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418M Optical Chopper

The 418M optical chopper consists of a modular control unit suitable for fitting in the 417 housing, and is coupled by a 2m long lead to the chopping head. Four easily-interchangeable chopping discs are provided as standard which allow chopping frequencies in the range of 5 Hz to 3kHz.

A variable aperture 2-slot disc and higher frequency discs are also available. The chopping frequency is indicated by a digital indicating dial and a squarewave reference output suitable for use with lock-in amplifiers is provided.


SPECIFICATION
Chopping Frequency 2-slot disc 5Hz - 200Hz
5-slot disc: 12.5Hz - 500Hz
10-slot disc: 25Hz - 1kHz
30-slot disc: 75Hz - 3kHz
Phase jitter 2-slot disc: 0.6° pk-pk over entire frequency range
5, 10 and 30-slot disc: 1° pk-pk over entire frequency range
Frequency selection By multi-turn potentiometer
Reference output 800mV positive-going wave from 200W. Sensed by IR LED/photodiode mounted on chopping head
Display LCD frequency display on free-standing controller turns counting dial on modular unit
Resolution 1Hz with 10-slot disc
Motor High quality 11-pole dc motor with precious metal commutator
Calibration Accuracy ±1% for setting between 15% and 100% of full scale
Variable aperture A variable aperture 2-slot disc is available for non-even mark space modulation
Frequency stability Versus temperature: Less than 0.01% change per K
Versus line voltage Less than 0.01% change results from a change in line voltage from 190V to 265(95V to 130V)