Test plug and cable for a glucose monitor

Methods and apparatuses for electrically connecting a medical glucose monitor to a glucose sensor set, as well as for testing the operation of the glucose monitor, monitor cable and glucose sensor set are provided. In one embodiment, an electric cable comprises a cable member, a first connector and a second connector. The cable member in turn comprises at least one insulated conductor, a conductive shielding layer disposed around the at least one insulated conductor; and an insulating layer disposed around the conductive shielding layer. A glucose monitoring system test plug provides for a releasable electrical connection with the electric cable. In one embodiment, the test plug comprises a housing and a fitting affixed thereto which is adapted to electrically couple the test plug with the electric cable. The test plug further includes an electrical circuit that produces a signal that is read by the glucose monitor to test the operational performance of the glucose monitor and the electric cable when the test plug is coupled to the electric cable and when the electric cable is coupled to the glucose monitor.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to methods and devices used for electrically connecting medical glucose monitors to glucose sensor electrodes as well as for testing the operation of the glucose monitors, monitor cables and glucose sensors.

2. Description of the Related Art

Over the years, a variety of implantable electrochemical sensors have been developed for detecting or quantifying specific agents or compositions in a patient's blood. For instance, glucose sensors are being developed for use in obtaining an indication of blood glucose levels in a diabetic patient. Such readings are useful in monitoring or adjusting a treatment regimen which typically includes the regular administration of insulin to the patient. Thus, blood glucose readings can improve medical therapies with semi-automated medication infusion pumps of the external type, as generally described in U.S. Pat. Nos. 4,562,751; 4,678,408; and 4,685,903; or automated implantable medication infusion pumps, as generally described in U.S. Pat. No. 4,573,994, which are incorporated herein by reference.

Generally, small and flexible electrochemical sensors can be used to obtain periodic readings over an extended period of time. In one form, flexible subcutaneous sensors are constructed in accordance with thin film mask techniques in which an elongated sensor includes thin film conductive elements encased between flexible insulative layers of polyimide sheets or similar material. Such thin film sensors typically include a plurality of exposed electrodes at one end for subcutaneous placement with a user's interstitial fluid, blood, or the like, and a corresponding exposed plurality of conductive contacts at another end for convenient external electrical connection with a suitable monitoring device through a wire or cable. Typical thin film sensors are described in commonly assigned U.S. Pat. Nos. 5,390,671; 5,391,250; 5,482,473; and 5,586,553 which are incorporated herein by reference.

Thin film sensors generate very small electrical signals which can be read by external glucose monitors. These monitors can be portable, and can be attached to the patient, such as for example, on a belt clip. Applicant's clinical studies have shown that an electrical cable maybe provided for the transmission of these small signals from the sensors to the glucose monitor. But given the environment in which these cables are used, special characteristics can be useful.

Thus a glucose monitoring system includes connectors between the cables, leads, electrodes and monitors such as those described in pending U.S. patent application Ser. No. 09/346,835, filed Jul. 2, 1999 and entitled “Insertion Set for a Transcutaneous Sensor” and U.S. patent application Ser. No. 09/377,472, filed Aug. 19, 1999 and entitled “Telemetered Characteristic Monitor System and Method of Using Same, both of which are incorporated herein by reference. Although a well designed system will have minimal operational problems, it is possible that a problem might arise with the integrity of the cables, sensor electrodes or monitor during their use. The system connectors or the cables may become loose or bent, resulting in a poor or open circuit. The sensor electrodes could degrade. The glucose monitor could become inoperative due to any number of causes. Thus, it is desirable to provide a system that is simple to use so that a patient can easily identify any operational problems with the system.

SUMMARY OF THE PREFERRED EMBODIMENTS

A glucose monitoring system test plug as well as an electric cable for electrically connecting a glucose monitor to a glucose sensor set are provided. In one embodiment, the electric cable comprises a cable member, a first connector and a second connector. The cable member in turn comprises at least one insulated conductor, a conductive shielding layer disposed around the at least one insulated conductor; and an insulating layer disposed around the conductive shielding layer.

In one aspect, the first connector comprises a housing having a first bore which is adapted to receive a sensor set cable fitting and a first conductive contact disposed within the first bore. The first conductive contact is electrically coupled to the insulated conductor and is adapted to be removably electrically coupled to a sensor set conductive contact. In one embodiment of the present invention, a key fitting is formed within the first bore and is adapted to mate with the glucose sensor set in one orientation. There is further provided a releasable coupler disposed on the housing which is adapted to releasably couple the housing with the glucose sensor set.

