KR100904225B1 - Apparatus for measuring water level - Google Patents

Abstract

The present invention relates to a water level measuring device that enables accurate and stable level detection by improving the inconvenience and instability of the zero offset adjustment of the pressure level detecting pressure sensor. To this end, the reference voltage generator for outputting a reference voltage; A signal processor for differentially inverting and amplifying a differential voltage (Vdiff) between a positive voltage and a negative voltage output from a water level detection pressure sensor based on a reference voltage output from the reference voltage generator and outputting the voltage signal as a voltage signal. ; And an AD converter configured to convert the voltage signal output from the signal processor into a digital signal based on the reference voltage output from the reference voltage generator, and output the digital signal, wherein the reference voltage is simultaneously transmitted to the signal processor and the AD converter. The voltage signal output from the signal processor is converted into a digital signal regardless of the zero offset voltage of the pressure sensor. Therefore, there is an advantage that it is possible to provide accurate and stable measurement information by improving the inconvenience and instability of the zero offset adjustment of the pressure sensor for detecting the water level.

Water level measurement, pressure sensor

Description

Water level measuring device {APPARATUS FOR MEASURING WATER LEVEL}

1 is an electric circuit diagram showing a pressure sensor for detecting a water level according to the prior art.

2 is a waveform diagram showing a zero offset adjustment and a pressure / voltage signal of an amplified signal output from a pressure sensor for detecting a water level according to the prior art;

3 is an electrical circuit diagram illustrating a zero offset adjustment of a pressure sensor for detecting a water level using a variable resistor according to the prior art.

4 is an electric circuit diagram showing a pressure sensor for detecting a water level using a differential amplifier circuit according to the prior art.

5 is a block diagram showing the configuration of a water level measuring device according to the present invention;

6 is an electrical circuit diagram illustrating an embodiment of a differential amplifier of the signal processor of FIG. 5.

FIG. 7 is a waveform diagram showing a pressure / voltage signal in which a positive zero offset voltage is output from the water level measuring device of FIG.

8 is a waveform diagram showing a pressure / voltage signal in which a negative zero offset voltage is output from the water level measuring device of FIG.

9 is an electrical circuit diagram illustrating another embodiment of the differential amplifier of FIG. 6.

FIG. 10 is an electrical circuit diagram illustrating still another embodiment of the differential amplifier of FIG. 6. FIG.

11 is an electrical circuit diagram illustrating still another embodiment of the differential amplifier of FIG. 6.

(Description of Major Symbols in Drawings)

100: pressure sensor 200: signal processing unit

210, 210a, 210b, 210c: differential amplifier

211, 213a, 213b, 214, 215a, 215b: op amp

212a, 212b: ultra short amplification unit

220: voltage divider 300: AD converter

400: reference voltage generation unit 500: control unit

The present invention relates to a level measurement of groundwater, and more particularly, to a level measurement apparatus which enables accurate and stable level detection by improving the inconvenience and instability of zero offset adjustment of a pressure level detecting pressure sensor.

In general, the most important measurement item for groundwater level measurement is groundwater level. This is because it provides various information in terms of utilization or analysis of measurement results. As a sensor for measuring the groundwater level, various measuring sensors are used, such as capacitive type, bubble type, and pressure type, and most of the level sensor used in Korea is a pressure type sensor that is easy to install and use.

The capacitive water level sensor has a depth between the two conductors in air, a bottom in the water, and an electrical induction of water much greater than that of air, depending on the depth. After calibrating the characteristics of the capacitor, measure the capacitance and convert it to water depth.

However, since the composition and temperature of water change frequently, errors occur even when the electrical resistance is precisely measured, and since the change in the electrical resistance is very small, noise is easily included in the process of amplifying and processing the electrical signal of the DC component, and the electronic circuit is complicated. It is very difficult to use in real open-air problems.

The bubble level sensor is not affected by water pressure measurement even if the water pressure tube is tilted or arbitrarily bent, but it requires a small air compressor or a compressed air tank such as nitrogen, because it needs to blow air in the tube. There is a problem of using only the water level measurement.

