KOBOLD limit switches model NEH are used for level monitoring and pump control of conductive liquids. The instruments operate on the conductive principle. A low a. c. voltage is applied between the conductive side of the tank or the earth electrode (longest electrode) and a switching point electrode. If the conductive medium touches the electrodes, a negligible alternating current flows across the electrodes and the conductive medium to the electrode relay. Suspended electrodes are ideally suited for installation when space is at a premium. The relay amplifies the alternating current and operates a switching relay or a pump controller.