JP4881068B2 - Water quality meter - Google Patents

Description

  The present invention relates to a water quality meter suitably used for measuring the water quality of a liquid to be measured, in particular, the concentration of residual chlorine contained in tap water, the pH of the liquid, the ORP (oxidation-reduction potential), and the like.

  As this type of water quality meter, for example, a device for measuring the residual chlorine concentration in tap water has been conventionally provided (see, for example, Patent Document 1). This water quality meter has a pair of electrodes formed of different kinds of metals, immerses the pair of electrodes in the liquid to be measured, and measures the chlorine concentration in the liquid from the electromotive voltage generated between the electrodes. One of the pair of electrodes is formed of a platinum wire and the other is formed of a silver wire, and the electrode made of the silver wire has a silver chloride film formed at a portion immersed in the liquid. Constitute. And when this sensor head is immersed in the liquid to be measured, for example, tap water, an electromotive voltage corresponding to the chlorine concentration in the liquid is generated between the pair of electrodes, so the chlorine concentration is calculated from the electromotive voltage generated between the electrodes. It can be measured.

By the way, in such a water quality meter, by changing the metal used for the electrode, it is possible to measure the impurity concentration, pH or oxidation-reduction potential other than chlorine, so in addition to the chlorine concentration in the liquid, There is a desire to simultaneously measure the pH or redox potential of a liquid, and water quality meters capable of measuring a plurality of measurement items have been proposed. FIG. 3 is a block diagram of a conventional water quality meter capable of measuring both chlorine concentration and pH. When immersed in the liquid 100 to be measured, a pair of electromotive voltages that generate a magnitude corresponding to the chlorine concentration in the liquid is generated. A sensor unit composed of electrodes 21a and 21b, connection terminals t1 and t2 to which both electrodes 21a and 21b are connected, and a solution 100 to be measured and a comparative solution 102 having a known pH are brought into contact with both surfaces of the glass thin film 101. , connection terminals and the sensor unit for taking out a voltage generated between control solution 102 and the liquid 100 respectively contact to that electrodes 22a in the liquid 100 and the comparative solution 102, the electrodes 22b, the electrodes 22a, 22b are connected, respectively An amplifier circuit 23 that amplifies the voltage between the electrodes 21a and 21b inputted through t3 and t4 and the connection terminals t1 and t2, and an electrode 2 inputted through the connection terminals t3 and t4 An amplifying circuit 24 that amplifies the voltage between 2a and 22b, and a measuring circuit 25 that measures the chlorine concentration and pH from the outputs of the amplifying circuits 23 and 24 are provided.

In this water meter, chlorine concentration measurement electrodes 21a, and 21b, when immersed and electrodes 22a for pH measurement to the measurement object liquid 100, electrodes 21a, force corresponding to the concentration of chlorine in the liquid 100 between 21b Since a voltage is generated and an electromotive voltage corresponding to the pH of the liquid 100 is generated between the electrodes 22a and 22b, the chlorine concentration in the liquid is measured in the measurement circuit 25 based on the voltage value amplified by the amplifier circuits 23 and 24. And pH can be measured simultaneously. In addition, the sensor includes a pair of electrodes formed of different metals, and includes a sensor unit that generates an electromotive voltage between the electrodes according to the ORP of the measurement liquid when both electrodes are immersed in the liquid to be measured. A water quality meter that measures ORP from the output of the unit has also been provided.

  By the way, the electrodes for measuring the chlorine concentration, pH and ORP described above are all electromotive force sensor units, and the electromotive voltage generated between the electrodes 21a and 21b and the voltage generated between the electrodes 22a and 22b are When measurement is performed simultaneously using amplifier circuits (that is, amplifier circuits that are not insulated from each other) 23 and 24 that operate with the same power source, if there is a common line (common line) between the amplifier circuits 22 and 23, both sensor units Thus, there is a possibility that a measurement error may occur due to a current flowing between the two sensor parts. In order to solve such a problem, it is sufficient to use an amplifier circuit and a measurement circuit that are insulated from each other for each sensor unit. However, a power supply unit that supplies operating power to each sensor unit is also required. Therefore, there was a problem that the cost of the water quality meter was increased.