Pressure sensors have a diffusion type and a thin film type, and both of them utilize the piezo resistance effect of semiconductors whose resistance changes according to the applied pressure, and are easier to install than other level sensors and have a wider measuring range. Have.

1 illustrates a pressure sensor 10 according to the prior art, in which a plurality of resistors 20a, 20b, 20c, and 20d constituting a bridge detection circuit of the pressure sensor 10 compensate for a change in atmospheric pressure and a temperature change. For this purpose, it is appropriately placed at the position of mutual compensation to perform stable water level measurement regardless of atmospheric pressure change and water temperature change.

However, the pressure sensor 10 made of such a bridge detection circuit has a problem in that the output value of manufacturing, that is, the Vdiff (+ Vout--Vout) voltage does not accurately balance at atmospheric pressure. In addition, even if the pressure sensor is balanced, there is an offset inside the amplifying circuit.

That is, the pressure sensor 10 is output including a zero offset voltage value within a certain tolerance range in a positive (+) direction or a negative (-) direction. The output a of the pressure sensor 10 in FIG. 2 has a negative zero offset voltage, for example.

In order to correct the zero offset voltage value, when zero adjustment is performed using a variable resistor at the output terminal of the pressure sensor 10, the output of the pressure sensor 10 may be adjusted as shown in (b).

As a zero offset voltage correction method of the pressure sensor 10, as shown in FIG. 3, a variable resistor 30 is provided at an output terminal of the pressure sensor 10, or an op amp 40 illustrated in FIG. 4. It is possible to use the offset control of the control.

However, such a configuration causes a non-linearity of the measurement circuit, and a temperature drift occurs due to an input imbalance of the operational amplifier 40, resulting in instability of the output voltage.

In addition, the manufacturer of the pressure sensor provided a variable resistor for the correction of the offset voltage to adjust the zero point of the offset voltage, but the offset at the time of measurement due to changes in the adjustment value due to changes in temperature, humidity, vibration, etc. If the calibration is not performed, there is a problem in that it is impossible to provide a measurement value of the correct level.

In addition, the frequent inspection and calibration of the pressure sensor requires a lot of time and effort to increase the management cost, there is a problem that the efficiency is reduced.

In order to solve the above problems, an object of the present invention is to provide a water level measuring apparatus that enables accurate and stable water level detection by improving the inconvenience and instability of zero offset adjustment of a pressure level detecting pressure sensor.

It is also an object of the present invention to provide a level measurement apparatus capable of providing a stable level measurement value for a long time regardless of removal, inspection and calibration of the level sensor.

In order to achieve the above object, the level measurement apparatus according to the present invention includes a reference voltage generator for outputting a reference voltage; A signal processor for differentially inverting and amplifying a differential voltage (Vdiff) between a positive voltage and a negative voltage output from a water level detection pressure sensor based on a reference voltage output from the reference voltage generator and outputting the voltage signal as a voltage signal. ; And an AD converter configured to convert the voltage signal output from the signal processor into a digital signal based on the reference voltage output from the reference voltage generator, and output the digital signal, wherein the reference voltage is simultaneously transmitted to the signal processor and the AD converter. The voltage signal output from the signal processor is converted into a digital signal regardless of the zero offset voltage of the pressure sensor.

In addition, the present invention stores any output voltage set by the user among the digital voltage signal output from the AD converter unit as a zero point and a span point, respectively, and the pressure output at any level between the stored zero point and the span point It is preferable to further include a control unit for calculating and outputting the output voltage of the sensor.

The signal processor may include a differential amplifier configured to differentially invert and amplify the output differential voltage of the pressure sensor and output the voltage signal as a voltage signal; And a voltage divider configured to divide the voltage signal output from the differential amplifier and output the divided voltage signal to the AD converter.

The signal processor may further include an ultrashort amplifier configured to correct an impedance difference between the pressure sensor and the differential amplifier.

