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User name Bryon
Log entry time 21:43:34 on February 7,1998
Entry number 3143
This entry is a followup to: 3142
keyword=SOS Cerenkov LEDs
The SOS Cerenkov detector now has LEDs mounted on the outside of each of the
4 phototube Winston cones. At the Present time the LED's can be driven from the
hall C counting house via old lucite Cerenkov signal cables which have been
connected to the LED feedthroughs as:
Phototube # Lucite Channel Patch panel #
1 LC5- I575
2 LC6- I576
3 LC7- E262
4 LC8- E263
Note that LC7- has some problem because a fast signal is attenuated and broadened
on this cable; there seems to be a reflection at or very near the patch panel
feedthrough in the counting house.
The signal cables for the LED's DO NOT have current limiting resistors; the
LEDs can therefore generate a lot of light. The LEDs should be drive by a
fast (~10-20 nanosecond) pulse of +2 to +5 volts and should NEVER be driven by
a DC voltage or any voltage above 5 volts. The best device I have found to drive
the LEDs is a BNC pulse generater, model 8010. This device has a single positive
polarity output with adjustable peak voltage and pulse width (down to
~10 nanoseconds). When the peak width is 10ns the peak voltage can be adjusted
until the phototube generates an average of 1 photoelectron per pulse. This can then
be used to measure the single photoelectron spectrum.