Intelligent Elimination Technique For Power Line Interference From Electrocardiogram

Power line interference is an unavoidable problem in the measurement of electrocardiogram signals. In this artical, digital control technique was used in the field of electrocardiogram measurement, an intelligent system based on the embedded system was successfully accomplished and had overcome the interference of electrocardiogram signals. With the kernel of SCM Epson 33209, besides the function of electrocardiogram signals measurement, it had functions of skin-electrode impedance matching automatically and drive-right-leg circuit phase compensation. The imbalance of skin-electrode impedance will alter common mode interference to different mode interference. At present, the only remedy is skin preparation and adding gel to reduce the degree of its mismatch. A method for skin-electrode impedance automatic matching was presented based on the system analysis of the body and the measurement device. Skin-electrode impedance balance was approached through a circuit for automatic matching and gradual approximation optimization algorithm. The drive-right-leg circuit is often used to reduce common mode interference. Considering system stability, the cut-off frequency of the drive-right-leg amplifier is lower. Consequently, not only the high-frequency interference mitigate ability is depressed, but also the power line interference mitigate efficiency is influenced for the phase shift introduced by the capacitances. This thesis s presented an improved drive-right-leg circuit. Drive-right-leg signal phase compensation was accessed by three steps: acquiring the drive-right-leg amplifier's output signal and converting it to digital signal, digital signal processing, feeding back the processed signal to the right leg through DA conversion and filter net at last. Experiments showed that the skin-electrode impedance automatic matching method in this article could reduce the power line interference to the original's 2/3-1/3 while the improved drive-right-leg circuit could reduce it to 1/2. According to principle of superposition in a linear system, the intelligent system could depress the interference to its 1/3-1/6 and the total effect was excellent.