In addition, the differential amplifier has a positive output terminal of the pressure sensor connected to a negative input terminal, a negative output terminal of the pressure sensor and an output terminal of the reference voltage generator is connected to a positive input terminal. An operational amplifier for differentially inverting and amplifying the output differential voltage of the pressure sensor and outputting the voltage signal; And a plurality of resistors connected to the (+) and (−) input terminals of the op amp to determine an amplification ratio of the op amp.

In addition, the voltage divider has a plurality of resistance ratios set in advance such that the voltage signal output from the differential amplifier is divided so that the output of the half-cup differential amplification is less than the reference voltage Vref, which is the upper limit of the voltage measurement of the AD converter. It is characterized by consisting of a resistor.

Hereinafter, exemplary embodiments of the present invention will be described with reference to the accompanying drawings.

5 is a block diagram showing the configuration of the water level measurement device according to the present invention, Figure 6 is an electrical circuit diagram showing the water level measurement device of FIG.

As shown in FIG. 5 and FIG. 6, the water level measuring device according to the present invention differentially inverts and outputs a voltage signal by differentially inverting and amplifying a difference voltage (Vdiff) between a positive voltage and a negative voltage output from the pressure sensor 100. Is equal to the signal processor 200 and the AD converter 300 for converting and outputting a voltage signal output from the signal processor 200 into a digital signal. Among the reference voltage generator 400 for outputting the reference voltage Vref and the digital voltage signal output from the AD converter 300, an arbitrary output voltage is stored as zero and span points, respectively, and the stored zero and span points are respectively stored. And a controller 500 for calculating and outputting an output voltage of the pressure sensor 100 output at any level therebetween.

In the pressure sensor 100, a plurality of resistors constituting the bridge detection circuit are properly disposed at mutual compensation positions for correction of atmospheric pressure change and temperature change, thereby performing stable water level measurement irrespective of atmospheric pressure change and water temperature change.

In addition, the pressure sensor 100 outputs a positive (+) Vout voltage and a negative (-) Vout voltage including a zero offset voltage value within a certain tolerance range, and the pressure sensor 100 is conventional You may use the well-known pressure sensor shown in FIG. 1, FIG.

The signal processor 200 receives a reference voltage Vref output from the reference voltage generator 400, and outputs a positive voltage output from the water level detection pressure sensor 100 based on the input reference voltage Vref. The differential voltage Vdiff between + Vout) and negative voltage (-Vout) is differentially inverted and output as a voltage signal.

Here, the signal processor 200 divides the voltage signal output from the differential amplifier 210 and the differential amplifier 210 for differentially inverting and amplifying the output difference voltage Vdiff of the pressure sensor 100 and outputting the voltage signal. It includes a voltage divider 220 to be output to the AD converter 300.

The differential amplifier 210 outputs the positive voltage (+ Vout) output from the pressure sensor 100 through the resistor R3 to the negative input terminal and is output from the differential amplifier 210 through the resistor R4. The output voltage Va is connected to be input, the negative output voltage (-Vout) output from the pressure sensor 100 through the resistor R1 to the (+) input terminal, and the reference voltage generator through the resistor (R2) The op amp 211 and the op amp 211 are connected to input the reference voltage Vref output from the 400 to differentially invert and amplify the output differential voltage of the pressure sensor 100 to output the voltage signal Va. A plurality of resistors R1 to R4 are connected to the positive input terminals of the amplifiers to determine the amplification ratio of the operational amplifier 211.

That is, the resistor R1 has one side connected to the negative output terminal of the pressure sensor 100 and the other side connected to the positive input terminal of the operational amplifier 211 so as to output a negative voltage (-Vout) output from the pressure sensor 100. ) Is input to the operational amplifier 211, one side of the resistor R2 is connected to the reference voltage generator 400, the other side is connected to the (+) input terminal of the operational amplifier 211.

Therefore, if the amplification ratio is R1: R2 = R3: R4, and R1 = R3, R2 = R4, the differential amplification ratio is R2 / R1, and the resistance ratio (R1: R2) is the maximum measurement range of the pressure sensor to be used. In consideration of the span voltage, which is an output voltage, the amplified output voltage is determined to be within an input lower limit voltage range of the AD converter 300.

