Allen-Bradley GuardPLC 1753, Safety Reference Manual

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Publication 1753-RM002C-EN-P - September 2008 103
Configuring Communication Chapter 9
Reaction Times for
DeviceNet Safety
Communication
The system reaction time is the amount of time from a safety-related
event as input to the system until the system is in the Safety state.
Each of the times listed is variably dependent on factors such as the
type of DeviceNet Safety I/O modules and instructions used in the
program. Faults within the system can also have an effect upon the
reaction time of the system.
Between PES and DeviceNet Safety I/O Modules
The worst-case reaction time between changing a value on the first
DeviceNet Safety I/O module and the reaction of the outputs of the
second DeviceNet Safety I/O module can be calculated as follows.
T
R
= input path + output path, where:
T
R
= Worst-Case Reaction Time
input path = t
A
+ t
B
+ t
C
output path = t
D
+ t
E
+ t
F
WDZ = Watchdog Time
t
A
= Reaction time of DeviceNet Safety input node
t
B
= Reaction time of DeviceNet Safety connection to input node
t
C
= 2 x WDZ
PES
t
D
= Max Scanner Response Time
t
E
= Reaction time of DeviceNet Safety connection to output
node
t
F
= Time of DeviceNet Safety output node
An example of using an 1791DS-IB8XOB8:
t
A
= 16.2 ms + setting time of ‘ON/OFF delay time’
t
A
= 16.2 ms + (0, 6, 12,…ms)
t
A
= 16.2 ms + 0
t
A
= 16.2 ms
t
B
= CRTL = 24 ms default (12 ms in normal operation). The
CRTL is based on 6 ms RPI, timeout multiplier of 2, network
delay multiplier of 200%. You can find these values in
RSNetWorx Adv. Safety Connections Property tab.
t
C
= 2 x 50
t
C
= 100 ms
t
D
= 8 ms
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