CN103411525B - A kind of cylindrical capacitance displacement sensor and modulate circuit - Google Patents

Abstract

The invention provides a kind of cylindrical capacitance displacement sensor, adopt the differential structure of three layers of cylinder, by in the process of active cylinder movement, the measuring error brought with spacing d skew and the center of circle shifted by delta d of inner cylinder and out cylinder is eliminated, and also eliminates the impact of the specific inductive capacity of medium simultaneously.Owing to being the difference reflection displacement of upper and lower sensing capacitance, sensitivity is improved.

Description

A kind of cylindrical capacitance displacement sensor and modulate circuit

Technical field

The invention belongs to displacement measuring technology field, more specifically say, relate to a kind of cylindrical capacitance displacement sensor and modulate circuit.

Background technology

Capacitance displacement sensor is a kind of sensor change in displacement of non electrical quantity being converted to electric capacitance change.Electric capacity is an electronic component that can charge and can discharge, and the basic structure of electric capacity is by two metal polar plates, and middle interval forms with insulator.Although capacitance displacement sensor in appearance difference is comparatively large, organization plan is two classes substantially: parallel plate type and cylinder coaxial-type.

Fig. 1 is the structure principle chart of variable area cylinder displacement-capacitance sensor.

Variable area cylinder displacement-capacitance sensor is a kind of cylinder coaxial-type capacitance displacement sensor, and when ignoring edge effect, its capacity is:

$C_0=\frac{2\mathrm{\π\ϵ}}{\ln \frac{R}{r}}L---\left(1\right)$

In formula (1):

The length (m) of L---out cylinder and inner cylinder cover part;

ε---the specific inductive capacity (F/m) of medium between capacitor plate;

R, r---outer pole cylinder inside radius and interior pole cylinder external radius (m).

Keeping under the prerequisite that the spacing d of inner cylinder and out cylinder is constant, movable cylinder and inner cylinder be translation x along its length, then capacity becomes:

$C=\frac{2\mathrm{\π\ϵ}}{\ln \frac{R}{r}}(L-x)=C_0(1-\frac{x}{L})=C_0-\mathrm{\ΔC}---\left(2\right)$

In formula (2), the variable quantity of capacity is:

$\mathrm{\ΔC}=\frac{x}{L}{C}_0---\left(3\right)$

Relatively being changed to of capacity:

$\frac{\mathrm{\ΔC}}{C_0}=\frac{x}{L}---\left(4\right)$

Linearly, and the range measured is by the restriction of the range of linearity, is suitable for measuring larger straight-line displacement for the output characteristics (C ~ x) of visible this sensor.The sensitivity of this sensor is:

$k=\frac{\mathrm{\ΔC}}{x}=\frac{C_0}{L}=\frac{2\mathrm{\π\ϵ}}{\ln \frac{R}{r}}---\left(5\right)$

The output conclusion linearly of existing variable area cylindrical capacitance displacement sensor is keeping drawing under the constant prerequisite of the spacing d of inner cylinder and out cylinder.In the process of movable inner cylinder movement, if the spacing d of inner cylinder and out cylinder can not accurately remain unchanged, measuring error will be caused.

Summary of the invention

The object of the invention is to overcome the defect that existing variable area cylindrical capacitance displacement sensor is subject to the spacing variable effect of inner cylinder and out cylinder, provide a kind of cylindrical capacitance displacement sensor, during to eliminate displacement, the center of circle offsets.

For realizing above object, cylindrical capacitance displacement sensor of the present invention, is characterized in that, comprising:

The radius of horizontal alignment is R ₁, R ₃upper metal inside and outside cylinder S ₁₁, S ₁₂and the radius of horizontal alignment is R ₁, R ₃cylinder S inside and outside lower metal ₂₁, S ₂₂, cylinder S inside and outside upper metal ₁₁, S ₁₂and cylinder S inside and outside lower metal ₂₁, S ₂₂height be L, and respectively vertical alignment and the center of circle be point-blank;

Radius is R ₂active cylinder S _m, its metallic member height is L+l, and wherein, l is the distance inside and outside upper and lower metal between cylinder, active cylinder S _mmetallic member be placed in inside and outside metal between cylinder, align with the upper end of cylinder inside and outside upper metal and can move downward in its upper end, until align with the lower end of cylinder inside and outside lower metal in lower end;

