step 7 mathmatical calculations

hello everyone.

I am new to programming and have been asked to find out if the following mathematical calculation is possible on step 7.
I am using a 2 wire AI from a PH sensor to a PIW.

I require :

ph (in)= average of probe over 15 mins=11
ph (out)= average of probe over 15 mins=7

S04= sulphate measurement

S04= 575000*(10^11-14)-(10^7-14)

I don't know if step 7 is even capable of this, however I did see that TIA Portal V12 has a calculate function.

I hope someone can help me , even if it is to tell me it cant do it lol

Thanks in advance

Andy

Yes it is possible, but won't be as straight forward as using calculate function.
To calculate average of ph you need store values of ph at selected time interval and then calculate average.

There's no (as far as i know) function for raising numbers to power in TIA portal, but it can be done using ln function.

Hi and welcome to the forum!


IF you use Step7 AND (S7300 OR S7400 OR SIMILAR) THEN

it can be wise to check out the free library overview "oscat_basic_333_en.pdf" in this link;

http://www.oscat.de/component/jdownloads/category/2-oscat-basic.html?Itemid=0

END_IF

Kalle

Dear all , good day ,
In this formula some parentheses is missing , otherwise , written in this way, the number 14 is insignificant.
So , you have to restore the formula first of all.
This is correct : 575000*((10^11)-14)-((10^7)-14)
This is another: 575000*(10^(11-14))-(10^(7-14))
Another one : (575000*((10^11)-14))-((10^7)-14)

Ragards.

If you are using an S7-300/400, you could also write the code in SCL, and use the ** operator instead of ^ for the power. SCL is often the easiest way to do math.

If you are using a 1200/1500, then use a computer block, as you suggested, with ** for the power. You could also use EXPT if you want, but compute would probably be easier.

This assumes you already have the averages you want to use in the equation. If not, then that is a whole different question.