CN217954572U - Capacitance sensor capable of measuring non-grounded target plate - Google Patents
Capacitance sensor capable of measuring non-grounded target plate Download PDFInfo
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- CN217954572U CN217954572U CN202220694251.4U CN202220694251U CN217954572U CN 217954572 U CN217954572 U CN 217954572U CN 202220694251 U CN202220694251 U CN 202220694251U CN 217954572 U CN217954572 U CN 217954572U
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Abstract
The utility model discloses a capacitive sensor of measurable quantity non-ground connection target board belongs to sensor technical field. The utility model discloses a: the two current sources are used for supplying alternating current, and the current directions of the two current sources are opposite; the two current sources respectively excite the two capacitance sensor circuits; the two probes are used as first electrode plates of the capacitive sensor; the second electrode plate of the capacitive sensor is the same conductor target plate; the second electrode plate and the two first electrode plates form two capacitors to be tested; the target plate is not grounded, and stray capacitance is introduced between the target plate and the circuit ground; the current source forms a voltage drop on the capacitor to be measured, and the voltage drop reflects the size of the capacitor to be measured after passing through the demodulation filter circuit. The utility model relates to a two probe structures with the cooperation of the reverse current source circuit of same width of cloth, realize the electric capacity measurement under the target board non-ground connection condition, be applicable to the unable occasion that realizes effectively connecting of target boards such as high-speed rotation axis.
Description
Technical Field
The utility model relates to a sensor technical field especially relates to a capacitive sensor of measurable quantity non-ground connection target board.
Background
The capacitance sensor is a sensor for measuring based on the change relation of capacitance along with other physical quantities, and the capacitance value C of the capacitor is related to the dielectric constant epsilon between two polar plates of the capacitor, the polar plate area S and the polar plate distance d according to a capacitance calculation formula C = epsilon S/d. By fixing both quantities, the change in capacitance can reflect the change in the other quantity, e.g. by fixing the capacitor plates to both surfaces to be measured, i.e. by measuring the capacitance of the capacitor, the distance between the surfaces to be measured can be measured.
In general, the probe of a capacitive sensor is one plate and the other plate is the side of the probe, and the two plates form a capacitor. Thus, the target plate must be metal when using a capacitive sensor and the target plate must be connected to an electrical circuit, typically circuit ground. However, in some measurement applications, such as high speed rotating parts like measuring shafts, the target plate cannot be grounded, so that capacitance cannot be formed and measurement cannot be completed.
Chinese patent publication No. CN 1551988A discloses a sensor capacitance detection device and a sensor capacitance detection method; the application is in a first operational amplifier OP 1 In the feedback circuit of (3), a capacitor C and an impedance converter H are inserted in series iz An electrode P is connected to a connection point of the capacitor and the inverter via a signal line L 1 . The signal line L passes through a high-resistance resistor R 3 Connected to a reference potential. When a capacitor is inserted into the feedback circuit, the signal line is in a floating state, and the circuit operation becomes unstable, but the signal line L passes through the resistor R 3 Is fixed at a predetermined potential, and therefore, the operation can be stabilized. Alternatively, the impedance converter may be formed by a voltage follower, and the resistor R3 may be connected to the output of the impedance converter. The application realizes accurate measurement of the tiny capacitance, which is similar to the current patent in the problem solving principle, but can not solve the problem that in some measurement occasions, the target plate can not be grounded, so that the shape of the target plate can not be changedCapacitance and measurement is completed.
Disclosure of Invention
1. Technical problems to be solved by the invention
In view of the problems in the prior art described above, the present invention provides a capacitive sensor capable of measuring a non-grounded target plate; the utility model relates to a two probe structures with the cooperation of the reverse current source circuit of same width of cloth, realize the electric capacity measurement under the target board non-ground connection condition, be applicable to the unable occasion that realizes effectively connecting of target boards such as high-speed rotation axis.
