Schneider Electric 890USE17700 - Manual (Page 183)

Glossary
890USE17700 April 2004 183
PDM power distribution module. A module that distributes either AC or DC field power to
a cluster of I/O modules directly to its right on the island bus. A PDM delivers field
power to the input modules and the output modules. It is important that all the I/O
clustered directly to the right of a PDM be in the same voltage group—either
24 VDC, 115 VAC, or 230 VAC.
PDO process data object. In CAN-based networks, PDOs are transmitted as unconfirmed
broadcast messages or sent from a producer device to a consumer device. The
transmit PDO from the producer device has a specific identifier that corresponds to
the receive PDO of the consumer devices.
PE protective earth. A return line across the bus for fault currents generated at a sensor
or actuator device in the control system.
peer-to-peer
communications In peer-to-peer communications, there is no master/slave or client/server
relationship. Messages are exchanged between entities of comparable or
equivalent levels of functionality, without having to go through a third party (like a
master device).
PLC programmable logic controller. The PLC is the brain of an industrial manufacturing
process. It automates a process as opposed to relay control systems. PLCs are
computers suited to survive the harsh conditions of the industrial environment.
preferred module An I/O module that functions as an auto-addressable node on an Advantys STB
island but is not in the same form factor as a standard Advantys STB I/O module and
therefore does not fit in an I/O base. A preferred device connects to the island bus
via an STB XBE 1000 EOS module and a length of STB XCA 100x bus extension
cable. It can be extended to another preferred module or back into a standard island
segment. If it is the last device on the island, it must be terminated with a 120 Ω
terminator.
premium
network
interface An Advantys STB network interface module designed at a relatively high cost to
support high module densities, high transport data capacity (e.g., for web servers),
and more diagnostics on the island bus.
prioritization An optional feature on a standard NIM that allows you to selectively identify digital
input modules to be scanned more frequently during a the NIM’s logic scan.
process I/O An Advantys STB I/O module designed for operation at extended temperature
ranges in conformance with IEC type 2 thresholds. Modules of this type often feature
high levels of on-board diagnostics, high resolution, user-configurable parameter
options, and higher levels of agency approval.