  The present invention has been made in view of the above problems, and an object thereof is to provide a water quality meter capable of measuring a plurality of measurement items with high accuracy without causing an increase in cost.

In order to achieve the above object, the invention of claim 1 has a first electrode pair formed of different metals, and both electrodes of the first electrode pair are immersed in the liquid to be measured. A first sensor for concentration measurement in which an electromotive voltage having a magnitude corresponding to the impurity concentration of the measurement target contained in the measurement target liquid is generated between the first electrode pair, and a comparison solution having a known pH A glass thin film in which one surface is in contact with the comparison solution and a glass electrode including an internal electrode immersed in the comparison solution and an electrode immersed in the liquid to be measured . an electrode pair, the the second electrode pair is immersed in the liquid of the measurement target, electromotive force corresponding to the pH value of the measurement target liquid is generated between the second electrode pair pH A second sensor, which is a sensor, and a first electrode pair; The first and second connection terminals connected, the third and fourth connection terminals connected to the respective electrodes of the second electrode pair, the voltage of the first connection terminal, and the second A differential amplifier circuit that amplifies a voltage difference from a voltage at a connection terminal; a bias circuit that applies a constant bias voltage to one of the third connection terminal and the fourth connection terminal; a memory for the relationship between the electromotive voltage and the impurity concentration is generated between the electrode pairs, stores calibration data showing respective relationships between the previous SL electromotive voltage and pH value generated between the second electrode pair, the difference together determine the impurity concentration based on the output of the dynamic amplification circuit wherein the calibration curve data, the voltage obtained by subtracting the bias voltage from the other of the voltage of said third connection terminal and the fourth connection terminal calibration measurement times to determine the pH value on the basis of the line data A connection terminal that is one of the third connection terminal and the fourth connection terminal, and a connection terminal that is on a low voltage side among the first connection terminal and the second connection terminal. The space is electrically connected through an impedance element having a resistance value of 10 MΩ or more and 100 MΩ or less.
The invention of claim 2 has a first electrode pair formed of different metals, and when both electrodes of the first electrode pair are immersed in the liquid to be measured, the liquid to be measured An electromotive voltage having a magnitude corresponding to the concentration of impurities contained in the measurement target includes a first sensor for concentration measurement generated between the first electrode pair and a second electrode pair formed of different metals. When the second electrode pair is immersed in the liquid to be measured, an electromotive voltage having a magnitude corresponding to the oxidation-reduction potential of the liquid to be measured is generated between the second electrode pair. A second sensor which is a sensor; first and second connection terminals connected to the respective electrodes of the first electrode pair; and third and second connected to the respective electrodes of the second electrode pair. 4 and the difference voltage between the voltage of the first connection terminal and the voltage of the second connection terminal. A differential amplifier circuit that widens, a bias circuit that applies a constant bias voltage to one of the third connection terminal and the fourth connection terminal, and an electromotive voltage generated between the first electrode pair Memory for storing calibration curve data showing the relationship between the impurity concentration and the relationship between the electromotive voltage generated between the second electrode pair and the oxidation-reduction potential, the output of the differential amplifier circuit and the calibration curve The impurity concentration is obtained based on the data, and the redox potential is obtained based on the calibration curve data and the voltage obtained by subtracting the bias voltage from the other voltage of the third connection terminal and the fourth connection terminal. A measuring circuit for obtaining a low-pressure side of one of the third connection terminal and the fourth connection terminal and the first connection terminal and the second connection terminal. Between the connection terminals Resistance is characterized by being electrically connected through and 100MΩ following impedance element than 10 M.OMEGA.

