Binary to Scale data with 4472

[educhene]

I'm continuous acquiring and writing to file binary values input from a PXI-4472 card.
This card is configured in +- 10V (hard).

I want to convert those binary values to scaled data, but I don't understand how to do that : AI read returns data in I16 form, and When I do this convertion : binary * 10 / 2^15 (I'm with gain 1) it miss a 2 factor to my scale data (I must *2 the result to get the effective scale data).

What's the problem ???

[LucaP.]

Hi,

I suppose that the 10 in your equation should be the voltage range, but you're using +-10V range, this are 20V and not 10. That's the factor 2.
Please look into this two KB's too:
http://digital.ni.com/public.nsf/websearch/E943889030F3D9D886256930007C430F?OpenDocument
http://digital.ni.com/public.nsf/websearch/24AEA7688B27C2A186256ED30071662D?OpenDocument

Hope this helps.

Regards,
Luca

[educhene]

But the value I read from the AI read is a 16 bit value => normally 10 V <-> 32767 and -10 V <-> -32768

And when I put a 10 V DC signal at the input of the card , I get 16383 from AI Read.

[LucaP.]

The 4472 has 24 Bits, so the AI Read 16 Bit representation is not correct. Check this:
http://digital.ni.com/public.nsf/websearch/B48F5478BFD70F9F86256C1D005E33D9?OpenDocument
http://exchange.ni.com/servlet/ProcessRequest?RHIVEID=101&RNAME=ViewQuestion&HOID=50650000000800000038850000&ECategory=Measurement+Hardware.Dynamic+Signal+Acquisition+and+Analysis

Luca

[Sanaa]

Hello All,

Luca : You are right, the bit resolution of the NI 4472 board is 24-bit so, when you try to store 24 bits of information (4472) in a 16-bit element, information is lost. The eight less significant bits of the number will be lost in this case.
The links that you send :
http://digital.ni.com/public.nsf/websearch/B48F5478BFD70F9F86256C1D005E33D9?OpenDocument
can is very interesting to solve problem.

Sanaa TAZI
Applications Engineer
National Instruments