Karnaugh maps aren’t for ladder logic

The "Technology Update" on Karnaugh Mapping aids industrial control," (Control Engineering, Jan. '00, p.9), suggests Karnaugh mapping can help PLC programmers reduce scan time so lower-cost PLCs can be used, eliminate "bugs" in ladder logic rungs, and reduce maintenance costs on old ladder logic.

By Staff February 1, 2000

The “Technology Update” on Karnaugh Mapping aids industrial control,” ( Control Engineering , Jan. ’00, p.9), suggests Karnaugh mapping can help PLC programmers reduce scan time so lower-cost PLCs can be used, eliminate “bugs” in ladder logic rungs, and reduce maintenance costs on old ladder logic. Certainly the reduction of scan time may be important (theoretically) to someone (somewhere). However, repeated statements in rungs of logic meant to be read by humans are not necessarily redundant if they make the code less terse and easy to understand. Karnaugh maps are intended to optimize logic that never gets read by a human. This method isn’t useful for experienced PLC programmers using ladder logic.

Bob Barnett, owner, Power City Automation Technology, Niagara Falls, Ontario, Canada