Professional technique used for logging power consumption of a DC circuit

Question

I wonder how do the electronics device manufacturing companies log and plot the power consumption plot by time. I would think they sample both voltage and current simultaneously and multiply these two.

But if the data loggers are measuring voltages one needs to add a low value series resistor across the main Vcc line from the supply. But is special way of current to voltage conversion used to measure the current?

This is how I would do it:

Imagine DUT above is a low power device and it consumes power not constant way. And we want to leave it for a day connected to a power supply Vs and log voltage and current data it draws to plot the daily power consumption plot.

So the data acquisition can be done by sampling two channels simultaneously where (Vch1-Vch2)/Rs would give us the current data and Vch2 would give us the voltage data. So the power would be:

P = |(Vch1-Vch2)/Rs| * Vch2

Is that how companies make such a test during prototyping and verification procedure?

Answer 1

Current measurement is mostly converted to a voltage measurement. The reason behind this is that very precise and stable voltages are possible to build based on semiconductor physics (bandgap), but current references with such precision are not available.

There is no need to log two channels. With a difference amplifier a floating voltage can be measured and converted to single ended signal.

DC power supplies have built-in current measurement capability. They accomplish this usually by having a resistor in a feedback loop, so that the voltage drop on this resistor does not alter the output voltage. This resistor can be programmable to alter the resolution (uAs vs As).

Answer 2

The technique used to measure IC current depends on how big the current is. Most often a sense resistor is used, scaled to the appropriate current, and amplified by an op-amp that can accept the common-mode high-side voltage needed.

Power is dynamic for some devices so the current needs to be sampled in real-time and processed to get both an RMS and peak value during operation. A digital scope can do this.

Really large currents at low voltage (like 1V or less) might use a Hall sensor to measure instead of a sense resistor.