In addition, the differential amplifier 210 according to the present invention, the positive voltage (+ Vout) of the pressure sensor 100 is input through the resistor R3, and the output voltage Va of the op amp 211 is oppy through the resistor R4 The amplifier circuit is connected to the negative input terminal of the amplifier 211.

At this time, the output voltage range should not exceed the linear amplification section of the op amp and the measurement range (lower limit value) of the AD converter section when using a single power supply.

The voltage divider 220 outputs the voltage signal Va output from the differential amplifier 210 to scale the output of the half residual differential amplification to be less than the reference voltage Vref which is the upper limit of the voltage measurement of the AD converter 300. The voltage divider is divided by the resistor Ra and the resistor Rb having the predetermined resistance ratio, and the divided voltage signal Vb is input to the AD converter 300.

The AD converter 300 receives an analog voltage signal Vb output from the signal processor 200 and converts the analog voltage signal into a digital signal based on the reference voltage Vref output from the reference voltage generator 400.

The reference voltage generator 400 provides the reference voltage Vref, which is the largest factor of temperature change and long-term drift, to the signal processor 200 and the AD converter 300 in the same manner, thereby providing a pressure sensor 100. Irrespective of the zero offset voltage it has, the voltage signal Vb output from the signal processor 200 may be converted into a digital signal by the AD converter 300 to provide a digital signal, thereby enabling stable measurement in water level measurement.

In addition, by setting the reference voltage as high as, for example, about 2.5V, and providing the signal to the signal processing unit 200 and the AD converter unit 300 in common, the non-linear section of the operational amplifier can be avoided and a single power supply circuit can be configured. .

FIG. 7 is a waveform diagram illustrating a pressure / voltage signal at which a positive zero offset voltage is output from the water level measuring apparatus of FIG. 5, and FIG. 8 is a pressure / voltage signal at which a negative zero offset voltage is output from a water level measuring apparatus of FIG. 5. Is a waveform diagram showing.

7 and 8, when a difference voltage Vdiff having a positive offset voltage is detected, a voltage lower than the reference voltage Vref is output even when the output voltage Va of the operational amplifier 211 is inverted and amplified. As a result, the voltage Vb divided by the resistor Ra and the resistor Rb outputs a voltage lower than the reference voltage Vref.

In addition, when a difference voltage Vdiff having a negative offset voltage is detected, the output voltage Va of the operational amplifier 211 is inverted and amplified to output a voltage exceeding the reference voltage Vref. However, the Va voltage is divided by the resistor Ra and the resistor Rb so that the Vb voltage is output at a voltage lower than the reference voltage Vref.

Therefore, it is possible to provide a linear output voltage without adjusting the zero offset voltage of the pressure sensor.

Meanwhile, the controller 500 stores an arbitrary output voltage as a zero point and a span point among the voltage signals output from the AD converter unit 300, and the pressure sensor outputs at an arbitrary level between the stored zero point and the span point. The output voltage is calculated and output.

Referring to the control unit 500 in more detail, a zero point (measurement starting position set by the user) input by a user through an input unit (not shown), such as a keypad, among the output voltages digitally processed by the AD converter unit 300. For example, 0m) and a span point (for example, the maximum measurement position set by the user, for example, 50m) are detected, and the zero point and the span point are stored in a storage unit (not shown) such as a memory, and then pressure The sensor detects a voltage output at an arbitrary level between the zero point and the span point, and calculates and outputs the arbitrary level.

Here, the zero point and the span point may be arbitrarily set according to the environment in which the sensor is installed for detecting the water level or the user's convenience.

Since the method for calculating the position at the arbitrary level has a linearity between the zero point and the span point, it is possible to calculate the level from the output voltage of the pressure sensor measured at the arbitrary position using the zero point and the span point.

