Problem using the Keithley 6487 pAmmeter with voltage supply.

[ainat]

Hi cameron,

Sorry for the late reply. I was not at work for couple of days. Actualy, I didn't exactly use your program, but just did some small modifications. I am attaching the code for your perusal.

The problem as I said is that the program can't read the data when source volatge is 0.0001 i.e. starting from 0.1V and less it shows staircase like I-V plot instead of linear.

[CameronDean]

Hi ainat

Sorry for the late reply, I'm actually away on holiday just now so my replies will be a little sporadic until I'm back at work on the 22nd. As I'm away I don't have access to a 6487 but I do have access to LV. I have seen a 6485 exhibit step-like current and voltage behaviour before (although in our case this is what we were wanting) which was due to how an Agilent PS would supply voltage, maybe the 6487 works on a similar process but as it is a far more sensitive piece of equipement it is only noticable at small voltages?

If it is a coding issue then possibly it is due to how you are updating the voltage reading when you are outputting the results to your graph? Maybe try increasing your settling time from 1s or trying a method that doesn't involving looping the voltage and current?

Sorry that I can only speculate as to your problem without having access to equipement but hopefully we can find a solution to this. You could maybe try inserting a probe or breakpoint just before and after you update the voltage to see what is happening?

If you could, I would appreciate some screengrabs of your IV curves (both linear and step-wise) to be able to visualise what is going on. Thanks
Cameron

[ainat · Accepted solution]

Hi Cameron,

I guess I have solved the problem. Well the program was alright. It was just the problem with the meter. I mean the meter is not a good source for voltage below 5mV. That is why I was getting some irregular waveforms. Also the step like curve was due to the step size which I selected. It was supposed to be >200uV for the 10V range. But I selected to be less than that.

Thanks a lot once again for all your help!

Best Regards

Ainat

[ainat]

Hey Cameron,

I am kinda stuked with a problem with Keithley 6487 again :(.

Well, with the program which I kind of bulit using the code you sent me, itis working absoultely fine. However there is something I didn't notice before.

The problem is that when I am trying to sweep voltage >10V, its giving me wrong data. Seems like selecting the 50V or 500V range is not working. Its always by default taking 10V as the source range.And that is the maximum value I can use for sourcing as of now 😞

Can you please help me on this.

Code is attached

Thanks!

Best Regards

Ainat

[CameronDean]

Hi ainat

It sounds to me like you don't have your interlock closed. By default the 6487 will only allow you to ramp to low voltages without closing this. There should have been a small socket with pins arranged in a Y shape that came with your 6487. This should be wired as a short circuit to whatever your interlock system is and then attached to the back of your 6487.

Hopefully this helps. The 6487 I use is still in use by someone else so I can't test out your code but there may be a period where the 6487 becomes free and I can give your code a test at my end.

Cheers
Cameron

[CameronDean]

I've ran your vi with our 6487 and I was having no problems using the 50V and 500V ranges so your code is good. Your problem must be with the interlock.

Best of luck.
Cameron

[ainat]

Hey Cameron, Thanks!

You are right, its a problem with interlock 🙂

Thanks again.

[lplopez]

Hi,

We are planning to use Keithley 6487 to test our FET. Is it possible to supply +/- 40V on the gate (Vg) then measure the resistance from Va to Vb using the said instrument? Since Vg and Va-Vb are separated with SiO2 (shown in the attached image), this means that I am going to use KE6487 as voltage source and meter separately. 

PS. We will be using a separate power supply (Keithley 220) to provide for Isd.

Thank you,

-Lorenzo