JP2005241404A - Device for measuring electrical conductivity, and its control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an device for measuring electrical conductivity, capable of measuring electrical conductivity of measuring object solution with high sensitivity and high precision. <P>SOLUTION: The device for measuring electrical conductivity 100 detects the variation in the electrical conductivity in measuring object solution by measuring current difference between two sensors 61 and 62, contacting with time difference in the measuring object solution inside a conduit. The output voltage and output frequency of an alternating-current oscillator 11 in a power source 10 are controlled so that the measured value of the output current of one sensor 61 becomes a desired value. A calibration circuit 50 is used, when the electrical conductivity of the solution does not vary, and an electrical conductivity meter is calibrated by controlling a supply voltage of one sensor 62 so that the measured value of the current difference between the sensors 61 and 62 becomes zero. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for controlling an electrical conductivity measuring device, and more particularly to an electrical conductivity measuring device suitably used for measuring an ion concentration or the like in an aqueous solution and a control method therefor.

  In measuring the ion concentration in an aqueous solution, an electrical conductivity measuring device is used. An electrical conductivity measuring device generally detects an AC power source, a pair of electrodes (sensors) immersed in an aqueous solution to be measured and applied with an AC voltage from the AC power source, and a current value flowing between the pair of electrodes. And a signal processing unit. There are increasing demands for measuring the electrical conductivity of a measurement object with high sensitivity and high accuracy, and various proposals have been made in the past.

  In Patent Document 1, a characteristic value (for example, electrical conductivity) of a measurement target solution is obtained by using two sensors that are in contact with the measurement target solution with a predetermined time difference and obtaining a difference value between output signals of the sensors. ) Is measured with high sensitivity and high accuracy. FIG. 2 shows the principle of the measuring apparatus described in the patent document. The solution to be measured 64 flows in the direction of the arrow in the conduit 63 at a constant flow rate. The two sensors (A sensor, B sensor) 61 and 62 are each composed of a pair of electrodes, and are in contact with the solution flowing in the conduit 63 at a predetermined separation distance. That is, both the sensors 61 and 62 come into contact with the measurement target solution 64 with a certain time difference. An alternating voltage is applied to each of the sensors 61 and 62, and a difference in output currents of the sensors 61 and 62 flowing by the voltages is detected by a signal processing device 70 including an amplifier.

  FIG. 3 is a block diagram showing the overall configuration of the electrical conductivity measuring apparatus having the above configuration. The output voltage of the AC oscillator 80 configured as an AC power supply device is applied to one A sensor 61 with its polarity reversed, and is applied to the other B sensor 62 with the same polarity. As a result, the currents flowing through both sensors 61 and 62 are in opposite directions. The difference value between the output currents of both sensors 61 and 62 is input to the input stage amplifier 71 of the signal processing device 70 and amplified. The output of the input stage amplifier 71 is corrected by a temperature compensation circuit 72 for correcting the electrical conductivity at the temperature of the solution, and is supplied to the electrical conductivity indicator 75 via the synchronous rectifier circuit 73 and the DC amplifier 74 of the output stage. Is output.

In the electrical conductivity measuring device described in the above publication, the difference between the output currents of the two sensors 61 and 62 is taken out as an output signal of the electrical conductivity measuring device, thereby obtaining the magnitude of the electrical conductivity of the solution to be measured. Without depending, the measurement range of the difference value of both sensors can be set, and the difference value can be detected with high accuracy. As a result, there is an advantage that a change in electric conductivity of the solution to be measured can be measured with high sensitivity and high accuracy.
Japanese Patent Laid-Open No. 2003-270183

  Although the above-described type of electrical conductivity measuring device has the above-mentioned advantages, the following points are problematic. First, if there is a difference in characteristics between the two sensors themselves, or if there is a difference in wiring resistance or mounting structure between the two sensors, the difference directly affects the measurement result.

  In order to measure a wide range of electrical conductivity, it is necessary to adjust the measurement range by changing the voltage applied to the sensor over a wide range. In this case, if the voltage is too low, the sensitivity of the sensor will decrease. There is also a problem.

  In view of the problems in the above-described type of electrical conductivity measuring device, the present invention uses the electrical conductivity measuring device so that the electrical conductivity of the solution to be measured can be measured with higher accuracy and sensitivity. An object is to provide a method for controlling a measuring device.

