Weeks 16 17 pe 3231 maintenance and fault finding

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Prof. Charlton S. InaoDefence University College of EngineeringBishoftu,EthiopiaHydraulic Pneumatic System Design1/5/20161Prof .Charlton

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1/5/2016Prof .Charlton2PLC- Week 16Week 17 Maintenance and Fault FindingChapter 7,8 Week 16-17

2Chapter-1Prof. Charlton

Internal Relays1/5/2016Prof .Charlton3Internal relays in PLC serve as the hard wire relay, only they are using bits. Hundreds of thousand of relays are inside the PLC to help facilitate the controls of a circuit.Once the relay coil is energized it will make the NO contact to be closed and the normally closed(NC) contact to be open.In Mitsubishi and Siemens ,Internal relays oor flags are symbolized or represented by M.

SET and RESET Relays1/5/2016Prof .Charlton4SET function turn the bit memory from 0 to 1 and RESET function turns the bit memory from 1 to 0

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Siemens Shift Register1/5/2016Prof .Charlton14

Example:P LOGO

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Shift Register -Mitsubishi


Shift Register


i

M 0.0Q 0.1Q 0.2Q 0.3Q 0.4Q 0.5Q 0.6Q 0.7Q 0.0

I0.10UT I0.0I 0.2M 0.0M 0.2M 0.3M 0.4M 0.6M 0.5M 0.7SFTRSTM 0.1

Shift Register Siemens ConfigurationEND1/5/201621Prof .Charlton

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Week 17 Maintenance and fault finding1/5/2016Prof .Charlton23Common CausesPLC controller failure rates will be increased by the following factors (in order of most negative effect on failure rate)...Factor: EnvironmentFactor: Brand/ModelFactor: Electrical Design supporting PLCFactor:PLC Management

1/5/2016Prof .Charlton24The list of PLC module types just mentioned are in order of most reliable (part with lowest failure rate listed first), with output modules being the most likely to fail. This reliability/failure order is based on the basic equipment failure rate .Which are ...

Mechanical devices are more likely to fail than electrical,Electro-mechanical devices are more likely to fail then solid-state devices,High current devices are more likely to fail than low current devices.

While considering there are exceptions to every rule, PLC output modules are commonly electro-mechanical (relays) and/or higher current sinking PLC modules. Therefore, they are the first thing you look at for stocking spares and doing reliability improvement analysis on, second is PLC input modules

Common Cause of Fault in PLC1/5/2016Prof .Charlton25PLC Environment: If the electrical panel with PLC controller in it gets exposed to extreme heat or cold, liquids, vibration, dust, etc., the PLC controller failure probability increases.PLC Brand/Model: While a PLC in general has the lowest failure rate out of all automation control technologies, one brand may be more reliable than another brand. The various models of PLC controllers within any one vendor have a much greater reliability/failure distinction. Example a soft PLC installed on a standard consumer PC that cannot handle the rough industrial environment is almost sure to fail. Thus the reason you do not see hardly any of the soft PLC models each PLC vendor offers, being used anywhere.

1/5/2016Prof .Charlton26Electrical Design supporting PLC: Because the end user of PLC controlled equipment commonly choose the lowest bidder, the equipment designers (OEM) tend to cut corners in design so they can be the lowest bidder. A very common example of this is the combination of the OEM not putting line filters on control side of electrical panels transformer secondary and not putting an EEPROM in PLC. Therefore, it is not uncommon during lightning storms and other power noise conditions, that a PLC controller will lose it's program and production goes down.

PLC Management: The best example of this PLC controller failure factor is not having any PLC management or policies in place at all. Also under this category come many failure reduction actions to implement for little or no cost, like electrical PMs (as cleaning electrical panels cooling fan filter). Not having an up to date backup of program in PLC controller, not insuring the only personnel working with PLC controllers, have had PLC safety, reliability and best practices training, etc.. Most people working with PLCs today have only received scholastic and theory education, not training.

Fault Finding in PLC1/5/2016Prof .Charlton27The documentation required for effective fault-finding.

The use of the I/O List in fault Diagnosis

Using Electrical Drawings

Using the on board PLC facilities for fault-finding.

PLC Maintenance1/5/2016Prof .Charlton28Backup PLC Program Save a copy of your PLC program during routine maintenance to ensure a fairly up-to-date backup. In the event a PLC becomes inoperable and has to be replaced, this backup file can be downloaded onto a new PLC. Check LED Indicators Check the power and battery LED indicators. If the power LED indicator is off or flickering or if the battery LED indicator is on or flickering this may be a preliminary sign of a low battery or potential power issues. Replace the Battery If the Battery OK light is flickering or on, it is time to change the battery. Avoid catastrophic problems if you were to lose main control power by changing the battery regularly it easy watch these videos to learn more. Check Operating Environment Check temperature, humidity and other environmental factors to make sure that your PLC is operating within the proper conditions. Also make sure there is good airflow in the cabinet by cleaning filters in the enclosure.

PLC Maintenance1/5/2016Prof .Charlton29 Check Operating Voltage Check the input voltage that is powering your PLC to make sure that the voltage is within the appropriate range and free from power spikes or brown out conditions. Check Program Functionality During routine maintenance, check the functionality to make sure the system or equipment that is being controlled is operating as intended. Look For Indications Of Overheated Components Check the CPU and modules for distorted, warped, or discolored cases and burnt odors. Clear Dust And Check Venting Do not allow dirt and dust to accumulate on the PLCs components. The central processing unit and I/O system are not designed to be dust proof. Check to be sure none of the PLC and module cooling vents are clogged or blocked by dust or debris. Make sure that there is sufficient heat dissipation space around the PLC. If heat dissipation is obstructed, circuit malfunction can occur and if conductive dust reaches the electronic boards, it can cause a short circuit, resulting in possible permanent damage to the circuit board. Inspect Battery Status Check battery and replace if necessary.

PLC Maintenance1/5/2016Prof .Charlton30 Check Connections Make sure that all communication cables, plugs, sockets, terminal strips, wiring and modules are connected properly. If your PLC system is located in an area that experiences constant vibrations that could possible loosen terminal connections, perform this check more often and consider installing a vibration detector. Identify Updates Needed Check for any product notices, patches and upgrades and update as necessary. Remove Unnecessary Items Keep any items such as drawings, installation manuals or other materials away from the PLC system. Leaving these items on top of the CPU rack or other enclosures can obstruct airflow and create hot spots, ultimately causing a system malfunction. Audit Parts In Use Conduct an audit to check each component of your PLC system and determine if parts are good or need replacement. Take Inventory Of Replacement Parts Keep a stock of replacement parts on hand to minimize downtime resulting from component failure. Having the right spare in stock during a failure situation can result in shutdown for only minutes instead of hours or days.

Installation and Commissioning1/5/2016Prof .Charlton31Checking the hardwareTransferring and testing the softwareOptimization of the softwareCommissioning of the entire system






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