# Microampere current measurement?

Discussion in 'General Electronics Chat' started by tracecom, Jun 8, 2013.

1. ### tracecom Thread Starter AAC Fanatic!

Apr 16, 2010
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I would like to measure a low voltage DC current that is expected to be in the .25 to 2 microampere range. I have a Fluke 115; is there an inexpensive solution?

Thanks.

2. ### bountyhunter Well-Known Member

Sep 7, 2009
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Most good meters have an input impedance of about 10M Ohms. You could run the current through a resistor of 1 M Ohm and measure the voltage drop and correct for the input impedance value.

Aug 27, 2009
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4. ### crutschow Expert

Mar 14, 2008
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Can you measure the current in a ground connection? If so, you could use an op amp transimpedance connection with the current going into the "virtual ground" of the op amp.

5. ### tracecom Thread Starter AAC Fanatic!

Apr 16, 2010
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The μCurrent is more than I would like to spend, but it may be the best choice. In Dave Jones' typical fashion, he wrote a 19 page document explaining every detail, but I didn't find the user instructions. I presume the current being measured is run through the μCurrent device in series fashion, and the μCurrent converts it to a voltage. So, in the attached photo, how much current is the watch drawing?

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6. ### Jony130 AAC Fanatic!

Feb 17, 2009
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It's hard to say, because we don't see range switch position. But I suspect 1mV/1μA so we have 18.1μA

7. ### #12 Expert

Nov 30, 2010
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This is how you make a voltmeter pretend to be an amp meter.
But, you say, what about the voltage drop caused by the 10 million ohm resistor?
There it is on the display. 181 millivolts.
Do you have 181 millivolts more than you need to run the circuit?
Most of the time, you do.

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8. ### tracecom Thread Starter AAC Fanatic!

Apr 16, 2010
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I bought the μCurrent from adafruit. It works well; I was trying to build a timer circuit that would respond to a button push, but draw no current when idle, and minimal current when active. As it turns out, the best I could do was a 10nA idle current.

Last edited: Jun 16, 2013
9. ### nsaspook AAC Fanatic!

Aug 27, 2009
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Excellent news.

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