Real-time self-calibrating sensor system and method

A self-calibrating characteristic monitoring system for monitoring a characteristic of a user, said system comprising:

• a sensor for producing a signal indicative of said characteristic, the sensor including a counter electrode, a reference electrode, and a working electrode in communication with the user's blood or interstitial fluids;
• a sensor-calibration module having a first control unit, wherein the control unit comprises an operational amplifier (op amp) connected in an electrical circuit such that a voltage V1 equal to the measured difference between the working electrode voltage and the reference electrode voltage provides a first input into the op amp, an applied voltage V2 provides a second input into the op amp, and the output of the op amp is electrically connected to the counter electrode via a current-interrupt switch, said sensor-calibration module being configured to calibrate the sensor based on the value of the measured voltage V1 and the magnitude of an IR drop due to a resistance between the reference and working electrodes;
• and
• a remotely located data receiving device for receiving data indicative of said characteristic based on said signal.

A machine-readable medium for use in conjunction with a sensor configured to produce a signal indicative of a characteristic of a user, wherein the sensor includes a counter electrode, a reference electrode, and a working electrode, said electrodes being in communication with the user's blood or interstitial fluids and connected in an electrical circuit such that a first voltage V1 equal to the difference between the working electrode voltage and the reference electrode voltage provides a first input into an operational amplifier (op amp), a second voltage V2 provides a second input into the op amp, and the output of the op amp is electrically connected to the counter electrode via a current-interrupt switch, said medium being encoded with instructions that, when executed, cause a computer to perform a sensor-calibration process comprising:

• a. obtaining a measurement for V1 at a time when the current-interrupt switch is closed;
• b. transmitting an instruction to open the switch while obtaining a multiplicity of successive measurements for V1 during a pre-determined time period that starts prior to, and ends after, the opening of the switch;
• c. determining the magnitude of a voltage V3=V1t=0, wherein V3 is indicative of an overpotential at the working electrode, and V1t=0 is the magnitude of V1 at the point in time when the switch is opened;
• d. based on the determined value of V3 and a voltage Vset, calculating V2 in such a way as to have V3 become substantially equal to Vset, wherein Vset is the optimally desired voltage between the working and reference electrodes;
• and
• e. transmitting an instruction to close the current-interrupt switch and apply the calculated value of V2 as said second input to the op amp.

A method of calibrating a sensor configured to produce a signal indicative of a characteristic of a user, wherein the sensor includes a counter electrode, a reference electrode, and a working electrode, said electrodes being in communication with the user's blood or interstitial fluids and connected in an electrical circuit such that a first voltage V1 equal to the difference between the working electrode voltage and the reference electrode voltage provides a first input into a comparator, a second voltage V2 provides a second input into the comparator, and the output of the comparator is electrically connected to the counter electrode, said method comprising:

• a. measuring V1 between the working and reference electrodes;
• b. determining the magnitude of a third voltage V3, wherein V3 is indicative of an overpotential at the working electrode;
• c. based on the determined value of V3 and a voltage Vset, calculating V2 in such a way as to have V3 become substantially equal to Vset, wherein Vset is the optimally desired voltage between the working and reference electrodes;
• and
• d. applying the calculated value of V2 as said second input to the comparator.