CN104062327B - For capacity transducer complementation excitation and the linear detection circuit of oil plant detection - Google Patents

Abstract

The present invention relates to a kind of capacity transducer complementation excitation for oil plant detection and linear detection circuit, belong to detection technique field. This circuit is made up of capacity transducer, ginseng ratio capacitance, the inspection stream parts such as resistance, integrated operational amplifier, and the value of ginseng ratio capacitance is equal with the capacitance of capacity transducer when not feeling survey oil plant; Capacity transducer connect with ginseng ratio capacitance, and its public end is connected with the inverting input of operational amplifier, and the ac-excited signal of two-way that two not common ends are contrary with amplitude equal phase respectively is connected; Inspection stream resistance is connected between the inverting input of operational amplifier and output terminal, the in-phase input end ground connection of operational amplifier; Operational amplifier output terminal voltage is amplitude and the linear detected result signal of sensor capacitance variable quantity. The capacitance change of energy linearity test capacity transducer of the present invention, circuit is simple, highly sensitive, good stability, wide dynamic range, immunity from interference strong, is highly suitable for the capacitance sensing detection of oil plant performance.

Description

For capacity transducer complementation excitation and the linear detection circuit of oil plant detection

Technical field

The invention belongs to detection technique field, encourage capacity transducer and the detection circuit of linear detecting sensor capacitance change in particular to a kind of with complementary energisation mode.

Background technology

Oil plant is a kind of very complicated mixture, and its various parameter and performance being detected is the work having challenge, and the application of the new technologies such as various novel sensing technology, detection technique in oil plant detects also is the research emphasis of oil plant detection field. Capacity transducer is that the effect according to extraneous parameter causes the change of sensor electrical capacitance to detect extraneous parameter, has that structure is simple, dynamic response fast, environmental adaptation ability is strong, working reliability height, has the features such as average effect. The associated arguments of oil plant being detected with capacity transducer, have other detection methods a lot of and the incomparable peculiar advantage of means, this makes the application of capacity transducer in oil plant detects more and more be subject to people's attention. In recent years, in the context of detection of the parameter such as the dielectric properties of oil plant, chemical composition, category identification, moisture content, level height, the application of capacity transducer becomes the important directions of people's research all gradually.

Due to the special property of oil plant and self principle features of capacity transducer, when capacity transducer is used for oil plant detection, compared to other application scenarios, excitation and detection circuit to sensor have higher requirement, and these requirements mainly concentrate on the following aspects:

1, requiring that the ac-excited signal amplitude of sensor is as far as possible big, so that when tested parameter is certain, the variable quantity of capacity transducer charging and discharging currents is as far as possible big, thus the detection sensitivity making sensor is high as far as possible.

2, require that the amplitude height of ac-excited signal is stablized, to ensure high stability and the repeatability of detected result.

3, owing to the effect of oil plant causes the variable quantity (�� C) of sensor electrical capacitance relative to its initial capacitance value (C_R) normally very little, it is desirable to the variable quantity (�� C) of the output signal energy direct reaction sensor electrical capacitance of detection circuit, instead of the total capacitance value (C of sensor_R+ �� C), thus make sensing circuit possess stronger detection resolving power and wider dynamic detection range.

4, require that the output signal of detection circuit and the capacitance change of sensor meet linear relationship as far as possible.

5, due to the output impedance height of capacity transducer, driving carrying capacity is poor, therefore it is required that the input resistance height of detection circuit, output impedance is low, thus reduce detection circuit to the load effect of capacity transducer, and strengthen the driving force that follow-up signal is nursed one's health circuit by detection circuit.

6, its excitation of the principle mandates of capacity transducer itself and detection circuit all should be tried one's best and thoroughly be got rid of stray capacitance to the impact of sensor, thus strengthens the accuracy of sensor detected result.

