Optical Chopper0 pages

Optical Chopper
Model 300C/CD

Model 300C

Features
→ 5 Hz – 3 kHz standard frequency range, can be
extended to 15 mHz – 40 kHz
→ Choice of control units
→ Compact chopper head
→ Low noise and vibration
→ Photochemically etched non-magnetic discs
→ Variable aperture
→ Range of accessories
→ Scitec Instruments Model 300 is a high
stability variable frequency optical chopper. The
basic system consists of control unit, chopping
head and set of four chemically blacked photo
etched discs. This system provides operation
over the frequency range 5 Hz to 3 kHz. A wide
selection of additional discs and accessories is
available to extend the frequency range and to
satisfy individual requirements.

Model_300C/CD_issue1.1

Model 300CD

→ Two versions of the 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 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
or 30 slots each having a 1:1 mark-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 40 kHz.
Although the standard discs are chemically blacked other
finishes, such as gold plating, are available.
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