National Instruments Welding System 321645c-01 Manual De Usuario

Chapter 2

Function Reference — AO_VWrite

NI-DAQ FRM for PC Compatibles

2-46

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 National Instruments Corporation

If you set the output type to current by calling 

AO_Change_Parameter

, the floating-point 

value indicates the current in amps.

Default ranges (unipolar, internal voltage reference):
AO-2DC device:

0 to 0.02 A

VXI-AO-48XDC:

0 to 0.02047 A

AO_VWrite

 scales voltage to a binary value and then writes that value to the DAC in the 

analog output channel. If the analog output channel is configured for immediate update, the 
output voltage or current changes immediately. Otherwise, the output voltage or current 
changes on a call to 

AO_Update

 or the application if an external pulse.

If you have changed the output polarity for the analog output channel from the factory setting 
of bipolar to unipolar, you must call 

AO_Configure

 with this information for 

AO_VWrite

 to 

correctly scale the floating-point value to the binary value.

You also can use this function to calibrate the VXI-AO-48XDC. On this device, writes to 
channel number 48 affect the voltage or current offset calibration, depending on the output 
type of this channel as set by the 

AO_Change_Parameter

 function. In addition, writes to 

channel number 49 affect the voltage or current gain calibration, which also depends on the 
output type of the channel as set by the 

AO_Change_Parameter

 function.