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Following the collection of an event, a proportional counter will
be ``dead'' for a certain time interval during which no other
event can trigger the electronics and therefore be detected.
Nominally, the event dead time for the ROSAT PSPCs was
estimated to be 
s (the gate trigger time of
a single event).
However analysis of ground calibration data have revealed that the
PSPC dead time is a function of both the event pulse height
(i.e., incident photon energy) and the incident count rate.
There are also significant differences between the individual
PSPCs (with the dead times for PSPC-A and PSPC-D systematically
higher by 5-10% than those for PSPC-C and PSPC-B).
The actual PSPC dead times are therefore in the range 180- 
s.
The dead time properties are not a strong function of position
across the counters.
Most of the time, the PSPC dead time in orbit will be dominated by vetoed particle background events.