Measuring nanoamps

RE: Measuring nanoamps

mudz — Tue, 22 Oct 2019 17:44:03 GMT

Wow, you sure jumped deep into the nano world, it seems. [View:/resized-image/__size/16x16/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-75402a23-c0d8-41c2-9a15-eab21263b271/contentimage_5F00_1.png:16:16]
Great work.. Thumbs up for that..

-Mudz

RE: Measuring nanoamps

koudelad — Fri, 04 Oct 2019 08:10:00 GMT

Thank you for your comments. I am always surprised from what I learn when doing "basic" measurements like this current measurement.

All the tools I used were borrowed. And I have to confirm that U1282A is a bit slow when taking reading. That is why I had to do multiple thermometer measurements to see the multi-meter reading from a run mode. Otherwise it has a nice feature set.

At home, I have an inherited manual-ranging Metex 4660M. On the lowest range of 2 mA, it has the lowest resolution of 10 nA and accuracy of 6.03 uA . The readings were the same as with U1282A, in sleep mode the current jumps between 0.0000 and 0.0001 uA. However the thermometer doesn't start on 2 mA range, so I need to switch it to 200 mA to run and switch back to 2 mA after it gets to sleep mode.

Joulescope is good for energy profiling of battery operated gadgets, especially with wireless radios etc. I don't know about a similar device in this price range. If you wanted to head a podcast with the designer, here is a link: https://embedded.fm/episodes/278

One colleague has also recommended me a way of profiling 3V devices using one of EFM32 STK kits from Silicon Labs: https://uk.farnell.com/search?st=efm32%20stk . It requires installing the IDE, Simplicity Studio. More details are described here: https://www.silabs.com/community/mcu/32-bit/knowledge-base.entry.html/2015/08/03/profiling_an_externa-sRqf and in this discussion: https://www.silabs.com/community/mcu/32-bit/forum.topic.html/how_to_use_an_stkto-jLpQ . Primarily, it is supposed to be used with the MCU on the kit, but can be used to power an external device. Not sure about the range, I tried it a few months ago, probably between tens of nA and up to 100 mA. Definitely the cheapest option of all mentioned, so far.

The biggest advantage (when using on the embedded MCU from Silicon Labs) should be current measurement for specific parts of code. (I haven't tried it.)

RE: Measuring nanoamps

three-phase — Thu, 03 Oct 2019 19:50:12 GMT

Interesting set of experiments to read through. I too have a U1282A, but have found it very slow to settle when taking readings. I then looked at Joulescope when it was a Kickstarter, but could never justify the purchase probably, until a few weeks ago when I wanted to measure the inrush current drawn on some instruments I was testing. Ended up with a Picoscope across a shunt resistor, but couldn't really measure the current for a sleep-mode with this method.

Kind regards.

RE: Measuring nanoamps

dubbie — Thu, 03 Oct 2019 19:35:25 GMT

Very impressive low current measurement, as well as designing the low current electronics. I had a go at this once using a PIC microcontroller and only managed to get the sleep current into the hundreds of nanoamps. As the system only woke up once per minute to slowly flash an LED the average current consumption was very low. The whole system ran for two years on two ordinary alkaline AA batteries and would probably have gone on for longer if I hadn't had to turn it off.

Dubbie

RE: Measuring nanoamps

fmilburn — Thu, 03 Oct 2019 03:07:44 GMT

Hi David,

Nicely presented and great follow-up on your part… I found out about the need to set floating pins on the TI MSP430 sometime back in order to minimize power. Of interest, some of the smaller packages have the same modules as larger packages but do not have external accessible pins - nonetheless it is also necessary to set the inaccessible pins to minimize power. I wish I had access to equipment like that :-)

Frank

RE: Measuring nanoamps

clem57 — Thu, 03 Oct 2019 00:49:01 GMT

A great read and a bit surprise of the floating pins in MCU. My static digital view is shattered. Thanks [mention:00dfb01ff12548938b4b7669fc69e778:e9ed411860ed4f2ba0265705b8793d05]