Scitec Instruments Ltd

Scitec Instruments Ltd has been a specialist manufacturer of optical choppers and lock-in amplifiers for more than 30 years.  The company is based in Trowbridge, UK.

The company offers a wide range of products including:

On-Trak is Scitec Instrument’s distribution partner for North America.

OPTICAL CHOPPERS

Optical choppers are a mechanical method of repetitively switching light beams on and off. They consist of a slotted rotating disc through which the light beam passes producing the chopping action.

Scitec’s products include:

  • 300CD Rotating Optical Chopper 

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 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.

 
 
  • 300C OEM Rotating Optical Chopper 

Scitec Instruments Model 300C OEM is a high stability variable frequency optical chopper.  The basic system consists of a PCB drive board, a chopping head and a single chemically-blacked photo-etched disc which can be selected from either 2, 5, 10 or 30 slots.  The available frequency range depends on the disc selected. A wide selection of additional discs and accessories is available to extend the frequency range and to satisfy individual requirements.

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

  • 102 mm diameter disc 

  • Compact optical chopper head

  • Low noise and vibration

  • Photochemically etched non-magnetic discs

  • Variable aperture

  • Range of accessories

The 300C OEM PCB drive unit is based on the 300CD control unit, it doesn't have a frequency display, as the 300CD does, but still provides the same functions and performance.  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 chopping disc included with the system can be chosen from either 2, 5, 10 or 30 slots.  The discs have 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.

 
  • 310CD High Speed Rotating Optical Chopper

The Model 310CD is a high-speed optical chopper based on the standard 102 mm diameter discs. By spinning the discs many times faster than the standard system, chopping speeds up to 110 kHz can be achieved.

The high speed is reached by using a 50 W electrically commutated motor and drive unit. The high efficiency of the motor means that a large proportion of the energy is transferred to the disc. Wind resistance is the limiting factor on the speed discs can be spun at. The greater the number of slots, the higher the wind resistance produced by the edge of the slots and hence the slower the maximum speed. To minimize losses, the chopping disc is enclosed in a carefully designed blade protector which guides the air flow around the disc.

  • 340CD Large Rotating Disc Optical Chopper

The Model 340CD is an optical chopper based on 200 mm diameter discs. The larger disc size allows larger diameter beams to be chopped. Please note that it does not allow smaller diameter beams to be chopped at a faster rate.

The chopper system comes with a choice of two 200mm discs. 

 
 
  • 350CD Miniature Rotating Optical

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 9mm 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.

  • 360C Ultra Miniature Rotating Optical Chopper

Scitec Instruments Model 360 optical chopper system consists of a chopper head, drive board, photochemically etched discs and an interconnecting cable.  This optical chopper uses 30mm diameter discs. The drive board and chopping head have been designed to be as compact as possible. The small size of the chopping head allows positioning in areas where space is critical. As the system is designed for OEM use, each component is available separately.

  • 10 Hz - 14,000 Hz standard chopping frequency range

  • 30 mm diameter discs

  • Photochemically etched non-magnetic discs

  • Ultra-compact chopper head

  • Small size drive board

  • Low cost, for OEM applications

  • C-995 Rotating Disc Optical Chopper

Manufactured by Terahertz Technologies Inc., the C-995 has a microprocessor based control system that uses direct digital synthesis to provide precise optical chopping rates from 4 Hz to 5000 Hz. Equipped with a large 5-digit LED readout, the C-995 controller enables digital entry of the desired chopping rates from the front panel.  In addition, the C-995 is equipped with a bi-directional RS-232 port that permits the user to set the desired chopping rate with a resolution of 0.001 Hz and to read the status of the instrument.

The C-995, designed with a phase locked loop control system, allows the chopping rate to also be synchronized to an external clock in the range from 4 Hz to 5 KHz.  The controller can then be used to read the frequency of the external clock.

The C-995 chopping head is attached to the controller by a 3 m (10 foot) coiled cable.  The precision etched blade is fully enclosed for protection from inadvertent damage. There are two apertures and two sections (30 slots and 3 slots) for the high and low frequency ranges, respectively. The aperture diameter is 15 mm with a slot width of 4.5 mm (30 slot section) or 30 mm (3 slot section).

The small 12 cm (4.75 in) square outline and 51 mm (2 in) maximum depth permit easy integration into compact optical setups.  Dual #8-32 mounting holes permit the apertures to be placed at a height as low as 19 mm (0.75 in) above an optical bench, or with the included 12.7 mm (1/2 in) rod and stand, as high as 33 cm (13 in) above the mounting surface.

  • Wide frequency range

  • Single blade 4 Hz - 5 KHz

  • Crystal controlled stability

  • External clock synchronization

  • Bright 5-digit LED display

  • Adjustable aperture height

  • Enclosed blade

  • Frequency resolution of 1 mHz

  • Bidirectional RS-232 port

  • S310SYNCH Synchroniser

Scitec Instrument Synchroniser is a unit that allows an Optical chopper to be synchronized to an external reference signal.  The chopper is both phase and frequency locked to the positive going edge of the master reference signal and the time difference (lead/lag) can be controlled via the synchroniser's USB interface.

