JPH0382971A - Electromagnetic induction type conductivity meter - Google Patents

Abstract

PURPOSE:To correct a change of magnetic flux and to perform excitation at stable frequency by detecting the magnetic flux generated in a troidal coil on an exciting side by a magnetic flux detection coil and forming a fundamental wave by an exciting circuit to shape the same. CONSTITUTION:Troidal coils T1, T2 on exciting and detection sides are arranged in a liquid to be measured in a non-contact state and exciting and detection coils COIL1a, COIL3 are provided to the respective coils T1, T2. When an AC is supplied to the coil COIL1a, the coil T3 detects said AC by electromagnetic induction to calculate the signal proportional to the conductivity of the liquid to be measured by the coil COIL3. At this time, a magnetic flux detection coil COIL1b is provided to the coil T1 other than the COIL1a to detect the magnetic flux generated in the coil T1. The voltage generated in the coil COIL1b is inputted to an exciting coil 10 to be compared with reference voltage Vref by a comparator 13 and, as a result, a fundamental waveform is formed 15 on the basis of the reference frequency from an oscillator 14. This waveform is shaped 16 to a fundamental wave component to be outputted to the coil COIL1a.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to an electromagnetic induction conductivity meter that measures the conductivity of a liquid to be measured using electromagnetic induction.

<Conventional technology> Conventionally, two 1-lances covered with an insulating film are immersed in the liquid to be measured, a current is passed through the liquid to be measured by electromagnetic induction from one transformer, and this current is passed back to the liquid by electromagnetic induction in the other transformer. A method for obtaining a voltage signal proportional to the electrical conductivity of the liquid to be measured is conventionally known. Since such a conductivity meter is basically an immersion type, when measuring a liquid to be measured flowing inside a pipe, a case through which the liquid to be measured flows must be separately provided outside the detection section. Furthermore, when such a case is installed, the cell constant changes depending on the shape of the case, making this method unsuitable for measuring circulating liquids. Furthermore, in this method, the L lance and the insulating material are integrally molded, and it is not possible to remove the incorporated transformer later for purposes such as maintenance.

Therefore, in order to solve such problems, the applicant of the present application
Utility Application No. 63-94957 “Electromagnetic induction conductivity meter” (
(hereinafter referred to as "prior art"). This prior art realizes an electromagnetic induction conductivity meter that has a constant cell constant, is suitable for flow-type measurement, and has a detecting section including a transformer that can be attached and detached, making maintenance easy. The outline of its configuration is as follows: The ring-shaped core (hereinafter referred to as "excitation toroidal coil") that constitutes the ml magnetic transformer, and the center hole of the ring-shaped core (hereinafter referred to as "detection ffl + - Loytal coil") that constitutes the detection 1 to lance. It consists of a transformer assembly unit into which a tubular body through which the liquid to be measured can flow is inserted, and it can be tightly connected to the lance assembly, and when the lance assembly l is connected, the to-be-measured liquid A closed loop of the liquid to be measured is formed around the transformer assembly unit by a tube having m openings for liquid inflow and through which the liquid to be measured flows. At this time, the cell constant is determined by the state of the loop of the liquid to be measured, but in this prior art, the loop is fixed by the main body and the cell constant does not change.

FIG. 3 is a diagram showing the principle of this prior art electromagnetic induction conductivity meter.

In FIG. 3, two troital coils (T, , T2) are placed in the liquid to be measured (not shown).

Excitation II],! The excitation coil C0I1. is connected to the excitation power supply Em at both ends of the l-Roytal coil '■゛. +
The Royal coil is placed on the detection side).
A detection coil Co2 13 that can detect the detection voltage E0 from both sides is also wound around r2. The liquid to be measured will flow through the center holes of the two 1-loydal coils T1 and '1゛2, and to express this electrically, it will be linked to the two 1-loydal coils T1 and 'I'2, respectively. The interlinking coil CO]L2 is wound and arranged so that As the liquid to be measured flows inside in this way, a closed loop of the liquid to be measured is formed around the L-lance assembly.
When an alternating current is passed through the excitation coil CO]L+ by the excitation power source EW, an induced current proportional to the conductivity of the liquid to be measured is generated in the linkage coil (liquid to be measured) C0IL2 which interlinks with the excitation side toroidal coil 1゛1. 1 flows, this is detected again by electromagnetic induction in the detection 1 law 1-loidal coil 1-2, and the detection voltage E is output from the detection coil co r t3. By closing and taking out the detection voltage E. This makes it possible to measure the conductivity of the liquid to be measured in a non-liquid state.

<Problems to be Solved by the Invention> However, the electromagnetic induction conductivity meter of the prior art has the following problems.

■: Excitation coil C0I1. ．． Either current is flowing through the excitation coil C0JL+ while keeping the amplitude of the AC voltage applied to the excitation coil C0JL+ constant, or the excitation side toroidal coil 'F1
The excitation capacity of the toroidal coil T changes due to changes in magnetic permeability and drift of the excitation capacity of the electric circuit.

The magnetic flux inside changes, and this change causes an output error.

