pci-4461 id-vg fet sweep?

[david_i]

Hi,

I'm trying to use signal express with a PCI-4461 card to peform a voltage sweep on a FET. I'm using one analog output (gate voltage sweep) and one analog input (voltage from an amplifier which is amplifying the drain current). Drain voltage is being applied by a constant power supply. If I adjust the gate voltage manually using signal express, I don't have any problems. But when I try to use the "sweep" function, I can not get it to work. Even though I am applying a sweeping voltage to the gate, my input voltage (amplified drain current) corresponds to the first gate voltage in the sweep for all acquired data. It seems as if it is sampling only data from the first gate voltage in the sweep. I have tried adjusting the number of samples I'm reading with the AcquireDAQMX block to see if that solves the prolbem to no avail; as well as adjusting the number of samples generated. I'm certain that the gate voltage is being changed because I physically measured it with a digital multi-meter and it was sweeping as expected.

Does anyone know what a possible solution is?

Thanks.

[david_i]

The solution was to read a lot more data with the Acquire block than I was generating. If I am generating 100 samples (continuously) and reading 100 samples continously, I do not see my expected data. If am generating 100 samples (continously) and reading 1000 samples, I begin to see my data. I have to increase to 4000 samples (continuously) in order to see all my data. My sampling rate is 1000S/s for all blocks. I'm guessing maybe this problem occurs because of some delays within the board?