According to the present invention, in the signal processing unit, the voltage difference between the voltage of the first connection terminal to which each electrode of the first electrode pair included in the first sensor is connected and the voltage of the second connection terminal is calculated. The impurity concentration is obtained based on the calibration curve data from the voltage obtained by amplification with a differential amplifier circuit having a high input impedance. Further, a bias voltage is applied from one of the third connection terminal and the fourth connection terminal to which each electrode of the second electrode pair included in the pH sensor or the ORP sensor is connected, from the bias circuit, A pH or oxidation-reduction potential is obtained based on calibration curve data from a voltage obtained by dividing the bias voltage from the voltage of the connection terminal of the first connection terminal and the connection terminal on the low voltage side among the first connection terminal and the second connection terminal; Between the third connection terminal and the fourth connection terminal, an impedance element having a resistance value of 10 MΩ or more and 100 MΩ or less is connected between the connection terminal to which the bias voltage is applied. That is, the voltages of the first and second connection terminals to which the respective electrodes of the first electrode pair are connected are measured using a differential amplifier circuit having a high input impedance, and the respective electrodes of the second electrode pair are A constant bias voltage is added to the voltage between the third and fourth connection terminals to be connected, the connection terminal on the low voltage side among the first and second connection terminals, and the third and fourth connection terminals. Since the impedance element is connected between the connection terminals to which the bias voltage is applied among the four connection terminals, the current flowing between the two connection terminals can be suppressed, and the measurement error can be reduced. In addition, since the circuit for measuring the concentration and the circuit for measuring the pH or oxidation-reduction potential are not used, the measurement circuit can be manufactured at low cost.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 2A is a front view of the water quality meter A of the present embodiment, which includes a grip body 20 formed in a size that can be gripped by a hand, and displays measurement values and the like on the front surface of the grip body 20. The liquid crystal display 12 is disposed on one end side in the longitudinal direction, and operation buttons of a plurality of switches SW1 to SW7 are disposed at substantially the center in the longitudinal direction. Here, the switch SW1 is a switch for turning on / off the power, the switch SW2 is a switch for performing an operation such as a measurement start, the switch SW3 is a switch for performing an operation mode switching operation, and the switch SW4 is various operations. Switches for performing a determination operation, switches SW5 and SW6 are switches for changing a set value, inputting numerical values, and the like. Switch SW7 is a switch for switching the operation mode to a pH calibration mode at the time of measuring a chlorine concentration or pH. It is.

  Further, for example, a probe 21 (see FIG. 5B) for measuring the chlorine concentration in the liquid is connected to the end surface of one end in the longitudinal direction of the grip body 20 (the side where the liquid crystal display 12 is disposed). A connector CN1 and a connector CN2 to which either one of a pH detection probe or an ORP detection probe 22 (see FIG. 5C) is selectively connected are arranged side by side. The connector CN1 includes a connector CN1a for capturing signals from concentration measuring electrodes 1a and 1b, which will be described later, and a connector CN1b for capturing signals from the thermistor. The connector CN2 includes a connector CN2a for taking in a voltage between electrodes 2a and 2b or electrodes 3a and 3b, which will be described later, and a connector CN21b for taking in a signal from the thermistor.

The concentration measurement probe 21 serving as a concentration sensor has a round bar shape, a pair of concentration measurement electrodes 1a, 1b and a thermistor (not shown) disposed at the tip, a concentration measurement electrode 1a, A connector 24a for taking out the signal 1b and a connector 24b for taking out the signal of the thermistor are provided, and the electrode portion 23 and each of the connectors 24a, 24b are electrically connected via a cable 25. The pair of concentration measuring electrodes 1a and 1b is formed of different metals (for example, a platinum plate with the plus side attached to the front end surface of the electrode portion 23, and a negative side with a silver wire disposed in the recess at the front end of the electrode portion 23). When it is immersed in the liquid to be measured, an electromotive voltage having a magnitude corresponding to the chlorine concentration in the liquid is generated. At the time of non-measurement, a cylindrical protective cap 26 whose one end is closed is attached to the electrode portion 23 to prevent the electrode portion 23 from being stained or damaged. Here, a first electrode pair is constituted by the above-described concentration measuring electrodes 1a and 1b, and a first sensor is constituted by a concentration sensor provided with the concentration measuring electrodes 1a and 1b as the first electrode pair.