On the other hand, the measurement data such as the zero point and the span point stored in the storage unit such as the memory prevents the loss of the measurement data set during the operation such as removing the power supply of the sensor or replacing the sensor, thereby replacing and maintaining the water level measurement device. To be used.

Therefore, the voltage for any level output from the controller 500 is transmitted to a remote place through a communication unit (not shown), such as RS-485, for example, and the voltage for the arbitrary level transmitted to the remote place is displayed on the display unit. Is output via

In the above-described embodiment, the case where there is no correction of the impedance difference between the impedance of the pressure sensor 100 and the differential amplifier 210 of the signal processor 200 has been described.

Next, another embodiment of the differential amplifier including an ultra-short amplifier for correcting the impedance difference between the pressure sensor 100 and the differential amplifier 210 will be described.

9 is an electrical circuit diagram illustrating another embodiment of the differential amplifier of FIG. 6.

As shown in FIG. 9, the first stage amplifier 212a having a high input impedance and a low output impedance is installed at an input terminal of the differential amplifier 210a to differentially amplify the output impedance of the pressure sensor 100 (refer to FIG. 5). Distortion of the pressure sensor 100 due to the impedance of the input portion 210a is prevented.

That is, in the transmission of the signal voltage, when the output impedance of the output terminal of the signal is not very small or the input impedance of the input terminal is not very large, the first stage amplifying unit 212a is provided to solve the impedance mismatch.

The ultra-short amplifier 212a of FIG. 9 includes two op amps 213a and 213b, and the negative (-) Vin voltage output from the pressure sensor 100 and input to the differential amplifier 210a is the op amp 213a. ) Is input to the (+) input terminal of the input terminal, a voltage fed back from the output terminal is input to the (-) input terminal, and the output terminal differentially inverts and outputs the output differential voltage of the pressure sensor 100 to the voltage signal Va. It is connected to the negative input terminal of the output op amp 214.

In addition, a positive voltage input from the pressure sensor 100 and input to the differential amplifier 210a is connected to the positive input terminal of the operational amplifier 213b, and the negative input terminal is fed back from the output terminal. The input voltage is input, and the output terminal is connected to the positive input terminal of the operational amplifier 214 that differentially inverts and amplifies the output difference voltage of the pressure sensor 100 and outputs the voltage signal Va.

Therefore, the operational amplifier 214 outputs the voltage signal Va obtained by differentially inverting and amplifying the output voltage difference of the pressure sensor 100 output from the two operational amplifiers 213a and 213b according to the reference voltage Vref.

10 is an electrical circuit diagram illustrating still another embodiment of the differential amplifier of FIG. 6.

The differential amplifier 212b shown in FIG. 10 adds resistors R1 and R2 to the first stage amplifier 212a (see FIG. 9) for improving the amplification ratio to solve the impedance mismatch described in the embodiment of FIG. One embodiment. That is, the differential amplifier 212b of FIG. 10 has one or more gains in the differential amplifier 212a of FIG. 9.

The ultra-short amplification unit 212b of FIG. 10 includes two op amps 213a and 213b, and the negative (-) Vin voltage output from the pressure sensor 100 and input to the differential amplifier 210b is the op amp 213a. ) Is connected to the positive (+) input terminal, and the negative (-) input terminal receives a voltage fed back from the output terminal through the resistor R1, and the output terminal differentially amplifies the output difference voltage of the pressure sensor 100 by It is connected to the negative input terminal of the operational amplifier 214 which outputs the voltage signal Va.

In addition, the positive (+) Vin voltage output from the pressure sensor 100 and input to the differential amplifier 210b is connected to the positive input terminal of the operational amplifier 213b, and the negative input terminal is fed back from the output terminal. The voltage is input through the resistor (R2), the output terminal is connected to the (+) input terminal of the op amp 214 outputting the voltage difference (Va) by differential inverting and amplifying the output differential voltage of the pressure sensor 100 do.

Accordingly, it is possible to increase the amplification ratio of the differential amplifier 210b through the negative input terminals and the output terminals R1 and R2 of the op amps 213a and 213b, and the op amp 214 The voltage signal Va obtained by differentially inverting and amplifying the output differential voltage of the pressure sensor 100 output from the two op amps 213a and 213b is output.

