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Tuning Fork Chopper With Integrated Drive Electronics

		CH-25 DESCRIPTION CAD DRAWINGS

FEATURES AND ADVANTAGES ONE FIXED FREQUENCY from 200 Hz to 1000Hz Integrated driver Aperture up to 5mm Suitable for long life dedicated applications Simple to use Low power drive electronics Reference signal available Low Cost Small size/lightweight Always stops in the rest position High frequency stability High amplitude stability Withstands shock and vibration Rugged, no wearing parts Maintenance free High reliability High frequency stability High amplitude stability MEETS MILITARY SPECIFICATIONS1 Jitter free operation No radiated electromagnetic interference (EMI) Dark blades are standard, bright blades or mirrors are optional1 Single blade for alternate beam chopper1 1 Available on special order

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the model CH-25 tuning fork chopper with integrated drive electronics is low cost, compact size, lightweight and has virtually unlimited life; this makes it a device most suitable for small instruments and hand-held or portable systems. It is a great solution when working in tight spaces and especially suitable for long life, dedicated applications from prototypes to high volume applications.

This ONE FIXED FREQUENCY resonant optical chopper (modulator) is an electromagnetically driven tuning fork device, which uses vanes, of different shapes and surface characteristics, attached to moving tines, to chop a light beam with a sinusoidal motion. A range of factory set fixed frequency modulation waveforms (sine, half sine and pulse) is available. The modulating frequency range of the CH-25 chopper is from 200 Hz to 3 kHz, fixed at any one value within the range. The aperture is inversely proportional to the frequency, and is a function of the size of the vanes and the type (duty cycle). Operation at the natural resonant frequency is sustained by a feedback amplifier. The driver controls the aperture and provides a TTL output as a reference signal.

The most common type of aperture is the half open in the rest position, 90% duty cycle. It is used for a large beam diameter. When the modulator is operating in this configuration the maximum aperture is produced. The vanes are factory adjusted so that when fully illuminated the maximum excursion condition (controlled by the drive electronics) generates an almost complete sine wave as shown in table. Typically, the light is transmitted for 90% of each cycle. The 50% duty cycle modulation is used for a small beam diameter. The vanes are factory adjusted to be just closed in the rest position. Full aperture for 50% duty cycle is one half of the 90% duty cycle. Balanced operation and high "Q" insure frequency stability, low electrical drive power and low reaction forces. High flexural stiffness provides good resistance to shock and vibration. The standard operating temperature is 0°C to +65°C.

Tuning fork choppers are especially suitable for long life, dedicated applications, OEM, built into an instrument/system, and for portable systems. When working in tight spaces tuning fork choppers are the best solution.

Applications include: test equipment, noise detection (with a lock-in amplifier), pollution and gas detection, radiometry, radiation pyrometry, military systems, scientific and medical research, small size and hand held instruments. An important use of the chopper is in the communication and data acquisition environments, where optical signals are obscured by noise. A fixed frequency modulated signal can be filtered from background noise much more readily than an unmodulated signal. This is best achieved using a lock-in amplifier. In this arrangement, the detected signal and the reference signal, mixed with the frequency of the tuning fork chopper, cause the frequency of interest to appear as a pure dc output level. All other signals are filtered with the low pass filter. Once noise is removed, proper signal measurements can be obtained.

Tuning fork choppers are the most reliable choppers. They have an infinite lifetime and are used for chopping light, plasma, X-ray and laser light (VIS to DUV). The choppers are used in systems and portable instruments in industrial, scientific, medical, aerospace and military applications worldwide.

Special pricing for OEM applications.