Patent ID: 8160834

Claim:
A method of observing a state of a sensor having a plurality of electrodes, the method comprising: (a) applying a voltage to the sensor; (b) measuring a stable-state current (Ibase) produced in response to the voltage applied to the sensor; (c) applying the stable-state current measured in (b) to the sensor; (d) measuring sensor voltage during the application of the stable-state current; (e) changing applied sensor current to a second current comprising Ibase+deltaI, wherein deltaI comprises the difference between the Ibase and the second current; (f) measuring sensor voltage during the application of the second current; (g) observing a first voltage step between the voltage measured in (d) and the voltage measured in (f) that results from electrical resistance (R) in the sensor; so that the state of the sensor is observed; (h) changing applied sensor current to a third current comprising Ibase+deltaII, wherein deltaII comprises the difference between the Ibase and the third current; (i) measuring sensor voltage during the application of the third current; (j) observing a second voltage step between the voltage measured in (d) and/or (f) and/or (i) that results from electrical resistance (R) in the sensor; (k) calculating a voltage slope (dV/dt) using multiple voltage step measurements, wherein the voltage slope so calculated is correlated to a change in sensor capacitance (C) that results from the different currents applied to the sensor.