PLC parts and repairs can be expensive, but with the right maintenance plan they can also be avoided. When you properly maintain your system it can run for years, and just like with any machine, it needs basic care and maintenance.
Here are four maintenance tasks that make the biggest impact to keep your PLC system up and running.
Inspect Analog Input Devices
Make sure your analog components are always in good calibration. The manufacturer’s schedule for preventative maintenance is the key here, and we highly recommend you follow it.
We’ve often seen issues where initially it appeared that the system had a bad analog input module. On further inspection, however, the culprit was the transmitter hooked up to it. Likewise, pay special attention when inspecting the contacts on large contactors for output modules, as they are under a heavy load and may need to be cleaned.
Protect Your PLC from Airborne Contaminants
Your PLCs operate in some pretty harsh environments, and are often subjected to airborne contaminants. These can affect the operation of your PLCs in different ways.
Corrosive contaminants, such as chlorine and other caustics, will obviously degrade the performance of your components until they quit altogether.
Conductive contamination can be harder to notice, as components may operate normally much of the time with only an occasional error that’s hard to track down.
As part of your regular PM schedule, we highly recommend doing visual inspections of the cabinets where your components are housed. Look for evidence of dust (especially black dust, which is a sign of trouble).
When needed, blow off the board gently with canned air. If you regularly find dust inside the cabinets, be sure to check the cabinet seal.
Check Cables and Connections
This makes sense to you already, right? Of course it does, but we see too many calls that are simple loose connections. Save yourself the time and energy needed to call tech support by including this simple inspection as part of your regular PM schedule, especially in cabinets that are subject to lots of vibration.
Electromagnetic Interference (EMI)
EMI is always a concern when dealing with the higher voltages and high currents that are common with large machinery.
Too often, the initial PLC installation didn’t account for EMI interference. High current wires are a major producer of EMI and how those wires are physically located can cause problems with components that operate at a much lower level.
For example, a 480-volt, 20-amp cable will cause major problems for any nearby Ethernet or analog I/O cables.
Performing an audit of your existing wiring can help identify potential sources of EMI before they become a problem. You can do this check when creating or updating your wiring diagrams (which we’ll discuss later).
Also, check for EMI sources when you’re experiencing analog signals that are “all over the place.” If you’ve already checked the wiring and have eliminated high-current wiring as a source, look at the contactors on output modules. These can be a significant source of EMI, especially as they get older and it takes more for them to pull in and drop out.
Another symptom of EMI is when communications get flaky. After making sure PLC components are fine, check for EMI. If it’s not EMI, you may have a physical issue (like airborne contaminants corroding the grounding plug).
Inspect Power Sources
For constant, round the clock performance, your PLC equipment needs to have a continuous stream of power. Managing and maintaining your power sources is critical to the operation of your equipment.
For this reason, you need to keep an eye on your power and visually inspect each power supply. Any components that show evidence of a power surge or electrical short need to be replaced right away. Many people opt for redundant power supplies. In the event that one of the redundant supplies fails, you need to replace it immediately or risk losing power.
Additionally, you need to check the manuals of your power supplies to ensure that they protect you against power fluctuations (surges, brown outs, etc.) and overheating. Electric problems can be disastrous if they get out of control.
Verify Proper Network Connectivity
Many PLC components and systems are dependent on an active network connection. One of your regular maintenance tasks should be verifying that your network connectivity is active and healthy. More often than not, people choose to assign a static IP address for network stability.
However, sometimes after a power failure or misconfiguration, DHCP takes precedence. You will want to verify that your PLC component’s network address fits your IP addressing scheme.
Next, you will want to test connectivity across your local network to verify other devices can communicate with your PLC equipment. Simply initiate a ping test across the network to verify network connectivity. If you experience packet loss or are unable to ping your PLC’s network address, your problem may not necessarily be related to your PLC configuration. You may have a network configuration error.
However, it is best to check the network address of your PLC component before moving forward. There is the possibility that it received a new network address from DHCP. Verify the network address again and try to ping it. If you still cannot ping your PLC component, you may need to engage a member of your networking team.
Following these six basic maintenance tips can keep your PLC system running longer. You may also avoid costly downtime or the need for new parts. Maintaining the system takes dedication and time, but it is well worth it in the long run. It’s something that you have to be sure to stick to.