Can I use a PCI-6251 AO channel without reference to AO GND?

[jschwartz]

Hi jacsjj,

Without referencing to ground, there is no way of knowing the voltage of your signal because voltage is just a potential difference between two points.  The analog output is outputting a voltage that is a certain amount above or below the ground reference.  For information about wiring your DAQ card, please refer to the Developer Zone, Field Wiring and Noise Considerations. 

[jacsjj]

Thanks for the fast response.  I was hoping there would be a way to float the output without referencing ground (like a floating power supply).  The user manual mentions the following.  Would this allow me to output the signal as a differential output or am I misunderstanding the concept?

You can connect an external signal to APFI <0..1> to provide the AO

reference. The AO reference can be a positive or negative voltage. If AO

reference is a negative voltage, the polarity of the AO output is inverted.

The valid ranges of APFI <0..1> are listed in the device specifications.

[AnalogKid2DigitalMan]

You could use a module such as these to provide full isolation, there are many manufacturers. These have a response up to 10KHz.

http://www.dataforth.com/model.view.aspx?modelid=91

-AK2DM

[jacsjj]

Thanks.

[jschwartz]

Hi jacsjj,

The APFI line can be used as a reference to get better resolution on your AO signal.  If you provide an external reference to the APFI line, your range will change from +/-10V to +/-AO Reference.  You can find more information about this on pg. 86 of the M Series User Manual .  I don't think this is exactly what you want to have happen.  The 6251 cannot use an external reference like in a floating power supply.  You will either need an isolation module or an isolated DAQ card.  

[jacsjj]

Hi,

Thank you.  This clarifies it for me.  I appreciate your help.

jacsjj