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Programmable Thresholds

A dedicated electronics has been designed: after matching a first set of analogic thresholds, the signals from each LS are fed into a proper ADC converter. For each LS a set of three thresholds adjustable by telecommand is given ([PDS S/W User Manual, 1995], p. 151):
  1. a Low Level Threshold (LLT), nominally ranging from 20 to 90 keV (16 steps, 4.67 keV/step);
  2. an Upper Level Threshold (ULT), ranging from 200 to 600 keV (8 steps, 57.1 keV/step);
  3. an AntiCoincidence Threshold (ACT), ranging from 100 to 300 keV (8 steps, 28.6 keV/step); so called, because it is used as lower discriminator for any anticoincidence signal for the PDS.

As for the ULT, actually the ADC records events with energies up to more than 660 keV, as tested during the on-ground calibrations.

For a detailed report of the various threshold settings during the first phases of the mission, see [Feroci et al., 1997].

Cristiano Guidorzi 2003-07-31