A method for position sensing includes inserting a probe having a first probe-electrode and a second probe-electrode into a body of a subject, and coupling body-surface electrodes to a surface of the body. Currents passing between the first probe-electrode and the body-surface electrodes are measured, using first circuitry coupled to at least the first probe-electrode and having a first electrical ground, and position coordinates of the probe are determined responsively to the measured currents. Second circuitry, having a second electrical ground, is coupled to at least the second probe-electrode, and the first electrical ground is isolated from the second electrical ground.
