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Maintenance Management of your company's PLC

 

Maintenance management of Programmable Logic Controllers and other industrial automation.

By Don Fitchett

 

Maintenance Management of PLCs

(This article originally featured in Chemical Engineering Magazine, updated 9/26/2023)

 

 

What is a PLC?

How many PLCs is your Bottom line depending on?

Do you have an up-to-date list of all PLC model types, part availability, program copies, and details for your company?

Do you have At least one trained person per shift to maintain and troubleshoot your plant PLCs?

Does your maintenance personnel work with PLCs following written company or corporate policy and procedures?

 

If you cannot answer confidently, or you answered "No" to any of the above questions, you must read this article on PLC maintenance management. Why? Because the PLCs (Programmable Logic Controllers) are the brains of your operation. When the PLC is not functioning properly, lines shut down, plants shut down, and even city bridges and water stations could cease to operate. Just one little PLC loses thousands to millions in an electrical panel you never knew existed. But most importantly, damage to machines and personnel could result from improper maintenance management of your company's PLCs.

 

what is a plc What is a PLC?

First, I'd like to explain, in the most non-technical terms possible, What a PLC is. This article is not just for the maintenance technician but for maintenance managers, plant managers, and corporate managers. A PLC (Programmable Logic Controller) is the type of computer that controls most machines today. The PLC is used to control AND troubleshoot the machine. The PLC is the brain of the machine. Without it, the machine is dead. The maintenance technicians we train are the brain surgeons. That is also how I explain it to my doctor. (His mouth drops open, "... you train brain surgeons?") maintenance technician

 

Important Note: Just as a doctor asks the patient questions to determine what is wrong, a maintenance technician asks the PLC questions to troubleshoot the machine. The maintenance technician uses a laptop computer to see what conditions are required for the PLC to cause an action (like turning a motor on). In a reliable maintenance management environment, the maintenance technician will use the Programmable Logic Controller as a troubleshooting tool to reduce downtime.

 

 

A little more detailed definition of a PLC: A programmable controller is a small industrial-strength computer used to control real-world actions based on its program and real-world sensors. The PLC replaces thousands of relays in older electrical panels and allows the maintenance technician to change how a machine works without having to do any wiring. The program is typically in ladder logic, similar to the wiring schematics maintenance electricians already know. Inputs to a Programmable Logic Controller can be switches, sensors, bar codes, and machine operator data, to name a few. Outputs from the PLC can be motors, air solenoids, indicator lights, and others.

 

 

plc automation How many PLCs is your Bottom line depending on?

My company has had an ongoing PLC-related global maintenance survey since 2000. The majority of the participants, back in 2001, reported 3-6 PLCs in their facility that they know of. Granted, most participants are managers and don't open electrical panels much, but many are from Fortune 500 companies with hundreds of employees. The odds are that most of them have 12-30 PLCs in their facilities. Currently, the average is 10-20 reported, so the good news is that the industry as a whole is becoming more PLC-aware.

 

It is common to only learn about a PLC once the machine is down and the clock is ticking at a thousand dollars an hour or more. Unfortunately, it is often the case that after the fire is out, it's on to the subsequent fires without thoroughly learning what is needed to avoid these costly downtimes in the future and other similar machines in a company or corporation.

 

Some older electrical panels may only have relays, but a PLC controls most machines. A bottleneck machine in your facility may have a PLC. Most plant air compressors have a PLC. How much would it cost if the bottleneck or plant air shut down a line, a section of your facility, or even the entire plant?

 

 

plc types Do you have an up-to-date list of all PLC model types, part availability, program copies, and details for your company?

The first step to take is to perform a PLC audit. Open every electrical panel and write the PLC brand, model, and other pertinent information. Then, go the following two steps. Analyze the audit information and risk, then act on that analysis. To help you out, I want to share with you our company PLC audit form.

 

 

Collected Information

Recommended Action

Machine or Area Name

Ex: warehouse conveyor, pump station 3, Strapper 2, Line 7, Traffic signal west main.

PLC Program Name

Ex: 1789GAA1, P3, Strap2, 5872443, WestMainTL.

Network Node Address

All addresses will be different. Ex: 2, 3, 17, 21

Network Name

It is often the same as the Program name, but it is not mandatory.

PLC Brand

Ex: Allen Bradley, Siemens, Schneider, Mitsubishi, DirectSoft, Omron

PLC Model Number

Ex: PLC-5/25, SLC-504, SIMATIC S5, MELSEC FX1N, DL 405

Is Spare Available?

Yes, in less critical machines, no.

Date Program Last Backed Up

Make program backups part of your semiannual PM program

IIs discriptored program available?

Without a discriptored copy of the program, troubleshooting and downtime increase significantly.

Does PLC have EEPROM

Another method of storing a backup program in a chip on the PLC.

