A pump for pumping molten metal includes a refractory base that can be submerged in a bath of molten metal. One embodiment generates and conditions an excitation stimulus, drives a sensor with that stimulus, detects the user finger position through a change in the sensor output, and generates an appropriate signal for a downstream warning or other device. A preferred embodiment of a CT system which employs one of the specific formulas is described. Accordingly, it is possible to implement three current states, that is, hole current, electron current, and no current.