By cylinder S inside and outside upper metal ₁₁, S ₁₂link together as upper sensing capacitance C electrically ₁an output terminal, active cylinder S _mas upper sensing capacitance C ₁another output terminal, by cylinder S inside and outside lower metal ₂₁, S ₂₂link together as lower sensing capacitance C electrically ₂an output terminal, active cylinder S _mas lower sensing capacitance C ₂another output terminal;

Detect upper and lower sensing capacitance C ₁, C ₂difference with and ratio k _pthat is:

$k_p=\frac{C_1-C_2}{C_1+C_2}---\left(6\right)$

According to active cylinder S _mdisplacement x and ratio k _plinear relationship, displacement x is detected.

The object of the present invention is achieved like this:

Cylindrical capacitance displacement sensor of the present invention, adopt the differential structure of three layers of cylinder, by in the process of active cylinder movement, the measuring error brought with spacing d skew and the center of circle shifted by delta d of inner cylinder and out cylinder is eliminated, and also eliminates the impact of the dielectric general knowledge of medium simultaneously.Owing to being the difference reflection displacement of upper and lower sensing capacitance, sensitivity is improved.

Accompanying drawing explanation

Fig. 1 is the structure principle chart of the variable area cylinder displacement-capacitance sensor of prior art;

Fig. 2 is cylindrical capacitance displacement sensor structure principle chart of the present invention;

Fig. 3 is that the capacitance of the differential generator of variable area shown in Fig. 1 calculates schematic diagram;

Fig. 4 is the sectional view of cylindrical capacitance displacement sensor shown in Fig. 2 when offseting in the center of circle;

Fig. 5 is the modulate circuit of cylindrical capacitance displacement sensor shown in Fig. 2 schematic diagram;

Fig. 6 is the width modulator of difference pulse shown in Fig. 5 electrical schematic diagram;

Fig. 7 is the working waveform figure of differential width modulation modulator shown in Fig. 6.

Embodiment

Below in conjunction with accompanying drawing, the specific embodiment of the present invention is described, so that those skilled in the art understands the present invention better.Requiring particular attention is that, in the following description, when perhaps the detailed description of known function and design can desalinate main contents of the present invention, these are described in and will be left in the basket here.

Fig. 2 is cylindrical capacitance displacement sensor structure principle chart of the present invention.

In the present embodiment, as shown in Fig. 2 (a) and (b), cylindrical capacitance displacement sensor of the present invention is a kind of three cartridge type differential capacitor displacement transducers of changed area, comprising:

The radius of horizontal alignment is R ₁, R ₃upper metal inside and outside cylinder S ₁₁, S ₁₂and the radius of horizontal alignment is R ₁, R ₃cylinder S inside and outside lower metal ₂₁, S ₂₂, cylinder S inside and outside upper metal ₁₁, S ₁₂and cylinder S inside and outside lower metal ₂₁, S ₂₂height be L, and respectively vertical alignment and the center of circle be point-blank;

Radius is R ₂active cylinder S _m, its metallic member height is L+l, and wherein, l is the distance inside and outside upper and lower metal between cylinder, in the specific implementation, and can be little as much as possible.Active cylinder S _mmetallic member be placed in inside and outside metal between cylinder, aliging with the upper end of cylinder inside and outside upper metal in its upper end, as shown in Figure 2 (a) shows, and can move downward, and as Fig. 2 (b), its displacement is x, until align with the lower end of cylinder inside and outside lower metal in lower end; Therefore, its range is L, i.e. the maximum displacement can measuring L length.And active cylinder S _minside and outside upper metal, the reducing portion of cylinder is divided and is equaled active cylinder S _mthe increase part of cylinder inside and outside lower metal, formed one differential.

By cylinder S inside and outside upper metal ₁₁, S ₁₂link together as upper sensing capacitance C electrically ₁an output terminal and A end, active cylinder S _mas upper sensing capacitance C ₁another output terminal C hold, by cylinder S inside and outside lower metal ₂₁, S ₂₂link together as lower sensing capacitance C electrically ₂an output terminal and B end, active cylinder S _mas lower sensing capacitance C ₂another output terminal and C end;

Detect upper and lower sensing capacitance C ₁, C ₂difference with and ratio k _pnamely

$k_p=\frac{C_1-C_2}{C_1+C_2}---\left(6\right)$

According to active cylinder S _mdisplacement x and ratio k _plinear relationship, just displacement x can be detected.