Such as, for Fig. 1 with Fig. 2 these two kinds common exchange bridge-type measuring, just there is following shortcoming: one is owing to joining ratio capacitance C in two-arm_R(or sampling resistance R) and sensor C_X(=C_R+ �� C) series connection dividing potential drop effect, make sensor C_XThe true energizing voltage itself born is than the driving voltage on bridge roadLittle a lot, it reduce the detection sensitivity of metering circuit; Two is due to excitationAnd non-immediate is added to sensor C_XTwo ends, the impact of wire resistance, distribution parameter and interference etc. can cause sensor C_XThe energizing voltage born is unstable; Three is the output of two-armWithValue all bigger, and useful signal wherein (namely causes C by the effect of tested parameter_XChanges delta C causesOrVariable quantity) but very little, which greatly limits the dynamic detection range of sensor circuit and resolving power; Four is the output of detection circuit ${\stackrel{\·}{U}}_O={\stackrel{\·}{U}}_{O1}-{\stackrel{\·}{U}}_{02}$ Value all very little (to Fig. 1: ${\stackrel{\·}{U}}_O=\frac{Z_{CR}}{Z_{CR}+Z_{CX}}{\stackrel{\·}{U}}_i-\frac{Z_{CX}}{Z_{CR}+Z_{CX}}{\stackrel{\·}{U}}_i=\frac{\mathrm{\Δ}C}{2C_R+\mathrm{\Δ}C}{\stackrel{\·}{U}}_i;$ To Fig. 2: ${\stackrel{\·}{U}}_O=\frac{Z_R}{Z_R+Z_{CX}}{\stackrel{\·}{U}}_i-\frac{Z_R}{Z_R+z_{CR}}{\stackrel{\·}{U}}_i\≈\frac{j\mathrm{\ω}R\·\mathrm{\Δ}C}{{\mathrm{j\ωRC}}_R+1}{\stackrel{\·}{U}}_i,$ �� is the frequency of actuation signal), detection resolving power is lower, simultaneouslyAnd it is nonlinear relationship between �� C, poor linearity; Five is that the existence of distributed capacity all can have influence on to these two kinds of detection schemesWithThus reduce stability and the accuracy of detected result; Six is the output impedance height of circuit, drives the ability of follow-up conditioning circuit weak.

For another example, for excitation and detection scheme shown in Fig. 3, although avoiding multiple shortcomings of Fig. 1 and Fig. 2 two schemes, but due to useful signalStill only account for $({\stackrel{\·}{U}}_{O1}=-{\mathrm{j\ωRC}}_X\·{\stackrel{\·}{U}}_i=-j\mathrm{\ω}R(C_R+\mathrm{\Δ}C)\·{\stackrel{\·}{U}}_i)|$ A very little part, andWithRestriction by Power supply can not be very big, thus makes output signal $({\stackrel{\·}{U}}_O={\stackrel{\·}{U}}_{O1}-{\stackrel{\·}{U}}_{O2}=\mathrm{\Δ}{\stackrel{\·}{U}}_{O1}=-j\mathrm{\ω}R\·\mathrm{\Δ}C\·{\stackrel{\·}{U}}_i)$ Still very little, this result also in, and the dynamic detection range of this detection scheme is very narrow, detection sensitivity and resolving power all very low.

As the above analysis, conventional at present capacity transducer excitation and detection scheme can not meet oil plant detection application to its many-sided requirement, it is necessary to new excitation and detection scheme overcome existing shortcoming.

Summary of the invention

It is an object of the invention to provide a kind of structure simple, the oil plant many-sided service requirements of detection application can be met and overcome the capacity transducer complementation excitation for oil plant detection and the linear detection circuit of existing conventional scheme shortcoming, thus realize the linearity test of the highly sensitive to sensor capacitance changing value, high stability, pinpoint accuracy, great dynamic range.

The capacity transducer complementation excitation for oil plant detection that the present invention proposes and linear detection circuit are as shown in Figure 4, it is characterised in that: this detection circuit is by capacity transducer C_X, ginseng ratio capacitance C_R, inspection stream resistance R_SForm with integrated operational amplifier A, wherein, capacity transducer C_XWith ginseng ratio capacitance C_RAfter series connection, the inverting input of its public end and operational amplifier A (-) be connected;Inspection stream resistance R_SIt is connected between the inverting input of operational amplifier A and output terminal, makes operational amplifier A work in reverse feedback state; The in-phase input end of operational amplifier A (+) ground connection, make capacity transducer C_XWith ginseng ratio capacitance C_RPublic end be in the zero potential of empty ground state.

