JPS6140046B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a displacement detector suitable for use as, for example, a pressure gauge, and particularly to provide a displacement detector that has a simple structure and can be manufactured at low cost.

Conventionally, capacitive displacement detectors have been used as pressure gauges. In a conventional capacitive displacement detector, a diaphragm, for example, is provided as a pressure receiving element at both ends of a cylindrical container, and a connecting shaft is passed between the pressure receiving diaphragms.
A moving electrode is attached to the center of the connecting shaft, and fixed electrodes are held on both sides of the moving electrode insulated from the container, and the capacitance between the moving electrode and one fixed electrode and between the moving electrode and the other fixed electrode are An electrical signal corresponding to the difference in capacitance value is extracted to measure the difference in pressure applied to one pressure receiving diaphragm and the other pressure receiving diaphragm.

In other words, the conventional capacitive displacement detector has the structure of a differential pressure displacement detector. Therefore, even when simply measuring the pressure of gas, liquid, etc., a displacement detector with a differential pressure type structure must be used. A capacitive displacement detector having a differential pressure type structure has a complicated structure, and it is difficult to adjust the initial gap between the moving electrode and the fixed electrode so that they match, resulting in high cost. Therefore, it is uneconomical to use it for the purpose of simply measuring pressure.

An object of the present invention is to provide a displacement detector that has a simple structure and can be manufactured at low cost.

In this invention, there is only one pressure-receiving element and the fixed electrode is only provided on one side of the moving electrode, which simplifies the structure and also makes it easy to set the initial gap between the moving electrode and the fixed electrode. It is configured so that it can be done.

An embodiment of the present invention will be described in detail below with reference to the drawings.

FIG. 1 shows a detection section in one embodiment of the present invention. This example shows an example in which the present invention is applied to a pressure gauge. In the figure, 1 indicates a metal body. This metal body 1 is made by being divided into two parts, a non-pressure receiving part 1a and a pressure receiving part 1b. The non-pressure-receiving portion 1a is constituted by a cylindrical body with a bottom, and has a structure in which the open end surface thereof is closed by the pressure-receiving portion 1a. A through hole 2 is formed in the pressure receiving part 1a at an axial position thereof. The through hole 2 is closed by the pressure receiving element 3, and the inside of the body 1 and the side to be measured are shielded. In this example, a case is shown in which a bellows is used as the pressure receiving element 3. For this reason, both sides of the opening of the through hole 2 are tapered holes with diameters gradually increasing toward the opening surface, and a bellows as a pressure receiving element 3 is installed at the part where the diameter of this taper hole is narrowed to the smallest. One end is attached. One end of a connecting shaft 4 is attached to the inner surface of the other end of the bellows 3. The connecting shaft 4 extends to the center of the body 1, and is supported by a leaf spring 5 at approximately the center of the body 1 so as to be movable only in the axial direction. A moving electrode 6 is attached to the connecting shaft 4.

In this invention, the movable electrode 6 is electrically insulated from the body 1 and attached to the connecting shaft 4. For this reason, in this example, a flange portion and a threaded portion are formed on the connecting shaft 4, and insulating washers 8, 8' are interposed between the movable electrode 6 and the leaf spring 5 between the flange portion and the nut 7 screwed into the threaded portion. A case is shown in which the plate spring 5 and the movable electrode 6 are fixed in a state where they are tightened and electrically insulated from the connecting shaft 4. A boss 6a protruding toward the leaf spring 5 is formed on the periphery of the hole through which the connecting shaft 4 of the moving electrode 6 passes.
A gap is formed between the movable electrode 6 and the plate spring 5, and the plate spring 5 can be freely deformed by this gap. A metal ring 9 is attached to the periphery of the leaf spring 5. The metal ring 9 is an insulating material 10
and 11, and are insulated and fixed within the body 1. The insulating material 11 is the non-pressure receiving part 1a
It is fixed tightly to the bottom of the An annular projection 9a is formed on the metal ring 9, and this projection 9a is brought into contact with the insulating material 11. Depending on the amount of protrusion of the protrusion 9a, the metal ring 9 and the first and second fixed electrodes 12,
I am trying to set a gap between 13 and 13. The insulating material 10 is housed in an annular notch formed in the pressure receiving portion 1b and is pressed against the metal ring 9 via the spring 10a. In this way, the leaf spring 5, the moving electrode 6, and the metal ring 9 are insulated and supported within the body 1.

