Pls. i need your help

I need to read vacuum value from the sensor by using 4AI/4AO module, the range is 0 - 10 V

vacuum equation is: 

P=10^0.778(U-C)

P: Pressure value mbar

U: Measured value 0-10V

C: constant = 6.143

How to write this equation inside PLC program

Please refrain from making duplicate posts. Choose which system are you asking for: Step7 Classic or Step7 TIA. Then it is important to mention the PLC used.

About the formula:
P=10 ^{0.778 x (U-C)}

or

P=10^0.778 x (U-C)

Thank you for your reply!

I am using S7 300 CPU 315 2DP

and the Formula is:

P=10^0.778(U-C)

 thank you for your reply!

I tried it, but still have a problem, as the final step when I take the exponential of x.ln P as per attached picture, it gives me an alarm and I cannot get the final value, pls. any extra idea to solve this problem?.

thanks a lot.

.

Towome

Hi,

In STEP 7 there is only the option of using Euler's number e for exponential calculations. For your operation you need special FC1 from this link:

How do you calculate power, exponential, root, polynomial, logarithm and linear values and how do you convert trigonometric functions into degrees?

All other calculations are clear, right?

Regards,

Towome

Could you elaborate more about the alarm you got?

And possibly show your code.