Novel Principle for Flux Sensing in the Application of a DC + AC Current Sensor

This paper presents a new concept for measuring DC and AC magnetic flux densities within a ferromagnetic material. It is based on a measurement of the material´s magnetostriction, which is its relative change in length due to the magnetic flux density inside the material. This dimensional change is converted to an electrical signal using a piezoelectric strain sensor. An additional sinusoidal AC excitation of the core material provides higher sensitivity of the length measurement and overcomes the inherent high-pass characteristic of the piezoelectric sensor. Therefore, flux density signals from DC to the kilohertz range can be measured. The concept´s feasibility is demonstrated with the design and implementation of an isolated DC + AC current sensor with a measurement range of ±20 A and a bandwidth from DC to 20 MHz.