Power meters on the engine input and torque transducers on the engine output have traditionally been used to determine the energy conversion efficiency of electric motors and are still in use today. The difference between the measured electrical power and the mechanical output generated from it by the electric motor is the energy loss.
However, reliable conclusions regarding the causes of energy loss cannot be drawn in this manner. In addition, measuring instruments, often from different manufacturers, must be tediously synchronized before each test. That takes time. More often, the process ends in measurement errors. Highly dynamic power measurements with more than 50 measurements per second are difficult due to technical demands.
Another shortcoming of commercially available power meters is that they only supply final results; however, it is precisely this raw data that provides such rich knowledge that is critical for understanding the processes involved in fundamental research and leads to productive approaches in boosting efficiency.