Capacitive level meter

 

(57) Abstract:

The invention relates to a device for monitoring the liquid level and can be used on transport vehicles. Capacitive level meter fluid contains a two-electrode capacitive sensor, an operational amplifier, a stabilized power supply, standby multivibrator and the trigger. The first electrode two-electrode capacitive sensor and the level of negative feedback of the operational amplifier is connected to its inverting input. Link the positive connection of the operational amplifier is connected with its reinvestiruet entrance. The second electrode two-electrode capacitive sensor connected to the housing. The output of the operational amplifier is connected to the input standby-flop and the first input of the trigger. The standby output of the multivibrator is connected to a second input of the trigger. The technical result consists in increasing the accuracy of control of a given liquid level. 2 Il.

The proposed device relates to a device for monitoring the level of the dielectric liquid such as oil, and is designed for operation primarily on transport vehicles. Known capacitive sensors along.with. 1076763, G 01 F 23/26 [1] and and.with. 1201686 STU method of processing input signal.

The closest to the technical nature of the claimed device is a capacitive sensor according to the patent of the Russian Federation 2054633 [3], which contains two-electrode sensor, a second electrode which is connected to the housing of the capacitance-to-voltage made at the operational amplifier with the level of negative feedback, not inverting input of which is connected to the first electrode of the sensor out phase-sensitive rectifier, a voltage divider and connected in series stable source bipolar power supply, asymmetrical multivibrator, the first differentiator and a second differentiator, the output of which is connected to the inputs of the operational amplifier, the output of which is connected to the input out phase-sensitive rectifier, to the control input of which is connected to the output of the first differentiator, and the unbalanced output of the multivibrator is connected also to the input of the stabilized source of the bipolar power supply, a first outlet through which the voltage divider is connected to the input of the operational amplifier, and a common point of the voltage divider is connected to the housing, and first and second outputs stable source bipolar power supply connected to the inputs is ihade multivibrator periodically arise rectangular voltage pulses having a fixed repetition rate, this signal is fed to the input of the first differentiator, where the DC component of the signal of the multivibrator is suppressed and the output of the differentiator is only the variable component of the signal of the multivibrator, the negative output of the first differentiator out phase-sensitive rectifier is locked, and you receive a positive pulse through the first differentiator to the control input out phase-sensitive rectifier it opens and it is memorization switching voltage. The voltage output from the first differentiator is supplied also to the input of the second differentiator, where the DC component is suppressed, and the variable goes almost without distortion. From the output of the second differentiator pulse AC voltage is supplied to the inverting and non-inverting inputs of the operational amplifier to the inverting input of which is connected a link negative feedback, and not inverting one electrode of the two-electrode capacitive sensor. This inclusion of the operational amplifier provides a low pass filter of the first order as inverting and not inverting inputs, and the time constant in mestnogo sensor. The output of the operational amplifier a signal proportional to the difference between works of the signal output from the first differentiator on the transfer function of the inverting and einverseremove channels of the operational amplifier. Output out phase-sensitive rectifier, phase opening which coincides with the maxima of the useful signal from the output of the operational amplifier will be a signal proportional to the level of the measured liquid.

The disadvantage of the prototype is the lack of accuracy of the level measurement. The basic error of measurement of liquid level in the device prototype are:

1. error FCV, the output of which the pulsating signal and the error pulses included in the error changes;

2. error in processing method, which is an error processing the input signal in the form of steps of a first order filter for inverting and not inverting inputs.

The decomposition in Fourier series speed signal there are a number of harmonics:

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thus, changing the time constant of the filter by not inverting input twice will lead to the suppression of the fundamental wave signal twice, the third harmonic is six-fold, p the imposition of the capacitance sensor, which is proportional to the level of the liquid, causes a disproportionate change in the amplitude of the output signal of the operational amplifier, as well as sampling in out phase-sensitive rectifier is in the moment of the maximum amplitude of the output signal of the operational amplifier, and the output out phase-sensitive rectifier is a signal proportion to the level of the measured liquid.

The aim of the proposed solutions is to improve the accuracy of control of a given liquid level. This goal is achieved by the fact that capacitive level meter liquids containing two-electrode capacitive sensor, a second electrode which is connected to the housing, and an operational amplifier [4], stable power source, and the first electrode of the two-electrode capacitive sensor and the level of negative feedback of the operational amplifier is connected with its inverting input, and link the positive feedback of the operational amplifier is connected with its reinvestiruet input, inputs standby multivibrator and the trigger [5], while the output of the operational amplifier is connected to the input standby multivibrator and to the first input of the trigger, and the output idose is their diagram of the inventive device in comparison with the prototype by reducing the number of functional blocks, such as two differentiator and fotochuvstvitelen rectifier, which ultimately leads to increased reliability of the claimed device.

