The present invention relates to a high-precision impedance detection circuit that can overcome the influence of distributed parameters and
line resistance, which is composed of an
impedance sensor, an integrated
operational amplifier, and a current detection
resistor; during detection, a known excitation
voltage is applied to the measured medium through the sensor, and then the response current of the measured medium is detected; the excitation is connected to the non-inverting input terminal of the first
operational amplifier, and its output terminal is connected to the excitation
electrode of one plate of the sensor through the shielding layer of the shielded wire. The sensing
electrode of the same plate is fed back to the inverting input terminal of the first
operational amplifier through the inner core of the shielded wire; the sensing
electrode of the other plate of the sensor is connected to the inverting input terminal of the third operational
amplifier through the inner core of the triple
coaxial cable, and the excitation electrode is connected to the current detection
resistor through the inner shielding layer of the triple
coaxial cable and then connected to the output terminal of the third operational
amplifier, and its non-inverting input terminal is grounded; on the instrument side, the inner shielding layer of the triple
coaxial cable is connected to its outer shielding layer after being driven by the
voltage follower of the second operational
amplifier; the circuit impedance detection of the present invention has high precision and strong anti-interference ability.