In one of my project we have requirement of addition for simple FF loop(One FFAI and one FFAO). We came across below query from customer.
Scenario-
We have requirement of addition of a simple FF loop (One FFAI and one FFAO) in existing FF segment. After addition of these two devices, required macrocycle time(Calculated by system) of segment comes to 620ms, however we need fast response of FF loop. So customer requested us to configure schedule macrocycle time (500ms) less than required macrocycle time, which is not as per our standard practice. According to attached white paper and training material, if we keep Schedule macrocycle < required macrocycle then actual macrocycle will be equal to required macrocycle (500ms).
Query-
Is it possible to configure schedule macrocycle time less than required macrocycle time of FF segment? -
In attached white paper, on page 9 it is mentioned that “The Actual Macrocycle is the greater of the Schedule Macrocycle or the Required Macrocycle”. Not only as per white paper, but also as per the training slides, it is possible to keep schedule macrocycle time less that required macrocycle time. This statement in Emerson published document is a baseline for customer and they are demanding to implement the same which is practically not recommended by our FF Experts.
Since there are many floating discussions around topic your advice will help guide us on the way forward. So please let us know if is it recommended or advisable (in special case) to configure schedule macrocycle time less than required macrocycle? Customer would like to understand the reasons with facts.