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Intelligent electromagnetic flowmeter cross-correlation detection is a weak signal detection method that uses signal periodicity and random noise characteristics to remove noise through cross-correlation calculation. If the frequency of the transmitted signal is known, a "clean" local reference signal of the same frequency can be sent at the receiving end, which correlates with the input signal mixed with noise, which can significantly improve the circuit's immunity to interference.
s(r) is the cross-correlation function between S(£) and S(£). When S(£) and S(£) are two periodic functions with the same fundamental frequency, a reasonable choice of delay time f makes the integral The value reaches the maximum; R6. (r) is the cross-correlation function of 2(f) and S2(f). In general, there is no correlation between the reference signal S(£) and noise, z(£), and 52(f) is an exchange The signal has an average value of zero, so the integral value is everywhere zero.
Therefore, for a signal of a known frequency, by selecting an appropriate reference signal and performing a correlation operation, the weak signal can be detected and the interference signals of other frequencies can be shielded. At the same time, the anti-interference ability of the cross-correlation detection is limited by the integration time. The longer the integration time, the stronger the anti-interference ability and the longer the required measurement time.
For a high-frequency excitation capacitive electromagnetic flowmeter, the flow rate of the fluid to be measured changes slowly, so there is enough time to meet the requirements of the relevant operations on time. And the signal of the electromagnetic flowmeter is generated by the alternating magnetic field with the same frequency as the excitation current and has the same frequency as the excitation current. With rectangular wave excitation, the reference signal can be obtained from the excitation control signal. In general, various noises in the fluid and the interference introduced in the circuit are not related to the reference signal. Therefore, a cross-correlation detection method may be used to detect the flow signal in a strong noise background.
s(r) is the cross-correlation function between S(£) and S(£). When S(£) and S(£) are two periodic functions with the same fundamental frequency, a reasonable choice of delay time f makes the integral The value reaches the maximum; R6. (r) is the cross-correlation function of 2(f) and S2(f). In general, there is no correlation between the reference signal S(£) and noise, z(£), and 52(f) is an exchange The signal has an average value of zero, so the integral value is everywhere zero.
Therefore, for a signal of a known frequency, by selecting an appropriate reference signal and performing a correlation operation, the weak signal can be detected and the interference signals of other frequencies can be shielded. At the same time, the anti-interference ability of the cross-correlation detection is limited by the integration time. The longer the integration time, the stronger the anti-interference ability and the longer the required measurement time.
For a high-frequency excitation capacitive electromagnetic flowmeter, the flow rate of the fluid to be measured changes slowly, so there is enough time to meet the requirements of the relevant operations on time. And the signal of the electromagnetic flowmeter is generated by the alternating magnetic field with the same frequency as the excitation current and has the same frequency as the excitation current. With rectangular wave excitation, the reference signal can be obtained from the excitation control signal. In general, various noises in the fluid and the interference introduced in the circuit are not related to the reference signal. Therefore, a cross-correlation detection method may be used to detect the flow signal in a strong noise background.
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