PLCs only make sense when you have sequential events that are dependent on previous events, like motion fault detection. From what
I have gleaned from previous postings is that your equipment is mechanically timed. In my humble opinion I would concentrate on
using electronic trigger technology, solid state relays and motion validation logic (feedback). The value of doing this is first
reliability and secondly immediate system fault identification. You should be able to use a common family of components for all
your solutions.
Steve

"Buerste" wrote in message ...
I want/need to replace a few relay-logic controls with PLCs. Typically, a machine is using 6 to 8, 3 or 4 pole DT relays, 6 to 8
limit switches and 3 to 4 operator switches, and 4 to 6 hydraulic/pneumatic valves. Should be ideal for PLCs. I need to learn
ladder programming. On the web, there are plenty of tutorials but everything I've seen or tried is lacking in translating the
real-life process into a program. Any direction I should look? A lot of my stuff is old and doesn't have schematics yet alone a
flow chart. The guy I had that was very good at this retired and moved to SC.