IV sweep program

[Smahat]

I was given a ready-to-use VI which uses the Keithley 6517 electrometer to perform an IV sweep within a specified voltage range. The thing is the program can only be used to go from negative voltage to positive at a certain terminal. An error occurs if I want to go from say 50V to -50 V instead of the other way around. Although I have no experience or knowledge of programming in Labview, my professor insists that I should be able to fix this problem on my own. I have attached the VI. I hope anyone out here can help me out here.

[johnsold]

We will try to help but since this is an assignment from your professor, we will not do the work for you.

First, what is the exact error code or message that you get when you try to sweep from postive to negative? 

Second, will the instrument do that sweep if controlled from its front panel (not via the computer)?

Next, what have you tried?

Lynn

[Smahat]

thank you for replying. The error i get while sweeping from positive to negative voltage or even higher to lower voltage is ERROR CODE- 850 ( this means "invalid test sequence setting") on the Keithley 6517.

I do not know how to run an IV sweep without using the computer directly from the device.

My professor suggests there should be only a minor adjustment in the code somehwere. Since I have never used Labview before this, I have no idea how to do this.

PS - this isnt an assignment , he doesnt care how i get it done.:P

[johnsold]

Invalid Test Sequence sounds like the Keithley does not like the values you sent to it. That sounds like a instrument or data problem, not a programming problem.  Check the manual for the instrument to see what settings are required for a negative-going sweep.  Besides setting the Start and Stop voltages, does the Sweep Step need to be positive or negative?

Lynn

[Smahat]

Yes. The problem seems to be with the device. i used a built-in test sequence for diode IV sweep. It responds the same way when i try to go from higher to lower voltage. The same error is shown. I will contact Keithley. thanks for your help.

[Smahat]

I was unable to get in touch with Keithley. Do you think its completely a device issue or do you think it can be solved by rewriting the Labview code?

[TSJim]

Hi,

Just a thought - if it is an IV sweep for a diode, the +V will max out at about .7V when forward biased.  Maybe that is why it errors when trying to start at a high voltage and the sweep probably is designed to sweep from a large negative voltage to the forward biased voltage and stops when a certain amount of current is going through the diode. 

Jim

[Smahat]

The program is definitely written for a diode. However I am using it to characterize some highly resistive samples. The max current it passes is about 40 micro Amps. So i dont think thats the problem.

[theInfiniteOne]

I realized you must increment negatively, to go positive to negative. I can't figure out how the plot works seems to not work.