Capacitance sensor complementary excitation and linear detection circuit for oil detection

Abstract

The invention relates to a capacitance sensor complementary excitation and linear detection circuit for oil detection, belonging to the detection technical field. The circuit is composed of capacitive sensor, reference capacitor, current detection resistor, integrated operational amplifier and other components. The value of the reference capacitor is equal to the capacitance value of the capacitive sensor when no oil is sensed; the capacitive sensor is connected in series with the reference capacitor, and its common The terminal is connected to the inverting input terminal of the operational amplifier, and the two non-common terminals are respectively connected to two AC excitation signals with equal amplitude and opposite phase; the current detection resistor is connected between the inverting input terminal and the output terminal of the operational amplifier. The non-inverting input terminal of the amplifier is grounded; the voltage at the output terminal of the operational amplifier is the detection result signal whose amplitude is linearly related to the sensor capacitance variation. The invention can linearly detect the capacitance variation of the capacitance sensor, has simple circuit, high sensitivity, good stability, wide dynamic range and strong anti-interference ability, and is very suitable for capacitance sensing detection of oil properties.

Description

technical field [0001] The invention belongs to the technical field of detection, and in particular relates to a detection circuit which excites a capacitance sensor in a complementary excitation mode and linearly detects the capacitance variation of the sensor. Background technique [0002] Oil is a very complex mixture, and it is a very challenging task to detect its various parameters and properties. The application of various new sensing technologies, detection technologies and other new technologies in oil detection is also a field of oil detection. research focus. The capacitive sensor detects the external parameter according to the change of the capacitance value of the sensor caused by the effect of the external parameter. It has the characteristics of simple structure, fast dynamic response, strong environmental adaptability, high working reliability, and average effect. Using capacitive sensors to detect oil related parameters has many special advantages that cann...

AI Technical Summary

Problems solved by technology

[0010] For example, for figure 1 and figure 2 These two common AC bridge measurement methods have the following disadvantages: First, due to the reference capacitance C in the two arms R (or sampling resistor R) and sensor C X (=C R +ΔC) series pressure divider effect, so that the sensor C X The actual excitation voltage that it bears is higher than the driving voltage of the bridge Much smaller, which reduces the detection sensitivity of the measurement circuit; the second is due to the excitation not directly added to the sensor C X At both ends of the sensor, the influence of wire resistance, distribution parameters and interference will cause the sensor C X The excitation voltage endured is unstable; the third is the output of the two arms and The values ​​are relatively large, and the useful signal (that is, caused by the effect of the measured parameter C X Changes in ΔC caused by or The amount of change) is very small, which greatly limits the dynamic detection range and resolution of the sensor circuit; the fourth is the output of the detection circuit U · O = U · O 1 - U · 02 values ​​are very small (for figure 1 : U · O = Z C R Z C R + Z C X U · i - Z C X Z C R + Z C X U · i = Δ C 2 C R + Δ C U · i ; right figure 2 : U · O = Z R Z R + Z C X U · i - Z R Z R + z C R U · i ≈ j ω R · Δ C jωRC R + 1 U · i , ω is the frequency of the excitation signal), the detection resolution is low, and at the same time The relationship between ΔC and ΔC is nonlinear, and the linearity is poor; fifth, for these two detection schemes, the existence of distributed capacitance will affect and Thereby reducing the stability and accuracy of the detection results; Sixth, the output impedance of the circuit is high, and the ability to drive the subsequent conditioning circuit is weak

[0012] From the above analysis, it can be seen that the currently commonly used capacitive sensor excitation and detection schemes cannot meet the various requirements of oil detection applications, and new excitation and detection schemes are needed to overcome the existing shortcomings.

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