In another aspect, the second connector comprises a housing having a second bore. The second connector is adapted to releasably couple the second connector with the glucose monitor. There is a second conductive contact disposed within the second bore which is electrically coupled to the insulated conductor. The second conductive contact also is adapted to be removably electrically coupled to a glucose monitor conductive contact.

In yet another aspect, the glucose monitoring system test plug is for use with a glucose monitor cable which is adapted to electrically couple to a glucose monitor. The test plug comprises a housing and a fitting affixed to the housing. The fitting is adapted to electrically couple the test plug to the glucose monitor cable. The test plug further comprises an electrical circuit which is adapted to provide a known test signal to the cable and the glucose monitor in order to test the operational performance of the glucose monitor and the glucose monitor cable when the test plug is coupled to the glucose monitor cable and when the glucose monitor cable is coupled to the glucose monitor.

In an alternative embodiment, the test plug is provided for use with a glucose monitor. The test plug comprises a housing and a fitting affixed to the housing. The fitting is adapted to electrically couple the test plug to the glucose monitor. The test plug further comprises an electrical circuit which is adapted to provide a test signal to the glucose monitor to test the operational performance of the glucose monitor when the test plug is coupled to the glucose monitor.

In yet another embodiment, the test plug can alternatively provide a releasable electrical connection with either the electrical cable or the glucose monitor.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring toFIG. 1there is disclosed a shielded cable10constructed in accordance with aspects of the present invention. The cable10includes a flexible cable member13with a monitor connector11at one end and a sensor connector12at the opposite end.FIG. 2illustrates the use of the cable10in an exemplary glucose monitoring system. The system includes a subcutaneous glucose sensor set20which is coupled to a glucose monitor21by the cable10. The subcutaneous glucose sensor set20uses an electrode-type sensor, as described in more detail below. However, in other applications, the glucose sensor may use other types of sensors, such as chemical based, optical based or the like. The sensor shown inFIG. 2is a surface mounted sensor that uses interstitial fluid harvested from the skin. Other sensors may be of a type that is used on the external surface of the skin or placed below the skin layer of the user.

The glucose monitor21of the illustrated embodiment generally includes the capability to record and store data as it is received from the sensor set20, and includes either a data port or a wireless transmitter for downloading the data to a data processor, computer, communication station, or the like for later analysis and review. The data processor or computer uses the recorded data from the glucose monitor to determine the blood glucose history. Thus, one purpose of the glucose monitor system is to provide for improved data recording and testing for various patient conditions using continuous or near continuous data recording.

The sensor set20of the illustrated embodiment is provided for subcutaneous placement of a flexible sensor, or the like, at a selected site in the body of the user. The sensor set20includes a hollow, slotted insertion needle22and a cannula (not shown) inside the needle22. The needle22is used to facilitate quick and easy subcutaneous placement of the cannula at the insertion site. The cannula includes one or more sensor electrodes (not shown) which are exposed to the user's bodily fluids. After insertion, the insertion needle22is typically withdrawn to leave the cannula with the sensor electrodes in place at the selected insertion site.

The sensor set20includes a mounting base23adapted for placement onto the skin of a user. As shown, the mounting base23of the illustrated embodiment is a generally rectangular pad having an underside surface coated with a suitable pressure sensitive adhesive layer, with a peel-off paper strip24provided to cover and protect the adhesive layer, until the sensor set20is ready for use. Further description of suitable needles and sensor sets are found in U.S. Pat. No. 5,586,553, entitled “Transcutaneous Sensor Insertion Set” and U.S. patent application Ser. No. 09/346,835, filed Jul. 2, 1999, entitled “Insertion Set for a Transcutaneous Sensor,” which are incorporated herein by reference.

As shown inFIGS. 2 and 3, the glucose monitor21is coupled to the sensor set20by the cable10which electrically couples the monitor connector11to the connector block25of the sensor set20. The monitor connector11of the cable10is connected to the glucose monitor21through a plug receptacle26of the monitor21. The monitor connector11includes a plurality of pins31arranged in a pin snap-in configuration to connect to the receptacle26of the glucose monitor21. In this embodiment, there are four (4) pins31, three (3) of which are used for connection to 3 insulated conductors within the cable10and one of which is for a drain (or ground) conductor within the cable10.

