06-06-2019 01:36 AM
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.
06-06-2019 01:43 AM
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.
06-06-2019 02:16 AM
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?
06-06-2019 03:30 AM
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...
06-13-2019 03:36 AM
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.
06-13-2019 06:19 AM
so what value is your resistor ?
06-13-2019 06:20 AM
and whats the power voltage into the reistor ? 12 volts ?
06-13-2019 06:25 AM
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.
06-13-2019 06:31 AM
Your dead rigth @u4223374
Sorry I was in teacher mode, trying to get the student to engage as they now call it,