2. Technical scheme
In order to achieve the above purpose, the utility model provides a technical scheme does:
the utility model discloses a capacitive sensor of measurable quantity non-ground connection target board, include:
the two current sources are used for supplying alternating current, and the current directions of the two current sources are opposite; the two current sources respectively excite the two capacitance sensor circuits;
the two probes are used as first electrode plates of the capacitive sensor; the second electrode plate of the capacitive sensor is the same conductor target plate; the second electrode plate and the two first electrode plates form two capacitors to be tested;
the target plate is not grounded, and stray capacitance is introduced between the target plate and the circuit ground;
two operational amplifiers;
two demodulation filter circuits;
the current source excites the capacitor to be measured, a voltage drop is formed on the capacitor to be measured, and the voltage drop reflects the size of the capacitor to be measured after passing through the demodulation filter circuit.
Furthermore, the current source is an alternating current source with a constant amplitude, and the amplitude of the two current sources is identical.
The utility model discloses a capacitive sensor of measurable quantity non-ground connection target board, include:
excitation voltage U 0 ；
The transformer T converts the excitation voltage into two paths with the same amplitude and opposite directions, and respectively excites the two capacitance sensor circuits;
the two probes are used as first electrode plates of the capacitive sensor; the second electrode plate of the capacitive sensor is the same conductor target plate B; the second electrode plate and the two first electrode plates form two capacitors C to be tested x1 ，C x2 ；
The target board B is not grounded, and a stray capacitor C is introduced between the target board B and the circuit ground stray ；
Two operational amplifiers;
two demodulation filter circuits;
the excitation voltage and the operational amplifier act together on the capacitor C to be measured x1 ，C x2 And the voltage drop reflects the size of the capacitor to be measured after passing through the demodulation filter circuit.
Furthermore, the negative input ends of the two operational amplifiers are respectively connected with reference capacitors Cref1 and Cref2; the operational amplifier pulls the potential of the negative input end to the instrument ground through negative feedback, the same voltage drop as the alternating current voltage source is formed on the reference capacitors Cref1 and Cref2, the alternating current voltage source, the reference capacitor and the operational amplifier jointly form an alternating current source with constant amplitude, and the current source is arranged on the capacitor C to be measured x1 ，C x2 Creating a pressure drop.
Furthermore, the capacitance values of the reference capacitance Cref1 and the reference capacitance Cref2 are equal.
Furthermore, the two probes adopt the same capacitance sensor sensitive element, and the probes are connected with the main sensor circuit through a coaxial line L.
3. Advantageous effects
Adopt the technical scheme provided by the utility model, compare with existing well-known technique, have following apparent effect:
the utility model discloses a capacitive sensor of measurable quantity non-ground connection target board owing to taken same amplitude of current reversal source and two capacitance probe configuration, can absorb by another electric current source completely after two electric capacity from the electric current that a current source flows out, and measuring circuit need not got back to from the target board to the electric current, therefore the target board need not carry out any connection and can accomplish the measurement. Compare with general capacitive sensor the utility model discloses a it is more convenient to use, is applicable to the unable occasion that realizes effective connection of target boards such as high-speed rotation axis.
Drawings
FIG. 1 is a schematic diagram of an AC current source exciting a capacitive sensor;
FIG. 2 is a specific circuit configuration of FIG. 1;
fig. 3 is a schematic diagram of the capacitive sensor of the present invention in which the target plate is not grounded;
FIG. 4 is a schematic view of one embodiment of FIG. 3;
fig. 5 is a schematic diagram of a capacitive sensor without grounding the target board.
Detailed Description
For a further understanding of the present invention, reference will be made to the following detailed description taken in conjunction with the accompanying drawings and examples.
Example 1
The capacitive sensor has various circuit realization forms, wherein the voltage which is in linear relation with the distance between the polar plates can be directly output by using an alternating current source mode. The circuit is shown in figure 1, the current output by the constant amplitude AC current source passes through the capacitor C to be measured x In the capacitor C to be measured x And the voltage drop is formed, and the voltage is input to a post-stage circuit through a follower for demodulation and output. Where the input impedance of the follower is much greater than C x So that the shunting of the current source over the follower does not affect the measurement of the capacitance.
Wherein, the formula C x The electrode plate area S and the dielectric constant epsilon are constant values, C x As the plate spacing d varies. The amplitude value of the voltage drop formed on the capacitor to be measured by the AC current source with constant amplitude value is
In the formula, the other values except d are fixed values, U and d are in a linear relation, and the distance between the polar plates can be obtained by detecting U. In the circuit of FIG. 1C x The upper polar plate of the sensor is a capacitance sensor probe, the lower polar plate is a target plate, and the target plate needs to be grounded.
