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Keithley 3706 - electrical resistance measurement

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joanamaia
Posts: 16
Joined: January 24th, 2012, 2:16 am
Country: Portugal

Keithley 3706 - electrical resistance measurement

Post by joanamaia » January 24th, 2012, 2:34 am

Hello.
I have a 3706 multimeter and I'm doing some resistance measurements to identify corrosion on steel, with 4-wires.
The previous measurements I´ve did, some results present discontinuities (a variation on resistance that not recover the last value).
This is due to de DMM comands? I have DMM.nplc, DMM.autorange, DMM.offsetcompensation and DMM.linesync ON (=1), but DMM.autozero isn't definite.

This equipment has a "stand-by" or "sleeping" function?

Thanks for your help.

Derek M
Keithley Applications
Keithley Applications
Posts: 19
Joined: October 21st, 2010, 7:01 am
Country: United Kingdom

Re: Keithley 3706 - electrical resistance measurement

Post by Derek M » February 9th, 2012, 12:52 am

Hello,
Could you give me some examples of the variations that you are experiencing?
Also how are you communicating with the 3706 - LAN, GPIB?
What programming language are you using?
What is the firmware version of the 3706? (From the front panel at switch on, press "Slot", for example "01.40k")
Do you have a 3706 or a 3706A?
Thanks,
Derek

joanamaia
Posts: 16
Joined: January 24th, 2012, 2:16 am
Country: Portugal

Re: Keithley 3706 - electrical resistance measurement

Post by joanamaia » February 9th, 2012, 6:30 am

Hi Derek,
Thanks for your reply.

The variation I'm experiencing is something like the resistance is around 10mOhm and then breakdown or up to 9mOhm or 11mOhm. But the previous value of the resistance (10mOhm) do not recover. So it looks like a "jump".

I'm comunicating with the equipment with USB (pendrive), where the files are saved.

When I press the Slot key it shows that: "Slot 3721 Dual 1x20 Multiplexer; 01.40h"
I have a 3706, only.

I'm using the LUA language.
I send you the script I'm using, so you can see what I'm doing.

SCRIPT:

--loadscript ensaioconjunto
reset()
timer.reset()

--4 WIRE OHMS------------------------------------
dmm.func=dmm.FOUR_WIRE_OHMS
dmm.nplc=1
dmm.autorange=1
dmm.offsetcompensation=1
dmm.linesync=1
dmm.configure.set('resistencia')
dmm.setconfig('1002:1008','resistencia')
------------------------------------------------

--TEMPERATURE---------------------------------
dmm.func = dmm.TEMPERATURE
dmm.nplc=1
dmm.transducer=dmm.TEMP_THERMOCOUPLE
dmm.thermocouple=dmm.THERMOCOUPLE_K
dmm.refjunction=dmm.REF_JUNCTION_INTERNAL
dmm.units=dmm.UNITS_CELSIUS
dmm.configure.set('Temp_ambiente')
dmm.setconfig('1001','Temp_ambiente')
---------------------------------------------------------------------------

buffer1=dmm.makebuffer(5000)
buffer1.appendmode=1
buffer2=dmm.makebuffer(5000)
buffer2.appendmode=1
buffer3=dmm.makebuffer(5000)
buffer3.appendmode=1
buffer4=dmm.makebuffer(5000)
buffer4.appendmode=1
buffer5=dmm.makebuffer(5000)
buffer5.appendmode=1
buffer6=dmm.makebuffer(5000)
buffer6.appendmode=1
buffer7=dmm.makebuffer(5000)
buffer7.appendmode=1
buffer8=dmm.makebuffer(5000)
buffer8.appendmode=1


mem_pattern1 = {"1001", "1002","1003","1004","1005","1006","1007","1008"}
--mem_pattern2 = {"buffer1","buffer2","buffer3","buffer4","buffer5","buffer6","buffer7","buffer8"}

