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NI PXIe-4154 Conflicting Measurements -- Smartphone and USB

I am having some problem to calculate power consumption from android smartphone...

First my setup: Android smartphone is connected to PC with USB. Both smartphone and USB do not provide their own power, but instead, I provide power to them via PXIe-4154. To clarify, smartphone's battery is removed and replaced with probes from ch0, and red power wire on USB cable is cut and end going toward smartphone is connected to probes from ch1 (ground wire is connected as well). Also, ch0 is set to 4.1V and ch1 is set to 5V.

 

My problem now is to try to find right method to calculate power and energy usage in this setup for smartphone alone (without effect of USB). My initial calculation of power and energy (with USB connected) turned to be wrong when I tried to perform same measurements without USB (ch0 only) (which were different by a good degree). I still hope I can try to calculate corrent power that is used by smartphone alone based on current configuration (and current samples that I have). (I am using USB mostly because of convenience, since it allows me to control android smartphone with ADB commands, over USB).

 

Here are some of my measurements (with USB and without, which conflict): When I have USB connected, idle current from ch0 is -0.28A and active current is -0.1A (when I run my test task). At the same time, idle current on ch0 is 0.37, and active current is 0.405A. When I tried to perform same measurement without USB (I sent command for the task over wireless connection), my idle current on ch0 is 0.022A and active current is 0.28A. What I can't understand is why I seeing difference in delta current (0.17 + 0.035 vs 0.258).

 

Also, when I turned off the phone, currnet on ch0 is -0.345A and current on ch1 is 0.382A.

I am not sure if my PXIe board is configured incorrectly, or why would I get such conflicting results. Could anything give me some advise what I could try to do to solve this?

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Hi armendhz, 

 

I have a few questions that may help clarify your situation for me. 

 

1) Where are you getting your current readings?

2) How are you measuring a current when the phone is turned off? 

3) Do you have any other PXI modules? 

4) Can you attach a schematic of your connections for me? 

 

Hopefully we can get to the bottom of this soon. 

 

 

 

Best Regards,

Thomas B.
National Instruments
Applications Engineer
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