Model 350CD

Miniature rotating disc optical chopper

Please contact us for further information on this product.


Scitec Instruments Model 350 is a high stability variable frequency optical chopper. The basic system consists of a control unit and a chopping head. It is supplied with four chemically blacked 30 mm diameter discs. These discs are of 2, 4, 10 and 40 slots and allow operation over the frequency range 10 Hz to 10 kHz. Discs with 20 and 80 slots are also available. The small chopping head allows positioning in areas where space is critical.

  • 10 Hz – 10 kHz standard chopping frequency range
  • 30 mm diameter discs
  • Choice of control units
  • Very compact chopper head
  • Low noise and vibration
  • Photochemically etched non-magnetic discs

The control unit has a 10 turn dial for setting the operating frequency and a 5-digit display of the chopping frequency. Chopping frequency can be controlled externally by applying an analogue voltage to a “Control” BNC. A “Reference” BNC provides a TTL level output, generated directly from the opto-switch within the chopping head. This signal has constant phase relative to the chopping action and can be used as the reference for other instruments such as lock-in amplifiers.

The 350H chopping head completely encloses the chopping disc, drive motor and reference pick-up. Three optical apertures of 9 mm diameter provide flexibility in beam positioning. The chopper head has an M8 threaded hole in its base for mounting on an optical stalk (bench rod). Mountings are provided to enable parts, such as a high frequency accessory or blade protector, to be attached. For lower frequency operation, the chopper head can be fitted with a reduction gearbox motor.

350CDU Control Unit

  • Output Voltage: 6 V DC Maximum.
  • Frequency Control: Internal – Manual Control via 10 turn potentiometer. External – BNC connector for 0 to 15 V.
  • Frequency Read Out: 5 digit 14mm LED display with 0.01 Hz resolution, 0.1 Hz or 1 Hz resolution depending on frequency.
  • Frequency Stability: Short term – see phase jitter. Long term – ±1% of max frequency within 10 to 100% of maximum frequency.
  • Reference output: 5 V HCT TTL signal via BNC socket.
  • Power Requirement: 90-130 V or 180-260 V AC, 50 or 60 Hz, 12 VA.
  • Dimensions: 254(W) x 76(H) x 178(D) mm
  • Weight: 2.6 kg

The datasheet for the Model 350CD optical chopper is available in pdf format:

Model 350CD datasheet