Prior to beginning a system start up procedure, it is important to check and verify that PLC system has been installed according to the manufacturers specifications and that the installation meets local, state and national codes. Special attention should be given to system grounding.
Before applying power to the PLC controller, following is to be ensured:
Testing PLC Inputs PLC input module should illuminate. Failure of a LED TO illuminate indicates:
The second method uses the force function of the PLC system to energize outputs, one at a time. This allows the user to turn an output device ON and OFF without using a push button or other contacts.
For final system checkout, the following steps should apply:
Systematic approach towards PLC troubleshooting should consist of the following steps:
Before applying power to the PLC controller, following is to be ensured:
- Check all power and communication cables to ensure that connector pins are straight and not bent or pulled out.
- Connect all cables making sure that connectors are fully inserted into their sockets. Secure connectors as applicable.
- Ensure that all modules are securely held in the I/O rack.
- Place PLC System processor key switch to a safe position.
Testing PLC Inputs PLC input module should illuminate. Failure of a LED TO illuminate indicates:
- Improper input device operation
- Incomplete or incorrect wiring; check to be sure that the input device is wired to the correct input module and proper channel.
- Loss of power to the PLC input device
- Defective LED or input module
The second method uses the force function of the PLC system to energize outputs, one at a time. This allows the user to turn an output device ON and OFF without using a push button or other contacts.
For final system checkout, the following steps should apply:
- Place the processor in the program mode
- Clear the memory of any previous rung used for testing.
- Using a programming device, enter the program (ladder diagram) into memory.
- Place the processor in the test or disable output mode, depending on the PLC system and verify correctness of program.
- Once the circuit operation has been verified in the test or disable output mode, the PLC processor can be placed in the run mode for final verification.
- Make changes to the program as required (timer setting, counter presets etc.)
- Once the circuit is in final form and the machine or process is running correctly it is recommended that a copy of the program be made.
Systematic approach towards PLC troubleshooting should consist of the following steps:
- Symptom recognition
- Isolate the problem
- Corrective action
- DC Power ON if this LED is not lit, there is a fault in the DC power supply. Check the power supply fuse or incoming power.
- Mode indicates which operating mode the processor is in (Run, test, program etc.). The fault may simply be that the key switch is in the wrong position.
- Processor fault when this status light is on
- Memory fault this status light illuminates when a parity error exists in transmission of data between the processor module and memory module. Replace only one module at a time.
- I/O Fault this light indicates a communication error between the processor and the I/O rack.
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