The glucose monitor21includes a housing27that supports at least one printed circuit board, batteries, memory storage, a display screen28, the plug receptacle26, and the cable10and the monitor connector11when connected to the plug receptacle26of the monitor21. The lower portion of the glucose monitor21may have an underside surface that includes a belt clip, or the like, to attach to a user's clothing. Alternatively, the underside surface may be coated with a suitable pressure sensitive adhesive layer, with a peel-off paper strip normally provided to cover and protect the adhesive layer until the glucose monitor21is ready for use. Alternatively, the glucose monitor21may be secured to the body by other methods, such as an adhesive overdressing, straps, belts, clips, or the like. Further description of suitable glucose monitors are found in U.S. patent application Ser. No. 09/377,472, entitled “Telemetered Characteristic Monitor System and Method of Using the Same” which is incorporated herein by reference.

In other embodiments, the cable10may also have a flexible strain relief portion, as indicated at reference numeral14ofFIG. 1, to minimize strain on the sensor set20and minimize movement of the sensor set20relative to the body, which can lead to discomfort or dislodging of the sensor set20. The flexible strain relief portion is intended to also minimize sensor artifacts generated by user movements that causes the sensor set20to move laterally relative to the glucose monitor21by reducing lateral movement of the sensor connector12.

The glucose monitor21provides power or other signals, through the plug receptacle26to the monitor connector11of the cable10and then through the cable10to the sensor connector12of the sensor set20. These signals are used to drive the sensor electrodes and to speed the initialization of the sensor set20, when first placed on the skin.

FIGS. 4 and 5illustrate a connection arrangement between the sensor connector12portion of the cable10of the illustrated embodiment and the sensor set20. As shown, the sensor connector12has a low profile housing40for comfortable fitting against the body. The housing40is compact in size and can be constructed from lightweight molded plastic. The housing40defines a socket fitting51for mating slide-fit engagement with a rear cable fitting41of a sensor set mounting base23. The socket fitting51of the illustrated embodiment has a bore or cylindrical entry portion52which leads to a generally D-shaped or half-circle step portion53positioned within the entry portion52. The socket fitting51therefore forms a “keyhole” type fitting which is sized to receive the D-shaped “key” portion of the sensor set fitting41.

The socket fitting51includes a plurality of conductive contacts54(FIG. 5) positioned on the step portion53for electrically coupled engagement with correspondingly positioned contact pads of the cable fitting41, when the sensor set20and the sensor connector12are coupled together. The conductive contacts54of the illustrated embodiment have a leaf spring design to facilitate good electrical and mechanical contact to the sensor set fitting contact pads. When assembled, seal rings42of the sensor set fitting41sealingly engage the entry portion52of the socket fitting51to provide a water resistant connection between the components. Furthermore, the D-shaped geometry of the interfitting components41and53facilitate proper conductive coupling of the cable10to the sensor set20in the desired orientation.

The sensor set20and the sensor connector12are held together by releasable couplers, which in the embodiment ofFIGS. 4 and 5, include interengaging snap fit latch arms44of the sensor set20and latch recesses55of the connector12of the cable10. As shown, the insertion set mounting base23is formed to include the pair of rearwardly projecting cantilevered latch arms44which terminate at the rearward ends thereof in respective undercut latch tips43. The latch arms44are sufficiently and naturally resilient to provide a living hinge for movement relative to the remainder of the mounting base23to permit the latch arms44to be squeezed inwardly toward each other.

The permissible range of motion accommodates snap fit engagement of the latch tips43into a corresponding pair of latch recesses55formed in the housing40of the sensor connector12on opposite sides of the socket fitting51, wherein the latch recesses55are lined with indentations which act as latch keepers56for engaging the latch tips43. The components can be disengaged for uncoupling when desired by manually squeezing the latch arms44inwardly toward each other for release from the latch keepers56, while axially separating the mounting base23from the sensor connector12.

For use as a connector between a sensor set and a glucose monitor, the cable10includes one or more insulated conductors, and in order to increase user comfort, should be relatively long and have good flexibility. However, the electrical signals from the sensor set20electrodes can be very small (i.e., in the range of 1 to 200 nano amps) thus making the cable susceptible to external electrical noise. To reduce this susceptibility the cable is preferably shielded and relatively short. These characteristics would tend in general to make a cable less comfortable for a user.

