I'm using a PCI 6713 board to control a high voltage supplier.
The control ratio is 1V<->1kV, i.e. every 1mV AO Voltage corresponding to 1V high voltage output.
I just found the minimum AO voltage step produced by the board is about 5mV, so I can only change the high voltage by 5V every step. The AO Voltage precision I hope to reach is 1-2mV.
Obviously, it is practically very hard for a 12-bit board. Its specification as described on http://sine.ni.com/nips/cds/view/p/lang/en/nid/10702 says Range Accuracy=8.24mV.
Now I'm just trying find a solution without buying a more precise board. I found something may be helpful on the Page 38 of the user manual(http://www.ni.com/pdf/manuals/370735e.pdf) saying "Using AO EXT REF to reduce the output voltage range results in a higher resolution at the adjusted range." My understanding is by digitizing in a smaller range, the output resolution can be improved.
PCI 6713 has a output range -10-10V, but all I need is only 0-5V, so I connect a 5V DC signal to the AO EXT REF on the connector box. The VI I used is the DAQmx Create Channel(AO-Voltage-Basic).vi. Using external reference is done by setting the "output terminal configuration" input of the VI as 10200 following the Help file. The AO voltage value I need is written to the channel by using DAQmx Write (Analog DBL 1Chan 1Samp).vi. The external reference signal does limit the output range but not really results a higher resolution, the minimum step of AO voltage is still the same as before.
I didn't find further instructions on using the external reference, so I am not sure if I did it right. Does anybody have idea about how to use the external reference to improve the resolution of this PCI 6713? Or I really need to buy a 16-bits board?
You need to set the AO ref volatge to external using DAQmx Channel property node.