PLC programming has evolved into something more than simple relay logic. I know this is obvious to some, but it is a point of view not often considered by people who deal with it everyday. I personally do not think of ---||--- as a relay contact anymore, to me it translates as an IF ... THEN ... type of statement.
Personal opinion: That is the problem with those that program and create the programs for plc's.
For many years ladder logic has been effective, plc's have expounded on that concept...I will admit with more features and possibilities.
The problem with the aforementioned way of thinking is that it doesnt follow electrical training/thinking. Ladder diagrams were a product of POWER and control diagrams. Electricians to date are still taught power and ladder diagrams.
WHO has to deal with troubleshooting problesm with machines with relays or plc's? ELECTRICAL Maintenance! These are guys that usually go thru an apprentice program to run conduit and wire to follow a specific layout.
IF THEN OR ELSE is a product of working/studying in a programming environment and not specifically related to anything relay/electrical.
You can argue this concept till the moon turns black and I will not change my mind. Ladder logic is understood easily by many and can be enhanced (if the effort was made) to be more graphical ( who can't understand pictures?) so the many features offered using flowcharts, IL, FBD, etc could be readily understood by many electrical personnel.
WHY do you think it is so hard to understand the difference between hardwired and software applications?
BECAUSE there is a difference. In Relay logic there wasn't.
Hitler was a fool even though he controlled an empire. He created an environment that created a World War. He also cared about the working people and the Volkswagen was created from it, a machine that many could own and was easily understood.
I DO NOT care about the price of the machine/object, but do want it to be easily understood. TO ask that electricians/maintenance people understand programming concepts like IF, THEN< ELSE is ridicoulous.
Its kind of strange though, many electricians/maintenance people can understand the "BLACK BOX" theory..ie an item that is designed to perform a specific thing. Thats why plc's like Siemens S7 intrigue us, they offer this "black box" format in a way we can understand. Example being they offer a "box" that is titled "toggle". What does this do? Allows you to use one PB/input to on/off a bit/output.
I have no problem with YOUR way of thinking, PLEASE do not apply that to your WAY OF PROGRAMMING.
BTW I dont care how you program it, if a NO contact is used this should not be powered till it is closed.
A NC contact should reflect that power is there until it is OPENED.
HOW you program/document this does not matter. DOCUMENTATION is the KEY