300C and 300CD Rotating Optical Chopper

28 Nov 2012

Scitec Instruments Model 300 is a high stability variable frequency optical chopper. The basic system consists of a control unit, a chopping head and a set of four chemically blacked photo etched discs. This system provides operation over the frequency range 5Hz to 3kHz. A wide selection of additional discs and accessories is available to extend the frequency range and to satisfy individual requirements.

Features

5Hz - 3kHz standard optical chopping frequency range (0.015Hz to 40kHz options are available)

102mm diameter discs

Choice of control units

Compact optical chopper head

Low noise and vibration

Photochemically etched non-magnetic discs

Variable aperture

Two versions of the optical chopper control unit are available. The basic control unit is the 300CU, which has a 10 turn dial for setting the operating frequency. Alternatively, the 300CDU control unit has an additional 5-digit display of the chopping frequency. Other features are common to both control units. 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 on 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 300H optical chopper chopping head supplied with the standard system may be bench bolted or optical stalk (bench rod) mounted. 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.

The set of four chopping discs included with the system (part number 300D) provides a choice of 2, 5, 10 and 30 slots, each having a 1:1 mark to space ratio. Variable apertures can be achieved by mounting two identical discs simultaneously. Additional discs, with up to 445 slots, are available to extend the chopping frequency up to 40kHz. Although the standard discs are chemically blacked other finishes, such as gold plating, are available.