FPD-IG-175, FPD-UV-3000, FPD-VIS-300 User Manual
3
II.
Operation of your Ophir Fast Photodiode Detector
A.
Caution: Eye safety precautions must be followed with any equipment used in the vicinity of laser
beams. Laser beams may reflect from the surface of the detector or the optical mount and caution
must be exercised.
B.
Mount the detector to an optical stand using the mounting holes on the bottom of the detector housing.
Each detector is provided with an 8-32 threaded nylon standoff. If the detector is mounted to a metal
post, it is recommended to insert the standoff between the detector and the post in order to minimize
the potential for electrical noise pickup.
C.
Adjust the voltage scale of the oscilloscope to 100mV/division before connecting the detector. On
models with >3V bias supply, the signal may be large enough to damage the oscilloscope if this is
not done.
D.
Connect the detector to the oscilloscope using a 50Ω coaxial cable that is one meter or less in length.
E.
Use the 50Ω impedance input of the oscilloscope or other measurement instrument. If the
oscilloscope does not have a 50Ω input, connect a 50Ω terminator between the coax cable and
the oscilloscope’s high impedance input.
Note:
Current will be drawn from the batteries whenever a load is present at the output. In
order to avoid draining the batteries, the output connection should be disconnected
whenever the product is not in use.
F.
Verify that the laser power density is below the maximum recommended signal level and place
the detector in the laser beam. However, it is not necessary for the detector to be located directly
in the laser beam to measure properly. If the laser beam is too powerful and it saturates the
detector, the beam can be scattered from a white surface and the detector can be placed at a
distance from the beam to look at a small fraction of the beam intensity. The distance from the
scattering surface and the detector can be varied to get a good but not saturated signal. If the
intensity is still too high, or it is not convenient to measure scattered light, filters are available to
lower the laser intensity. See the Accessories section below.
III.
Batteries
Batteries will typically operate for several years, but operation with CW or high rep rate lasers can drain the
batteries much faster. Leaving the detector output connected to a load for long periods of time can also
drain the batteries. It is recommended to disconnect the output whenever the detector will not be in use for
long periods of time.
As the batteries become depleted, the bias voltage on the photodiode will decrease. This will increase the
rise and falls times of the detector and also reduce its saturation level. The ability of the battery to supply
current quickly will also be reduced which is manifested as saturation effects in the output signal.
The batteries can be accessed for checking their voltage and replacement by removing the top plate of the
housing. If necessary, replace with type CR2430 lithium cells. Check the specifications below for the
number of batteries required for each model. Install batteries with positive side down.
