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Agilent E3631A Measurement problem

Question asked by isaacwu on May 26, 2010
Latest reply on Jun 1, 2010 by soonchei
I am setting a voltage on the E3631A DC power supply using GPIB. There is no problem with doing that but I notice that when I take a measurement the voltage drops by a little, around 0.02V. The measured voltage differs from the Set voltage by that amount.

I use the IVI-COM drivers and wrote a Visual Basic .Net program to do this. I referred to 'example1' in the IVI-COM driver libraries for Agilent E36XX power supplies.
A segment of code is below:

            'initialise driver
            ividc.Initialize("GPIB::2", False, True, "Simulate=true")  'id query=false, reset=true

            pout1 = ividc.Outputs.Item("Output1")

            'set output voltage level
            pout1.VoltageLevel = 1.645

            'Measure output voltage
            measVal = pout1.Measure(IviDCPwrMeasurementTypeEnum.IviDCPwrMeasurementVoltage)

At first, setting the voltage level proceeds without error, the set voltage on the display is correct.          
But the command to measure voltage causes the voltage on the display to change and the measured voltage contained in the variable measVal is inaccurate.
Any idea what went wrong?