| Abstract |
A flow calorimetric system is proposed which measures the temperature rise of the air across the
room of the device under test. The mass flow of the air is stabilised by controlling a fan in such way,
that the temperature rise of a known dissipation is kept constant. The efficiency of power electronic converters is continuously increasing. The current and voltage
waveforms contain frequencies that can disturb a wattmeter. This is in particular true for variable
speed drives. The output voltage of frequency converters contains indeed slopes up to 20V/ns, which
reduce the accuracy of a wattmeter. The accuracy of a wattmeter is also limited due to the fact that
two similar values are subtracted. With an efficiency of 95% and a wattmeter accuracy of 1%, the
accuracy for the losses is only about 40%. A calorimeter based direct loss measurement can be much
more accurate. Calorimeters are mentioned as a possible method for magnetic materials [1], inductors
[2], for transformers [3], as a method for measuring motor losses [4] and for general apparatus and systems [5] [6]. |
