Guide to Programmable Logic Controller (PLC) Maintenance

What is a Programmable Logic Controller (PLC)

A programmable logic controller (PLC) is an industrial computer that works to control a computer system in an industrial organization. These systems have been adapted for the control of manufacturing processes, such as assembly lines, machines, robotic devices, or any activity that requires high reliability, ease of programming, and process fault diagnosis. Even in our agriculture industry, large farmers have adopted PLC systems for their feed distribution systems, which were sophisticated enough to even measure the amount of grain to each individual animal on poultry, swine, and cattle feedlots.

PLCs monitor the inputs to the system and then make decisions about related outputs. PLCs, which are typically used to monitor motors or machines, are frequently the core of a predictive maintenance system, which can alert organizations to possible issues before they result in significant breakdowns.

Types of PLCs

There are 4 different types of PLCs:

Fixed Integrated PLC

Fixed integrated PLCs have a single unit that houses both the controller and the Input/Output (IO). The main advantage of fixed-type PLCs is their lower cost. Some shortcomings are that fixed-type PLCs lack flexibility, have less memory, are difficult to repair, and are not suited for complex tasks. Additionally, if any component malfunctions, certain versions require the replacement of the entire system.

Distributed PLC

A network connects the controller and input/output devices. The main advantages of distributed PLCs are reduced space, higher reliability, ease of maintenance, and greater flexibility thanks to high processing speed. The distributed PLC costs more when used infrequently.

Soft PLC

A soft PLC is considered a fully complete embedded computer created using software technology. The advantages of soft PLCs are that they are easier to configure, any number of sensors and actuators can be networked in, they support a variety of programming languages, lower production costs, and offer sophisticated security solutions. One disadvantage is that a soft PLC does not come with any additional software.

Modular PLC

A modular PLC contains separate modules for the controller and IO that are inserted into a chassis. The individual modules make them easier to use, provide greater storage capacity, can handle more complicated processes, and can function in harsh environmental conditions. A few disadvantages include complex configuration and a higher price compared to a compact PLC.

How a Programmable Logic Controller Works

Each component of a PLC accepts inputs and regulates outputs, making it an input-output system. The third component of the system, logic programming, governs the interaction between inputs and outputs and takes place in the CPU.

Here’s how each element works:

Input Monitoring

The PLC keeps track of pertinent data inputs and provides that information to the CPU. PLCs with analog capability can accept analog inputs for continuous variables, but some PLCs only accept data inputs with discrete (on/off) inputs. IoT devices, robots, safety sensors, human-machine interfaces, and virtually any other form of data entry point are just a few examples of the sources of input.

Logic Programming

Every PLC has a microprocessor CPU, which can be 16-bit or 32-bit in size. The PLC CPU is configured by engineers and technicians to recognize specific values and conditions and to alter outputs in accordance with its preprogrammed rules. The CPU continually monitors the status of variables and takes actions in response to preset criteria. This simple premise allows a wide variety of designs and functions.

Output Control

The PLC manages a number of switches, motor starters, relays, and other devices attached to its outputs based on the programmed logic. This enables PLCs to take over mechanical activities like machine operation. By instructing PLCs to transfer their output signal to a subsequent PLC in a chain, engineers can also connect other system components.

Compact PLC Units

The CPU, inputs, and outputs are typically all contained within one device. The inputs and outputs of the PLC are found combined in the I/O module of rack-mount modular PLC systems that many industrial facilities utilize, while the logic processes take place in a separate CPU module. I/O modules can be situated far from the CPU, sometimes even in different buildings, or they might be adjacent to it.

Why PLC Maintenance Is Important

The successful operation of your production depends on your programmable logic controllers (PLCs). It is critical that they are always operational and running at their highest level of effectiveness. You might need to repair or replace a portion of your PLC if it develops a problem in order to keep it operating. Regular preventive maintenance of a PLC system is one of the most crucial strategies to keep it running well.

PLC preventive maintenance activities can be time-consuming, but they can spare you from a lot of problems, expensive repairs, and downtime. Here are some suggestions for maintaining programmable logic controllers to include on your preventive checklist.

PLC Maintenance Checklist

Backup Data

Every so often, perform an up-to-date and routine backup of the PLC’s programming.

Program Functionality

When carrying out PLC preventive maintenance, check the functionality of the operating program to ensure the equipment or process being controlled is functioning as required.

