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Troubleshooting
PLCs
By
Steve Mackay
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Welcome to this webinarWelcome to this webinar
There are at least 3 ways to interact with yourpresenter today.
1. Use the Texttab, near bottom left of yourscreen. Type the message in the space next tothe Send button, then enter or click Send.(Ensure All is selected in the drop-down menuunder the typing area)
2. Use the Emoticonsselection in the text window choose an emoticon then click send or enter.
3. Talk! Click the Push To Talkbutton. The buttonwill change to yellow when you are queued, thengreen to show that your microphone is live.
Remember to click it again when you havespoken
This 45 minute session w ill commence shortly
RH
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If you are having problems with your microphone, dont worry as long as you can hear the presentation thats OK you cancommunicate with the text box. However, after the sessionwe recommend you chat let us know so that we can help you.
If you are having trouble with your speakers, and cant hearanything and have tried the Audio Wizard dont worry. Wewill be recording the session, so you will get to view a
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We hope you enjoy the session, we will be starting in the nextslide
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EIT MicroCourse Series
Every two weeks we presenta 45 minute interactivecourse
Practical, useful with Q & Athroughout
PID loop Tuning / Arc FlashProtection presented, so far
Upcoming: Functional Safety Troubleshooting Conveyers
and much much more..
Go tohttp://www.eit.edu.au/free-courses
You get the recording andslides
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Objectives
Quickly interpret,isolate and fixcommon hardwareproblems related toPLC input/outputs
Troubleshoot PLCsoftware
Identify datacommunicationsproblems
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Topics
Introduction to PLC
Internal or ExternalProblem
Internal Problems External Problems -
I/O and Comms
Applications
Conclusion
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Industrial Automation Skills
Todays Industrial Automation engineer and technician should beable to troubleshoot, identify, prevent and fix common PLC andSCADA problems.
If you have worked in industry, you are probably familiar with PLCsand SCADA systems and understand their basic operation.
You want to be able to quickly diagnose problems using your PLCsoftware; know how to connect to the right PLC processor online,make minor changes to get the machine running and have the know-how to test new ideas and hardware components. In addition, youwant to be able to do troubleshooting and problem solving of yourassociated SCADA system.
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Introduction to the
PLC
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Introduction to the PLC PLC means Programmable Logic Controller.
The word Programmable differentiates it fromthe conventional hard-wired relay logic
The PLC as a unit consists of a processor toexecute the control action on the field dataprovided by input and output modules
In a programming device, the PLC control logic isfirst developed and then transferred to the PLC
PAC or Programmable Automation Controller
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What can a PLC do? It can perform relay-switching tasks. It can conduct counting, calculation and comparison of
analog process values.
It offers flexibility to modify the control logic, wheneverrequired, in the shortest time.
It responds to the changes in process parameters withinfraction of seconds.
It improves the overall control system reliability.
It is cost effective for controlling complex systems.
Trouble-shooting becomes simpler and faster.
An operator can easily interact with the process with thehelp of the HMI (Human-Machine Interface) computer.
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Basic block diagram of the
PLC
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Working of a PLC CPU
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Ladder diagram
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Ladder program execution
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Internal or External
Problem
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Internal or External Problem ?
Over 80% of malfunctions are with I/O
modules and field equipment Problems related to specific I/O
module or I/O device are externalproblems
Large groups of failures internals of
PLC
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Internal Problems
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Internal Problems
Check earthing/grounding is correct
Check power supply to PLC is withincorrect range and ac ripple on dcsupplies is not excessive
Batteries on PLC are OK
PLC program hasn't been corrupted
Examine internal diagnostics for acrash of PLC program
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External Problems
E t l P bl di it l
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External Problems digital
Inputs Check Power supply to module
Look for where power to digital Inputcomes from
Check fuses/breakers Adequate changes of voltage to Input
Digital input fine ===> PLC programproblem
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Discrete DC input module
External Problems digital
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External Problems digital
outputs Check Power supply to module
Check power output from PLC Check fuses
Force digital outputs on and off Use test load rather than open circuit
why ?
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Discrete DC output module
External Problems analog
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External Problems analog
inputs Move field device through
full range of current 4-20mA
Hook up signal
transmitter if you need tobe absolutely sure.
External Problems analog
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External Problems analog
outputs Force output to specific value and
observe Check external wiring
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Applications
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Remote troubleshooting
Be careful with remote troubleshooting
about industrial network security Hackers are about 24x7
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Thorny transients
Fiber Optics where possible
Good earthing/grounding for datacomms
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A typical shield
The purpose of the shield is to reduce the magnitude of the noise
coupled into the low-level signal circuits by electrostatic or magnetic
coupling. This has brushed up the above-mentioned concepts up to some extent
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Opto-electric coupler circuit
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When in doubt -disconnect
Test with dummy equipment not 1MW
ball mills
