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Enabling Switch with an Integrated Safety Controller and a POINT Guard I/O Safety Module Safety Function Application Technique
Programming
The Dual Channel Input Stop (DCS) instruction monitors dual-input safety devices whose main function is to stop a machine safely, for
example, a safety gate. If the Door OK tag is sealed in around the falling edge of the Safety Reset button, then the contactors are energized.
The Dual Channel Start (DCSRT) instruction energizes its output (O1) if the enable input is high (1), and both input channels are in the active (1)
state. In this example, the Slow_Machine_Mode enable input indicates that the machine is in a mode where use of the enabling switch is
allowed. You are responsible for driving this input, which you must base on your application and risk assessment. If use of an enabling
switch is allowed, and the operator squeezes the enabling switch to the idle position, then the contactors energize.
The DCS and DCSRT instructions monitor dual-input channels for consistency (Equivalent- Active High) and detect and trap faults when the
inconsistency is detected for longer than the configured Discrepancy Time (ms).
The automatic restart type allows the DCS output (O1) to reset automatically after a demand. The manual action that is typically required for
safety is provided in rungs 2 and 3 to reset the safety outputs.
Input Status typically represents the channel status of the dual-input channels. In this example, the Combined Input Status bit goes low (0) if
any of the eight input channels on the 1734-IB8S module have a fault. The Energize_K1K2 tag drives the Actuate input on the Configurable
Redundant Output (CROUT) instruction. Either a closed door or the enabling switch can set this tag to high (1).
The CROUT instruction controls and monitors redundant outputs. Essentially, this instruction verifies that feedback follows the safety
outputs appropriately. For the negative feedback used in this example, if the outputs are high (1), the feedback is low (0) and vice versa. In
this example, the feedback has 500 ms to change to the proper state. Because only one feedback circuit is used, the feedback tag is used
for both Feedback 1 and 2.
The two output tags from the CROUT instruction are used to drive the contactor outputs on the 1734-OB8S module.
Rockwell Automation Publication SAFETY-AT125C-EN-P - February 2022
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