Title :
Adding robustness to PLC using a software approach based on weighted median filters
Author :
Paredes, José L. ; Diaz, David
Author_Institution :
Dept. of Electr. Eng., Los Andes Univ., Merida, Venezuela
Abstract :
This paper addresses the problem of improving immunization of programmable logic controllers (PLC) to electromagnetic interference with impulsive characteristics. A filtering structure, based on weighted median (WM) filters, that does not require additional hardware and can be implemented in legacy PLC is proposed. The filtering operation is implemented in the binary domain and removes the impulsive noise present in the discrete input adding thus robustness to PLC. By modifying the sampling clock structure, two variants of the filter are obtained. Both structures exploit the cyclic nature of the PLC to form an N-sample observation window of the discrete input, hence, a status change on it is determined by the filter output taking into account all the N samples avoiding thus that a single impulse affects the PLC functionality. A comparative study, based on a statistical analysis, of the different filter´s performances is presented.
Keywords :
clocks; electromagnetic interference; logic circuits; logic programming; median filters; programmable controllers; statistical analysis; N-sample observation window; PLC; electromagnetic interference; filtering structure; programmable logic controllers; sampling clock structure; statistical analysis; weighted median filters; Clocks; Electromagnetic interference; Filtering; Filters; Hardware; Industrial control; Programmable control; Robustness; Sampling methods; Wires;
Conference_Titel :
Devices, Circuits and Systems, 2004. Proceedings of the Fifth IEEE International Caracas Conference on
Print_ISBN :
0-7803-8777-5
DOI :
10.1109/ICCDCS.2004.1393406