Ocean Optics S1024DW Install - Manual (Page 43)

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Sampling Optics: FVA-UV Fiber Optic Variable Attenuator
The FVA-UV F IBER O PTIC V ARIABLE A TTENUATOR is an opto-mechanical device that controls the
amount of light being transmitted by a fiber and the amount of light entering the optical bench of the
spectrometer. Each end of the attenuator has SMA 905 terminations for connecting the attenuator to light
sources, sample holders, and fibers. The FVA-UV attenuates light uniformly at all wavelengths.
Application Tips
•
The attenuator can be used for applications where more light reaches the spectrometer than likely can
be digitized successfully by the spectrometer's detector. Some absorbance experiments may also
require signal attenuation, as too much light can saturate the reference measurement.
•
In some instances, detector saturation can be avoided by adjusting (through software) the spectrometer
integration time to limit the interval during which the detector collects light -- somewhat akin to
changing the shutter speed on a camera to a faster exposure time. Other options include using different
gratings, changing the optical bench entrance aperture (by installing slits or using small-diameter
optical fibers), or adding neutral-density filters to the optical path. The FVA-UV fits in where these
intensity-reduction techniques are either unworkable or undesirable.
Operation
•
The attenuator comes with two collimating lenses, one screwed in at each side. The thumb wheel
position is held in place with a set screw.
•
A 6-32 white nylon screw pinches the mechanical adjustment wheel. Loosening the white nylon screw
allows the mechanical adjustment wheel to be turned. When the wheel is positioned to your liking,
tighten the white nylon screw to keep the wheel in place during your measurement. The wheel is
placed between two Teflon washers to provide smooth operation and is knurled along the edge for
fingertip gripping.
•
To completely close the attenuator, turn the wheel to the white line marking and tighten the white
nylon screw. You will hear a “snap” in the closed position.
Using the Adapters
With the FVA-ADP-UV and FVA-ADP-VIS, users can connect the attenuator directly to any light source
having a collimating lens at its aperture. To use these adapters, simply:
1. Use an Allen wrench to loosen the set screw of one of the collimating lenses on the attenuator and take
out the inner barrel.
2. Slip in the adapter and tighten the set screw.
3. Loosen the set screw on the collimating lens of the light source. Remove the inner barrel of the lens
and slide the adapter/attenuator into the collimating lens. Tighten the set screw.
Specifications
Dimensions: 1.5” x 1.5” x 1.0”
Assembly ports: 3/8-24 threads for collimating lenses
Adjustment wheel:
diameter = 3/32”
material = black anodized aluminum with knurled edge
Adjustment wheel lock: 6-32 Nylon thumb screw
Connector: SMA 905