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Sunday, March 23, 2008

Maintenance and reparation the PLC

This section explains matters that must be known in maintenance and reparation the PLC.


Applying the safety procedure
During execution of the work, the safety procedure must be executed truly so that the risk of the work accident can be avoided.
Example of applying the safety procedure;
  • Use the safety equipment
  • Follow the instruction of safety procedure
  • Comprehending fringe of writing on the wall or emergency

Checking the installation and power supply
To do the maintenance and reparation of the PLC system, one of the important matter that must be done is perform the inspection to the PLC installation as according to the manual instruction, for example;




Maintain and repair the PLC
The maintenance and reparation of the PLC is all activity which intentionally be done to the PLC by following a systematic procedure with target so that the PLC which we own always can be used in the best condition, fluent, peaceful and technically has along live.

Preventive maintenance
The main system components of a PLC system are semiconductors, and it contains few components with limited lifetimes. Poor environmental conditions, however, can lead to deterioration of the electrical components, making regular maintenance necessary. The standard period for maintenance checks is 6 months to 1 year, but more frequent checks are required if the PLC is operated in more demanding conditions. When inspecting one or two times per six months, check the following items.




Preventive maintenance consisted of several activity below;

Pre maintenance
Pre maintenance is a preparation activity, matters which require to be prepared for example;
  • Prepare the maintenance equipment
  • Prepare the maintenance material especially weared routinely, for example; cleanser material, Iubricant material, corrosion preventative material, etc.
  • Prepare the maintenance documentation
  • Prepare the power supply and air compressor

Daily maintenance
The following table shows the inspection and items which are to be checked daily.




Periodic maintenance
Check the following items once or twice every six months, and perform the needed corrective actions.





Several example of the maintenance activity on the Omron PLC is shown below;
CPU and Power Supply Fuses



To replace a fuse, follow the steps below:
  • Turn OFF the power to the PLC.
  • Remove the fuse holder by turning it approximately 50? counterclockwise with a standard screwdriver.
  • Remove the fuse from the holder.
  • Insert a new fuse.
  • Reattach the fuse holder by turning it approximately 50? clockwise with a standard screwdriver.

Output Unit Fuses
To replace a fuse, follow the steps below. Use only UL/CSA certified replacement
fuses.



  • Turn OFF the power to the PLC.
  • Detach the terminal block by unlocking the lock levers at the top and bottom of the terminal block.
  • While pushing down the lock lever on the Backplane with a screwdriver as shown below, remove the Output Unit.

  • Remove the screw from the top of the Unit (Phillips screwdriver).
  • Detach the case from the Unit (flat-blade screwdriver).

  • Pull out the printed circuit board.
  • Insert a new fuse. A spare fuse is provided inside the rear of the case when the Unit is delivered.
  • Reassemble in reverse order of assembly.

Output Unit Relays
To replace a Relay, follow the steps below:
  • Turn OFF the power to the PLC.
  • Detach the terminal block by unlocking the lock levers at the top and bottom of the terminal block.
  • While pushing down the lock lever on the Backplane with a screwdriver as shown below, remove the Output Unit.


  • Remove the screw from the top of the Unit (Phillips screwdriver).
  • Detach the case from the Unit (flat-blade screwdriver).

  • Pull out the printed circuit board. The Relays are placed on the PLC boards of individual Units as shown in the figures below.

  • A Relay puller is provided inside the rear of the case when the Unit is delivered. Use the Relay puller to pull out the Relay as shown below. Insert a new Relay.

  • Reassemble in reverse order of assembly.

Batteries
Some RAM Packs use a battery. When the battery is nearly discharged, the ALARM indicator blinks and the message “BATT FAIL” appears on the Programming Console. When this occurs, replace the battery within one week to avoid loss of data. The battery comes together with its connector as a set. To replace the Battery Set, follow the steps below. The entire replacement must be completed within five minutes to ensure that the
data will not be lost.
If you are using model C200H-CPU11-E as the CPU, the battery is installed in the Unit upon delivery.
  • Turn OFF the power to the PLC. (If the power was not already ON, turn the power ON for at least one minute before turning the power OFF.)
  • Remove the cover from the battery compartment of the RAM Pack.
  • Remove the old Battery Set.
  • Install the new Battery Set as shown shown in the following diagram.


  • Replace the cover of the battery compartment.
  • Press CLR, FUN, MONTR, MONTR or just turn the power to the PC OFF and then ON again to clear the error message on the Programming Console.


Reparation
Reparation is an activity which consist of troubleshooting, analysis or diagnosis and corrective actions. The following explains contents troubleshooting, diagnosis and corrective actions for various errors that can occur during system operation.

Basic Procedures of Troubleshooting
System reliability not only depends on reliable equipment but also on short down times in the event of faults. The short discovery and corrective action is needed for speedy operation of system.

The following shows the basic instructions for troubleshooting.
Visual checks
Check the following points.
  1. Machine operating condition (in stop and operating status)
  2. Power On/Off
  • Status of I/O devices
  • Condition of wiring (I/O wires, extension and communications cables)
  • Display states of various indicators (such as POWER LED, RUN LED, ERR. LED and I/O LED).
After checking them, connect peripheral devices and check the operation status of the PLC and the program contents. Use the error code list to determine the happening error.

Trouble Check
Observe any change in the error conditions during the following.
  • Switch to the STOP position, and then turn the power on and off.

Narrow down the possible causes of the trouble where the fault lies, i.e.:

  • Inside or outside of the PLC?
  • I/O module or another module?
  • PLC program?


Troubleshooting
The following example explains the procedure for determining the cause of troubles as well as the errors and corrective actions to the LG PLC.




Troubleshooting flowchart used when the POWER LED turns OFF
The following flowchart explains corrective action procedure used when the power is supplied or the power led turns off during operation.



Troubleshooting flowchart used when the ERR LED is flickering
The following flowchart explains corrective action procedure use when the power is supplied starts or the ERR LED is flickering during operation.



Troubleshooting flowchart used when the RUN LED turns off
The following flowchart explains corrective action procedure to treat the lights-out of RUN LED when the power is supplied, operation starts or operation is in the process.


Troubleshooting flowchart used when the I/O part doesn’t operate normally
The following flowchart explains corrective action procedure used when the I/O module doesn’t operate normally.








Troubleshooting flowchart used when a program cannot be written to the CPU
The following flowchart shows the corrective action procedure used when a program cannot be written to the PLC module.




The following example explains the procedure for determining the cause of troubles as well as the errors and corrective actions to the Omron PLC. Use the following flowcharts to troubleshoot errors that occur during operation.

Main Check



Power Supply Check



Fatal Error Check




Non-fatal Error Check



I/O Check
The I/O check flowchart is based on the following ladder diagram section.





Environmental Conditions Check




Memory Error Check




Troubleshooting Examples on the PLC electronic circuit
Possible troubles with various circuits and their corrective actions are explained.
Input circuit troubles and corrective actions
The followings describe possible troubles with input circuits, as well as corrective actions.




Output circuit troubles and corrective actions
The following describes possible troubles with input circuits, as well as their corrective actions.


Output circuit troubles and corrective actions (continued).





Error code list
The following example shows error code list on the LG PLC.

continued;

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