  In addition, the present invention provides an electrical conductivity measuring device that improves the conventional conductivity measuring device of the above-described type and can measure the electrical conductivity of the solution to be measured with higher sensitivity and accuracy. Objective.

  Furthermore, this invention aims at providing the electrical conductivity measuring apparatus which can measure the electrical conductivity of a measuring object solution not only with the above-described type electrical conductivity measuring apparatus with high sensitivity and accuracy.

In order to achieve the above object, a method for controlling an electrical conductivity measuring device according to the present invention includes a pair of electrical conductivity sensors that are in contact with a measurement target solution with a predetermined time difference, and each of the electrical conductivity sensors for operation. A method for controlling an electrical conductivity measurement device comprising: a power supply unit that applies an AC power supply; and a signal processing unit that measures a differential value of an output current of the electrical conductivity sensor and outputs the differential value as an electrical conductivity differential value of a solution to be measured In
The output current of one of the pair of sensors is measured, and the voltage and frequency of the AC power output from the power supply unit are adjusted so that the measured output current becomes a desired value.

  In a preferred aspect of the control method of the electrical conductivity measuring device of the present invention, when the electrical conductivity of the solution to be measured does not change with time, the electrical conductivity difference value output from the signal processing unit is zero. Thus, the voltage applied to at least one of the pair of sensors is adjusted.

The electrical conductivity measuring apparatus according to the first aspect of the present invention includes a pair of electrical conductivity sensors that are in contact with a measurement target solution with a predetermined time difference, and an AC power source for operating each of the electrical conductivity sensors. In an electrical conductivity measurement device comprising: a power supply unit to be applied; and a signal processing unit that measures a differential value of an output current of the electrical conductivity sensor and outputs the differential value of the electrical conductivity of the measurement target solution.
The power supply unit is characterized in that an output voltage and an output frequency can be variably set.

  In a preferred embodiment of the electrical conductivity measurement device according to the first aspect of the present invention, the electrical conductivity difference that operates when there is no temporal change in the electrical conductivity of the solution to be measured and is output from the signal processing unit. A calibration circuit is further provided for adjusting a voltage applied to at least one of the pair of sensors so that the value becomes zero.

Furthermore, an electrical conductivity measuring device according to a second aspect of the present invention includes an electrical conductivity sensor that detects electrical conductivity of a solution to be measured, and a power source that applies an AC power source for operation to the electrical conductivity sensor. And a signal processing unit that outputs the electrical conductivity of the measurement target solution based on the output of the electrical conductivity sensor.
The power supply unit is characterized in that an output voltage and an output frequency can be variably set.

  According to the electrical conductivity measuring device and the control method thereof of the present invention, it is possible to measure a wide range of electrical conductivity with a single measuring device by adjusting the voltage of the AC power source output from the power supply unit. In this case, when the electric conductivity of the solution to be measured is high, the output voltage of the AC power supply is lowered and the output frequency thereof is raised to prevent the sensor sensitivity from being lowered.

  Hereinafter, with reference to the drawings, the present invention will be described in more detail based on exemplary embodiments of the present invention. FIG. 1 is a circuit diagram showing an entire electrical conductivity measuring apparatus according to an embodiment of the present invention. The electrical conductivity measuring apparatus 100 includes an AC power supply unit 10, a pair of sensors (A sensor and B sensor) 61 and 62 each composed of a pair of electrodes, output currents of the pair of sensors 61 and 62, An AC amplifying unit 20 that selects and amplifies one of the difference values of both output currents, a synchronous rectifying unit 30 that synchronously rectifies the output of the AC amplifying unit 20 based on the output waveform of the AC power supply unit 10, DC amplifier 40 that amplifies the output of AC amplifier 20 output via rectifier 30, calibration circuit 50 that controls the voltage of power supply unit 10 based on the output of DC amplifier 40, and DC amplifier 40 And a panel meter PM for displaying the output.

  The pair of sensors 61 and 62 are composed of sensors having well-equipped characteristics, as in the conventional electrical conductivity measuring device shown in FIG. 2, and are in contact with the measurement target solution 64 with a predetermined time difference.

