Measuring Harvested Energy Using an Ultra-Low Duty Cycle Measurement System

摘要

A method for measuring energy harvested from at least one energy source for use in an access control system, comprising providing an access control device adapted to be at least partially powered by energy harvested from at least one energy source; providing at least one sensor receiving energy from the at least one energy source; providing an energy harvesting manager coupled to the at least one sensor, wherein the energy harvesting manager manages the amount of energy received by the at least one sensor; providing a capacitive storage device coupled to the energy harvesting manager, the capacitive storage device for storing energy harvested from the at least one sensor; charging the capacitive storage device to a voltage high threshold, V-HTH; applying a reference load to the capacitive storage device until the capacitive storage device discharges to a predetermined voltage value, Vo/e, the reference load having a predetermined resistance value; determining a time constant, the time constant defined as the length of time required for the capacitive storage device to discharge to the predetermined voltage value, Vo/e; and determining an exact or near exact capacitance of the capacitive storage device by comparing the time constant to the reference load predetermined value, by the expression: C=RC/RL, where C=capacitance (in farads), RC=time constant (in seconds), and RL=reference load resistance (in ohms).