Planet SGSW-24040 User Manual page 544

User's Manual of SGSW-24040 / 24240 Series
DC Disconnect
DC Disconnect detection involves measurement of current. Naturally, a disconnected PD stops consuming current, which can
be inspected by the PSE. The PSE must therefore disconnect power within 300 to 400 ms from the current flow stop. The lower
time boundary is important to prevent shutdown due to random fluctuations.
AC Disconnect
This method is based on the fact that when a valid PD is connected to a port, the AC impedance measured on its terminals is
significantly lower than in the case of an open port (disconnected PD).
AC Disconnect detection involves the induction of low AC signal in addition to the 48 VDC operating voltage. The returned AC
signal amplitude is monitored by the PSE at the port terminals. During normal operation, the PD's relatively low impedance
lowers the returned AC signal while a sudden disconnection of this PD will cause a surge to the full AC signal level and will
indicate PD disconnection.
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