KR20200011372A - Electric conductivity meter - Google Patents

Abstract

An objective of the present invention is to measure electrical conductivity with high precision by suppressing an influence of an interline capacitance of an electrode wiring connecting to an electrode. A sub-substrate (2) is arranged in a position near electrodes (T1, T2) attached to a measuring tube (3), and at least one side or both sides among a signal generation circuit (21) for generating a square wave signal and a buffer amplifier (22) for stabilizing and outputting a detection signal detected from the electrodes (T1, T2) are mounted on the sub-substrate (2).

Description

ELECTRIC CONDUCTIVITY METER

The present invention relates to an electrical conductivity measurement technique for measuring the electrical conductivity of a liquid.

As a device for measuring the electrical conductivity (conductivity) of a liquid, a two-electrode type electrical conductivity meter is known. A two-electrode type electrical conductivity meter is an instrument that obtains an electrical conductivity of a liquid by applying an alternating current signal such as a sine wave or a square wave between two electrodes and detecting an electrical signal generated between the electrodes. Patent Documents 1 to 3 disclose a prior art of a two-electrode type electrical conductivity meter.

For example, Patent Literature 1 discloses an electric resistance of a liquid to be measured by detecting a current flowing into the other electrode when an alternating voltage is applied to one electrode in a state where two electrodes are immersed in the liquid to be measured. A two-electrode electrical conductivity meter for measuring electrical conductivity is disclosed. In addition, Patent Documents 2 and 3 disclose an electric conductivity meter of a two-electrode system in which two electrodes are formed in a rod shape.

[Patent Document 1] Japanese Patent Publication No. 7-15490 [Patent Document 2] Japanese Patent Application Laid-Open No. 2005-148007 [Patent Document 3] Japanese Unexamined Patent Publication No. 2002-296312

In such a two-electrode type electrical conductivity meter, it is necessary to connect two electrodes and a circuit which derives electrical conductivity with a pair of wirings. Depending on the length of these wirings, the impedance of the wiring increases, and the electrical conductivity is measured. It cannot be ignored. Accordingly, there is a problem that deformation occurs in the signal waveform detected by the electrode due to the influence of the wiring impedance, and the measurement accuracy of the electrical conductivity is lowered.

This point is examined in patent document 1. 20 is a circuit diagram showing a signal processing circuit of a conventional electric conductivity meter. FIG. 21 is an equivalent circuit between the electrodes and the cable of FIG. 20.

In the signal processing circuit 50 shown in FIG. 20, the applied voltage Vg of the AC square wave generated by the signal generation circuit 51 is changed from the buffer amplifier U1 to the applied voltage Vg '. After it is stabilized, it is applied to the electrode T1 through the terminal N1 and the electrode wiring LT1. The detection current It generated in the electrode T2 is input to the operational amplifier U2 and the feedback resistor Rf through the electrode wiring LT2 and the terminal N2, and is converted into the detection voltage Vt. It is rectified by the synchronous rectification circuit 52, and is converted and output by the direct current voltage Et.

In the equivalent circuit shown in Fig. 21, Cp and Rp are polarization capacities and polarization resistances generated between the electrodes and the liquid when the electrodes T1 and T2 are in contact with the liquid, and Rl is the electrode ( Liquid resistance with respect to the liquid between T1 and T2). In addition, Cw is line capacitance which arises between electrode wiring LT1, LT2, and Rw is wiring resistance which LT1, LT2 has.

As shown in Fig. 21, when the electrodes T1 and T2 are viewed from the signal processing circuit 50 side through the terminals N1 and N2, the parallel circuit of the polarization capacitance Cp and the polarization resistance Rp and With respect to the series circuit with the liquid resistor Rl, the series circuit of the line capacitance Cw and the wiring resistance Rw seems to be connected in parallel.

In patent document 1, it is after the differential noise which generate | occur | produces immediately after the start of output of the applied voltage Vg ', for example, when the influence of the deformation | transformation of the detection voltage Vt by such Cp and Cw is small, and applied voltage Vg'. Vt is sampled a plurality of times in the period up to the stop of output, and Vt, which is not influenced by Cp and Cw, is calculated from the obtained plurality of sample voltages.

However, in the above formula, since the line capacitance Cw is assumed to be negligible, there is a problem that the electrical conductivity cannot be measured with high accuracy when the electrode wirings LT1 and LT2 are long and Cw cannot be ignored. .

In general, in order to suppress the influence of the polarization capacitance Cp, it is necessary to increase the frequency of the applied voltage Vg applied between T1 and T2. However, when the frequency of the applied voltage Vg is increased, the influence of the line capacitance Cw is increased, and the deformation of the detection voltage Vt obtained from T1 and T2 is increased, which causes a decrease in the measurement accuracy of the electrical conductivity. Further, the longer the electrode wirings LT1 and LT2, the larger the Cw, the larger the deformation of the detection voltage Vt, and the lower the measurement accuracy of the electrical conductivity.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and an object thereof is to provide an electrical conductivity measurement technique that can suppress the influence of line capacitance of electrode wirings connecting electrodes and measure electrical conductivity with high accuracy.

In order to achieve this object, the electrical conductivity meter according to the present invention is an electrical conductivity meter for measuring electrical conductivity with respect to a liquid in a measurement tube, and includes a signal generation circuit for generating a square wave signal having a predetermined signal frequency, and the measurement. First and second electrodes attached to the tube to apply the square wave signal to the liquid, a buffer amplifier for stabilizing and outputting a detection signal detected from the first and second electrodes, and sampling the output of the buffer amplifier. A detection circuit that detects an amplitude of the detection signal, an arithmetic processing circuit that calculates an electrical conductivity with respect to the liquid based on the amplitude by arithmetic processing, and a printed wiring board disposed at positions near the first and second electrodes And at least one or both of the signal generation circuit and the buffer amplifier are formed on the printed wiring line. It is mounted on the board.

In addition, one configuration example of the electric conductivity meter according to the present invention is such that the signal generation circuit generates a square wave constant voltage signal consisting of a square wave voltage of AC having a constant amplitude as the square wave signal.

In addition, one configuration example of the electric conductivity meter according to the present invention is such that the signal generation circuit generates a square wave constant current signal composed of an alternating square wave current having a constant amplitude as the square wave signal.

Moreover, one structural example of the said electrical conductivity meter which concerns on this invention consists of a contact electrode which the said 1st electrode contacts with the said liquid, The said 2nd electrode is formed in the outer peripheral part of the said measurement tube, The said liquid It consists of a non-contact electrode which is not in contact with the liquid.

In addition, in one configuration example of the electrical conductivity meter according to the present invention, the printed wiring board has a tube hole into which the measuring tube is inserted, and the tube hole and the outer peripheral surface of the measuring tube are attached to the outer peripheral surface. will be.

Moreover, one structural example of the said electrical conductivity meter which concerns on this invention is the electrode connection terminal for connecting the electrode wiring to the said 1st and 2nd electrode to the pattern surface of the said printed wiring board, the said signal generation circuit, and A wiring pattern for connecting at least one or both of the buffer amplifiers and the electrode connection terminal is formed.