  The power supply unit 10 includes an AC oscillator 11 in which an output voltage and an output frequency are variably set, a voltage control unit 12 that controls a voltage output from one of the two output terminals of the AC oscillator 11, and a voltage An addition unit 13 that adds the output voltage of the control unit 12 and the output voltage of the AC oscillator 11; a polarity inversion unit 14 that receives the output voltage of the addition unit 13 and inverts the polarity of the voltage input to the B sensor 62; Comparing the output voltage of the AC oscillator 11 with a predetermined voltage value, the comparator 15 has an output “1” when the output voltage of the AC oscillator 11 is equal to or higher than the predetermined value. The output voltage output from the other output terminal of the two output terminals of the AC oscillator 11 is applied to the A sensor 61 as it is.

  The AC amplifying unit 20 includes a head amplifier 21 housed together with the sensors 61 and 62 in a container having an electromagnetic shield and electrostatic shield function, a temperature compensation circuit 25 that performs temperature correction of the output of the head amplifier 21, and a head. A range measuring circuit 27 for measuring the output range of the amplifier 21;

  The head amplifier 21 inputs one of the output currents of the sensors 61 and 62, or a selection switch 22 for selecting a difference value thereof, and an output current from the sensor via the selection switch 22, and converts the output current into a current-voltage. Iv converter (amplifier) 23 for performing the above and a range setting unit 24 including a variable resistor for feeding back a signal from the output side to the input side of the iv converter 23. In the head amplifier 21 and wiring between the head amplifier 21 and the temperature compensation circuit 25, shield wires capable of electromagnetic and electrostatic shielding are used to reduce the influence of external noise.

  The temperature compensation circuit 25 is arranged in the vicinity of the sensors 61 and 62 and a differential amplifier 26 for temperature compensation in which one input is connected to the ground GND and the other input is connected to the output of the iv converter 23. The thermistor Th is configured to measure the temperature of the solution to be measured and feed back the output of the differential amplifier 26 to the other input side. The range measurement circuit 27 includes a rectifier circuit 28 that half-wave rectifies the output of the iv converter 23, and a comparator 29 that has one input connected to a predetermined power source and the other input connected to the output of the rectifier circuit 27. And a light emitting diode LD that generates an optical output in response to the output result of the comparator 29.

  The synchronous rectifier circuit 30 has an input connected to the output of the temperature compensation circuit 25 via a DC cut capacitor 31. The synchronous rectifier circuit 30 has a function of passing the output of the AC amplifying unit 20 when the output of the comparator 14 of the power supply unit 10 is “1”.

  The DC amplifying unit 40 includes a smoothing circuit 41 that removes ripples from the output of the synchronous rectifier circuit 30 and a feedback resistor 42 for gain setting, and amplifies the output of the smoothing circuit 41 to output signals from the electrical conductivity measuring device. And a drift removing circuit 44 for removing drift from the output of the DC amplifier 43. The calibration circuit 50 includes a comparator 51 that compares the output of the DC amplifier 43 with the zero voltage, and a zero adjustment circuit 52 that selects a control signal to be output to the voltage control unit 12 of the power supply unit 10 based on the comparison result of the comparator 51. Consists of

  In the operation of the measuring apparatus 100, the selection switch 22 of the head amplifier 21 is either the output current of the A sensor 61 alone, the output current of the B sensor 62 alone, or the difference output of the output currents of both the sensors 61 and 62. Select. When measuring the static electrical conductivity of the solution to be measured, the output current of the A sensor 61 alone is selected. Further, when the difference value of the measurement target solution is obtained, the measurement target solution is first introduced into the conduit. Therefore, even when the magnitude of the electric conductivity of the solution cannot be predicted in advance, first, the output of the A sensor 61 is output. A single measurement of current is selected. In the case of measuring the output current of the A sensor 61 alone, the AC oscillator 11 generates an AC voltage having a predetermined voltage and frequency specified by default and supplies the AC voltage to the A sensor 61. The signal current that is the output of the A sensor 61 is converted into an AC signal voltage by the iv converter 23.

