EEVblog uCurrent - Precision nA Current Measurement Assistant - v3
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An essential companion when working on a ultra-low-power projects! If you've ever used a portable multimeter (even your $300 Fluke!) to measure sub-uA currents - say for a low power microcontroller or sensor project - you may notice that you're not getting the precision you expect, or that your project is acting finicky.
How is this possible? – It’s called Burden Voltage. Many people are aware of Burden Voltage, but few people are aware of how bad this effect can be in practical circuit current measurements with a multimeter. Don't believe it?, take this simple test with your multimeter:
- Try to measure 190mA on the 200mA current range (pretty simple huh?)
- Read your manual to find out your meters "burden voltage" (I bet you don’t know it off the top of your head) (e.g. a Fluke 87V is 1.8mV/mA)
- Do the simple math to see what voltage your meter is dropping (e.g. 190(mA) * 1.8mV = 0.342V
- Now calculate what effect this drop has on your circuit at 5V, 3.3V, or something like today’s modern devices that need 1.2V supplies.
Is your 1.2V circuit going to work the same at 0.86V?, or your 3.3V circuit at 2.96V?, or even your 5V circuit at 4.66V? That's what a high-end Fluke 87V meter will do to your measurement!, and that's a GOOD meter. Even if your circuit "works", what will that change in voltage do to your current consumption?
The solution? Use a precision op-amp circuit designed specifically for measuring ultra-low currents. That's what the uCurrent is! Keep it handy for when you need to tackle those low-power projects.
Each order comes with a pre-built and tested Rev 3 uCurrent adapter. Australian Made ABS box. Fully assembled and tested in Australia. PCB is made in New Zealand by CircuitLabs. No test leads are supplied, you have to supply your own for your own purpose.
For more details, including schematic and layout files, visit the uCurrent project page
Check our own review by Kevin Townsend:
I was messing around with a personal project today (that’s what weekends are for, after all!), and was trying to get the current consumption on a small wireless board as low as possible in power-down mode (to keep the thing running for years of a single battery). I trust my Agilent 34410A, but measuring very low current can be a challenge, and I thought it was a good excuse to try out the uCurrent I picked up a while back from the shop here. $1400 DMM versus $60 red box, and the results were bang on. If you just need to accurately measure current, the uCurrent will definately leave a much smaller hole in your wallet without compromising on accuracy or reliabilty!
- 3 Current ranges:
- +/- 0-300mA (70µV / mA burden voltage typical)
- +/- 0-1000µA (10µV / uA burden voltage)
- +/- 0-1000nA (10µV / nA burden voltage)
- Output Voltage Units:
- Resolution (nA range): 100pA (3.5digit meter), 10pA (4.5 digit meter)
- Accuracy (typical): <0.2% on µA and nA ranges, <0.5% on mA range.
- Output Offset Voltage: Negligible on 4.5 digit meter
- Bandwidth: 2KHz nominal (+/-0.1dB)
- Temperature Drift: Insignificant over normal ambient range
- Noise: < -90dBV
- THD: < -60dB
- Battery: CR2032 Lithium coin cell
- Battery Life: >200 hours (LED OFF), >50 hours (LED ON)