Playing the field

Opposites attract and, in this instance, it is a case of old meets new. According to Autonnic Research, the simplicity of magnetics has been given a new lease of life by using the latest processor technology. By measuring magnetic fields, fluxgate magnetometry offers a variety of novel applications. Magnetometers are used to measure the strength of a magnetic field and have been around ever since the discovery that the Earth’s magnetic field could be used as an indicator of where North is. The simplicity of suspending a magnet in the Earth’s field and allowing the torque resulting from misalignment to restore the magnet to the aligned position has much to recommend: simplicity, robustness, easily gimballed, stable and easy to read. Electrical magnetometers are used when a signal is required to measure the angle of a shaft for example. A steady field is not easily measurable as it cannot generate voltage. What was needed was a simple, robust and stable component and, over many years, a form of parametric amplifier called a fluxgate magnetometer has evolved to meet these requirements. Autonnic’s fluxgate magnetometers are ring devices in which the excitation is the circumferential field generated by a toroidal winding to modulate the permeability of the core. This permeability change, in turn, modulates the amount of flux due to the steady field which is threaded through a sense winding around the outside of the ring. The key is that, if you change the flux in the winding, it generates a voltage from the Earth’s field. Most of Autonnic’s magnetometers are made with two sense windings at 90° to each other, so as to be able to resolve the direction of the steady field in the plane of the core.