the hydrated state of the membrane. This gives the advantages of: 
ready-to-use sensors, establishment of a stable electronic operation with 
stable potential for potentiometric type sensors and maintenance of 
electrolytic contact between electrodes in amperometric sensors, 
electrolyte present for reference electrodes, and/or reduced voltage drift 
like that experienced during a hydration step for dry sensors with 
hydratable membranes. 
Placement of the all of the components, including the heater, on the wiring 
board can result in the maximum utility and capability of these components 
and minimize power consumption. 
SUMMARY OF THE INVENTION 
The foregoing objects and others gleaned from the following disclosure are 
accomplished by the sensor assembly of the present invention. 
The preconditioned electrochemical sensor assembly of the present invention 
has a sensor element that is a nonconducting substrate having at least one 
hydrophilic membrane and an electrical circuitry means, a housing to 
enclose the sensor element where the housing allows for at least one 
channel to pass over at least one sensor, a hydrating fluid occupying the 
portion or portions of the channel or channels over the sensor or sensors, 
and seals that are substantially impervious to at least moisture placed in 
or on the channel to maintain the hydrating fluid in contact with the 
hydrophilic membrane. The sensor and the electrical circuitry are in 
electrical contact with the sensor at least to convey the electrical 
impulses from the sensor to an instrument to read the electrical signals. 
Additionally, the electrical circuitry can have additional components such 
has additional electrodes and leads therefor and heater and temperature 
regulator. The housing encloses the sensor element, and the electrical 
circuitry of the sensor element is electrically isolated from the 
hydrating fluid in the channel or channels to avoid leakage current or 
short circuiting of the electrical circuitry means. The channel is 
constructed to provide fluid flow to, over, and from the one or more 
sensors and to allow for ingress and egress from the housing. 
In a narrower aspect of the present invention, the preconditioned 
disposable electrochemical sensor assembly for measuring analytes in 
fluids has: a) a housing, b) sensor element that has a nonconducting 
substrate with more than one hydrophilic-membrane-containing analyte 
sensors and with electrical circuitry means in electrical contact with the 
sensors at least to convey the electrical impulses from the sensor, c) a 
hydrating fluid positioned in fluid contact with the hydrophilic polymeric 
membrane of the sensor, d) seals that are substantially impervious to at 
least moisture to maintain the hydrating fluid in contact with the 
hydrophilic polymeric membrane of the sensor, e) electrical isolating 
means to maintain electrical separation between the hydrating fluid and 
electrical circuitry means of the sensor element. 
In this aspect of the invention, the housing has a first and second 
opposing section where each section has an exterior and interior surface. 
The sections when matched together form an interior space and at least one 
channel. The former allows for placement of the sensor element within the 
housing while the latter allows for fluid contact between the hydrating 
fluid and the hydrophilic polymeric membrane or membranes of the sensors. 
The channel has two opposing openings to allow fluid flow through the 
channel from a receiving opening before to an exit opening after the 
sensors. The receiving opening is suitable for attachment to a sample 
receiving means and the exit opening is suitable for attachment to a 
collection means such as a syringe or reservoir in general. The interior 
space of the housing communicates with the channel to contain the sensor 
element so that the sensor or sensors that are on the substrate are so 
disposed to lie in the path of the channel for fluid contact with the 
hydrating fluid. The first and second sections can be adhesively connected 
to improve their attachment to each other. The housing also allows for 
communication from the electrical circuitry means to the reading 
instrument. Such an instrument could be one that takes the signals from 
the sensor through the electrical circuitry and as a self-contained, 
hand-held, preferably battery powered monitoring instrument or analyzer 
processes the signals and displays the information in a digital or paper 
mode to the operator. 
The other components of the invention are arranged in or on the housing in 
a manner to allow the sensor's use in detecting the component of interest 
in the fluid and to maintain the hydrophilic polymeric membranes of the 
electrochemical sensor in a hydrated state prior to use, and to isolate 
the hydrating fluid and the electrical circuitry means. The sensor element 
is configured, arranged, and placed in the interior space of the housing 
to assist in maintaining electrical isolation between the electrical 
circuitry and the hydrating fluid. The hydrating fluid is chiefly an 
aqueous fluid with an effective composition to hydrate at least to a 
partial degree but better to a substantial degree the hydrophilic 
polymeric membranes. The sealing means covers the receiving opening of the 
channel and the exit opening of the channel and can be two separate seals 
in adhering association to the housing so as to cover these openings. The 
seal can have one or more surfaces where at least one surface is 
substantially non-oxidizing metal such as aluminum that is useful with an 
adhesive-type polymer. The adhesive-type polymer can be used either as an 
application to the surface to be sealed or as another surface of the seal. 
The seal is fixedly attached to the housing by a chemical means and/or by 
a mechanical means. The electrical isolating means occupies an effective 
portion of the interior space of the housing not occupied by the sensor 
element or the channel and not interfering with the contact between the 
sensor element and the channel in order to obtain electrical isolation of 
the electrical circuitry means from the hydrating fluid in the channel. 
The electrical circuitry means for use with the sensor element with the 
aforediscussed sensors and with the housing or other sensors and housings 
known to those skilled in the art can be an improved wiring board that 
includes the nonconducting substrate. In addition to the at least one 
analyte sensor and the substrate, the electronic wiring board of the 
present invention can have: 1) a thermistor in close relation to the at 
least one analyte sensor supported on or to the substrate, and 2) a 
heater, also supported on the substrate. The heater provides heat in 
response to the temperature sensed by the thermistor to at least the 
region where the thermistor and the analyte sensor are positioned on the 
board. This arrangement controls the temperature of the region of the 
board within a narrow distribution of temperatures and thereby increase 
the sensor's accuracy, and connecting means supported on the board for 
connecting the board to an external electrical source. 
In a narrower aspect, the improved electronic wiring board is manufactured 
using thick film or thin film layered circuit technique or a combination 
of these, and the thermistor and the one or more analyte sensors are 
supported in the same plane on the substrate wherein the analyte sensors 
are blood gas sensors of one or more of the following types: an oxygen 
sensor, a carbon dioxide sensor, and a pH sensor. Also the connecting 
means includes plurality of external leads, and a resistor is supported on 
the substrate on the same side as the heater and commonly connected to one 
of the external leads with the thermistor, dividing the voltage 
therebetween. Although it is possible to have the resistor and the heater 
each electrically connected to external leads. The temperature coefficient 
of the thermistor can be positive or negative and the temperature 
coefficient of the resistor is substantially zero. Also the thermistor and 
resistor values are allowed to vary over several orders of magnitude as 
lone as the two can be made equal at the calibration temperature. 
Additionally, the connecting means further includes a plurality electronic 
conducting pathways individually and electrically connecting each of the 
sensors and the thermistor with external leads provided on the substrate 
at the end of the pathways. 
Also, the heater can be powered by a controlled DC voltage whereby the 
heater is regulated by a combination of proportional, integral and/or 
derivative controls thereby reducing the amount of overshooting or 
undershooting by the heater of a predetermined temperature. The external 
leads are positioned on the same side of the substrate as the resistor and 
the heater. The electronic conducting pathways of improved electronic 
wiring substrate can individually and electrically connect each of the 
sensors and the thermistor on one side of the board with external leads 
provided on the other side of the board through a plurality of holes in 
the board. Additionally the temperature sensor including the thermistor 
and the resistor can be calibrated by laser trimming of the resistor to 
produce a ratiometric output proportional or inversely proportional to 
temperature. 
Also, the improved electronic wiring board wherein the oxygen sensor is an 
electrochemical cell can have a anode and a cathode, each connected to an 
external lead. Also the oxygen sensor can include an oxygen permeable 
membrane covering, in a fluid tight manner, and an opening in the board 
can contain an electrolyte, and the anode can be grounded on the board to 
thereby assure that the potential of the electrolyte is the same as the 
anode potential. 
Additionally, the improved electronic wiring board can have at least one 
reference electrode, to provide an accurate reference potential, supported 
on the board and it can be electrically connected to a electronic 
conducting pathway. Although it is possible to have one reference 
electrode present on the substrate and it is supported on the substrate 
and it is electrically connected to a electronic conducting pathway 
extending from the anode. The nonconducting substrate is a flat 
substantially thin ceramic substrate layer that has a patterned metallic 
layer provided on the ceramic substrate layer. The metallic layer can be 
formed on the substrate by depositing a metallic printing paste on the 
substrate to form electronic conducting pathways and the electrodes of the 
sensors and the electrode of a reference electrode. The metallic layer can 
be encapsulated with at least one layer of a chemically stable and 
moisture resistant encapsulant that provides electrical isolation of the 
electronic conducting pathways from the electrolyte and sample like blood. 
The wiring substrate as described can operate even after several months of 
storage. The thermistor provided on the ceramic substrate layer, can be 
encapsulated with at least one substantially thin layer of a chemically 
stable and moisture resistant encapsulant.

