阅读说明：本技术 一种差动电容交流电桥传感测控电路 (Differential capacitance alternating current bridge sensing control circuit ) 是由 陈征 李宏 吴立恒 董云开 王文博 于 2020-04-24 设计创作，主要内容包括：本发明提供了一种差动电容交流电桥传感测控电路,包括：交流激励源,在交流信号输出端设置2个反向输出的压控型运算放大器,形成双端差分输出的交流激励源；程控DAC单元为压控运算放大器提供参考电压；通过控制该参考电压,可以改变差分激励源两端信号的幅度,从而使差分激励的中心点发生双向偏移；差动电容传感器由三极板电容构成,两侧极板间距保持不变,中极板可向两侧移动；差动电容传感器的两侧极板分别与差分输出的交流激励源两端相连,形成交流电桥；通过调整差分激励源的中心点,可以使交流电桥达到近平衡状态；此时当中极板发生移动,由此导致的电桥不平衡电压经信号放大、相敏检波、低通滤波后输出,从而将电容中极板的位移转变为电压信号。(The invention provides a differential capacitance alternating current bridge sensing control circuit, which comprises: the alternating current excitation source is characterized in that 2 voltage-controlled operational amplifiers with reverse outputs are arranged at an alternating current signal output end to form a double-end differential output alternating current excitation source; the program-controlled DAC unit provides reference voltage for the voltage-controlled operational amplifier; by controlling the reference voltage, the amplitude of signals at two ends of the differential excitation source can be changed, so that the central point of the differential excitation is subjected to bidirectional offset; the differential capacitance sensor is composed of a three-pole capacitor, the distance between the pole plates at two sides is kept unchanged, and the middle pole plate can move towards two sides; two side electrode plates of the differential capacitance sensor are respectively connected with two ends of an alternating current excitation source of differential output to form an alternating current bridge; the alternating current bridge can reach a near-balance state by adjusting the central point of the differential excitation source; at the moment, the middle polar plate moves, so that the unbalanced voltage of the bridge caused by the movement is output after signal amplification, phase-sensitive detection and low-pass filtering, and the displacement of the polar plate in the capacitor is converted into a voltage signal.)

1. A differential capacitance AC bridge sensing control circuit, comprising: a differential AC excitation source, a program-controlled DAC unit, a voltage-controlled operational amplifier, a differential capacitance sensor and a modulation and demodulation circuit, wherein,

the differential alternating current excitation source is used for generating sine wave signals with required frequency, two output ends of the differential alternating current excitation source are formed by the voltage-controlled operational amplifier, the program-controlled DAC unit provides reference voltage for the voltage-controlled operational amplifier, the differential alternating current excitation source and the differential capacitance sensor form an alternating current bridge, the output end of the differential capacitance sensor is connected with the modulation and demodulation circuit,

the program-controlled DAC unit changes the amplitude of signals at two ends of the differential alternating current excitation source by controlling the reference voltage of the voltage-controlled operational amplifier, so that the central point of the differential alternating current excitation source is subjected to bidirectional offset, the bridge reaches a balanced state,

when the differential capacitance sensor generates a bridge unbalanced signal, the bridge unbalanced signal is output through the modulation and demodulation circuit, so that the displacement of a polar plate in the capacitor is converted into a voltage signal.

2. The differential capacitance AC bridge sensing and controlling circuit according to claim 1, wherein 2 voltage-controlled operational amplifiers with inverted outputs are provided at the AC signal output end of the differential AC excitation source to form a double-ended differential output AC excitation source.

3. The differential capacitance AC bridge sensing and control circuit of claim 2, wherein the programmable DAC unit comprises a programmable component and a DAC element, the programmable component controls the DAC element to provide a reference voltage for the voltage-controlled operational amplifier.

4. The differential capacitance ac bridge sensing and control circuit of claim 1, wherein the differential capacitance sensor is formed by a three-plate capacitor, the two side plates are fixed by ceramic spacers to maintain a constant spacing, and the middle plate can be moved to both sides to generate a bridge imbalance signal.

5. The differential capacitance AC bridge sensing and controlling circuit according to claim 4, wherein said two side plates of said differential capacitance sensor are respectively connected to two ends of an AC excitation source of differential output to form an AC bridge.

