How to Extend the Lifespan of Your Control System

At the center of your operation is a control system. It's the brain, made of processors and parts that have worked well for years. But now, those parts are getting old. The original makers no longer support them, they're hard to find, and they cause a lot of worry. Many factories are running on old equipment without a real plan, which is a huge risk. It's time to stop waiting for a breakdown and start managing the system you have.

How to Assess and Plan for Obsolescence Risk

To get control, you first need to see what you have. Planning for old parts starts with a complete list of every single component in your control system. This isn't just the big hardware like I/O modules; it also includes the small things like software and firmware versions, which are key for getting parts to work together.

Once you have your list, you can turn it into a tool for seeing your risks. A risk chart, or criticality matrix, is perfect for this. It helps you show everyone, from the factory floor to the main office, which parts are the biggest problems. You can rank each part—like the main processor (CPU), power supply, or operator screen (HMI)—with a simple formula: How Bad is a Failure? × How Hard is it to Replace? × How Long Does it Take to Get a New One? The final number shows you exactly where to focus first.

Criticality Assessment Matrix Template

After mapping out your parts, you need to give each one a lifecycle status. This helps you predict future problems. There are four main stages:

• Active: The part is still being made and is easy to buy from the original company.
• Mature: The part is still available, but a newer version is out. It will likely be discontinued soon.
• Last-Time-Buy (LTB): The maker has announced they will stop producing the part. This is your last chance to buy it new from them.
• Obsolete: The part is no longer made or sold by the original company. You can only find it from other sellers in the surplus market.

Finally, you need to show what these risks mean in terms of money. The Annualized Downtime Risk Cost is a simple way to do this. The formula is:

Annualized Risk Cost=(Cost per Downtime Hour)×(Hours of Downtime per Failure)×(Annual Probability of Failure)

This is easier to figure out than it looks. An hour of downtime in a factory can cost anywhere from $10,000 to over $250,000. The hours of downtime depend on how long it takes to get a replacement part, which could be days or weeks for an old part. You can find the chance of failure from your own maintenance history or from public data. With this formula, an "old PLC processor" is no longer just a technical issue. It's a "$500,000 annual risk," which makes it much easier for everyone to understand why it's important to invest in a solution.

How Many Spares to Stock and Which Parts Matter Most

Once you know your risks, you can build a smarter plan for your spare parts. You don't need to stock everything. The idea is to stock the right parts to protect against your biggest problems. A simple formula can help you decide how many spares to keep:

Minimum Stock Level=(Annual Failure Rate×Lead Time in Years)+Safety Stock

The failure rate can come from your own records. Safety stock is your backup for surprises, like a sudden failure or a shipping delay. But for old parts, the most important and unpredictable factor is Lead Time. For a new part, you know how long it will take to arrive. For an old part, it's a guess. A part that took a week to find last year might take three months this year, or it might be gone for good.

This changes how you think about inventory. For old systems, you're not just managing stock; you're managing the risk that your supply could vanish. The cost of keeping a spare part on the shelf is no longer just an expense—it's insurance against a long, costly shutdown.

So, which parts need this insurance the most? Here is a "must-have" list of spares to focus on first:

• The Brains: The main PLC or DCS controllers are the heart of your system. If one fails, everything stops. Always have a tested spare, especially if you don't have a backup system running.
• The Power: Power supplies are a common point of failure and are your first defense against electrical problems. They are cheap to stock compared to the cost of the downtime they prevent.
• The Nerves: Communication cards connect your controllers to the rest of the plant. If one card fails, you can lose control over a whole section of your process.
• The Interface: HMI screens are how your operators see and control the process. A blank screen means they are flying blind. A spare HMI, already loaded with your program, can get you running again in minutes instead of days.
• The Hands: Critical I/O modules are the parts that read sensors and control motors and valves. Figure out which modules are tied to your most important functions and keep spares for them.

Just having a part isn't enough. You need to know it will work. A spare part with the wrong firmware is as useless as no spare at all. Your records must keep careful notes on what works with what, including firmware versions and any other special requirements.

