Yes, you are right, thanks.

I get that for 15bit resolution all bit are used, but there is 16bit resolution module "SM 1231 AI 4 x RTD x 16 bit", it doesn't use sign or use 17bits or 3 bytes?

And about this:

So when I want to get analog voltage 0-10V with 8bit ADC in S1200, I use func norm_x(min=0 max=32767 or 32640 or 27648?) and then scale_x(min=0 max=10 or 11,852?)

Answer:
norm_x(min=0 max=27648) and then scale_x(min=0 max=10)

if AI is 27648 then voltage is 10V
if AI is 32767 then voltage is 11.85149V
I didn't know that norm_x can give value bigger than 1.0 and scale_x can accept value bigger then 1.0

or we can use norm_x(min=0 max=32767) and then scale_x(min=0 max=11,85149), which makes more sense

The 15% over range is provided to prevent your digital value from going negative, when connected to most instruments.

Many instruments will report analog values over 20mA if the sensed value exceeds the calibrated range of the instrument. This is useful to many people who analyze the process, and troubleshoot instruments and systems.

On old systems, when 20mA was set to 32767, if the design of the instrument circuit had just a small error, and your PLC card measured 32768 or higher, many PLCs interpret this value as a signed value, so your instrument value suddenly goes negative, which will upset the process if you are not prepared for this.

So this has nothing to do with the Siemens side, it is all to accommodate everyone else who makes 4-20mA instruments.

 Mr. Dcharitier, It was very helpful...

dchartier

Hello Iyyappan S;
The value 27648 has simply been selected as the maximum normal range value of any analog signal transfered to the CPU by a Siemens analog module.This numerical value is independant of the resolution of the particular analog module used (this is a way to standardize all scaling of analog readingsin the processor)
For unipolar data, this would mean 0 to 27648 represents full range; above 27648, overrange, below 0, underrange.See the attached illustration for the equivalent numeric values iof a 4-20 mA or 0-20 mA signal.
The basic configuration of the analog modules is best explained in the S7-300 module Data manual:
http://support.automation.siemens.com/WW/view/en/8859629
Look at the chapters on Principles of Analog value processing and Representation of the analog values of analog modules.
Hope this helps,
Daniel Chartier

IYYAPPAN S

Dear All,

Can U Please Explain me in detail how the Decimal value 27648 has been derive for Maximum Value in Analogue I/O's


Regards

Iyyappan S

 Very good quastion

Possible answer:

2^15*0.85=32768*0.85=27852=6CCC

the rounded of 6CCC is 6C00=27648

Dear IYYAPPAN,

If i am able to understand your point kindly check this table:

27648 was a good choice:  

Hello,

Good time to all my friends, can someone guide me on what reasoning was used to select the number 27648 in the analog inputs?

For example, regarding the highest value of the counters, we know that the memory architecture is the left four bits unused and the next 12 bits  can count up to 999 as 3 BCD nibbles, but I did not find a logical reason  for this number (27648).

I will be happy to help you.

Best Regards 

Navid