A further source of electrical noise in cables is the triboelectric effect which is caused by the use of certain electrical insulators. Certain types of insulators, such as for example, Teflon, can be so effective that when the cable is bent, the electrical charge on the cable will separate but will not reform quickly. When the charge belatedly reforms, this can appear as a voltage spike or noise on the cable. Thus, while an effective insulator is useful for glucose monitor cables, the insulator preferably should not permit unacceptable levels of triboelectric noise. Certain insulation materials may provide a good solution to the triboelectric effect. However, many of them would not result in as flexible a cable as is desired.

FIG. 6shows a cross sectional view of an exemplary embodiment of the flexible cable member13of the glucose monitor cable10. This design strikes a satisfactory balance between cable flexibility, high insulation, and low noise characteristics. The cable member13includes three (3) center conductors61as well as a drain line62. The center conductors61are electrically coupled to the conductive contacts54(FIG. 5) of the sensor connector12at one end and are coupled to 3 of the 4 pins31of the monitor connector11at the opposite end. (FIG. 3) The drain line62is electrically coupled to the remaining one of the pins31of the monitor connector11which is electrically grounded. In this embodiment, the center conductors61each are constructed of 30 AWG 40×46 BC bunched stranded copper with a nominal OD of 0.013 inches. It is believed that alternative constructions for the conductors61may achieve acceptable flexibility if gauges of a number greater than 30 and strand counts greater than 40 are employed. The drain line62is constructed of 30 AWG 7×0.004 TC concentric stranded copper with a nominal OD of 0.012 inches. Other gauges, strand counts and OD's for the conductors61and the drain line62may be used, however depending upon the application.

The three conductors61are each surrounded by a first insulating jacket63, which in the illustrated embodiment is 8 mils nominal PVC insulation with a nominal OD of 0.026 inches. An alternative insulation material to PVC is believed to be a polyester material, such as Mil-ene™ which is available from W. L. Gore & Associates of Newark, Del. The drain line62of the illustrated embodiment is not surrounded by a first insulating jacket.

The three conductors61, their insulating jackets63and the drain line62are collectively surrounded by a shield64. The shield64is constructed of 44 AWG tinned copper braid with a nominal thickness of 0.007 inches. Other thicknesses and gauges may be used however, depending upon the particular application. The shield64serves to prevent or minimize external electromagnetic interference fields from affecting the low level signals being transmitted on the conductors61. The drain line62is adjacent to and therefore in electrical contact with the shield64throughout the length of the cable member13. Because the drain line62is electrically coupled to the one of the pins31which is grounded, this serves to ground the shield64. By grounding the shield64in this manner, a separate electrical termination of the shield to any sort of alternative grounding on the monitor connector11of the cable10may be eliminated.

The shield64is surrounded by a second insulating jacket65. The second insulating jacket65of the illustrated embodiment is constructed of PVC (USP class VI) which is a “food grade” PVC and has a nominal thickness of 0.010 inch. Alternative acceptable materials to PVC are believed to include thermoplastic elastomers such as Santoprene™ which is available from Advanced Elastomers (a division of Monsanto) of Akron, Ohio, or a reinforced elastomer based material, Sil-Kore™, which is available from W. L. Gore & Associates of Newark, Del. The OD of the insulating jacket65, and therefore of the cable10, is approximately 0.090 inches. Although the illustrated embodiment of the outer jacket65has a nominal thickness of 0.010 inches and an OD of 0.090 inches, it is believed that nominal thicknesses of 0.006 inches or greater and OD's of 0.110 inches or less may be employed and achieve acceptable results.

When constructed in accordance with the previously-described embodiment, it is believed that the cable10will have triboelectric noise characteristics of no more than approximately 50 to 150 micro volts per AAMI ECG 5/83 test. This construction results in a cable member13which strikes a satisfactory balance between maximum insulation and minimal triboelectric noise. Moreover, the cable10is small in diameter and relatively long and flexible, thus providing a greater degree of user comfort. However, these embodiments may also be used for shorter cables used to connect various components in telemetered systems, such as that described in U.S. patent application Ser. No. 09/377,472 and entitled “Telemetered Characteristic Monitor System and Method of Using Same.”

