A vehicle speed measurement method and system for identifying a violating vehicle utilizing single image capturing unit. The device includes a voltage source, a first ion optical element coupled with the voltage source, a second ion optical element resistively coupled with the first ion optical element; and a pulse generator capacitively coupled with the second ion optical element. The loop has two drive capacitors and a tuning capacitor, all of which in series. The replacement card may be drawn from a plurality of possible face-up or face-down cards.