According to the present invention, the length of the electrode wiring connecting the signal generation circuit, the buffer amplifier and the first and second electrodes can be shortened, and the line capacitance between the electrode wirings can be reduced. Therefore, even when a relatively high signal frequency is used, the electrical conductivity can be measured with high accuracy.

1 is a block diagram showing a circuit configuration of an electrical conductivity meter according to a first embodiment.
2 is a side view of the electric conductivity meter according to the first embodiment.
3 is a top view of the electrical conductivity meter according to the first embodiment.
4 is a perspective view of an electrical conductivity meter according to the first embodiment.
5 is another perspective view of the electrical conductivity meter according to the first embodiment.
6 is a front view illustrating a sub substrate.
7 is a rear view of a sub substrate.
8 is a signal waveform diagram showing the operation of the electrical conductivity meter according to the first embodiment.
9 is an equivalent circuit on the electrode side according to the first embodiment.
10 is a characteristic diagram showing a correspondence relationship between amplitude data and electrical conductivity.
11 is another signal waveform diagram showing the operation of the electrical conductivity meter according to the first embodiment.
12 is a block diagram showing the circuit configuration of the electric conductivity meter according to the second embodiment.
13 is a structural example of a square wave current source.
14 is a signal waveform diagram showing the operation of the electrical conductivity meter according to the second embodiment.
15 is an equivalent circuit on the electrode side according to the second embodiment.
16 is a side view of an electric conductivity meter according to a third embodiment.
17 is a top view of an electric conductivity meter according to the third embodiment.
18 is a perspective view of an electrical conductivity meter according to a third embodiment.
19 is another perspective view of the electrical conductivity meter according to the third embodiment.
20 is a circuit diagram showing a signal processing circuit of a conventional electric conductivity meter.
FIG. 21 is an equivalent circuit between the electrodes and the cable of FIG. 20.

Next, embodiment of this invention is described with reference to drawings.

[First Embodiment]

First, with reference to FIGS. 1-5, the electrical conductivity meter 10 which concerns on 1st Embodiment of this invention is demonstrated. 1 is a block diagram showing a circuit configuration of an electrical conductivity meter according to a first embodiment. 2 is a side view of the electric conductivity meter according to the first embodiment. 3 is a top view of the electrical conductivity meter according to the first embodiment. 4 is a perspective view of an electrical conductivity meter according to the first embodiment. 5 is another perspective view of the electrical conductivity meter according to the first embodiment.

In the electrical conductivity meter 10 according to the present invention, as shown in FIGS. 1 to 5, a square wave signal SG of alternating current is applied between two electrodes T1 and T2 attached to the measurement tube 3. Then, it has the function of calculating | requiring the electrical conductivity with respect to the liquid in the measurement tube 3 based on the detection signal detected from T1, T2, ie, the amplitude of the detection voltage Vt.

As shown in FIG. 1, the electric conductivity meter 10 is a main circuit portion, and includes a detection circuit 11, an arithmetic processing circuit 12, a setting / display circuit 13, a transmission circuit 14, and a signal generating circuit. 21, the buffer amplifier 22 is provided.

According to the present invention, at least one or both of the signal generating circuit 21 and the buffer amplifier 22 are attached to a position near the electrodes T1 and T2 on the outer circumferential surface of the measuring tube 3. (Printed wiring board) 2 is mounted, and electrodes T1 and T2 are electrically connected to the sub board | substrate 2 through jumper wires J1 and J2. Hereinafter, the detection circuit 11, the arithmetic processing circuit 12, the setting / display circuit 13, and the transfer circuit 14 are mounted on the main board (printed wiring board) 1, and the signal generation circuit 21 is provided. ) And the case where the buffer amplifier 22 is mounted on the sub substrate 2 will be described as an example.

The detection circuit 11 controls the signal generation circuit 21 to apply an AC square wave signal SG having a preset signal frequency fg to the electrodes T1 and T2 and the electrode T1. , T2 detects the amplitude of the detected voltage Vt and outputs it to the arithmetic processing circuit 12.

As for the variation of the electrical conductivity meter 10 according to the present invention, a non-contact electrode which does not come into contact with the liquid may be used as the electrode T2, or a contact electrode that comes into contact with the liquid may be used. As the square wave signal SG, a square wave constant voltage signal composed of an alternating square wave voltage having a constant amplitude may be used, or a square wave constant current signal composed of an alternating square wave current having a constant amplitude may be used.

In this embodiment, the case where the electrode T2 is a non-contact electrode and the square wave signal SG is a square wave constant voltage signal is demonstrated as an example. On the other hand, the case where the square wave signal SG is a square wave constant current signal and the case where the electrode T2 is a liquid contact electrode are mentioned later in another embodiment.

The detection circuit 11 includes a clock generation circuit 11A, a sample hold circuit (SH circuit) 11B, and an A / D conversion circuit (ADC circuit) 11C as a main circuit portion.

The clock generation circuit 11A, based on the clock signal CLK0 from the arithmetic processing circuit 12, clock signals CLKs for generating square wave signals SG and clock signals CLKh and CLKl for sampling control. Has the function to generate

The sample hold circuit 11B controls the switches SWh and SWl on and off based on the clock signals CLKh and CLKl from the clock generation circuit 11A, thereby outputting the output voltage Vt 'from the buffer amplifier 22. ) Is sampled and the detected voltages VH and VL are output to the A / D conversion circuit 11C.

The A / D conversion circuit 11C performs A / D conversion on the difference voltages of VH and VL from the sample hold circuit 11B, that is, the amplitude voltage of Vt, and converts the obtained amplitude data DA into the arithmetic processing circuit 12. It has a function to output to.

The connector CN1 mounted on the main board 1 is connected to the connector CN2 mounted on the sub board 2 through the four-core connection wiring LC. Thereby, the main board | substrate 1 and the sub board | substrate 2 are electrically connected. Specifically, clock signals CLKs are supplied from the terminal T11 of CN1 to the terminal T21 of CN2 via LC. The reference voltage Vs is supplied from the terminal T12 of CN1 to the terminal T22 of CN2 via LC. The ground voltage GND is supplied from the terminal T13 of CN1 to the terminal T23 of CN2 via LC. The output voltage Vt 'of the buffer amplifier 22 is supplied from the terminal T24 of CN2 to the terminal T14 of CN1 via LC.

In addition, the sub board | substrate 2 is electrically connected with the 1st and 2nd electrodes T1 and T2 through jumper lines J1 and J2. Specifically, the pad (electrode connection terminal) P1 formed on the sub board | substrate 2 is connected with the 1st electrode T1 through the jumper line J1, and the pad (electrode formed on the sub board | substrate 2) is provided. The connecting terminal P2 is connected to the second electrode T2 via the jumper wire J2. P1 is connected with the ground voltage GND on the sub board | substrate 2 through the wiring pattern LP1 formed in the sub board | substrate 2, and P2 is connected through the wiring pattern LP2 formed in the sub board | substrate 2. The signal generating circuit 21 and the buffer amplifier 22 on the sub substrate 2 are connected.

