PLC Failure Probability
PLC Failure Probability
(OP)
Hi,
I am wondering if anybody has done a PLC failure probability study especially in oil and gas industry? Or anybody knows a good resource about it.
Thanks,
I am wondering if anybody has done a PLC failure probability study especially in oil and gas industry? Or anybody knows a good resource about it.
Thanks,





RE: PLC Failure Probability
I do know that GE-IP has a lot of hardware in oil & gas industries in both production and transportation of each. I suggest that you contact them and ask. http://support.ge-ip.com/support/index?page=spage&...
RE: PLC Failure Probability
Thanks,
RE: PLC Failure Probability
TTFN

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RE: PLC Failure Probability
Thanks,
RE: PLC Failure Probability
Actually, in 217, all the factors but voltage are listed. Section 3.4.3 Table 3.2 lists a series of environments that encompass certain vibrations and temperatures. Time is inherent in the failure rate λp since that's what goes into the exponential failure rate equation. The last page in section 5.6 lists the acceleration factors for the different environments.
TTFN
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RE: PLC Failure Probability
"What is the probability that the system will get destroyed by lightening on July 4, 2021?"
What are the facts that need to be known to calculate this, the more facts one has the more accurate one can be?
Where is it located? Central Florida or Death Valley?
How is it protected from surviving a lightening strike or near by strike?
etc.
YMMV
RE: PLC Failure Probability
That's why when I get asked this question, I like to also bring in the concept of MTTR, Mean Time To Repair. MTBF numbers are important, but WHEN your PLC fails, if the manufacturer is gone or has moved on to a new model and no longer supports yours, the MTTR goes out the roof!
"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington
RE: PLC Failure Probability
Telecom companies in the late 1980s paid premium dollar to maintain production of 1970s-era parts that should have gone obsolete. We were outsourcing 10-micron metal gate PMOS parts when 2-micron CMOS parts were being mass produced, because the original PMOS parts were thoroughly characterized and qualified, and the re-qualification of replacement parts was more expensive than the premiums paid for continued manufacturing of the obsolete parts. One method of maintaining adequate repair inventory is to make "lifetime" buys, i.e., you buy additional inventory in the present to cover future attrition and failure. Of course, that requires you to have extremely good reliability analysis and data.
TTFN

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RE: PLC Failure Probability
Thanks,
RE: PLC Failure Probability
TTFN

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RE: PLC Failure Probability
I have met many failures in analogue and digital systems and, depending on what kind of system it is, you usually have:
1. Connectors and cables.
2. Vibration.
3. Temperature cycling and condensation.
4. ESD.
5. EPROMs that lose their contents.
6. Dust,Corrosive fumes, flooding.
7. Theft.
And, very often, documentation and know-how that has disapeared
The order may vary, but this is what I have seen in my active life in industrial automation and drives for more than 50 years.
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: PLC Failure Probability
Pamela K. Quillin, P.E.
Quillin Engineering, LLC
RE: PLC Failure Probability
RE: PLC Failure Probability
Can one rate vibration higher than temperature without knowing some actual values? Temperature impact on electronics is typically characterized by a doubling of the failure rate for a mere 3 deg C increase in temperature. In fact, accelerated life testing for integrated circuits was typically done solely with temperature, reducing 20 years of operating life to 2000 hrs simply by running the parts at high temperatures. MIL-HDBK-217's acceleration factors only go to about 20x for for a combination of temperature and vibration, while for discrete components, it has factors up to 40, driven mostly by temperature.
TTFN

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RE: PLC Failure Probability
9. PPP (Pi55 Poor Planning) of the design and use considerations. I'm guilty of that myself; had one where the user ignored 48 flashing red pilot lights lights meant to warn them of a temporary manual override. He ran it that way for 6 months with all 48 red lights flashing once/sec. (he put on sunglasses, I'm not kidding). I had used relay outputs in the I/O cards, it wore them out and the contacts welded.
"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington
RE: PLC Failure Probability
- Mechanical
- Electro-Mechanical
- High Current
- Low Current
- Solid State
As you eluded to, environment can be an exception to the general rule.(Relay card most likely, and MTBF is useless unless solid state, as frequency PLC program activates, dictates failure rate as well as environment.)
The above probability guide translate to PLCs as ...
- Output Cards
- Input Cards
- Power Supply
- Backplane
- CPU (processor Card)
Environment can change basic order above. a couple examples, in a foundry, the metal dust causes backplane to fail more frequently. In the machining industry, penetrating fluid getting into sensors causes input cards to fail more than output cards because the liquid causes input card to sink more current than designed to. In wire manufacturing where a lot of high voltage insulation testing is going on, CPUs fail more often because control voltage for PLC does not have line filter in line with it. etc. etc. Other variables that effect the failure rate are improper design, alight not allowing the 20% extra when calculating relay card or power supply current, etc etc.Don
BIN Industrial & PLC Training
http://bin95.com
RE: PLC Failure Probability
Or could be the time that company goes bankrupt, ships all the equipment overseas, or whatever corporate decision is made to make it obselete due to different process or new product being made.
RE: PLC Failure Probability
Pamela K. Quillin, P.E.
Quillin Engineering, LLC