Where to Source Obsolete Control System Parts Safely

When you can't buy from the original maker, you have to look at the secondary market. To do this safely, you need to look in different places so you don't rely on just one source. These places include:

• OEM Surplus: Sometimes, the original companies have leftover stock they will sell.
• Authorized Distributors: Your local seller might still have parts on their shelves.
• Third-Party Specialists: These companies are experts at finding, testing, and stocking old parts from all over the world.
• Asset Recovery Programs: You can also get tested, used parts from plants that have shut down or upgraded their systems.

Finding a part is only the first step. You have to check it to make sure it's good. Never take a part out of a shipping box and put it straight into your spare parts cabinet. You need a solid process for checking every part that comes in. This should include:

1. Visual Inspection: Look for any damage, like bent pins or corrosion. Check for signs of fake parts, like bad labels.
2. Firmware Version Verification: Power up the part on a test bench and check that the firmware version is the one you need.
3. Burn-in Test: Don't just turn it on and off. Let it run on a test system for a day or two. This helps find hidden problems that could cause it to fail soon after you install it.
4. ESD & Packaging Check: Make sure the part came in the right anti-static packaging. If it didn't, that's a bad sign about the supplier.
5. Traceable ID Logging: Write down the serial number, the supplier, and the date you received it. This is important if you need to make a warranty claim.

When you buy an old part, you're not just paying for the part itself; you're paying for the confidence that it works. A good supplier invests in testing to remove the risk. So, when you talk to a supplier, don't just ask about the price. Ask about their process. How do you test your parts? What is your warranty? What happens if a part is dead on arrival (DOA)?

A good supplier will be open about this and will offer clear terms, such as:

• A Clear DOA Window: A set time, like 30 days, to return a part that doesn't work for a replacement or a refund.
• A Simple RMA Procedure: An easy, clear process for returning a bad part.
• A Meaningful Warranty: A warranty of 6 to 24 months shows that the supplier is confident in their testing.
• Serial Number Tracking: The supplier should be able to track the part you bought back to its source and test history.

How to Store and Maintain Spare Parts in Good Condition

A great plan for spare parts can be ruined by a leaky roof or a dusty shelf. A spare part that doesn't work when you need it is a huge waste. Proper storage is something you have to do all the time, not just once.

Your storage room for electronics needs to have a controlled environment. The key things to manage are:

• Temperature and Humidity: Keep the room at a steady temperature, around 68-77°F, with humidity between 30% and 50%. Big temperature changes can create moisture, which causes rust, and high humidity can make parts break down faster.
• Dust and Contaminants: Keep all spares in sealed, anti-static bags inside clean, closed cabinets. Dust can cause short circuits.
• ESD Protection: Your storage room should be a static-safe area. Anyone who handles parts should wear a grounded wrist strap. Storing electronics in anything other than anti-static bags is asking for trouble.

One of the most important—and most forgotten—parts of maintaining spares is testing them from time to time. Electronic parts, especially capacitors, can go bad over time even when they're not being used. It's like a battery losing its charge on a shelf. If you suddenly apply power to a part that has been sitting for years, it can fail completely.

To prevent this, you should have a schedule to power up your critical spares. Every one or two years, take parts like CPUs and power supplies out of storage, put them in a test system, and turn them on for a few hours. This keeps them healthy and confirms that your "insurance policy" is still good.

To manage all this, you need a detailed inventory record. It should track more than just how many parts you have. For each critical spare, your record should include:

• Part number, serial number, and where it's stored.
• The firmware version on the device.
• The date you got it.
• A log of every power-up test, with the date and the result.
• Automatic reminders for the next test or when a warranty is about to expire.

Thinking of your spares as assets that can degrade, not just sit there, is the sign of a strong maintenance program.

Replacing High-Risk Modules and Using Asset Recovery Wisely

The information from your risk chart helps you move from fixing things when they break to replacing them before they fail. The parts with the highest risk should be replaced during planned shutdowns. This is much cheaper and less disruptive than an emergency shutdown caused by a surprise failure.