Referring now toFIG. 7, a test plug70is disclosed that can simulate the glucose sensor electrodes, or the combination of the glucose sensor electrodes and the cable10of a glucose monitoring system. If an operating problem occurs while the glucose monitoring system is being used, the test plug70provides diagnostic information that can help indicate if a glucose sensor, the cable or the glucose monitor is operating normally.

The test plug70includes two connectors. Each connector facilitates the testing of a different component of a glucose monitoring system. A monitor connector72allows the device to plug into the glucose monitor21in place of the cable10so the monitor can be checked independently from the rest of the system. A cable fitting73allows the device to plug into the cable10in place of the sensor set20so that the operation of the cable10can also be verified.

As will be described in more detail below, the test plug70is a sensor simulator that, in one embodiment, can return a constant current of the same magnitude as is produced by the sensor electrodes during normal in-vivo operation. This current is measured by the monitor21and is reported on the display screen28of the monitor21. (FIG. 2) From the display screen28, the user can view the test current and verify that the monitor is reporting the correct signal current with the expected accuracy. This can be accomplished when the test plug70is plugged directly into the monitor or when it is plugged into the distal end of the cable10.

The ability to perform such simple performance checks in the field is expected to offer users the opportunity to troubleshoot system problems with greater ease and confidence.

Referring toFIG. 10, the test plug simulates the presence of an actual sensor electrode to produce a signal current that the monitor can measure. Monitor connector pins79–82are disposed in the monitor connector72portion of the test plug70(FIG. 7) and are adapted for direct connection to the plug receptacle26of the glucose monitor21. (FIG. 2) In one embodiment, the simulator has an electrical circuit1003that includes a first resistor1001connected between the monitor connector pin80which simulates a reference electrode connection and the monitor connector pin79which simulates a working electrode connection. The test current produced depends upon the voltage provided by the monitor21and the value of the resistor between the simulated reference and working electrode connections. In one embodiment, a test current of 27 nA is developed with a nominal monitor voltage of 535 mV where the first resistor1001is 20 million ohms.

A second resistor1002is placed between the monitor connector pin81which simulates a counter electrode connection and the monitor connector pin80. The second resistor1002is chosen to be of equal value, or 20 million ohms, so that the voltage at the simulated counter electrode81will be twice that of the monitor voltage as measured between simulated electrodes79and80. Choosing the second resistor value to produce a voltage twice that of the monitor voltage facilitates verifying the monitor voltage value. Monitor connector pin82simulates a connection to the cable drain line62(FIG. 6) and therefore is electrically isolated from the resistors1001and1002.

Still referring toFIG. 10, a plurality of contact pads75are disposed in the cable fitting73portion of the test plug70(FIG. 7) and are adapted for electrical connection to the sensor connector12of the cable10. (FIG. 5) When connected to the cable10, the test plug70continues to simulate the presence of an actual sensor electrode. However, it produces a signal current that travels through the cable10to the monitor for measurement.

The contact pads75are connected to the resistors1001and1002in the same fashion as the monitor connector pins79–81. Therefore, the manner in which the test current is generated through the contact pads75and through the cable10is the same as was previously described.

It will be appreciated that although the electrical circuitry shown inFIG. 10has resistors arranged to produce a test current, many other circuitry arrangements comprised of other, known, electrical components, such as capacitors, inductors, semiconductor devices and voltage sources, can be incorporated in the test plug70to provide a suitable test current or other test signal.

Referring now toFIGS. 7–9, one embodiment of the test plug70of the present invention is shown. The test plug70includes a housing71which encloses the electrical circuitry, such as that shown inFIG. 10. At one end of the test plug70is the monitor connector fitting72. At the opposite end is the cable fitting73.

The cable fitting73is sized for mating slide-fit engagement with the socket fitting51of the cable10. (FIG. 5) The cable fitting73connects to the cable10in the same manner as the glucose sensor set20. Accordingly, the cable fitting73is the same as or similar to the sensor fitting41and likewise includes a D-shaped fitting key74which is received by the cylindrical entry portion52of the socket fitting51. (FIG. 5) The generally D-shaped step portion53of the fitting51receives the D-shaped fitting key74of the cable fitting73portion of the test plug70. (FIG. 7) As shown, the cable fitting73includes the plurality of conductive contact pads75positioned on the flat portion of the fitting key74(FIG. 8) for electrically coupled engagement with the conductive contacts54(FIG. 5) of the cable10. The conductive pads75are further coupled to the resistors1001and1002shown inFIG. 10.

