Analog convertion From S7 1500 card into Step5

Hi guys,

In my rack, i've installed throught the IM 308-C, a new IO Rack with one DI, one DO, and one AI of the S7 1500 family.

For the DI and DO no one problem, and to be honest neither for the AI, but, i meet some strange things when i've tried to convert from the integer value (in S7 format) to a real.

What i've tried to do, is:

L IWxxx              (LOAD THE INPUT VALUE IN S7 FORMAT 0-27648)

SLD16                (SHIFT 16 BITs LEFT)

SVD16                (SHIFT 16 BITs RIGHT)

FGD                  (CONVERT DWORD IN A FLOAT)

L  KG +2764800+05    (LOAD 27648 IN FLOAT FORMAT)

:G                   (DIVIDE)

L KG  +9999999-01    (MULTIPLY X 100)

A DB90               (OPEN DB90)

T DD50               (TRANSFER THE VALE IN THE DD50)

 The problem is that when set a constant value of 100.0, the Step5 overwrite my value with
 KG  +9999999-01 , i dont understand why, what i would expect, should be KG  +1000000+02, isn't it?

 Does anyone have some suggest?

Regards.

Duccio.

Hello Duccio,

the REAL-numbers at the S5 are a little bit different to S7.

Please look at this link at page 41 at the pdf.

https://support.industry.siemens.com/cs/ww/en/view/1087149

There is a explanation for REAL numbers in S5.

At your program you should write for 100.0  - you do it right at 27468

 L KG +1000000 +03 // 0.1 10exp3

I hope this is helpful.

regards
CaOd

Duccio

The problem is that when set a constant value of 100.0, the Step5 overwrite my value with

KG  +9999999-01 , i dont understand why, what i would expect, should be KG  +1000000+02, isn't it?

Does anyone have some suggest?

Hello,

i think this problem is related to floating point accuracy.

If you push this key in your keyboard :

"L K G 1 0 0"

S5 editor "understands" :

mantissa=1 and exponent=0 that is 0,1.

In S5 notation "L KG+1000000+00"(rounded value)

but editor shows :"L KG+9999999-01"(unrounded value).

Same thing appens if you push this key in your keyboard :

"L K G 1" or 

"L K G 1 0" or 

"L K G 1 0 0 0".

S5 editor always "understands" 0,1 and shows :"L KG+9999999-01".

To write 100.0 you have to push this key in your keyboard :

"L K G 1 + 3"

then S5 show "L KG+10000000+03"that is 0,1x10^3=100

here you can find some theory : What every computer scientist should know about floating-point arithmetic.

Hope this helps

ciao

Hi guys,

Thanks to everyone for the support.

Regards.

Duccio.

Hello Duccio

Apart from the representation problem, I think there is a multiply instruction missing.

L 100.0

XG (missing)

Kind regards,
BV

Hi BeVee,

Yes i saw that, and already fixed.

Thanks for suggest.

Regards.

Duccio.