How to Smoothly Upgrade an Old Siemens PLC Control System

How to Smoothly Upgrade an Old Siemens PLC Control System? This upgrade guide will help you successfully complete the technical transformation and improve production efficiency!

Hello everyone, I am Hanhan. Today we will talk about how to give an old Siemens PLC control system a “big health check”. Many factories are still using the S7-300 series PLC from over a decade ago. Although they are durable, with the changes in production demands, these old machines should retire. Upgrading is not just a simple replacement; it requires skill. Today I will share my practical experience to help you avoid detours.

1.

Evaluate Existing System

First, we need to give the old system a comprehensive check-up. Just like seeing a doctor, we need to understand the current situation of the system:

1. Hardware Configuration: CPU model, I/O modules, communication modules, etc.
2. Software Version: PLC firmware version, programming software version
3. Program Structure: Organization of program blocks, instruction set used
4. Communication Protocol: Interface with HMI and SCADA systems
5. Field Devices: Types and quantities of sensors and actuators

Note: Don’t forget to check the size and wiring of the field cabinet; new equipment may require more space or different wiring methods.

2.

Select Upgrade Plan

Based on the evaluation results, we have several upgrade options:

1. Direct Replacement: Replace S7-300 with S7-1500
2. Partial Upgrade: Retain some old modules while replacing the CPU and key modules
3. Virtualization Migration: Use S7-1500 Soft PLC while retaining the original I/O modules

Each option has its pros and cons. For example, direct replacement is the most thorough but costly; partial upgrades can reduce costs but may have compatibility issues; virtualization migration offers high flexibility but requires additional IT infrastructure.

Practical Experience: I once encountered a chemical factory that wanted to directly replace all S7-300 with S7-1500. They found that the existing explosion-proof cabinet couldn’t fit the new equipment, resulting in a redesign of the control cabinet and delays. When choosing a plan, always consider the actual situation on-site.

3.

Program Migration

Assuming we choose the direct replacement plan, the next step is program migration. Siemens provides a migration tool in TIA Portal, but don’t think you can just click a few times and be done.

1. Export Original Program: Use STEP 7 Classic to export the source files
2. Import to TIA Portal: Use the migration tool to import
3. Check Compatibility: Review the migration report and resolve compatibility issues
4. Optimize Program: Utilize new features of S7-1500 to refactor some code

// Old version timer instruction
UN    M      0.0
L     S5T#10S
SE    T      1
// New version optimized timer instruction
#myTimer(IN := NOT "StartBit",
PT := T#10S);
"TimerDone" := #myTimer.Q;

Warning: There are many changes in the instruction set from S7-300 to S7-1500. For instance, some old instructions are no longer recommended in the new system. I once directly migrated and ended up with numerous yellow warnings in the program, which was quite frustrating. It is advisable to carefully review each program block after migration, optimizing where necessary.

4.

Hardware Update

While hardware replacement seems straightforward, there are many details to pay attention to:

1. Wiring Method: The terminal blocks of S7-1500 may differ from S7-300
2. Communication Modules: Check if network configuration needs updating
3. Power Requirements: The new CPU may require a different power supply scheme
4. I/O Address: I/O addresses may need to be remapped

Practical Tip: When replacing hardware, use a marker to label the wiring order on the old module and take a photo for reference. This way, you won’t miswire when connecting the new module.

5.

Communication Interface Adaptation

After upgrading the PLC, don’t forget to update the communication interfaces with other systems:

1. HMI Update: You may need to update the HMI program to adapt to the new PLC
2. Database Interface: Check if the data acquisition program is compatible
3. Upper Computer Software: Update drivers or communication configurations

# Modify upper computer Python program example
import snap7
# Old version connection
client = snap7.client.Client()
client.connect('192.168.0.1', 0, 1)  # IP, Rack, Slot
# New version connection (may require adjustments)
client = snap7.client.Client()
client.connect('192.168.0.1', 0, 2)  # IP, Rack, Slot may change

Experience: Once I upgraded the PLC and found that the SCADA system could not read data. It turned out that the PLC’s IP address range had changed, and the address in SCADA was not updated. Therefore, always double-check communication configurations.

6.

Testing and Debugging

After the system upgrade is complete, don’t rush to put it into production. Comprehensive testing is essential:

1. I/O Point Testing: Check each input and output for normal operation
2. Function Testing: Test each functional module according to the production process
3. Communication Testing: Ensure normal data exchange with other systems
4. Stress Testing: Simulate high load conditions to check system stability
5. Exception Handling: Test the system’s response under various exceptional conditions

Safety Reminder: Always pay attention to safety during testing! Especially for systems involving high-power equipment or hazardous processes, be sure to ensure safety precautions.

7.

Document Updates

Don’t think that once the renovation is complete, everything is fine; follow-up work is also very important:

1. Update system diagrams: Including electrical diagrams, PLC configuration diagrams, etc.
2. Modify operation manuals: If the operation interface changes, update the instructions in a timely manner
3. Write an upgrade report: Document the upgrade process, encountered problems, and solutions
4. Train operators: Familiarize on-site personnel with the new system’s features

Hard Lesson: I once neglected document updates, resulting in a fault six months later. The new engineer was confused by the outdated documents and took a long time to find the problem. Document updates are crucial; don’t be lazy!

8.

Practical Exercise Suggestions

Talking without practice is just empty talk. To truly master PLC upgrade skills, try these exercises:

1. Build a small S7-300 test system and try to upgrade it to S7-1500
2. Use the migration tool in TIA Portal to practice converting some typical PLC programs
3. Write a simple upper computer program to achieve communication between new and old PLCs
4. Simulate a real production line control program and conduct a full upgrade drill

Remember, knowledge gained from books is shallow; true understanding comes from practice. The more you practice and summarize, the better you can become a PLC upgrade expert!