VSD Speed Controller

[PrecisionPLC 0]

Can any one advise me, I have just taken over a project and I'm looking at how they scale a value from HMI to controller speed of conveyor. The way it is done is the are multiplying the valve by a factor (1.38). I am just wondering where they would of got the fixed value for this factor number from. Does it depend on type of vsd/motor etc?

[pturmel 157]

2 hours ago, PrecisionPLC said:

Does it depend on type of vsd/motor etc?

Yes.  Some drive products expect motor RPM or 10x RPM as an integer, some use full range binary over some number of bits (0 to 2ⁿ - 1) to represent 0 - 100% speed, some few have scaling in the drive to accept any desired engineering units.  Completely dependent on the type of drive and the communication interface used.

[Joe E. 259]

I tend to call this "Magic Math", where there's a mysterious, unexplained scale factor. I really don't care for it, but I've seen it a lot. When I do scaling, I tend to show each step of the calculation so it's clear what's going on in the future. Also, if someone changes a sprocket or sheave or motor or something, it's easy to see which number to change and what to change it to.

So...that 1.38 value could have been calculated based on the engineering parameters of the system, or it could have been empirically figured out to be the magic number that gets  the desired result. If anything in the system ever changes later, you'll have to figure out how to change the number to make everything right again.