6. The differential capacitance ac bridge sensing and controlling circuit according to claim 1, wherein the modulation and demodulation circuit comprises a signal amplification circuit, a phase sensitive detection circuit and a low pass filter circuit.

Technical Field

The invention relates to the technical field of displacement measurement and differential alternating current bridge measurement, in particular to a differential capacitance alternating current bridge sensing control circuit.

Background

A differential capacitance ac bridge circuit is a high-precision measurement circuit, and is often used for displacement measurement. In the prior art, the balance adjustment and measurement and control of the bridge are generally realized by changing the grounding point of the center tap of the ratio transformer or mechanically adjusting the distance between the polar plates of the capacitive sensor. All the above adjustment modes need to introduce a special mechanical adjustment mechanism, an electronic switch component or power, which can increase the hardware cost of the device and introduce certain interference to affect the precision of the measurement circuit.

Disclosure of Invention

Aiming at the defects of the prior art, the differential capacitance alternating current bridge sensing control circuit is provided, a special mechanical adjusting mechanism is not required to be introduced, and the hardware cost is reduced.

The invention relates to a differential capacitance AC bridge sensing control circuit, which comprises: the differential AC excitation source is used for generating sine wave signals with required frequency, two output ends of the differential AC excitation source are composed of the voltage-controlled operational amplifier, the program-controlled DAC unit provides reference voltage for the voltage-controlled operational amplifier, the differential AC excitation source and the differential capacitance sensor form an AC bridge, and the output end of the differential capacitance sensor is connected with the modulation and demodulation circuit,

the program-controlled DAC unit changes the amplitude of signals at two ends of the differential alternating-current excitation source by controlling the reference voltage of the voltage-controlled operational amplifier, so that the central point of the differential alternating-current excitation source is subjected to bidirectional offset, and the bridge reaches a balanced state; when the differential capacitance sensor generates a bridge unbalanced signal, the bridge unbalanced signal is output through the modulation and demodulation circuit, so that the displacement of a polar plate in the capacitor is converted into a voltage signal.

Preferably, 2 voltage-controlled operational amplifiers with inverted outputs are arranged at the alternating current signal output end of the differential alternating current excitation source to form the double-end differential output alternating current excitation source.

Preferably, the program-controlled DAC unit includes a program-controlled component and a DAC element, and the program-controlled component controls the DAC element to provide a reference voltage for the voltage-controlled operational amplifier.

Preferably, the differential capacitance sensor is composed of a three-plate capacitor, the two side plates are fixed through a ceramic gasket, the distance is kept unchanged, and the middle plate can move towards the two sides, so that a bridge imbalance signal is generated.

Preferably, the two side electrode plates of the differential capacitance sensor are respectively connected with two ends of an alternating current excitation source of the differential output to form an alternating current bridge.

Preferably, the modulation and demodulation circuit includes a signal amplification circuit, a phase-sensitive detection circuit, and a low-pass filter circuit.

The invention has the beneficial effects that: the invention does not need to introduce a special mechanical adjusting mechanism, and only sets 2 voltage-controlled operational amplifiers with reverse output at the output end of the alternating current signal through program-controlled electronic elements such as DAC and the like to form an alternating current excitation source with double-end differential output. The program control unit provides reference voltage for the voltage-controlled operational amplifier by controlling the DAC element, and changes the amplitude of signals at two ends of the differential excitation source by controlling the reference voltage of the voltage-controlled operational amplifier, so that the central point of the differential excitation is subjected to bidirectional offset. The polar plates on the two sides of the differential capacitance sensor are respectively connected with the two ends of the differential output alternating current excitation source to form an alternating current bridge. The program control unit can adjust the balance of the bridge by adjusting the output amplitude of the 2 voltage-controlled operational amplifiers with reverse outputs. When the polar plate in the capacitance sensor moves, the middle polar plate moves to cause unbalance of the alternating current bridge, unbalanced voltage is output by the middle polar plate after signal amplification, phase-sensitive detection and low-pass filtering, and therefore displacement of the polar plate in the capacitance can be converted into a voltage signal. Because a special mechanical adjusting mechanism is not required to be introduced, the hardware cost can be reduced, interference is not introduced, and the precision of the measuring circuit can be improved.