The signal generation circuit 21 has a function of generating a square wave signal SG having a preset signal frequency fg, here a square wave constant voltage signal composed of an AC square wave voltage having a constant amplitude. Specifically, in the signal generation circuit 21, one input terminal is connected to the reference voltage Vs of T22, the other input terminal is connected to the ground voltage GND of T23, and the control terminal is connected to T21. The connected switch SWg and one end are connected to the output terminal of SWg, and the other end is provided with the resistance element Rg connected to P2 via LP2. The signal generation circuit 21 switches and controls the switch SWg based on the clock signal CLKs from the detection circuit 11, whereby the square wave signal having a signal frequency fg whose amplitude is equal to CLKs at Vs. SG).

The buffer amplifier 22 is formed of, for example, an operational amplifier or a buffer circuit, and stabilizes the detection voltage (detection signal) Vt detected from the electrodes T1 and T2 and outputs the output voltage as the output voltage Vt '. Have Specifically, in the buffer amplifier 22, the input terminal is connected to the pad P2 via LP2, and the output terminal is connected to T24.

The arithmetic processing circuit 12 cooperates with a CPU and a program, and calculate | requires the function of calculating | requiring the electrical conductivity with respect to the liquid in the measurement tube 3 by arithmetic processing based on the amplitude data DA obtained by the detection circuit 11. Have The arithmetic processing circuit 12 is equipped with the electrical conductivity calculation part 12A and the empty state determination part 12B as a main processing part.

The electrical conductivity calculation unit 12A has a function of calculating the electrical conductivity with respect to the liquid in the measurement tube 3 based on the amplitude data DA obtained by the detection circuit 11. Specifically, the electrical conductivity corresponding to the amplitude data DA from the detection circuit 11 may be calculated using the electrical conductivity calculation formula set in advance, but the correspondence relationship between the amplitude data DA and the electrical conductivity may be calculated. The electrical conductivity with respect to the liquid in the measuring tube 3 may be derived by measuring in advance and setting the obtained characteristic as a lookup table in advance and referring to the lookup table based on the amplitude data DA from the detection circuit 11. .

The empty state determination unit 12B has a function of determining the presence or absence of liquid in the measurement tube 3 based on the electrical conductivity calculated by the electrical conductivity calculation unit 12A. Specifically, the empty state determination unit 12B compares the electric conductivity calculated by the electric conductivity calculation unit 12A with a preset threshold conductivity, and the calculated electric conductivity is smaller than the threshold conductivity. It is determined that there is no liquid in the measuring tube 3, that is, the empty state.

The setting and display circuit 13 is provided with display devices, such as an operation button, LED, and LCD, and detects and outputs the setting operation input of an operator to the arithmetic processing circuit 12, and the arithmetic processing circuit 12 It is equipped with the function to display various data from.

The transfer circuit 14 performs a function of performing data transfer between a host device (not shown) such as a controller via the transfer path LT, and the electric conductivity obtained from the arithmetic processing circuit 12 or the empty state determination result. And a function for transmitting to the host apparatus.

[Electric conductivity meter structure]

Next, with reference to FIGS. 2-5, the structure of the electrical conductivity meter 10 which concerns on this embodiment is demonstrated. In addition, below, the direction in which the measurement tube 3 extends is called 1st direction X for convenience, and the left-right direction of the measurement tube 3 orthogonal to 1st direction X is called 2nd direction Y The vertical direction of the measurement tube 3 orthogonal to the 1st and 2nd direction X and Y is called 3rd direction Z.

The measuring tube 3 is made of a material having excellent insulation and dielectric properties, such as a ceramic or resin forming a cylindrical shape, and is housed inside the lower case 4. The lower case 4 is comprised from the bottomed box-shaped resin or metal case which has an opening 4D in the upper side.

The pair of side surfaces 4A orthogonal to the first direction X among the side surfaces of the lower case 4 are provided with a pipe (not shown) and a measurement tube 3 provided outside the electrical conductivity meter 10. Connectable tubular joints 5A, 5B made of metal material (eg SUS) are arranged. The measuring tube 3 is housed in the lower case 4 along the first direction X, and at both ends of the measuring tube 3, the joint 5A is provided with a pair of O-rings OR interposed therebetween. And joint 5B are respectively connected.

Here, at least one of the joints 5A and 5B functions as an electrode (first electrode) T1. For example, the joint 5A is connected to the ground voltage GND (common potential), thereby not only connecting the external pipe and the measurement tube 3 but also functioning as the electrode T1.

Thus, by realizing the electrode T1 by the joint 5A made of metal, the area where T1 comes into contact with the liquid is increased.

As a result, even if adhesion or corrosion of foreign matter occurs in T1, the area of the portion where adhesion or corrosion of foreign matter occurs is relatively small relative to the entire area of T1. Therefore, it is necessary to suppress measurement errors due to changes in polarization capacity. It becomes possible. Since the ground voltage GND is applied to the joint 5A, even if the external pipe connected to the joint 5A is metal, the external pipe becomes an antenna and does not radiate electromagnetic noise. In addition, since the joint 5A is also used as the electrode T1, it is not necessary to provide T1 separately, so that the electric conductivity meter 10 can be miniaturized.

On the other hand, a pair of side surfaces 4B orthogonal to the second direction Y among the side surfaces of the lower case 4 and an outer surface of the bottom surface 4E of the lower case 4 are formed of a metal plate having a cross-shaped U shape. The shield 6 which consists of is attached. Thereby, the noise radiated externally from the electrical conductivity meter 10 can be reduced.

Moreover, the surface electrode (2nd) which consists of a thin film conductor over the perimeter of the measuring tube 3 in the outer peripheral surface 3A of the measuring tube 3 on the opposite side to the joint 5A with the sub board | substrate 2 in between. The electrode) T2 is pattern-formed as a non-contact electrode. Moreover, the pad P3 protrudes toward the sub board | substrate 2 in the side end part of the side of the sub board | substrate 2 among T2.

As described above, at least one of the signal generating circuit 21 and the buffer amplifier 22 is attached to a sub-substrate attached to a position near the electrodes T1 and T2 of the outer peripheral surface 3A of the measuring tube 3 ( It is mounted on the printed wiring board) 2, and the electrodes T1 and T2 are electrically connected to the sub board | substrate 2 through jumper wires J1 and J2.

6 is a front view illustrating a sub substrate. 7 is a rear view of a sub substrate.

As shown in FIG. 6, in the sub-substrate 2, the side surface of the tube hole 2H along the second direction Y in the substrate surface 2A on the electrode T1 side formed of the joint 5A. The pad P1 is formed in the pattern, and this P1 and T1 are connected through J1. J1 is soldered to the outer surfaces of P1 and T1.

In addition, as shown in FIG. 7, in the substrate surface 2B on the electrode T2 side of the sub substrate 2, the pad P2 is located at an upper position of the tube hole 2H along the third direction Z. As shown in FIG. ) Is patterned and connects this P2 and P3 via J2. J2 is soldered to P2 and P3.

