Input range binary

[mheien]

Hi, I am collecting data using a M-series 6221.  Because I am collecting a lot of data, I am collecting and storing it in binary format.  The card is 16 bit, and I have the voltage range set up to +/- 10 V. 

So, when converting the binary data back to voltage, I need to multiply my binary number by 20 V  / 2^ 16 bits to get the binary number back in bits.  But there is a problem here....when I apply 5 V and measure it, I only read ~ 15 000 bits instead of 16 384 (converting to ~4.7 V).  I have tried this with multiple cards.  The number seems to be off by ~ 8-9% each time at different voltages.  I am runnning in differential mode.  Am I doing something wrong?   Is the range of the bits really larget than +/- 10 V?

Thanks,

Michael

[Wayne.C]

Post the part of your code that is doing the conversion to bits.

[Robert_F]

Hello Michael,

The working range for the 6221 (6221 Detailed Specifications) series is +/- 11V.  This is to allow a little bit of calibration room and guarantee that you can measure the full range of +/- 10V.  If you are using unscaled or raw data, then you need to use +/- 11V range.  If you use this value in your calculations, then you should be able to convert the data correctly. 

[ChrisR.]

You can't just assume ±11V. The actual scaling coefficients for the board are stored in its EEPROM. You can access them through a property node. I can't remember exactly how to find it at the moment.

Chris