A novel coordinated detection method for transmissive/reflective sensors against strong in-band interference

Abstract

Accuracy of transmissive/reflective sensors is usually degraded by strong in-band interference, especially those with frequencies very close or even equal to that of the measured signal. To tackle this challenge, this paper proposes a novel detection method including three units: a coordinated modulator (CM), a high-performance analog narrow-band filter (ANBF), and a smart digital filtering algorithm (SDFA). The CM performs a mixed function of amplitude modulation and phase modulation, and is used to control the sensor’s transmitter to circularly transmit the signal modulated according to the coordinated time-sequence requirement from the SDFA. The ANBF has a very narrow passband to make the analog signal sampled by the SDFA only include the measured signal and an in-band interfering component. The SDFA utilizes the properties of odd/even functions and the definitions of power in A.C. circuit to filter out the in-band interfering component, with the coordination of the CM and ANBF. Effectiveness of the proposed method is validated via simulations and laboratory tests setting up based on a real application case of electromagnetic mold level detection under mold-electromagnetic stirring operating condition. Test results show that the proposed method can effectively deal with strong in-band interfering signal with the frequency very close or even equal to that of the measured signal. In the total of 20000 simulation cases, attenuations of in-band interference can exceed −76 dB. Moreover, in the experimental tests under a condition of −40 dB signal-to-noise ratio, measurement errors of the amplitude of the measured signal can be achieved less than 1.88%.