Calculate exponent in FX2

[arnoldzw 1]

Hi All,

I need to do some math in an FX2 PLC.
I`m using GXWorks2.

What i need is the function " ** / Exponentiation "  (but in help i see this function is only available in FX3U)

For Example:
d := s1 ** s2;

The problem is my exponent is also an FLOAT value, 1.5.

What is need to calculate is:     result :=  Measurement_value ** 1.5

How can this math been done in an FX2N, hope someone can give me some advice?

Best regards,
Arnold

 

 

Edited 5 Dec 2019 by arnoldzw

[Inntele 60]

6 hours ago, arnoldzw said:

What is need to calculate is:     result :=  Measurement_value ** 1.5

How can this math been done in an FX2N, hope someone can give me some advice

This is an initial school arithmetic rule: Y=X**1.5=X**(1+0.5)=(X**1)*(X**0.5)=X*SQRT(X)

Edited 5 Dec 2019 by Inntele

[arnoldzw 1]

On 5-12-2019 at 9:45 PM, Inntele said:

This is an initial school arithmetic rule: Y=X**1.5=X**(1+0.5)=(X**1)*(X**0.5)=X*SQRT(X)

Thank you for you`re answer,

The SQRT instruction isn`t available in my FX2 CPU and GXWorks.

 

Searching in the manuals only gives  the SQR / SQRP / DSQR / DSQRP  instructions, but these are only for word format.

 

I need the float value, then the DESQR instruction and DESQRP are available. But these instructions only do square root operation.

I have also an float exponent (1,5)

 

Don`t know how to calulate Y="float value"**1,5

 

My math skills from school are not that good anymore

 

[Inntele 60]

[arnoldzw 1]

Sorry,  i still don`t get it when i read the example with DESQR an DEMUL as decribed above,   

 

My base value is from an analog measurement and is an floating value.

The power raising factor is also an float value, but fixed 1,5.

 

For example:  let`s say my measurement value is 0,25.

What to calculate is:    Y = 0,25**1,5     (0,25 to the 1,5th)   or  ( in excel function   POWER(0.25;1.5)   )

 

Can someone explain how to do this in an FX2 CPU?

 

 

[panic mode 246]

EXACTLY as already shown....

 

X to power of 1.5 is same as

X to power to 3/2

which is same as X to power of (1+1/2)

which is the same as X*sqrt(X)

 

when X=0.25, using power function you get: 0.25^1.5 = 0.125

note that sqrt(0.25)=0.5 and 0.25*0.5 = 0.125

0.125 = 0.125 

it is the same result.

you just need to replace function you want with the equivalent function that you got.

and in this case that just happen to be square root and multiplication instead of power.

but result is still the same. regardless what value of X you start with. 

and here is what Excel says:

 

B5 cell "=POWER(A5,1.5)"

C5 cell "=A5*SQRT(A5)"

D5 cell "=ABS(B5-C5)<0.00000001"

[arnoldzw 1]

16 hours ago, panic mode said:

X to power of 1.5 is same as

X to power to 3/2

which is same as X to power of (1+1/2)

which is the same as X*sqrt(X)

 

when X=0.25, using power function you get: 0.25^1.5 = 0.125

note that sqrt(0.25)=0.5 and 0.25*0.5 = 0.125

 

That make sense! thank you!

Didn`t knew those where the same, only another way  of notation!

 

Have tested it, and it works now, thank you!

[panic mode 246]

that's good. should thank Inntele, he was the one to respond promptly

btw correct solution was handed months ago. if there was any doubt, why not simply try it? it would take mere minutes.