As shown in Fig. 2 (b), cylindrical capacitance displacement sensor of the present invention is made up of four electric capacity generally, and its equivalent electrical circuit as shown in Figure 2 (c).Its upper and lower sensing capacitance C ₁and C ₂(wherein C ₁=C ₁₁+ C ₁₂, C ₂=C ₂₁+ C ₂₂) form differential structure, i.e. active cylinder S _mwhen pulling downwards, upper sensing capacitance C ₁capacitance reduce, lower sensing capacitance C ₂capacitance increase.

If active cylinder S _mpulled down distance and displacement are x, can obtain according to formula (2):

$C_1=\frac{2\mathrm{\π\ϵ}}{\ln \frac{R_2}{R_1}}(L-x)+\frac{2\mathrm{\π\ϵ}}{\ln \frac{R_3}{R_2}}(L-x)---\left(7\right)$

$C_2=\frac{2\mathrm{\π\ϵ}}{\ln \frac{R_2}{R_1}}x+\frac{2\mathrm{\π\ϵ}}{\ln \frac{R_3}{R_2}}x---\left(8\right)$

In the present embodiment, displacement is with active cylinder S _mmetallic member upper end and upper metal inside and outside the upper end of cylinder be aligned to starting point.Can certainly with lower end to it for starting point, up move, only need again to demarcate.

When displacement x is by when changing in the scope of 0 → L, upper sensing capacitance C ₁capacitance by maximal value fade to minimum value of zero, and lower sensing capacitance C ₂capacitance fade to maximal value by minimum value of zero $\frac{2\mathrm{\π\ϵ}}{\ln \frac{R_2}{R_1}}L+\frac{2\mathrm{\π\ϵ}}{\ln \frac{R_3}{R_2}}L.$

And there is following linear relationship:

$\frac{C_1-C_2}{C_1+C_2}=(1-2\frac{x}{L}).$ Namely $x=\frac{1}{2}L-\frac{1}{2}\frac{C_1-C_2}{C_1+C_2}L---\left(9\right).$

It should be noted that, cylindrical capacitance displacement sensor of the present invention is described in a vertical manner and illustrates, but it also can be placed in other any modes, identical during its principle of work.

One, sensitivity and center of circle shift analysis

1, about the problem of sensitivity

The variable area cylinder displacement-capacitance sensor of prior art, as Fig. 3, when under the prerequisite that the spacing d of inner cylinder and out cylinder is constant, inner cylinder along its length namely downward translation x time, capacitance is:

$C=\frac{2\mathrm{\π\ϵ}}{n\frac{R_2}{R_1}}(L-x)=C_0(1-\frac{x}{L})=C_0-\mathrm{\ΔC}$

Its variable quantity is Δ C as can be seen here.

Cylindrical capacitance displacement sensor of the present invention, as shown in Figure 2, as maintenance active cylinder S _min the process of movement, with under the prerequisite that the spacing d of inner cylinder and out cylinder is constant, active cylinder S _mwhen being downward translation x along its length: sensing capacitance C up and down ₁, C ₂capacitance be:

C ₁=C ₁₁+C ₁₂,C ₂=C ₂₁+C ₂₂

Therefore, $C_1=\frac{2\mathrm{\π\ϵ}}{\ln \frac{R_2}{R_1}}(L-x)+\frac{2\mathrm{\π\ϵ}}{\ln \frac{R_3}{R_2}}(L-x)$

$C_2=\frac{2\mathrm{\π\ϵ}}{\ln \frac{R_2}{R_1}}x+\frac{2\mathrm{\π\ϵ}}{\ln \frac{R_3}{R_2}}x$

From above, $\frac{C_1-C_2}{C_1+C_2}=\frac{\frac{2\mathrm{\π\ϵ}}{\ln \frac{R_2}{R_1}}(L-x)+\frac{2\mathrm{\π\ϵ}}{\ln \frac{R_3}{R_2}}(L-x)-\frac{2\mathrm{\π\ϵ}}{\ln \frac{R_2}{R_1}}x-\frac{2\mathrm{\π\ϵ}}{\ln \frac{R_3}{R_2}}x}{\frac{2\mathrm{\π\ϵ}}{\ln \frac{R_2}{R_1}}(L-x)+\frac{2\mathrm{\π\ϵ}}{\ln \frac{R_3}{R_2}}(L-x)+\frac{2\mathrm{\π\ϵ}}{\ln \frac{R_2}{R_1}}x+\frac{2\mathrm{\π\ϵ}}{\ln \frac{R_3}{R_2}}x}$

