Very low frequency active filter (5G28) circuit diagram

As shown in the figure is a very low frequency active filter circuit . This is a Butterworth fourth-order active low-pass filter, suitable for filtering out very low-frequency random impulse noise interference voltage on DC level signals. Its cut-off frequency (-3dB) is about 8Hz. At 18Hz, the gain drops by 20dB. . The inherent attenuation within the passband is 0.467. The input resistance is approximately 40kΩ. The filter network resistors are made of several metal film precision resistors connected in series. If the 1μF capacitor can achieve considerable accuracy, the cutoff frequency fc is close to the theoretical value.