KR100760005B1 - Solution concentration measuring device - Google Patents

Abstract

An apparatus for measuring the concentration of a solution is provided to lower a manufacturing cost, to simplify the manufacturing process and to improve the precision of measurement. An apparatus for measuring the concentration of a solution comprises a temperature sensing part(200) which has a temperature sensor(20) for measuring the temperature of a solution and outputs the first oscillation frequency corresponding the resistance of the temperature sensor; a conductivity sensing part(300) which has an electrode sensor(30) for measuring the conductivity of a solution and outputs the second oscillation frequency corresponding the resistance of the electrode sensor; a counter which determines the oscillation frequency of the temperature sensing part and the conductivity sensing part; and a control part(100) which calculates the concentration of a solution based on the first and second oscillation frequency determined by the counter. The temperature sensing part and the conductivity sensing part are provided with a first switch for selecting a Schmitt trigger circuit(41,51) and the feedback input of a Schmitt trigger circuit.

Description

Solution concentration measuring device

1 is a block diagram showing a concentration measurement device of a typical solution.

Figure 2 is a block diagram showing an apparatus for measuring the concentration of a solution according to an embodiment of the present invention.

*** Brief description of the main parts of the drawing ***

20: temperature sensor, 30: electrode sensor,

41, 51: Schmitt trigger circuit, 100: control unit,

200: temperature detector, 300: conductivity detector.

The present invention relates to a concentration measuring device for measuring the concentration of the solution standing in a certain place, and in particular to a low-cost, easy to manufacture and precisely measuring the concentration of the solution to be able to measure the concentration of the solution.

In general, in the chemical field and the environmental field, the concentration of a specific component contained in water, that is, the concentration of a solution is frequently performed. As a method for measuring the concentration, a method of measuring the electrical conductivity and temperature of a solution is widely used.

1 is a block diagram showing an apparatus for measuring the concentration of a solution currently being used in general.

The concentration measuring apparatus shown in FIG. 1 includes a control unit 10, a temperature sensor 20, an electrode sensor 30, a temperature detector 40, a conductivity detector 50, an oar circuit 60, and a counter 70 that control the entire apparatus. It is configured to include).

The control unit 10 controls the entire apparatus and calculates the concentration of the solution to be measured based on the detection results of the temperature detector 40 and the conductivity detector 50.

The temperature sensor 20 consists of a thermistor, for example. The temperature sensor 20 has a resistance value that varies depending on the temperature of the solution. The electrode sensor 30 is configured with two electrode plates spaced apart at regular intervals. The electrode sensor 30 is recognized as a form in which the resistance value varies depending on the concentration of the solution because the electrical conductivity between the two electrode plates is changed depending on the concentration of the component contained in the solution.

The temperature detector 40 is basically configured to include a Schmitt trigger NAND gate (41). One input terminal of the Schmitt trigger circuit 41 is coupled to the selection signal output terminal S1 of the controller 10, and the other input terminal is coupled to the output terminal through the offset resistor 43 and the temperature sensor 20. In addition, a charge / discharge capacitor 42 is coupled to the connection node between the other input terminal and the offset resistor 43.

When the high level signal is input from the selection signal output terminal S1 of the controller 10, for example, the Schmitt trigger circuit 41 executes the oscillation operation. It is input to the counter 70 to be described. At this time, the oscillation frequency of the Schmitt trigger circuit 41 is set by the capacitance of the capacitor 42 and the resistance of the resistor 43 and the temperature sensor 20.

The temperature sensor 20 changes its resistance value according to the temperature of the solution, and the temperature detector 20 inputs a frequency signal corresponding to the resistance value of the temperature sensor 20 to the counter 70.

The conductivity detector 50 has substantially the same configuration as the temperature detector 40. That is, the conductivity detector 50 has one input terminal of the Schmitt trigger circuit 51 coupled to the selection signal output terminal S2 of the controller 10, and the other input terminal of the Schmitt trigger circuit 51 is an offset resistor 53. And through its electrode sensor 30 to its output end. A charging / discharging capacitor 52 is coupled to the connection node between the other input terminal and the resistor 53.

The Schmitt trigger circuit 51 performs an oscillation operation when a high level signal is input from the selection signal output terminal S2 of the controller 10, for example, and the output of the oscillation frequency signal is countered through the OR circuit 60. 70 is input. At this time, the oscillation frequency of the Schmitt trigger circuit 51 is set by the capacitance of the capacitor 52 and the resistance of the resistor 53 and the electrode sensor 30.