$=\frac{\frac{2\mathrm{\π\ϵ}}{\ln \frac{R_2}{R_1}}L+\frac{2\mathrm{\π\ϵ}}{\ln \frac{R_3}{R_2}}L-2(\frac{2\mathrm{\π\ϵ}}{\ln \frac{R_2}{R_1}}x+\frac{2\mathrm{\π\ϵ}}{\ln \frac{R_3}{R_2}}x)}{\frac{2\mathrm{\π\ϵ}}{\ln \frac{R_2}{R_1}}L+\frac{2\mathrm{\π\ϵ}}{\ln \frac{R_3}{R_2}}L}$

$=\frac{C_0+C_0^{\′}-2(\mathrm{\ΔC}+\mathrm{\Δ}{C}^{\′})}{C_0+C_0^{\′}}$

Its variable quantity is 2 (Δ C+ Δ C ') as can be seen here, and sensitivity of the present invention is improved.

2, about the problem of center of circle shifted by delta d

The variable area cylinder displacement-capacitance sensor of prior art, if when inner cylinder is downward translation x along its length, for sensor capacitance C be:

$C=\frac{2\mathrm{\π\ϵ}(L-x)}{\ln [\frac{R_1^2+R_2^2-\mathrm{\Δ}{d}^2}{2R_1{R}_2}+\sqrt{{\left(\frac{R_1^2+R_2^2-\mathrm{\Δ}{d}^2}{2R_1{R}_2}\right)}^2-1}]}$

Now center of circle shifted by delta d has impact to two kinds of structure sensor.

Cylindrical capacitance displacement sensor of the present invention is the differential capacitance displacement transducer of intermediate cylindrical changed area, when center of circle skew is for Δ d, as Fig. 4, for this differential capacitance displacement transducer, as active cylinder S _mwhen being downward translation x along its length, upper and lower sensing capacitance C ₁, C ₂capacitance be:

$C_1=\frac{2\mathrm{\π\ϵ}(L-x)}{\ln [\frac{R_1^2+R_2^2-\mathrm{\Δ}{d}^2}{2R_1{R}_2}+\sqrt{{\left(\frac{R_1^2+R_2^2-\mathrm{\Δ}{d}^2}{2R_1{R}_2}\right)}^2-1}]}+\frac{2\mathrm{\π\ϵ}(L-x)}{\ln [\frac{R_3^2+R_2^2-\mathrm{\Δ}{d}^2}{2R_3{R}_2}+\sqrt{{\left(\frac{R_3^2+R_2^2-\mathrm{\Δ}{d}^2}{2R_3{R}_2}\right)}^2-1}]}$

$C_2=\frac{2\mathrm{\π\ϵx}}{\ln [\frac{R_1^2+R_2^2-\mathrm{\Δ}{d}^2}{2R_1{R}_2}+\sqrt{{\left(\frac{R_1^2+R_2^2-\mathrm{\Δ}{d}^2}{2R_1{R}_2}\right)}^2-1}]}+\frac{2\mathrm{\π\ϵx}}{\ln [\frac{R_3^2+R_2^2-\mathrm{\Δ}{d}^2}{2R_3{R}_2}+\sqrt{{\left(\frac{R_3^2+R_2^2-\mathrm{\Δ}{d}^2}{2R_3{R}_2}\right)}^2-1}]}$

From above formula therefore the impact completely eliminating center of circle shifted by delta d in such cases and bring, also eliminates the impact of the specific inductive capacity of medium simultaneously.

Two, cylindrical capacitance displacement sensor modulate circuit of the present invention

1, circuit theory

As shown in Figure 5, it is made up of difference pulse width modulator (PWM), low-pass filter, differential amplifier, AD converter, single-chip microcomputer cylindrical capacitance displacement sensor modulate circuit schematic diagram of the present invention;

Fig. 6 is the width modulator of difference pulse shown in Fig. 5 electrical schematic diagram.

