Overview
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, in common with all SIGNAL RECOVERY light choppers, 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 these choppers to be used in conjunction with the dual reference modes offered by our model 7124, 7265, 7270, and 7280 lock-in amplifiers to implement twochannel source compensation experiments.
Specifications
| General | |
| Dual-aperture self-contained chopper with internal or external refence frequency. Two sync outputs. | |
| Frequency outer sector inter sector |
15 Hz to 3000 Hz
150 Hz to 3000 Hz 15 Hz to 300 Hz |
| Control manual external |
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
accuracy |
±20 ppm at 25 ºC |
| Jitter (measured pk-pk and presented as a % of a full cycle) | |
| outer sector 150 to 500 Hz 500 to 3000 Hz |
blade only: 0.5%; blade + electronics: < 1.5%
blade only: 0.5%; blade + electronics: < 1% blade only: 0.5%; blade + electronics: < 1.5% |
| 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 |
| Outputs | |
| 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. |
| General | |
| 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 |
| Dimensions Width Height Depth |
43/4" (122 mm) 4" (104 mm) 13/4" (44 mm) |
| Weight | 1 lb (0.45 kg) excluding power supply |
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