When you replace a high-risk part, don't just throw the old one away. That old part still has value. Many companies that sell old parts also have programs to buy your used equipment. They will fix it, test it, and sell it to another company that needs it.

This creates a circular economy for automation parts and changes the cost of an upgrade. The cost of replacing a high-risk part is no longer just an expense. It becomes:

Net Replacement Cost=(Cost of New Part)−(Value of Recovered Part)

This turns a cost into a smart investment, which is much easier to get approved. You're not just spending money; you're reducing risk and getting value back at the same time.

Repair vs. Replace Decision Framework

After you replace any part, the job isn't done until you've fully tested the system. This is called regression testing—it's a process to make sure the change you made didn't accidentally break something else. Your checklist after a replacement should include:

• Communication: Does the new part talk to all the other devices on the network correctly?
• I/O Mapping: Are all the inputs and outputs working as they should?
• Redundancy: If you replaced a backup part, test it to make sure it takes over correctly.
• Alarms and Diagnostics: Trigger some alarms to make sure they show up correctly on the HMI.
• Full Functional Test: Run the machine through its normal cycle to make sure everything works as designed.

Planning a Gradual Migration Path Without Disrupting Operations

For most places, shutting down to replace an entire control system all at once isn't an option. It costs too much and takes too long. A better way is a gradual, step-by-step upgrade that lets you modernize your system over time without stopping production.

This approach is based on proven upgrade paths. For example, many plants have successfully moved from older systems like Siemens S5 to the newer S7, or from Allen-Bradley PLC-5 to the modern ControlLogix family.

The key piece of technology that makes this possible is a protocol gateway. Think of a gateway as a universal translator. It lets devices that speak different languages (or different industrial protocols) talk to each other. An old I/O rack can communicate with a brand-new processor through a gateway.

This is a game-changer because it lets you upgrade on your own schedule. You can create a hybrid system—a mix of old and new parts working together. You can replace the most critical part first, like an old CPU, and use gateways to let it control your existing older I/O. Then, later, you can replace the I/O racks one by one, spreading the cost and work over several years.

This turns a huge, risky project into a flexible, manageable process. It lets you match your spending to your real-world needs. The main goal for every step should be simple: every change should lower your risk and make it easier to find spare parts.

A Practical Action Checklist to Guide Your Spare Parts Strategy

To use these ideas, follow this checklist to build a strong and smart plan for managing your spare parts and their lifecycle.

1. Create a Critical Asset Register: Make a complete list of every part in your control systems, including all hardware and software versions.
2. Develop a Lifecycle Status Sheet: For every part on your list, assign a status—Active, Mature, Last-Time-Buy, or Obsolete—and keep it updated.
3. Establish a Minimum Spare Calculation Sheet: Use the formula to set clear targets for how many spares of your most critical parts you need to keep in stock.
4. Implement an Incoming Spares Inspection Checklist: Create a formal process. No part goes into your inventory until it passes a visual check, firmware verification, and a functional test.
5. Maintain a Periodic Power-Up Test Schedule & Log: Actively manage the health of your stored spares. Schedule and record regular power-up tests for critical parts to keep them from going bad.
6. Develop a High-Risk Component Replacement Plan: Use your risk chart to find your biggest problem areas and schedule their replacement during planned maintenance.
7. Establish an Asset Recovery Partnership: Find a supplier who will buy your used parts, turning old equipment into new funds.

Managing aging control systems is not a matter of luck; it's a matter of strategy. A proactive approach, grounded in rigorous risk assessment, intelligent inventory management, and carefully planned migration, can transform a major operational liability into a manageable, predictable cost. You don't have to be at the mercy of obsolescence. Need help building a robust obsolescence plan or sourcing hard-to-find DCS, PLC, or HMI spares? A specialist partner, such as Amikong, can help you build your parts list and dramatically cut the risk of unplanned downtime. Reach out to us today.