  The output voltage of the iv converter 23 is subjected to temperature correction by the temperature compensation circuit 25 and then converted to a DC voltage signal by the synchronous rectification circuit 30. This DC voltage signal is amplified by the output stage DC amplifier 42 via the smoothing circuit 41, is instructed to the panel meter PM as an instruction value of the electric conductivity of the solution to be measured, and the electric conductivity signal of the measurement result Is output to the outside. The output of the light emitting diode LD of the range measuring circuit 27 is monitored, and the sensitivity of the iv converter 23 is adjusted depending on whether or not the light emitting diode LD emits light. Further, even when the sensitivity adjustment of the iv converter 23 is performed, if the instruction value of the electrical conductivity does not fall within the range of the panel meter PM, the settings of the output voltage and output frequency of the AC oscillator 11 are changed.

  When the electric conductivity of the solution to be measured is too high, the output voltage of the AC oscillator 11 is lowered to reduce the current flowing through the sensor 61. In this case, the output frequency of the AC oscillator 11 is increased as necessary in order to compensate for the sensitivity reduction of the sensor 61. When the electric conductivity of the solution to be measured is too low, the output voltage of the AC oscillator 11 is increased and the current flowing through the sensor 61 is increased. When the indicated value of the panel meter PM is within the appropriate range, the range setting and power supply setting by the measurement of the A sensor 61 alone are finished. Subsequently, in order to measure the electrical conductivity of the same type of measurement target solution or the measurement target solution having the same degree of electrical conductivity using the present measuring apparatus 100, the output current of the A sensor 61 is selected, Make that measurement. In setting the range or the like, the output current of the B sensor 62 may be selected instead of the output current of the A sensor 61 and the output voltage of the power supply control unit 12 may be set to zero.

  When measuring the change in the electrical conductivity of the solution to be measured by the measurement apparatus 100, first, prior to the measurement, measurement is performed by selecting the output current of the A sensor 61 alone. Zero adjustment between the sensors is performed. The zero point adjustment is performed when the measurement target solution is retained or when there is no temporal variation in the electrical conductivity of the measurement target solution. First, the selection switch 22 selects the difference current between the outputs of the A sensor 61 and the B sensor 62. The AC oscillator 11 generates an output of voltage and frequency set by the measurement of the A sensor 61 alone. As a result, AC voltages having the same voltage value and different polarities are applied to both sensors 61 and 62, respectively. The difference signal of the outputs of both the sensors 61 and 62 is instructed to the panel meter PM via the AC amplifier 20, the synchronous rectifier 30, and the DC amplifier 40. In the calibration circuit 50, when the output of the DC amplifier 43 in the output stage does not become zero, the control signal input to the voltage control unit 12 of the power supply unit 10 is changed by the action of the comparator 51 and the zero point adjustment circuit 52. For example, when the difference signal between both outputs is zero or more, the voltage supplied to the B sensor 62 is increased to increase the output current of the B sensor 62. As a result, the difference current between the sensors 61 and 62 is reduced. When the indicated value of the difference current between the sensors 61 and 62 becomes zero, the zero point adjustment is finished. The voltage control unit 12 is configured as a D / A converter having a multiplication function, for example, and multiplies the digital voltage signal output from the zero adjustment circuit 52 and the output voltage of the AC oscillator 11.

  In this measuring apparatus 100, when the electrical conductivity of the solution to be measured changes with time, the difference in electrical conductivity is measured by measuring the difference signal between the output of the A sensor 61 and the output of the B sensor 61. taking measurement. The selection switch 22 selects a difference signal between output currents of the A sensor 61 and the B sensor 62. The AC oscillator 11 outputs an AC power supply having the same voltage value and frequency as when the zero point adjustment is performed, and the output of the voltage control unit 12 generates the same output voltage as the end point of the zero point adjustment. The setting by the range setting unit 24 of the head amplifier 21 is performed while monitoring the indicated value of the panel meter PM. In this case, it is possible to set a range that is about 1 to 2 digits lower than the range set by the measurement with the A sensor 61 alone. For this reason, the difference current can be measured with high sensitivity. In addition, since the influence due to the difference in characteristics between the A sensor 61 and the B sensor 62 is removed in advance by the zero point adjustment, the difference signal can be measured with high accuracy.

