An AM-EWOD device includes a plurality of array elements arranged in an array of rows and columns; each column including a column addressing line that applies control signals to a corresponding column of array elements, and each row including a row addressing line that applies control signals to a corresponding row of array elements; each array element including an element electrode for receiving an actuation voltage and a switch transistor, wherein the switch transistor is electrically connected between the column addressing line and the element electrode and is switched by the row addressing line; and a column detection circuit comprising an addressing circuit that applies an electrical perturbation during a sensing operation to the column addressing line of an array element being sensed, and a measuring circuit that measures an output signal from one of the column addressing lines, wherein the output signal varies based upon a capacitance present at the element electrode.