In addition, a circuit mounting area 2G is formed above the tube hole 2H including the pad P2 in the substrate surface 2B, and the signal generating circuit 21 and the buffer amplifier 22 are further provided. The connector CN2 is mounted, and P1 and P2 are connected via the wiring patterns LP1 and LP2 (not shown).

Thereby, the length of the electrode wiring connecting the sub board | substrate 2 and electrodes T1 and T2, ie, jumper wires J1 and J2 can be made very short, and the impedance of J1 and J2 can be suppressed very low. . In addition, since the signal generation circuit 21 or the buffer amplifier 22 is mounted on the sub board 2, the impedance of the connection wiring LC connecting the main board 1 and the sub board 2 can be reduced. Can be. For this reason, in the measurement of electric conductivity, the impedance of jumper wires J1 and J2 and the connection wiring LC can be ignored.

As shown in FIG. 2, the upper case 9 is attached to the upper portion of the lower case 4 so as to cover the opening 4D. The main board 1 is fixed in the upper case 9, and circuit parts such as the detection circuit 11, the arithmetic processing circuit 12, the setting / display circuit 13, the transmission circuit 14, and the like are mounted. It is. The connector CN2 of the sub board | substrate 2 is connected with the connector CN1 of the main board | substrate 1 via the connection wiring LC.

In addition, you may form the ground pattern connected with the ground voltage GND in the area | regions other than a circuit component and a wiring pattern among the sub board | substrates 2. Thereby, the noise mixed in the electrode T2 from the outside of the electric conductivity meter 10 can be reduced, and the measurement error can be suppressed.

About the sub board | substrate 2, as long as it is 3A of outer peripheral surfaces of the measuring tube 3, you may attach to any direction, but in this embodiment, the measuring tube 3 is attached to the pipe hole 2H formed in the sub board | substrate 2. In FIG. The sub-substrate 2 is fixed to the measurement tube 3 by press fitting.

As shown in FIG. 6 and FIG. 7, a pipe hole for press-fitting the measuring tube 3 to a central position in the left and right directions Y in the left and right directions toward the surface of the sub-substrate 2 ( 2H) is formed. Thereby, the sub board | substrate 2 can be fixed to the measuring tube 3 with a very simple structure, without using fixing members, such as a mounting screw.

The size of the tube hole 2H is set equal to or slightly smaller than the size of the outer peripheral portion of the measuring tube 3. At this time, the tube hole 2H does not need to have a round shape in accordance with the outer circumferential shape of the measuring tube 3, and may be a substantially polygonal shape, and an approximately octagonal shape in FIGS. 6 and 7. Thereby, the edge part of the tube hole 2H comes in partial contact with 3 A of outer peripheral surfaces, and compared with the structure which contact | connects the outer peripheral surface 3A over the perimeter of the edge part of the tube hole 2H, the measuring tube 3 The influence of heat transmitted to the signal generating circuit 21 and the buffer amplifier 22 mounted on the sub substrate 2 can be suppressed.

In addition, since the gap 2S is formed between the tube hole 2H and the measurement tube 3 in a discrete manner, the measurement tube 3 can be easily pressed into the tube hole 2H and press-fitted. It is not necessary to prepare exclusive jig and can reduce work burden.

On the other hand, the shape of the tube hole 2H is not limited to a substantially polygonal shape, and a plurality of convex portions may be provided on the hole wall surface of the tube hole 2H, and the convex portion may be in contact with the outer peripheral surface 3A. Alternatively, a part of the periphery of the tube hole 2H may be formed to have a cutout that is directly opened toward the side end portion of the sub substrate 2 or a slit that is indirectly opened. Thereby, the effect similar to the above can be obtained.

In addition, in this embodiment, the pair of guide parts 7X and 7Y which consist of a convex or concave rail is formed in 4 C of inner wall parts of the side surface 4B of the lower case 4. As shown in FIG. The sub board | substrate 2 is inserted by inserting from the opening part 4D of the lower case 4 so that the side end parts 2X and 2Y of the sub board | substrate 2 may fit in these guide parts 7X and 7Y. Through the measuring tube 3 is attached to the lower case (4). Thereby, the sub board | substrate 2 and the measuring tube 3 can be attached in the inside of the lower case 4 with a very simple structure.

On the other hand, with respect to the guide parts 7X and 7Y, the convex part or the concave part does not need to be extended and formed, but the convex part or the concave part is spaced at the interval which the side ends 2X and 2Y are inserted smoothly. You may separate and form in multiple numbers. In addition, although the case where the guide parts 7X and 7Y consist of two protrusion parts is shown as an example in FIG. 3, the groove | channel in which the side end parts 2X and 2Y are inserted instead of a protrusion part may be sufficient.

In addition, it is not necessary to fix the sub board | substrate 2 with the guide parts 7X and 7Y, On the contrary, in the case of screwing by the joint 5A, 5B which has a little space on the contrary, the measuring tube 3 or the sub board | substrate ( The mechanical stress applied to 2) can be alleviated.

[Operation of First Embodiment]

Next, with reference to FIG. 8, operation | movement of the electrical conductivity meter 10 which concerns on this embodiment is demonstrated. 8 is a signal waveform diagram showing the operation of the electrical conductivity meter according to the first embodiment.

Here, the case where the electrode T2 is a non-contact electrode and the square wave signal SG is a square wave constant voltage signal is demonstrated as an example.

The clock generation circuit 11A, based on the clock signal CLK0 from the arithmetic processing circuit 12, clock signals CLKs for generating square wave signals SG and clock signals CLKh and CLKl for sampling control. Create Here, the case where the frequency of CLKs, ie, the signal frequency fg of the square wave signal SG, is 3 MHz is shown.

The signal generation circuit 21 controls the switch SWg on and off based on the CLKs. Thereby, as shown in FIG. 8, the reference voltage Vs and the ground voltage GND supplied from the detection circuit 11 are switched every half cycle of the signal frequency fg by the switch SWg, and resistance It is applied to the electrode T2 through the element Rr. Therefore, the reference voltage Vs supplied from the signal generation circuit 21 is divided by the impedance between the resistance element Rg and the electrodes T1 and T2, and the divided voltage is the voltage between the electrodes T1 and T2. That is, the detection voltage Vt is obtained.

The sample hold circuit 11B has a high voltage Vs supplied from the output voltage Vt 'obtained by stabilizing (impedance conversion) Vt in the buffer amplifier 22 based on CLKh from the clock generation circuit 11A. The detection voltage VH in the level period TH (half cycle of SG) is sampled. Further, the sample hold circuit 11B is based on the CLKl from the clock generation circuit 11A, and the detection voltage VL in the low level period TL (half period of SG) to which GND is supplied among Vt '. Sampling).

As for the timing of sampling VH and VL, a time position that is not affected by the waveform change of Vt caused by the switching of TH and TL and the saturation of Vt is preferable. In addition, it is preferable to sample VH and VL at the same time position on the basis of the start time of TH and TL. Therefore, what is necessary is just to sample VH and VL in the center position of TH and TL (semi-period of SG) which Vt stabilizes, for example.

