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SIMATIC S7-300 / S7-300F

How 27648 Analaog Maximum Value ?

Thread Starter: IYYAPPAN S   Started: 1/29/2009 11:47 AM   Replies: 15

Tags Analog Signals--Selected threads by Ayman Elotaify

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  1/29/2009, 11:47 AM
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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

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  1/29/2009, 2:38 PM
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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 readings in 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

Attachment: analog_range.jpg  (1492 Downloads)



=== Edited by dchartier @ 1/29/2009 2:40 PM [GMT ] ===


=== Edited by dchartier @ 1/29/2009 2:40 PM [GMT ] ===


=== Edited by dchartier @ 1/29/2009 2:40 PM [GMT ] ===



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  1/29/2009, 5:27 PM
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Hi,

read this in technical forum ... Analog Value

regards zenta
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  1/30/2009, 9:55 AM
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Dear dchartier,

Thnaks for the reply

But Still the manual is not informing how the value ( 27648 )  has been derived , Can u please explain me becasue for the last 6 years i am having the problem to derive the value 27648

Regards

Iyyappan S
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  1/30/2009, 2:05 PM
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Hello Iyyappan S;
I don't know why you would wonder for so long about how a system was "derived".
As I said before, I believe a system was designed, and values selected.
The closest explanation I can find, if you examine the table I proposed earlier, and others in the Module Data manual, is that:

27648/32767= 0.839....
32512/32767= 0.992...

So this allows about 85% of the full range for the rated range values, a zone between 85% and 99% for overrange, and above 99% for overflow values.
Also, 27648 = hex(6C00) and 32512=hex(7F00); possibly the "00" ending of the hex values can be used easily as markers in their math calculations and compares. We did this alot when programming microcontrollers, in the past.

As noted, this is purely an educated guess on my part.
Hoep this helps,
Daniel Chartier





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  2/1/2009, 9:32 AM
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Hello,
the value 27648 is a digital value which representing the phyisical analog value. If you have a pressure transducer (4-20mA) and you will connect it to an AI. How the CPU sence the pressure. The changes in the pysical value (pressure) affect the electrical analog signal (4-20mA) and that happens inside the transducer. Then the changes of analog signal (4-20mA) is to be translated into digital values using the ADC "Analog to digital converter (0-27648). And that happens inside the Analog module. Then this value; the digital value is transferred to the CPU.
The reverse of the above senario is applied with Analog Outputs.

Siemens have also something important called the resolution of the analog channel ( min. 8 bits and max. 15bits)
The resolution is a factor when increase, then the precision increased. Thus because if you have 15-bit resolution AI module. for a very small changes in physical values, the CPU can mesure and sense that changes [i.e it would be able to measure (1/27648)*20mA.].
For 8-bit resolution; it would be able to measure (8/27648)*20mA.

I hope the above summary was useful for you to understand how the analog signals been read or written.

Also see the attachments and I am sure you will found in it more info.

Regards,




=== Edited by CS Moderator @ 7/3/2014 3:03 PM [GMT ] ===
Attachment removed


Ayman Elotaify
MISC Egypt
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  2/4/2009, 8:39 AM
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Dear Mr.Ayman Elotaify,

Thanks Very Much

Regards

Iyyappan S

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  2/4/2009, 9:13 AM
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Hello Iyyappan,
You are welcome.
Greatings.

Ayman Elotaify
MISC Egypt
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  6/17/2009, 11:29 AM
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Hi,

Please find the attachement in that you can find the answer for Analog Value.

Ammy

Attachment: Analog Module.pdf  (1035 Downloads)

Ammy

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  5/30/2010, 7:41 PM
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thank you very much MR.Ayman
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