Since a pH measurement probe (not shown) as a pH sensor has substantially the same structure as the concentration measurement probe 21, common constituent elements are denoted by the same reference numerals, and the description thereof is as follows. Omitted. The electrode portion 23 of the probe 21 is provided with a glass thin film whose both surfaces are in contact with a liquid to be measured and a comparative solution having a known pH value, and a voltage generated between the liquid to be measured and the comparative solution. in order to detect, and includes a conductive electrode 2a that Sessu the liquid to be measured, and that electrodes 2b Sessu the comparison solution. The electrode section 23 is provided with a thermistor for temperature measurement. The voltage between the electrodes 2a and 2b is taken out from the connector 24a and the signal of the thermistor is taken out from the connector 24b. Here, a glass electrode is provided by the glass thin film provided in a container containing a comparative solution having a known pH and having one surface in contact with the comparative solution and the electrode 2b (internal electrode) immersed in the comparative solution. The glass electrode and the electrode 2a immersed in the liquid to be measured constitute a second electrode pair, and the pH sensor provided with the second electrode pair constitutes the second sensor.

Further, the ORP measuring probe 22 as an ORP sensor has a round bar shape and takes out signals from the electrode part 27 having a pair of ORP measuring electrodes 3a and 3b disposed at the tip and the ORP measuring electrodes 3a and 3b. The connector 28 is electrically connected via the cable 29 between the electrode portion 27 and the connector 248. A pair of ORP measuring electrodes 3a, 3b are formed by different metals (e.g. positive side attached platinum plate on the distal end surface of the electrode portion 23, a silver wire minus side is disposed in the recess of the electrode portions 23 tip) When it is immersed in the liquid to be measured, an electromotive voltage having a magnitude corresponding to the oxidation-reduction potential of the liquid is generated. At the time of non-measurement, a cylindrical protective cap 30 whose one end is closed is attached to the electrode portion 27 to prevent the electrode portion 23 from being stained or damaged. Here, the ORP measurement electrodes 3a and 3b constitute a second electrode pair, and the ORP sensor including the ORP measurement electrodes 3a and 3b as the second electrode pair constitutes a second sensor.

  FIG. 1 shows a circuit diagram of a water quality meter A. The water quality meter A includes connectors CN1 to which connectors 24a and 24b of a concentration measurement probe 21 are connected, respectively, and the connector CN1 has a pair of concentration measurement devices. First and second connection terminals (hereinafter abbreviated as connection terminals) t1 and t2 to which the electrodes 1a and 1b are connected, respectively, and connection terminals t5 and t6 to which the thermistor is connected are provided. The water quality meter A includes a connector CN2 to which either a pH measurement probe or an ORP measurement probe 22 is connected. The connector CN2 includes a glass electrode 2a and a comparison electrode 2b or ORP measurement electrodes 3a and 3b. The third and fourth connection terminals (hereinafter abbreviated as connection terminals) t3 and t4 to which one of the above is connected, and the connection terminals t7 and t8 to which the thermistor is connected are provided. The water quality meter A includes a differential amplifier circuit 4 that amplifies a difference voltage between the voltage at the connection terminal t1 and the voltage at the connection terminal t2, a successive approximation circuit 5, a signal processing unit 6 that constitutes a measurement circuit, and a power supply circuit. 7, a bias circuit 8, a buzzer circuit 9, a switch input circuit 10, a reset circuit 11 that resets the signal processing unit 6, and a liquid crystal display 12.

