Relation between value at different instances.

[Erik&Robin 0]

We are working on an automatic system for pressure testing and flushing of hydraulic tubes. There will be different demands for how much the pressure is allowed to drop, according to different standards. They will be on the form X% drop in Y minutes. Our problem is to find a way to know when for instance the current value divided by the same value 5 minutes ago, will be more than the required percent. The time the process takes is not very critical, so one idea is to assign the value to a variable every minute. This way you only need to store 5 values. Does anybody know how to accomplish this the way I just described, or a totally different way? We are pretty novice working with PLC´s, but have some experience from earlier education and programming in general.

[lostcontrol 23]

What PLC model are you using? Attached simple example that captures a value every second & shifts the previous values down the stack... ErikRobin.cxp