a new trick for the old dog? ...
Greetings STL??? ...
I'll admit that I'm intrigued by your statement ...
however the use of MCR's elieviate the issue.
I'm always eager to learn something new – especially if it's potentially useful ... can you please give us an example of how the system that you mentioned works? ...
here's how I (currently) interpret your statement ... where am I going wrong? ...
suppose that we have TWO separate OTE rungs to control a single field output – a simple LAMP for example ...
suppose that the first OTE is located in an MCR (Master Control Reset) zone that we'll call "Zone A" for discussion ... and suppose that the second OTE is located in another MCR zone that we'll call "Zone B" ...
now suppose that the conditions for the MCR "controlling" Zone A happen to be TRUE – so that this particular MCR is "enabled" and working normally ... let's also suppose that within Zone A the conditions controlling the OTE for the LAMP are also TRUE ...
in simplest terms, everything about MCR Zone A is trying its dead level best (bless its little heart) to turn the LAMP in the field ON ...
but then LATER IN THE SCAN ...
let's also suppose that the conditions for the MCR "controlling" Zone B happen to be FALSE – so that this particular MCR is "disabled" and trying to turn all of its outputs OFF ... just to play devil's advocate, let's also suppose that within Zone B the conditions controlling the OTE for the LAMP also happen to be TRUE ... (actually in this demonstration the TRUE/FALSE status of the OTE rung in this particular "disabled" zone won't make any difference at all) ...
so ... in simplest terms, under these conditions MCR Zone B is trying to "reset" the lamp's bit – and therefore (being LAST IN THE SCAN) it will turn the LAMP in the field OFF ...
when I run the sample code from an SLC-5/04 system (attached) I find that the LAMP in the field is indeed OFF – just as I expected it to be ... and this is regardless of the fact that everything about MCR Zone A is trying to turn it ON ... more specifically, anytime Switch B (controlling the second MCR) happens to be OFF, then the LAMP in my example is certain to be OFF in the field (regardless of any of the other switch settings) ... personally I'd sum this up by saying that the FALSE condition of the MCR for Zone B is "RESETTING" (or writing a ZERO into) the bit/box for the LAMP at the end of every scan ... the poor old MCR for Zone A never stands a chance of turning the LAMP in the field ON unless the MCR controlling Zone B (later in the ladder) decides to go along with the plan ...
so then – this is where I'm getting confused by what you said ... I'm having a hard time understanding how the use of MCR (Master Control Reset) instructions could (in any way) alleviate the confusion caused by this obvious "double coil" arrangement ... now I really don't doubt that what you say is true, so quite probably I'm just misunderstanding how the MCRs you're describing are actually set up ... to the best of my current understanding, any use of MCRs would tend to exacerbate the "double coil" problem – rather than alleviate it ... I'd sincerely appreciate it if you could post a little more detail on the programming arrangement that you have in mind ... this truly sounds like a new programming technique that I've never run across before – and I'd really like to learn more about it ...
just for any beginners who might be reading this post: the part that confuses MANY people is the mistaken belief that any OTE rungs located in a FALSE-conditioned MCR zone will simply be "skipped over" or just "ignored" ... this is NOT correct ... actually any OTE instructions in such a zone will indeed still be executed by the processor – but they will be executed with FALSE logic ... this causes the OTEs to "reset" or write zeros into their bit/boxes - and THAT'S the effect that's being demonstrated in the figure below ...