Agilent 4156c: getting NaN when trying to measure transconductance

[ClintN]

Hello,

I'm using labview to drive an Agilent 4156c.  In the past I have used it to generate transistor curves when sweeping drain voltage and reading drain current with no problems.  I'm working with these experimental transistors in which I need to hold the drain voltage (Vdd) constant and sweep the gate voltage (Vgs) while reading drain current (Id).  Labview is returning viable data for Vdd and Vgs, but I'm getting NaN for Id.  Basically, if I sweep Vdd I get viable data for Id, but if Vdd is constant then Id = NaN.

I have no problems if I do try to do this from the front panel of the 4156, but can't seem to get it to work in labview.

Any help or feedback would be greatly appreciated.  Thank you.

[amezam]

Hello ClintN,

Are you using the Agilent Technologies 4156C driver or VISA functions? This is a direct measurement, or are you calculating it from other values?

Best Regards,

Alina M

Applications Engineering

National Instruments

[ClintN]

Hi amezam,

Thanks for responding.  I'm using the plug and play driver, and it's a direct measurement.

Regards,

ClintN

[amezam]

Hello ClintN,

Which function are you using? Could you post a picture of the VI? 

Best Regards,

Alina M

Applications Engineering

National Instruments

[ClintN]

amezam,

I've attached images of the VI, split into 3 parts.  The first one is channel configuration, second is measurement, third is data writing.

After configuring, I use the VI "measurement actions" followed by "read trace data" to get variable data.  This is sent to a mathscript node which outputs a 2D array for a spreadsheet string.  This works fine whenever Vdd is my primary sweep function; it reads and properly stores Id and Vdd.  I run into trouble if Vgs is my sweep function and Vdd is constant; if I try to read and store Id and Vgs I get NaN for Id.  I've also tried writing Id to a local variable and reading the data later which didn't work.

Thanks

ClintN

[amezam]

Hello ClintN,

Thanks for posting those pictures. If you use probes in the wires that come into the mathscript node and the array Data that comes out from it, do you see the right values?

Best Regards,

Alina M

Applications Engineering

National Instruments

[JÞB]

I suspect something is not quite right with your hardware setup. 

I am actually pretty curious as to why you went with a mathscript node when "Build Array" (Right-click>>deselect concatanate arrays and you get a 2D array out) and "Transpose 2D Array" (LabVIEW is Row, Col vs Matlabs Col, Row convention) are easilly accessable?

[ClintN]

Hi amezam,

I used a probe, and the NaNs are coming out of the 'read trace data' vi before getting to the node, as if it's not reading the data.  Data for Vg looks good.

Thanks,

ClintN

[ClintN]

---

@JÞB wrote:

I suspect something is not quite right with your hardware setup. 

I am actually pretty curious as to why you went with a mathscript node when "Build Array" (Right-click>>deselect concatanate arrays and you get a 2D array out) and "Transpose 2D Array" (LabVIEW is Row, Col vs Matlabs Col, Row convention) are easilly accessable?

---

I'm still a labview novice, and I think the person who worked in this lab before me had a few vi's on the computer that I used to study from.  I've gone back and used 'build array' and 'transpose' instead of the mathscript node.  That is simpler, but I'm still gettting NaNs for Id.

ClintN

[JÞB]

NaN is the agilient way of saying overrange. some setting is not right.

asside : autocorrect for agilient is ailment.