The A / D conversion circuit 11C A / D converts and outputs the difference voltage ΔVt between VH and VL obtained by the sample hold circuit 11B into amplitude data DA.

In general, a method of full-wave rectifying the detection voltage Vt of alternating current, for example, a method of adding the detection voltage Vt in TL back to the intermediate level of Vt and adding it to the Vt of TH. However, in such a method, if the Vt of TL and TH is not the same, a ripple remains even after full-wave rectification and since it does not become a stable DC voltage, it becomes a cause of a measurement error.

According to this embodiment, the differential voltage of VH and VL obtained by sampling separately from TL and TH is acquired as amplitude data, without full-wave rectifying AC detection voltage Vt.

For this reason, the influence on the amplitude data can be avoided even when the vibration is contained in the Vt due to the change in the liquid flow rate or when the common mode noise is mixed in the Vt through the liquid from the outside. It is possible to realize stable measurement of electrical conductivity.

The electrical conductivity calculation unit 12A calculates the electrical conductivity of the liquid based on the DA from the A / D conversion circuit 11C.

In addition, the empty state determination unit 12B determines whether or not the measurement tube 3 is in an empty state by comparing the electrical conductivity obtained by the electrical conductivity calculation unit 12A with a threshold conductivity.

9 is an equivalent circuit on the electrode side according to the first embodiment. As described above, the applied voltage Vg representing the amplitude of the square wave signal SG is divided by the impedance between the resistance element Rg and the electrodes T1 and T2. For this reason, as shown in FIG. 9, the equivalent circuit of the electrode side seen from the sub board | substrate 2 has the resistance of the signal generation circuit 21 with respect to the square wave voltage source VG corresponded to the signal generation circuit 21. As shown in FIG. The device Rg and the equivalent circuit Zt on the side representing the impedance between the electrodes T1 and T2 are connected in series.

At this time, in Zt, the polarization capacity Cp and the polarization resistance Rp are generated between the electrodes and the liquid when the electrodes T1 and T2 are in contact with the liquid, and since T2 is a non-contact electrode, the liquid and the electrode ( The electrode capacitance Ct is generated between T2). Therefore, if the liquid resistance with respect to the liquid between electrodes T1 and T2 is Rl, Zt is a parallel circuit of polarization capacitance Cp and polarization resistance Rp, liquid resistance Rl, and electrode capacitance Ct. ) Appears as an equivalent circuit connected in series. Here, when the signal frequency fg of the square wave signal SG is relatively high, the impedances of Cp and Ct become very small, as shown in FIG. 8, the voltages Vcp between the ends of Cp and Rp and the voltages between the ends of Ct. (Vct) is a level that can be ignored. Thereby, Zt can be regarded only as liquid resistance Rl.

When the square wave signal SG is considered to be an AC signal having an amplitude of ± Vs / 2 centered on the midpoint Vs / 2 of Vs, the detected voltage Vt detected in the high level period TH with Vg = Vs. If VH is the voltage at both ends of Rg, VrgH = Vs-VH, and the voltage at both ends of Vt (Vz), that is, the voltage at both ends of liquid resistor Rl, is VrlH = VH-Vs / 2. If the detected voltage Vt detected in the low level period TL with Vg = GND is VL, the voltage across Rg is VrgL = VL, and the voltage across the liquid resistor Rl is VrlL = Vs / 2. -VL

Therefore, when VrgHL = VrgH + VrgL and VrlHL = VrlH + VrlL, the ratio of VrgHL and VrlHL becomes the following equation (1).

[Equation (1)]

Here, since the ratio of VrgHL and VrlHL can be considered to be almost the same as the ratio of Rg and Rl (≒ Zt), Rl is obtained from the following equation (2).

[Equation (2)]

At this time, in the formula (2), Rg and Vs are known, and the differential voltages VH-VL are detected by the SH circuit 11B and converted into amplitude data DA by the A / D conversion circuit 11C. It is input to the arithmetic processing circuit 12. Therefore, the electrical conductivity calculation unit 12A can easily calculate Rl based on these data.

10 is a characteristic diagram showing a correspondence relationship between amplitude data and electrical conductivity, and the vertical axis represents amplitude data DA and the horizontal axis represents electrical conductivity. By performing a calibration operation using a plurality of standard fluids whose electrical conductivity is known, the corresponding relationship between the amplitude data DA and the electrical conductivity is measured in advance, and the obtained characteristics are used as a look-up table, for example, a semiconductor memory (not shown). The electrical conductivity calculation unit 12A may derive the electrical conductivity with respect to the liquid in the measurement tube 3 with reference to the lookup table based on the amplitude data DA from the detection circuit 11. .

11 is another signal waveform diagram showing the operation of the electrical conductivity meter according to the first embodiment. In FIG. 8, the case where fg = 3 MHz as a signal frequency of the level which can ignore the impedance of Cp and Ct was demonstrated as an example. However, when fg is relatively low, for example, when fg = 150 kHz, as shown in Fig. 11, the impedances of Cp and Ct cannot be ignored. For this reason, Vct, Vrl, and also Vt change exponentially with each time constant, and VH and VL cannot be stably detected.

In this way, when the waveform of Vt is deformed, an error is likely to be included in the detection of the amplitude data DA, and as a result, it becomes a factor of the decrease in the measurement accuracy regarding the electrical conductivity. For this reason, as fg, it is necessary to use a frequency high enough to ignore the impedance of Cp and Ct. On the other hand, when fg is made high, like the conventional equivalent circuit shown in FIG. 21, the influence by the line capacitance Cw of an electrode wiring becomes large, and signal leakage occurs in an electrode wiring, and it causes a waveform of Vt to deform.

In the present embodiment, at least one or both of the signal generating circuit 21 and the buffer amplifier 22 are attached to positions near the electrodes T1 and T2 of the outer peripheral surface 3A of the measuring tube 3. The substrate 2 is mounted, and the electrodes T1 and T2 are electrically connected to the sub substrate 2 through the jumper wires J1 and J2. Thereby, the length of the electrode wirings corresponding to J1 and J2 can be made very short, and the line capacitance Cw between J1 and J2 can be made small. For this reason, even if a high frequency such that the impedances of Cp and Ct can be neglected as fg is used, signal leakage between J1 and J2 can be suppressed low. Therefore, it becomes possible to measure electric conductivity with high precision.

[Effect of 1st Embodiment]

Thus, in this embodiment, the signal generation circuit 21 which arrange | positions the sub board | substrate 2 in the vicinity of the electrodes T1 and T2 attached to the measuring tube 3, and produces | generates the square wave signal SG is carried out. And at least one or both of the buffer amplifiers 22 which stabilize and output the detection signals detected from the electrodes T1 and T2 are mounted on the sub substrate 2.

More specifically, the signal generation circuit 21 generates a square wave constant voltage signal composed of an alternating square wave voltage having a constant amplitude as the square wave signal SG. In addition, the electrode T1 consists of a liquid contact electrode which contacts liquid, and the electrode T2 is formed in the outer peripheral part of the measuring tube 3, and consists of a non-contact electrode which does not contact liquid.

