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378 Views
Registered: ‎02-24-2019

Power measurement

Hi,

I am working on Zedboard and I have implemented a partial reconfiguration project on zedboard. I used vivado power estimator to estimate power consumption. My next target is to use Teledyne oscilloscope to measure the power on the zedboard. 
It has been documented that one can measure the power by using j21 (which is a current sense) and it straddles the shunt resistor R292 which is available on the board. I tried using that for my measurement but somehow it is not giving me the required results. if i connect a single pin of the current sense with one of the probe of the scope and the other with the ground, i get 12 volts reading.

Please guide me how should i take measurements so that i get power consumption correctly of the board after and during programming? Waiting for the response. Thanks in advance.

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8 Replies
Scholar drjohnsmith
Scholar
370 Views
Registered: ‎07-09-2009

Re: Power measurement

Power is meassured by volts dropped across the resitor ,

W = V * V / R

Easiest to use a volt meter to measure the volts across the resistor, as th evolt meter is floating , no ground conection like a scope.

  

 

 

 

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362 Views
Registered: ‎02-24-2019

Re: Power measurement

I think i did not make myself clear. There are two pins that measures the current across the resistor i am talking about. With either of the pin, i get 12 volts with the ground. and if i connect them with the proble, together, without the ground, i get 0 volts. Obviously i know the formula that you have suggested in your post but the point is if i am getting zero volts, it means power is zero (according to formula) and that is not possible. 
What i meant was, i am unable to measure the volts drop acorss the resistor. Is there any way to meausre the voltage drop across the resistor?

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Scholar drjohnsmith
Scholar
351 Views
Registered: ‎07-09-2009

Re: Power measurement

Have a think

 

What is the resitor value ?  say 10 mOHM

   what is the current your expecting, say 1 Amp,

          So what sort of voltag edrop across the reisistor would you expect ?

Now think , would you see that on top of the12 volts ? 

  

Use a multimeter across the resistor...

 

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311 Views
Registered: ‎02-24-2019

Re: Power measurement

I totally understand your point Sir. Before physically taking readings, i used vivado power estimator and according to that i should atleast get 50 to 80 milivolts voltage drop across my resistor. By using multimeter, i only get 2.5 mvolts. which i think is noise and not the correct measurement. Please guide me in this regard. 

 

 

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Scholar drjohnsmith
Scholar
299 Views
Registered: ‎07-09-2009

Re: Power measurement

so what value is your resistor ?

 

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Scholar drjohnsmith
Scholar
297 Views
Registered: ‎07-09-2009

Re: Power measurement

and whats the power voltage into the reistor ? 12 volts ?

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Scholar u4223374
Scholar
296 Views
Registered: ‎04-26-2015

Re: Power measurement

50mV drop across a 10mOhm resistor = 5 amps. 12V at 5A = 60W. You might pull 60W with a big Virtex chip, but there is no way that the Zedboard's Zynq 7020 could ever be using that much power.

 

2.5mV drop across a 10mOhm resistor = 0.25A. At 12V, that would be equivalent to 3W, which is a pretty reasonable power draw for a Zynq 7020.

 

I think you have mis-interpreted Vivado's power estimator.

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Scholar drjohnsmith
Scholar
288 Views
Registered: ‎07-09-2009

Re: Power measurement

Your dead rigth @u4223374 

 

Sorry I was in teacher mode, trying to get the student to engage as they now call it,

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