Abstract: A reference electrode of an electrochemical sensor includes a substrate having well, a channel, and a conductive element therein. The well extends from a first surface of a substrate towards a second surface of the substrate. The channel is within the substrate. A longitudinal axis of the channel may be substantially perpendicular to a longitudinal axis of the well. The channel has a first end connected to the well and the conductive element is exposed to a second of the channel. The channel and the wells form a flow path of a conductive medium. A valve is coupled to the flow path and configured to control a flow of the conductive medium to the electrically conductive element through the flow path.