ucurrent micro amp measurements - Page 1
Forum section: electronics / projects

author: mumilover
author_rank: Newbie
timestamp: January 31, 2015, 08:10:10 pm
content: I just got my self a µCurrent GOLD.I want to measure current consumption of a Nordic Semiconductor nRF51822 BLE module.What i want to measure is the actual current consumption (CC), but that is a little tricky.When the device is in idle mode the CC is around 3.5 µA. But when the device is communicating the CC is around 15 mA.Is it possible to measure CC (using the µCurrent GOLD) when the difference between the two states is that much ?And what will be a good setup to measure the CC ?Maybe also how ?So fare i have been using a picoscope3204 together with a known accurate resister to measure the voltage drop over it... then simple ohm's law calculations.But the measurements are ALL OVER THE PLACE... from 50 µA to 5µA (only in idle mode)... i cannot rely on such measurements..Pls advice :0)

author: plazma
author_rank: Frequent Contributor
timestamp: January 31, 2015, 11:19:31 pm
content: How do you power the BLE module?If you can use a PSU with sense lines then you can add a current measurement resistor between one supply and sense output ( take the current from the sense line, sense line compensates the voltage drop of the resistor).With uCurrent I shorted the current input when changing the range switch. My uCurrent is dead atm.

author: mumilover
author_rank: Newbie
timestamp: January 31, 2015, 11:23:17 pm
content: i'm using 2xAAA with a voltage regulator... i'm getting clean 3.3 V...I don't have access to psu with sense... can you recommend one witch can sense around 1-3 µA ?

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: January 31, 2015, 11:44:58 pm
content: I'm a grumpy old man, this is my microammeter.I used this to measure sleep mode current on a uC, and measure watch dog timer wake ups. I just switch it out when I want to run normally.The burden voltage is quite high though.I like the sense line idea.

author: MLXXXp
author_rank: Frequent Contributor
timestamp: February 01, 2015, 01:55:46 am
content: If you want to measure with a µCurrent:You can still use your PicoScope to do the measuring by putting the µCurrent in place of the resistor that you've been using as a measurement shunt.3.5µA is higher than what the µCurrent's nA range can measure, so you would have to use the µA range. 3.5µA is a pretty low value for the µA range, so your readings in that region won't be too accurate, but you'll have to live with that.When the current jumps to the "around 15mA" that you stated, or actually anything over about 1.2mA, the µCurrent will pin at around 1.2V output (looking like 1.2mA) so you won't be able to measure these high currents while on the µA range. However, I've made estimates that say that the µCurrent should safely be able to handle 28mA on the µA range, at all times, and up to 85mA while powered on, so your 15mA shouldn't do any damage to the µCurrent.So, you'll first have to integrate the readings on your scope that are below the 1200µA limit, using the µCurrent's µA range, then switch to the mA range and integrate the areas that are above 1200µA. Adding the two integrations should allow you to calculate the average current. 15mA is a small percentage of the full scale mA range, so accuracy will again suffer, but that's a limitation of the µCurrent's available ranges.Here's a video that Dave did about using integration with an oscilloscope:http://youtu.be/Dh0xYu8YvaEMy calculations for maximum safe currents for the µCurrent can be found in the following post and the one that is referenced in it:https://www.eevblog.com/forum/crowd-funded-projects/current-gold-on-kickstarter/msg376311/#msg376311If you're interested in adding protection so that the µCurrent can safely handle higher currents when powered off, you can look at this post about the mods that I've made to mine:https://www.eevblog.com/forum/crowd-funded-projects/current-gold-on-kickstarter/msg448208/#msg448208

author: mumilover
author_rank: Newbie
timestamp: February 01, 2015, 02:24:36 am
content: Quote from: MLXXXp on February 01, 2015, 01:55:46 amVery useful info indeed :0)It is possible to increase the gain.. right now it will multiply the current by 100... can we get to it do 200.. 500..1000 ?It is possible to change the resister in the µA range to allow it to handle more current.. say 150 mA ?

author: MLXXXp
author_rank: Frequent Contributor
timestamp: February 01, 2015, 02:39:32 am
content: You could increase the gain at the expense of lower bandwidth, higher noise and less accuracy. Gains not a multiple of 10 would make calculation of the current from the output voltage more difficult.You could also change one or more shunt resistors to change the range(s). Again, changing the range so that current to voltage isn't a multiple of 10 would mean harder current calculations.You could also increase the positive range (up to nearly double), at the expense of reducing the negative range, by shifting the virtual ground, without changing the gain, like I did with my µCurrent.

author: MLXXXp
author_rank: Frequent Contributor
timestamp: February 01, 2015, 02:49:58 am
content: Quote from: mumilover on February 01, 2015, 02:24:36 amTo be able to read up to 150mA, or just be able to safely handle 150mA while still having a range of only 1.2mA?

author: mumilover
author_rank: Newbie
timestamp: February 01, 2015, 02:52:53 am
content: the latter... simply handle higher current without board damage

author: MLXXXp
author_rank: Frequent Contributor
timestamp: February 01, 2015, 03:06:47 am
content: If you go by my limit of allowing only 1.5V across the shunt while power is on (or with power off protection diodes), then you could safely handle 150mA if the µA range shunt, R9, could safely handle 0.225W. You couldn't go above 150mA regardless of the wattage capability of R9.Note that if you added some kind of input protection that worked when power was on, then maximum input current would be limited by the capabilities of whatever protection you added.

author: qwaarjet
author_rank: Regular Contributor
timestamp: February 01, 2015, 04:10:55 am
content: We have about 20 of the original Ucurrent (gold isn't that different) in our lab and routinely change the gain for various experiments, typically after someone blow one up.Though we are typically going from ~10nA to ~100uA the concept is the same.

author: LarryMartin
author_rank: Contributor
timestamp: February 01, 2015, 05:42:25 am
content: FYI, the Real Time Current Monitor from ee-equipment.com is a really nice tool for measuring such wide variations in current. It handles 1uA to 1A on a log scale. I find it incredibly useful for stuff like this.

author: mumilover
author_rank: Newbie
timestamp: February 01, 2015, 02:42:44 pm
content: Thank you all for your input

author: cyounkins
author_rank: Newbie
timestamp: April 03, 2015, 04:34:33 pm
content: Quote from: LarryMartin on February 01, 2015, 05:42:25 amI think you meanthttp://www.ee-quipment.com/. ee-equipment.com is a tractor dealership.