PLC Power Failure Data Retention: Enhance Your Program’s Memory

Hello everyone, I am Ouyang. Today, let’s talk about a very practical topic in PLC programming – power failure data retention. Have you ever encountered a situation where all your painstakingly adjusted parameters were lost after a power outage? Don’t worry, today Ouyang will teach you how to make your PLC remember important data like an elephant, even after a power failure.

What is Power Failure Retention?

Power failure retention, as the name suggests, is the ability to retain data even after the PLC loses power. This feature is a lifesaver for automation systems that need to run continuously or frequently start and stop. Imagine if your production line had to reset parameters every time it lost power – how troublesome that would be!

Principle of Power Failure Retention

PLC achieves power failure retention mainly through two methods:

1. 1. Battery Backup: Some PLCs come with a small internal battery that continues to power the memory when the main power is disconnected, ensuring that data is not lost.

2. 2. Non-volatile Memory: More advanced PLCs use non-volatile memory such as EEPROM or Flash, which can retain data even without power.

How to Use the Power Failure Retention Feature

The methods of using this feature may vary slightly between different brands of PLCs, but the basic principle is the same. Taking Siemens S7-1200 as an example, let’s see how to use power failure retention:

// Define a data block for power failure retention
DATA_BLOCK "Retain_Data"
{ S7_Retain := 'TRUE' }  // Set Retain attribute to TRUE
VERSION : 0.1
NON_RETAIN
   VAR 
      normal_var : Int;  // Normal variable, data lost after power failure
   END_VAR

RETAIN
   VAR
      retain_var : Int;  // Power failure retention variable, data retained after power failure
   END_VAR

BEGIN
   normal_var := 0;
   retain_var := 0;
END_DATA_BLOCK

In this example, normal_var is a normal variable, while retain_var is the power failure retention variable. When you power off and then power on the PLC, normal_var will be reset to 0, while retain_var will retain its value before the power failure.

Application Scenarios for Power Failure Retention

1. 1. Production Counting: Record the production quantity, which will not be lost even during downtime.

2. 2. Recipe Parameters: Save production parameters for different products to avoid resetting every time.

3. 3. Fault Logging: Retain fault information for subsequent analysis and handling.

4. 4. Runtime Statistics: Accumulate the runtime of equipment for preventive maintenance.

Tips

1. 1. Not all data is suitable for power failure retention. Frequently changing data may shorten the lifespan of the memory if retained.

2. 2. Power failure retention data usually has capacity limits; be cautious about controlling the amount of data used.

3. 3. When using the power failure retention feature, pay special attention to data initialization. Sometimes we may need to manually clear the retained data.

// Example of clearing power failure retention data
IF "Reset_Retain_Data" THEN
    "Retain_Data".retain_var := 0;  // Reset power failure retention variable to 0
END_IF;

Practical Exercises

1. 1. Try creating a data block for power failure retention in your PLC and test whether the data is retained after a power outage.

2. 2. Design a simple production counter that uses the power failure retention feature to record production quantities. Ensure that the count is not lost even if the PLC loses power.

Conclusion

Mastering power failure retention technology is like equipping your PLC with a super memory chip. It can make your automation system more stable and reliable, saving you a lot of unnecessary trouble. Remember, using the power failure retention feature wisely can greatly enhance the practicality and robustness of your PLC programs.

That’s all for today’s lesson. Ouyang hopes this article helps you better understand and utilize the PLC power failure retention feature. Remember to practice, and feel free to ask me any questions. See you next time!