Power electronics remains an emerging technology. Two important factors in power electronics system are the switching speed of the devices and the total power loss in the system. If the switching speed can be increased ,improvements may be possible i.e. current ripples in an electrical machine or physical size of passive components may be reduced. Increased switching speed may cause additional losses in a power electronics system and increase the system cooling requirement. A common problem is that high-frequency phenomena like proximity effect, skin effect, hysteresis losses ,and eddy current losses appear in the systems. these losses are very difficult to treat . It is often difficult to measure the effect of increasing the switching frequency electrically because the system efficiency is high and a pure input-output measurement gives an unsatisfactory resolution and accuracy. A promising solution is to use a calorimetric measuring system. Two calorimetric wattmeter systems have been designed and built. One system is useful for low-power measurement (<50 W ),and the other system can measure upto 1.5 KW power losses. A rotating load is provided on this system. Demands and specifications of the two systems are described in this topic.