S7-300 Analog value representation

Hello,
I am trying to get into the basics of that magic no. 27648 & some how not able to decode it
Here's the problem - I have S7-300 with AI card SM331-7Kf02,12bit resolution. Now the manual says that 12 bit resolution is stored as left-aligned. with LSB's padded with zero.
My understanding is that a 12 bit resolution means 0 to 4095
OR 0FFF Hex. So when I put these in 16 bit format and shift by 3 bits, the number comes to 32767 & not 27648.
Any one can throw some light on this:wish:

Thanks

Siemens uses the values between 27648 and 32767 for over-voltage detection. Where the 27648 value for 100% actually came from is something only Siemens can explain! The difference between 12 Bit, 13 Bit etc. is purely one of resolution - in practice you don't need to worry about it, 100% is always 27648.

You can use FC105 "Scale" from the Standard Library to scale your values to engineering units.

All of the Siemens manuals I have referred to show a table giving the values returned for different voltages.
+/-27648 is the nominal range for +/- 100%, however, the unit will still give values up to +117.588% (32511) and down to -117.592% (-32512), anything outside this range gives +32767 or -32768 (this is from an ET200B manual for example)

Thanks guys for your inputs. It bugs me why Siemens can't be clear on these information, afterall it's about mathematical calculations only.

Cheers

It bugs me why Siemens can't be clear on these information

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Actually I think this is one of the areas where Siemens is clear, very clear. As "L D[AR2,P#0.0]" says, every I/O module manual I have ever seen from Siemens includes not just one but multiple tables showing how the analogue values are related to signal levels and percentage of full-scale for voltage inputs, current inputs (both with and without 20% offset), thermocouple inputs, RTD inputs, etc etc. It's all abundantly clear. Just unhook your mind from the preconceived ranges of 0 to 4095 and -32768 to +32767, read what it says, and believe it.

Regards

Ken

Siemens

It bugs me why Siemens can't be clear on these information

Click to expand...

If it would be easy, we wouldn't call it Siemens.

All of the Siemens manuals I have referred to show a table giving the values returned for different voltages.
+/-27648 is the nominal range for +/- 100%, however, the unit will still give values up to +117.588% (32511) and down to -117.592% (-32512), anything outside this range gives +32767 or -32768 (this is from an ET200B manual for example)

Click to expand...

We have 4 to 20mA inductive distance-sensors, we measure up to 22mA (these sensors can do this), but we know that the 2mA above the 20mA not a good thing is, not lineair as in the range specified.

Greetz