I'm working with an electric resistor (oven resistor) and I want to compute the active power with an embedded system.

My idea is to use a current probe around the phase wire to acquire the current values. I would avoid to acquire the voltage values because this implies the addition of a circuit to sample the voltage.

With the oscilloscope I can compute the active power: V(t) * I(t).

Is it possible to compute the active power only sampling the current? Is it possible to use a sampled voltage period to perform the computation?

Thanks for the help!


1 Answer 1


Yes, it is possible, if the resistance is constant. There are 3 equations for power (W).

P= I^2R = VI = V^2/R

One of these does not use V. There's the one you want. If you have a variable R value, then you may have to also sample the voltage too, unless anyone else has a better suggestion!

  • \$\begingroup\$ thanks for the reply. I will check the resistance value because I don't know if this value remains constant with the temperature or what ever. \$\endgroup\$
    – Federico
    Commented Mar 22, 2018 at 8:18
  • \$\begingroup\$ It will likely change slightly with temperature, but hopefully not too much \$\endgroup\$
    – MCG
    Commented Mar 22, 2018 at 8:22

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