Methods, systems, and devices for electrode capacitance calculation and application
The double layer capacitance of a working electrode of a sensor may be measured with minimal disruption to the sensor equilibrium by open circuiting the working electrode and measuring the voltage drift on a periodic, or as-needed, basis. The values of the double layer capacitance may be monitored over time to determine, e.g., sensor age and condition.
1. A method for determining whether a used glucose sensor is being used by a user for measuring the level of glucose in the user's body, said sensor being a subcutaneous or implantable glucose sensor and including physical sensor electronics, a microcontroller, and a working electrode (WE) in an electrical circuit that provides an input current to the working electrode, the method comprising:
(a) measuring, by said sensor electronics, a first current level for the working electrode current;
(b) after measuring said first current level, open circuiting, by said microcontroller, the working electrode by discontinuing said input current to the working electrode for a time period having a predefined duration, wherein said predefined duration is shorter than 30 seconds;
(c) during said time period, measuring, by said sensor electronics, a first WE voltage value and a second WE voltage value, said first value being measured at a first point in time after open circuiting the working electrode, said second value being measured at a second point in time after open circuiting the working electrode, and said first and second values being measured when the current level for the working electrode current is substantially zero;
(d) resuming said input current to the working electrode after said second point in time and calculating the working electrode's capacitance by the relation C=(I)/(dV/dT), wherein I is the first current level, dV is the difference between said first and second WE voltage values, and dT is the difference between said first and second points in time;
(e) periodically repeating steps (a)-(d) and monitoring the working electrode's capacitance over a predetermined time interval;
(f) determining, by said microcontroller, that the sensor is a used sensor when the change in the working electrode's capacitance over said predetermined time interval is less than a threshold value; and
(g) based on said determination that the sensor is a used sensor, prompting the user, by the microcontroller, to replace the used sensor with a new sensor.
2. The method of claim 1 , wherein said predetermined time interval is between about 15 and about 30 minutes.
3. The method of claim 1 , wherein said threshold value is between about 3% and about 5%.
4. The method of claim 1 , wherein steps (a)-(d) are repeated about once every 5-15 minutes.
5. The method of claim 1 , wherein said dT is between about 7 seconds and about 15 seconds long.
6. A method for determining whether a used glucose sensor is being used by a user for measuring the level of glucose in the user's body, said sensor being a subcutaneous or implantable glucose sensor and including physical sensor electronics, a microcontroller, and a working electrode (WE) in an electrical circuit that provides an input current to the working electrode, the method comprising:
(a) measuring, by said sensor electronics, a first current level for the working electrode current;
(b) after measuring said first current level, open circuiting, by said microcontroller, the working electrode by discontinuing said input current to the working electrode for a time period having a predefined duration;
(c) during said time period, measuring, by said sensor electronics, a first WE voltage value and a second WE voltage value, said first value being measured at a first point in time after open circuiting the working electrode, said second value being measured at a second point in time after open circuiting the working electrode, and said first and second values being measured when the current level for the working electrode current is substantially zero;
(d) resuming said input current to the working electrode after said second point in time and calculating the working electrode's capacitance by the relation C=(I)/(dV/dT), wherein I is the first current level, dV is the difference between said first and second WE voltage values, and dT is the difference between said first and second points in time, wherein said dT is between about 7 seconds and about 15 seconds long;
(e) periodically repeating steps (a)-(d) and monitoring the working electrode's capacitance over a predetermined time interval;
(f) determining, by said microcontroller, that the sensor is a used sensor when the change in the working electrode's capacitance over said predetermined time interval is less than a threshold value; and
(g) based on said determination that the sensor is a used sensor, prompting the user, by the microcontroller, to replace the used sensor with a new sensor.
7. The method of claim 6 , wherein said predetermined time interval is between about 15 and about 30 minutes.
8. The method of claim 6 , wherein said threshold value is between about 3% and about 5%.
9. The method of claim 6 , wherein steps (a)-(d) are repeated about once every 5-15 minutes.