High-precision absolute measurement, not only with high precision, but also overcome the “tracking error” or “can not detect the absolute position” and other traditional contact sensors; main and expansion controller cascade, saving wiring, the main module can provide power for the expansion module The main module can provide power for the expansion module, the expansion module does not need to be separately energized, which further saves wiring; easy to read the data. 1 main module connects to up to 14 expansion modules, realizes bulk data communication and calculation, and outputs the real value immediately after powering on the device.