for i = 1, 4115 do
--for j = 1,8 do
--dmm.close(mem_pattern1[j])
--dmm.measure(mem_pattern2[j])
--end
dmm.close(mem_pattern1[1])
dmm.measure(buffer1)
dmm.close(mem_pattern1[2])
dmm.measure(buffer2)
dmm.close(mem_pattern1[3])
dmm.measure(buffer3)
dmm.close(mem_pattern1[4])
dmm.measure(buffer4)
dmm.close(mem_pattern1[5])
dmm.measure(buffer5)
dmm.close(mem_pattern1[6])
dmm.measure(buffer6)
dmm.close(mem_pattern1[7])
dmm.measure(buffer7)
dmm.close(mem_pattern1[8])
dmm.measure(buffer8)


dmm.savebuffer('buffer1', '/usb1/ensaioconjunto_ch1',dmm.buffer.SAVE_RELATIVE_TIME)
dmm.savebuffer('buffer2', '/usb1/ensaioconjunto_ch2',dmm.buffer.SAVE_RELATIVE_TIME)
dmm.savebuffer('buffer3', '/usb1/ensaioconjunto_ch3',dmm.buffer.SAVE_RELATIVE_TIME)
dmm.savebuffer('buffer4', '/usb1/ensaioconjunto_ch4',dmm.buffer.SAVE_RELATIVE_TIME)
dmm.savebuffer('buffer5', '/usb1/ensaioconjunto_ch5',dmm.buffer.SAVE_RELATIVE_TIME)
dmm.savebuffer('buffer6', '/usb1/ensaioconjunto_ch6',dmm.buffer.SAVE_RELATIVE_TIME)
dmm.savebuffer('buffer7', '/usb1/ensaioconjunto_ch7',dmm.buffer.SAVE_RELATIVE_TIME)
dmm.savebuffer('buffer8', '/usb1/ensaioconjunto_ch8',dmm.buffer.SAVE_RELATIVE_TIME)


delay(60)
end

print('finish_ensaioconjunto')
display.settext('End medidasensaioconjunto')
time=timer.measure.t()
print(time)

--endscript

Now I have another problem. I want to do 10 readings at intervarls of 0,01sec between them.
I've tried so many things(change nplc, aperture) but nothig results. I never have a fixed time step between the readings.
Can you give me some help with this?

Thank you so much again.
Waiting for your answer.

Derek M
Keithley Applications
Keithley Applications
Posts: 19
Joined: October 21st, 2010, 7:01 am
Country: United Kingdom

Re: Keithley 3706 - electrical resistance measurement

Post by Derek M » February 10th, 2012, 3:33 pm

Hi Joanna,
The variation in resistance between 9mOhm and 11mOhm does not look that bad a result. However, I experimented with your script and I changed the resistance range from "Auto" to a fixed value. I used the 100ohms range (dmm.range=100), but you could experiment with lower ranges.
In terms of trying to measure every 10ms, with an NPLC=1, it means that each measurement will be integrated over 1 power line cycle which in Europe means 1/50Hz =20ms. Therefore to be able to measure every 10ms, you will need to reduce the NPLC rate perhaps to 0.1 (integration period of 200us). However be aware that the quality of the measurement will suffer due to now having much increased 50Hz interference.
Hope this helps,
Derek

joanamaia
Posts: 16
Joined: January 24th, 2012, 2:16 am
Country: Portugal

Re: Keithley 3706 - electrical resistance measurement

Post by joanamaia » February 13th, 2012, 3:28 am

Hi Derek,

I've tried a new script with the changes you prupose.
With dmm.range=100 the resistance results are very unstable, so with autorange ON I have better ones.
With dmm.nplc=0.01 the time step between readings is closer to 10ms only on temperature measures. On resistance measures the time step is different in each channel and not closer to 10ms (is about 0.8sec). This is due to the oder dmm commands? It is possible to define a constant time step?

Thanks a lot for your help and interest.

Tomislav
Posts: 9
Joined: January 31st, 2017, 2:39 am
Country: Austria

Re: Keithley 3706 - electrical resistance measurement

Post by Tomislav » August 28th, 2017, 2:54 am

Hello,

I have a same issue, when I change dmm.func from 2wireohms to dcvolts I get a time delays. Meaning, time steps between measurement are not equal.
Did you maybe find a reason of the issue?

Thank you

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