Inspect Connections

Make sure that all connections are secure by routinely inspecting plugs, sockets, and terminals. Check connections more often in high-vibration areas, paying particular attention to fasteners like screws and bolts.

Check LED Lights

If your system has LED indicators, be sure to check them regularly.

Inspect Sensors

If sensors are part of your PLC system, be sure they are maintained per manufacturers’ recommendations.

Source EMI

To see if you are experiencing any problems with electromagnetic interference, examine your local wiring. To prevent static electricity issues, make sure your lower-level components are far away from high-current lines.

Inspect Battery Status

The status of this indicator shows whether the available battery voltage is sufficient to provide backup power for the EPROM stored in the PLC in the event of a power failure or when the machine is switched off for maintenance.

Inspect the Overall Condition of the PLC Components

Examine the CPU and other PLC modules visually for signs of wear, warping, distortion, or overheated parts, such as burnt scents or discoloration.

Spare Inventory

Be sure that you have enough spares to handle your maintenance needs, ultimately minimizing downtime.

Clean Dust

Be sure to remove all dirt or dust that has accumulated on the PLC components including its I/O modules, such as the CPU unit and the I/O system.

Clean and Change Filters

Regularly clean or replace any ventilation filters installed in the PLC enclosures.

Maintain Ventilation

Regularly change the ventilation filters, and keep items such as installation manuals, tools, drawings, papers, or other materials away from the PLC system.

Keep Your PLC Insulated Against Airborne Debris

Try to keep floating debris during regular machine operation to a minimum.

Audit the PLC Systems in Use

Keep an up-to-date inventory of your PLCs.

Software Updates

Check for any product notices, patches, recalls, or required upgrades for any of the PLC components and update accordingly.

Calibrate Devices

If any of your input or output devices require calibration, be sure to include those tasks, along with the circuit cards, in your preventive maintenance program.

Check Environmental Conditions

Be sure to monitor things like humidity levels and temperature as they can hurt your PLC components. Sensors can help you monitor these conditions around the clock.

Inspect for Potential EMI or RFI Sources

Radio-frequency interference (RFI) or electromagnetic interference (EMI) are major causes of erratic PLC processor issues without a clear indication of the specific problem. Ideally, during preventive maintenance, you should perform an audit of the local wiring to identify potential sources of EMI that could disrupt the operation of your PLC system.

Replace Modules

You might occasionally need to replace input or output modules due to wear and tear. When replacing modules, make sure you adhere to the instructions and cut off power as directed.

Error History

Take a look at regular reports to see if your PLC system has noted any scanning or error flags. Be sure to find the cause of these problems early.

Equipment Location

PLCs should be near the machine they are controlling. Keep other equipment, particularly those that generate noise or heat, away from your PLC.

Increase Awareness

Pay attention to unusual activity. For example, if you find that input and output devices are frequently burning out, you may want to check for power spikes or shorts.

Keep Current

If your system has recalls, patches, product notices, or upgrades, be sure to incorporate them into your preventive maintenance program to stay current.

Maintenance Scheduling

The PLC’s application and operational environment determine how frequently it needs preventive maintenance. Some maintenance operations will need to be carried out more often if the PLC system is used in harsh environments or high-vibration applications. To keep the PLC system in good working order, it is best to perform everyday duties like dusting or cleaning ventilation filters. Nevertheless, some operations, such as backing up the PLC’s programming, are less dependent on the working environment and are frequently completed twice a year.

Before you schedule any PLC preventive maintenance, you should carry out some routine inspections. Other preventive maintenance procedures will need to be planned according to either time or usage. Utilizing historical data to create the best preventive maintenance schedule is simple if you have a computerized maintenance management system (CMMS). For instance, you would want to plan to replace a certain component twice a year if you notice that it tends to break every 8 to 9 months, in order to avoid that breakdown.

Industry PLC Applications

PLC systems are adaptable and suitable throughout many different industries. Below are just a few examples of the applications using PLC technology today.

Manufacturing Production

Plant managers and others can use analysis tools to better leverage resources, batch scheduling of jobs, logistics, supplier timing, and other essential operations in order to develop more efficient manufacturing processes. PLC provides reliable data, such as sensor performance and other information, which can be combined with cloud computing to create a more holistic picture, or “big data.”

