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Low Current Measurement Suitability


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#1 jacobvc

jacobvc
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Posted 02 August 2014 - 07:12 AM

I have an application where I need to measure current consumption of microcontrollers under development.

 

The current is in the range from a few hundred milliamps to a few microamps. 4k samples per second should be adequate. This seems like a good application for a U6, but I'm not an analog guy and I would like some confirmation about whether some sort of voodoo is required to reliably measure such a low current.

 

Is is correct to assume that your reference WRT measuring 4-20 ma is sufficient?

 

Do you agree that the U6 is up to the task?



#2 LabJack Support

LabJack Support
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Posted 02 August 2014 - 02:37 PM

I think the U6 can perform this task.  If you use a precision 1Ω resistor, the output voltage would be on the order of mV to µV, which is in the measurement range of the U6. 4000 samples per second requires streaming, so your settings should be as follows:

 

Connect the 1Ohm resistor in series with the micro controller supply line

Wire AIN0 to the high side of the resistor, and AIN1 to the low side of the resistor.

Stream-Mode Settings
1x Analog input (AIN0, with AIN1 set as the negative channel)

Range = ±1V

Resolution Index = 2  (maximum of 4000 samples/sec), use Res index=1 for 4400 samples/sec

 

These settings will give you an effective resolution of 34µV, so that you can accurately measure current down to about 50µA.  If you need to measure lower current, you can also upsize the resistor slightly, to ~5Ohms, but then you might exceed the ±1V range configuration if your current is above 200mA.

(0.000050A * 1Ω) = 50
µV

 

Edit: Support links
http://labjack.com/s...uide/appendix-b
http://labjack.com/s...users-guide/3.2
 




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