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Measuring Micro Amps with Pico4424 DSO

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Measuring Micro Amps with Pico4424 DSO

Postby hexibot43 » Thu Feb 06, 2014 8:23 pm

I've just started working with Arduino boards, and my current project has me using a battery to power my circuit. I would like to be able to display and record the power usage of the unit with my Picoscope. The majority of the time the Arduino (Moteino - Arduino Clone) is sleeping. I wanted to record one cycle of Awake-Asleep-Awake, so that I could get the best guess of my power usage over time.
How could I take readings down to the level of micoramps? The low amp current probe is good to 10ma. That's 10,000 micoamps resolution. No where near what I am hoping to be able to read. Any ideas?
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Re: Measuring Micro Amps with Pico4424 DSO

Postby alan » Sat Feb 08, 2014 10:16 pm

Hi,

Few (non contact) current clamps will resolve to under 1mA. The K110 probe is one exception, but its fairly expensive http://www.amazon.com/AEMC-K110-Micro-P ... B008S0JLEK

There are a couple of other options. Firstly its possible to amplify the signal measured by a current clamp by passing the current carrying wire through the jaws of the clamp multiple times - pass the current through a 10x or 100x loop of wire to increase the sensitivity.

Another option is to use ohms law to measure the voltage drop across a resistor. Place say a 1K resistor between GND (0V) and your circuit. 1mA current flow will cause 1V drop. If this is too high for the circuit to work properly then drop to 100R or 10R.

Which ever method you choose, PicoScope maths channels can be used to scale the readings on the screen into mA or uA as required.

Regards
Alan
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Re: Measuring Micro Amps with Pico4424 DSO

Postby hexibot43 » Tue Feb 11, 2014 8:23 pm

Thanks Alan,
I appreciate you ideas. I've been doing a lot of reading on the subject, and it is not as easy as one would think to make such measurements. Many of the chips I'm working with for temperature sensing have idle current rated in the nano-amp range. I am realizing that it is not too realistic to look at the idle time. I liked your idea of the wire wrap. I hadn't thought of that, and am going to give it a try. :shock: :?
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Re: Measuring Micro Amps with Pico4424 DSO

Postby hexibot43 » Fri Mar 07, 2014 12:38 pm

Just ran into this while waiting for my alarm clock to say it's time to start the day. I guess I'm not alone in wanting to do this...

https://www.kickstarter.com/projects/eevblog/current-gold-precision-multimeter-current-adapter


I guess I'll be picking one of these up and give it a go.
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