In the present embodiment, as shown in Figure 6, difference pulse width modulator is by comparer A ₁, A _2,, RS trigger flip-flop and electric capacity charge and discharge control circuit composition;

U _rfor comparer A ₁, A ₂dC reference voltage, receive comparer A ₁, A ₂anode, its value is greater than diode forward forward voltage;

Electric capacity charge and discharge control circuit comprises:

Resistance R ₁, R ₂, comparer A ₁, A ₂negative terminal respectively by resistance R ₁, R ₂be connected with power supply negative terminal;

Driving gate N ₁, N ₂, the Q of RS trigger flip-flop holds, end respectively with driving gate N ₁, N ₂input end connect, driving gate N ₁, N ₂output terminal is respectively by backward dioded D ₁, D ₂be connected to comparer A ₁, A ₂negative terminal; Driving gate N ₁, N ₂export after negate is carried out to input voltage;

Cylinder S inside and outside the upper metal of cylindrical capacitance displacement sensor ₁₁, S ₁₂tie point meet driving gate N ₁negative terminal, cylinder S inside and outside lower metal ₂₁, S ₁₂tie point meet driving gate N ₂negative terminal, active cylinder S _mground connection;

Low-pass filter is held the Q of RS trigger flip-flop respectively, after the PWM that end exports carries out filtering, feeding differential amplifier amplifies, then send into AD converter conversion, finally conversion value is sent into single-chip microcomputer processes, and calculates displacement x.

As shown in Figure 6, C ₁, C ₂for the sensing capacitance up and down of cylindrical capacitance displacement sensor, comparer A ₁, A ₂dC reference voltage U is greater than at its negative terminal input voltage _rtime, export S, R pulse R-S trigger flip-flop being carried out to set and reset respectively, two output terminal Q of rest-set flip-flop and export as pwm pulse ripple.

As shown in Figure 6,7, if the t of power supply connection ₀in the moment, RS trigger flip-flop is in " 0 " state and Q end is electronegative potential, end is noble potential, therefore, and driving gate N ₁output terminal G point be noble potential, reverse diode D ₁cut-off, 5V power supply begins through resistance R ₁to upper sensing capacitance C ₁charging; Driving gate N ₂output terminal point is electronegative potential, reverse diode D ₂conducting, lower sensing capacitance C ₂by reverse diode D ₂rapid electric discharge, cylinder S inside and outside lower metal ₂₁, S ₁₂tie point B point be 0.7V, comparer A ₁, A ₂output is high level, does not affect the state of RS trigger flip-flop;

As upper sensing capacitance C ₁from 0V charging, until cylinder S inside and outside upper metal ₁₁, S ₁₂tie point A point potential rise to DC reference voltage U _rt ₁moment, comparer A ₁output polarity changes (by high step-down), produces the S pulse of a negative polarity, make RS trigger flip-flop overturn for one state (Q end becomes noble potential, end becomes electronegative potential).Now driving gate N ₁output terminal G point become electronegative potential, make backward dioded D ₁conducting, upper sensing capacitance C ₁be discharged to rapidly 0.7V(backward dioded D ₁forward voltage); Meanwhile, the electronegative potential of end makes driving gate N ₂output terminal for noble potential, backward dioded D ₂cut-off, so+5V power supply is by resistance R ₂downward sensing capacitance C ₂charging, cylinder S inside and outside metal instantly ₂₁, S ₁₂tie point B point voltage charge to DC reference voltage U from+0.7V _rt ₂moment, comparer A ₂produce the R pulse of a negative polarity, make rest-set flip-flop overturn back again " 0 " state, (Q end becomes electronegative potential again, end become noble potential again), repeat said process, so go round and begin again, make RS trigger flip-flop two output terminal Q and respective generation one width is by upper sensing capacitance C ₁, lower sensing capacitance C ₂the pwm pulse ripple of modulation.Its course of work can illustrate with table 1 briefly.

