Allen-Bradley GuardPLC 1753, Safety Reference Manual

Page: 101 / 120

Publication 1753-RM002C-EN-P - September 2008 101
Configuring Communication Chapter 9
Between PES1 and PES2
The Worst-case Reaction Time, T
R
, (maximum response time) from the
occurrence of an input signal change at PES
1
to the reaction of the
output signal at PES
2
can be calculated as follows:
T
R
= t
1
+ t
2
+ t
3
+ t
4
, where:
T
R
= Worst-Case Reaction Time
WDZ = Watchdog Time
t
1
= 2 x WDZ
PES1
t
2
= 0 ms, if Production Rate = 0, “normal condition”
otherwise = Rece WDZ
PES1
t
3
= ReceiveTMO
t
4
= 2 x WDZ
PES2
The Worst-Case Reaction Time, T
R
, depends on the application and
must be coordinated with the approving board.
T
R
can be read in the Worst Case column of the Peer-to-Peer Editor.
Terms
Peer-to-peer communication uses the following terms.
ReceiveTMO
The monitoring time, within which a valid response must be received.
Safety communication is terminated if the ReceiveTMO expires.
ResendTMO
The monitoring time after which a transmission is repeated, if its
receipt has not been acknowledged.
Production Rate
The minimum interval between two data transmissions.
Watchdog
The maximum permissible duration of a run cycle.
Allen-Bradley Parts