
Position 7 allows simultaneous observation through slits 3 and 5. Dark count-corrected counts are
stored in the BASIC F() array (refer to the Preliminary Data Reduction document for details). The
following algorithm is used to derive a value for instrument deadtime:
Assume Poisson statistics:
where:
N
o
is the true count-rate (counts/sec),
N is the observed count-rate,
τ is the deadtime (sec). (The BASIC variable T1 is used for τ .)
1. As a first approximation set the true (unknown) count-rates equal to the observed count-
rates:
2. Compute an estimate for deadtime:
3. Revise the estimates for the true count-rates:
4. Iterate steps 2 and 3 until the value for T1 converges.
Deadtime measurements are made at both high and moderate light intensity levels by using two
different neutral-density filter settings (positions 0, 1 for Filterwheel #2); five measurements are
taken at the higher intensity, ten at the lower intensity.
Method:
The command DT is issued.
Following the usual five minute lamp warm-up, and a further 10 minutes for test to run, results will
be printed in a format similar to the following:
FILTER #1/1 AND FILTER #2/0
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