The electrode sensor 30 varies in electrical conductivity between the positive electrodes according to concentrations of other components included in the solution. This electrical conductivity is recognized as a change in resistance value in an external circuit. The conductivity detector 50 inputs a frequency signal corresponding to the resistance value of the electrode sensor 30 to the counter 70.

The counter 70 counts the frequency of the signal input from the temperature detector 40 or the conductivity detector 50 and inputs it to the controller 10.

The controller 10 first sets the selection signal output terminal S1 to a high level, inputs a detection result of the temperature detector 40, that is, a frequency value of a signal output from the temperature detector 40, and based on this, the temperature of the solution. Determine. Of course, in this case, the selection signal output terminal S2 is set at the low level, and accordingly, the output of the conductivity detector 50 is set at the "1" level.

When the temperature detection is completed, the controller 10 sets the selection signal output terminal S1 to a low level and the selection signal output terminal S2 to a high level to input a frequency value of a signal output from the conductivity detector 50. Based on this, the conductivity of the solution is determined.

Then, the final concentration of the solution is calculated based on the determined temperature and conductivity of the solution.

However, the above-mentioned conventional apparatus has the following problem.

1. In the conventional apparatus, the capacitance value of the components, in particular the capacitors 42 and 52, varies depending on the ambient temperature at which the apparatus is installed, thereby causing the oscillation frequency of the Schmitt trigger circuits 41 and 51 to fluctuate. Will occur. And, in order to prevent this, there is a problem of using an expensive capacitor or executing an additional circuit complementary design.

2. In the case of the electrode sensor 30 described above, when measuring the conductivity for a long time using the electrode sensor 30, ions are accumulated on both electrodes of (+) and (-), thereby causing a problem of fluctuation in electrical conductivity between both ends of the electrode. .

Accordingly, the present invention has been made in view of the above circumstances, and an object of the present invention is to provide a solution concentration detection device which is simple in manufacturing and inexpensive and can accurately measure the concentration of a solution.

In order to achieve the above object, the solution for detecting concentration of a solution according to the first aspect of the present invention includes a temperature sensor for measuring the temperature of the solution and an electrode sensor for measuring the conductivity of the solution. In the solution concentration detection device for determining the concentration of the solution based on the temperature detection unit for outputting a first oscillation frequency corresponding to the resistance value of the temperature sensor, and a second oscillation frequency corresponding to the resistance value of the electrode sensor A conductivity detector for outputting, a counter for determining oscillation frequencies of the temperature detector and the conductivity detector, and a controller for calculating the concentration of the solution based on the first and second oscillation frequencies determined by the counter, The temperature detection unit and the conductivity detection unit each of the first switch for selecting the feedback input of the Schmitt trigger circuit and the Schmitt trigger circuit And a selection signal input to one input terminal, the other input terminal is grounded through a capacitor, coupled to one side of an offset resistor, and a reference resistor and a sensor are parallel to the other side of the offset resistor. And the first switch selectively couples the reference resistor and the sensor to an output terminal of the Schmitt trigger circuit according to a switching signal from a controller.

In addition, the solution for detecting the concentration of the solution according to the second aspect of the present invention for realizing the above object is provided with a sensor for measuring the conductivity of the solution, to determine the concentration of the solution based on the resistance value of the sensor A concentration detecting apparatus, comprising: a detector for outputting an oscillation frequency corresponding to a resistance value of the sensor, a counter for determining an oscillation frequency of the detector, and a concentration of a solution based on an oscillation frequency determined by the counter And a detection switch including a Schmitt trigger circuit and a first switch for selecting a feedback input of the Schmitt trigger circuit. The Schmitt trigger circuit has a selection signal input to one input terminal. And the other input terminal is grounded through a capacitor and coupled to one side of an offset resistor, and the other side of the offset resistor is Is coupled to the reference resistor and the sensor in parallel, the first switch is characterized in that for coupling to the output of the Schmitt trigger circuit of the reference resistance and the sensor selectively in accordance with the switching signal from the control unit.

In addition, the controller determines the oscillation frequency Fr of the Schmitt trigger circuit through a counter in a state in which the output terminal of the Schmitt trigger circuit and the reference resistor are coupled through a first switch, and the output terminal of the Schmitt trigger circuit through the first switch. When the oscillation frequency Ft of the Schmitt trigger circuit is determined in the state where the sensor and the sensor are combined, the resistance value of the offset resistance is Ro, the resistance value of the reference resistance is Rr, and the resistance value of the sensor is Rt.