  The differential amplifier circuit 4 includes a series circuit of a resistor R1 and a capacitor C1, and includes a low-pass filter that removes high frequency noise from the voltage at the connection terminal t1, and a series circuit of the resistor R2 and the capacitor C2, and the voltage at the connection terminal t2. A low-pass filter that removes high-frequency noise, operational amplifiers OP1 and OP2 in which voltages across the capacitors C1 and C2 are respectively applied to the non-inverting input terminals, and output terminals and non-inverting input terminals of the operational amplifiers OP1 and OP2, respectively. A series circuit of connected resistors R3 and R4, a resistor R5 connected between the inverting input terminal of the operational amplifier OP1 and the inverting input terminal of the operational amplifier OP2, a resistor R6 connected between both ends of the resistor R5, and the switch S1 A series circuit of a resistor R7 and a switch S2 connected between both ends of the resistor R5, an inverting input terminal, and an operation The resistor R8 is connected between the output terminal of the amplifier OP1, the resistor R9 is connected between the output terminal and the inverting input terminal, and the non-inverting input terminal is connected to the output terminal of the operational amplifier OP2 via the resistor R10. And an operational amplifier OP3 connected to. The non-inverting input terminal of the operational amplifier OP3 is connected to the circuit ground through a series circuit of a resistor R11 and a capacitor C3, and the connection point between the resistor R11 and the capacitor C3 is a voltage dividing resistor R12, R13 that divides the circuit voltage Vcc. Is electrically connected to the middle point. The output voltage of the operational amplifier OP3 is input to an input port PI1 of the signal processing unit 6 described later. Since the differential amplifier circuit 4 is a conventionally known differential amplifier called an instrumentation amplifier, description of its operation is omitted. The switches S1 and S2 are turned on / off by signals input from the output ports PO1 and PO2 of the signal processing unit 6, and the impedance between the inverting input terminal of the operational amplifier OP1 and the inverting input terminal of the operational amplifier OP2 is switched. The amplification factor of the differential amplifier circuit 4 is adjusted.

  The successive approximation circuit 5 includes a series circuit of a resistor R14 and a capacitor C4. The smoothing circuit 5a smoothes the PWM signal input from the output port PO3 of the signal processing unit 6, and the voltage at the connection terminal t4 is a low-pass filter (resistor R5 And a comparator CP1 to which the voltage V6 smoothed by the smoothing circuit 5a is applied to the inverting input terminal via the buffer amplifier BUF1. Is input to the input port PI2 of the signal processing unit 6. By the way, the voltage generated between the glass electrode 2a and the comparison electrode 2b is about 60 mV per pH, whereas the electromotive voltage generated between the ORP measurement electrodes 3a and 3b is ± 1500 mV (3 V in the full range). When the signal processing unit 6 is composed of an inexpensive 4-bit microcomputer, the built-in A / D conversion unit of the 4-bit microcomputer is at most about 10 bits, so the resolution is not sufficient, and is generated between the glass electrode 2a and the comparison electrode 2b. When the same A / D conversion unit tries to A / D convert the voltage to be generated and the electromotive voltage generated between the ORP measurement electrodes 3a and 3b, the conversion error of the voltage generated at the electrodes 2a and 2b increases. There is. Since a general-purpose microcomputer generally includes a PWM signal output unit 6b of about 16 bits, in this embodiment, the successive approximation circuit 5 is configured using the PWM signal output from the PWM signal output unit 6b. The successive approximation circuit 5 and the signal processing unit 6 constitute a successive approximation type A / D conversion circuit. An electromotive voltage generated between the glass electrode 2a and the comparison electrode 2b by this A / D conversion circuit, ORP An electromotive voltage generated between the measurement electrodes 3a and 3b is A / D converted.

  The signal processing unit 6 is composed of, for example, a 4-bit microcomputer, and A / D-converts the voltage input to the input port PI1 by a 10-bit A / D conversion unit 6a. The signal processing unit 6 performs A / D conversion by an A / D conversion unit that incorporates voltages input to the input ports PI8 and PI9, respectively. Further, by outputting a PWM signal with a variable duty ratio from the built-in 16-bit PWM signal output unit 6b, the output voltage V6 of the smoothing circuit 5a is changed with a resolution of 16 bits. Further, a liquid crystal display unit 12 is connected to the signal processing unit 6 and controls the display of the liquid crystal display unit 12. In addition, the signal processing unit 6 includes calibration curve data indicating the relationship between the electromotive voltage generated between the concentration measuring electrodes 1a and 1b and the impurity concentration, and the voltage and pH generated between the glass electrode 2a and the comparison electrode 2b. A memory 6c that stores calibration curve data indicating the relationship and calibration curve data indicating the relationship between the electromotive voltage generated between the ORP measurement electrodes 3a and 3b and the oxidation-reduction potential is incorporated.