Drawings

FIG. 1 is a schematic diagram of a differential capacitance AC bridge sensing control circuit according to the present invention;

fig. 2 is a schematic structural diagram of an ac bridge of the differential capacitance ac bridge sensing and controlling circuit of the present invention.

Fig. 3 is a schematic structural diagram of a differential capacitance sensor of the differential capacitance ac bridge sensing and controlling circuit according to the present invention.

Fig. 4 is a schematic structural diagram of a program controlled DAC unit of the differential capacitance ac bridge sensing control circuit according to the present invention.

Fig. 5 is a schematic structural diagram of a modem circuit of the differential capacitance ac bridge sensing control circuit according to the present invention.

FIG. 6 is a schematic diagram of a phase sensitive detector circuit of the differential capacitance AC bridge sensing control circuit of the present invention.

Detailed Description

The invention is further illustrated by the following examples, which are intended only for a better understanding of the contents of the study of the invention and are not intended to limit the scope of the invention.

Fig. 1 is a schematic structural diagram of a differential capacitance ac bridge sensing control circuit according to the present invention. Fig. 2 is a schematic structural diagram of a program controlled DAC unit of the differential capacitance ac bridge sensing control circuit according to the present invention. Fig. 3 is a schematic structural diagram of an ac bridge of the differential capacitance ac bridge sensing and controlling circuit of the present invention. Fig. 4 is a schematic structural diagram of a differential capacitance sensor of the differential capacitance ac bridge sensing and controlling circuit according to the present invention. Fig. 5 is a schematic structural diagram of a modem circuit of the differential capacitance ac bridge sensing control circuit according to the present invention. FIG. 6 is a schematic diagram of a phase sensitive detector circuit of the differential capacitance AC bridge sensing control circuit of the present invention. The structure of the present invention will be described in detail with reference to fig. 1 to 6.

As shown in fig. 1, the measurement and control circuit of the present invention includes a differential ac excitation source 1, a programmable DAC (Digital-to-analog converter) unit 2, a voltage-controlled operational amplifier 3, a differential capacitance sensor 4, and a modulation and demodulation circuit 5.

The differential alternating current excitation source 1 is used for generating a sine wave signal with a required frequency, and two output ends of the differential alternating current excitation source 1 are composed of 2 voltage-controlled operational amplifiers 3. Specifically, 2 voltage-controlled operational amplifiers 3 with reverse outputs are arranged at an alternating current signal output end of a differential alternating current excitation source 1 to form a double-end differential output alternating current excitation source. The program-controlled DAC cell 2 provides a reference voltage for the voltage-controlled operational amplifier 3. The differential ac excitation source 1 and the differential capacitive sensor 4 form an ac bridge. The differential capacitive sensor 4 is formed by a three-plate capacitor, the two side plates 41 are fixed by a ceramic gasket 43 with stable performance, so that the distance is kept constant, and the middle plate 42 can move towards two sides, thereby generating a bridge unbalance signal (see fig. 4). The two side electrode plates 41 of the differential capacitance sensor 4 are respectively connected with two ends of the AC excitation source 1 with differential output, so that an AC bridge is formed. The output terminal of the differential capacitance sensor 4 is connected to the modulation and demodulation circuit 5.

Based on the structure, the program-controlled DAC unit 2 changes the amplitude of signals at two ends of the differential ac excitation source by controlling the reference voltage of the voltage-controlled operational amplifier 3, so that the center point of the differential ac excitation source 1 is shifted in two directions, and the bridge reaches a balanced state. When the differential capacitor sensor 4 generates a bridge unbalanced signal due to the movement of the middle pole plate, the bridge unbalanced signal is output through the modulation and demodulation circuit 5, so that the displacement of the middle pole plate of the capacitor is converted into a voltage signal.