The analysis of the prior art, including searching by the patent and scientific and technical information sources and identify sources that contain information about the equivalents of the claimed invention, has allowed to establish that the authors have not found analogues characterized by signs, identical with all the essential features of the claimed invention, therefore, the claimed invention meets the criterion of "novelty". The newly introduced features, namely waiting multivibrator and a trigger, the technique is widely known, but not detected the use of these features in this relationship with other signs to achieve the above technical result, therefore, the claimed invention meets the criterion of "inventive step".

The essence of the claimed device may be, for example, illustrated in the following graphics:

in Fig.1 shows a block diagram of the inventive device;

in Fig.2 shows the stress distribution.

The inventive device in accordance with electrod capacitive sensor connected to the inverting input of the operational amplifier 2 and through the link negative feedback, formed by the resistor R1, the output of the operational amplifier. Link the positive feedback formed by the resistors R2 and R3, connects the output of the operational amplifier with its reinvestiruet entrance. The output of the operational amplifier is connected to the input standby multivibrator 3 and to the first input of the trigger 4, the standby output of the multivibrator 3 is connected to a second input of the trigger 4, the device is powered by a stabilized power source 5.

Capacitive level meter operates as follows.

After turning on the power at the output of the operational amplifier 2, you receive the positive voltage Uo.OS(plot of the voltage Uo.OSshown in Fig. 2A), the resulting capacity With two-electrode capacitive sensor included in the link negative feedback With R1, starts to charge, and as soon as the voltage on the inverting input of the operational amplifier exceeds the voltage on reinvestiruet the entrance of the shelter (the voltage set by the resistors R2, R3, link positive feedback), the voltage at the output of the OS will change the sign, and the cycle will repeat indefinitely, with period 2,2R1, and cycle time will vary depending on aprimer oil, between the electrodes of the two-electrode capacitive sensor its resulting capacity With minimal, and in the presence of oil With a maximum. The capacitance sensor 1 is proportional to the level of the dielectric liquid.

The output voltage pulses from the output of the operational amplifier 2 are served at the first input of the trigger 4 and the input of the standby multivibrator 3 which at its output produces pulses are stable in time (plot output voltage standby multivibrator Uo.animation.shown in Fig.2B). Using a trigger is a comparison of the durations of the pulses from the output of the operational amplifier toand pulses standby multivibrator 3 tanimation.(t1= toy1-tanimation.), the pulse duration of the output standby multivibrator 3 can be regulated and depends on the monitored level of oil. When the oil level is above the setpoint of the controlled values, a positive differential voltage pulse to a second input (clock input) trigger overwrites the information from the first input (input data) to the output of the trigger 4, i.e. in accordance with Fig.2A and 2B each such operation of the operational amplifier 2 output trigger 4 will be completed>pulses from the output of the operational amplifier (because it decreases the resultant capacity (two-electrode capacitive sensor 1), and as soon as the duration of tobecomes shorter than the duration of the waiting period of the multivibrator tmult,(t2= toy1-tanimation.) positive differential voltage pulse to a second input (clock input) trigger 4 overwrites the information from the first input (input data) flip-flop 4 to the output of the trigger 4, i.e. in accordance with Fig.2G and 2D on the trigger output 4 is set to low level output voltage Fig.2C, which corresponds to the oil level below the specified value.

The inventive device more accurately controls the oil level in comparison with the prototype, as the frequency of oscillations in the circuit of the operational amplifier in the inventive device is a linear function of the capacitance of the sensor, while the amplitude processed in the prototype signal is nonlinear, increasing the level of higher harmonics in the signal leads to error on the high side compared with the actual liquid level and the lower level of higher harmonics to the error underestimated compared to the actual level of the liquid.

Thus, by offering the th sample.

References

1. A. C. 1076763, G 01 F 23/26.

2. A. C. 1201686, G 01 F 23/26.

3. RF patent 2054633, G 01 F 23/26, G 01 F 23/24.

4. P. Horowitz. U. hill, "the Art circuitry", M, "World", 1993, pp. 301-303.

5. Shyla C. L. "Popular digital circuits". Chelyabinsk., "Metallurgy", 1989, pages 227-229.

Capacitive level meter liquids containing two-electrode capacitive sensor, a second electrode which is connected to the housing, and an operational amplifier, a stabilized power supply, and the first electrode of the two-electrode capacitive sensor and the level of negative feedback of the operational amplifier is connected with its inverting input, and link the positive feedback of the operational amplifier is connected with its reinvestiruet entrance, characterized in that it additionally introduced waiting multivibrator and a trigger, the output of the operational amplifier is connected to the input standby-flop and the first input of the trigger, and the output of the standby multivibrator is connected to a second input of the trigger.

 

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EFFECT: expanded functional capabilities.

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