How to Smoothly Upgrade Siemens PLC Systems? Upgrade Strategies to Minimize Downtime!

Hello everyone! Today, let’s discuss an unavoidable topic in factories—PLC system upgrades. Every time the topic of ‘upgrading the PLC system’ comes up, the boss frowns, and when ‘production stoppage’ is mentioned, the finance team gets a headache. However, with the right methods, PLC system upgrades can be performed with minimal or even ‘painless’ operations. After 10 years of automation transformation in an automotive parts factory, I have developed a low-risk upgrade method, which I will share with you today.

Why Upgrade the PLC System?

In simple terms, there are a few key reasons:

• – The old system frequently malfunctions, leading to high maintenance costs.
• – The old PLC model has been discontinued, making spare parts hard to find.
• – New production demands cannot be met and require stronger performance.
• – System integration is needed, such as upgrading the company’s MES system.

No matter the reason, the core goal is the same: to complete the upgrade while ensuring production continuity.

Preparation Before the Upgrade

This stage determines the success or failure of your upgrade. Do not think about just ‘getting it done and seeing what happens.’ I made this mistake during my first upgrade, which resulted in a production line being down for three days, and I was severely reprimanded by my boss.

1. Complete Backup of Current Programs and Configurations– Not only back up the main program but also the data blocks (DB) and configuration parameters.– If upgrading from S7-300/400 to S7-1200/1500, pay attention to the differences in instruction sets.– Record communication parameters separately, including all devices’ IP addresses, station numbers, etc.

2. Thoroughly Organize the I/O Point Table– Create a detailed I/O correspondence table, marking the function of each point.– Verify that the on-site wiring matches the program (often, wires added during emergency repairs are not updated on the drawings).– Record the parameter settings of special function modules.

3. Develop a Transition Plan– Determine if upgrades can be done in phases.– Assess the shortest downtime possible.– Prepare a rollback plan (to restore to the original state immediately if issues arise).

Smooth Upgrade Strategies

I highly recommend the ‘Shadow Mode’ upgrade method, where the new system runs in parallel with the existing system without controlling the devices, collecting the same signals, executing the same logic, but the outputs are not connected to actual loads.

Specific steps include:

1. Signal Diversion Phase– Use terminal blocks or signal distributors to allow input signals to enter both the new and old systems simultaneously.– The new system runs but the output terminals are left open.– Compare the operational status of the new and old systems through data recording, observing for at least a week.

2. Gradual Switching– Start switching from non-critical control points, such as indicator lights and alarms.– Choose production off-peak times or weekends for switching critical control points.– Leave a rollback channel during the switch, such as preparing temporary jumpers on the terminal blocks.

3. Communication Integration– If the new and old systems need to coexist for a period, use S7-PROXY or communication gateways.– Pay attention to differences in S7 protocol versions, especially when connecting third-party devices.

Case Study Sharing

Last year, I was responsible for upgrading an injection molding machine control system from S7-300 to S7-1500. The key was that we designed a ‘dual-track parallel’ plan:

1. First, use a signal distributor to allow all sensor signals to enter both the new and old PLCs simultaneously.
2. Utilize the break time between shifts (20 minutes) to complete the switching of all input terminals.
3. In the following week, use one hour each day after work to switch various actuators by module.
4. The most critical part of the injection molding machine control was scheduled to be completed over the weekend.

Ultimately, we successfully compressed the originally estimated five days of downtime for the upgrade to zero downtime, with only the weekend’s production capacity being affected, while daily production capacity remained completely unaffected.

Common Issues and Solutions

1. Program Migration Incompatibility– A typical example is the differences in timer instructions between S7-300 and S7-1500.– Solution: Use the program verification function in TIA Portal in advance to identify all incompatibilities.

2. On-site Wiring Does Not Match Drawings– Solution: Use a multimeter to test each point and redraw the wiring diagram.

3. Communication Protocol Issues– Some older devices may not support the communication methods of the new PLC.– Solution: Add communication conversion modules or gateway devices.

Practical Recommendations

Prepare a detailed ‘step-by-step upgrade table’ that includes the operation content, estimated time, responsible person, and verification method for each step.Break down large upgrades into multiple small steps, with a rollback mechanism for each step.

For critical production lines,it is strongly recommended to set up a small-scale simulation system before the upgrade for practice, even if it only simulates key processes, it is much safer than going straight to the field. As I often say: ‘It is better to spend a day simulating on the test bench than to risk an hour on-site.’

Remember, the success of a PLC system upgrade is not determined by how strong your technology is, but by how comprehensive your plans are!