The NI ELVIS III provides a one positive and one negative variable power supply. The positive supply can provide adjustable output voltage from +1 V to +15 V and negative supply can provide -15 V to -1 V.
The NI ELVIS III gets the set point from the Variable Power Supply SFP. A DAC is used to convert the digital set point to the control voltage.
The amplifier stage scales the control voltage of the DAC output to the correct adjust voltage, which is the input of the regulation loop.