197 Optical Chopper

Precision Light Chopper

The model 197 is a compact, high performance chopper, offering features and benefits that are ideal for use in modern photometric systems.

The unit is self contained, comprising a dual aperture chopper blade, motor and the necessary driving electronics. Each aperture provides an independent reference output allowing simultaneous dual frequency operation (10:1 ratio) for dual-path experiments. Frequency control is by a precision internal oscillator set by a 4-digit push-button selector on the unit or by the application of an external AC reference signal. The unit is powered via an external line power supply module.

Mounting holes are provided in the base and right-hand side of the housing (viewed from the front) to allow for mounting the model 197 onto an optical bench or support post.

Quartz Crystal Frequency Accuracy and Stability
The model 197 uses a quartz crystal oscillator as its primary frequency standard. The oscillator signal is divided down to yield the required chopper frequency, and then the motor speed is continuously adjusted to phase lock the actual chopper frequency to this required value. The result is a chopper with an output frequency as stable as any other modern frequency source.

External Frequency Control
Like many other choppers, the frequency can be controlled externally. However, unlike other units the control is via an applied TTL reference rather than an analog voltage. This means that the modulation frequency generated is exactly that required which allows this chopper to be used in conjunction with the dual reference modes offered by all our lock-in amplifiers to implement two channel source compensation experiments.
  • Documents +

  • Specifications +

    Dual-aperture self-contained chopper with internal or external refence frequency. Two sync outputs.

    outer sector

    inter sector
    15 Hz to 3000 Hz

    150 Hz to 3000 Hz

    15 Hz to 300 Hz

    Digital push-button
    Application of 0.5 v to 10 V pk-pk sine or squarewave, 150 Hz to 3000 Hz to EXT SYNC BNC connector
    Internal Frequency


    ±20 ppm at 25 ºC
    ±30 ppm/ ºC (range 10 ºC to 60 ºC
    Jitter (measured pk-pk and presented as a % of a full cycle)
    outer sector
    150 to 500 Hz

    500 to 3000 Hz

    inter sector
    15 to 50 Hz
    50 to 500 Hz

    blade only: 0.5%; blade + electronics: < 1.5%

    blade only: 0.5%; blade + electronics: < 1%

    blade only: 0.5%; blade + electronics: < 1.5%
    blade only: 0.5%; blade + electronics: < 1%
    Lock indication Bicolor LED - red when unlocked and green when locked
    Setting Time 7 s nomimal at 1 kHz from switch-on; 9 s nominal for frequency change from 150 to 3000 Hz; 30 a nominal for frequency change from 3000 tp 150 Hz
    Sync Out 1 10 V pk-pk squarewave at outer sector chopping frequency, 150-3000 Hz
    Sync Out 2 10 V pk-pk squarewave at inner sector chopping frequency, 15-300 Hz
    Connectors BNC
    Impedance 10 kΩ. Note that although the output voltage is 10 v pk-pk, the high output impedance means that the outputs can be directly connected to the external reference input of any SIGNAL RECOVERY lock-in amplifier without causing problems.
    Power Requirements Via separate power adapter for 110 V AC, 50/60 Hz or 220/240 V AC, 50/60 Hz supply. State which voltage is required when ordering

    43/4"(122 mm)
    4" (104 mm)
    13/4"(44 mm)
    Weight 1 lb (0.45 kg) excluding power supply