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How to cheaply measure low current over time while sourcing a constant voltage?

Hi!

 

I am working on a research project which involves me building and characterizing transistors. I do not have access to expensive current sensing intruments but I do need to plot the current (in micro-apms) over time at a constant source-drain voltage (200 millivolt) and see how this current changes when I manually apply different gate volatges.

 

I am new to the field of measurement and characterisation. I am also low on financial funding so I was hoping that someone here can guide me towards the right Data Aquisition System and the appropriate LABView code to do this measurement. It would be a great help.

 

I apologise in advance if I sound way out of my depth in this field. But I am in dire need for some guidance. Any help would be HUGELY appreciated.

Thanks in advance!

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Message 1 of 12
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Hi Rhydo,

 

measuring µA is not that easy.

 

Either use (rather expensive) DAQ devices - or try your luck with an OpAmp to amplify the voltage across a shunt resistor. But don't complain about noise in your measurement data!

Best regards,
GerdW

using LV2011SP1 + LV2017 (+LV2020 sometimes) on Win10+cRIO
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Message 2 of 12
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There are op amps out there specifically for conditioning current shunt voltages.  uA will be kind of hard.  You will want a decently sized current shunt and an op amp with a lot of gain.  From there, just use a standard DAQ to read the signal from the op amp.


GCentral
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Cheap, Reliable, Accurate solutions are seldom seen in the wild.  You MIGHT be able to pick two if you exclude Cheap


"Should be" isn't "Is" -Jay
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@JÞB wrote:

Cheap, Reliable, Accurate solutions are seldom seen in the wild.  You MIGHT be able to pick two if you exclude Cheap


If you go with cheap you likely won't have reliable, or accurate.

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Message 5 of 12
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Hi Rhydo,

like the others already said. A cheap, reliable and accurate Data Acquisition System is very difficult to accomplish. Maybe you can give some additional Information what equipment you already have or which new equipment you can afford. (That is the equipment you would normally need: http://www.ni.com/white-paper/5448/en/)

The appropriate LabVIEW code shouldn´t be any problem. Simple go to Help--> Find Examples -->Hardware Input and Output . There you could find many examples (deepending which Hardware you are using), which you can customize to your needs.

Kilian H.
Applications Engineering
National Instruments

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Message 6 of 12
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Hi Rhydo,

 

You should use a feedback ammeter for the uA range - the question is what is your budget and what is the current range that you need to measure?

 

Cheers,

J.

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Message 7 of 12
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Hi!

 

Thankyou for all the answers.
 

My current measurement range would be within 0.1 to 300 microamperes. I DO have limited access to a Keithley 2612A test bench. But I am pretty sure that I would need the appropriate LABview code to get continuous current measurements over time. 

 

Would this be of help??

 

p.s. - as for my budget, I have to keep it way below 300 euros i,e, approximately $400.

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Message 8 of 12
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I'm not sure what the specs of the Keithley are but getting the LabVIEW driver is as simple as using Help> Find Instrument Drivers. You'll have an example as noted above.
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Message 9 of 12
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Ok, got it. Hopefully I get some ideas there. 

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