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Analog I/O Count

Created by: nin at: 8/5/2008 12:14 PM (6 Replies)

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8/5/2008 12:14 PM	Rate (0)
nin Posts: 3 Rating: (0)	Would some one please tell me,why Analog countis 27648?
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8/5/2008 12:42 PM	Rate (0)
Gebhardt Karl Platinum Member Joined: 7/16/2006 Last visit: 1/2/2024 Posts: 1502 Rating: (176)	>Would some one please tell me, >why Analog countis 27648? >Analog Analog input ? >count Counter ? >is 27648? ? Please tell us the Siemens-Number from the Part.
	Karl
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8/5/2008 1:21 PM	Rate (0)
nin Posts: 3 Rating: (0)	Sorry, I couldn't elaborate my question well. I wann ask why siemens has standardised analog input countfrom 0 to 27648?
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8/5/2008 2:14 PM

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In S7, the analog value (only <16 bit resolution)is represented left justified. i.e: 15th bit is sign and irrespective of you resolution of the ADC, the count remains same except the least significant bits

Resolution	Analog value
Bit	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
16-bit analog value	0	1	0	0	0	1	1	0	0	1	1	1	0	0	1	1
13-bit analog value	0	1	0	0	0	1	1	0	0	1	1	1	0	0	0	0

Here you can see that for 13 bit value, the LSBs are just set to zero. By doing this all resolution cards give same RAW value range.

Now, For analog value, you need to have undeshoot, and over shoot ranges. The table below may make it is easy to understand. Look at the Hex numbers, it is kind of understandable how they arrived at the 'magical number'of 27648 :)

dec	hex	±20 mA
32767	7FFF	23.70 mA	Overflow
32512	7F00		Overflow
32511	7EFF	23.52 mA	Overshoot range
27649	6C01		Overshoot range
27648	6C00	20 mA	Rated range
20736	5100	15 mA
1	1	723.4 nA
0	0	0 mA
-1	FFFF
-20736	AF00	-15 mA
-27648	9400	-20 mA
-27649	93FF		Undershoot range
-32512	8100	-23.52 mA	Undershoot range
-32513	80FF		Underflow
-32768	8000	-23.70 mA	Underflow

Hope this maked it clear.

Last edited by: JMJ at: 8/5/2008 2:23 PM

Last edited by: JMJ at: 8/5/2008 2:22 PM

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8/5/2008 2:31 PM	Rate (1)
Gebhardt Karl Platinum Member Joined: 7/16/2006 Last visit: 1/2/2024 Posts: 1502 Rating: (176)	You have many Part. This are all Analog Inputs 0..20mA 0...5Volt 0...10Volt 0...400Ohm PT100 Sensor (100hm 20°C) PT1000 Sensors (1000Ohm 20°C) NiCrNi THermoelemente Wich number shold by an 10Volt or 5 Volt ? and so on. And all Units have as Example 27648 is 100% from all Units (Normaly) 0...5Volt 100% 27648 0..10Volt 100% 27648 I hove that ist the answer for your question.
	Karl
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3/4/2010 7:14 PM	Rate (0)
TWW Posts: 1 Rating: (0)	Can someone please post a link to the manual where the above table can be found. Thanks
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3/4/2010 8:17 PM	Rate (0)
dchartier Grandmaster Joined: 9/27/2006 Last visit: 12/20/2024 Posts: 12307 Rating: (2695)	Hello TWW; Have a look at the S7-300 Module data manual: http://support.automation.siemens.com/WW/view/en/8859629 Pay special attention to the chapter on Analog Value Representation, you will find similar tables for various analog signals; you should find it instructive. Other chapters cover analog and digital modules available on the platform. Hope this helps, Daniel Chartier

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Created by: nin at: 8/5/2008 12:14 PM (6 Replies)

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Last edited by: JMJ at: 8/5/2008 2:23 PM

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