As a result, the lengths of the electrode wirings that connect the signal generation circuit 21, the buffer amplifier 22, and the electrodes T1 and T2, that is, the jumper lines J1 and J2, can be greatly shortened, and the line between the electrode wirings The capacity can be made small. Therefore, even when a relatively high signal frequency is used, the electrical conductivity can be measured with high accuracy. Moreover, the influence by the line capacitance of the electrode wiring which connects an electrode can be suppressed, and electrical conductivity can be measured with high precision.

In addition, since the electrode T2 is a non-contacting electrode, generation of measurement errors caused by adhesion of dirt to the electrode surface and corrosion of the electrode can be suppressed. In addition, it is not necessary to use an expensive liquid contact electrode such as platinum black, so that a significant cost reduction can be achieved.

In the present embodiment, a tube hole 2H into which the measuring tube 3 is inserted is formed in the sub-substrate 2, and the tube hole 2H and the outer peripheral surface 3A of the measuring tube 3 come into contact with each other. You may make it adhere to 3 A of outer peripheral surfaces.

Thereby, the sub board | substrate 2 can be fixed to the measuring tube 3 with a very simple structure, without using fixing members, such as a mounting screw.

In addition, according to such a structure, the sub board | substrate 2 can be arrange | positioned orthogonally to the longitudinal direction of the measurement tube 3 between electrode T1 and electrode T2. For this reason, the electrode wiring from the sub board | substrate 2 to the electrodes T1 and T2, ie, jumper wires J1 and J2, can be arrange | positioned and connected in different positions and directions, and the line capacitance between electrode wirings is very small. can do. In addition, when the metal pipe is connected to the joint 5A which is the electrode T1, the current applied to the liquid may return to the metal pipe and measurement errors may occur. And T2 can be easily disposed. Therefore, the return of the applied current to the metal pipe can be suppressed, and the electrical conductivity can be measured with high accuracy.

In addition, in this embodiment, the pad (electrode connection terminal) for connecting the electrode wiring to the electrodes T1 and T2 to the pattern surface of the sub board | substrate 2, the signal generation circuit 21, and the buffer amplifier 22 ), A wiring pattern for connecting the pad with at least one or both sides may be formed.

This makes it very easy to use the jumper wires J1 and J2 to connect the signal generating circuit 21, the buffer amplifier 22, and the electrodes T1 and T2 mounted on the sub board 2 without using a connector. Can be connected.

Second Embodiment

Next, with reference to FIG. 12, the electrical conductivity meter 10 which concerns on 2nd Embodiment of this invention is demonstrated. 12 is a block diagram showing the circuit configuration of the electric conductivity meter according to the second embodiment.

In this embodiment, the case where the electrode T2 is a non-contact electrode and the square wave signal SG is a square wave constant current signal is demonstrated as an example.

As shown in Fig. 12, the signal generating circuit 21 generates a square wave signal SG having a preset signal frequency fg, here an AC square wave constant current signal having a constant amplitude (set current Is). Has the ability to Specifically, the signal generation circuit 21 is composed of a square wave current source IG which is turned on and off as a whole, and is connected to the reference voltage Vs of T22 and the ground voltage GND of T23, and the clock signal of T21. Based on CLKs, it has a function of generating a square wave signal SG having a signal frequency fg equal to CLKs at the set current Is.

13 is a structural example of a square wave current source. As shown in FIG. 13, the square wave current source IG includes a switch SWi, an operational amplifier Ug, and a current detection circuit DET. SWi is an analog switch that switches between Vs and GND based on CLKs. DET is a circuit for detecting the current value of the applied current Ig output from IG. Ug has a function of holding and controlling the current value of Ig at the set current Is based on the current detection output from the DET, and controlling the output of Ig on and off based on the output of SWi.

Since the above-described resistance element Rg is unnecessary, the output of the signal generation circuit 21, that is, the output terminal of the IG is connected to the pad P2 via the wiring pattern LP2 formed on the sub substrate 2. .

Other circuit configurations and structures of the measurement tube 3, the electrodes T1 and T2, the sub-substrate 2 and the like relating to the electric conductivity meter 10 according to the present embodiment are the same as those in the first embodiment. The detailed description thereof will be omitted.

[Operation of Second Embodiment]

Next, with reference to FIG. 14, operation | movement of the electrical conductivity meter 10 which concerns on this embodiment is demonstrated. 14 is a signal waveform diagram showing the operation of the electrical conductivity meter according to the second embodiment.

Here, the case where the electrode T2 is a non-contact electrode and the square wave signal SG is a square wave constant current signal is demonstrated as an example. In addition, about the basic calculation process of the electrical conductivity based on amplitude data DA, it is the same as that of 1st Embodiment, and the description here is abbreviate | omitted.

The clock generation circuit 11A, based on the clock signal CLK0 from the arithmetic processing circuit 12, clock signals CLKs for generating square wave signals SG and clock signals CLKh and CLKl for sampling control. Create Here, the case where the frequency of CLKs, ie, the signal frequency fg of the square wave signal SG, is 150 Hz is shown.

The signal generation circuit 21 controls the square wave current source IG on and off based on the CLKs. As a result, as shown in FIG. 14, the applied current Ig is switched between the preset setting current Is and zero at every half period of the signal frequency fg to be applied to the electrode T2. . Therefore, the voltage generated by the liquid resistance of the liquid between the electrodes T1 and T2 by the applied current Ig supplied from the signal generation circuit 21 causes the voltage between the electrodes T1 and T2, that is, the detection voltage. (Vt).

The sample hold circuit 11B is a high voltage in which Is is supplied among the output voltages Vt 'obtained by stabilizing (impedance conversion) Vt in the buffer amplifier 22 based on CLKh from the clock generation circuit 11A. The detection voltage VH in the level period TH (half cycle of SG) is sampled. Further, the sample hold circuit 11B is based on the CLKl from the clock generation circuit 11A, and the detection voltage VL in the low level period TL (half period of SG) to which zero is supplied during Vt '. Sampling).

The A / D conversion circuit 11C A / D converts and outputs the difference voltage ΔVt between VH and VL obtained by the sample hold circuit 11B into amplitude data DA.

The electrical conductivity calculation unit 12A calculates the electrical conductivity of the liquid based on the DA from the A / D conversion circuit 11C.

In addition, the empty state determination unit 12B determines whether or not the measurement tube 3 is in an empty state by comparing the electrical conductivity obtained by the electrical conductivity calculation unit 12A with a threshold conductivity.

15 is an equivalent circuit on the electrode side according to the second embodiment. In the present embodiment, since the square wave constant current signal is used as the square wave signal SG, it is not necessary to use the resistance element Rg. For this reason, as shown in FIG. 15, the equivalent circuit of the electrode side seen from the sub board | substrate 2 has the impedance between electrodes T1 and T2 with respect to the square wave current source IG of the signal generation circuit 21. The equivalent circuit Zt on the side shown is connected.

