Method and Apparatus for Providing Leak Detection in Data Monitoring and Management Systems
Method and apparatus for providing a leak detection circuit for a data monitoring and management system using the guard trace of a glucose sensor by applying a leak detection test signal to determine whether a leakage current is present is provided. The leak detection circuit may include an interface circuit, such as a capacitor, coupled to the guard trace to detect the leakage current when the leak detection test signal is applied to the guard trace, such that the user or patient using the data monitoring and management system, such as glucose monitoring systems, is notified of a failed sensor and prompted to replace the sensor.
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The present application is a continuation of U.S. patent application Ser. No. 11/118,794 filed Apr. 29, 2005 entitled “Method and Apparatus for Providing Leak Detection in Data Monitoring and Management Systems,” the disclosure of which is incorporated herein by reference for all purposes.
BACKGROUNDThe present invention relates to data monitoring and management systems. More specifically, the present invention relates to method and apparatus for providing leak detection in sensors used in data monitoring systems such as glucose monitoring systems.
Glucose monitoring systems including continuous and discrete monitoring systems generally include a small, lightweight battery powered and microprocessor controlled system which is configured to detect signals proportional to the corresponding measured glucose levels using an electrometer, and radio frequency (RF) signals to transmit the collected data. One aspect of such glucose monitoring systems include a sensor configuration which is, for example, mounted on the skin of a subject whose glucose level is to be monitored. The sensor cell may use a three-electrode (work, reference and counter electrodes) configuration driven by a controlled potential (potentiostat) analog circuit connected through a contact system.
The current level detected by the work electrode of the sensor is relatively small such that even a small amount of leakage current from the reference or counter electrodes typically will affect the signal quality, and thus may have adverse effect upon the accuracy of the measured glucose level. This is especially true when foreign matter is present that causes a false high glucose reading, and which may lead to improper patient treatment. Furthermore, when the glucose monitoring system is calibrated, the offset and gain of the sensor-transmitter pair is established. If the leakage current level changes (i.e., either increases or decreases), then the offset established will likely change and a resulting gain error may result for future calibration points.
In view of the foregoing, it would be desirable to have an approach to detect leakage current in sensor configuration of data monitoring systems such as in glucose monitoring systems such that detective sensors resulting from leakage current may be identified that are not detecting signals accurately.
SUMMARY OF THE INVENTIONIn view of the foregoing, in accordance with the various embodiments of the present invention, there is provided a method and apparatus for performing leak detection in the sensor of a glucose monitoring system such as continuous or discrete glucose monitoring system. The sensor may include subcutaneous or transcutaneous sensor and configured to detect glucose levels of a patient, in particular, diabetic patients.
In one embodiment, there is provided a capacitance to a guard electrode of the sensor, and a test signal is applied to the guard electrode to determine whether a current flow can be detected over the capacitance. If the test signal results in the current flow, it is determined that the current flow is as a result of the existence of leakage current in the sensor, and the user or patient is alerted that the sensor is not functioning properly. In other words, a detection of the leakage current prompts the patient that the sensor is no longer measuring accurate glucose levels, and that replacement of the sensor is recommended.
In one embodiment of the present invention, the sensor 101 is physically positioned on the body of a user whose glucose level is being monitored. The sensor 101 may be configured to continuously sample the glucose level of the user and convert the sampled glucose level into a corresponding data signal for transmission by the transmitter 102. In one embodiment, the transmitter 102 is mounted on the sensor 101 so that both devices are positioned on the user's body. The transmitter 102 performs data processing such as filtering and encoding on data signals, each of which corresponds to a sampled glucose level of the user, for transmission to the receiver 104 via the communication link 103.
In one embodiment, the glucose monitoring system 100 is configured as a one-way RF communication path from the transmitter 102 to the receiver 104. In such embodiment, the transmitter 102 transmits the sampled data signals received from the sensor 101 without acknowledgement from the receiver 104 that the transmitted sampled data signals have been received. For example, the transmitter 102 may be configured to transmit the encoded sampled data signals at a fixed rate (e.g., at one minute intervals) after the completion of the initial power on procedure. Likewise, the receiver 104 may be configured to detect such transmitted encoded sampled data signals at predetermined time intervals. Alternatively, the glucose monitoring system 100 may be configured with a bi-directional RF communication between the transmitter 102 and the receiver 104.
