PNOZ Safety Communication in PLC: Ensuring Safety for Personnel and Equipment

Hello everyone, I am Engineer Zhang. Today, I will explain a very important topic in industrial automation – the communication applications of the PNOZ safety relay module. In industrial settings, the safety of personnel and equipment is always the top priority, and PNOZ is a key device specifically designed to ensure this safety.

Basic Concepts

The PNOZ safety relay is a PLC module specifically used for safety control, acting like a “safety guardian” on the production line. Its working principle is quite easy to understand; for example, when you use an electric kettle, if the water boils dry, the temperature control switch will automatically cut off the power to prevent damage – the role of PNOZ is similar, but it protects the entire production line and the operators.

Key Points of Hardware Configuration

1. Dual-channel input design

• The main channel and the monitoring channel must meet the conditions simultaneously to operate.
• Any abnormality in either channel will trigger a safety shutdown.
• Pay attention to the isolation of signal grounds during wiring.

1. Feedback loop configuration

• An EDM (External Device Monitoring) loop must be configured.
• Auxiliary contacts of the contactor should be connected in series to the feedback loop.
• Be aware of the timing requirements for feedback signals.

Communication Configuration

1. PROFINET Safety Communication

awk copy

// Example: Configuring the data block for safety communication
DATA_BLOCK "Safety_Data"
{ S7_Failsafe := 'true' }
VERSION : 0.1
NON_RETAIN
   VAR 
      Emergency_Stop : Bool;   // Emergency stop button status
      Guard_Door : Bool;      // Safety door status
      Reset_Required : Bool;  // Reset request
   END_VAR
BEGIN
END_DATA_BLOCK

Typical Application Cases

Taking a robotic workstation as an example:

1. Emergency stop loop: Press the emergency stop button → PNOZ detects → Cut off the robot’s power.
2. Safety door monitoring: Open the protective door → PNOZ responds → Robot slows down and stops.
3. Light curtain protection: Personnel intrusion → Light curtain triggers → PNOZ acts → Equipment shuts down.

Common Issues and Solutions

1. False trigger issues

• Check for interference in the wiring.
• Verify if the sensor installation position is appropriate.
• Investigate grounding faults.

1. Difficulties in resetting

• Confirm that all safety conditions are met.
• Check the connections of the feedback loop.
• Review fault codes for troubleshooting.

Safety Precautions

• A risk assessment must be conducted before any changes.
• Regularly test the effectiveness of safety functions.
• Complete functional verification is required after program changes.
• Configuration parameters should be reviewed by a designated person.
• Maintain complete records of parameters.

Debugging Tips

1. Troubleshooting communication failures

• Use a network analyzer to monitor communication quality.
• Check the grounding of the communication cable shielding.
• Verify the site address settings.

1. System optimization suggestions

• Set appropriate fault response times.
• Adjust filtering parameters as needed.
• Plan the division of safety zones effectively.

Practical exercise suggestion: Start by building a simple emergency stop loop to familiarize yourself with the basic configuration and debugging process of PNOZ. Once mastered, gradually add functions such as safety doors and light curtains, and finally conduct communication joint debugging. The key is to understand the concept of safety levels and the significance of dual-channel design.

Remember: The debugging of safety systems must be gradual, and each step must be confirmed before proceeding to the next. Do not neglect safety verification steps in a rush to meet deadlines. Record any anomalies promptly, and identify the root cause before continuing.