136 PI-MAX/PI-MAX2 System Manual Version 5.F
PTG
Signal Delay
Cable Delay from External Timer to Laser: 10 ns (6 ft cable is assumed)
Delay (at laser); Trigger to Laser Pulse: 50 ns
Delay; Laser Pulse to Sample: 10 ns
Delay; Fluorescence Signal to Detector: 45 ns
Total Signal Delay: 115 ns
Gate On Delay
Cable Delay from External Timer to PTG: 15 ns (10 ft cable is assumed)
PTG Insertion Delay; Trigger to Start of Gate Open Pulse: 25 ns
Cable Delay from PTG to Detector: 22 ns (15 ft cable is assumed)
Detector Insertion Delay: 15 ns
Total Gate On Delay: 77 ns
DG535
Signal Delay
Cable Delay from External Timer to Laser: 10 ns (6 ft cable is assumed)
Delay (at laser); Trigger to Laser Pulse: 50 ns
Delay; Laser Pulse to Sample: 10 ns
Delay; Fluorescence Signal to Detector: 45 ns
Total Signal Delay: 115 ns
Gate On Delay
Cable Delay from External Timer to DG535: 15 ns (10 ft cable is assumed)
DG535 Insertion Delay; Trigger to Start of Gate Open Pulse: 85 ns
Cable Delay from DG535 to Detector: 10 ns (6 ft cable is assumed)
Detector Insertion Delay: 15 ns
Total Gate On Delay: 125 ns
In this example, although the Signal Delay and the Gate On Delay are close, if the signal
is a pulse lasting only a few nanoseconds, it will have come and gone before the Gate
opens, and no valid experimental data could be taken. Obviously, this sample time budget
is unlikely to match any actual system and the values for both the Signal Delay and the
Gate On Delay could be very different from those indicated here. Nevertheless, it
illustrates the importance of making a record of the delays that will be encountered in any
system to determine their possible impact on experimental results.
Measuring Coincidence
In addition to preparing a Time Budget, it is advantageous if you can directly measure the
timing of the critical signals. A fast oscilloscope can be used for this purpose. Without an
oscilloscope to monitor the signals, it will be difficult to determine the timing with
sufficient accuracy.
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