As shown in fig. 2, the differential ac excitation source 1 may be a high-precision signal generating unit (e.g., an SWR200 chip), and may be connected in series with different capacitors as required to obtain a sine wave signal with a desired frequency. The sine wave signal is output to the input terminals of the first voltage-controlled operational amplifier 31 and the second voltage-controlled operational amplifier 32 (for example, VCA810) via the first operational amplifier 12 as a power amplifier. The signal is connected to the positive input end of the first voltage-controlled operational amplifier 31 and the negative input end of the second voltage-controlled operational amplifier 32, amplified by the two voltage-controlled operational amplifiers 31 and 32, and then outputs two opposite homologous alternating current signals, which are respectively connected to the upper and lower electrode plates of the differential capacitance sensor 4 to form a capacitance bridge.

As shown in fig. 3, the differential capacitance sensor 4 is composed of a three-plate capacitor, the two side plates 41 are fixed by a ceramic spacer 43 with stable performance, the distance d is kept constant, the middle plate 42 can move towards two sides, a differential capacitor (difference between C1 and C2) is formed along with the displacement of the middle plate 42, and the voltage to ground output by the middle plate 42 is the bridge circuit unbalanced voltage formed by the reverse excitation output by the two voltage-controlled operational amplifiers 31 and 32 and the differential capacitor. The voltage-controlled amplification factor of the two voltage-controlled operational amplifiers 31 and 32(VCA810) is controlled by reference voltages VG0 and VG1, and the output voltage of the two voltage-controlled operational amplifiers can be changed within the amplitude range of 0-5V by changing the two reference voltages VG0 and VG 1.

As shown in FIG. 4, the program control DAC unit 2 is composed of a program control part 21 and a DAC element 22, signals of reference voltages VG0 and VG1 are generated by the DAC element 22 (such as a chip L TC2666), L TC2666 can be a numerical control DAC, and is controlled by the program control part 21 (such as a single chip microcomputer 89C2051), the single chip microcomputer sends commands to L TC2666 through an SPI bus, so that VG0 and VG1 generate output changes of 0-5V/DC, and the single chip microcomputer is connected to a user side through a TT L serial port.

In one embodiment, the total voltage applied across the sensor 4 may be constant at 5V so that the voltage balance adjustment does not affect the sensitivity of the measurement circuit, since the supply voltage of the two voltage controlled operational amplifiers 31, 32(VCA810) is ± 5V, so that the single-side maximum voltage output cannot exceed 5V, and since the rated input operating voltage of the DAC element 22 (L TC2666) is also 5V, the voltage controlled operational amplifiers 31, 32(VCA810) also use a 5V supply voltage for matching.

When the bridge is balanced, the unbalanced signal of the bridge is output via the modem circuit 5 as the middle plate 42 is displaced, to convert the displacement of the middle plate of the capacitor into a voltage signal. As shown in fig. 5, the modulation and demodulation circuit 5 includes a signal amplification circuit 51, a phase-sensitive detection circuit 52, and a low-pass filter circuit 53. The amplifying circuit 51 may be a two-stage amplifying circuit.

Fig. 6 shows a schematic diagram of the phase-sensitive detector circuit 52. The unbalanced signal after two-stage amplification output by the electrode plate 42 in the capacitor is divided into a reverse signal by the second operational amplifier 54, and the reverse signal is matched with Q1 and Q2 to form a phase-sensitive detection circuit. Phase shift circuit module 55 and comparator circuit 56 provide reference signals for the phase sensitive detection circuit. The phase shift circuit module 55 extracts the signal Yi from the excitation source output from the first operational amplifier 12, and performs phase shift processing so that the reference signal and the detection signal are in phase. The comparator circuit 56 changes the phase-shifted sinusoidal signal of the phase-shift circuit module 55 into two opposite square waves, controls Q1 and Q2, forms a gate multiplication circuit, and changes the sinusoidal signal into a half-wave sinusoidal signal. Finally, the second-order low-pass filter circuit 53 filters the ac component of the signal, retains the dc amplitude information of the signal, and outputs the signal by a follower (not shown), thereby converting the displacement of the plate in the capacitor into a voltage signal.

It will be apparent to those skilled in the art that the above embodiments are merely illustrative of the present invention and are not to be construed as limiting the present invention, and that changes and modifications to the above described embodiments may be made within the spirit and scope of the present invention as defined in the appended claims.