PLC or a Programmable logic controller is a device that is very commonly used for implementing electrical controls for industrial automation and processes. A PLC is a complex hardware platform that can be very easily programmed using Ladder Logic. PLCs are always shipped with factory settings and configurations which are changed during the course of programming. In many cases, simply reprogramming the PLC does not reset some of its configuration parameters back to factory settings. As most PLCs do not have a reset switch, different methods have to be adopted to reset a PLC.
Remove the back plate of the PLC that conceals the batteries. Remove the batteries from the PLC and close the back plate. A PLC has large capacitors that are capable of storing charge for many hours even after the batteries are removed. Simply plugging the batteries back into the PLC immediately will not reset the PLC. Keep the PLC without the batteries for 14 to 16 hours.
Plug batteries into the PLC again and power it up. If the capacitors had been completely discharged, the PLC would be reset to factory settings.
Unplug the batteries from the PLC again if the PLC has not been reset after 16 hours of remaining without batteries. Keep the PLC without batteries for at least 10 to 12 hours. Wear thick rubber gloves and shoes with rubber soles. Open the back cover of the PLC exposing the hardware inside.
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Locate the large capacitors on the circuit board inside the PLC body. Take an electrical wire and short the two legs of each capacitor respectively to completely discharge them. Plug in the batteries again and power up the PLC. The PLC should be reset to factory settings.