How does the PEM work?

The PEM is a resonant device whose precise oscillating frequency is determined by the physical properties of the optical element/transducer assembly. The electronic head, optical head and the cables that connect them make up a circuit that operates like a crystal-controlled oscillator circuit.

The PEM controller controls the amplitude of the PEM oscillations and generates a reference signal. A feedback signal from the head assembly is used by the controller to monitor the PEM oscillation amplitude and to provide timing for the generation of the reference.