Table 1

As the equal i.e. C of upper and lower sensing capacitance ₁=C ₂time, on circuit, each point voltage waveform is as shown in Figure 7 (a), pulsewidth T in figure ₁=T ₂, Q, 2 are square wave, and they are after low pass electrical ripple, and its average voltage is 1/2U _s, the DC voltage difference (E of point-to-point transmission ₁-E ₂) be zero.As the unequal i.e. C of upper and lower sensing capacitance ₁≠ C ₂time, as worked as the unequal C of upper and lower sensing capacitance ₁>C ₂time, C ₁, C ₂discharge and recharge time constant changes, pulsewidth T ₁>T ₂each point voltage waveform as shown in Figure 7 (b) shows, Q, the waveform widths of 2 there occurs change, the average voltage E of Q point after low-pass filtering ₁be greater than 1/2U _s, the average voltage E of point ₂be less than 1/2U _s, there is DC potential difference (E in point-to-point transmission ₁-E ₂) >0.Otherwise, if as the unequal C of upper and lower sensing capacitance ₁<C ₂time, then (E ₁-E ₂) <0.

2, performance evaluation

At t ₀-t ₁interval, direct supply E(+5V) by resistance R ₁to upper sensing capacitance C ₁the voltage equation of charging is:

$u_{c1}=E(1-e^{-t/R_1{C}_1})---\left(10\right)$

At upper sensing capacitance C ₁charging reaches DC reference voltage U _rtime (t ₁moment), comparer A ₁export S negative pulse, make RS trigger flip-flop state turnover (putting 1).At t ₁moment (t=T ₁) have:

$u_{c1}=U_R=E(1-e^{-T_1/R_1{C}_1})---\left(11\right)$

Above formula solves and can obtain capacitor C ₁duration of charging T ₁:

$T_1=R_1{C}_1\ln \frac{E}{E-U_R}---\left(12\right)$

In like manner can descend sensing capacitance C ₂duration of charging T ₂:

$T_2=R_2{C}_2\ln \frac{E}{E-U_R}---\left(13\right)$

As seen from Figure 7, at Q and the pwm pulse that end exports, after the voltage stabilizing of stabilivolt amplitude limit, formation amplitude is U _s, and width is respectively T ₁and T ₂rectangular wave pulse (namely through upper and lower sensing capacitance C ₁and C ₂the PWM ripple of modulation), they are through low-pass filter, the period average U of output voltage ₀₁and U ₀₂be respectively:

$U_{01}=\frac{T_1}{T_1+T_2}{U}_S,U_{02}=\frac{T_2}{T_1+T_2}{U}_S---\left(14\right)$

Their differential output voltage U ₀for:

$U_0=U_{01}-U_{02}=\frac{T_1-T_2}{T_1+T_2}{U}_S---\left(15\right)$

As resistance R ₁=R ₂time, formula (12) and (13) being substituted into formula (15) then must the DC voltage U that exports of this circuit ₀:

$U_0=\frac{C_1-C_2}{C_1+C_2}{U}_S---\left(16\right)$

From above formula, the change of differential capacitor makes the duration of charging different, thus the square-wave pulse width that trigger flip-flop output terminal is produced is different, and its output signal need only can obtain direct current through low-pass filter and export.This metering circuit only needs the direct supply that a voltage-regulation coefficient is higher, and than needing in other metering circuit, the AC power of the Frequency and Amplitude Stabilization of high stability is easy accomplishes for this.

Can obtain according to formula (7) and formula (8):

$C_1-C_2=\frac{2\mathrm{\&pi;\&epsiv;}}{\ln \frac{R_2}{R_1}}(L-x)+\frac{2\mathrm{\&pi;\&epsiv;}}{\ln \frac{R_3}{R_2}}(L-x)-\frac{2\mathrm{\&pi;\&epsiv;}}{\ln \frac{R_2}{R_1}}x-\frac{2\mathrm{\&pi;\&epsiv;}}{\ln \frac{R_3}{R_2}}x---\left(17\right)$

$C_1+C_2=\frac{2\mathrm{\&pi;\&epsiv;}}{\ln \frac{R_2}{R_1}}L+\frac{2\mathrm{\&pi;\&epsiv;}}{\ln \frac{R_3}{R_2}}L---\left(18\right)$

Formula (17) and (18) are substituted into formula (16), can U be obtained ₀:

$U_0=\frac{C_1-C_2}{C_1+C_2}{U}_S=(1-2\frac{x}{L})U_s---\left(19\right)$

Above formula shows, as x=0, and U ₀=U _s; As x=1/2L, U ₀=0; As x=L, U ₀=-U _s, adopt changed area differential capacitance sensor, the impact of Δ d can be offset further, output voltage U ₀linear with input variable quantity x.

