218M Optical Chopper & Control Module

  • 218M modular optical chopper with chopper wheels and control unit

Four easily-interchangeable chopping discs are provided as standard which allow chopping frequencies in the range of 5Hz to 3kHz.

Key features of the 218M, such as phase jitter, frequency stability and a long motor life, have been prioritised over more esoteric features not required in most applications to offer outstanding performance in a cost effective solution.

Core benefits




  • Modular optical chopper control unit with remote chopper providing frequencies of 5Hz-3kHz
  • Square wave reference output for use with lock-in amplifiers
  • Front panel control
  • Arrest function for source integrated arrestable choppers
  • Fully programmable via USB 2.0 interface




Chopping Frequency with 2-slot blade

10Hz to 250Hz

Chopping Frequency with 5-slot blade

12.5Hz to 500Hz

Chopping Frequency with 10-slot blade

25 Hz to 1kHz

Chopping Frequency with 30-slot blade

75 Hz to 3kHz

Phase Jitter with 2-slot blade

0.6° peak-to-peak over entire frequency range.

Phase Jitter with 5-, 10- and 30-slot blades

1° peak-to-peak over entire frequency range.

Reference Output

3V peak-to-peak square wave with 1kΩ output impedance


1Hz with 10-slot disc


High quality 11-pole DC motor with precious metal commutator

Temperature Dependence of Frequency Stability

Less than 0.01% change per K

Line Voltage Dependence of Frequency Stability

Less than 0.01% change results from a change in line voltage from 190V to 265/ 95V to 130V

Interface & Mechanical


Front panel

Front Panel Controlled Features

Chopping frequency set, chopper on/off


Single width module, 3U high


Amphenol (chopper), BNC (reference)

Ordering Information


218M Optical Chopper & Control Module


Blade set (2, 5, 10 and 30 slot)


Chopping head


Chopper mounting plate for monochromator entrance slit


Chopper mount for IL1, IL6, IL7 and IL8

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