  The power supply circuit 7 includes a three-terminal regulator IC1 that stabilizes the DC voltage supplied from the battery B. The DC voltage Vcc (for example, DC4V) stabilized by the three-terminal regulator IC1 is used as an operating voltage for the signal processing unit 6 or the like. Supply.

  The bias circuit 8 includes a series circuit of voltage dividing resistors R15 and R16 that divides the DC voltage Vcc and a capacitor C6 connected in parallel to the voltage dividing resistor R16 on the low voltage side, and is obtained by dividing the DC voltage Vcc. A bias voltage Vb (for example, 2 V) is applied to one connection terminal t3. A resistor R17 (impedance element) is connected between the connection terminal t3 and the connection terminal t1 that is on the low voltage side when immersed in the measurement liquid. The resistor R17 is a high-resistance resistor such that the current flowing between the connection terminals t1 and t3 becomes substantially zero. For example, a resistor of 10 MΩ is used. In this circuit, the influence of the impedance element is the largest when the pH measuring electrodes 2a and 2b having an internal impedance of 500 MΩ or less are used. Therefore, when the probe for pH measurement and the probe for concentration measurement are connected at the same time, the resistance of the impedance element is set to such a resistance value that mutual interference does not occur when the temperature of the water is lowered and the impedance of the sensor and water is maximized. The water quality meter A of this embodiment can be determined, and it has been found that the influence of mutual interference can be ignored if the impedance element is set from about 10 MΩ to about 100 MΩ.

  The buzzer circuit 9 includes a transistor Tr1 that is turned on / off by a signal from the output port PO4 of the signal processing unit 6, and causes the buzzer BZ1 to ring by causing the transistor Tr1 to flow a pulsed current to the buzzer BZ1.

  The switch input circuit 10 monitors operation inputs of a plurality of switches SW1 to SW7 connected between the input ports PI3 to PI5 and the input ports PI6 and PI7.

  Next, operation | movement of the water quality meter A of this embodiment is demonstrated. Here, the operation when the concentration measurement probe 21 is connected to the connector CN1 and the pH measurement probe is connected to the connector CN2 will be described. At this time, the concentration measuring electrodes 1a and 1b are connected to the connection terminals t1 and t2, the glass electrode 2a and the comparison electrode 2b are connected to the connection terminals t3 and t4, and the connection terminals t7 and t6 are connected between the connection terminals t5 and t6. Each thermistor is connected during t8.

  Here, when the probe 21 for concentration measurement and the probe for pH measurement are immersed in the measurement liquid, an electromotive voltage having a magnitude corresponding to the chlorine concentration in the liquid is generated between the concentration measurement electrodes 1a and 1b. A voltage having a magnitude corresponding to the pH of the liquid is generated between the glass electrode 2a and the comparison electrode 2b.

  At this time, voltages V1 and V2 are generated at the connection terminals t1 and t2 due to the electromotive voltages generated at the concentration measurement electrodes 1a and 1b. In the differential amplifier circuit 4, the voltage V1 at the connection terminal t1 and the voltage V2 at the connection terminal t2 are generated. Is amplified with a predetermined gain and output to the input port PI1 of the signal processing unit 6. In the signal processing unit 6, the A / D conversion unit 6a performs A / D conversion on the voltage V3 input to the input port PI1, and the output of the A / D conversion unit 6a and the calibration curve data stored in the memory 6c The chlorine concentration is obtained by calculation based on the above, and temperature compensation is performed based on the temperature data obtained by A / D conversion of the input voltage of the input port PI8. It is displayed.