FIG. 2 is a view of the tool of FIG. 1In the bulk circuit structure, the operational amplifier pulls the potential of the negative input end to the instrument ground through negative feedback, so that the same voltage drop as the alternating current voltage source is formed on the reference capacitor Cref, and the current passing through the Cref is the alternating current with a fixed amplitude. Meanwhile, the impedance of the input end of the operational amplifier is very large, and shunt is not formed at the input end; the AC voltage source, the reference capacitor and the operational amplifier form an AC current source with a constant amplitude together, and the current source is arranged in the capacitor C to be measured x A voltage drop is formed, and the voltage drop can reflect the size of the capacitor after demodulation and filtering. However, in some measurement applications, such as high speed rotating parts like measuring shafts, the target plate cannot be grounded, so that capacitance cannot be formed and measurement cannot be completed.
In order to solve the above problem, in conjunction with fig. 3, the present embodiment provides a capacitance sensor capable of measuring an ungrounded target plate, including:
two current sources I 1 ，I 2 The two current sources are used for supplying alternating current and have opposite current directions; the two current sources respectively excite the two capacitance sensor circuits;
the two probes are used as first electrode plates of the capacitive sensor; the second electrode plate of the capacitive sensor is the same conductor target plate; the second electrode plate and the two first electrode plates form two capacitors to be tested;
the target board B is not grounded, and a stray capacitor Cstray is introduced between the target board and the circuit ground;
two operational amplifiers;
two demodulation filter circuits;
the current source and the operational amplifier act together to form a voltage drop on the capacitor to be measured, and the voltage drop reflects the size of the capacitor to be measured after passing through the demodulation filter circuit.
When two opposite current sources are used, the upper plates of the two capacitors in the circuit are probes, the lower plates of the two capacitors in the circuit are the same conductor target plate, the target plate is not grounded, and stray capacitance between the target plate and the ground is Cstray. Due to I 1 And I 2 Same in size and opposite in direction, therefore I 3 And =0. Therefore, the voltage drop across the stray capacitance Cstray is zero, which can be equivalently the targetThe plate is grounded, for two capacitors to be measured, U =2 x pi I0 x d/epsilon/S (the phase difference is 180 degrees), the distances from the two probes to the target plate can be respectively obtained, and the two paths of outputs are not interfered with each other. The displacement measurement of the non-grounded suspension target plate can be realized by using the structure. Theoretically, when I1 and I2 are opposite in direction and have the same size, even if there is no stray capacitance, the two channels can be completely measured independently, but in practice, this condition is difficult to achieve perfectly, and therefore, a larger stray capacitance helps to improve the measurement accuracy.
In the embodiment, because the same-amplitude reverse current source and the double-capacitor probe are adopted, the current flowing out of one current source can be completely absorbed by the other current source after passing through the two capacitors, and the current does not need to return to a measuring circuit from the target board, so that the target board can finish measurement without any connection. Compare with general capacitive sensor the utility model discloses a it is more convenient to use, is applicable to the unable occasion that realizes effective connection of target boards such as high-speed rotation axis.
Example 2
Referring to fig. 4, in this embodiment, a transformer T is used to convert the excitation voltage into two paths with the same amplitude and opposite directions, and respectively excite two capacitance sensor circuits, so that Cref1= Cref2, thereby forming two current sources with the same amplitude and opposite directions. Two capacitors to be measured share one electrode, a small amount of stray capacitance exists between the electrode and the ground, and ideally, the stray capacitance flows through C x1 And C x2 The currents of the stray capacitors are mutually offset, the currents on the stray capacitors are zero, no voltage drop exists, the stray capacitors can be equivalent to target board grounding, and the stray capacitors are equivalent to two independent capacitance measuring circuits. When the two current sources cannot be strictly offset, a larger stray capacitor is helpful for reducing the voltage drop between the target plate and the ground, and the measurement accuracy is improved.