DETAILED DESCRIPTION AND PREFERRED EMBODIMENT OF THE INVENTION 
In the side elevational view of FIG. 1, the general arrangement of the 
sensor assembly is shown. Housing 10 is made of any fairly rigid moldable 
material such as rigid thermoplastic polymers although thermosetting 
polymers can also be used. A suitable example is a methyl methacrylate 
styrene butadiene terpolymer and rigid plastics such as polyesters like 
polyethyleneterephthlate or polycarbonate or blends or alloys thereof and 
other similar materials known to those skilled in the art. The housing 10 
can be any basic geometric shape suitable for containing a channel 12 and 
sensor element 14. The number of parts comprising the housing can range 
from 1 to a plurality, but two parts are preferred. A single part housing 
is at least that which sufficiently provides the channel for fluid 
communication with the one or more sensors 18 on sensor element 14. In 
this arrangement the sensor element 14 can actually form one side of the 
housing. The housing also supplies an opening for an electrical attachment 
means 16 for electric attachment to the electrical circuitry of sensor 
element 14. The sensor element 14 has at least one sensor 18 with a 
hydrophilic membrane where part of the sensor is electrically connected to 
electrical circuitry 20 and both the sensor 18 and electric circuit means 
20 are on a nonconducting substrate of sensor element 14. The sensor 18 is 
located on element 14 and channel 12 and element 14 are arranged in 
housing 10 in a manner so that sensor 18 and channel 12 can be in fluid 
contact with each other when channel 12 is filled with a hydrating fluid 
22. 
Housing 10 has at least one and preferably two openings, 24 and 26, 
arranged along channel 12 at different locations from each other in 
relation to sensor element 14. This arrangement allows hydrating fluid 22 
that is subjected to fluid pressure from either opening 24 or 26 to flow 
across sensor element 14 and contact the one or more sensors 18. Channel 
12 can have any shape that allows for laminar flow of fluid through it in 
the vicinity of the one or more sensors 18 along channel 12. Also, the 
openings 24 and 26 are sealed by a substantially moisture impervious seal 
28 and 30, respectively. The opening 26 can serve as an inlet to or outlet 
from housing 10 that is preferably formed by conical tip 36. Also, the 
housing at the other end of the sensor element 14 from opening 26 can have 
a flared end 40 encompassing opening 24 that is formed by tip section 38, 
which preferably has a cylindrical exterior and a conical interior. The 
tip 38 is surrounded by flared end 40 which has an inner annular space 42 
between the external rim 44 of the flared end 40 and the external surface 
of tip section 38. The openings 24 and 26 for housing 10 shown in FIGS. 1 
and 2 are preferably aligned in the same plane and along the same axis at 
opposite ends of the channel 12 so channel 12 passes longitudinally 
through the housing along the same central axis. This arrangement provides 
sufficient support of the channel by the housing to receive and/or expel 
fluid through the channel with pressurized movement. Preferably, the 
sections 36 and 38 of housing 10 are at opposite ends of the housing 10 
and contain portions of the channel 12 along with openings 24 and 26. The 
flared end 40 can also have one or more external ribs like 50 for ease of 
manipulation or handling of the housing 10. The attachment of sections 32 
and 34 can be assisted by a guiding member and guiding slot shown together 
in FIG. 1 as 52 
Tip sections 36 and 38 allow for connection or coupling to a device to 
provide fluid pressure, rapid fluid flow, or suction to cause the fluid 
with an analyte, for example, to be measured to pass, preferably in 
non-capillary action or flow, in measuring contact with the one or more 
sensors 18. The tip section 38 distally located from tip section 36 can be 
similar to tip section 36 as shown in FIG. 4 or can be adapted and 
preferably is adapted to connect with a distal or needle-end end of a 
syringe. The distal end of the syringe fixedly engages the housing 10 
through the annular space 42 and fixedly engages with the housing through 
attaching means 46 and 48. Preferably, the shape of tip 36 is of a 
standard outer diameter to allow for connection to sample gathering means 
or fluid withdrawing means such as needles or tubing or conduit from 
catheters or tubing in multi-sequential analyzing equipment. Most 
preferably, the shape is suitable for Leur attachment either slip or lok 
(lock) to a sample gathering means not shown in FIG. 1 such as a needle 
for a syringe. 
Housing 10 preferably has one section 32 and another section 34 which have 
matched attachment means (not shown in FIG. 1 but shown in subsequent 
Figures) for connection to each other. Sections 32 and 34 fixedly engage 
to form the housing 10 having one or more internal spaces (a portion of 
which is shown in FIGS. 4, 5 and 7 as 82) for placement of sensor element 
14. The internal space 82 need not be of any particular geometric 
configuration just so long as sensor element 14 fits into the space. The 
internal space 82 and sensor element 14 are preferably of matched 
configuration and are preferably generally rectangular. Preferably, one 
section 32 comprises a substantial portion of housing 10 as shown in FIG. 
4 and the other section 34 is a cover for the back of sensor element 14 
occupying internal space 82 of FIG. 4. With this arrangement and with the 
internal space 82 having dimensions that closely match those of the sensor 
element 14 for a snug fit of the latter into the former, the sections 32 
and 34 can assist in providing electrical isolation between the hydrating 
fluid 22 and the electric circuit means 20. The former is at least in 
channel 12 and the latter is on sensor element 14. Preferably, section 32 
has the tip sections 36 and 38 and all of the flared end 40 and forms a 
portion of channel 12 and any other channels that are present. The 
remaining portions of the channel 12 or other channels are formed by 
sensor element 14 occupying the internal space 82 so that the surface with 
one or more sensors as 18 actually forms a wall of the channel 12 as shown 
in FIG. 1. Any arrangement or configuration other than that shown in FIG. 
1 can be used that allow the two sections 32 and 34 to engage and form 
housing 10 with one or more internal spaces for placement of sensor 
element 14 so that the sensor 18 is in fluid contact with hydrating fluid 
22 that is in channel 12. 
Similar numerals are used throughout the drawings to denote the same 
feature in each of the drawings. The bottom view of sensor housing 10 
shown in FIG. 2 along lines 2--2 of FIG. 1 highlights the preferred 
matched configuration of sections 32 and 34 in a top and bottom 
relationship. Section 34 preferably matchedly engages section 32 through 
guide member and slot 52 of sections 34 and 32, respectively, shown better 
in subsequent drawings from the inner surface of bottom 34. In FIG. 2, the 
slot of 52 is shown in phantom as is channel 12 except for the cutaway 
portion showing hydrating fluid 22. Also shown in phantom is electrical 
cable means 16 as it enters housing 10. Slot 48 clearly shown in FIG. 2 
provides for fixed attachment with a syringe not shown in FIG. 2 at the 
distal or outlet end of housing 10. Preferably, as shown in FIG. 2 an 
electrical insulating means 56 is present. The electrical insulating means 
54 can be any material that can occupy spaces between housing sections 32 
and 34 and sensor element 14 other than the one or more channels and 
electrical attachment means 16 to assist in providing for electrical 
isolation. The insulation can restrict any contact between any hydrating 
fluid 22 and the electric circuit means 20 to reduce the possibility of 
any short circuits or leakage current. This material should have the 
following characteristics: an insulation factor of around 10.sup.14 
ohms/cm.sup.2 and substantially impervious to moisture and preferably 
curable at a temperature of less than around 60 degrees Centigrade. 
Nonexclusive examples of a suitable material include: epoxy polymer, 
modified epoxy molding compound such as brominated epoxies, epoxy molding 
compounds, polyimides, unmodified polyimides like PMDA-ODA and BTDA 
ODA-based polyimides, Poly(amide-imide) polymers, modified polyimides 
having modification from diamic acid additives, siloxane polyimides, and 
high temperature polymers like silicone polymers, and polyarylene ether 
polymers. A particularly suitable material is a bisphenol A 
epichlorohydrin type epoxy polymer like that available from the Hysol 
Division of The Dexter Corporation in Industry, Calif. 91749 under the 
trade designation EE4207. 
Seals 28 and 30 FIGS. 1, 2, 4 and 5 can be and preferably are substantially 
impervious to air, and they may be comprised of a single layer or 
multilayer laminate. A suitable single layer material includes metal foil 
that is capable of sealing by a polymeric material that can be 
heat-treated or RF (radio frequency) treated for sealing. The multilayer 
laminate material ordinarily has an interior layer of polymeric material 
and outside this layer a metal foil layer. A typical laminate can have two 
or more layers and may have an additional outer polymeric layer to 
facilitate abrasion resistance or printing on top of the metal foil layer. 
A non-exclusive example of the metal foil is aluminum. A three layer 
laminate suitable for the seal of the present invention can have from the 
exterior surface to the interior layer the following: 1) nylon, polyester, 
polyethylene or polypropylene, 2) aluminum foil, and 3) an inner heat 
sealable polymeric layer such as polyethylene, polypropylene, 
polyvinylidene chloride or nylon. A nylon-foil-polypropylene laminate of, 
i.e., 17 grams per square meter nylon, 32 grams per meter squared 
aluminum, 45 grams per meter squared polypropylene or of a suitable 
example is a polyfoilpolylaminate which is a three-layer composite having 
an aluminum foil intermediate layer and an inner and outer layer of 
polypropylene. The seals are puncturable and preferably can and form a 
seal that can withstand gamma radiation sterilization. The seals 
preferably have at least two sections--one section 28a and 30a away from 
the mouth or opening of the channel and another section 28b and 30b in 
contact with the housing 10 to seal the openings 24 and 26, respectively 
of the channel 12. The "a" seal sections can be at least an air impervious 
metal foil, preferably aluminum, and the "b" seal sections can be an 
adhesive material. Preferably, the seals 28 and 30 are a paper-backed 
aluminum foil coated with a clear heat sealable coating. The coating can 
be a blend of a high molecular weight ethylene and vinyl acetate 
copolymer. A nonexclusive example of a suitable material is an aluminum 
foil having a heat seal polyester film available under the trade 
designation "Foilseal 3-6" available from Selig Sealing Products, Inc. 
