CN2304109Y - Capacitor water-level sensor - Google Patents

Abstract

The utility model relates to a capacitive water level sensor for realizing the spacing and control of the position of liquid surfaces. A capacitive probe, a sensor body and a lead wire are enclosed in an entirety, and the core part of a probe capacitance measuring circuit adopts a high-frequency oscillator which is composed of a Schmidt gate circuit, a feedback resistor R and a capacitor Cx. Compared with traditional capacitive water level sensors, the utility model has the advantages that the sensor can be immersed in liquid to be detected, and the sensor is free from the influences of viscous objects and sediment incrustation; the utility model also has the advantages of convenient installation, safe operation, high reliability, long service life, high measuring precision, and convenient assembly and debugging.

Description

The condenser type level sensor

The utility model relates to a kind of level detection sensor, and particularly a kind of capacitance type liquid level acquisition sensor is used for realizing liquid level position is surveyed and controlled.

At present, the capacitance type liquid level acquisition sensor that uses in the prior art has limited its usable range in some aspects because of the reason of its structure and installation.The chamber wall that generally all requires to be detected liquid such as this class sensor is a metal material; Simultaneously the body of sensor all can not invasion water in, thereby when liquid level being done spacing detection, sensor body can only be installed on the outside or top cover of canister.This is suitable for beyond doubt for the micro metal container, but for this class container of cesspool, owing to generally all be located at underground, and wall mostly is the nonmetallic materials of cement one class, thereby just can't use, and can only rely on reliability and serviceable life all unsafty float-ball type limit switch to survey.On the other hand, the probe capacitance measurement circuit in the traditional capacitance type liquid level acquisition sensor adopts AC bridge circuit or starting of oscillation failure of oscillation circuit usually.The formation relative complex of AC bridge circuit, and the balance of electric bridge and the unbalance probe electric capacity that not only depends on also are associated with the direct current resistance of fluid to be measured.Like this, when fluid to be measured was sewage, because sewage situation more complicated, along with the difference of sewage composition, its changes in resistance scope was very big, thereby was difficult to determine the bridge balance condition.Starting of oscillation failure of oscillation circuit also has similar problem, and measurement sensitivity is on the low side.

In order to overcome the deficiencies in the prior art and defective, the purpose of this utility model and task are to provide a kind of novel condenser type level sensor to cesspool or other fluid to be measured container, make it not only have the convenient and higher advantages such as measuring accuracy of reliability height, long service life, assembling and debugging, and can all be immersed in the fluid to be measured, be convenient to install and use.

The purpose of this utility model is achieved through the following technical solutions: it has the A electrode by one and the B electrode adds the capacitance probe that intermediate medium constitutes, sensor body and lead portion that the probe measurement circuit is housed are formed, described capacitance probe, sensor body and lead portion thereof are sealed into an integral body; Probe capacitance measurement circuit in the metering circuit adopts one by the schmidt door circuit, a feedback resistance and the high frequency oscillator that electric capacity is formed, feedback resistance in this oscillator is connected between the output terminal and input end of schmidt door circuit, and its electric capacity is connected between the input end and ground of schmidt door circuit.

The probe capacitance measurement circuit of the sensor adopts a simple schmidt door circuit and electric capacity and feedback resistance to constitute high frequency oscillator, and the electric capacity of this oscillator is probe electric capacity.Because the dielectric constant of water is much larger than air, thereby when water does not soak probe or part immersion probe or all soaks probe, significant change will take place in the electric capacity of capacitor, the utility model has utilized above-mentioned characteristic just, in the mode of totally-enclosed, the liquid level of water is done spacing detection by the variation of sensor self interelectrode capacity.Again because the long-pending relation of being inversely proportional to of oscillation frequency and electric capacity and resistance, thereby under the definite situation of resistance, oscillation frequency only depends on probe electric capacity.Like this, just can be by change to the change measuring sonde electric capacity of the output frequency of high frequency oscillator, and then realize spacing detection to liquid level position

Cause and survey wrong and improve measuring accuracy that choosing of the feedback resistance R resistance of this oscillator must be rationally in order when surveying, to be unlikely, promptly require the R resistance＜＜water resistance.

Accompanying drawing 1 is a structural principle synoptic diagram of the present utility model.

Accompanying drawing 2 is the use and the installation situation of this sensor.

The circuit theory diagrams of the high frequency oscillator that constitutes by the schmidt door circuit that accompanying drawing 3 is adopted for the probe capacitance measurement circuit of this sensor.

Accompanying drawing 4 is a specific embodiment of the probe capacitance measurement circuit of this sensor.

Specify principle of the present utility model, concrete structure and preferred forms below in conjunction with accompanying drawing.