In the complementation excitation of described capacity transducer and linear detection circuit, ginseng ratio capacitance C_RCapacitance and capacity transducer C_XInitial capacitance value when not experiencing tested parameter is equal, the complementary ac-excited signal of the two-way that amplitude equal phase is contraryWithIt is connected to capacity transducer C respectively_XWith ginseng ratio capacitance C_RNot common end, the output end voltage of operational amplifier AIt is the detected result signal of representative sensor capacitance change �� C.

The feature of the present invention and effect:

In the capacity transducer complementation excitation and linear detection circuit of the present invention's proposition, due to capacity transducer C_XWith ginseng ratio capacitance C_RPublic end be in the zero potential of empty ground state, complementary excitation signalsWithThe not common end being connected on again the two respectively, therefore the two actuation signal size of bearing is all 100%Actuation signal amplitude obtains maximumization, and the detection sensitivity of sensor obtains sufficient guarantee.

Secondly, inspection stream resistance R_SDirectly will flow through capacity transducer C_XWith ginseng ratio capacitance C_RDifference between currents be converted to output voltage and make ${\stackrel{\·}{U}}_O=-(\frac{+{\stackrel{\·}{U}}_i}{Z_{CX}}+\frac{-{\stackrel{\·}{U}}_i}{Z_{CR}})\·R=-j\mathrm{\ω}R\·\mathrm{\Δ}C\·{\stackrel{\·}{U}}_i$ (effect that �� C is tested parameter causes capacity transducer C_XAt its initial value C_RCapacitance change on basis). Owing to this detected result outputs signalVery wide voltage range can be covered, and only reflect sensor C_XCapacitance variation amount �� C, therefore both fully ensure that this circuit had extremely wide dynamic detection range and extremely high detection resolving power, also ensure that the ideal linearity relation between detected result and sensor capacitance variable quantity simultaneously.

3rd, in this scenario, due to capacity transducer C_XWith ginseng ratio capacitance C_RNot common end directly connect exciting signal sourceWithThe distributed capacity of not common end is equivalent to and sensor C_XOr ginseng ratio capacitance C_RIt is connected to corresponding excitation source after in parallel; Meanwhile, due to sensor C_XWith ginseng ratio capacitance C_RPublic end be in the zero potential of empty ground state, the distributed capacity of its public end is equivalent to be shorted to ground. Therefore sensor C_XWith ginseng ratio capacitance C_RThe stability that it all can not be born actuation signal by the distributed capacity of two ends line forms interference, ensure that the program has very strong immunity from interference, very high detection accuracy and stability.

4th, owing to adopting integrated transporting discharging to form detection circuit, therefore the program also has the feature of high input impedance and low output impedance.

As can be seen here, the present invention can meet oil plant detection application to many-sided requirement of capacity transducer excitation and detection circuit, can realize the linearity test of the highly sensitive of capacity transducer capacitance variations value, high stability, pinpoint accuracy, great dynamic range in the way of a kind of simple economy.

Accompanying drawing explanation

Fig. 1 is the capacity transducer exchange bridge-type excitation and the detection scheme schematic diagram that use ginseng ratio capacitance.

Fig. 2 uses ginseng ratio capacitance to exchange bridge-type excitation and detection schematic circuit diagram with the capacity transducer of sampling resistance.

Fig. 3 is the capacity transducer discharge and recharge detection scheme schematic diagram using ginseng ratio capacitance and integrated operational amplifier.

Fig. 4 is the schematic circuit diagram realizing the present invention.

Fig. 5 is embodiments of the invention figure.

Embodiment

Below in conjunction with accompanying drawing, specific embodiments of the invention are described in detail.

The capacity transducer complementation excitation for oil plant detection that the present invention proposes and linear detection circuit, it is characterised in that: this detection circuit is by capacity transducer C_X, ginseng ratio capacitance C_R, inspection stream resistance R_SForm with integrated operational amplifier A, wherein, capacity transducer C_XWith ginseng ratio capacitance C_RAfter series connection, the inverting input of its public end and operational amplifier A (-) be connected;Inspection stream resistance R_SIt is connected between the inverting input of operational amplifier A and output terminal, makes operational amplifier A work in reverse feedback state; The in-phase input end of operational amplifier A (+) ground connection, make capacity transducer C_XWith ginseng ratio capacitance C_RPublic end be in the zero potential of empty ground state.