  On the other hand, a voltage V5 obtained by adding a bias voltage Vb to V4 generated between the glass electrode 2a and the comparison electrode 2b is applied to the successive approximation circuit 5. In the signal processing unit 6, the duty ratio of the PWM signal output from the PWM signal output unit 6b is set to the minimum value at the start of measurement, and then the duty ratio is gradually increased from the minimum value to the maximum value to output the output voltage V6 of the smoothing circuit 5a. Is gradually increased. The output of the comparator CP1 that compares the level of the voltage V5 and the output voltage V6 of the smoothing circuit 5a is input to the input port PI2 of the signal processing unit 6, and the voltage level of the input port PI2 is inverted from high to low. The signal processing unit 6 determines that the output voltage V6 of the smoothing circuit 5a corresponding to the duty ratio at this time is the voltage V5 obtained by adding the bias voltage Vb to the voltage V4 between the electrodes 2a and 2b. Then, the signal processing unit 6 obtains the voltage V4 generated between the glass electrode 2a and the comparison electrode 2b by subtracting the bias voltage Vb from the voltage V5, and the calibration curve stored in the memory 6c from this voltage V4. Based on the data, the pH is obtained by calculation, and temperature compensation is performed based on temperature data obtained by A / D converting the input voltage of the input port PI9, and the pH value after temperature compensation is displayed on the liquid crystal display unit 12. It is displayed. When the A / D conversion unit built in the signal processing unit 6 is used, only a resolution of 10 bits can be obtained. However, by using the 16-bit PWM signal output unit 6b built in the signal processing unit 6, the resolution of 16 bits can be obtained. Since the A / D converter circuit is configured, the connection terminals t3 and t4 can be connected with higher resolution than the built-in A / D converter without using an expensive microcomputer with a built-in high-resolution A / D converter. Can be A / D converted. Here, the case where the pH measurement electrodes 2a and 2b are connected to the connection terminals t3 and t4 has been described, but the operation when the ORP measurement electrodes 3a and 3b are connected to the connection terminals t3 and t4 is also described. Since it is the same as the above-mentioned, the description is abbreviate | omitted.

  As described above, in the signal processing unit 3, the differential voltage between the voltage at the connection terminal t1 to which the concentration measuring electrodes 1a and 1b are connected and the voltage at the connection terminal t2 is amplified by the differential amplifier circuit having a high input impedance. The impurity concentration is obtained from the obtained voltage based on the calibration curve data. Further, the bias voltage from the bias circuit 8 to one of the third and fourth connection terminals t3 and t4, to which one of the pH measurement electrodes 2a and 2b or the ORP measurement electrodes 3a and 3b is connected. Vb is applied to determine pH or ORP based on calibration curve data from the voltage at the other connection terminal t4, and the connection terminal t1 that is on the low voltage side among the first and second connection terminals t1 and t2 A high-resistance resistor R17 is connected to the connection terminal t3 to which the bias voltage Vb is applied. That is, the voltages at the connection terminals t1 and t2 to which the concentration measuring electrodes 1a and 1b are connected are measured using the differential amplifier circuit 4 having a high input impedance, and the pH measuring electrodes 2a and 2b or the ORP measuring electrodes 3a, A constant bias voltage Vb is added to the voltage between the connection terminals t3 and t4 to which one of 3b is connected, and a high resistance impedance element is connected between the connection terminals t1 and t3. The measurement error can be reduced by suppressing the current flowing between the connection terminals t1 and t3. In addition, since the circuit for measuring the concentration and the circuit for measuring pH or ORP are not insulated from each other, the measurement circuit can be manufactured at low cost.

  By the way, in the above description, chlorine is described as an example of the impurity dissolved in the liquid. However, the impurity to be measured is not limited to chlorine, and the present invention is applied to all media in which the concentration measuring electrode has sensitivity. The concentration of impurities such as dissolved ozone, dissolved oxygen, dissolved carbon dioxide, and dissolved hydrogen can be measured.

  It should be noted that, as described above, it is obvious that a wide variety of different embodiments can be constructed without departing from the spirit and scope of the present invention, so that the present invention is not limited to the specific implementation except as defined in the appended claims. It is not restricted by form.

