USER
MANUAL
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51331-006
Power Control
You can select whether you are using 1 or 2 USB ports. Note that the Photic automatically detects when external
power is applied.
Note that when using a single USB port, the Photic will automatically limit its power consumption to 0.5A, which
is the maximum available from a single port. This will reduce the light output from the unit at high repetition rates
when combined with high intensities and with maximum flash duration selected.
At the maximum flash duration, the intensity is reduced as follows:
y
At > 35Hz, the maximum intensity is 6
y
At > 45Hz, the maximum intensity is 5
y
At > 55Hz, the maximum intensity is 4
At the maximum flash duration and using 1 USB port means that the intensity is not less than 4 up to the maximum
repetition rate of 60Hz. This level of reduction is small and only comes into effect at extremes of operating condi-
tions and using the limited power availability from 1 USB port, as detailed.
To maintain the maximum intensity at the maximum repetition rate, use 2 USB ports with the optional USB splitter
cable (p/n 1243).
NOTE: The flash duration also affcts the power consumption in a linear relationship, So, if for example, the duration
is 8ms and using 1 USB port, then the intensity is reduced as follows (using a 10/8 multiplication factor):
y
At > 44Hz, the maximum intensity is 6
y
At > 56Hz, the maximum intensity is 5
This means that setting the duration to 6ms and using a single USB port, the maximum intensity is maintained up
to the maximum repetition rate.
Many host USB ports and powered Hubs can supply the intermittent power requirements of the Photic in full
power mode, so the ‘One USB port Double Power” option can be selected. Strictly speaking, a USB power splitter
cable allowing the connection of 2 USB ports should be used. If in any doubt, select the “One USB port Auto
Power” option or manually reduce the intensity or flash duration as described above.
Auto Duration Duty Cycle
This is the mode whereby the flash duration is proportional to the repetition rate according to a set duty cycle. In
this way, the intensity is increased at low frequencies. Duty Cycle can be set to 20, 30, 40 or 50% with a maximum
flash duration selectable between 50 and 200ms. This latter setting avoids very long flash durations at low
repetition rates. The Auto Duration feature is enabled/disabled with the check box. Note that when enabled, the
flash duration adjustments in other parts of the program are removed.
Photic Stimulator Setup Software