The resistance value of the sensor is calculated on the basis of the equation.

In addition, the second switch is coupled in parallel with the electrode sensor, the control unit is characterized in that for setting the second switch in the non-measurement state of the electrode sensor.

Hereinafter, an embodiment according to the present invention will be described with reference to the drawings.

2 is a block diagram showing an apparatus for detecting a concentration of a solution according to an embodiment of the present invention. In FIG. 2, the same reference numerals are assigned to parts substantially the same as those in FIG. 1, and a detailed description thereof will be omitted.

The apparatus for detecting the concentration of the solution according to the present embodiment includes the temperature sensor 20, the electrode sensor 30, the OR circuit 60, and the counter 70, as shown in FIG. 1, and the controller 100 and the temperature detector 200. And a conductivity detector 300.

In the above configuration, the temperature detector 200 is configured to include the Schmitt trigger circuit 41 as in the prior art. The Schmitt trigger circuit 41 has one input terminal coupled to the selection signal output terminal S1 of the controller 100 and the other input terminal grounded through the charge / discharge capacitor 42 and coupled to one end of the offset resistor 43. do. The other end of the offset resistor 43 may be a reference resistor 45 or a temperature sensor having a resistance value fixed by the switch 44 on / off controlled by the switching signal SW1 from the controller 100. 20 is selectively coupled to the output terminal of the Schmitt trigger circuit 41. The oscillation frequency signal output from the Schmitt trigger circuit 41 is input to the counter 70 through the OR circuit 60.

The conductivity detector 300 has the same configuration as the temperature detector 200 described above. That is, the selection signal output terminal S2 of the controller 100 is coupled to one input terminal of the Schmitt trigger circuit 51, and the other input terminal of the Schmitt trigger circuit 51 is grounded through the capacitor 52 for charge and discharge. Is coupled to one end of the offset resistor 53. The other end of the offset resistor 53 may be a reference resistor 55 or an electrode sensor having a resistance value fixed by the switch 54 on / off controlled by the switching signal SW2 from the controller 100. 30 is selectively coupled to the output terminal of the Schmitt trigger circuit 51.

On the other hand, in the conductivity detection unit 300, the switch 56 is coupled in parallel with the electrode sensor 30. The switch 56 is controlled on / off by the switching signal SW3 applied from the controller 100. The switch 56 is for preventing ion accumulation problems occurring at both electrodes of the electrode sensor 30 by discharging ions accumulated in the electrode sensor 30.

The oscillation frequency signal output from the Schmitt trigger circuit 41 is input to the counter 70 through the OR circuit 60.

Next, the operation of the device having the above configuration will be described.

First, the oscillation operation of the Schmitt trigger circuit 41 will be described.

As described with reference to FIG. 1, in the related art, oscillations of the Schmitt trigger circuits 41 and 51 due to characteristic variations depending on the temperature of the components constituting the temperature detector 200 and the conductivity detector 300, in particular, the capacitors 42 and 52. There is a problem that the frequency fluctuates.

In the present embodiment, the control unit 100 first controls the switches 44 and 54 to couple the output terminal of the Schmitt trigger circuit 41 to the reference resistors 45 and 55 to detect the reference oscillation frequency Fr. Then, by combining the switch 44, 54 to the temperature sensor 20 and the electrode sensor 30 to detect the frequency (Ft) according to the temperature and conductivity of the solution through the method of changing the characteristics of the capacitor (42, 52) Remove it.

In other words, the temperature detector 41 is described as an example. The capacitance value of the capacitor 42 is C, the resistance value of the offset resistor 43 is R43, the resistance value of the reference resistor 45 is R45, and the temperature sensor 20 is used. The resistance value of Rt is referred to as Rt, and the oscillation frequency of the Schmitt trigger circuit 41 when the output terminal of the Schmitt trigger circuit 41 is coupled to the reference resistor 45 by the switch 44 is Fr and the switch 44 When the oscillation frequency of the Schmitt trigger circuit 41 when the output terminal of the Schmitt trigger circuit 41 is coupled to the temperature sensor 20 by Ft, Fr and Ft are represented by the following equations (1) and (2). Is displayed.

In Equations 1 and 2, k is a proportional constant.

On the other hand, k and C values in Equations 1 and 2 are the same, so that Equations 1 and 2 can be combined and arranged as in Equation 3 below.

In Equation 3, Ft and Fr are values obtained by measurement, and R43 and R45 are previously known values set at the time of manufacture.