It is a circuit diagram of the water quality meter concerning the embodiment of the present invention. The water quality meter is shown. (A) is a front view of the main body, and (b) and (c) are external perspective views of the probe. It is a circuit diagram of the conventional water quality meter.

Explanation of symbols

1a, 1b Concentration measurement electrode 2a, 2b pH measurement electrode 3a, 3b ORP measurement electrode 4 Differential amplification circuit 6 Signal processing unit 6c Memory 8 Bias circuit R17 Resistance t1-t4 Connection terminal

Claims (2)

When the first electrode pair is formed of different metals and both electrodes of the first electrode pair are immersed in the liquid to be measured, the impurity concentration of the measurement object contained in the liquid to be measured An electromotive voltage having a magnitude corresponding to the first sensor for concentration measurement generated between the first electrode pair;
A glass electrode comprising a glass thin film whose surface is in contact with the comparison solution and an internal electrode immersed in the comparison solution, and an electrode immersed in the liquid to be measured. a second electrode pair comprising bets, the the second electrode pair is immersed in the liquid of the measurement target, electromotive force corresponding to the pH value of the measurement target liquid is, the second electrode A second sensor which is a pH sensor generated between the pair;
First and second connection terminals connected to the respective electrodes of the first electrode pair;
Third and fourth connection terminals connected to the respective electrodes of the second electrode pair;
A differential amplifier circuit for amplifying a difference voltage between the voltage of the first connection terminal and the voltage of the second connection terminal;
A bias circuit for applying a constant bias voltage to one of the third connection terminal and the fourth connection terminal;
Memory and for storing calibration curve data illustrating each of a relation between said first relationship between the electromotive voltage and the impurity concentration is generated between the electrode pair, electromotive voltage and pH values occurring between before Symbol second electrode pair ,
An impurity concentration is obtained based on the output of the differential amplifier circuit and the calibration curve data, and a voltage obtained by subtracting the bias voltage from the other voltage of the third connection terminal and the fourth connection terminal; and a measurement circuit for determining the pH value based on said calibration curve data,
A resistance between one connection terminal of the third connection terminal and the fourth connection terminal and a connection terminal on the low voltage side of the first connection terminal and the second connection terminal is a resistance. A water quality meter characterized by being electrically connected through an impedance element having a value of 10 MΩ or more and 100 MΩ or less. When the first electrode pair is formed of different metals and both electrodes of the first electrode pair are immersed in the liquid to be measured, the impurity concentration of the measurement object contained in the liquid to be measured An electromotive voltage having a magnitude corresponding to the first sensor for concentration measurement generated between the first electrode pair;
When the second electrode pair has a second electrode pair formed of different metals, and the second electrode pair is immersed in the liquid to be measured, a magnitude corresponding to the oxidation-reduction potential of the liquid to be measured is generated. A second sensor that is an ORP sensor generating a voltage between the second electrode pair;
First and second connection terminals connected to the respective electrodes of the first electrode pair;
Third and fourth connection terminals connected to the respective electrodes of the second electrode pair;
A differential amplifier circuit for amplifying a difference voltage between the voltage of the first connection terminal and the voltage of the second connection terminal;
A bias circuit for applying a constant bias voltage to one of the third connection terminal and the fourth connection terminal;
A memory for storing calibration curve data indicating the relationship between the electromotive voltage generated between the first electrode pair and the impurity concentration, and the relationship between the electromotive voltage generated between the second electrode pair and the oxidation-reduction potential; ,
An impurity concentration is obtained based on the output of the differential amplifier circuit and the calibration curve data, and a voltage obtained by subtracting the bias voltage from the other voltage of the third connection terminal and the fourth connection terminal; A measurement circuit for obtaining an oxidation-reduction potential based on the calibration curve data,
A resistance between one connection terminal of the third connection terminal and the fourth connection terminal and a connection terminal on the low voltage side of the first connection terminal and the second connection terminal is a resistance. water quality meter you characterized in that the value has been electrically connected via the following impedance elements 10MΩ or more and 100 M.OMEGA.

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