Linearity of Pulse Excited Coil-Less Fluxgate

In this paper, we study the open-loop linearity of pulse excited coil-less fluxgate. Narrow current pulses can be used instead of classical sinewave for the excitation of the coil-less fluxgate. This method has shown several advantages, mainly regarding reduction of power consumption, normally in order of tens of microwatts. The disadvantage is that traditional phase-sensitive detection cannot be used as it results in a very small sensitivity. Using pulse excitation, the output signal is obtained by integrating a part of the positive pulse and a part of the negative pulse, and then summing up the resulting voltages. This process was realized using two boxcar averagers SR 4153. The achieved open-loop linearity error is much higher than for sinewave excitation and it is not sufficient for precise applications. We show that the linearity strongly depends on the symmetry of the two integrating windows. In order to obtain precise timing, we realized an excitation board using PIC microcontrollers, which provides both the pulsing signals for excitation current and the gating signals for integration. Using this board and optimum position of the integrating window, we obtained a 0.6% maximum nonlinearity in plusmn100-muT range, which is sufficient for portable compass.