PROGRAMABLE LOGIC CONTROLLER
Posted by Debyendu Chakraborty on Monday, April 8, 2013
Under: Fault Troubleshoot
* check to ensure main power is on( 110 VAC)
* check 24V dc power available
* identify problem area
* check sensor operation in problem area
* check sensor Inputs to PLC
* check on PLC that a change in sensor state causes the corresponding Input LED on the PLC to go on or off
* identify Output controlled by Input on PLC ladder diagram
* ensure that Output LED is cycling on/off with Input
* check that Output voltage is correct and cycling on/off with Input
* locate Output device and ensure that voltage is reaching device and cycling with Input
* ensure that Output device is working correctly (solenoid coil, relay coil, contactor coil, etc.)
* an Input or Output module can be defective in one area or circuit and work correctly in all other circuits
* if each field circuit is not fuse protected, the modular internal circuit becomes a fuse and can be destroyed by a field short circuit or any other over-current condition
* check modular circuit; if bad, module must be replaced after correcting field fault
* shut down PLC prior to changing any module -main power and 24V power
* locate fault in field circuit by disconnecting wires at module and field device, check between wires for short circuit and to ground for short circuit; replace wire is short circuit found
* check device for ground, short circuit, mechanical and electrical operation, even when problem found in wires, always also check device for another fault, problem in wires can cause problem in device or vice versa; if device defective, replace device and then check total circuit before placing in operation and after restoring circuit, check again to ensure circuit and module are operating correctly
* check power supply module; if no output, shut down power and replace supply module
* back plane can go bad, some of the modules with power and others with no power, replace backplane
* sometimes, the PLC can be reset using the Reset key switch; ensure that turning the PLC off won't interrupt other running sub-set programs, turn keys witch to far right, after 15 seconds, turn to far left wait, then return to middle position; this operation should reset program and enable a restart
* the PLC program can have a latch relay with no reset under certain conditions, the key switch reset may have no affect on the latch, try turning the power to the PLC off and back on, this operation may reset the latch and allow the program to be restarted
* the PLC is usually part of a control circuit supplied with 110 VAC through a 440V/110V transformer as part of a system with motors, controllers, safety circuits, and other controls; occasionally, cycling the main 440V power off/on will be necessary to try to reset all the safety and control circuits
* possession and use of an up-to-date ladder diagram, elementary wiring diagram, manufacturer's manuals & diagrams, troubleshooting skills, operator's knowledge, and time are all required to solve issues involved in maintaining a modern manufacturing production line.
* check 24V dc power available
* identify problem area
* check sensor operation in problem area
* check sensor Inputs to PLC
* check on PLC that a change in sensor state causes the corresponding Input LED on the PLC to go on or off
* identify Output controlled by Input on PLC ladder diagram
* ensure that Output LED is cycling on/off with Input
* check that Output voltage is correct and cycling on/off with Input
* locate Output device and ensure that voltage is reaching device and cycling with Input
* ensure that Output device is working correctly (solenoid coil, relay coil, contactor coil, etc.)
* an Input or Output module can be defective in one area or circuit and work correctly in all other circuits
* if each field circuit is not fuse protected, the modular internal circuit becomes a fuse and can be destroyed by a field short circuit or any other over-current condition
* check modular circuit; if bad, module must be replaced after correcting field fault
* shut down PLC prior to changing any module -main power and 24V power
* locate fault in field circuit by disconnecting wires at module and field device, check between wires for short circuit and to ground for short circuit; replace wire is short circuit found
* check device for ground, short circuit, mechanical and electrical operation, even when problem found in wires, always also check device for another fault, problem in wires can cause problem in device or vice versa; if device defective, replace device and then check total circuit before placing in operation and after restoring circuit, check again to ensure circuit and module are operating correctly
* check power supply module; if no output, shut down power and replace supply module
* back plane can go bad, some of the modules with power and others with no power, replace backplane
* sometimes, the PLC can be reset using the Reset key switch; ensure that turning the PLC off won't interrupt other running sub-set programs, turn keys witch to far right, after 15 seconds, turn to far left wait, then return to middle position; this operation should reset program and enable a restart
* the PLC program can have a latch relay with no reset under certain conditions, the key switch reset may have no affect on the latch, try turning the power to the PLC off and back on, this operation may reset the latch and allow the program to be restarted
* the PLC is usually part of a control circuit supplied with 110 VAC through a 440V/110V transformer as part of a system with motors, controllers, safety circuits, and other controls; occasionally, cycling the main 440V power off/on will be necessary to try to reset all the safety and control circuits
* possession and use of an up-to-date ladder diagram, elementary wiring diagram, manufacturer's manuals & diagrams, troubleshooting skills, operator's knowledge, and time are all required to solve issues involved in maintaining a modern manufacturing production line.
In : Fault Troubleshoot
Tags: plc relay coil field instruments solenoid ladder logic module