Additionally, in one aspect, the receiver 104 may include two sections. The first section is an analog interface section that is configured to communicate with the transmitter 102 via the communication link 103. In one embodiment, the analog interface section may include an RF receiver and an antenna for receiving and amplifying the data signals from the transmitter 102, which are thereafter, demodulated with a local oscillator and filtered through a band-pass filter. The second section of the receiver 104 is a data processing section which is configured to process the data signals received from the transmitter 102 such as by performing data decoding, error detection and correction, data clock generation, and data bit recovery.
In operation, upon completing the power-on procedure, the receiver 104 is configured to detect the presence of the transmitter 102 within its range based on, for example, the strength of the detected data signals received from the transmitter 102 or a predetermined transmitter identification information. Upon successful synchronization with the corresponding transmitter 102, the receiver 104 is configured to begin receiving from the transmitter 102 data signals corresponding to the user's detected glucose level. More specifically, the receiver 104 in one embodiment is configured to perform synchronized time hopping with the corresponding synchronized transmitter 102 via the communication link 103 to obtain the user's detected glucose level.
Referring again to
Within the scope of the present invention, the data processing terminal 105 may include an infusion device such as an insulin infusion pump, which may be configured to administer insulin to patients, and which is configured to communicate with the receiver unit 104 for receiving, among others, the measured glucose level. Alternatively, the receiver unit 104 may be configured to integrate an infusion device therein so that the receiver unit 104 is configured to administer insulin therapy to patients, for example, for administering and modifying basal profiles, as well as for determining appropriate boluses for administration based on, among others, the detected glucose levels received from the transmitter 102.
Further shown in
In one embodiment, a unidirectional input path is established from the sensor 101 (
As discussed above, the transmitter processor 204 is configured to transmit control signals to the various sections of the transmitter 102 during the operation of the transmitter 102. In one embodiment, the transmitter processor 204 also includes a memory (not shown) for storing data such as the identification information for the transmitter 102, as well as the data signals received from the sensor 101. The stored information may be retrieved and processed for transmission to the receiver 104 under the control of the transmitter processor 204. Furthermore, the power supply 207 may include a commercially available battery.
The transmitter 102 is also configured such that the power supply section 207 may provide power to the transmitter for a minimum of three months of continuous operation after having been stored for 18 months in a low-power (non-operating) mode. In one embodiment, this may be achieved by the transmitter processor 204 operating in low power modes in the non-operating state, for example, drawing no more than approximately 1 .mu.A of current. Indeed, in one embodiment, the final step during the manufacturing process of the transmitter 102 may place the transmitter 102 in the lower power, non-operating state (i.e., post-manufacture sleep mode). In this manner, the shelf life of the transmitter 102 may be significantly improved.
Referring yet again to
Referring yet again to
Additional detailed description of the continuous glucose monitoring system, its various components including the functional descriptions of the transmitter are provided in U.S. Pat. No. 6,175,752 issued Jan. 16, 2001 entitled “Analyte Monitoring Device and Methods of Use”, and in U.S. Pat. No. 7,811,231 issued Oct. 12, 2010 entitled “Continuous Glucose Monitoring System and Methods of Use”, each assigned to the Assignee of the present application, and the disclosures of each of which are incorporated herein by reference for all purposes.
Referring again to
Referring now to
Referring back to FIGS. 3 and 4A-4B, in accordance with one embodiment of the present invention, the current to voltage circuit 301 and the counter-reference servo unit 302 are operatively coupled to the remaining sections of the analog interface 201 of the transmitter 102, and configured to convert the detected glucose level at the sensor unit 101 (
In one embodiment, the guard electrode bias voltage source may be the work voltage source (Vw) shown in
The processor 204 in one embodiment may be configured to transmit a leak detection test signal to the leak detection circuit 214. More specifically, when the processor 204 transmits a leak detection test signal discussed in further detail below, if leakage resistance is present in the sensor 101 (for example, due to contamination or water presence), a leakage current will flow from the work electrode 210 to the guard electrode 211 over the resistor 501 and capacitor 503 in the leak detection circuit 214. In turn, due to the current flow from the work electrode 210 to the guard electrode 211, the current to voltage circuit 301 (
On the other hand, if the leakage resistance level is below a nominal threshold level (and thus not substantially impeding sensor 101 function), then substantially no leakage current exists from the work electrode 210 to the guard electrode 211 that can be detected by the current to voltage circuit 301 in the analog front end of the transmitter 102.