The utility model mainly is made up of capacitance probe 1, sensor body 2 and 3 three parts that go between, and this three part all is sealed into an integral body, generally adopts engineering plastics that it is airtight, or adopts other thin and corrosion-resistant material; Purpose is when it all is immersed in the liquid and do not influence its operate as normal.Capacitance probe is to add that by A electrode 4 and B electrode 5 medium between the two constitutes.The A electrode adopts the annular slice electrode, and the B electrode adopts cylinder electrode.Because the specific inductive capacity of water is much larger than air, thereby when water does not soak probe or part immersion probe or all soaks probe, significant change will take place the electric capacity of this capacitor.

The core of the detection circuit of condenser type level sensor is the probe capacitance measurement circuit.Its adopts one by schmidt door circuit 6, a feedback resistance R and the high frequency oscillator that probe capacitor C x constitutes, as shown in Figure 3.The oscillating capacitance of this oscillator is probe electric capacity; Its oscillation frequency $f_0=\frac{1}{{0.8\mathrm{RC}}_X},$ Thereby under the situation that R determines, oscillation frequency only depends on probe capacitor C x.Above-mentioned schmidt door circuit adopts the 74HC14 chip, wherein feedback resistance R resistance should＜＜water resistance; In view of the water resistance of water purification is generally hundreds of K Ω, and the often not enough 100K Ω of the water resistance of sewage, for the feedback resistance R that guarantees high frequency oscillator＜＜water resistance, the feedback resistance R resistance in this sensor is generally got 10K Ω and is advisable.

Probe measurement circuit of the present utility model also comprises frequency dividing circuit except that comprising this core of high frequency oscillator, F/V change-over circuit, several parts of comparator circuit and output circuit.Promptly the high-frequency oscillation signal that is produced by high frequency oscillator is transformed to low frequency signal through frequency dividing circuit, becomes voltage signal by the F/V circuit conversion then, exports after forming switching signal by comparator circuit again.

Fig. 4 expresses whole circuit theory diagrams of probe capacitance measurement.U1, R1 and probe electric capacity constitute high frequency oscillator among the figure; U2 and U3 are frequency divider, can adopt 74HC161 and CD4020 chip respectively.The frequency division progression of this frequency divider can change by the J2 jumper zone.R2, R3, R4, R5, D1, D2, D4 and T1, T2 constitute the frequency signal output circuit, and output terminal is FOUT, and this output signal can be used to indirect survey sensor probe changes in capacitance.C4, C5, C6, C7, R6, R7, R8 and U4 (7555) constitute the F/V converter among the figure, and the frequency signal that frequency divider is exported is transformed to voltage signal.R9, R10, R12, W1 and U5 (358) constitute the voltage comparator with Schmidt's characteristic, and regulator potentiometer W1 can change this voltage comparator upset level.R11, R13, R14, R16 and T3, T4 constitute the output circuit of this sensor, the drive current about its exportable 10mA, in order to the measuring equipment interface.

The utility model compared with prior art has the following advantages and beneficial effect: this electric capacity The formula level sensor is owing to its whole electronic circuits, capacitance probe and lead portion all are sealed Become an integral body, thereby can be immersed in easily in the fluid to be measured, both the side of installing and using Just, be not subjected to again the impact of viscous mass and incrustation, the reliability height, the life-span is long; Simultaneously, this sensing A better simply schmidt door circuit is adopted in the core of the probe capacitance measurement circuit of device The high-frequency generator that consists of, no high frequency transformer and inductance coil, thereby assemble and debug all very Convenient, its certainty of measurement and sensitivity are all higher.

Claims (3)

1, a kind of condenser type level sensor, it comprises that has the capacitance probe that A electrode and B electrode add that intermediate medium constitutes, the sensor body and the lead portion of probe capacitance measurement circuit are housed, it is characterized in that described capacitance probe [1], sensor body [2] and lead portion [3] thereof are sealed into an integral body; The probe capacitance measurement circuit adopts 9 one by schmidt door circuit [6], a feedback resistance R and the high frequency oscillator that capacitor C x forms, feedback resistance in this oscillator is connected between the output terminal and input end of schmidt door circuit, and its electric capacity is connected between the input end and ground of schmidt door circuit.

2, a kind of condenser type level sensor according to claim 1, it is characterized in that above-mentioned feedback resistance R resistance should＜＜water resistance.

3, a kind of condenser type level sensor according to claim 1 and 2, it is characterized in that also comprising the frequency dividing circuit that high-frequency oscillation signal is transformed to low frequency signal in the probe capacitance measurement circuit of this sensor, frequency transformation is become the F/V change-over circuit of voltage signal, voltage signal is formed the comparator circuit and the output circuit of switching signal.

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