Greetings Chris ...
while the SQO (Sequencer Output) instruction mentioned by my distinguished colleague Bob_O might be exactly what you were looking for, attached below is another programming technique that you might find helpful ...
it’s sort of a “cookie cutter” approach that I’ve used to help beginner programmers several times in the past ... usually this works well for someone who has invented a widget-maker in his home workshop and just wants to sequence the thing from one well-defined step to the next - based solely on elapsed time ... suddenly he finds that the PLC everyone recommended to control his new-fangled mousetrap isn’t nearly as “user friendly” as the salesman made it sound ... back in my working-for-a-distributor days, I was able to turn several irate customers into satisfied programmers in less than an hour by guiding them through this simple approach ...
the example I’ve posted only has three steps, but once you see how it’s done, it’s very easy to cut and paste in as many additional steps as you desire ...
notice that the various functions (time, transfer, control) are kept in separate sections ... keeping the same pattern helps makes it easy to add in more steps ...
many programmers would tend to use only one timer - with comparison instructions to control the duration of each individual step ... personally I’ve found that timers are cheap - and using a separate one for each step makes it very easy for a technician with only limited knowledge of ladder logic to go in and tweak the amount of time required for each individual step ...
yes, there are more elegant ways of writing the program - but this way is simple and straightforward enough for use in many cases where the personnel who are maintaining and adjusting the equipment are less familiar with PLCs ...
along the same lines of keeping things simple, notice that I've started numbering with T4:1 and bit B3/1 for Step ONE - and used T4:2 and B3/2 for Step TWO ... etc. ... if you start out numbering with the more customary T4:0 and B3/0 as most programmers do, you'll set up a trap for many technicians with limited PLC knowledge who will "miss it by one" ... for example, they'll often try to adjust the time duration of Step 2 - by mistakenly tweaking the value of timer T4:1 ... yes, they should know better - but skipping one timer, etc. while writing the program will often make things a lot easier for the guys in the field ... like I said, timers are cheap ... downtime is expensive ... most humans (at least the non-programming variety) usually start counting the "steps" of operation at ONE and not at ZERO ...
hope this helps ...
