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Model 197
Precision Light Chopper
General
The model 197 is a compact, high performance, low-cost optical
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) or 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 a remote line power supply.
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 rod.
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 signals is divided down to yield the required
chopper frequency, and then the motor speed is continuous adjusted to
phase lock the actual chopper frequency to this required value. The result
is a chopper with an output frequency as stable as other modern frequency
sources.
External Frequency Control
Like many other choppers, the frequency can be controlled
externally. However, unlike other units the control is via an applied
reference signal (TTL levels may be used) rather than an analog voltage.
This means that that the modulation frequency generated is exactly that
required, and allows the units to be used in conjunction with the dual
reference modes offered by our model 7265 and 7280 lock-in amplifiers to
implement two-channel source compensation experiments - see diagram below
or consult applications
note AN1000. Usually, however, the model 198A
is chosen in preference to the model 197 for this application since the
two frequencies it generates are relative primes.
Using the Model 197 with a Model 7265 to implement a
dual-channel source compensation experiment
Mechanical Dimensions
Blade Dimensions
| Operation |
|
|
Frequency |
15 Hz to 3000 Hz |
|
outer sector |
150 Hz to 3000 Hz |
|
inner sector |
15 Hz to 300 Hz |
|
Control |
|
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manual |
Digital push-button |
|
external |
Application of 0.5 V to 10 V sine or
squarewave, 150 Hz to 3000 Hz to Sync In BNC connector |
|
Internal Frequency |
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accuracy |
±20 ppm at 25 °C |
|
stability |
±30 ppm/ °C (range -10 °C to 60 °C) |
|
Jitter (measured pk-pk and presented as a
% of a full cycle) |
|
|
outer sector |
|
|
150 to 500 Hz |
blade only: 0.5%; blade + electronics:
1.5% |
|
500 to 3000 Hz |
blade only: 0.5%; blade + electronics:
1.0% |
|
inner sector |
|
|
15 to 50 Hz |
blade only: 0.5%; blade + electronics:
1.5% |
|
50 to 300 Hz |
blade only: 0.5%; blade + electronics:
1.0% |
|
Lock indication |
Bicolor LED, showing Red when unlocked
and Green when locked |
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Settling Time
|
7 s nominal at 1 kHz from switch-on;
9 s nominal for frequency change from 150 to 3000 Hz;
30 s nominal for frequency change from 3000 to 150 Hz |
| Outputs |
Sync Out 1 |
10 V pk-pk squarewave at outer sector
chopping frequency, 150 - 3000 Hz |
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Sync Out 2 |
10 V pk-pk squarewave at inner sector
chopping frequency, 15 - 300 Hz |
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Connectors |
BNC |
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Impedance |
10 kW. 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 Reference Frequency input
of any SIGNAL RECOVERY lock-in
amplifier without causing problems. |
| Power Requirements |
Via power adapter for 110 V AC, 50/60 Hz
or 220/240 V AC, 50/60 Hz or external isolated 17 V to 20 V DC
or AC rms. supply. State which voltage is required when ordering |
| Dimensions |
4" high x 4.8" wide x 1.7"
deep
(104 mm wide x 122mm wide x 44mm deep) |
| Weight |
1 lb (0.45 kg) excluding power
supply |
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is
a trademark of AMETEK, Inc.