User Program Triggered Safe Stop

What does 8704 mean?

This indicates that the safety PLC's own user-defined program has intentionally initiated a safe stop condition. This is typically a designed response to a specific condition detected by the application logic, such as a sensor input or an internal process state deemed unsafe. It is usually not a fault of the PLC hardware itself, but rather a protective action taken by the software.

• A specific safety input device (e.g., emergency stop button, safety light curtain, safety gate switch) has been activated, triggering a programmed safe stop sequence.
• A safety-related limit switch or sensor has detected an out-of-bounds condition (e.g., over-travel, hazardous area intrusion) as defined in the safety program.
• An internal process value (e.g., speed, position, temperature) exceeded a safety threshold defined in the user's safety program, causing a controlled shutdown.
• A safety function block (e.g., Safe Torque Off - STO, Safe Operating Stop - SOS) within the PLC program has been commanded by upstream logic to execute a safe stop.
• Monitoring of an external safety device (e.g., safety relay, drive with integrated safety function) reported a fault, causing the PLC program to react with a safe stop.

Click steps to track your progress.

1. 1

   Access the safety PLC's diagnostic buffer and identify the specific safety input or program logic that triggered the safe stop condition.

2. 2

   Inspect the physical status of all safety-related input devices (e.g., E-stop buttons, light curtains, safety interlock switches) and verify their expected operation.

3. 3

   Using the engineering software, monitor the logic associated with the safe stop trigger condition (e.g., input states at terminal X1.0, internal flags, safety function block parameters).

4. 4

   Measure the voltage levels at the terminals of the implicated safety input devices (e.g., 24VDC at input 0.0 for a safety gate switch) to confirm signal integrity.

5. 5

   If a limit switch or sensor caused the stop, mechanically verify its position and adjustment; then confirm its signal state in the PLC's I/O table.

6. 6

   Acknowledge the fault via the operator panel or engineering software, then attempt to reset the safety function and restart the controlled process.