FIG. 11 is an electrical circuit diagram illustrating still another embodiment of the differential amplifier of FIG. 6.

The differential amplifier 210c shown in FIG. 11 is configured to allow impedance matching and amplification degree to be changed using two op amps 215a and 215b.

That is, the positive Vin voltage output from the pressure sensor 100 (refer to FIG. 5) and input to the differential amplifier 210c is connected to the positive input terminal of the first operational amplifier 215a, and the first operational amplifier ( The output voltage fed back from the output terminal of the first op amp 215a is connected to the negative input terminal of 215a and the negative input terminal of the second op amp 215b from the output terminal of the second op amp 215b. The output voltage fed back to is input.

In addition, a variable resistor RG is provided between the negative input terminal of the first operational amplifier 215a and the negative input terminal of the output terminal of the second operational amplifier 215b so that the amplification degree can be varied. .

The negative Vin voltage input to the differential amplifier 210c is connected to the positive input terminal of the second operational amplifier 215b and is input to the negative input terminal of the second operational amplifier 215b. The output differential voltage of the pressure sensor 100 is differentially inverted and output as a voltage signal Va by using the output of the operational amplifier 215a and the output signal fed back through the output terminal of the second operational amplifier 215b. .

Therefore, the two op amps 215a and 215b can be used to correct the amplification degree together with the elimination of impedance mismatch.

 As described above, the water level measuring apparatus according to the present invention has an advantage of providing accurate and stable measurement information by improving the inconvenience and instability of the zero offset adjustment of the pressure sensor for detecting the water level.

In addition, the present invention has the advantage that it is possible to provide a stable level measurement by receiving a reference voltage equally, improving the instability due to temperature changes and long-term drift.

In addition, the present invention has the advantage that it can be configured as a single power supply circuit by avoiding the non-linear section of the op amp in the amplification process.

In addition, there is an advantage that can reduce the power consumption and simplify the circuit.

In the above, the present invention has been shown and described with respect to certain preferred embodiments. However, the present invention is not limited to the above-described embodiments, and those skilled in the art to which the present invention pertains can vary as many as possible without departing from the spirit of the present invention as set forth in the claims below. Changes may be made.

Claims (6)

A reference voltage generator for outputting a reference voltage; Differential amplification by differentially inverting and amplifying the differential voltage (Vdiff) between the positive voltage and the negative voltage output from the water level detection pressure sensor based on the reference voltage output from the reference voltage generator A signal processor having a circuit and a voltage divider circuit for dividing a voltage signal output from the differential amplifier circuit; An AD converter unit converting the divided voltage circuit provided from the voltage divider circuit to the signal processor to a digital signal based on the reference voltage output from the reference voltage generator; And Among the digital voltage signals output from the AD converter unit, an arbitrary output voltage set by a user is stored as zero and span points, respectively, and an output voltage of the pressure sensor output at an arbitrary level between the stored zero and span points. It includes a control unit for calculating and outputting, And applying the reference voltage simultaneously to the signal processor and the AD converter to convert the voltage signal output from the signal processor into a digital signal regardless of the zero offset voltage of the pressure sensor. delete delete The method of claim 1, And the signal processor further comprises an ultra-short amplification unit configured to correct an impedance difference between the pressure sensor and the differential amplifier circuit. The method of claim 1, In the differential amplifier circuit, a positive output terminal of the pressure sensor is connected to a negative input terminal, and a negative output terminal of the pressure sensor and an output terminal of the reference voltage generator are connected to a positive input terminal to supply the pressure. An operational amplifier for differentially inverting and amplifying the output difference voltage of the sensor and outputting the voltage signal; And And a plurality of resistors connected to the (+) and (-) input terminals of the op amp to determine an amplification ratio of the op amp. The method of claim 1, And the voltage divider circuit comprises a plurality of resistors having a predetermined resistance ratio such that the voltage signal output from the differential amplifier circuit is divided.

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