Example 3
In this embodiment, the sensor is designed as shown in fig. 5, the probe includes two identical capacitive sensor sensing elements, which are equivalent to two common capacitive sensors disposed side by side, and the probe is connected to the main sensor circuit through a coaxial line L. The current sources with opposite directions and the same amplitude are used for excitation on a sensor circuit, enough stray capacitance is introduced on a target board and a circuit ground (the required stray capacitance is different according to different precision), and data read from any probe can be used as measured data.
The present invention and its embodiments have been described above schematically, and the description is not limited thereto, and what is shown in the drawings is only one of the embodiments of the present invention, and the actual structure is not limited thereto. Therefore, if the person skilled in the art receives the teaching of the present invention, without departing from the inventive spirit of the present invention, the person skilled in the art should also design the similar structural modes and embodiments without creativity to the technical solution, and all shall fall within the protection scope of the present invention.
Claims (6)
1. A capacitive sensor for measuring a non-grounded target plate, comprising:
the two current sources are used for supplying alternating current, and the current directions of the two current sources are opposite; the two current sources respectively excite the two capacitance sensor circuits;
the two probes are used as first electrode plates of the capacitive sensor; the second electrode plate of the capacitive sensor is the same conductor target plate; the second electrode plate and the two first electrode plates form two capacitors to be tested;
the target plate is not grounded, and stray capacitance is introduced between the target plate and the circuit ground;
two operational amplifiers;
two demodulation filter circuits;
the current source excites the capacitor to be measured, a voltage drop is formed on the capacitor to be measured, and the voltage drop reflects the size of the capacitor to be measured after passing through the demodulation filter circuit.
2. The capacitive sensor of claim 1, wherein said capacitive sensor is configured to measure a non-grounded target plate, and wherein: the current sources are alternating current sources with constant amplitude, and the amplitude of the two current sources is completely the same.
3. A capacitive sensor capable of measuring a non-grounded target plate, comprising:
excitation voltage U 0 ；
The transformer T converts the excitation voltage into two paths with the same amplitude and opposite directions, and respectively excites the two capacitance sensor circuits;
the two probes are used as first electrode plates of the capacitive sensor; the second electrode plate of the capacitive sensor is the same conductor target plate B; the second electrode plate and the two first electrode plates form two capacitors C to be tested x1 ，C x2 ；
The target board B is not grounded, and a stray capacitor C is introduced between the target board B and the circuit ground stray ；
Two operational amplifiers;
two demodulation filter circuits;
the excitation voltage and the operational amplifier act together on the capacitor C to be measured x1 ，C x2 And a voltage drop is formed, and the voltage drop reflects the size of the capacitor to be measured after passing through the demodulation filter circuit.
4. The capacitive sensor of claim 3, wherein said capacitive sensor is adapted to measure a non-grounded target plate, and further comprises: the negative input ends of the two operational amplifiers are respectively connected with reference capacitors Cref1 and Cref2; the operational amplifier pulls the potential of the negative input end to the instrument ground through negative feedback, the same voltage drop as the alternating current voltage source is formed on the reference capacitors Cref1 and Cref2, the alternating current voltage source, the reference capacitor and the operational amplifier jointly form an alternating current source with constant amplitude, and the current source is arranged on the capacitor C to be measured x1 ，C x2 Creating a pressure drop.
5. The capacitive sensor of claim 4, wherein said capacitive sensor is capable of measuring a non-grounded target, and wherein said capacitive sensor comprises: and the capacitance values of the reference capacitor Cref1 and the reference capacitor Cref2 are equal.
6. A capacitive sensor for measuring a non-grounded target as claimed in claim 2 or 5, wherein: the two probes adopt the same capacitance sensor sensitive elements and are connected with a main sensor circuit through a coaxial line L.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202220694251.4U CN217954572U (en) | 2022-03-28 | 2022-03-28 | Capacitance sensor capable of measuring non-grounded target plate |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202220694251.4U CN217954572U (en) | 2022-03-28 | 2022-03-28 | Capacitance sensor capable of measuring non-grounded target plate |
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| Publication Number | Publication Date |
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| CN217954572U true CN217954572U (en) | 2022-12-02 |
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| Application Number | Title | Priority Date | Filing Date |
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| CN202220694251.4U Active CN217954572U (en) | 2022-03-28 | 2022-03-28 | Capacitance sensor capable of measuring non-grounded target plate |
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