Maintenance Management of your company's PLC (Programmable Logic
Controller).
* 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 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.
* What is a PLC?
First I'd 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 surgeons?")
Important Note: 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.
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 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.
* How many PLCs is your bottom line depending on?
My company has had an ongoing PLC related global maintenance
survey since the year 2000.
(http://www.bin95.com/survey/survey.asp)
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 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 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.
Some older 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?
* 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 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.
http://www.bin95.com/Download/PLC-Audit.zip
Once you 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.
* Do we have the most common spares for the PLC?
* Is the OEM (Original Equipment Manufacturer) available 24/7?
Or even in business any more?
* Do we have a back up copy of the PLC program?
* Does our program copy have descriptions so we can work with
it reliably and efficiently?
* 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 insure reliability.
* 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? (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.
Then the 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.
1. The training you decide on, should stress working with PLCs
in a Safe and Reliable way. (not just textbook knowledge or
self learned knowledge)
2. Secondly, 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.
* Does your maintenance personnel work with PLCs following
written company or corporate policy and procedures?
It seems 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.
1. Write PLC policies and procedures into your existing
maintenance policy and procedures. (SOP)
2. All personnel working with PLCs will be trained on that
PLC equipment.
3. Backup copies of the PLC programs will be made every 6 months
regardless of change status.
4. If a PLC program has been changed ...
a. It will be documented in the software copy, in the printed
copy and in the CMMS program.
b. Copies of the PLC program will be stored on a media more
reliable than floppy disk (CD, USB, etc.).
c. Multiple copies will be stored on laptop, maintenance
manager's office and off site (corporate).
d. If available, EEPROM will be updated with new changed
program.
i. If outside vendor changes, a-d will be performed by
maintenance personnel
5. Future equipment purchases ...
a. A common PLC brand in all equipment will be sought out
(Standardization of PLC types)
b. OEM will be required to provide a descriptor copy of PLC
programs in the customer's native language.
c. All PLC 110v control voltage will have a line filter on it.
d. 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 shall not be forced on or off with out a
clear understanding of complete effect on PLC program and a
second opinion.
a. If forces are installed, they shall be removed with in 24
hours and a more permanent solution found.
b. All forces should be documented in software and a written
log before being enabled.
8. Online programming is somewhat of a safety risk, normal
procedure is to change offline and download to the PLC.
Hope this helps, if you have a specific question you can find
me in our PLC discussion area at the PLC Discussion Forum.
http://www.idcon.com/toastforum6503/toast/toast.asp?sub=show&action=topics&fid=10
For a print version of this article, click
http://www.bin95.com/maintenance_management_plc_print.pdf
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