JPH01280258A - Measuring instrument for conductivity of liquid - Google Patents

Abstract

PURPOSE:To secure a sufficient output level regardless of variation in ambient temperature and a mechanical shock and to improve detection sensitivity and detection accuracy by canceling magnetic flux produced at the core of a detection troidal coil with a liquid current. CONSTITUTION:The liquid current I2 which is generated by an AC power source 1 and an exciting troidal coil 2 is cross-linked with the detection troidal coil 3 and an external amplifier 4 supplies the coil 3B of the detection troidal coil 3 with such a current I0 that the magnetic flux phi in the core 3A is all eliminated by canceling magnetic flux produced at the core 3A of the detection troidal coil 3 with the liquid current I2. This current I0 is converted into a voltage, which is compared with the output voltage of the liquid whose conductivity is already known to find the conductivity of the liquid 100.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a liquid conductivity measuring device using a so-called electromagnetic induction method.

(Prior Art) As is well known, the electromagnetic induction method is a method of measuring the conductivity of a liquid by detecting an alternating liquid current flowing through the liquid by electromagnetic induction. The equivalent circuit shown in Fig. 4 is as follows.

That is, in the figure, 51 is an AC power source, 52 is an excitation toroidal coil (hereinafter referred to as an excitation toroid) connected to the AC power source 51, and 53 is a liquid 1 whose conductivity is to be measured.
a detection toroidal coil (hereinafter referred to as detection toroid) electromagnetically coupled to the excitation toroid 52 via 00;
54 is a resistor connected to both ends of the detection toroid 53;
indicates an amplifier, and 56 indicates an indicator, respectively.

In this measuring device, the current I flowing through the resistor 54. is liquid 1
Since it is inversely proportional to the resistance r of 00, the conductivity of the liquid 100, X, is determined by detecting the voltage across the resistor 54.

Here, the AC power supply voltage is E, the primary inductance of the exciting toroid 52 is L, the number of turns on the negative side is nl, the negative current is 1, and each toroid in the liquid 100 is caused by electromagnetic induction from the exciting toroid 52 side. 52. The liquid current flows interlinking with I2. The secondary inductance of the excitation toroid 52 is I2, and the primary inductance of the detection toroid 53 is I3. Similarly, the secondary inductance. , the number of secondary turns is n. , calculate the secondary current. , the value of the resistor 54 is R.

Analysis of this equivalent circuit yields the following.

First, since the leakage magnetic flux of each toroid 52 and 53 can be ignored, if we consider the liquid current circuit as one coil, the mutual inductance M between the primary and secondary coils of the excitation toroid 52
The mutual inductance M 30 between L 2 and the primary and secondary coils of the detection toroid 53 is M 2 = f 2 M;
. = fr7π −(1). Also, each current 11.
L, I. For a closed circuit in which , the following simultaneous equations hold according to Kirchhoff's second law. In addition, 'X' for AC type? 'j and pressure E are sinusoidal waves of angular frequency ω.

In this equation (2), the determinant on the left side is M1□, M,
.

Substituting the above equation (1) into and finding the value of the determinant, =
jωL, (jωL, r + jωL, R+ rR)≠0
−(3). Therefore, the current I. becomes . Therefore, the voltage E0 generated at the output side resistor 54
is, and since L1=n1''I2, we also have L,=no''1. Therefore, it becomes . If the resistance value R is made sufficiently large compared to ωL0,
Since the absolute value of the second term in the denominator parentheses is sufficiently smaller than the first term, the following formula is obtained. Here, r is liquid resistance, ωL is detection toroid 5
Since the actance of a single-turn coil is 3, under normal measurement conditions, r)ωL3 (6) holds true. Conversely, the resistance value R is made sufficiently smaller than ωL0 to be R'. That is, ωL.

□ ) 1...(8) If R' and the output voltage at this time are E0', then equation (5) (
6), From the conditions of equations (8), the second term in the denominator of the above equation is the first term.
Since it is sufficiently small compared to the term, it can be ignored.
r Also, from equations (7), (8), and (9), the following equation can be obtained.