  In the above embodiment, the electric conductivity measuring device that measures the difference value between the pair of electric conductivity sensors has been described as an example. However, the power supply unit that can set the output voltage and the output frequency of the AC power supply is the sensor. The present invention can also be applied to an electric conductivity measuring device that is provided alone. Also in this case, the electric conductivity of the solution to be measured can be measured in a wide range with high sensitivity and high accuracy.

  Moreover, the electrical conductivity measuring apparatus of the said embodiment can also perform the whole control using CPU. For example, according to the program, the CPU measures the first mode in which the range setting and the power supply setting are performed, the second mode in which the difference value between the output currents of both sensors is zeroed, and the actual change in electrical conductivity of the solution. The third mode is selected sequentially. The CPU controls the operations of the power supply unit 10, the AC amplifying unit 20, the DC amplifying unit 40, and the like in each mode by a program portion that executes each mode. After the solution to be measured is introduced into the measurement device, the absolute value of electrical conductivity and the temporal change in electrical conductivity are automatically measured by selecting and executing these modes in sequence. .

  As mentioned above, although this invention was demonstrated based on the suitable embodiment example, the electrical conductivity measuring apparatus of this invention is not limited only to the structure of the said embodiment example, From the structure of the said embodiment example. Various modifications and changes are also included in the scope of the present invention.

1 is a block diagram showing an entire electrical conductivity measuring device according to an embodiment of the present invention. The typical block diagram which shows arrangement | positioning of the sensor in the conventional electrical conductivity measuring apparatus. The block diagram which shows the whole conventional electric conductivity measuring apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100: Electrical conductivity measuring apparatus 10: Power supply part 11: AC oscillator 12: Voltage control part 13: Addition part 14: Polarity inversion part 20: AC amplification part 21: Head amplifier 22: Selection switch 23: iv converter 24 : Range setting resistor 25: Temperature compensation circuit 26: Differential amplifier 27: Range measurement circuit 28: Half-wave rectifier circuit 29: Comparator 30: Synchronous rectifier circuit 31: DC bypass capacitor 40: DC amplifier 41: Smoothing circuit 42: Feedback Resistance 43: DC amplifier 44: Drift removal circuit 50: Calibration circuit 51: Comparator 52: Zero point adjustment circuit 61, 62: Sensor 63: Conduit 64: Solution to be measured Th: Thermistor LD: Light emitting diode PM: Panel meter

Claims (5)

A pair of electrical conductivity sensors that are in contact with the solution to be measured with a predetermined time difference, a power supply unit that applies an AC power supply for operation to each of the electrical conductivity sensors, and a difference value between output currents of the electrical conductivity sensors. In a method for controlling an electrical conductivity measuring device comprising a signal processing unit that measures and outputs the electrical conductivity difference value of a solution to be measured,
Electrical conductivity characterized by measuring one output current of the pair of sensors and adjusting the voltage and frequency of the AC power supply output by the power supply unit so that the measured output current becomes a desired value. Control method of rate measuring device.   Furthermore, when there is no temporal change in the electrical conductivity of the solution to be measured, it is applied to at least one of the pair of sensors so that the electrical conductivity difference value output from the signal processing unit becomes zero. The method of controlling an electrical conductivity measuring device according to claim 1, wherein the voltage is adjusted. A pair of electrical conductivity sensors that are in contact with the solution to be measured with a predetermined time difference, a power supply unit that applies an AC power supply for operation to each of the electrical conductivity sensors, and a difference value between output currents of the electrical conductivity sensors. In an electrical conductivity measuring device comprising a signal processing unit that measures and outputs the electrical conductivity difference value of the solution to be measured,
The power supply unit is capable of variably setting an output voltage and an output frequency.   It operates when there is no temporal change in the electric conductivity of the solution to be measured, and is applied to at least one of the pair of sensors so that the electric conductivity difference value output from the signal processing unit becomes zero. The electrical conductivity measuring device according to claim 3, further comprising a calibration circuit for adjusting the voltage. An electrical conductivity sensor that detects the electrical conductivity of the solution to be measured, a power supply unit that applies an AC power supply for operation to the electrical conductivity sensor, and an electric power of the solution to be measured based on the output of the electrical conductivity sensor In an electrical conductivity measuring device comprising a signal processing unit that outputs as conductivity,
The power supply unit is capable of variably setting an output voltage and an output frequency.

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