why my electrometer 6517A measure negative surface resistivity?

[Nanotech2007]

My measurements with Electrometer 6517A and with the 8009 resistivity test fixture are negative... I make a surface and volume resistivity measurements in polyurethane samples with these proportion: ctpu/san~100/0 , tpu/san2~75/25 etc.. and the volume resistivity is ok I think typical values are 2.5x10^11 until
1.5x10^11 in alternative voltages 30-60V ... but the surface resistivity is negative and I dont know why and if sometimes is positive it has a lot of changes...can anyone help me?

[Andy L]

Hi Nanotech2007,

I have a few questions about your system. 

            What version of LabVIEW are you using?

            Who manufactures the Electrometer 6517A and the 8009?

            What interface do they use for communication (Ethernet, GPIB, or Serial)?

You might want to check ni.com/idnet for a plug and play instrument driver for LabVIEW.  I have attached a link explains Interchangeable Virtual Instruments (IVI) drivers in more detail. 

http://www.ni.com/ivi/

Regards,

[wildcat_600]

Since Keithley makes the 6517A you will want to check with them for hardware related issues.  Make sure you are selecting the lowest range, otherwise you should contact them.

Brian P.

[Nanotech2007]

Dear Brian

thanks about the reply, I have not problems with hardware issues but with range I saw some differences. I cant select the lowest range and I do this: 
In surface resistivity I choose autorange and auto uprange only sometimes , and in volume resistivity I choose auto uprange only. But in every measurement I have a lot of parameters such as time and voltage.

I measure the sample in different time first in 1sec and 3 reading by measurement and the alternative voltage from 20V to 30V. Next the same but with more time 15 sec.
Next the same from 30V to 60V. this is for the surface and next the same for the volume.

Lets go to the problem again, why in some measurements the resistivity is negative? I check the sample I check the electrodes and the sample is between two electrodes and all the other are ok.

[Nanotech2007]

Dear Andy,

thanks for your reply and your interest

I am not using Labiew I am using 6517A Hi-R Sweep Test. This is software from Keithley and the elctrometer and the test fixture are from Keithley.
The communication that they use is GPIB.

Do you suggest to me to use another software with more ''moves''? Do you know if my measurement are good?

[Dennis_Knutson]

Questions about Keithley hardware and software are probably best addressed to Keithley. If you do decide to switch software, there is a LabVIEW driver available for your instrument and you can write your own program.

p.s. Even if you were using any NI software or hardware, you posted to the wrong board. This board is for NI DMMs and is not intended for general DMM questions.

Message Edited by Dennis Knutson on 09-05-2007 05:55 AM