Three, conclusion

(1), the linear measurement range of cylindrical capacitance displacement sensor of the present invention is not limited in principle, is applicable to the straight-line displacement that measurement is larger;

(2), the structure of cylindrical capacitance displacement sensor of the present invention can obtain higher sensitivity;

(3), the in parallel and differential structure of the intermediate plate of cylindrical capacitance displacement sensor of the present invention, have and well offset characteristic, eliminate the impact of d change;

(4), modulate circuit Parameters variation can disappear compensation mutually, and eliminate many kinds of parameters and change the error caused, realizing circuit is simple;

(5), cylindrical capacitance displacement sensor of the present invention, convenience independently carry out debugging and calibrating.

Although be described the illustrative embodiment of the present invention above; so that those skilled in the art understand the present invention; but should be clear; the invention is not restricted to the scope of embodiment; to those skilled in the art; as long as various change to limit and in the spirit and scope of the present invention determined, these changes are apparent, and all innovation and creation utilizing the present invention to conceive are all at the row of protection in appended claim.

Claims (2)

1. a cylindrical capacitance displacement sensor, is characterized in that, comprising:

The radius of horizontal alignment is R ₁, R ₃upper metal inside and outside cylinder S ₁₁, S ₁₂and the radius of horizontal alignment is R ₁, R ₃cylinder S inside and outside lower metal ₂₁, S ₂₂, cylinder S inside and outside upper metal ₁₁, S ₁₂and cylinder S inside and outside lower metal ₂₁, S ₂₂height be L, and respectively vertical alignment and the center of circle be point-blank;

Radius is R ₂active cylinder S _m, its metallic member height is L+l, and wherein, l is the distance inside and outside upper and lower metal between cylinder, active cylinder S _mmetallic member be placed in inside and outside metal between cylinder, align with the upper end of cylinder inside and outside upper metal and can move downward in its upper end, until align with the lower end of cylinder inside and outside lower metal in lower end;

By cylinder S inside and outside upper metal ₁₁, S ₁₂link together as upper sensing capacitance C electrically ₁an output terminal, active cylinder S _mas upper sensing capacitance C ₁another output terminal, by cylinder S inside and outside lower metal ₂₁, S ₂₂link together as lower sensing capacitance C electrically ₂an output terminal, active cylinder S _mas lower sensing capacitance C ₂another output terminal;

Detect upper and lower sensing capacitance C ₁, C ₂difference with and ratio k _pthat is:

$k_p=\frac{C_1-C_2}{C_1+C_2}$

According to active cylinder S _mdisplacement x and ratio k _plinear relationship, displacement x is detected.

2., for a modulate circuit for cylindrical capacitance displacement sensor described in claim 1, it is characterized in that being made up of difference pulse width modulator, low-pass filter, differential amplifier, AD converter, single-chip microcomputer;

Difference pulse width modulator is by comparer A ₁, A _2,, RS trigger flip-flop and electric capacity charge and discharge control circuit composition;

U _rfor comparer A ₁, A ₂dC reference voltage, receive comparer A ₁, A ₂anode, its value is greater than diode forward forward voltage;

Electric capacity charge and discharge control circuit comprises:

Resistance R ₁, R ₂, comparer A ₁, A ₂negative terminal respectively by resistance R ₁, R ₂be connected with power supply negative terminal;

Driving gate N ₁, N ₂, the Q of RS trigger flip-flop holds, end respectively with driving gate N ₁, N ₂input end connect, driving gate N ₁, N ₂output terminal is respectively by backward dioded D ₁, D ₂be connected to comparer A ₁, A ₂negative terminal; Driving gate N ₁, N ₂export after negate is carried out to input voltage;

Cylinder S inside and outside the upper metal of cylindrical capacitance displacement sensor ₁₁, S ₁₂tie point meet driving gate N ₁negative terminal, cylinder S inside and outside lower metal ₂₁, S ₁₂tie point meet driving gate N ₂negative terminal, active cylinder S _mground connection;

Low-pass filter is held the Q of RS trigger flip-flop respectively, after the PWM that end exports carries out filtering, feeding differential amplifier amplifies, then send into AD converter conversion, finally conversion value is sent into single-chip microcomputer processes, according to active cylinder S _mdisplacement x and ratio k _plinear relationship, displacement x is calculated.