A sigma–delta fluxgate magnetometer for space applications

• Published in: Measurement science & technology 2003-07, Vol.14 (7), p.1003-1012
• Main Authors: Magnes, W, Pierce, D, Valavanoglou, A, Means, J, Baumjohann, W, Russell, C T, Schwingenschuh, K, Graber, G
• Format: Article
• Language: English
• Subjects: Exact sciences and technology; Instruments, apparatus, components and techniques common to several branches of physics and astronomy; Magnetic components, instruments and techniques; Magnetometers for magnetic field measurements; Physics
• ISSN: 0957-0233; 1361-6501
• DOI: 10.1088/0957-0233/14/7/314

This paper describes the concept and development of an innovative combination of conventional fluxgate magnetometer readout electronics with the control loop of a sigma-delta modulator in order to achieve a new magnetometer design that provides direct digital output without the use of a separate analogue-to-digital converter chip. The new concept is especially aimed at the measurement of extraterrestrial magnetic fields within a dynamic range of approximately +or-2000 nT aboard scientific space missions which are affected by high radiation doses. A digital domain model of the new magnetometer electronics is presented, which is essential for a successful hardware implementation, and the test results of a single-axis prototype are discussed. The test results show that the fluxgate and sigma-delta modulator control loops can be merged for dynamic ranges up to +or-2000 nT without significant deterioration of the overall performance of the magnetometer. The remaining quantization noise in the signal bandwidth (10 Hz) was minimized to below the sensor's noise level (7 pT Hz]-]1] /]2 at 1 Hz) due to the noise-shaping effect of the sigma-delta principle. An offset stability of 0.25 nT over four days was achieved and the linearity error is less than +or-3.3 x 10]-]5 even though the fluxgate sensor is not kept at near-zero field as for traditional fluxgate magnetometers. A technological model of this new fluxgate magnetometer concept will be built for a test flight aboard the NASA discovery mission DAWN.