The compressors for air conditioners require high efficiency and reliability. A rotary compressor usually has several micron-size gaps , which may deteriorate its efficiency and/or reliability ; therefore, it is necessary to figure out the behaviors of such gaps while the compressor is in motion, as the first step in developing them. Since the rotary compressors for air conditioners are small, it is difficult to install commercially available sensors to them to measure the gaps. Even it can be done, those sensors may have unacceptable measurement errors due to the temperature drift, because they are placed in the severe refrigerant and oil environment. Consequently, it is need to develop a new advanced sensor for those measurements. This paper describes the newly developed eddy current gap sensor, which is compact-size, heat-resisting and has less temperature drift. Furthermore, the dynamic behavior of the gaps of a rotary compressor in operation is also described, which was measured by it. Each gap was found to be smaller than the pre-estimated designed value. It also tuned out that one of factors was the deformation caused by the cylinder pressure.
