Rockwell REAL Exponent Question

[TemporalDistortion]

Hi all

I'm trying to figure out a way to put something to an exponential fraction and having difficulty getting it to work

I'm using an Allen Bradley MICRO850 and the connected components workbench currently.

What I need is to put a variable to the exponent 2.5

ie: X^2.5

The problem is that the in built EXPT function doesn't allow for Real numbers as an input to the exponent.

I also need to find the 2.5 Root, but this can be solved as well if I can figure out how to do a REAL exponential.

I've tried looking up using LOGS as a work around,
but can't figure out how to get the Anti-log

Can anyone give any advice or solutions?

 

[kolyur]

This is just a shot from the hip, but since the quotient rule for exponents is:
a^m / a^n = a^(m-n)

couldn't you do it in two operations like this:

x^3 - x^0.5

which is the same as:

x^3 - sqrt(x)

(I'm assuming your controller has a square root function.)

 

[TemporalDistortion]

This is just a shot from the hip, but since the quotient rule for exponents is:
a^m / a^n = a^(m-n)

couldn't you do it in two operations like this:

x^3 - x^0.5

which is the same as:

x^3 - sqrt(x)

(I'm assuming your controller has a square root function.)

Ah yes!

I think your formula is a little wrong, but your idea is sound, breaking it down into it's SQRT available functions may be key!

As

X^2.5 = X^2.X^0.5
= X^2.SQRT(X)

now to just think on how to work out

2.5√X

I guess thats equal to

X^1/2.5 = X^0.4

Now how to break X^0.4 into Square roots

Thanks for the idea!

 

[kolyur]

You're right, I meant to put

x^3 / x^0.5

and

x^3 / sqrt(x)

Your next problem is a little trickier!

 

[TemporalDistortion]

Hmmm.. it seems I solved my own problem

Apparently the POW function does the exact same job but does accept REAL values..

strange... I wonder why they have both the POW and EXPT functions