In the present invention, first and second fixed electrodes 12 and 13 are further provided opposite one surface of the movable electrode 6. These first and second fixed electrodes 12 and 13 are formed on the surface of the insulating material 11. 1st
The fixed electrode 12 has a disk shape, and its entire surface faces the movable electrode 6. The second fixed electrode 13 is ring-shaped and faces a part of the periphery of the movable electrode 6 and the metal ring 9 while straddling the same. The moving electrode 6 and the first and second fixed electrodes 12 and 13 are connected to airtight terminals 14 and 15, respectively.
16 to the outside of the body 1. The first and second fixed electrodes 12 and 13 are connected, for example, through conductive patterns 12a and 13a formed on the same surface of the insulating material 11 as the first and second fixed electrodes 12 and 13, as shown in FIG. It is connected to airtight terminals 15 and 16.

A through hole 1d is formed in the closed end surface 1c of the non-pressure receiving portion 1a of the body 1, and a through hole is also formed in the insulating material 11 in communication with the through hole 1d. A diaphragm 17 is stretched on the outer surface of the body 1, and a sealing liquid such as silicone oil is sealed in the cavity formed between the pressure receiving element 3 and the diaphragm 17, and the capacity changes within the body 1 as the pressure receiving element 3 expands and contracts. It is made to absorb by expansion and contraction of 17. The diaphragm 17 also absorbs changes in the volume of the sealing liquid due to temperature changes.

As described above, according to the structure of the detection section of the displacement detector according to the present invention, the pressure-receiving element 3 only needs to be provided on one side, so the number of parts can be reduced accordingly, and it can be manufactured at low cost. However, since the fixed electrodes 12 and 13 are provided only on one side of the moving electrode 6, the initial gap between the moving electrode 6 and the fixed electrode 12 can be uniquely set, and the setting is easy. can be done. Therefore, since the structure is simple and adjustment is easy, the overall advantage is that it can be manufactured at a lower cost than conventional differential pressure type pressure gauges.

Furthermore, according to the present invention, since the moving electrode 6 and the metal ring 9 are insulated from the body 1, the structure of the converter that converts the moving amount of the moving electrode 6 into an electrical signal corresponding to the amount of movement of the moving electrode 6 can be simplified.

In other words, in the conventional differential pressure type displacement detector, the moving electrode is attached to the body in a conductive state. On the other hand, in a displacement converter that converts the amount of movement of a moving electrode into an electrical signal, an oscillator generates an alternating current signal, and the alternating current signal is applied between the moving electrode and the fixed electrode. The amount of movement of the moving electrode is determined from the current value of the difference. For this reason, since the movable electrode is fixed to the body, the movable electrode is strongly electrically connected to a common potential point, so that the output of the oscillator cannot be directly connected to the movable electrode. For this reason, it is necessary to insert a transformer or the like between the oscillator and the movable electrode to provide DC insulation, which has the disadvantage of complicating the circuit configuration of the converter.

Therefore, according to this invention, since the movable electrode 6 and the metal ring 9 are mounted insulated from the metal body 1, there is no need to insert a transformer or the like between the oscillator and the movable electrode 6, and the circuit configuration of the converter can be simplified accordingly. can be simplified.

FIG. 3 shows an example of the converting section in the displacement detector of the present invention. According to this converter, it is possible to obtain an electrical signal proportional to a change in pressure applied to the displacement detector. That is, according to the displacement detector according to the present invention, the movable electrode 6, the metal ring 9, and the fixed electrode 1
2 and 13 can be represented as shown in FIG. In Figure 4
C ₁ indicates a first variable capacitance section formed between the second fixed electrode 13 and the movable electrode 6 and metal ring 9, and C ₂ indicates a first variable capacitance section formed between the movable electrode 6 and the first fixed electrode 12. A second variable capacitance section is shown. The first variable capacitance section C ₁ has a variable capacitance C _x formed between the moving electrode 6 and the second fixed electrode 13 and a fixed capacitance C _s formed between the metal ring 9 and the second fixed electrode 13 .
It consists of a parallel circuit with Here, assuming that the opposing areas between each electrode are equal to each other and S ₀ , the initial gap between the moving electrode 6 and the first fixed electrode 12 is
Suppose that the moving electrode 6 is displaced by Δd due to d ₀ and pressure P, then C ₁ =C ₀ +C ₆ d ₀ /d ₀ −Δd (1) C ₂ =C ₀ d ₀ /d ₀ −Δd…… (2) becomes. Therefore, either the capacitance value C ₀ +C ₀ d ₀ /d ₀ -Δd of the first variable capacitance section C ₁ or the capacitance C ₀ d ₀ /d ₀ -Δd of the second variable capacitance section C ₂ is extracted using an electrical signal. The electrical signal also changes according to C ₀ d ₀ /d ₀ −Δd. For this reason, the relationship between the pressure change ΔP and the electrical output is non-linear, resulting in a disadvantage that the display becomes difficult to read. Further, even if the difference between these first and second variable capacitors C ₁ and C ₂ is extracted as an electrical signal, the difference is constant and it is not possible to obtain an electrical signal corresponding to a change in pressure.