At this time, in Zt, the polarization capacity Cp and the polarization resistance Rp are generated between the electrodes and the liquid when the electrodes T1 and T2 are in contact with the liquid, and since T2 is a non-contact electrode, the liquid and the electrode ( The electrode capacitance Ct is generated between T2). Therefore, if the liquid resistance with respect to the liquid between electrodes T1 and T2 is Rl, Zt is a parallel circuit of polarization capacitance Cp and polarization resistance Rp, liquid resistance Rl, and electrode capacitance Ct. ) Appears as an equivalent circuit connected in series. Here, when the signal frequency of the square wave signal SG is fg = 150 kHz, the impedance of Cp is relatively small, but the impedance of Ct is somewhat increased, so that the voltage Vct at both ends of Vt, and Vt changes transiently. Done.

As shown in Fig. 11, when a square wave constant voltage signal composed of an alternating square wave voltage having a constant amplitude is used as the square wave signal SG, the voltage Vrl at both ends of the Vct or the liquid resistor Rl, and thus Vt, respectively It is changed exponentially with the time constant of and it becomes impossible to detect VH and VL stably.

In this way, when the waveform of Vt is deformed, an error is likely to be included in the detection of the amplitude data DA, and as a result, it becomes a factor of the decrease in the measurement accuracy regarding the electrical conductivity. For this reason, as fg, it is necessary to use a frequency high enough to ignore the impedance of Cp and Ct. On the other hand, when fg is made high, like the conventional equivalent circuit shown in FIG. 21, the influence by the line capacitance Cw of an electrode wiring becomes large, and signal leakage occurs in an electrode wiring, and it causes a waveform of Vt to deform | transform.

In contrast, in the present embodiment, since the square wave constant current signal is used as the square wave signal SG, even when fg = 150 kHz, the inclinations of Vct and Vt become linear, whereby VH and VL can be stably detected. Can be.

If the detected voltage Vt detected in the high level period TH in which the applied current Ig is the set current Is is VH, and Vrl and Vct at that time are VrlH and VctH, then VH = VrlH + VctH. . If the detected voltage Vt detected in the low level period TL at Ig = 0 is VL, and Vrl and Vct at that time are VrlL and VctL, then VL = VrlL + VctL.

At this time, Vct is included in the detected VH and VL, but since CLKh and CLKl represent the center positions of TH and TL (semi-period of SG), the VctH and VctL included in the sampled VH and VL become the same. As a result, by adopting the difference voltage ΔVt between VH and VL, VctH and VctL are canceled to obtain amplitude data DA without Vct.

That is, ΔVt = VH-VL = VrlH-VrlL. Thereby, since Ig is constant, Rl is calculated | required by following formula (3).

[Equation (3)]

In Equation (3), Ig is known, and the differential voltage VH-VL is detected by the SH circuit 11B, converted into amplitude data DA by the A / D conversion circuit 11C, and the arithmetic processing circuit ( 12) is entered. Therefore, the electrical conductivity calculation unit 12A can easily calculate Rl based on these data.

Thereby, even when fg = 150 Hz, VH and VL can be detected stably and accurately. Thereby, compared with the case where fg = 3 MHz, the influence by the line capacitance of electrode wiring, ie, jumper wires J1 and J2 can be made very small, and electrical conductivity can be measured with very high precision.

[Effect of 2nd Embodiment]

Thus, in this embodiment, the signal generation circuit 21 which arrange | positions the sub board | substrate 2 in the vicinity of the electrodes T1 and T2 attached to the measuring tube 3, and produces | generates the square wave signal SG is carried out. And at least one or both of the buffer amplifiers 22 which stabilize and output the detection signals detected from the electrodes T1 and T2 are mounted on the sub substrate 2.

More specifically, the signal generation circuit 21 generates a square wave constant current signal composed of an alternating square wave current having a constant amplitude as the square wave signal SG. In addition, the electrode T1 consists of a liquid contact electrode which contacts liquid, and the electrode T2 is formed in the outer peripheral part of the measuring tube 3, and consists of a non-contact electrode which does not contact liquid.

This makes it possible to shorten the length of the electrode wiring connecting the signal generating circuit 21, the buffer amplifier 22, and the electrodes T1 and T2, that is, the jumper lines J1 and J2, and the line capacitance between the electrode wirings Can be made small. Therefore, even when a relatively low signal frequency is used, the electrical conductivity can be measured with high accuracy.

Further, by using a square wave constant current signal composed of an alternating square wave current having a constant amplitude as the square wave signal SG, the electrode capacitance generated between the liquid and the electrode T2 peculiar to the case where the non-contact electrode T2 is used The influence of (Ct) can be greatly reduced. As a result, since a relatively low frequency can be used as the signal frequency fg of the square wave signal SG, it is possible to further reduce the influence of the line capacitance of J1 and J2, and to measure the electrical conductivity with a very high precision. It becomes possible.

In the present embodiment, the detection circuit 11 may cause the detection voltage Vt to be sampled at the center time position of the half cycle of the square wave signal SG.

As a result, even when a non-contact electrode is used as T2, the voltage VctH at both ends of the electrode capacitance Ct of T2 included in the VH sampled in the high level period TH is sampled in the low level period TL. The voltage VctL of both ends of Ct contained in VL becomes the same. Therefore, by adopting the difference voltage ΔVt between VH and VL, VctH and VctL are canceled to obtain amplitude data DA without Vct. For this reason, it becomes possible to measure electrical conductivity with high precision.

In the present embodiment, the square wave current source IG of the signal generating circuit 21 includes a current detection circuit DET for detecting the magnitude of the square wave constant current signal, and a clock signal CLKs indicating the signal frequency fg. The operational amplifier Ug may maintain the amplitude of the applied current Ig, which is a square wave constant current signal, as the set current Is based on the detection result from the eddy current detection circuit DET.

Thereby, the stable applied current Ig with high precision can be produced with a comparatively simple structure.

[Third Embodiment]

Next, with reference to FIGS. 16-19, the electrical conductivity meter 10 which concerns on 3rd Embodiment of this invention is demonstrated. 16 is a side view of an electric conductivity meter according to a third embodiment. 17 is a top view of an electric conductivity meter according to the third embodiment. 18 is a perspective view of an electrical conductivity meter according to a third embodiment. 19 is another perspective view of the electrical conductivity meter according to the third embodiment.

In 1st and 2nd embodiment, the case where the non-contact electrode which does not contact liquid is used as the electrode T2 was demonstrated as an example. In this embodiment, the case where the liquid-contacting electrode which contacts liquid is used as electrode T2 is demonstrated. In addition, this embodiment is applicable to all of 1st and 2nd embodiment.

[Electric conductivity meter structure]

Next, with reference to FIGS. 16-19, the structure of the electrical conductivity meter 10 which concerns on this embodiment is demonstrated. In addition, below, the direction in which the measurement tube 3 extends is called 1st direction X for convenience, and the left-right direction of the measurement tube 3 orthogonal to 1st direction X is called 2nd direction Y The vertical direction of the measurement tube 3 orthogonal to the 1st and 2nd direction X and Y is called 3rd direction Z.

The measuring tube 3 is made of a material having excellent insulation and dielectric properties, such as a ceramic or resin forming a cylindrical shape, and is housed inside the lower case 4. The lower case 4 is comprised with a bottomed box-shaped resin or a metal case.

