The 218 optical chopper consists of a free-standing or modular control unit 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 0.5Hz to 4kHz (3kHz for the modular control unit).

A variable aperture 2-slot disc and higher frequency discs are also available. The free-standing control unit includes LCD display of chopping frequency, while the modular unit uses a digital indicating dial. Both units provide a square wave reference output suitable for use with lock-in amplifiers.

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
External control: The chopping frequency can be externally control via a front panel socket. Maximum input is = 15V into 20kW.
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)

 

Dimensions