Optimizing PLC Protocol: Communication Frame Compression Technology to Improve Bandwidth Utilization Efficiency!

Introduction

**Hello everyone! Today I want to share a technology that can make your PLC communication efficiency “soar” — communication frame compression! “What? PLC communication can be compressed?” **That’s right! With this technology, your PLC network bandwidth utilization can be improved by over 50%! Want to know how this is achieved? Follow my lead, and I guarantee you will gain a lot!

Why is Communication Frame Compression Needed?

Imagine your PLC network as a highway, and communication frames as the vehicles traveling on it. Traditional communication methods are like **”each vehicle occupies 3 lanes” even if there is only one person in the car (a small amount of data), it still occupies all the space. “Isn’t that a waste?”**

Communication frame compression technology allows these vehicles to dynamically adjust the number of lanes they occupy based on actual passenger load. Specifically:

1. Reduce redundant data: For example, duplicate status flags, fixed-format padding bits

2. Optimize data structure: Represent data like “00000000” in a more concise way

3. Dynamically adjust frame length: Automatically scale based on real-time data volume

**”How amazing are the results?”** In a real-world test on an automotive welding production line, the communication load dropped from 85% to 35%, saving a full 50% of bandwidth!

Three Core Compression Technologies

1. Bit Packing Technology

“The most basic compression trick!”

• Compress 8 Boolean values (each originally occupying 1 byte) into 1 byte of 8 bits

• Example Code (using Siemens SCL as an example):

// Traditional method: 8 Bool variables occupy 8 bytes

VAR

    Sensor1 : BOOL;

    Sensor2 : BOOL;

    ...

    Sensor8 : BOOL;

END_VAR


// After compression: only 1 byte

VAR

    SensorPack : BYTE; // Each bit corresponds to a sensor state

END_VAR

“Don’t underestimate this change; it can save hundreds or thousands of bytes in large systems!”

2. Delta Encoding

“Specializes in eliminating duplicate data!”

• Only transmit the change amount instead of the complete data

• Typical application scenarios:

  • Temperature monitoring (when the change is <0.5°C per second, only transmit a difference like “±0.3”)

  • Position sensors (transmit displacement instead of absolute coordinates during continuous movement)

A case study from a packaging machinery factory: Through delta encoding, the communication data volume dropped from 12KB per second to 3KB, a reduction of 75%!

3. Dictionary Compression

“The secret weapon for advanced users!”

• Create an “abbreviation dictionary” for commonly used data

• For example:

  | Original Data | Compressed Code |

  |—|—|

  | “EMERGENCY_STOP” | 0x01 |

  | “CYCLE_START” | 0x02 |

**”Note!** The PLC and HMI must use the same dictionary; it is recommended to manage it through a global data block.”

Practical Application Case

A photovoltaic panel production line faced communication congestion issues:

• Original situation: 300 devices communicating via PROFINET, transmitting 500 bytes of data every 100ms

• Problem: Network latency reached 80ms, with frequent communication timeouts

Solution:

1. Use bit packing for status words (saving 40% space)

2. Use delta encoding for analog quantities (saving 60% space)

3. Use dictionary compression for command words (saving 30% space)

Final results:

✅ Average frame size reduced from 500 bytes to 150 bytes

✅ Network latency reduced from 80ms to 20ms

✅ Communication error rate reduced from 5% to 0.1%

“The most surprising part is — no hardware changes were made!”

Pitfall Guide

1. Compression/decompression requires CPU time: It is recommended to use in scenarios where communication cycles are >10ms

2. Be aware of byte alignment issues: Some PLCs have very low efficiency for unaligned data access

3. Version compatibility: Ensure all devices use the same compression algorithm

4. Debugging tips:

   • Test with one device first

   • Use Wireshark to capture packets and verify compression effects

   • “Always perform stress testing!”

Interactive Time

1. What is the biggest communication bottleneck in your PLC network?

2. What communication optimization methods have you tried? How effective were they?

3. If you were given a “communication optimization toolkit”, what features would you most want it to include?

Feel free to share your practical experiences in the comments!

Conclusion

Communication frame compression is not **”an unattainable black technology” but a practical skill that every engineer can master**. Remember:

🔹 Start with simple bit packing

🔹 Delta encoding is suitable for slowly changing data

🔹 Dictionary compression is most effective for fixed commands

“Don’t let precious bandwidth go to waste!” Try these techniques to make your PLC network run at **”high-speed rail speed”**!

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