However, by using the transducer shown in FIG. 3, it is possible to obtain an electrical output that varies linearly with changes in pressure.

In this example, an oscillator that applies an alternating current signal to the first variable capacitor C ₁ and the second variable capacitor C ₂ is provided, and a signal flowing through the second variable capacitor C ₂ is extracted so that the signal is always constant. A control means is provided for controlling the output amplitude of the oscillator.

That is, in FIG. 3, 18 indicates the detection section explained in FIG. 1. The first variable capacitance section C ₁ and the second variable capacitance section C ₂ are connected between the terminals 14-16 and 14-15 of the displacement detector 18 as explained in FIG.
A series circuit of a diode D 1 and a resistor R ₁ is connected between the terminal 16 of the detection unit 18 and the common potential point 19, and a diode D ₂ and a resistor R ₁ are connected between the terminal 15 and the common potential point 19. Connect ₂ series circuits. The output terminal of the oscillator 20 is connected between the terminal 14 of the displacement detector 18 and the common potential point 19, and the first variable capacitance section
An alternating current voltage is applied across each of a series circuit consisting of C ₁ - diode D ₁ - resistor R ₁ and a series circuit consisting of second variable capacitance section C ₂ - diode D ₂ - resistor R ₂ . . Therefore, the first variable capacitor C ₁
The alternating current flowing through the second variable capacitance section _C2 is half-wave rectified by the diodes _D1 and _D2 , respectively, and the resistors _R1 and _R2 are connected to the first variable capacitance section _C1 and the second variable capacitance section C2. A voltage proportional to the capacitance value of ₂ is generated. Note that the terminals 15 and 16 of the detection unit 18 are connected to diodes D ₁ ,
One ends of diodes D ₃ and D ₄ facing opposite to D ₂ are connected, and the other ends of these diodes D ₃ and D ₄ are commonly connected and connected to a common potential point 19 through a resistor R ₃ . A circuit consisting of these diodes D ₃ and D ₄ and the resistor R ₃ constitutes a circuit that discharges the charges stored in the first variable capacitor C ₁ and the second variable capacitor C ₂ , and the resistor R ₁ and _R2 so that, for example, a positive half-cycle half-wave rectified current flows through them. Further, capacitors C ₃ , C ₄ , and C ₅ are connected in parallel to the resistors R ₁ , R ₂ , and R _{3 ,} respectively, to smooth the half-wave rectified voltage generated in the resistors R ₁ to R ₃ .

This conversion section is provided with a control means 21 that detects an electrical signal corresponding to the capacitance of the second variable capacitance section _C2 and controls the amplitude of the output of the oscillator 20 so that the detected signal always has a constant value. This control means 21 can be constituted by an operational amplifier 22 that compares and calculates the DC voltage generated across the resistor R ₂ with the reference voltage E ₀ . That is, the voltage generated across the resistor R ₂ is supplied to, for example, the inverting input terminal of the operational amplifier 22, and the reference voltage E ₀ is supplied from the reference voltage source 24 to the non-inverting input terminal of the operational amplifier 22. The output of the operational amplifier 22 is connected to the amplitude control terminal 20 of the oscillator 20.
supply to a.

In the above configuration, when pressure is applied to the displacement detector 18, the capacitance value of the second variable capacitance section _C2 increases. Therefore, the current flowing through the resistor _R2 increases and the voltage _e2 increases. As a result, the output of the operational amplifier 22 constituting the control circuit 21 is biased toward the negative polarity, and the output amplitude of the oscillator 20 is controlled in the direction of decreasing. When the output amplitude of the oscillator 20 is narrowed down, the resistor
The voltage e ₂ generated across R ₂ decreases and eventually stabilizes at a state where the voltage e ₂ is equal to the reference voltage E ₀ , e ₂ =E ₀ . In this state, the voltage e ₁ generated across resistor R ₁ is connected to resistor R ₄ ,
A two-wire transmission line 27 is formed by a voltage-current conversion circuit composed of R ₅ , R ₆ , R ₇ , R ₀ , a potentiometer VR ₁ , an operational amplifier 25 , and a transistor 26 as an output current control element. -27, _{the output current I0 can} be changed in proportion to the displacement amount Δd of the moving electrode 6.