(2) In such a configuration, even if the excitation voltage frequency changes, an output error occurs, or there is no simple electric circuit for generating an excitation voltage with a stable frequency.

The present invention has been made in view of the problems of the prior art, and its purpose is to correct changes in magnetic flux within the excitation side toroidal coil and to excite at a stable frequency. The present invention provides an electromagnetic induction conductivity meter equipped with such an excitation circuit.

Means for Solving the Problems> In order to achieve the above object, the electromagnetic induction conductivity meter of the present invention has the following features: An excitation-side troital coil and a detection-side toroidal coil are placed in a liquid to be measured in a non-contact manner with the liquid to be measured. The excitation side toroidal coil is arranged in such a state that the excitation side toroidal coil is connected to the excitation side toroidal coil.
A detection coil is provided in each of the detection side 1 to the loidal coil, and an alternating current is supplied to the excitation coil to cause a current to flow through the liquid to be measured by electromagnetic induction, and the current is detected by the detection side 1 to the loidal coil by electromagnetic induction. In an electromagnetic induction conductivity meter that obtains a signal proportional to the conductivity of the liquid to be measured in a detection coil, the excitation side toroidal coil detects magnetic flux generated in the excitation toroidal coil in addition to the excitation coil. A magnetic flux detection coil is installed.The voltage generated by this magnetic flux detection coil is input and compared with a reference voltage by a comparator circuit.The waveform generation circuit generates a basic waveform based on the comparison result based on the reference frequency from the oscillator. , an excitation circuit is provided in which the waveform shaping circuit shapes the output from the waveform generation circuit into a fundamental wave component and outputs the fundamental wave component to the excitation coil.

<Example> Examples will be described with reference to the drawings.

In the following drawings, parts that overlap with those in FIG. 3 are given the same numbers, and their explanations will be omitted.

FIG. 1 is a block diagram showing an embodiment of the electromagnetic induction conductivity meter of the present invention.

In Fig. 1, C0IL+ a is an exciting coil, 001
[1h is a magnetic flux detection coil, 10 is an excitation circuit. In the excitation circuit 10, 11 is a rectifier/smoothing circuit, 12 is a reference voltage generation means, 13 is a comparison circuit, 14 is an oscillator, 15 is a waveform generation circuit, 16 is a waveform shaping circuit, and 20 is a detection circuit section.

FIG. 2 is a diagram showing an example of a circuit in which the electromagnetic induction ring shown in FIG. 1 is made concrete.

The electromagnetic induction conductivity meter of the present invention will be further described in detail with reference to FIG.

In Fig. 2, magnetic flux detection H, (4 coils C0IL+ b
detects the magnetic flux generated in the excitation measurement toroidal coil 'I'1.

Each part of the excitation circuit 10 can be specifically configured as follows. The rectification/smoothing circuit 11 includes a magnetic flux calibration coil C0I.
The voltage generated at L+b is input and rectified and smoothed by a circuit that can be configured, for example, with an operational amplifier Q, a rectifying element D1, a capacitor C4, and the like. The reference voltage generating means 12 consists of a circuit configuration that outputs a reference voltage vref. The comparison circuit 13 includes a magnetic flux detection coil COI from the rectification/smoothing circuit 11. Rectifying the voltage generated at +11
A circuit composition, such as a comparator 13a, that stabilizes the output (comparison result) when the deviation between the smoothed voltage and the reference voltage VTI3f from the reference voltage generation means 12 becomes zero; It can be configured with an integrating circuit 13b. The oscillator 14 can be configured using, for example, a crystal oscillator that oscillates at a reference frequency. The waveform generation circuit 15 uses the output (voltage) of the comparison circuit 13 and the oscillator 14.
The output (fundamental frequency) of In order to create a rectangular wave with a value corresponding to the stripes, and then generate a triangular wave from this rectangular wave and output it as a basic waveform, for example, a switching operation is performed based on the output frequency of the oscillator 14 for comparison. switching means 15a consisting of a transistor or the like that converts the output into a rectangular wave;
It is composed of an impedance conversion circuit 15b that converts the rectangular wave amplitude of the value corresponding to the comparison output converted by this switching means 15a into impedance, and a capacitor C2 that cuts the DC component of the signal whose impedance has been converted by this impedance conversion circuit 15b. DC cut hand Ji1
5c, and a triangular wave generating means 15d comprising, for example, an integrating circuit, which generates a triangular wave based on the signal whose DC component has been cut by the DC cutter 115c and outputs it as a fundamental wave. The waveform shaping circuit 16 outputs and applies a fundamental wave component of a sinusoidal voltage E@s j nω to the exciting coil C0IL+a by passing the square wave from the waveform generating circuit 15. It can be configured as follows.

On the other hand, the detection circuit unit 20 detects the detection Efj (I
In order to input t, perform the necessary processing, and output it, for example, an amplifier circuit 21, a rectification/smoothing circuit 22, and a compensating circuit for compensating the temperature of the liquid to be measured and calculating the conductivity of the liquid to be measured by converting it to a certain temperature. It was proportional to! & By obtaining an appropriate output, it can be configured with a temperature compensation circuit 23.

