An optical chopper is an electromechanical instrument that periodically interrupts a beam of light. The MC2000 Optical Chopper, utilizing advanced features to meet the most demanding applications, is a rotary type that is composed of a control console, motor head assembly and slotted chopper wheel. The MC2000 uses a phased-locked loop (PLL) motor speed control design to precisely maintain the chopping speed and phase to a reference signal. An internal, crystal-stabilized, frequency synthesizer provides an accurate and stable reference frequency for long-term stable performance.
Unlike conventional, open-loop speed control designs, the PLL speed control circuit also allows the MC2000 chopper to be synchronized to external reference signals, including other MC2000 choppers and reference sources such as DSP lock-in amplifiers.
For more advanced measurements, the MC2000 can lock to a harmonic, sub-harmonic, or fractional-harmonic of an external reference frequency. The on board microprocessor is used to multiply the external reference up to the 15th harmonic or to divide the reference down to the 15th sub-harmonic. By combining both the frequency multiplication and division together, a fractional harmonic can be obtained.