In the complementation excitation of described capacity transducer and linear detection circuit, ginseng ratio capacitance C_RCapacitance and capacity transducer C_XInitial capacitance value when not experiencing tested parameter is equal, the complementary ac-excited signal of the two-way that amplitude equal phase is contraryWithIt is connected to capacity transducer C respectively_XWith ginseng ratio capacitance C_RNot common end, the output end voltage of operational amplifier AIt is the detected result signal of representative sensor capacitance change �� C.

As shown in Figure 5, the composition of each several part is described as follows embodiment of the present invention circuit:

1. the present embodiment circuit comprises mutual supplementary signal generation circuit and complementary excitation linear involved in the present invention detection circuit two portions.

2. the mutual supplementary signal generation circuit of the present embodiment comprises a voltage follow device and a voltage inverter, in order to by signal sourceTurn into the actuation signal of two-way complementationWithVoltage follow device is by operational amplifier A₁With resistance R₁��R₂Composition; R₁One end and signal sourceOutput be connected, the other end and operational amplifier A₁In-phase input end (+) be connected; R₂It is connected to operational amplifier A₁Inverting input (-) and output terminal between. Voltage inverter is by operational amplifier A₂With resistance R₃��R₄Composition; R₃It is connected to signal sourceOutput and operational amplifier A₂Inverting input (-) between, R₄It is connected to operational amplifier A₂Inverting input (-) and output terminal between, A₂In-phase input end ground connection. Resistance R₁��R₄Being all accurate resistance, and resistance is equal, size can be taken as 10k ����100k ��. Operational amplifier A₁And A₂Input resistance height should be selected, the operational amplifier that offset voltage is little.

Mutual supplementary signal generation circuit, except can being made up of the operational amplifier in the present embodiment and resistance, also realizes by other approach such as transformers.

3. the complementary excitation linear detection circuit of the present embodiment is by operational amplifier A, inspection stream resistance R_S, ginseng ratio capacitance C_R, capacity transducer C_XForm. Capacity transducer C_XWith ginseng ratio capacitance C_RMutually it is connected to complementary actuation signal after series connectionWithBetween, capacity transducer C_XWith ginseng ratio capacitance C_RPublic be terminated at operational amplifier A inverting input (-), inspection stream resistance R_SBe connected to operational amplifier A inverting input (-) and output terminal between, the in-phase input end of operational amplifier A (+) ground connection. Resistance R in the present embodiment_SFor accurate fixed resistor, it may also be numeral potentiometer or other forms of resistor network. Ginseng ratio capacitance C_RUsually the capacity transducer C surveying tested object is not felt by another_XForm, it is possible to use other forms of electrical condenser is formed. Operational amplifier A is high input impedance, the accurate operational amplifier of Low-bias Current, offset voltage, and its output end voltage is detected result output signal, and the amplitude of this signal and the capacitance change of capacity transducer are linear.

The capacitance change of energy linearity test capacity transducer of the present invention, and there is the advantages such as circuit is simple, highly sensitive, good stability, wide dynamic range, immunity from interference are strong, the capacitance sensing detection being not only highly suitable for oil plant, is also applicable to capacity transducer to the detection of other material object.

Claims (1)

1. for capacity transducer complementation excitation and the linear detection circuit of oil plant detection, it is characterized in that: the basic circuit part of this detection circuit comprises capacity transducer, ginseng ratio capacitance, inspection stream resistance and integrated operational amplifier, wherein, capacity transducer is connected with ginseng ratio capacitance, its public end is connected with the inverting input of integrated operational amplifier, inspection stream resistance is connected between the inverting input of integrated operational amplifier and output terminal, the in-phase input end ground connection of integrated operational amplifier;The capacitance of ginseng ratio capacitance is equal with the initial capacitance value of capacity transducer when not feeling the tested object of survey; The complementary ac-excited signal of two-way that the capacity transducer of series connection is contrary with amplitude equal phase respectively with two not common ends of ginseng ratio capacitance is connected; The voltage signal of integrated operational amplifier output terminal is the detected result output signal of capacity transducer capacitance change.