Why go for one OR the other. Surely a "PowerMeter" contains a collection of "PowerSensors". (amongst other things )
So my "PowerMeter.GetPowerFromSensor(1..n)" would actually be "PowerMeter.GetPowerFromSensor(PowerSensor)".
I would also say you would need a lot of knowledge about the power meter since you probably won't be able to talk to any sensors and it will be the device that contains range, scaling, math functions and probably calibration data (unless the cal is on-board the sensor). So you will need things like PowerMeter.SetRange, PowerMeter.SetSamples, PowerMeter.Calibrate etc, etc. So from my viewpoint, the sensor is just a value. The PowerMeter makes that value meaningful. And PowerMeter, Ammeter, Voltmeter are semantics.