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Delta and DFIL Question

2182 Series Support
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gelmand
Posts: 26
Joined: May 16th, 2012, 12:06 pm
Country: Canada

Delta and DFIL Question

Post by gelmand » June 22nd, 2012, 8:05 am

Hello,

I have a 2182A nanovoltmeter along with a 2400 source meter performing delta measurements. I basically used the 2182Delta_LV6.vi on this website with an added digital filter (0.01% window with 100 readings). I believe that the digital filter controls how many samples per direction of current (sourcing)... so 100 readings means that going in the positive direction of current > take 100 samples... then negative direction of current > take 100 samples ... etc and then perform the delta. If this is not the function of the digital filter, please correct me. (Using NPLC or 1, sometimes 5)

I feel like this is screwing up my results. After performing like 50-100 pairs, the resistance of the sample goes up and sometimes down VERY LINEARLY with NO noticable noise. This scales on the uOhms to nOhms. I believe this might be due to the heat generation of the sample due to passage of current, but I am wondering if this added DFIL removes all the scattering (noise).

Thanks,
Danny

Dale C
Keithley Applications
Keithley Applications
Posts: 2848
Joined: June 10th, 2010, 6:22 am
Country: United States
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Re: Delta and DFIL Question

Post by Dale C » June 22nd, 2012, 11:06 am

The Model 2400 and 2182A can certainly do the delta mode when programmed properly.
The trouble with this combination is the low resistance DUT could be drifting with thermal effects.
The Model 6221/2182A delta mode has a provision to help with this.
It is called the "Pulsed" delta mode.
It basically takes three readings.
The Model 6221 manual explains this in detail.
Here is the link to the Model 6221 reference manual. Look at page 5-32.
http://www.keithley.com/support/data?asset=15975
The filters slow down the source/measure process and allow time to pass while thermals can be created and then skew the data.

gelmand
Posts: 26
Joined: May 16th, 2012, 12:06 pm
Country: Canada

Re: Delta and DFIL Question

Post by gelmand » June 22nd, 2012, 12:30 pm

Hello Dale, again

The scaled of resistances I expect to measure are in the 100nOhms --> uOhms. Does the 2182A/2400 combo work for such results? In a couple of days the 6221 should be arriving and I can see the thermal effect results in the 2182A/6221 combo. I thought delta mode took care of these thermal drifts, how am I getting them? Over a 30-50 pairs or so, the shift is within the nOhm scale but this can still effect my results.

The SCPI commands I use are below, please let me know if you see something interesting. Also right below those commands is another set of commands that I slightly modified to continuously run 100 delta measurement pairs in a loop (current testing with 5 pairs). I am getting timed out at the RQS stage after the 1st iteration, if you have any input on that issue that would be great. I have been stuck on it for a while.\

Edit: Playing around with the SCPI, the 1st iteration runs fine, and the 2nd interation goes through but times out at the RQS looks like the 2nd SRQ is not generating, even though I am reseting the bit after clearing the buffer...


2182A SETUP
:SYST:PRES;
:TRAC:CLE;
:SENS:VOLT:DFIL:WIND 0.01;
:SENS:VOLT:DFIL:COUN 10;
:SENS:VOLT:DFIL ON;
:SENS:VOLT:DELT ON;
:SENS:VOLT:NPLC 1;
:TRIG:DEL 0.1;
:TRIG:SOUR EXT;
:TRAC:POIN 100;
:TRAC:FEED:CONT NEXT;
:STAT:MEAS:ENAB 512;
:*SRE 1

2400 SETUP
:*RST
:TRIG:SOUR TLIN;
:TRIG:DIR SOUR;
:TRIG:OUTP SOUR;
:TRIG:DEL 0;
:SYST:AZER:STAT OFF;
:TRIG:COUN 200;
:SOUR:FUNC CURR;
:FUNC 'VOLT';
:VOLT:NPLC 0.01;
:VOLT:PROT:LEV 0.2;
:VOLT:RANG 0.2
:SOUR:CURR:MODE LIST;
:SOUR:LIST:CURR 100E-3, -100E-3;

READ AND TRACK
:OUTP ON; (2400)
:INIT; (2400)
<RQS STAGE> (2182A)
:TRAC:DATA? (2182A)
...
:ABORT; (2400)
:OUTP OFF; (2400)
:TRAC:CLE; (2182A)
:*RST; (2182A)
:*CLS (2182A)


Modified for continuous Delta measurements:

2182A SETUP
:SYST:PRES;
:TRAC:CLE;
:SENS:VOLT:DFIL:WIND 0.01;
:SENS:VOLT:DFIL:COUN 10;
:SENS:VOLT:DFIL ON;
:SENS:VOLT:DELT ON;
:SENS:VOLT:NPLC 1;
:TRIG:DEL 0.1;
:TRIG:SOUR EXT;
:TRAC:POIN 100;
:TRAC:FEED:CONT NEXT;
:STAT:MEAS:ENAB 512;
:*SRE 1

2400 SETUP
:*RST
:TRIG:SOUR TLIN;
:TRIG:DIR SOUR;
:TRIG:OUTP SOUR;
:TRIG:DEL 0;
:SYST:AZER:STAT OFF;
:TRIG:COUN 200;
:SOUR:FUNC CURR;
:FUNC 'VOLT';
:VOLT:NPLC 0.01;
:VOLT:PROT:LEV 0.2;
:VOLT:RANG 0.2
:SOUR:CURR:MODE LIST;
:SOUR:LIST:CURR 100E-3, -100E-3;

LOOP BEGINS
:OUTP ON; (2400)
:INIT; (2400)
<RQS STAGE> (2182A)
:TRAC:DATA? (2182A)
...
:ABORT; (2400)
:OUTP OFF; (2400)
:*CLS; (2182A)
:*SRE 0; (2182A)
END LOOP

:ABORT; (2400)
:OUTP OFF; (2400)
:TRAC:CLE; (2182A)
:*RST; (2182A)
:*CLS (2182A)


Thank you kindly,
Danny

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