Plant Maintenance Management
your company's PLC
(Programmable Logic Controller)
By Don Fitchett
could not answer with confidence or you answered ‘No’ to any of the above
questions, you need to read this article
on maintenance management of PLCs. Why? Because the PLCs
(Programmable Logic Controllers) are the brains of your operation. When the
PLC is not functioning properly, lines shut down, plants shutdown, even city
bridges and water stations could cease to operate. Thousands to millions could
be lost by one little PLC in an electrical panel that you never even knew
existed. But most importantly, damage to machine and personnel could result from
improper maintenance management of
your company’s PLCs.
is a PLC?
like to explain in the most non-technical
terms possible, What a PLC is. As 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
to 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 how I explain
it to my doctor any way. (His mouth drops open, “... you train brain
Just as a doctor asks the patient questions to figure out 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 have to be
met in order for the PLC to cause
an action to occur (like turn a motor on). In a reliable maintenance management
environment, the maintenance technician will be using the PLC as a
troubleshooting tool to reduce downtime.
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 that were in older electrical panels, and allows
the maintenance technician to change the way a machine works without having to
do any wiring. The program is typically in ladder logic, which is similar to the
wiring schematics maintenance electricians are already accustomed to working
with. Inputs to a PLC can be switches, sensors, bar codes, machine
operator data, etc. Outputs from the PLC can be motors, air solenoids,
indicator lights, etc.
many PLCs is your bottom line depending
has had an ongoing PLC related global maintenance
survey since the year 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 of the
participants are from fortune 500 companies having hundreds of employees. The
odds are most of them have 12-30 PLCs in their facilities. Currently the average
is 6-9 reported, so the good news is the industry as a whole is becoming more
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 also common
that after the fire is out, it's on to the next fire, without fully learning
what can be done to avoid these costly downtimes in the future, and in other
similar machines in a company or corporation.
electrical panels may only have relays in them, but most machines are controlled
by a PLC. 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?
you have an up to date list of all PLC
model types, part availability, program copies and details for your company?
step to take is to perform a PLC audit. Open every electrical panel, and write
down the PLC brand, model, and other pertinent information. Then go the next 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.
have collected the basic information in your Plant wide and/or corporate audit,
you need to analyze the information 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 will need to ask
more important questions.
we have the most common spares for the PLC?
the OEM (Original Equipment Manufacturer) available 24/7? Or even in business
we have a back up copy of the PLC program?
our program copy have descriptions so we can work with it reliably and
we have the software needed to view the PLC program? Are our maintenance
personnel trained on that PLC brand?
some of the questions our managers must ask, to avoid unnecessary risk and to
you have at least one trained person per
shift to maintain and troubleshoot your plant PLCs?
your maintenance staff trained on the PLC? (Silly to squander over a couple
thousand in maintenance training when the lack of PLC knowledge could cost you
10 thousand an hour. ...
or worse. I can give you a couple good reasons why you should have at least one
trained person per shift, to work reliably with PLCs. You do not want to see
greater downtime on off shifts because the knowledge base is on day shift only.
Also with all the baby boomers (our core knowledge base in the industry) about
to retire, it is not smart management to place all your eggs in one basket.
question should be asked, what should we look for in training. Well I have been
training individuals for over a decade and could easily write another article on
just PLC training alone. I can tell you here, that you should seek training with
two primary objectives.
training you decide on, should stress working with PLCs in a Safe and Reliable
way. (not just textbook knowledge or self learned knowledge)
the training should be actually centered around the PLC products you are using
or plan to use in your facility.
I feel the
two criteria above are the most important. Some other good ideas 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 be working with
in the facility. Insure your personnel have the software, equipment and
encouragement to continue with self education. PLC Training CBT (Computer Based
Training) CDs are a great way for employees to follow up 6 months after the
initial training. Some other ideas you could do is to provide them with
simulation software and/or a spare PLC off the shelf to practice with.
your maintenance personnel work with PLCs following written company
or corporate policy and procedures?
that in our industrial culture, if policy and procedures are not written and
enforced, we eventually stray back to the old unreliable ways. I have
reviewed many policy and procedures as well as books on the topic matter and
hardly ever see 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 PLC 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.
PLC policies and procedures into your existing maintenance policy and
personnel working with PLCs will be trained on that PLC equipment.
copies of the PLC programs will be made every 6 months regardless of change
a PLC program has been changed ...
will be documented in the software copy, in the printed copy and in the CMMS
of the PLC program will be stored on a media more reliable than floppy disk (CD,
copies will be stored on laptop, maintenance manager’s office and off site
available, EEPROM will be updated with new changed program.
outside vendor changes, a-d will be performed by maintenance personnel
equipment purchases ...
common PLC brand in all equipment will be sought out (Standardization of PLC
will be required to provide a descriptor copy of PLC programs in the
customer’s native language.
PLC 110v control voltage will have a line filter on it.
PLCs will have the backup EEPROM option for zero downtime in some failure modes.
inputs and outputs on or off shall be treated as a Safety issue. (See safety
and outputs shall not be forced on or off with out a clear understanding of
complete effect on PLC program and a second opinion.
forces are installed, they shall be removed with in 24 hours and a more
permanent solution found.
forces should be documented in software and a written log before being enabled.
programming is somewhat of a safety risk, normal procedure is to change offline
and download to the PLC.
Training - The best for less
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