Agriculture

The agricultural process involves seeding, plowing, irrigation, planting, fertilizing, weeding, and harvesting. Modern agriculture relies directly and indirectly on automated equipment for growing, processing, and transporting these products. Today companies are using PLCs to revamp existing agricultural equipment automation systems and improve efficiency.

Oil & Gas

Companies operating in the oil and gas industry often add well pad sites as part of their expansion plans. Each of these well pads, which may have one to six wells, must have an individual PLC. These systems use pumps, valves, and sensors to work effectively and efficiently. By developing a single, scalable PLC system that incorporates Human Machine Interface (HMI), oil and gas companies can get a handle on all their well pads quickly and easily.

Glass Manufacturers

PLCs and bus technologies are used by producers of glass products to control material ratios and manufacturing workflows. Glass businesses must use complex, sophisticated procedures that necessitate data collection and exact quality control. Technology using PLCs can assist with both.

HVAC

A PLC allows an HVAC technician to access a system through the internet. They are able to wirelessly connect with other technicians and simultaneously automate several tasks. Previously, each operation required its own unique controllers. The PLC is a standardized approach to modern HVAC/R technology that improves diagnostic evaluations and system management.

Food Processing

PLCs are used in food processing systems to monitor contaminant levels in water, control flow rates in major parts of water treatment plants, and remotely control valves that regulate in-process water flow.

Cement Manufacturing

PLC plays a critical role in cement manufacturing. The process involves mixing various raw materials and compounds in a kiln. A PLC program ensures the use of the right quality and quantities of raw materials during the mixing process, which determines which output can result in the best possible quality.

Healthcare

The healthcare industry deploys PLC systems in central utility plants for integration, remote monitoring, and automated control of mechanical-electrical systems.

Chemical, Pharmaceutical, and Nuclear Plants

These industries depend on PLCs for precise, reliable, and automated control of complex research, development, and production processes.

PLC Risks

Many of the PLC concerns are interconnected and could become more serious as your system gets bigger. These are the key things to look out for:

I/O Device Modules and Field Devices

The entire PLC system is at risk if either an input device or an output device fails. This can be brought on by a power failure and could result in the system stopping abruptly. The PLC typically waits for a signal before starting its subsequent set of actions. An engineer often needs to identify the root cause of the stop and track it back to the individual device in order to fix the issue. There could be a power fluctuation, internal fault, or power loss when numerous devices are frequently having issues.

Ground Integrity

Correct grounding is necessary to keep a PLC and the maintenance team safe. In addition to shielding against electrical white noise, ground integrity also acts as a sound barrier.

Power Problems

Outages due to local or regional blackouts are the most common sources of power failure, and fluctuations can lead to PLC risks. The majority of industrial buildings in use today include backup power sources to eliminate the chance of a power outage. The facility’s most essential operations continue to run continuously during a mainframe blackout, or at least long enough to be appropriately shut down, thanks to the backup power source. Some facilities employ what is referred to as an uninterrupted power supply, which serves as a backup power source.

Electrical Noise Interference

Electrical noise interference from foreign signals can have a significant negative effect on a PLC’s performance. Electromagnetic interference is the most frequent reason for electrical noise, and it often happens when a large motor starts up or when lightning strikes nearby. Radio frequency interference, which can be caused by adjacent antennae and mobile transmitters, is another reason for electrical noise. On an industrial premise, handheld devices that could cause interference should be prohibited on the floor.

Temperature Problems

Excessive heat is one of the biggest threats to electronic components. If not properly protected, a PLC system surrounded by heat-emitting equipment could fail. In general, all equipment should be kept at temperatures significantly lower than the highest limit recommended by the manufacturer. If not, the PLC and/or peripheral components can overheat and stop functioning altogether.

Corrupted Memory

External influences like frequency interference and power outages can corrupt a PLC’s memory. For instance, a brownout or blackout could make the code unintelligible to the central processing unit. Similarly, a PLC that was unable to shut down properly due to an unexpected power outage would not read correctly once restarted.

Managing the Risks

In order to reduce the possibility of PLC problems, you need to have a good preventive maintenance plan in place and the tools — like a computerized maintenance management system (CMMS) — to help you keep on top of risks and avoid downtime. Facility engineers need to set up inspections and follow proper procedures to ensure all parts are properly connected. The operating environment of a PLC system should be well maintained to ensure no electric noise, moisture, or excess heat are present. Most importantly, it is crucial to ensure a spare power supply backs a PLC system at all times. This way, if the main power source goes down, factories can operate at full or at least necessary capacity. Although some failures are beyond our control, having preventive maintenance procedures in place will help minimize the impact.