In Equation 3, the capacitance value C of the capacitor 42 whose value varies with temperature is removed. Therefore, according to the above-described method, the resistance value of the temperature sensor 20 can be calculated precisely by excluding the variation characteristic of the component according to the temperature.

This basic concept is equally applicable to the conductivity measuring unit 300.

Next, the operation of the apparatus shown in FIG. 2 will be described based on the above description.

First, in the state in which the concentration measurement of the solution is not performed, the controller 100 turns on the switch 56 of the conductivity detector 300 through the switching signal SW3 to discharge ions accumulated at both ends of the electrode sensor 30. do.

Subsequently, in the case of measuring the concentration of the solution, the controller 100 sequentially drives the temperature detector 200 and the conductivity detector 300 as in FIG. 1 to measure the temperature and the conductivity of the solution. Of course, in this case, the conductivity of the solution may be measured first, and then the temperature of the solution may be measured.

In the case of measuring the temperature of the solution, the control unit 100 first controls the switch 44 through the switching signal SW1 to couple the output terminal of the Schmitt trigger circuit 41 to the reference resistor 45 as well as the selection signal. The high level signal is output to the output terminal S1 to oscillate the Schmitt trigger circuit 41. In this case, the control unit 100 sets the selection signal output terminal S2 to a low level, sets the conductivity measurement unit 300 to an inactive state, and switches the switch 56 to the on state through the switching signal SW3. Will be set.

When the high level signal is input from the control unit 100 through the selection signal output terminal S1, the Schmitt trigger circuit 41 executes the oscillation operation, and the oscillation frequency signal output through the output terminal is passed through the OR circuit 60. It is input to the counter 70 and counted. The counter value by the counter 70 is input to the controller 100, and the controller 100 stores the counter value by the counter 70 as the reference frequency Fr.

When the measurement for the reference frequency (Fr) is finished, the controller 100 controls the switch 44 through the switching signal SW1 to couple the output terminal of the Schmitt trigger circuit 41 to the temperature sensor 20, The oscillation frequency Ft of the Schmitt trigger circuit 41 is measured according to the resistance value of the temperature sensor 20 through the counter 70.

When the measurement of the oscillation frequency Ft is completed, the resistance value of the temperature sensor 20 is calculated through the above equation (3).

As described above, when the temperature measurement for the solution is finished, the controller 100 performs conductivity measurement through the electrode sensor 30.

In the conductivity measurement, the controller 100 first sets the selection signal output terminal S1 to a low level, while setting the selection signal output terminal S2 to a high level. In addition, the switch 56 is turned off through the switching signal SW3.

The conductivity measurement is also performed in the same manner as the temperature measurement described above. That is, the controller 100 controls the switch 54 through the switching signal SW2 to measure the reference frequency Fr in a state in which the output terminal of the Schmitt trigger circuit 51 is coupled to the reference resistor 55. . Subsequently, when the measurement of the reference frequency Fr is completed, the oscillation frequency Ft of the Schmitt trigger circuit 51 is controlled by controlling the switch 54 to couple the output terminal of the Schmitt trigger circuit 51 to the electrode sensor 30. Measure

As described above, the resistance value of the electrode sensor 30 is calculated based on the equation (3).

As described above, when the resistance values of the temperature sensor 20 and the electrode sensor 30 are measured, the concentration of the solution is calculated based on these values as in the conventional configuration of FIG. 1. In addition, when the resistance measurement of the electrode sensor 30 is finished, the switch 56 is turned on through the switching signal SW3 to discharge ions accumulated between both ends of the electrode sensor 30.

As described above, according to the above-described embodiment, the reference frequency Fr is measured by oscillating the Schmitt triggers 41 and 51 through the reference resistors 45 and 55 whose values are known. By measuring the resistance values of the temperature sensor 20 and the electrode sensor 30 using the reference frequency Fr, the concentration of the solution can be accurately measured without excluding the influence of the component whose characteristics are changed according to the surrounding environment. It becomes possible.

In the above-described embodiment, the switch 56 is provided between both ends of the electrode sensor 30, and when the electrode sensor 30 is not measured, the switch 56 is turned on to accumulate at both ends of the electrode sensor 30. By discharging the ions, the concentration of the solution can be measured more accurately.

The embodiment according to the present invention has been described above. However, the above embodiment shows one preferred embodiment of the present invention, which is not intended to limit the scope of the present invention. The present invention can be carried out in various modifications without departing from the spirit thereof.