For example, referring back to
In operation, during the leak detection test, the leak detection test signal (normally held at 3 Volts) from the processor 204 is switched from the three (3) Volts to zero (0) Volts. If moisture or other conductive contamination is present in the sensor 101, leakage current will flow into the capacitor 503 from the guard electrode 211 at a rate that is a function of the leakage resistance between the work electrode 210 and the guard electrode 211. This current produces a corresponding output signal from the transimpedance operational amplifier 402 (
Referring to
Referring back to
By comparing the responses shown in these Figures, the difference in response between a 500 millisecond test signal and a 250 millisecond leakage test signal period can be seen. In other words, the length of the leak detection testing period is directly correlated with the sensitivity of the leakage detection and thus the accuracy of the leakage detection. That is, the longer the duration of the leak detection test signal, the higher the resolution of the test signal or accuracy. In other words, referring to
Referring to
If the response compared at step 804 is not greater than the normal sensor level, then at step 805, it is determined that no leakage current is detected, and the procedure terminates. Referring back to the Figure, if at step 804 it is determined that the response measured at step 803 is not greater than the normal sensor level, then at step 806, the iterative variable is retrieved and compared to determine whether it exceeds a leakage confirmation value. In one embodiment, the leakage confirmation value may be three. In other words, if three consecutive response measurement detects the response to be greater than the normal threshold level (step 804), then the leakage in the sensor 101 is configured and flagged for the user to replace the sensor 101. Referring back to
In an alternate embodiment of the present invention, the routine may also include an additional step of measuring the sensor signal level at the sensor 101 (
In the manner described above, an apparatus including a leak detection circuit in one embodiment of the present invention includes a guard contact, an interface circuit coupled to the guard contact, a processor coupled to the interface circuit, the processor configured to drive a leak detection test signal via the interface circuit to the guard contact, where the processor is further configured to detect a leakage signal in response to the leak detection test signal.
The interface circuit may in one embodiment include a capacitor, and further, the leak detection test signal may include a digital signal or an analog signal.
Moreover, the guard contact may include in one embodiment the guard electrode of a sensor.
Furthermore, the sensor may include a plurality of electrodes, one of the plurality of electrodes including a work electrode and a guard electrode, the guard electrode including the guard trace, where the leakage signal detected by the processor includes a sensor signal from the sensor.
An apparatus including a leak detection circuit in another embodiment includes a guard electrode, a capacitor coupled to the guard electrode, and a processor coupled to the capacitor, the processor configured to drive a leak detection test signal via the capacitor to the guard electrode, where the processor is further configured to detect a leakage signal in response to the leak detection test signal.
The capacitor in one embodiment may include a ceramic capacitor.
In a further embodiment, the apparatus may also include a sensor, the sensor having a plurality of electrodes, one of the plurality of electrodes including a work electrode and the guard electrode, and further, where the leakage signal detected by the processor may include a sensor signal from the sensor.
A method of providing a leak detection circuit in a further embodiment of the present invention includes the steps of providing a guard contact, coupling an interface circuit to the guard contact, driving a leak detection test signal via the interface circuit to the guard contact, and detecting a leakage signal in response to the leak detection test signal.
In one aspect, the detecting step may include the step of consecutively detecting the leakage signal a predetermined number of iterations, where in one embodiment, the predetermined number of iterations includes three.
Further, the step of driving the leak detection test signal may include the step of setting a leak detection bit to zero.
In the manner described above, in accordance with the various embodiments of the present invention, there is provided a method and apparatus for performing leak detection in a sensor configuration for use in data monitoring and management system such as glucose monitoring systems (continuous or discrete). In particular, in accordance with the present invention, it is possible to easily and accurately detect leakage current in the sensor configuration such that the signal integrity of the measured signals from the sensor can be maintained, and further, the user or patient of the data monitoring and management system may be alerted of the leakage detection in the sensor to replace the same in the system.
Various other modifications and alterations in the structure and method of operation of this invention will be apparent to those skilled in the art without departing from the scope and spirit of the invention. Although the invention has been described in connection with specific preferred embodiments, it should be understood that the invention as claimed should not be unduly limited to such specific embodiments. It is intended that the following claims define the scope of the present invention and that structures and methods within the scope of these claims and their equivalents be covered thereby.