The pair of side surfaces 4A orthogonal to the first direction X among the side surfaces of the lower case 4 are provided with a pipe (not shown) and a measurement tube 3 provided outside the electrical conductivity meter 10. Connectable tubular joints 5A, 5B made of metal material (eg SUS) are arranged. At this time, the measurement tube 3 is accommodated in the lower case 4 along the longitudinal direction X, and a joint (with a pair of O-rings OR) is disposed between both ends of the measurement tube 3. 5A) and joint 5B are respectively connected.

Here, at least one of the joints 5A and 5B functions as an electrode (first electrode) T1. For example, the joint 5A is connected to the ground voltage GND (common potential), thereby not only connecting the external pipe and the measurement tube 3 but also functioning as the electrode T1.

Thus, by realizing the electrode T1 by the joint 5A made of metal, the area where T1 comes into contact with the liquid is increased. As a result, even if adhesion or corrosion of foreign matter occurs in T1, the area of the portion where adhesion or corrosion of foreign matter occurs is relatively small relative to the entire area of T1. Therefore, it is necessary to suppress measurement errors due to changes in polarization capacity. It becomes possible.

On the other hand, a pair of side surfaces 4B orthogonal to the second direction Y among the side surfaces of the lower case 4 and an outer surface of the bottom surface 4E of the lower case 4 are formed of a metal plate having a cross-shaped U shape. The shield 6 which consists of is attached. Thereby, the noise radiated externally from the electrical conductivity meter 10 can be reduced.

In addition, in the outer peripheral surface 3A of the measuring tube 3, the sub-substrate 2 is sandwiched between the joint 5A and the side opposite to the joint 5A so as to project through the wall of the measuring tube 3 into the measuring tube 3, A liquid contact electrode (second electrode) T2 made of a metal rod body is attached. The part which protrudes in the measurement tube 3 comes into contact with the liquid in the measurement tube 3.

As described above, at least one of the signal generating circuit 21 and the buffer amplifier 22 is attached to a sub-substrate attached to a position near the electrodes T1 and T2 of the outer peripheral surface 3A of the measuring tube 3 ( 2) and the electrodes T1 and T2 are electrically connected to the sub substrate 2 through the jumper wires J1 and J2. At this time, specifically, J1 is soldered to the outer surfaces of P1 and T1, and J2 is soldered to P2 and T2.

[Operation of Third Embodiment]

Next, operation | movement of the electrical conductivity meter 10 which concerns on this embodiment is demonstrated.

When the electrode T2 is changed from the non-contact electrode to the contact electrode, the electrode capacitance Ct between T2 and the liquid in the case of the non-contact electrode is lost. For this reason, the equivalent circuit Zt shown in FIG. 9 and FIG. 15 is shown by the parallel circuit of polarization capacitance Cp and polarization resistance Rp, and the equivalent circuit with liquid resistance Rl connected in series. The other electrical conductivity measurement operation | movement which concerns on this embodiment is the same as that of 1st and 2nd embodiment, and detailed description here is abbreviate | omitted.

[Effect of 3rd Embodiment]

Thus, in this embodiment, the electrodes T1 and T2 consist of a liquid contact electrode which liquid contacts with a liquid. Thereby, the influence of the capacitance Ct generated between the liquid and the electrode T2, which is unique when the non-contacting electrode is used as T2, can be eliminated, and the signal frequency of the square wave signal SG is relatively low. Can be used. For this reason, the influence by the line capacitance of electrode wiring, ie, jumper wires J1 and J2 can be made very small, and electrical conductivity can be measured with a very high precision.

Extension of Embodiments

As mentioned above, although this invention was demonstrated with reference to embodiment, this invention is not limited to the said embodiment. Various changes which can be understood by those skilled in the art can be made to the structure and details of the present invention within the scope of the present invention. In addition, about each embodiment, it can implement combining arbitrarily in the range which does not contradict.

10: electrical conductivity meter 1: main board
2: sub substrate 2A, 2B: substrate surface
2G: circuit mounting area 2H: tube hole
2S: clearance 2X, 2Y: side end
3: measuring tube 3A: outer peripheral surface
4: lower case 4A, 4B: side
4C: Inner Wall 4D: Opening
4E: Bottom 5A, 5B: Joint
6: shield 7X, 7Y: guide part
9: upper case 11: detection circuit
11A: Clock Generation Circuit 11B: Sample Hold Circuit (SH Circuit)
11C: A / D conversion circuit (ADC circuit) 12: Operation processing circuit
13: Setting and Display Circuit 14: Transmission Circuit
21: signal generation circuit 22: buffer amplifier
VG: square wave voltage source IG: square wave current source
T1, T2: electrodes P1, P2, P3: pad
J1, J2: Jumper wire LC: Connection wiring
CN1, CN2: Connector LP1, LP2: Wiring Pattern
SWg, SWh, SWl, SWi: Switch Rg: Resistor
CLK0, CLKs, CLKh, CLKl: Clock Signal Vs: Reference Voltage
GND: Ground Voltage SG: Square Wave Signal
Vg: applied voltage Ig: applied current
Vt, VH, VL: Detection voltage Vt ': Output voltage
DA: amplitude data

Claims (6)

An electrical conductivity meter for measuring electrical conductivity with respect to a liquid in a measuring tube,
A signal generating circuit for generating a square wave signal having a preset signal frequency;
A first electrode and a second electrode attached to the measuring tube to apply the square wave signal to the liquid;
A buffer amplifier for stabilizing and outputting detection signals detected from the first electrode and the second electrode;
A detection circuit for detecting an amplitude of the detection signal by sampling an output of the buffer amplifier;
An arithmetic processing circuit for calculating an electric conductivity for the liquid by arithmetic processing based on the amplitude;
A printed wiring board disposed in the vicinity of the first electrode and the second electrode,
At least one or both of the signal generation circuit and the buffer amplifier are mounted on the printed wiring board.
Electrical conductivity meter, characterized in that. The method of claim 1,
And the signal generating circuit generates a square wave constant voltage signal composed of an alternating square wave voltage having a constant amplitude as the square wave signal. The method of claim 1,
And the signal generating circuit generates a square wave constant current signal composed of an alternating square wave current having a constant amplitude as the square wave signal. The method according to any one of claims 1 to 3,
The first electrode is composed of a liquid contact electrode which is in contact with the liquid, and the second electrode is formed at an outer periphery of the measuring tube, and is made of a noncontact liquid electrode which is not in contact with the liquid. Electrical conductivity meter. The method according to any one of claims 1 to 3,
The printed wiring board has a tube hole into which the measuring tube is inserted, and the electrical conductivity meter is attached to the outer peripheral surface by contact between the tube hole and the outer peripheral surface of the measuring tube. The method according to any one of claims 1 to 3,
An electrode connection terminal for connecting electrode wirings to the first electrode and the second electrode to a pattern surface of the printed wiring board, at least one or both of the signal generation circuit and the buffer amplifier and the electrode connection An electrical conductivity meter, wherein a wiring pattern for connecting the terminals is formed.

Images