In such a configuration, the operation is as follows.

Magnetic flux detection coil Co11. Excitation 1 with b! l! I l-
The magnetic flux generated within the Loytal coil T1 is detected and guided to the excitation UgJ#110 as a voltage output. The led voltage is rectified and smoothed by a rectification/smoothing circuit 11 and output to a comparison circuit 13 . In this comparison circuit 13, the rectification/smoothing circuit 1
The rectified and smoothed voltage from 1 is compared with the reference voltage VTGf, and the voltage deviation is controlled to be zero. That is, when there is a deviation voltage (this may also occur due to temperature changes, etc.), the integration circuit 13b performs an integration operation in response to the deviation voltage from the comparator 13a, and when the deviation voltage becomes zero, the integration circuit 13b The voltage at the output terminal of is stabilized at the voltage value connected to capacitor C5. In the six waveform generation circuit 15 in which such an output voltage is output from the comparison circuit 13 to the waveform generation circuit 15, the output voltage of the comparison circuit 13 is changed by operating the switching means 15a at the reference frequency from the oscillator 14. A rectangular wave signal corresponding to the voltage value is obtained, which is impedance-converted by the impedance conversion circuit 15b and converted to D
After cutting the DC component into a rectangular wave signal centered on the circuit common in the C cutting means 15c, the triangular wave generating means 1
5d, a triangular wave centered on the circuit common is generated and output as a basic waveform to form a sine waveform to be described later. Through such a process, the fundamental wave from the waveform generation circuit 15 is passed through the waveform shaping circuit 16 to generate a sine wave voltage "EHs".
jnωt" is output and applied to the excitation coil C0IL,a. By providing the triangular wave generating means 15d here, the rectangular wave signal centered on the circuit common from the DC cutting means 15c is simply converted into a waveform. By passing through the shaping circuit 16, it is possible to obtain a sine waveform that is several orders of magnitude better than the waveform when obtaining the sine wave voltage.In this way, finally, the base 1F
- An alternating magnetic flux corresponding to the voltage Vref is controlled and applied (acts) in the excitation side 1-Roytal coil TI so that it is always kept constant.

That is, excitation IN! ! By providing a magnetic flux detection coil C0JL+b in Il~Roytal coil 1'', the voltage generated in this magnetic flux detection coil C011,b is controlled to be a reference voltage ■rei of a certain value, so the excitation one-law toroidal coil' If the magnetic flux generated in I'1 is constant and the voltage VTef is constant, then the magnetic flux generated in
Even if there is a change in magnetic permeability due to a change in temperature or the like, an electrical drift in the excitation circuit 10, etc., it is always kept constant. This means that the output of the conductivity meter has been able to overcome the influence of fluctuations on the excitation side, which are error factors, as explained in FIG.

By the way, once the value of the reference voltage Vrei is determined at the time of design, the magnetic flux commensurate with it will automatically be kept constant within the excitation troytal coil T1. There is no need to make any adjustment regarding the magnetic flux within +, which is advantageous in terms of manufacturing and assembly. Furthermore, regarding the oscillator 14, by using the frequency of a highly accurate crystal oscillator as the frequency of the excitation voltage sine wave, a stable applied voltage can be easily produced at low cost.

<Effects of the Invention> Since the present invention is configured as described above, it produces the following effects.

■: An excitation circuit with stable frequency can be produced with a simple electric circuit configuration.

■: The configuration of the excitation circuit is such that the AC voltage applied to the excitation coil is always controlled to a constant value even if there are changes in magnetic permeability due to temperature changes in the excitation coil or electrical drift inside the excitation circuit. Therefore, it is not affected by these changes, and therefore output errors caused by these changes can be removed.

[Brief explanation of drawings]

Fig. 1 is a block system diagram showing an embodiment of the electromagnetic induction conductivity meter of the present invention, Fig. 2 is a diagram showing an example of a specific circuit of the @magnetic induction conductivity meter shown in Fig. 1, FIG. 3 is a diagram showing the principle of a prior art electromagnetic induction conductivity meter. 1゛... Excitation side troytal coil, T2... Detection side troytal coil, C0IL+ a... Excitation coil, C0IL1b... Magnetic flux detection coil, 10... Excitation circuit, 11... Rectification. Smoothing circuit, 12... Reference voltage generating means, 13... Comparison circuit, 14... Oscillator, 15
... Waveform generation circuit, 16... Waveform shaping circuit, 20.
...Detection circuit section. 4

Claims (1)

[Claims] In addition to the excitation side toroidal coil, the excitation side toroidal coil includes a magnetic flux detection coil that detects the magnetic flux generated in the excitation side toroidal coil, and a voltage generated in the magnetic flux detection coil is input, and is compared with a reference voltage, and a comparison result is output. comparison circuit,
an excitation circuit comprising a waveform generation circuit that outputs a fundamental waveform based on the output of the comparison circuit based on a reference frequency, and a waveform shaping circuit that shapes the output of the waveform generation circuit into a fundamental wave component and outputs the fundamental wave component to the excitation coil; An electromagnetic induction conductivity meter characterized by comprising: