Alternating two motors-Algorithms ?

[Einstein_86]

Hello

I have wrote a PLC code to alternate two motors each two hours, i.e. M1 operates for two hours then stops & M2 runs for another two hours (as long as there's not fault with it) and so on. I used two timers for this.

Can you please suggest any other algorithms for alternating two motors ?

[actually mine is working but it gives some conflicts when i assume test cases, and i wish i can find another algorithm more efficient]

Thank you

 

[DamianInRochester]

One Self resetting timer with two comparators based off the accumulated value.

What do you meam by "gives some conflicts when i assume test cases"

 

[Einstein_86]

One Self resetting timer with two comparators based off the accumulated value.

What do you meam by "gives some conflicts when i assume test cases"

I mean when I simulate my code it malfunctions in some cases (for ex when i assume that one of the motors was faulted in a certain way, the other - sometimes- does not start) It's only a part of my program but the whole program depends upon it and i still cant reach coordination between the whole program

I am sorry i did not get your idea, i dont understand what is "based off the accumulated value", would you please clarify it more ?

 

[OkiePC]

Tell us what PLC platform you are working with, and more about the loads and how you start and stop them (contactors, brakes, VFDs, etc.).

I normally have a minimum run time and a minimum off time for each motor which, in addition to any fault or disconnect inputs, renders them unavailable to the logic that selects which motor to run. This prevents short cycling of the motor controls as well as the loads. These timers should be set greater than the expected normal (in some cases the longest) time for the load plus some safety margin. In this part of the code, the motors are not necessarily interlocked with each other, unless there are mechanical or process safety reasons to do so. You may be able to slightly overlap the start/stop of each motor to minimize a bump in the system but do that with the machine logic section of the logic, and treat your min. on and off timer logic for each motor as a distinct motor driver section of logic that you tie into with internal coil bits.

For two motors, it's pretty simple, for three, you can end up with 8 different combinations and for four or more, depending on how many are allowed to run and what triggers demand changes...that is when I normally just start the one that has been stopped the longest, by continuing to time the stop duration even when it has surpassed the minimum stop time. This can sometimes lead to compound timer/counter set-ups if the off time can extend into values that exceed the range of a normal PLC timer.

Hope this helps
Paul