Encoder-Less Acquisition System for Rotating-Coil Measurements

The established approach to rotating-coil measurements involves the integration of the induced voltage signal, triggered by an angular encoder, to re-parameterize the signal from time to the traveled arc length. The encoder is thus deemed necessary to ensure the rejection of speed variation errors. However, the encoder introduces additional constraints on the measurement system design and has limited performance in certain applications, such as field measurements at cryogenic temperatures. This paper presents an alternative method for rotating-coil measurement that does not require an angular encoder. The induction-coil signals themselves are used to reconstruct the rotation speed and the angular position. This is possible thanks to the field quality of particle accelerator magnets, with errors in the range of 10(-4) relative to the main field. The approach also leverages the compensation capabilities of induction-coil magnetometers. A feasibility study and a metrological characterization of a prototype system are presented, which includes phase-shifted coils and measurements of the absolute field orientation.