You can use the Sequence mode example that ships with drivers.
Just pass in array of ramp values and associates delays between each value of the ramp signal.
To make your life easier, refer to this example
C:\Users\Public\Documents\National Instruments\NI-DCPower\Examples\DotNET 4.5\Sequence\Hardware-Timed Voltage Sweep\cs
There is a similar one for .NET 4.0 too (vb or cs)