Scitec Instruments Model 300CD 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.

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
Range of accessories

The 300CD control unit has 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 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.

Specifications:

300CD Control Unit

Output Voltage 15V DC Maximum
Stability ±0.01%/°C
Frequency Control Internal - Manual Control via 10 turn potentiometer. External - BNC connector for 0 to 15V
Frequency Read Out 5 digit 14mm LED display with 0.01Hz resolution, 0.1Hz or 1Hz resolution depending on frequency
Frequency Stability Short term - see phase jitter, Long term - ±0.1% of maximum frequency
Reference output 5V HCT TTL signal via BNC socket
Power Requirement 100-130V or 200-260V AC, 50 or 60Hz, 12 VA
Dimensions 254(W) x 76(H) x 178(D)mm
Weight 2.6kg

Chopper Head 300H Chopping Head

Motor 11 pole DC motor, sleeve bearings with more than 6000 hours lifetime, 0-6000rpm reversible
Reference pick-up IR led and phototransistor pair with Schmitt trigger
Dimensions 73(H) x 75(L) x 32(W)mm, without disc
Mounting Optical stalk - adjustable between 6.5 and 14.0mm diameter. Mounting holes - 2 x 3mm

300D Set of Chopping Discs

Disc types 2, 5, 10 and 30 slot
Material Half hard brass, 0.5mm thick
Diameter 102mm
Surface Finish Chemically blacked
Mark to Space Ratio 1 to 1 with one blade