By using a double phase lock in amplifier to measure the AC strain, the measurement error can be decreased to 0.4% of the total measurement range.

Full-range capacity stepless control is one of the methods of capacity regulating for reciprocating compressor, and it possesses economic, safe and well-fixing character.

While complex spectral OCT can not only (eliminate) ambiguities noise and improve the images resolution, but also realize valid measuring depth in full range.