An LVDT is mainly divided into both ac and dc output form, in the form of measuring rebound and the springback. Dc output commonly 0-10 v, 4-20 ma two more see, range from 1 mm to 1000 mm, too big range an LVDT is bad to do. Communication in general use in more harsh environments, usually can use communication under high temperature and high pressure, and then leads to pick up the signal transmitter, the signal transmitting into dc to gather, some devices can communicate directly to collect the signal. Displacement sensor communication conditions of heat-resistant and 55 to 200 degrees Celsius, resistance to water pressure in the highest within 150 mpa,