17w745 Butterfield Road, Oakbrook Terrace, Ill. 60181 . Such materials can 
have a gas transmission for oxygen that is nil and a water vapor 
transmission which ranges from around 0.005 to 0.059 GS 
(grams)/CSI(100in.sup.2)/24 hours at 90 percent relative humidity. Such 
materials provide a seal that when securely attached across the openings 
24 and 26 of the channel 12 provide substantial imperviousness to air. 
These values are obtained on a Permatran-W6 for water transmission and an 
Ox-tran 1000 for oxygen transmission, and both pieces of equipment are 
available from Mocon, Modern Controls, Inc., 4220 Shingle Creek Parkway, 
Minneapolis, Minn. 55430. The thickness of the seals 28 and 30 can range 
from an overall thickness of around 1 to around 10 mils with the heat seal 
coating ranging in thickness from around 0.5 mil to around 4 mils and more 
preferably from around 0.5 to around 2 mils and the aluminum foil ranging 
in thickness from around 0.1 to around 8 and more preferably from around 
0.3 to around 2 mils. 
Alternatively, seals 28 and 30 can have an adhesive material as the "b" 
section which is a thermoplastic resin suitable for hot melt deposition or 
extrusion lamination. Suitable examples of these thermoplastic resins 
include resins known as the so-called hot-melt type adhesive, such as 
polyethylene, an ethylene/vinyl acetate copolymer (EVA) or a partially 
saponified EVA. For instance, a graft copolymer can be used that is a 20 
to 60 percent saponification product of an ethylene/vinyl acetate 
copolymer (EVA) having a vinyl acetate content of 15 to 45 percent by 
weight as a trunk polymer and a polymer of an unsaturated carboxylated 
acid in a quantity of 0.1 to 10 percent by weight of the partially 
saponified EVA as a branch polymer. Also, the seals 28 and 30 can be a 
composite of an aluminum/polypropylene film with a heat sealable resin 
such as a polyamide, polyolefin, and saturated polyesters. When sealing to 
adhere the resin to the plastic surface and thereby adhere the seal to 
channel 12 is performed by heat sealing, any induction sealing or any heat 
sealing method known to those skilled in the art can be used. The method 
of sealing depends to a degree on any securing means used to maintain the 
seals 28 and 30 in a snug relationship to the tips 38 and 36, respectively 
18. The seals 28 and 30 can have any shape suitable for covering 
completely openings 24 and 26 and providing for a snug fitting with the 
flat surface of the rims 50 as shown in FIGS. 6 and 7 of the tips 36 and 
38. Preferably, the seal is in the form of a disc having a diameter 
similar to the diameter across the opening and tip for attachment to the 
tip rim to cover the opening 24 and 26. 
The sectional elevational view of the sensor apparatus shown in FIG. 3 is 
along lines 3--3 of FIG. 1. As shown in this figure, on housing 10 ridges 
56 and 58 can be present for ease of handling. Flared end 40 is shown from 
this view from the front of the apparatus. The electrical attachment means 
16 is shown as a cable extending from the bottom of housing 10. This view 
shows the preferred embodiment of the invention having a plurality of 
channels. In addition to channel 12, the housing 10 and sensor element 14 
forms two additional channels 60 and 62 which also can and preferably do 
contain hydrating fluid 22. As shown in FIG. 3, channel 12 is in fluid 
contact with sensor 18 which is on sensor element 14. Also shown in fluid 
contact with channels 60 and 62, respectively, are electrodes or sensors 
64 and 66. Also as shown in FIG. 3 there may be and preferably are present 
two longitudinal slots 68 and 70 which are in the top section 32 of 
housing 10. These slots are for mold enhancements for plastic molding of 
the housing 10 to assist in obtaining flat external and internal surfaces 
for a larger housing section 32. The ridges 56 and 58 are on housing 
section 34 which securely fastens to housing section 32 by matching 
fastening means 72 on top section 32 and 74 on bottom section 34. Mirror 
image fastening means are present on the opposite side of housing 10. 
These fastening means can be on the sides of housing 10; one on each 
interior side of bottom section 34 and two on the top section 32 of 
housing 10 where one is on each side of housing 10. 
In FIGS. 1-3 and the remaining figures, the sensor element 14 can have one 
or more sensors like sensor 18 having one or more hydratable membranes 
known to those skilled in the art. Preferably, sensor element 14 is a 
nonconducting substrate with electrical circuitry 20 electrically 
connected to at least one sensor through at least one electrode. 
Generally, the nonconducting substrate can be a glass or ceramic including 
sheet or chip or nonconducting substrate like nonconducting polymers or 
commercially available frit that can be used as the substantially smooth 
flat surface for the nonconducting substrate. Nonexclusive examples 
include borosilicate glass as is known to those skilled in the art for 
producing thick film or layered circuits. A nonexclusive but preferred 
example of which includes a ceramic base having around 96% A1203 such as 
that available commercially from Coors Ceramic Company, Grand Junction, 
Colo. Generally the electrical circuitry 20 is any electrical circuit 
means known by those skilled in the art. Both the sensor 18 and the 
electrical circuitry 20 can be prepared from any number of well known 
layered circuit or integrated circuit technologies, as for example, thick 
film, thin film, plating, pressurized laminating and photolithographic 
etching, and the like, however, the thick film technique is preferred. A 
suitable sensor element is that described in the allowed U.S patent 
application Ser. No. 07/343,234, filed on Apr. 26, 1989, U.S. Pat. No. 
5,046,496 and titled, "Sensor Assembly for Measuring Analytes in Fluids, 
which is commonly assigned, and which is incorporated herein by reference. 
The at least one sensor 18 can be a potentiometric or amperometric sensor, 
in that the former has one electrode and the latter has two, both an anode 
and a cathode. In the situation where the sensor 18 is potentiometric, an 
additional electrode is usually present as a reference electrode. Any 
reference electrode known to those skilled in the art can be used. The 
potentiometric or amperometric sensor preferably has a hydrophilic 
polymeric membrane and the sensor preferably has an aqueous-based 
electrolyte with suitable ionized chemical species like those in 
silver/silver chloride, calomel and mercury sensors or electrodes. 
Suitable examples of such membranes that may be present in electrochemical 
sensors for use in determination of blood gases are described in U.S. Pat. 
Nos. 3,088,905; 3,912,614; 4,133,735; and 4,454,007 and European patent 
specifications 0015075 and 0027385 and the article in the Journal entitled 
"Medical and Biological Engineering Computing", 1978, Vol. 16, pages 
599-600. The publications describe blood gas detectors requiring the 
presence of membranes and a number of useful or potentially useful 
membrane materials. Suitable nonexclusive examples of a hydrophilic 
polymeric membrane include polyvinylchloride and modified 
polyvinylchloride and any similar hydrophilic hydratable polymeric 
membrane known to those skilled in the art. 
In addition to channel 12 having fluid contact with a sensor, sensor 18 on 
the substrate of sensor element 14 as shown in FIG. 3, the sensor assembly 
of the present invention may have a plurality of channels. The arrangement 
of the channels and the sensors is such that when a plurality of channels 
and a plurality of electrodes for the sensor or sensors are present at 
least one channel can be in fluid contact with at least one sensor. With 
this type of arrangement, the one or more side channels are in fluid 
contact with at least channel 12 or with another channel connected to 
channel 12 so that each of the one or more side channels can provide fluid 
contact with the at least one electrode associated with that channel. This 
sensor or electrode to channel relationship is shown in FIGS. 3 and 18, 
while the channel to channel relationship is shown in FIG. 5. In FIG. 3 
channels 60 and 62 are formed by the one housing section 32 and the 
adjacent positioning of sensor element 14 in the internal cavity or space 
formed by the joined two housing sections 32 and 34 in a fashion similar 
to the aforementioned formation of channel 12. Sensors or electrodes but 
preferably reference electrodes 64 and 66, respectively, are in contact 
with channels 60 and 62. Preferably, these channels contain fluid like 
hydrating fluid 22 as contained in channel 12 or any fluid known in the 
art to act as an electrolyte for the reference electrode. Preferably, the 
potentiometric and/or amperometric sensors are located in channel 12 and 
only the reference electrodes are located in the one or more additional or 
side channels 60 and 62 and most preferably each reference electrode is 
located in a separate side channel as shown is FIG. 18. 
The electric circuitry 20 is shown in FIG. 3 by line 20, which connects to 
electrical attachment means 16 preferably by a cable 16 electrically 
connecting to the nonconducting substrate of sensor element 14. Cable 16 
can be any suitable electronic multiple conductor with suitable leads to 
carry analog signals and preferably not binary signals. Preferably the 
cable is a ribbon-type cable with a plurality of wires in one tape-like 
strip to provide the sensor element 14 with electrical communication from 
the at least one sensor 18. The connection of the electrical circuit means 
or cable 16 to the nonconducting substrate of 14 is in a manner to 
communicate electrically with at least the one or more sensors or 
electrodes but to avoid contacting the hydrating fluid 22 which may cause 
short circuits or current leakage. 