Last date Program Changed

Remember to log when outside consultants or OEMs make program changes.

Last date EEPROM Burned

Save to EEPROM (Burned) after every successful program change.

The date battery was last changed

See the manufacturer's data for recommended change frequency.

OOther information you may need

For example, a facility location when corporate HQ is using this form.

 

 

Once you have collected the essential information in your plant or corporate audit, you need to analyze the data to develop an action plan based on risk analysis. In the risk analysis, bottlenecks and other factors will help you assess priorities. Starting with the highest priority PLC, you must ask more critical questions.

 

O        Do we have the most common spares for the PLC?

O        Is the OEM (Original Equipment Manufacturer) available 24/7? Or even in business anymore?

O        Do we have a backup copy of the PLC program?

O        Does our program copy have descriptions so we can work with it reliably and efficiently?

O        Do we have the software needed to view the PLC program? Are our maintenance personnel trained on that PLC brand?

 

 

These are some of the questions our managers must ask to avoid unnecessary risk and to ensure reliability.

 

 

maintenance Do you have At least one trained person per shift to maintain and troubleshoot your plant PLCs?

Is your maintenance staff trained on the PLC? It is silly to squander over a couple thousand in maintenance training when the lack of Proper PLC Training could cost you 10 thousand an hour. ... or worse. Here are a couple of reasons you should have at least one trained person per shift to work reliably with PLCs. You want to avoid seeing more significant downtime on off shifts because the knowledge base is on the day shift only. Also, with all the baby boomers (our core knowledge base in the industry) about to retire, it is risky management to place all your eggs in one basket.

 

What should we look for in training? I have been training individuals for over a decade and could write another article on PLC training alone. Here, you should seek training with two primary objectives.

1.  The training you decide on should stress working with PLCs safely and reliably. (not just textbook knowledge or self-learned knowledge)

2.  Secondly, the training should center around the PLC products you use or plan to use in your facility.

 

The two criteria above are the most important. Another good idea to get more out of your PLC training investment would be to get hands-on training using the actual PLC programs and software the maintenance technician will work on within the facility. Ensure your personnel has the software, equipment, and encouragement to continue with self-education. PLC Training Software Courses (Computer Based Training) are an excellent way for employees to follow up six months after the initial training. Some other ideas you could do is to provide them with simulation software or a spare PLC off the shelf to practice with.

 

 

plc safety Does your maintenance personnel work with PLCs following written Company or corporate policy and procedures?

In our industrial culture, if policies and procedures are not written and enforced, we eventually return to the old, unreliable ways. I have reviewed many policies, procedures, and books on the topic and have yet to see the maintenance management of the PLCs included. It amazes me how an organization can write guidelines for what they believe is the health of the entire organization's body and leave out the brain (the PLC). Once again, a complete automation control policy and procedure manual is out of the scope of this article. However, I will donate a few random items below to get you started.

 

  1. Write PLC policies and procedures into your existing maintenance policy and procedures. (SOP)
  2. Train all personnel working with automation equipment.
  3. The best practice is to make backup copies of the PLC programs every six months regardless of the change status.
  4. Actions to take after a Programmable Logic Controller program is modified:
    1. Document changes in the copy of software (Revision Notes), the printed copy, and the CMMS program.
    2. Copies of the control programs are stored on a media more reliably than on a floppy disk and stored on USB instead).
    3. Store multiple copies on the laptop, the maintenance manager's office, and off-site (corporate).
    4. Update EEPROM with the newly changed program.
    5. If an outside vendor changes the program, maintenance personnel must perform a-d above.
  5. For future equipment purchases:
    1. The same PLC brand in all equipment will be sought out (Standardization of PLC types)
    2. OEM must provide a descriptor copy of programs in the customer's native language.
    3. All PLC 110v control voltage will have a line filter on it.
    4. All PLCs will have the backup EEPROM option for zero downtime in some failure modes.
  6. Forcing inputs and outputs on or off shall be treated as a Safety issue. (See safety SOP)
  7. Inputs and outputs being forced on or off should be done only as a last resort. And then, only with a clear understanding of the complete effect on the PLC program and a second opinion.
    1. In the rare event that forces are installed in automation controllers, remove them within 24 hours and find a more permanent solution.
    2. Document all forces in software in a log before being enabled.
  8. Online programming is a safety risk. The standard procedure is to change offline and then download to the Programmable Logic Controller.

 

I hope this helps, and if you have a specific question, you can find me on LinkedIn.

 

Don Fitchett (President)

Business industrial network

Plc training - the best for less

Bin95.com

 

To print this page, click https://bin95.com/maintenance_management_plc_print.pdf

 

Our instructors teach this kind of valuable money-saving, safety, and reliability information. Request a quote for onsite PLC Training today!

 

Also, see our Troubleshooting PLC Control Circuits training software.

 

 

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