Design of an Inductive Long Displacement Measurement Instrument

To enlarge the measuring range of inductive displacement sensor, the proposed displacement measurement instrument consists of four elements: the first is a movable coil with short length supplied with DC voltage. The second is a fixed iron rod acting as a core, its shape is designed carefully and the cross-section is varying along the axis. The third is an iron cover. It works as the external path of magnetic flux. When the coil moves on the rod, the current induced in the coil is proportional to the axis-direction displacement of the iron rod. The last one is a measurement circuit used to transform the current signal to the voltage signal and then processed by a microprocessor. This sensor offers excellent features of smart structure, low cost, large sensing length (1400mm), high accuracy (0.5%) and good linearity. An application of this instrument has been put on use in the underwater displacement measurement of a water station lift-gate control system