  • Phase difference between the positive going edge of both the phase reference and chopper reference input signals is minimized

  • Phase lock typically achieved within 10 seconds over the full operating range of chopper

  • Phase lock maintained to within 2 degrees, 90% of the time

  • Relative Signal/Reference time delay in increments of 200 ns from 0 to +/- 13.1068 ms

  • Phase lock to multiples and sub-multiples of the Phase Reference input frequency (operating limits to be determined)

  • Output compatible with 300CD,310CD and 360C OEM choppers fitted with any compatible Scitec disc

  • Inputs filtered with single pole roll-off at 160kHz

  • USB 2.0 Interface with a control application with push-button style increment/decrement/reset of time delay. Set delay values retained on next power up

 
 
 
 

LOCK-IN AMPLIFIERS

Lock in amplifiers are instruments designed to recover signals that are buried in noise.  They require a reference signal at the same frequency as the signal that is being measured and then use this to demodulate the input signal before filtering.

Scitec produces a range of lock-in amplifiers to meet various requirements.

  • 410 Analogue Lock-In Amplifier 

Scitec Instruments Model 410 is a single phase analogue lock-in amplifier. It is suitable for making amplitude and phase measurements.

  • Single phase instrument 

  • Differential or single-ended input 

  • Gain settings from 3 μV to 1 V 

  • 10 Hz to 100 kHz 

  • High performance wide bandwidth input gain stage

  • Analogue meter for display of output signals 

  • Output offset controls 

  • Output time constants from 100 μs to 30 s 

  • 1F and 2F reference signal operation 

  • 90° step and fine phase control

A key figure of merit used for lock-in amplifiers is dynamic reserve. The dynamic reserve of a lock-in amplifier is defined as the ratio of the noise to signal that is allowed before saturation occurs. The dynamic reserve for the Model 410 is 60dB, allowing an input signal buried in noise 1000 times larger to be recovered.

 
 
  • 420 Analogue Lock-In Amplifier (Dual-Phase)

Scitec Instruments Model 420 is a dual phase analogue lock-in amplifier. Both the single-phase Model 410 and dual-phase Model 420 are suitable for making amplitude and phase measurements but it is significantly easier with the Model 420.

  • Dual phase instrument

  • Differential or single-ended input

  • Gain settings from 3 µV to 1 V

  • 10 Hz to 100 kHz

  • High performance wide bandwidth input gain stage

  • Analogue meter for display of output signals

  • Output offset controls

  • Output time constants from 100 µs to 30 s

  • 1F and 2F reference signal operation

  • 90° step and fine phase control

  • 430 and 441 Analogue OEM Lock-In Amplifiers

Scitec Instruments Model 430 and Model 441 are OEM analogue lock-in amplifiers.  Both the single phase Model 430 and dual phase Model 441 are suitable for making amplitude and phase measurements but it is significantly easier with the Model 441.  These PCB lock-in amplifiers offer a low cost solution to recovering noisy signals in many situations.

  • Single and dual phase versions

  • Differential or single-ended input

  • Sensitivities from 1 µV to 10 V for 1 V output

  • High performance wide bandwidth input gain stage

  • Low pass filter output time constants from 100 µs to 30 s

  • 1F and 2F reference signal operation

  • 90° step and fine phase control

Model 430

430 A single phase lock-in amplifier with manual setting, using jumpers, of input mode, sensitivity, low pass filter time constant and reference signal course phase control.

  • Sensitivity: 3 µV to 10 V in 1, 3, 10 steps for 1 V output (Gain settings of x0.1 to x330,000)

  • Reference input: TTL/CMOS with mark/space of 1:10 to 10:1 (triggered from rising edge only)

  • Power: -15 V, 0 V, +15 V and +5 V dc at 50 mA per supply rail.

Model 441

441 A dual phase lock-in amplifier with manual setting, using jumpers, of input mode, sensitivity, low pass filter time constant and reference signal course phase control. Can be used in either of the following three modes:

Dual phase operation - one input signal with two demodulators operating 90° apart providing both X and Y components of the input signal.

  • R calculation - on board circuitry provides the modulus of the X and Y components. 

  • Single channel 1F and 2F operation - one input signal and two demodulators operating at 1x and 2x the reference frequency to measure the first and second harmonics of the input signal

  • Sensitivity: 3 µV to 10 V in 1, 3, 10 steps for 1 V output (Gain settings of x0.1 to x330,000)

  • Reference input: TTL/CMOS with mark/space of 1:10 to 10:1 (triggered from rising edge only)

  • Power: -15 V, 0 V, +15 V and +5 V dc at 50 mA per supply rail.

Please contact us for additional detail on these products and others

 
 

14 Goodyear, Suite 130 Irvine, CA 92618 | Phone: +1-949-587-0769 | Fax: +1-949-587-9524 | Email: us.sales@on-trak.com

© 2019 On-Trak Photonics, Inc.

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