The reason will be explained in more detail. 1st and 2nd
The current flowing through variable capacitors _C1 and _C2 is a diode
It is half-wave rectified by D ₁ and D ₂ and smoothed by capacitors C ₃ and C ₄ . At this time, the currents flowing through the resistors R ₁ and R ₂ are as follows: i=a・E・ωC ₁ , i ₂ =a・E・ωC ₂ (3). Note that a is a constant, ω is the angular frequency of the oscillation signal of the oscillator 20, E is the amplitude of the oscillation signal, and therefore the resistor
The voltages e ₁ and e ₂ generated at R ₁ and R ₂ are e ₁ = R ₁ i ₁ , e ₂ = R ₂ i ₂ (4) e ₂ is set by the oscillator 20 so that e ₂ = E ₀ . The amplitude E of is controlled. In this state, the voltage _e1 generated across the resistor _R1 is converted into an output current _I0 by the voltage-current conversion circuit. Taking the potential of the voltage-current conversion circuit as the potential of the common potential point 19, V−e ₁ =−αE _f ………(5) E _f =−R ₁ I ₀ +E ₁ ………(6) However, It is assumed that the resistance values of resistors R ₄ , R ₅ , R ₆ , and R ₇ are all equal. Here E _f is a potentiometer
Indicates the voltage applied across VR ₁ , α is the voltage division ratio at potentiometer VR ₁ , and V is the power supply voltage.
Further, the potentiometer _VR1 is used to set the span of the voltage-current conversion circuit.

From the above relational expression, if R ₁ = R ₂ , then e ₁ /e ₂ = R ₁ i ₂ /R ₂ i ₂ = a・E・ωC ₁ /
a・E・ωC ₂ = C ₁ / C ₂ = 2-Δd/d ₀ , so e ₁ = (2-Δd/d ₀ ) E ₀ ………(7) (5), (6), (7 ) From the formula, V-(2-Δd/d ₀ ) E ₀ = αR ₀ I ₀ −αE ₁ I ₀ = E ₀ /αR ₀・Δd/d ₀ +1/αR ₀ (V-2E
₀ + αE ₁ ), and I ₀ ∝Δd/d ₀ .

Therefore, the output current I ₀ changes in proportion to the displacement Δd of the moving electrode 6, and a voltage signal proportional to the pressure can be obtained at the receiving resistor R _L in the receiver 28 of the two-wire transmitter.

Therefore, even when using the displacement detector according to the present invention, which has a simple structure and can be manufactured at low cost, it is possible to obtain an electrical signal proportional to the displacement position to be measured.

Although the displacement detector according to the present invention is applied to a pressure gauge in the above description, it is easy to understand that it can also be applied to other applications such as a weight scale.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing a detection part of an embodiment of a displacement detector according to the present invention, FIG. 2 is a front view showing an example of first and second fixed electrodes used in the embodiment of FIG. 1, and FIG. Figure 3 is a connection diagram showing an example of a converting section for converting the displacement input of the displacement detector according to the present invention into an electric signal proportional to the displacement input, and Figure 4 is a connection diagram of the
FIG. 3 is a connection diagram for explaining the electrical configuration of the detection unit shown in the figure. 1: Metal body, 3: Pressure receiving element, 4: Connection shaft,
5: Leaf spring, 6: Moving electrode, 9: Metal ring, 1
0, 11: Insulating material, 12: First fixed electrode, 13:
2nd fixed electrode, C ₁ : 1st variable capacitance part, C ₂ : 2nd
Variable capacitance section.

Claims (1)

[Claims] 1. A moving electrode installed in a body so as to be able to move according to displacement, a metal ring mechanically isolated outside the outer periphery of this moving electrode and electrically connected to this moving electrode, and said moving electrode. A part faces the metal ring, and the other part faces the metal ring,
Detection by a first fixed electrode that is insulated and attached to the body, and a second fixed electrode that is insulated and attached to the body and faces the moving electrode from the same side as the first fixed electrode. a first variable capacitance section consisting of the first fixed electrode, the movable electrode facing the same, and the metal ring; and the second fixed electrode and the movable electrode facing the first variable capacitance section. An alternating current signal is applied from an oscillator to a second variable capacitance section, a signal proportional to the current flowing through the second variable capacitance section is extracted by a rectifier circuit, and the oscillator is controlled by a control means so that this signal becomes constant. A signal proportional to the current flowing through the first variable capacitance section is taken out by a rectifier circuit and applied to one input of an operational amplifier, and the output of this operational amplifier is applied to an output current control element, which controls the output current. A voltage obtained by dividing a sum voltage of a feedback voltage proportional to the output current of the element and a constant voltage is applied to the other input of the operational amplifier, so that a signal proportional to the displacement of the moving electrode is obtained from the output current. displacement detector.