Some question about uCurrent  - Page 1
Forum section: electronics / beginners

author: ccmake23
author_rank: Newbie
timestamp: February 04, 2015, 04:09:56 pm
content: Hi!I'm searching a tool to measure the system current which I'm working on in my company.My system is a eMMC NAND controller, and I need to measure the current in the standby mode and in the active mode.In standby mode, it might just consume few uA, but it consumes hundreds of mA in active mode.I'm wondering of uCurrent is suitable for this measure.I need to measure the current from power-on => standby => active =>standby mode.Is uCrrrent able to measure such wide range current?Thanks a lot!!David

author: barry14
author_rank: Regular Contributor
timestamp: February 05, 2015, 01:06:13 am
content: The latest version of the UCurrent device can measure from nanoamperes up to 1.25 amperes so it is suitable for your project.

author: EEVblog
author_rank: Unknown
timestamp: February 05, 2015, 02:48:30 am
content: The only problem with uCurrent is one of the ranges. It only has 3 fixed ranges, and about +/-1.3V maximum output voltage.i.e:+/- 1300uA on the uA range.+/- 1300mA on the mA range.So if you need a wide dynamic range signal that switched between say 1.5mA down to 1.5uA then you are in trouble.If you want to use the same range you are forced to use the mA range, and therefore your resolution is limited to say 10uA on that range (meter dependent).You could tweak the shunt resistor value to maximise the dynamic range you are after and/or increase the supply voltage.But dynamic range is the problem with any such current meter. That's whey there is shorting switch to let you change ranges without interrupting your circuit.Usually you'd fix this sort of problem in test firmware that keep the various modes on so you can measure each one separately and accurately.

author: ccmake23
author_rank: Newbie
timestamp: February 05, 2015, 03:30:16 am
content: Quote from: EEVblog on February 05, 2015, 02:48:30 amHi!Thanks for the explanation!Indeed, I need a "dynamic" wide range current meter to measure the current changing from uA to mA.We use the Aglient scope with current probe to achieve this task, but the cost is really high.I'm just wondering if uCurrent Gold be able to do this with much lower task.....Looks like if wI choose uCurrent, I've to measure the current separately with different mode.Do you guys know other way to dynamically measure the wide range current, except using the scope method?Thanks a lot!!David

author: EEVblog
author_rank: Unknown
timestamp: February 05, 2015, 03:53:48 am
content: Quote from: ccmake23 on February 05, 2015, 03:30:16 amDepends how much resolution you need at the low end.e.g. to get 0.1uA resolution and say 200mA, you would need a 200.0001 FS meter and appropriate uCurrent range resistor.That would need a 100mOhm shunt resistor, a high voltage supply (3 x AAA's), and a 6.5 digit meter to get the uCurrent to do that. It's tricky, but possible. Low range errors would need to be stable and nulled out.

author: lgbeno
author_rank: Frequent Contributor
timestamp: February 05, 2015, 12:38:50 pm
content: I believe that I saw a post in the 43oh forum regarding a current sense amplifiers with logarithmic out. This could likely solve your dynamic range issue. He just uses the eval board to measure current

author: suicidaleggroll
author_rank: Super Contributor
timestamp: February 05, 2015, 05:59:41 pm
content: As Dave alluded to, is it not possible to just measure them separately? Modify your firmware so the controller is always in standby mode, and set the uCurrent to uA. Once you have a good reading for the standby current, switch your firmware to the normal mode with the uCurrent set to mA so you can capture the active current.

author: hari
author_rank: Contributor
timestamp: March 06, 2015, 03:59:19 pm
content: As I don't want to fry my uCurrent Gold nor measure crap, I thought I'd better be safe than sorry and ask the experts around. I've built a sensor with an ESP8266 board. During wake-up it consumes around 20-300mA (not yet measured in detail, just watched the supply indicator). In sleep mode, the esp is said to use around 50-70uA. I can measure with an HP 3478A or with a Fluke 87V. So how would I measure in uA mode? I'm using the nodemcu lua firmware, and before my script is even executed (init.lua), the firmware does set up the Wifi link. Even if I'd put a deep sleep command on top of init.lua, it probably would still draw some hundreds mA during bootup. Would this kill the uCurrent uA shunt resistor? Can I short the terminals of the uCurrent (set to uA mode) until the MCU has booted up and went into deep sleep? Then remove the short wire and do the measurement?thanks for your help,br Hari

author: suicidaleggroll
author_rank: Super Contributor
timestamp: March 06, 2015, 04:10:04 pm
content: Quote from: hari on March 06, 2015, 03:59:19 pmI don't see anything wrong with that.

author: dannyf
author_rank: Super Contributor
timestamp: March 06, 2015, 04:16:11 pm
content: QuoteDo you need to measure the current continuously in that process or you just need to measure the current in each of the phases?the former is tough to do - HP has a patent on that; the latter is quite easy to do.

author: hari
author_rank: Contributor
timestamp: March 13, 2015, 12:45:26 pm
content: How would I connect the uCurrent to a scope? I already realised that he non-floating inputs of the rigol introduce a connection to ground in my circuit, so I inserted the uCurrent on the negative supply line. But i'm picking up a lot of noise, and in 1M Ohm mode I get no usable signal at all. In 50Ohm mode, the measurement is not correct (showing around 120mA - also on the HP 3478A hooked up in parallel) and also very noisy. Without the scope, the 3478 shows about 68mA, which is the same when using the uCurrent with the HP or with a Fluke 87V. So that is what I would expect to read on the scope.The setup: Toellner 8852-32 PS, positive output going to a esp8266 + pin. - pin goes to uCurrent + input, - input goes to Toellner negative output. The HP3478 is hooked up to the voltage output of the uCurrent. The scope is connected in parallel (ch2). Ch1 is triggering on the RST pin of the esp8266.So what am I doing wrong with the scope?

author: suicidaleggroll
author_rank: Super Contributor
timestamp: March 13, 2015, 02:10:50 pm
content: The - voltage output on the uCurrent is not at the same potential as the - current input, it's 1-2v higher (half the battery voltage). Either your scope or the DUT needs to be floating.

author: TerminalJack505
author_rank: Super Contributor
timestamp: March 14, 2015, 01:32:59 am
content: Quote from: ccmake23 on February 04, 2015, 04:09:56 pmI went looking for a USB device that basically does what you are looking for.I never did find exactly what I was looking for but seethis threadfor some ideas on how to implement such a device.