For example, in the above-described embodiment, the oscillation frequency output from the temperature measuring unit 200 and the conductivity measuring unit 300 is configured to be input to the counter 70 through the OR circuit 60, but the OR circuit ( It is also possible to use a Schmitt trigger circuit instead of 60), and it is also possible to configure the oscillation output from the temperature measuring unit 200 and the conductivity measuring unit 300 directly input to the counter (70).

In addition, in the above embodiment, the temperature sensor 20 and the electrode sensor 30 were described to measure the temperature and the conductivity of the solution together, but the conductivity of the solution was measured through the electrode sensor 30 as necessary. It is also possible to measure the concentration of the solution just by doing so.

In addition, the present invention can be implemented by applying the same method to any device that is to measure the desired value by using a sensor whose resistance value varies depending on the surrounding environment, not the concentration of the solution.

As described above, according to the present invention, it is possible to implement a solution concentration detection apparatus that is simple to manufacture and low cost, and can accurately measure the concentration of the solution.

Claims (6)

In the solution for detecting the concentration of the solution having a temperature sensor for measuring the temperature of the solution, and an electrode sensor for measuring the conductivity of the solution, based on the resistance value of the sensor, A temperature detector for outputting a first oscillation frequency corresponding to the resistance value of the temperature sensor; A conductivity detector for outputting a second oscillation frequency corresponding to the resistance value of the electrode sensor; A counter for determining oscillation frequencies of the temperature detector and the conductivity detector; And a control unit for calculating the concentration of the solution based on the first and second oscillation frequencies determined by the counter. The temperature detector and the conductivity detector are each provided with a first switch for selecting a feedback input of the Schmitt trigger circuit and the Schmitt trigger circuit. The Schmitt trigger circuit has a selection signal input to one input terminal, the other input terminal is grounded through a capacitor and coupled to one side of the offset resistor, and the other side of the offset resistor is coupled to the reference resistor and the temperature / electrode sensor in parallel, And the first switch selectively couples the reference resistance and the temperature / electrode sensor to an output terminal of the Schmitt trigger circuit according to a switching signal from a controller. The method of claim 1, The control unit determines the oscillation frequency Fr of the Schmitt trigger circuit through a counter in a state in which the output terminal of the Schmitt trigger circuit and the reference resistor are coupled through a first switch, After determining the oscillation frequency Ft of the Schmitt trigger circuit with the output terminal of the Schmitt trigger circuit coupled with the temperature / electrode sensor through the first switch, When the resistance value of the offset resistance is Ro, the resistance value of the reference resistance is Rr, and the resistance value of the temperature / electrode sensor is Rt,

The concentration detection device of the solution, characterized in that for calculating the resistance value of the sensor based on the equation. The method of claim 1, A second switch is coupled in parallel with the electrode sensor, And the control unit sets the second switch to an on state in a non-measuring state of an electrode sensor. In the solution concentration detection apparatus comprising a sensor for measuring the conductivity of the solution, and determines the concentration of the solution based on the resistance value of the sensor, A detector for outputting an oscillation frequency corresponding to the resistance of the sensor; A counter for determining the oscillation frequency of the detector; And a controller for calculating the concentration of the solution based on the oscillation frequency determined by the counter. The detection unit is configured to include a first switch for selecting a feedback trigger of the Schmitt trigger circuit and the Schmitt trigger circuit, In the Schmitt trigger circuit, a selection signal is input to one input terminal, the other input terminal is grounded through a capacitor, coupled to one side of an offset resistor, and a reference resistor and a sensor are coupled to the other side of the offset resistor in parallel, and the first And a switch selectively couples the reference resistor and the sensor to an output terminal of the Schmitt trigger circuit according to a switching signal from a controller. The method of claim 4, wherein The control unit determines the oscillation frequency Fr of the Schmitt trigger circuit through a counter in a state in which the output terminal of the Schmitt trigger circuit and the reference resistor are coupled through a first switch, After determining the oscillation frequency Ft of the Schmitt trigger circuit in the state in which the output terminal of the Schmitt trigger circuit and the sensor are coupled through the first switch, When the resistance value of the offset resistance is Ro, the resistance value of the reference resistance is Rr, and the resistance value of the sensor is Rt,

The concentration detection device of the solution, characterized in that for calculating the resistance value of the sensor based on the equation. The method of claim 4, wherein A second switch is coupled in parallel with the sensor, And the control unit sets the second switch to an on state in a non-measuring state of an electrode sensor.

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