The hydrating fluid 22 is any liquid suitable for maintaining the membrane 
of sensor 18 in a non-dried state. For instance, the liquid will have some 
amount of water although a minor quantity of organic liquids may also be 
present. Preferably, the liquid is a stable liquid for storage ranging 
from a short time (days or weeks) to prolonged periods of time of several 
months. Preferably, the liquid is an aqueous solution that is isotonic 
with any electrolyte in the one or more sensors. More preferably, the 
hydrating fluid 22 is also isotonic to act as the electrolyte for any 
reference electrodes that may be present on the sensor element 14 as 
reference electrodes 64 and 66 as shown in FIG. 3. A suitable example of a 
hydrating fluid is an aqueous solution comprising: disodium hydrogen 
phosphate, potassium dihydrogen phosphate, sodium bicarbonate, and sodium 
chloride. Such a solution can have a varying range of amounts for the 
individual constituents but most preferably for the aforelisted salts the 
amounts are in millimoles per kilogram of water in the order listed as 
follows: 4.8, 13, 22, and 12.5. The quantity of hydrating fluid in channel 
12 or the plurality of channels is at least that which is sufficient to 
cover or remain in contact with the one or more sensors. For example, 
seals 30 and 28 of FIGS. 1 and 2 could be in channel 12 rather that at the 
opening so as to maintain the hydrating fluid 22 in contact with the one 
or more sensors. In this situation the seals 28 and 30 would be more plugs 
rather than foil-backed seals. 
FIG. 4 shows an alternative embodiment of housing 10 to that depicted in 
FIGS. 1 and 2 in that tip section 38 is a mirror image or near mirror 
image of tip section 36 at the other end of the housing. Hence, the 
difference between the embodiment of FIG. 4 and that of FIG. 1 is that the 
housing 10 with the near mirror image of tip sections 36 and 38 does not 
have the flared end 40 of FIG. 1. FIG. 4 is a side section without the 
back portion 34, the sensor element 14, and electrical attachment means 16 
as shown in FIG. 1 and the electrical insulating means 54 shown in FIG. 2. 
FIG. 4 has at least one channel 12 with openings 24 and 26 sealed by seals 
28 and 30. With this view the internal space 82 is shown where sensor 
element 14 is placed. Since the sensor element 14 can have any geometric 
shape, the internal space should be of a matching shape to accommodate the 
sensor element and to minimize the possibility of gaps that would allow 
hydrating fluid to leak into contact with the electrical circuit means 20 
or cable 16. Also shown in FIG. 4 is the slot 84 which is a portion of the 
slot and tab assembly shown in FIG. 1 as 52. This slot assists in aligning 
the attachment of back 34. As shown in FIG. 2, the slot runs transversely 
across the bottom of the upper section 32 of housing 10. In addition the 
void space 86 of FIG. 4 can be present or absent depending on the molding 
process for producing the sensor assembly. 
FIG. 5 is another bottom view taken along a transverse line 5--5 of FIG. 1. 
Here, internal space 82 is of adequate dimensions to hold a comparably 
dimensioned sensor element (not shown) to completely fill the space to 
provide walls for not only channel 12 but also channels 60 and 62. 
Preferably, channels 60 and 62 are joined to channel 12 through joining 
sections 88 and 90. As an alternative embodiment, although not shown in 
FIG. 5, similar joining sections can be present at the other end of 
channels 60 and 62 connecting to channel 12. The difference between 
channels 60 and 62 and channel 12 is that the former are side channels 
which do not flow through the housing 10 but are joined for fluid flow to 
the main channel 12. The diameters of the channels can be the same or the 
diameter of channels 60 and 62 can be smaller than that of channel 12. 
As shown in FIG. 18 the plurality of channels preferably associate with the 
electrodes and sensors so that the one or more sensors 18 of sensor 
element 14 are positioned in channel 12, while other sensors or electrodes 
18 are on sensor element 14 for positioning in side channels 60 and 62. 
With this arrangement it is preferred that sensors for measuring the 
partial pressure of oxygen and electrodes or sensors for measuring the 
partial pressure of carbon dioxide and for measuring pH are in channel 12, 
while channels 60 and 62 each have a reference electrode 64 and 66, 
respectively. When hydrating fluid 22 is in the channels, the fluid in 
channel 12 is more easily displaced with the sample fluid to be measured 
relative to the fluid 22 in channels 60 and 62. Therefore, reference 
electrodes 64 and 66 are measuring as a reference a known fluid for 
comparison for the measurement of the sample fluid in channel 12. 
The housing 10 has a plurality of attachment ports to assist in holding the 
sensor element 14 in place in the internal space 82 and to assist in 
attachment between top section 32 and bottom section 34. The preferred 
rectangular shape of internal space 82 is shown in FIG. 5. The number of 
ports can range from around 2 to around 8 although higher numbers can be 
present and the ports can range in geometric configuration from circles to 
slots to square and the like for mechanical or chemical attachments. The 
mechanical attachments can be plastic or metal rivets or fasteners like 
screws and the chemical attachment can be adhesives, preferably curing 
adhesives such as a UV-curing adhesive. FIG. 5 shows eight ports 
(92A-92H). The preferred number of eight ports are arranged such that two 
of the ports, 92C and 92E, are positioned between channel 12 and side 
channel 62 and two ports, 92D and 92F, are positioned between main channel 
12 and side channel 60. The other four ports are located outside of the 
channel array and preferably near the corners of the internal space 82 so 
that ports 92A and 92B are at the two corners of one end of internal space 
82 and ports 92G and 92H are located at the other two corners of internal 
space 82. The ports extend from the internal surface 94 of housing member 
32 to the external surface 80 shown in FIG. 4 of housing section 32 to 
provide for placement of the attachment means from the outside or external 
to housing 10 and into the internal space 82 when it contains the sensor 
element 14. 
Also shown in FIG. 5 is inner annular space 42, in phantom, slot 48, 
opening 24 and seal 28. At the distal end of the housing 10, the tip 36 is 
shown with a partial cutaway showing channel 12 that is sealed with seal 
30 over opening 26. Also a void 86 is shown in FIG. 5 which is present to 
decrease the amount of material used and to reduce the weight of the 
sensor assembly. The void 86 can extend completely through the housing 
sections 32 and 34, respectively, of housing 10. The attachment means of 
member 32 for engagement with member 34 are shown in FIG. 5 at 72 and 76 
as longitudinal ridges along the exterior sides of the planar portion of 
housing member 10. 
FIG. 6 is a sectional view of the proximate end of the sensor assembly 
showing opening 24 of channel 12. The channel extends into the flared end 
section 40 of the sensor assembly to form tip 38 for channel 12. Between 
tip 38 and rim 44 of flared end 40 is the inner annular space 42. 
Extending beyond annular space 42 into housing 10 in the direction of 
internal space 82 is detent 96 on both external sides of tip 38 for 
formation of the more or less planar portion of housing 10. Extending 
outwardly from and normal to the peripheral surface of flared end 40 are 
projections 98 and 100. These projections extend outwardly a short 
distance and preferably in the same plane so they continue along the same 
longitudinal axes of housing 10 as ridge members 56 and 58 shown in FIG. 
3. These projections assist in handling of the sensor assembly when it is 
connected to a syringe (not shown). As previously discussed, the inner 
annular space 42 accepts a Leur fitting for attachment as depicted in FIG. 
6 to a conventional syringe. 
FIG. 7 shows the distal end of sensor housing 10 in a sectional view. The 
tip section 36 provides a housing for channel 12 which has opening 26 at 
this distal or receiving end. Also shown are ridges 56 and 58 which extend 
from housing 10. As mentioned for and shown in FIG. 6, the projections 98 
and 100 are extensions of these ridges since FIGS. 6 and 7 are the 
opposite ends of the housing 10 rotated in the same horizontal plane 
180.degree.. The internal space 82 is shown above and below and to one 
side of channel 12. Tip section 36 extends beyond the shoulder region 102 
of the essentially planar section of the housing 10 as shown in FIG. 5. 
FIG. 8 shows a sectional view along line 8--8 of FIG. 5 of the housing 
section 32 of the sensor assembly. Member 32 has a portion of internal 
space 82 which is completed upon attachment of housing member 34 as shown 
in FIG. 1. FIG. 8 is rotated 90.degree. in the clockwise direction in the 
same plane in regards to FIG. 3. Also shown are fastening ports 92F and 
92E. The fastening ports are interspersed one above and one below channel 
12. Above port 92F and below 92E are secondary channels 60 and 62, 
respectively. Fastening means 72 and 76 of housing member 32 are shown in 
engaged fashion with fastening means 74 and 78 of housing member 34 for 
engagement of the two housing members 32 and 34. Another section of the 
slots 68 and 70 that extend longitudinally along the exterior surface of 
housing member 32 as depicted in FIG. 4 as 80 is shown in FIG. 8. 
FIGS. 9, 10 and 11 show the housing member 34 of the sensor assembly. 
FIG. 9 is the side section elevational view of the back portion of the 
sensor assembly 10 having a tongue section 104 which when attached to 
member 32 covers void space 86 as shown in FIG. 5. When housing members 32 
and 34 are attached, tongue 104 conforms to the shape of the shoulders 102 
of the upper section as more clearly shown in FIG. 10. Also, lip 106 
extends from the exterior surface 108 of housing member 34 so that when 
member 34 engages member 32 a slot-like opening is available for cable 
attachment means 16 for electronic communication of the sensor assembly. 
