The invention provides a partially filled
pipe detection circuit of an
electromagnetic flowmeter. The partially filled
pipe detection circuit comprises a CPU drive
signal waveform transforming circuit, a first-grade passive lowpass filtering circuit, a differential
signal amplification circuit, an
active power filter circuit, and an absolute value transforming circuit. One end of the CPU drive
signal waveform transforming circuit acquires high-frequency pulse signals, and the other end is connected with the first-grade passive lowpass filtering circuit. The first-grade passive lowpass filtering circuit is connected with the differential
signal amplification circuit. A
voltage follower circuit in the
active power filter circuit is connected with a second-order active high-pass filtering circuit. The
differential amplification circuit is also connected with the
voltage follower circuit. The second-order active high-pass filtering circuit is connected with the absolute value transforming circuit. The absolute value transforming circuit outputs detection signals. A [pi] type filter circuit formed by a RC is used in the input end of a differential
operational amplifier, and the [pi] type filter circuit can effectively filter spike
noise caused by liquid flow when pipes are partially filled, so as to reduce interference. The partially filled
pipe detection circuit is advantaged by real-time online monitoring, fast response speed, relatively good
noise inhibiting ability, stable and reliable
detection performance.