Plc

[JHarbin]

I understand it ok but I have been doing this foe a long time, during that time I have seen several new people to PLC programming get confused when using a NC contact in a field device but use a xic instruction in the program such as a stop button. Yes it is easy enough to get your head around but when communicating to other people it does save confusion if talking in XIC and XIO terms. but I also agree it can be just as simple to refer to it as high and low or on and off.

I haven't been programming PLCs long - just 25 years or so, but I have never understood why A-B used the word "Examine" in XIC and XIO. It certainly isn't intuitive to me what that word means in the context.

Don't get me wrong, I know how to use XIC and XIO, but I don't like the terms - the only part I like is the IF in the middle - that word is pretty self-explanatory.

I'm one of those who like to use NO and NC because I understand that each element must be considered in relation to the Coil or Input that it is tied to or is acting on it.

Maybe the fact that I have used Relay Logic for 30 years or so makes it easy for me to transition between NO and NC in Relays and NO and NC in PLCs. I understand both very well - or maybe it is because I use ladder logic as well as Boolean logic in my programming.

To me, it is much more important that you understand the concepts than sticking to a particular set of terms, except that it is probably best to use the terms that apply to the particular PLC or Device you are programming.

 

[GlennA]

Active high or active low

To add to the confusion, some PLC's use active high, or active low. Also can be called sourcing or sinking. The Omron PLC's that I worked with could be wired with either common +24 or common 0 VDC. Depending on this wiring, +24 VDC could be logic 1 or logic 0.

 

[hagos]

Normally Open & Normally Closed

The best way is to look at it like that:

-I I- is Look for a 1 in the memory location, if it is 1 then
logic is true

-I/I- is look for a 0 in the memory location, if it is 0 then
logic is true


Cheers
Hagos

 

[Branded]

Threads like this make me happy computers can't count to 2.