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====== DT ======

=== Dead Time Measurement ===
Dead Time is a measure of how long a photon counting circuit is “dead” (or cannot count a second photon) after a first photon has been detected. This characteristic of counting circuits can lead to counting errors especially at high photon rates if not compensated for. The DT command initiates a test for the measurement of the dead time of the Photon counting circuits of the Brewer. The DT command is normally executed as part of the ED routine and the test results are recorded in the DTOAVG file. Times differences of greater than 5% should be investigated. \\
The dead time for each instrument is manually record in the Instrument Constants File and can be seen on the PO command printout. For this test the iris is closed, FW#1 is put to position 1. Measurements are made at high intensities (FW#2=0), and at low intensities (FW#2=1) while measuring counts produced by the Standard Lamp (SL bulb). \\

{{:misc:dt.png?600|}}

The above image shows the measured dead time in nanoseconds and the counts/second recorded from the photomultiplier tube at both high and low intensity configurations. Ideally, for the DT test to produce optimal results, the instrument configuration will cause the SL bulb to produce between 2.5-3.0 million c/s during the high intensity measurement.