Rockwell Automation 1752-L24BBBE SmartGuard 600 Controllers User Manual - Manual (Page 284)

284 Rockwell Automation Publication 1752-UM001E-EN-P - June 2014
Glossary
polled A type of standard I/O data communication in which a polled message solicits a
response from a single, specified device on the network (a point-to-point transfer
of data).
probability of failure on demand
(PFD)
The average probability of an operational system to fail to perform its design
function on demand.
probability of failure per hour (PFH) The probability of an operational system to have a dangerous failure occur per
hour.
requested packet interval (RPI) When communicating over a network, this is the expected rate in time for
production of data.
safety I/O Safety I/O has most of the attributes of standard I/O except it features
mechanisms certified to SIL 3 to verify data integrity and timeliness.
safety network number (SNN) Uniquely identifies a network across all networks in the safety system. The end
user is responsible for assigning a unique number for each safety network or
safety subnet within a system. The safety network number makes up part of the
unique node identifier (UNID).
standard Any object, task, tag, program, or component in your project that is not a safety-
related item.
strobed A type of standard I/O data communication in which a message solicits a
response from each strobed device (a multi-cast transfer). It is a 64 bit message
that contains 1 bit for each slave device on the network.
Each slave node can return a maximum of 8 bytes in response to the master’s
strobe.
system reaction time The worst-case time from a safety-related event as input to the system or as a fault
within the system, until the time that the system is in the safety state. System
reaction time includes sensor and activator reaction times as well as the controller
reaction time.
test pulse A signal used to detect when external wiring comes into contact with the power
supply (positive), or to identify short-circuits between signal lines.