Tab 110 is for mating attachment to slot 84 of housing member 32. Tab 110, 
which is a portion of assembly 52 shown in FIG. 1, projects preferably at 
around a 90.degree. angle from the interior surface 112, shown in FIG. 11 
of member 34. The tab slidably engages or fills slot 84 which both 
traverse the longitudinal axis of members 34 and 32, respectively, as a 
guide for engagement of these members. Of course, the tab and slot 
arrangement can be any guiding mechanism arranged in any fashion and at 
any location on members 32 and 34 to assist in their engagement as long as 
there is no interference with the sensor element 14. 
The tab 110 and slot 84 and lip 106 for the cable slot are preferably 
located where shown in the Figures. This arrangement allows for the cable 
attachment means 16 to associate with the housing 10 at or near the 
proximate end of the housing and travel to around the distal end of the 
housing for attachment to the electric circuit means 20. This way the 
cable can travel a substantial distance of the longitudinal axis of the 
internal space 82 to retard the loss of heat from the sensor element 14 
through the cable. 
As shown in FIG. 9, member 34 has a side element laterally extending at 
around a 90.degree. angle from each side of internal surface 112 of member 
34. One of these sides is shown in FIG. 9 as 114, while a mirror image 
laterally extending side 116 is behind side 114 in FIG. 9 as shown in FIG. 
11. The laterally extending sides 114 and 116 extend in connecting fashion 
to engage the housing member 32 preferably on its lateral sides. As shown, 
lateral side 114 has a ridge which is ridge 56 of FIG. 3 that travels the 
longitudinal axis of the lateral side and that extends outwardly 
preferably at an angle of around 90.degree. from side 114. 
FIG. 10 is a bottom view of member 34 taken along lines 10--10 of FIG. 9 
showing tongue member 104 and lip member 106 both beginning at one lateral 
side and extending transversely almost or to the other lateral side. In 
addition, hole 118 is in the back for insertion of chemical electronic 
insulation means 54. Tab 110 is shown in phantom and the laterally 
extending sides are approximately normal to the plane of exterior surface 
108. 
As shown in FIG. 11, a forward end view of member 34 taken along lines 
11--11 of FIG. 10, tab 110 projects laterally and approximately normal to 
the plane of surface 108 in this view. The laterally extending sides 114 
and 116 each have the attachment means 74 and 78 to matchedly engage the 
attachment means 72 and 76, respectively, on member 32. Also, the ridges 
56 and 58 are shown extending from laterally extending sides 114 and 116, 
respectively. Also shown in phantom is hole 118. 
FIG. 12 shows channel 12 as it longitudinally passes through housing 10 in 
a plan elevational view of the contour of channel 12 formed along the 
longitudinal axis on the interior of the housing. The contours shown in 
FIGS. 12 and 13 are depicted in phantom and FIGS. 1 and 2, respectively. 
FIG. 12 is a top view of the channel taken on lines 13--13 of FIG. 13. The 
12a portion indicates that portion of the channel passing from the tip 36 
in FIG. 1. Portion 12b is that part of the channel which passes through 
the shoulder section, 102 of FIG. 5, of housing 10 into the interior 
cavity. Portion 12c is that part in the internal space 82 of housing 10 
formed from housing member 32 and the sensor element 14 occupying space 82 
in between top member 32 and bottom member 34. Preferably, cable 
attachment means 16 is in between sensor element 14 and housing member 34. 
Portion 12c preferably has a wider diameter than that of 12a or 12b 
although it could have the same diameter. Portion 12d is that section of 
the housing enclosed by tip 38 passing from the internal space 82 into the 
flared end 40 of the housing. This portion preferably has a wider diameter 
for coupling to a fluid collection pressure device such as a syringe. 
The side elevational view of FIG. 13 again shows portion 12a, where a cross 
section along line 14--14 is shown in FIG. 14. As shown in FIG. 14, the 
channel at this location has a circular cross section and is the portion 
formed by the tip 36. As shown in FIG. 13, the slope of the bottom of the 
channel increases as the bottom ascends to the bottom level as shown in 
FIG. 13 around the cross sectional line 15--15. The cross sectional view 
shown in FIG. 15 along a line 15--15 in FIG. 13 details a flat bottom 
portion of the channel for a portion of 12b. Here, the channel has a flat 
bottom as the channel 12 enters the planar section of the housing 10. 
Portion 12c extends along the longitudinal axis of the planar section of 
the housing and has a cross section as shown at FIG. 16, which is along 
line 16--16 of FIG. 13. At cross sectional line 17--17 of FIG. 3 the 
bottom is notched by the detent 96 of FIG. 6 to provide for coupling to 
the device like a syringe. After the point in FIG. 13 at line 17 the 
diameter of the channel widens again. The constriction and widening of the 
diameter of the channel is for the purpose of obtaining an opening that is 
a minimum diameter for accepting a standard Leur fitting like that on a 
syringe. The portion of the channel shown in FIG. 13 is that which is 
preferably formed by the housing section 32. Preferably, the other housing 
section 34 forms little, if any, of the portion of the channel 12. The 
beginning of portion 12d has the cross section shown in FIG. 17 just as 
the channel exists the planar section into the flared end section 40 of 
the housing 10. A cross section of the end of the channel 12 is shown in 
FIG. 6 formed by the tip 38. 
The sensor assembly is prepared by placing the sensor element 14 with one 
or more sensors 18 having unhydrated membranes, preferably three sensors, 
one for measuring the partial pressure of oxygen, another for measuring 
the partial pressure of carbon dioxide and a third for measuring the pH of 
fluids, preferably fluids like blood. The sensor element 14 is placed in 
the internal space 82 of housing member 32 as shown in FIGS. 1, 2, 4 and 
5. The electrical attachment means 16 is electrically connected to sensor 
element 14. When the sensor element 14 is placed in internal space 82, 
this electrical connection is preferably at the distal end although it 
could be at the proximate end of housing 10. The cable stretches along the 
length of the sensor element 14 between the element 14 and the housing 
member 34 and exits housing 10 at the near proximate or exiting end 40. 
The attachment of the cable 16 to the nonconducting substrate of the 
sensor element 14 can be by any attachment means known to those skilled in 
the art for attaching cables to substrates for electronic circuits. 
Additionally, it is preferred to have a foam pad shown as 109 in FIG. 11 
between the electrical attachment means 16 and housing member 34 so that 
there is uniform compression of sensor element 14 to the bottom of housing 
section 32. Housing member 34 is aligned with housing member 32 through 
the tab-and-slot arrangements 110 and 84 and preferably snapped through 
attachment means 72, 74, 76 and 78 as shown in FIG. 8. 
An adhesive that is curable by ultra-violet light is placed in at least 
some of the ports 92a through 92h and also preferably along the interior 
surface of the housing member 32 by wicking. Any suitable adhesive known 
to those skilled in the art of joining polymeric parts to glass or ceramic 
substrates can be used, but it is preferred to use an ultraviolet light 
curable adhesive that is substantially water insoluble in the cured state. 
A nonexclusive example of a suitable material is the UV curable epoxy 
adhesive P/N 10033 available from an electronic materials vendor. Also 
this adhesive may be used with about 0.005 percent by weight polychrome 
blue organic dye to highlight the details of the adhesive. Before placing 
the housing with the adhesive in a UV-curing zone to cure the adhesive, it 
is preferred to allow the adhesive to wick within the internal opening 82 
along the surface of housing member 32. The wicking of the adhesive within 
the cavity is preferably on both sides of the side channels. Preferably, 
the quantity of adhesive that is used allows for wicking lengthwise along 
the bottom of section 32 on both sides of channel 12 and under the channel 
so the bead of adhesive is near continuous on both sides of the channel 
12. The curing can occur in any commercially available UV-curing oven with 
or without a conveyor. After curing the wicked adhesive, the housing 10 is 
cooled to ambient temperature. Preferably, now the UV-adhesive cured by 
ultraviolet light is placed in the ports and again placed in the UV-curing 
oven. 
After the joining of the housing members with the adhesive, the electronic 
isolation means, preferably an epoxy, that is cured at room temperature 
and atmospheric pressure is filled through hole 118 in member 34 as shown 
in FIG. 10 into the internal space 82 that is not already occupied. To 
increase the rate of cure, the housing is preferably placed and maintained 
in an oven for about two hours at 60.degree. C. After the electronic 
insulating material has hardened or cured, as in the case of an epoxy 
material, the housing 10 can be pressure tested at an air pressure of 
around 10 to around 15 psi. 
Upon joining of the housing members to contain the sensor element 14 and 
cable 16, one opening of the channel 12 is sealed which can be either 
opening 24 sealed with seal 28 or opening 26 sealed with seal 30 by a heat 
sealing but preferably an induction sealing process. After the sealing of 
one end, the hydrating fluid is added to channel 12 and any side channels 
to fill substantially all of the channels although small amounts of air 
bubbles can be tolerated in the channels but preferably the channels are 
filled to capacity. The remaining opening of the housing is sealed with 
the other seal through a heat sealing process but preferably an induction 
sealing process. 
