Symbol names

[kolonelvonklink]

Hi How do you people develop symbol names. In a rather large PLC with +100 I/O, how do you make names so you dont make mistakes. (you can't remember all the adresses.) The IEC61131-3 standard doesn't allow signs wich makes it even more difficult, I think. eg cilinder activated detection of a rod of an activated cilinder

[Ken Moore]

Write structured programs. All the code for one "piece" of the project is grouped together, and/or all code for similar devices are grouped together such as pumps or valves. Since I mostly work in the Process industry there always P&ID drawings on hand, drawings help ALOT. I try to incorporate the P&ID tag into the symbol. That way years from now, someone with a copy of the drawing can follow the logic.

[paulengr]

For you and me, using a P&ID is second nature. Outside of that industry, P&ID is much less common. It really doesn't make sense in discrete manufacturing for instance because there are few pipelines and very few flows involved in anything. The whole P&ID concept kind of falls apart. So even if I used just the numbering scheme, everyone would be completely confused by ZSH103 (they would think it's a radio station). Everything is in terms of a descriptive name. Even the asset numbers specifying equipment in the work order system are virtually unknown outside of the planners and the accountants. Any P&ID I have is usually in my files and I use it but unless I tape it to the door of a panel, nobody else knows where to find them or what to do with them. The only place we have them anyways is on our burner control systems. As an alternative, I try to use camelBackNotation and go from least to most specific, and I try to write out myself a cheat sheet before I even get started because naming on the fly never works out well. Unfortunately, my main HMI/Scada package likes screaming at everyone...it only accepts capital letters, dots, and underscores. So in that system, I used dots instead so it becomes CAMEL.BACK.NOTATION or for two-word tags, CAMEL_BACK.NOTATION. I use the distribution gear lettering system (not ISA) but at the end of the notation, not the beginning, for convenience. LS=limit switch, PS=pressure switch, PL=pilot light, PB=push button, PX=proximity switch (standard is PRS but that's 3 letters), etc. They know these things and it saves a lot of typing on my part to describe I/O's this way. So instead of PB115, it might be AutoStartPB. In the HMI, it would be AUTO.START_PB. Since I'm dealing more with CLX now, I try to establish the controller-level tags first before coding (coding to a standard instead of the other way around). This can be done with UDT's if you are working offline for efficiency in PLC/HMI communication. All other tags then end up as program-level tags and there it's a lot more fluid since I rarely have more than a couple dozen tags. In a PLC-5 or SLC, it's pretty much a free-for-all. I tried and gave up on the symbol system a long time ago. It's there but it seems to be more annoying than useful.

[TimWilborne]

I strongly disagree with relying on symbols also. I think they cause more trouble than they help...but Chakorules has an article on Symbol Programming http://www.mrplc.com/kb/index.php?article=25

[panic mode]

not all platforms support symbols and even descriptions may have limitations (Mitsubishi GX Developer for example) i normally use system that contains station, type and function. i list all abbreviations at program begin so everyone can use it since exact format may vary from project to project (depends on used software etc.). as a result of such restrictions, station is rarely more than three characters, type of device is allways two character such as: PB - push button RS - reed switch PE - photo eye PX - proxy sensor CR - control relay SV - solenoid valve LT - indicator light etc. function is description of actual purpose or function of the device. instead of 'cylinder activated' or 'cylinder extended' it would be something like 'gripper open' or 'lift down' etc. (unless there is only one 'cylinder' and everyone calls it that way).

[IamJon]

Assuming RSLogix5 or 500 is what you mean by symbols.... I think they are too complicated. if you delete a file, the symbols stay. you have to delete the symbols first (maybe you can do this in the symbol groups under databases) descriptions are just as good. just set up a new file for each peice of equipment and have all data in the same place. like all start commands are in NX:14/0.