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Due to its simple structure and the absence of flow-blocking components inside, the electromagnetic flowmeter is widely used for measuring the volumetric flow rate of water, water-coal slurry, and pulp. The output signal from electromagnetic flowmeter sensors often contains a large amount of noise: differential interference, in-phase interference, harmonic interference, flow noise, slurry noise, common-mode interference, and differential-mode interference. Among them, thermal noise and flow noise exhibit low-frequency random drift, causing changes in the bias of the sensor’s output signal, a phenomenon known as bias interference. Generally, in the sensor output signals, the amplitude of the flow signal from the electromagnetic flowmeter is much smaller than the amplitude of the bias interference. If the flow signal with bias is amplified directly, the operational amplifier will saturate, preventing further processing and causing the electromagnetic flowmeter to fail to function properly. The traditional solution is to perform pass filtering before signal amplification in order to remove the bias amount. However, this leads to reduced sensor dynamics, attenuation of the fundamental frequency of the low-frequency excitation signal, and a decrease in measurement accuracy. To address this issue, a periodic feedback method for drift signals is proposed, which outputs the mean values of the signals under positive and negative excitation as a feedback value to adjust the bias. The Yellow River Instrument Factory studied three methods for bias adjustment: 1. The method of point dynamic complementary correlation, which involves using a sample-and-hold circuit to break down the flow signal generated by a 3-level square wave excitation into two signals with complementary points, thereby enabling point-complementary dynamic correction. 2. The feedback-based signal amplification method performs feedback regulation on the signal when the rectangular wave is excited in the positive or negative direction, thereby adjusting the flow signal to the reference value. This method can dynamically eliminate drift and provide linear gain amplification for weak flow signals, outperforming Method 1). 3. A feedback-based signal processing method for baseline control, which performs baseline feedback adjustment on the signal during the excitation process to adjust the signal at the time of excitation to a set reference value. Method 3) involves making adjustments during excitation, providing more time for processing the positive or negative excitation signals, which helps to improve the accuracy of signal measurement and is superior to Method 2). However, both methods 2) and 3) require sub-bias adjustments within each cycle, which are carried out very frequently. When the signal bias voltage fluctuates rapidly, significant jumps can occur during these bias adjustments, and such interference may affect the measurement accuracy ； When the excitation frequency is low, the signal bias within the same cycle also changes; if only the amplitude of the signal in the current cycle is used for demodulation, errors will be introduced. A bias adjustment method based on threshold control is proposed and implemented in real time on a DSP-based electromagnetic flowmeter signal processing system. This method is applicable to square-wave excitation and three-level wave excitation scenarios; with appropriate signal processing techniques, there is no need to periodically adjust the bias. When the signal is within the threshold voltage range, no bias adjustment is made, which ensures the continuity of the sensor’s output signal and facilitates subsequent processing such as filtering ； When the signal exceeds the threshold, the bias adjustment voltage is output through the DAC to adjust the sensor’s output signal to around 0, and subsequent signal processing methods are improved to eliminate the noise caused by the bias adjustment. For more information, please visit the company’s official website at http://www.yb1518.com/. Please retain this link when reproducing the content! http://www.yb1518.com/UploadFiles/2012717174126829.jpg