The sealing of seals 28 and 30 to channel 12 at the top and essentially 
flat rim portion 50 in FIGS. 6 and 7 depends on the presence or absence of 
any mechanical attachment means such as caps or the like and the type of 
thermoplastic adhesive polymer 24. When the cap is present, either the 
heat or induction sealing process can be used and any cap known to those 
skilled in the art for covering an opening in a plastic vessel can be used 
such as a screw cap or a snap cap. With the use of screw or snap caps, the 
seals 28 or 30 can be placed in the cap, and the cap applied to one of the 
openings 24 or 26 of the channel 12. When the cap is absent, induction 
sealing should be used to avoid the escape of any hydrating fluid (gas) 
from or the influx of gas into the channel 12. In general, the sealing 
needs to overcome the hurdle of adhering the seal to a plastic or 
polymeric substrate in a possibly moist environment since there may be 
moisture or liquid on the surface of tips 36 and 38 after the addition of 
the hydrating fluid. 
With the capped channels a plurality of housings 10 can be heat or 
induction sealed. The heat sealing temperature and the pressure applied by 
the cap can vary depending on the type of heat sealable resin that is used 
with seals 28 and 30. In general, however, sufficient results are obtained 
by conducting the heat sealing at a temperature higher than the softening 
or melting point of the heat sealable resin and the pressure is sufficient 
if it doesn't cause excessive or substantial flow of heat sealable resin 
away from the area to be sealed. For heat sealing of a polypropylene heat 
sealable resin, the seal pressure by the screw-type cap is in the range of 
2 to 5 kilograms per centimeter.sup.2 (Kg/cm.sup.2) for the temperature of 
heat sealing in the range of 180.degree. C. to 280.degree. C. For a 
polyamide, like Nylon 12, heat sealable resin the pressure is in the range 
of 2 to 7 Kg/cm.sup.2 for the temperature of sealing of around 200.degree. 
C. to 300.degree. C. For polytetramethylene terephthalate the seal 
pressure is around 2 to 7 Kg/cm.sup.2 for the sealing temperature in the 
range of 220.degree. C. to 320.degree. C. The time required for heat 
sealing varies depending on the thickness of the heat sealable resin 
layer. 
Generally, the heat sealing is conducted for a time sufficient to perform 
melting and bonding of the sealable resin, for example 0.1 to 5 seconds. 
The heat sealing operation can be performed in an operation comprised of 
one stage or two or more stages. In the latter case, the same or different 
temperature and pressure conditions as those aforementioned can be adopted 
at these stages. The formed sealed area is cooled, if necessary, under 
application of pressure by optional means to form a sealed area with good 
sealing efficiency. For instance, immediately after completion of the heat 
sealing operation, the heat sealed area in which the resin is still in the 
softened or molten state is pressed by two positively cooled press bars 
whereby the resin is solidified. Although any operation known to those 
skilled in the art to cool and harden the adhesive polymer can be used. 
For induction sealing, generally any induction sealing process known to 
those skilled in the art of induction sealing can be used. A nonexclusive 
example of a suitable process involves placing the housing 10 with seal 28 
or 30 in place over the opening 24 or 26, respectively, of the channel 12 
on the flat surface of the rim 50 of one of the tips 36 or 38, 
respectively. With the seal in place over the opening, that end of the 
housing with the seal over the opening is held with the application of 
pressure against a region where it is exposed to high-frequency 
electromagnetic waves. A suitable piece of equipment is that available 
from Giltron, Inc., Medfield, Mass. 02052, referred to as Foil Sealer 
Induction Heat Sealer, Model PM1. The aluminum foil of the seal is locally 
heated to a point whereby it heats and melts the adjacent resin layer. The 
melted resin layer adheres to the top horizontal surface of the rim of the 
tip that surrounds the opening. The hydrating fluid is placed in the 
channel in the aforementioned manner and the other seal is placed over the 
other opening at the other tip and subjected to induction heating in the 
same manner to seal the other end. 
When the sensor assembly needs to be sterilized, the sensor assembly with 
the sealed channel can be sterilized by gamma-sterilization or 
pasteurization sterilization. A nonexclusive example of a pasteurization 
technique that can be used with the sterilizable container of the present 
invention is heating one or more of them at a temperature of around 
70.degree. C. for eight hours. The gamma-radiation sterilization can occur 
with the use of any gamma-sterilization equipment known to those skilled 
in the art. 
A nonexclusive example of the sensor element is shown in FIGS. 19-22 with 
the preferred sensor element 14 shown in FIG. 21. The following 
description of these figures new reference numbers are used for components 
that may have been previously discussed in regards to the aforedescribed 
electrochemical sensor assembly. 
As previously described the preferred electrical circuitry 20 for the 
sensor element 14 has several electronic components. This preferred 
embodiment in shown in FIG. 21. An alternative embodiment utilizing one 
reference electrode is shown in FIG. 19, which is a top planar view of one 
side of the wiring substrate, hereinafter referred to as "board" with at 
least one electrochemical sensor 18 of the present invention, where the 
components have particular shapes. Any other shapes than those shown in 
FIG. 19, that are known to those skilled in the art for the particular 
components, can be used. 
The substrate 111 on both sides of the board 14 is any glass or ceramic 
including sheet or chip or nonconducting substrate like wood or 
nonconducting polymers or commercially available frit that can be used as 
the substantially smooth flat surface of the substrate layer 111. 
Nonexclusive examples include borosilicate glass as is known to those 
skilled in the art for producing thick film or layered circuits. A 
nonexclusive but preferred example of which includes a ceramic base having 
around 96% A1203 such as that available commercially from Coors Ceramic 
Company, Grand Junction, Colo. 
The substrate layer 111 is essentially flat and any substrate known to 
those skilled in the art for forming printed wiring circuits can be used. 
It is preferred that the composition of the substrate can endure the 
presence of electrolyte that has a pH in or over the range of 6 to 9 and 
remain unaffected for a substantial period of time. 
As can best be seen in FIG. 19, the board 14 is provided with a number of 
electrodes and more particularly, electrodes useful in the measurement of 
blood gas oxygen, carbon dioxide and pH. The board 14 is also provided 
with a thermistor and resistor arrangement to indicate the temperature at 
any time on the board 14 as well as reference electrodes for establishing 
an accurate reference potential; all of which will be described in further 
detail below. 
On the substrate layer 111 is a patterned metallic layer 113 with a number 
of extensions which act as the electronic conducting pathway between a 
voltage or current source external to the board 14 (not shown) and each of 
the components. The extensions constitute the transmission section, where 
each extension has a component at its end. The several extensions also 
have the ability to transmit changes in voltage from the components of the 
board 14 to the Analyzer (not shown in this Figure). 
The pH sensing electrode 115 is located at the end of extension 117; the 
carbon dioxide sensing electrode 119 is located at the end of extension 
122; the oxygen sensor 124 is provided with an anode 126 located at the 
end of extension 128; the reference electrode 130 is located at the end of 
extension 132 which extends from anode 126 of the oxygen sensor 124; the 
oxygen sensor 124 is further provided with a cathode 134 which is located 
at the end of extension 136; thermistor 138 is located at the end of 
extensions 140 and 142. 
As shown in FIG. 20, the patterned metallic layer 113 has metallic external 
leads 146-160 on the other side of the substrate 111. Although the 
external leads are shown on the opposite side of the substrate 111, they 
can also be on the same surface as their associated metallic lead patterns 
and components. 
External leads 148-158 are conductively associated with the components on 
the FIG. 19 side of the substrate layer 111 and external leads 146 and 160 
are in metallic electrical conducting contact with a thick film heater 174 
which is provided on the FIG. 20 side of the substrate layer 111. The 
heater 174 traverses the board in a serpentine fashion to provide a grid 
of heat to the nonelectrically conducting substrate and its function will 
be described below. 
External leads 152 and 156 are in metallic electrical conducting contact 
with a resistor 176 which is also provided on the FIG. 20 side of the 
substrate layer 111. The resistor is in a half-bridge relationship with 
the thermistor 138 and, as such, it commonly shares external lead 152 with 
the thermistor 138; thermistor 138 also being in metallic electrical 
conducting contact with external lead 152. The function of the thermistor 
138 and resistor 176 arrangement will be described below. 
The patterned metallic layer 113 is formed by printing pastes deposited 
onto a substrate in the desired pattern to act as ohmic conductors. 
Nonexclusive examples of suitable heat resisting metals include; noble 
metals such as platinum (Pt), ruthenium (Ru), palladium (Pd), rhodium 
(Rh), iridium (Ir), gold (Au) or silver (Ag) or other metals traditionally 
used as Clark cells and other ISE's and mixtures thereof. A nonexclusive 
but preferred example of a suitable paste is a silver paste of the type 
produced and available from Electro-Science Laboratories, Inc. under the 
trade designation ESL 99112. 
The metallic layer 113 is dried to produce the above noted patterned 
conductive pathways 117, 122, 128, 132, 136, 138 and 140 of FIG. 19 Any 
method known to those skilled in the art for producing a sufficient 
thickness of metallic tracing can be used. Preferably pathway 128 has 
ground 129. 
