Safety Reaction Times
While offline, you an configure the Requested Packet Interval (RPI) and Connection Reaction Time
Limit. While online, you can monitor the Max Observed Network Delay.
To set the safety reaction time parameters, select Advanced Connection Reaction Time Limit.
The RPI is not configurable for the safety output as it is determined by the period of the
Safety Tasks.
Advanced Connection Reaction Time Limit
IMPORTANT:
The values that you define for the timeout
multiplier and the network delay multiplier provide resilience for variations in network
reliability and performance. Use caution when reducing the values as this action increases the
likelihood of spurious trips.
The input reaction time is the time from when the signal changes on an input terminal to when
safety data is sent to the controller.
The output reaction time is the time from when safety data is received from the controller to
when the output terminal changes state.
For information on how to determine the input and output reaction times, see the product
documentation for your specific safety I/O device.
Connection Reaction Time Limit (CRTL)
Displays the calculated Connection Reaction Time Limit, which are based on the other
parameters. If the connection reaction time ever exceeds the Reaction Time Limit, a
connection fault occurs. This value is recalculated immediately when you adjust the RPI,
Timeout multiplier, and Network delay multiplier values.
The values in the following table define the CRTL.
Value | Default | Description |
|---|---|---|
Requested packet interval (RPI) | 10 ms (input RPI) | The RPI determines how often the input and output packets are placed on the
network. |
Timeout multiplier | 2 | The timeout multiplier determines the number of retries before a timeout
occurs. |
Network delay multiplier | 200% | The network delay multiplier accounts for known delays on the network. When known
delays occur, timeouts can be avoided with this parameter. |
If you adjust these values, then you can adjust the CRTL. If a valid packet is not received
within the CRTL, the safety connection times out, and the input and output data is placed in
the safe state (Off).
IMPORTANT:
The default values generate an input connection
reaction time limit of 40 ms. If no edits are made to the defaults, verify that this
connection reaction time limit is used in the safety reaction time calculations.
IMPORTANT:
For applications with safety I/O, the default
connection reaction time limit can result in connection loss to the safety I/O modules. In
some cases, it is necessary to increase the values from their defaults. Make sure that you
use the new connection reaction time limit in the safety reaction time calculations.
The following equations determine the CRTL:
Input Connection Reaction Time Limit = Input RPI x [Timeout Multiplier + Network Delay
Multiplier]
Output Connection Reaction Time Limit = Safety Task Period x [Timeout Multiplier + Network
Delay Multiplier - 1]
Requested Packet Interval (RPI)
The Requested Packet Interval is the amount of time (in ms) between updates of the data
from a safety I/O device input connection. This parameter is the minimum rate at which the
controller receives data.
TIP:
For output devices, the RPI is not configurable and is
equal to the safety task period (the time interval between successive executions of the
safety task).
The CRTL is adjusted immediately when you change the RPI value.
For safety output connections, the RPI is fixed at the safety task period. If the
corresponding CTRL is not satisfactory, you can adjust the safety task period on the Safety
Task Properties panel.
For typical applications, the default CRTL for input connections of 4 x RPI and the default
CRTL for output connections of 3 x RPI is sufficient. For more complex requirements, use the
Advanced button to modify the CTRL parameters.
Maximum Observed Network Delay
The maximum observed network delay is shown on the Safety view of the Device
Properties. When the safety controller is online, click Reset to reset the maximum observed
network delay.
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