Safety I/O
Safety I/O has most of the attributes of standard I/O except it features mechanisms that are certified to SIL 2 or SIL 3 for data integrity.
Before you use safety I/O, do the following:
- Read, understand, and follow all safety information in the product documentation for those products.
- Commission all devices with a node or IP address and communication rate before their installation on a safety network.
Safety I/O devices, like sensors and actuators, can be connected to safety input and output modules. The controller monitors and controls the devices. For safety data, I/O communication is performed through safety connections by using the
CIP Safety™
protocol. Safety logic is processed in the controller.Safety I/O treats the following as the safe state:
- Safety outputs: OFF
- Safety input data to controller: OFF
Safe State
Use safety I/O devices for applications that are in the safe state when the safety output turns OFF.
Diagnostics
Safety I/O devices perform self-diagnostics when the power is turned ON and periodically during operation. If a diagnostic failure is detected, safety input data to the controller and local safety outputs are set to their safe state (OFF).
Status Data
Safety I/O devices support status data to monitor device and I/O circuit health. For specific product capabilities, see the product documentation for your device.
Status Indicators
Safety I/O devices include status indicators. For details on status indicator operation, see the product documentation for your specific device.
On-delay or Off-delay Function
Some safety I/O devices support on-delay and off-delay functions for input signals:
- Safety inputs can require an on-to-off delay to filter out the low pulse test in an output signal switching device (OSSD). Though the pulse test duration is measured in microseconds, the safety inputs can detect the low pulse as a transition to the safe state. The smallest configurable millisecond delay can be enough to filter out the pulse test.
- An on-to-off delay filter can help to filter out noise that affects the input logic level.
- Be sure to count any configured delays into the system reaction time.
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