Microampere current measurement?

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.

 

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.

 

You could buy a Fluke 116 or use a low burden voltage converter.
http://www.adafruit.com/products/882

http://www.alternatezone.com/electronics/ucurrent/uCurrentArticle.pdf

 

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.

 

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?

 

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

 

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.

 

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.

 

Excellent news.

 

Excellent info, thank you.