The cable fitting73includes positioning rings76situated around the tubular portion of the cable fitting73. Because the insertion set20includes seal rings42for a seal tight engagement with the socket fitting51of the cable10(FIG. 4), the positioning rings76on the test plug70serve as a counterpart to the seal rings42and are used to properly center the cable fitting73in the socket fitting51. The D-shaped geometry of the interfitting components74and53insure proper orientation for correct conductive coupling of the cable10to the test plug70. Although a D-shaped geometry is shown inFIG. 4, other geometries, such as triangles, notches and the like, can be employed to provide proper orientation.

Referring again toFIGS. 5 and 7, the test plug70and the sensor connector12portion of the cable10are retained in releasable coupled relation by interengaging snap fit latch members. As shown, the test plug housing71is formed to include a pair of rearwardly projecting cantilevered latch arms77which terminate at the rearward ends thereof in respective undercut latch tips78. The latch arms77are sufficiently and naturally resilient for movement relative to the remainder of the housing71to permit the latch arms77to be squeezed inwardly toward each other.

The permissible range of motion accommodates snap fit engagement of the latch tips78into a corresponding pair of latch recesses55formed in the sensor connector housing40on opposite sides of the socket fitting51, wherein the latch recesses55are lined with latch keepers56for engaging the latch tips78. With this arrangement, the user is able to hear a clicking noise and feel the test plug snap into place. The components can be disengaged for uncoupling when desired by manually squeezing the latch arms77inwardly toward each other for release from the latch keepers56, while axially separating the test plug70from the sensor connector12portion of the cable10.

The monitor connector72portion of the test plug70can be electrically coupled directly to the glucose monitor21through the plug receptacle26of the monitor21. (FIG. 2) The monitor connector72connects to the glucose monitor21in the same manner as the cable10. The monitor connector72has a plurality of pins79–82for a snap-in configuration to the glucose monitor21. (FIG. 9) In this embodiment, the pins79–81are used for connection to the test plug resistors1001and1002as shown inFIG. 10.

Having described the structure of the test plug70, it can be seen how the test plug70can be used to provide diagnostic information that can help indicate if a glucose sensor, the cable or the glucose monitor is operating normally. Referring generally toFIGS. 2 and 7, if the display28of the monitor21indicates that there is a malfunction, the sensor set20can be disconnected from the cable10. The sensor connector12portion of the cable can then be connected to the cable fitting73portion of the test plug70. By pressing the appropriate buttons on the monitor21, the monitor21can apply a test voltage through the cable10and the resistors1001and1002of the test plug70and measure the resulting current. The value of the current can be displayed on the monitor screen28. If the value of the current falls within an acceptable range, then it is known that the monitor21and the cable10are operating properly. The operational problem therefore likely lies in the sensor set20which can be replaced by the user.

On the other hand, if the measured current is outside of the acceptable range of values, then the problem may lie in either the cable10or the monitor21or both. The user then disconnects the cable10from the monitor21and from the test plug70. The monitor connector72portion of the test plug70may then be connected directly to the plug receptacle26of the monitor21. Once again the appropriate buttons on the monitor21are pressed by the user to cause a test voltage to be applied from the monitor21directly to the test plug70thereby measuring the resulting current. If the value of the current as displayed on the monitor screen28falls within an acceptable range, then it may be deduced that the monitor21is likely operating properly and that the problem likely lies in the cable10. The cable10can be replaced and the system tested with a new cable to verify proper operation. On the other hand if the value of the current falls outside the acceptable range, then the monitor21is likely to have a problem. If the user is unable to locate and correct the monitor21problem, the monitor can be sent to a repair facility.

Although shown for use with the cable10and the monitor21, further embodiments of the test plug may be used in telemetered systems to test the various components, such as shown and described in U.S. patent application Ser. No. 09/377,472 and entitled “Telemetered Characteristic Monitor System and Method of Using Same.”

While the description above refers to particular embodiments of the present invention, it will be understood that many modifications may be made without departing from the spirit thereof. The accompanying claims are intended to cover such modifications as would fall within the true scope and spirit of the present invention. The presently disclosed embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.