Claims
1. An analyte monitoring apparatus, comprising:
- a leak detection circuit operatively coupled to at least one electrode of a transcutaneously positioned analyte sensor; and
- a processor operatively coupled to the leak detection circuit, the processor configured to generate a leak detection test signal; wherein the leak detection circuit is configured to detect a leakage current based on the leak detection test signal and to generate a leakage signal upon detection of a leakage current, and further wherein the processor is configured to receive the leakage signal from the leak detection circuit in response to the leak detection test signal.
2. The apparatus of claim 1 further including an interface circuit operatively coupled to the processor, the interface circuit configured to transfer the leak detection test signal to the at least one electrode of the analyte sensor.
3. The apparatus of claim 2 wherein the processor is configured to drive the leak detection test signal to the interface circuit.
4. The apparatus of claim 2 wherein the interface circuit includes a capacitor.
5. The apparatus of claim 1 wherein the processor is configured to drive the leak detection test signal to the at least one electrode of the analyte sensor.
6. The apparatus of claim 1 wherein the leak detection test signal includes one of a digital signal or an analog signal.
7. The apparatus of claim 1 wherein the leakage signal received by the processor includes an analyte related signal from the analyte sensor.
8. The apparatus of claim 1 wherein the processor is further configured to determine whether the received leakage signal exceeds a predetermined sensor signal level.
9. The apparatus of claim 8 wherein the predetermined sensor signal level includes a measured sensor signal level, wherein the measured sensor signal level is measured by the processor at a predetermined time interval.
10. The apparatus of claim 8 wherein the predetermined sensor signal level includes a tolerance level that corresponds to an acceptable current leakage level.
11. The apparatus of claim 8 wherein the processor is further configured to output a notification corresponding to the received leakage signal when the received leakage signal exceeds the predetermined sensor signal level a predetermined number of consecutive times.
12. The apparatus of claim 1 wherein the processor is further configured to generate and transmit subsequent leak detection test signals at predetermined time intervals.
13. The apparatus of claim 1 wherein the leak detection circuit comprises a resistor operatively coupled to a capacitor, the capacitor operatively coupled to the processor.
14. The apparatus of claim 13 wherein the resistor is operatively coupled to the at least one electrode.
15. The apparatus of claim 1 wherein the leak detection circuit has a leakage resistance between 100 MegaOhms and 10,000 MegaOhms.
16. The apparatus of claim 1 wherein the leak detection test signal has a duration of less than one second.
17. The apparatus of claim 16 wherein the leak detection test signal has a duration of between 250 milliseconds to 500 milliseconds.
18. A method of providing leak detection, comprising:
- generating, using a processor, a leak detection test signal;
- detecting, using a leak detection circuit operatively coupled to at least one electrode of an analyte sensor, a leakage current based on the leak detection test signal;
- generating, using the leak detection circuit, a leakage signal upon detection of a leakage current;
- receiving, using the processor, the leakage signal from the leak detection circuit in response to the leak detection test signal.
19. The method of claim 18 further including transferring, using an interface circuit, the leak detection test signal to the at least one electrode of the analyte sensor.
20. The method of claim 19 further including driving, using the processor, the leak detection test signal to the interface circuit.
21. The method of claim 18 further including driving, using the processor, the leak detection test signal to the at least one electrode of the analyte sensor.
22. The method of claim 18 wherein the leak detection test signal includes one of a digital signal or an analog signal.
23. The method of claim 18 wherein the leakage signal received by the processor includes an analyte related signal from the analyte sensor.
24. The method of claim 18 further including determining, using the processor, whether the received leakage signal exceeds a predetermined sensor signal level.
25. The method of claim 24 wherein the predetermined sensor signal level includes a measured sensor signal level, wherein the measured sensor signal level is measured by the processor at a predetermined time interval.
26. The method of claim 24 wherein the predetermined sensor signal level includes a tolerance level that corresponds to an acceptable current leakage level.
27. The method of claim 24 further including outputting, using the processor, a notification corresponding to the received leakage signal when the received leakage signal exceeds the predetermined sensor signal level a predetermined number of consecutive times.
28. The method of claim 18 further including generating and transmitting, using the processor, subsequent leak detection test signals at predetermined time intervals.
29. The method of claim 18 wherein the leak detection test signal has a duration of less than one second.
30. The method of claim 29 wherein the leak detection test signal has a duration of between 250 milliseconds to 500 milliseconds.
Type: Application
Filed: Feb 6, 2012
Publication Date: May 31, 2012
Applicant: Abbott Diabetes Care Inc. (Alameda, CA)
Inventor: Martin J. Fennell (Concord, CA)
Application Number: 13/367,347