Preferably, the silver pastes are oven dried and fired at a high 
temperature in a furnace. Firing can be accomplished at a temperature in 
the range of around 800.degree. C. to 950.degree. C. for a period of 
around 1 to 20 minutes. With this procedure, the thickness of the layer of 
the metallic conducting tracing is usually in the range of around 0.0005 
to 0.001 inches. Although the aforementioned are preferred conditions, 
general conditions for obtaining a proper thickness can be used where the 
thickness can be generally range from about 0.0004 to 0.0015 inches. 
The aforementioned conductive patterns are encapsulated with a glass 
ceramic mixture or a ceramic insulating material such as alumina or 
spinal. This encapsulation can range from a total encapsulation to 
encapsulation except at the end of the metallic pattern. 
The aforementioned electrodes are preferably produced by one of the layered 
circuit techniques. This involves leaving the respective shaped ends 
uncovered while the metallic patterns are completely covered by the 
encapsulant. The encapsulation of the metallic patterns can range from 
encapsulating each from the other to a sufficient degree for electrical 
insulation of the conductive patterns and any conductive layers from each 
other. 
As shown in FIG. 19, the encapsulant can extend across the whole board from 
edge to edge as generally shown at numeral 144. Preferably, the thickness 
of the encapsulant layer is that which is adequate to seal the underlining 
metallic layer and to provide insulation for the metallic patterns. 
Preferably, the thickness of the layer is around 120-130 microns. 
A preferred glass ceramic mixture useful as the encapsulant is the type 
produced and available from Electro-Science Laboratories, Inc. under the 
trade designation ESL 4904. 
The several electrodes may be masked during the encapsulation to keep them 
suitably uncovered for the addition of active materials (e.g. polymer 
liquids and pre-cut dry film membranes) over the appropriate electrodes on 
the surface of the substrate layer 111. 
This process involves masking the electrodes by the use of polymer film 
coating on the screen used to screen print the encapsulant. This leaves 
the underlying silver exposed to form the electrodes for active materials. 
It is also possible to use multiple layers of the metallic conductive 
layer or encapsulant. 
Preferably, the glass composition for the encapsulant as with the substrate 
111 is selected to possess good chemical stability and/or moisture 
resistance and to possess high electrical insulation resistance. Also, the 
metallic and encapsulant materials are selected so that they can endure 
the presence of an electrolyte in a similar manner as the substrate 
composition. 
The geometry of the several electrodes could be made by a laser beam to 
carve or cut or trim the electrode, however, they are preferably prepared 
by the aforementioned layered circuit technique. 
The serpentine formed heater 174 and the resistor 176 on the FIG. 20 side 
of the board may be prepared by a number of commercially available 
techniques, however, they are preferably thick film devices prepared by 
the aforementioned layered circuit technique. 
Holes 162-172 may be drilled by a laser through the substrate 111 to 
conductively connect the metallic extensions 117, 122, 128, 138, 140 and 
136 traced on the FIG. 1 side of the substrate layer 111 with their 
respective metallic external leads 148-158 on the FIG. 20 side of the 
substrate layer 111. In general, these openings 162-172 are produced by 
the focused laser beam drilling a hole by heating a small volume of 
material to a sufficiently high temperature for localized melting and/or 
vaporization. 
The external leads 146-160 may be produced on the other side of the side of 
the substrate layer 111 with the see paste and firing as that done for 
aforementioned metallic patterns. The metallic external leads 146-160 are 
in metallic electrical conducting contact with the various components on 
each side of the board. As before mentioned external leads 146 and 160 are 
in metallic electrical conducting contact with the heater 174 and external 
leads 152 and 156 are in metallic electrical conducting contact with a 
resistor 176 which commonly shares external lead 150 with the thermistor 
138; thermistor 138 also being in metallic electrical conducting contact 
with external lead 150. External lead 158 is in metallic electrical 
conducting contact with the CO.sub.2 sensing electrode 119; external lead 
148 is in metallic electrical conducting contact with the pH sensing 
electrode 115; external lead 148 is in metallic electrical conducting 
contact with the CO.sub.2 sensing electrode 119; external lead 152 is in 
metallic electrical conducting contact with the anode 126 of the oxygen 
sensor 124, the anode 126 having an electrical ground 129; external lead 
152 is also in metallic electrical conducting contact with the reference 
electrode 130 which is located at the end of extension 132 which extends 
from anode 126 of the oxygen sensor 124, the anode 126 and external lead 
154 is in metallic electrical conducting contact with the cathode 134 of 
the oxygen sensor 124; external lead 154 is in metallic electrical 
conducting contact with the cathode 134 of the oxygen sensor 124. 
The holes 162-172 have been drilled through the substrate layer 111 and 
when the metallic layers are screened such electrical connections are 
formed. Alternatively, the metallic external leads 146-160 can be produced 
and preferably are produced by a very high powered carbon dioxide laser. 
This can be accomplished by the supplier of the nonconducting substrate 
and in this case the metallic layer is added to the substrate so each 
conducting pathway electrically connects with an external lead. 
As described above, the process of masking the electrodes by the use of 
polymer film coating on the screen, is used to screen print the 
encapsulant. This leaves the underlying silver exposed to form the 
electrodes for active materials. It is also possible to use multiple 
layers of the metallic conductive layer or encapsulant and the outer layer 
of the encapsulant may be solvent or thermoplastically bondable and may 
include polymers, as for example, acrylates or polyvinyl chloride as the 
major component in the encapsulant. The purpose of the outer coating or 
encapsulant is to enhance bonding of the active materials and, in 
particular, to provide a reliable surface for the attachment of the liquid 
or solid film type membrane materials. 
Each of the sensing electrodes are fabricated to perform their specific 
task and may be selected from many commercially available electrode 
components. The pH electrode 115, CO.sub.2 electrode 119 and the Oxygen 
sensor 124 are each fabricated with a membrane which maintains their 
respective electrolytes in a fluid tight manner in the cavities or 
openings in which the electrodes are positioned. 
The pH electrode 115 and the CO.sub.2 electrode 119 may be similar in 
regards to the circuit geometry and electrolyte and may be provided with 
membranes suitable for the particular characteristic being measured. 
For pH electrode 115, for example, the use of cation permeable and 
particularly hydrogen ion permeable membrane may be used. A number of such 
cationic exchange materials may be utilized, as for example, membranes 
fabricated from copolymeric vinyl ethers as manufactured by E.I. duPont 
under registered trademark NAFION. 
The membrane for the CO.sub.2 electrode 119 may be fabricated from a wide 
range of commercially available carbon dioxide permeable polymeric 
materials. The electrolytes of the pH electrode 115 and the CO.sub.2 
electrode 119 are bound by their respective membranes. 
The membrane for the oxygen sensor may be fabricated from a polymeric 
material such as polystyrene in an organic or inorganic solvent. The 
oxygen permeable electrolyte of the oxygen sensor 124 bathes the anode 126 
and cathode 134 to provide electrical ionic contact between the two. The 
electrolyte can be any electrolyte known to those skilled in the art for 
Clark Cell as, for example, a saline solution based on potassium chloride 
or sodium chloride. 
The anode 126 of the oxygen sensor 124 is electrically grounded at 129 to 
assure that the electrolyte potential does not change and that the opening 
to the electrolyte is held at some voltage which is the same as the anode 
potential so that the electrolyte is grounded in the electrode 
configuration. 
The reference electrode 130, which is located at the end of extension 132 
and which extends from anode 126 of the oxygen sensor 124, provides a 
highly stable reference potential. This reference potential provided by 
the reference electrode 130 facilitates accurate measurement of the blood 
gases. The reference electrode 130 may be fabricated from a number of 
suitable materials known to those skilled in the reference electrode art 
such as a silver and silver chloride composite using the aforementioned 
layered circuit technique. 
The thermistor 138 is a thick film thermally sensitive resistor whose 
conductivity varies with the changes in temperature. The thermistor 138 
may be fabricated from a number semi-conductive materials as, for example, 
oxides of metals. The thermistor and may be formed and applied to the 
substrate layer 111 by the use of the aforementioned layered technique. 
The temperature coefficient of the thermistor 138 is large and negative 
and is used to sense the temperature of the board 14 at all times when the 
board 14 is coupled to its associated electronic Analyzer (not shown). It 
is operated at relatively low current levels so the resistance is affected 
only by the ambient temperature and not by the applied current. 
As before described, external leads 152 and 156 are in metallic electrical 
conducting contact with a thick film resistor 176 which is provided on the 
FIG. 20 side of the substrate layer 111. The resistor 76 is in an 
half-bridge relationship with the thermistor 138 and, as such, it commonly 
shares external lead 152 with the thermistor 138; thermistor 138 also 
being in metallic electrical conducting contact with external lead 152. 
The half-bridge circuit configuration is a voltage divider and generates a 
ratiometric output to the Analyzer. This is important for it allows the 
actual resistance values to float and results in highly consistent and 
accurate temperature sensing and control of the board 14 on a board to 
board basis. Accuracy and consistency of the resistor 176 and thermistor 
138 arrangement is achieved by calibrating the board 14 by laser trimming 
of the resister 176 to produce zero volts at 37.degree. C. The laser beam 
is precisely deflected across the thick film resistor 176 to produce the 
desired temperature voltage relationship. A current is applied at external 
leads 150 and 152 by the Analyzer until zero volts is achieved. This gives 
a linear output so that the temperatures can be measured other than 
37.degree. C. from the slope of the line from the calibration at room 
temperature and 37.degree. C. The resister 176 has essentially zero 
temperature coefficient and, accordingly, may be placed without any 
adverse effect on the sensing capability of the associated thermistor 138, 
on the FIG. 20 side of the board 14 with the heater 174. 