Benefits of PLC

Although PLC systems have some risks, they also have many benefits. PLC systems, among other things, are simple to integrate, take up minimal room, and improve productivity.

When you make an investment in a good preventive maintenance program, you can anticipate cost savings, increased productivity, and other advantages. Here are some typical PLC maintenance system benefits.

Save Money

PLCs can be thought of as a long-term investment because the likelihood of a defect is quite low. PLCs are unquestionably among the most cost-effective solutions available, and the cost of a PLC recovers within a short period.

Prolonged Life and Reliability

The ruggedness of these devices is outstanding. Due to the small number of moving parts, the likelihood of a defect or damage is quite low.

Increased Productivity

When properly programmed, PLCs are essential for enabling automation, minimizing power consumption, increasing system control, keeping records, and redistributing the available workforce to increase productivity.

Small Space Footprint

PLCs are completely solid-state devices, making them far more compact than hard-wired controllers, which employ electro-mechanical devices.

Tremendous Flexibility

You have more flexibility for every project because data is stored in a group of devices rather than throughout a disjointed system. Additionally, it makes it simpler to expand the overall system by adding devices and PLC hardware as necessary.

Easy to Maintain

Problems are simple to recognize and fix since PLCs are made up of a variety of input and output devices. Each component has a limited number of things to be examined, making it easy to identify problem areas.

Security

The majority of PLC systems have extensive safety and security measures in place to safeguard the data they contain. Additionally, businesses can access private data more securely than they can on older, larger systems.

Machines That Use PLCs

PLC systems can be found everywhere in our highly technological world, from factories to office buildings to even directing traffic on our streets. PLCs are at the very heart of the control of many critical technologies that most of us don’t give a second thought to — they are so seamlessly and invisibly integrated into our daily lives.

Following are some common mechanical systems that are managed by PLCs:

Air compressor	Conveyor belt	Laser cutter	Plastic injection molding machine
Air conditioning system	Cooling tower	Lathe	Press brake
Air handling unit	Crane	LED assembly machine	Printing machine
Asphalt plant	CNC lathe	Level sensor	Pump
Automatic door	CNC milling machine	Machining center	Robot arm
Automatic guided vehicle (AGV)	CNC plasma cutter	Measuring instrument	Robotics assembly line
Automatic labeling machine	CNC punch press	Metal cutting machine	Sawmill
Automatic packaging machine	CNC router	Metalworking machine	Shearing machine
Automatic palletizing robot	CNC waterjet cutter	Milling machine	Slitter
Automatic welding robot	Compressor	Motor control center (MCC)	Sorting machine
Bagging machine	Concrete mixer	Packaging machine	Stamping press
Bandsaw	Control panel	Paint booth	Steel rolling mill
Batch mixer	Die casting machine	Paper cutting machine	Temperature controller
Beverage bottling plant	Electric motor	Pick and place robot	Textile weaving machine
Blast furnace	Elevator	Plastic blow molding machine	Ultrasonic welding machine
Blow molding machine	Extrusion line	Plastic extrusion machine	Vacuum pump
Boiler	Fanuc robot	Plastic recycling machine	Valve
Bridge crane	Filling machine	Plastic thermoforming machine	Waterjet cutting machine
Bulk material handling equipment	Flow meter	Pneumatic cylinder	Welding machine
CNC boring mill	Furnace	Pressure sensor	Wind turbine
CNC drill press	Gearbox	Punch press	Wrapping machine
CNC flame cutter	Generator	Quality control equipment	Yarn spinning machine

Bottom Line

PLCs (Programmable Logic Controllers) are essential for many industries because they provide a reliable, efficient, and cost-effective way to control and automate processes. Proper maintenance of PLCs is crucial to ensure that they continue to function properly and do not fail, which can result in downtime, lost production, and other costly problems. PLCs are also the foundation for predictive maintenance, which uses data and algorithms to predict when equipment is likely to fail and schedule maintenance before it happens. This can help to prevent unplanned downtime and improve overall efficiency. Regular maintenance of PLCs includes tasks such as checking for signs of wear and tear, replacing faulty components, and performing regular software updates. Proper maintenance can also help to extend the life of PLCs and prevent costly repairs or replacements. Overall, PLCs and maintenance are critical for maintaining the smooth operation of many industries.