Accurate sensing of the ambient temperature of the board 14 is required to 
precisely control the heater 174 to ultimately maintain, within a narrow 
distribution of temperatures, the desired operating surface temperature on 
the FIG. 19 or sensor side of the board 14. 
Placement of the thermistor 138 can affect the accuracy of the measurement 
of the temperature. As can be seen in FIG. 19, the thermistor 138 is 
placed in the same plane and in close relation to the sensors 115, 119 and 
124 to thereby accurately sense the ambient temperature at or near such 
sensors. This physical placement of the thermistor 138 allows for the 
rapid adjustment of the heater 174 by the Analyzer to maintain the desired 
operating temperature. The thermistor 138 resistor 176 arrangement 
provides for very accurate temperature measurement. This physical 
placement of the thermistor 138, so close to the sensors, requires that it 
be correctly fabricated to ensure that it is electrically isolated from 
the electrolytes of the several sensors. The encapsulant for the 
thermistor 138 must be thick enough to accomplish the electrical isolation 
yet thin enough so as not to lose any response time. 
The heater 174, provided on the FIG. 20 side of the board 14, rapidly and 
accurately produces the necessary heat in response to any temperature 
change sensed by the thermistor 138; the thermistor 138 and the several 
sensors 115, 119, and 124 all being in the heated region produced by the 
heater 174. Thick film heaters are not generally considered to be rapid 
response devices and their heat output tends to take a relatively long 
time, in terms of electronic devices, to change. To improve the 
responsiveness of the heater 174, it is powered by a controlled DC voltage 
whereby the heater is regulated by a combination of proportional (P), 
integral (I) and/or derivative (D) controls, preferably PID control 
thereby reducing the amount of overshooting or undershooting by the heater 
of a predetermined temperature. This not only increases the responsiveness 
of the heater 174 but also allows for better overall thermal control 
including avoiding the heater 174 from overshooting or undershooting the 
desired temperature. 
The timing sequence for the production of the heat by the heater 174 to the 
several sensors is provided by the natural state of power supplied to the 
board 14 when it is connected to the Analyzer. This same power will also 
produce the read-out from the measurements by the sensors of the blood gas 
oxygen, carbon dioxide and pH. This timing sequence facilitates a room 
temperature calibration of the board 14; an elevated temperature 
calibration at 37.degree. C. and then the measurement of the blood gas 
oxygen, carbon dioxide and pH. 
Prior to any measuring of the blood gases by the several sensors 115, 119 
and 124, all or part of the board 14 may be exposed to or stored with a 
calibration liquid, with the several sensors being exposed to the fluid. 
To measure the blood gases, the several sensors are brought in contact 
with the volume of the blood sample to be measured. The volume of the 
blood sample may be quite small, ranging from as small as a few 
microliters. 
FIGS. 21 shows the preferred embodiment of the substrate of the present 
invention where two reference electrodes 130A and 130B are present in 
offline alignment to the alignment of the sensors 119, 115 and 124 and 
thermistor 138. The axial alignment shown in FIG. 21 allows the sensors to 
be in contact with a sample in a chamber covering their alignment, while 
the reference electrodes can be in contact with reference fluid or 
electrolyte in another chamber placed in fluid contact with the reference 
electrodes. Any alignment pattern can be used that separates the reference 
electrode from the sensors in the aforedescribed manner. The other 
components of the wiring board are as described for the other figures. 
FIG. 22 shows a broader aspect of the invention where only one sensor 119 
is present with one reference electrode 130. If the sensor does not 
require a reference electrode as in the case of most amperometric 
electrodes the reference electrode need not be present. 
FIG. 23 shows the block diagram of the functions and interrelationship of 
these functions for the Analyzer with its electrical connection to the 
sensor element 14 of FIGS. 1-22. The analog input processing unit 180 of 
the Analyzer 12 interfaces with the electric circuitry 20 of the previous 
figures by the electrical connector 16 to allow signals from the sensors 
18 and any temperature detector 138 of FIGS. 19-22. Also the electrical 
connection 16 allows for electrical current to be supplied to any heater 
174 and resistor 176 on board 14 as shown in FIG. 20 and for any current 
or voltage that may be needed by the sensors 18 on the board 14. The 
electrical connections can be separate but are preferably individual 
connections in a bundle connector or ribbon cable. Connection 181 can 
carry current to an amperometric oxygen sensor 124 of FIG. 19. 
Respectively, connections 182, 183, 184, and 185 can carry signal and/or 
supply current or voltage to: the sensors 115 and 119, the thermistor 138, 
and heater 174 all shown in the previous FIGS. 19 and 20. The processing 
unit 180 can be electrically connected to the microcomputer 187 by 186 to 
the function of a 12 bit analog to digital converter 188. Converter 188 
can be electrically connected by 189 to line 200 a type of buss line. 
Through line 200 connections are made to the central processing unit (CPU) 
201 which has is a date/time circuit and battery backup random access 
memory device and can be and preferably is an 8-bit central processing 
unit (CPU) microprocessor. In addition the encoded information reader and 
drive circuit unit 190 is connected by line 191 to the microprocomputer 
187 through Input/Output (I/O) port 192 for two way communication. The CPU 
is connected through I/O port 195 to the display and keyboard unit 196, 
and this unit is connected through I/O port 197 and through line 202 to 
line 200 for communication with the microcomputer 187. The CPU 201 is 
connected for external communication by RS232 and drive circuit unit 203 
through serial port 204. The microcomputer 187 is connected to a power 
supply 205 and battery pack 206 for power. Also input output port 208 is 
connected electrically to a printer mechanism 210 for a hard copy display. 
In the preferred embodiment, the printed wiring board whose functions are 
depicted in FIG. 23 is divided into two boards subassemblies. First a 
primary board subassembly which is divided into five subsystems: the 
microcomputer, the bar code reader system, the printer subsystem, the 
sensor input circuits, and the RS232 drive circuit. The second subassembly 
is the power supply board subassembly which is a switch power supply with 
four outputs. One pair provides .+-.5 volts for the digital and the analog 
circuits. The other pair provides an isolated .+-.5 volts for the RS232 
drive circuits. The microcomputer consists of four major subsections--the 
central processing unit, the program memory, the random axis memory, and 
address decoder and the analog digital converter. The CPU is preferably an 
80 C51FA8 bit CMOS microcontroller with a 256.times.8 internal random axis 
memory and four 8 bit bi-directional parallel ports and three 16-bit 
timer/event counters and with full duplex programmable serial interface 
and reduced power modes. The CPU can address 64,000 bits of programmed 
memory and 64,000 bits of random access memory or memory map input/output. 
The program memory is preferably a 27G256 which is a high-density CMOS 
electrically programmable read only memory organized as a 32,768.times.8 
configuration. The random access memory is divided into two types. First 
an 8,000.times.8 volatile static random access memory and a 2,000.times.8 
nonvolatile RAM with a built-in real time clock that uses an embedded 
lithium energy cell to maintain the watch information and retain the RAM 
data for over five years. The address decoder is a GAL that selects seven 
memory mapped areas of random access memory and two are selected as data 
memory and the rest are selected as inputs or outputs. The analog digital 
converter is an ML2208 data acquisition peripheral that has an eight 
channel single ended multiplexer, a programmable game instrumentation 
amplifier, a 2.5 volt band gap reference, and a 12-bit+analog to digital 
converter with built-in sample-and-hold. The 8D converter interfaces to 
the microcontroller through the general purpose 8-bit port. Also, the 
ML2208 includes a programmable processor, data buffering, a 16-bit timer 
and limit alarms. The bar code read system consists of a 70 nanometer 
precision optical reflective sensor and the system uses the HPHBCS-1100 
sensor and HP sapphire lens. A printer subassembly is a thermal printer 
subassembly having four main components--the 8-bit latch, a printer head 
drive, a motor drive circuit and the printer mechanism. The sensor input 
circuits are analog signal conditioning circuits that receive the signals 
from the sensors and electronically control the sensors. There are two 
types of signals from the sensors, voltage or current. In addition, there 
is the heater control circuit. The serial or port driver circuit consists 
of the RS232 input buffer and line driver that are optically isolated from 
the internal circuits of the analyzer. Isolation is necessary in order to 
comply with the UL544 leakage current requirement. The power supply 
circuit supplies the five volts to the logic circuits and the analog 
circuit and an isolated five volts for the serial port. Power to the 
printer motor and printer heads is supplied directed from the battery pack 
which is typically six volts. 
Any components known to those skilled in the art to accomplish the 
aforementioned functions can be used in the analyzer and the electrical 
circuitry of the present invention. 
Although a particular preferred arrangement for the functional units of the 
Analyzer has been specifically set forth variations are possible that may 
delete one or more of the functional units. As long as the processing unit 
180, and converter unit 188 are present when analog signals are used, and 
a processor is functionally tied into these units and power is supplied 
and a read out can be obtained the Analyzer is usable for use with the 
sensor element 14 in the housing of previous figures. Appropriate software 
resides in the CPU to accomplish these connections and to convert signals 
from the sensors and to perform the calibration and analysis of samples 
and to give values indicating the specific amounts of the known types of 
analytes present in the analyzed fluids.