(Problem to be Solved by the Invention) As described above, if the resistance value R is increased, the absolute value IE,l of the output voltage can be detected by the equation (7), and the number of turns n of the toroid 53. It is possible to increase the detection sensitivity. However, equation (7) includes an inductance L3, and this inductance is proportional to the magnetic permeability of the core of the detection toroid 53, as is well known. Therefore,
There was a problem in that changes in magnetic permeability due to changes in ambient temperature directly affected the output voltage, resulting in low detection accuracy.

On the other hand, if the resistance value R (R') is made smaller with respect to ωL0, the influence of changes in magnetic permeability can be reduced as shown in equation (9), but as shown in equation (10), the output voltage IEol(l
E, 'l) becomes relatively low. Therefore, in order to realistically reduce the influence of magnetic permeability changes and obtain a certain level of output voltage, it is necessary to increase the detection toroid 5.
The number of turns of the coil of 3 is n. cannot be made smaller. Since the toroid core is a ferromagnetic material, magnetostriction cannot be avoided, and when a mechanical shock is applied to the core, a minute change in magnetization occurs, resulting in a minute change in magnetic flux.

For this reason, when the number of turns of the coil of the detection toroid 53 is large, there is a problem in that this minute change in magnetic flux is detected as noise.

The present invention was proposed to solve the above problems, and its purpose is to ensure a sufficient output level regardless of changes in ambient temperature or mechanical shock, thereby increasing detection sensitivity and accuracy. An object of the present invention is to provide a liquid conductivity measuring device that makes it possible to improve the conductivity of a liquid.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a detection toroidal coil 3 which is linked to a liquid current generator 2 generated by an AC power source 1 and an excitation toroidal coil 2, as shown in FIG. , an electric current generator that cancels the magnetic flux generated in the core 3A of the detection toroidal coil 3 by the liquid electric current generator 2 to make the total magnetic flux φ in the core 3A zero. is supplied to the coil 3B of the detection toroidal coil 3 by an external amplifier 4.

(Function) If the number of turns of the coil 3B of the detection toroid 3 is no, then the liquid electric current 2 and the current ■. When the magnetomotive forces of are equal.

That is, ■2=n, I. -(11), then the magnetic flux φ in the core 3A becomes zero, and if this condition is satisfied, the inductance L,, L, of the coil of the detection toroid 3 becomes zero.

Here, since the excitation toroid 2 is substantially equivalent to a transformer, it can be assumed that an AC power source with an electromotive force E/n consisting of the AC power source 1 and the excitation toroid 2 is connected to the liquid current circuit. can. Therefore, the flow (2) in the liquid ' is n□ r Therefore, by converting Io into a voltage and comparing it with the output voltage of a liquid whose electric constant is known, the conductivity k of the liquid 100 can be determined.

That is, in the present invention, the current work is such that the magnetic flux φ of the core 3A is zero. If we find the conductivity k of liquid 100,
can be found. At this time, since there is no magnetic flux φ in the core 3A, there is no current flow even if the magnetic permeability changes due to temperature changes. Also, the number of turns n of the coil 3B of the detection toroid 3. The number of turns n can be increased by selecting a high amplification degree of the amplifier 4 under the conditions shown in each of the following embodiments. can be selected to a suitably small value, so even if a mechanical shock is applied to the toroid core 3A, the generated magnetostrictive noise can be made sufficiently low.

(Example) The present invention will be described in detail below with reference to the drawings.

Note that both the following first and second embodiments differ in the configuration of the amplifier 4 from FIG. 1.

First, FIG. 2 shows a first embodiment of the present invention, and in the figure, 10 is an AC power supply, and this AC power supply 10 is
Similarly to the figure, an electromotive force E/n is generated by combining an AC power supply 1 with a voltage E and an excitation toroid 2 whose primary coil has a number of turns n□.
It is shown as having a

In addition, 30 is a liquid current I2 induced by the excited toroid.
is a detection toroid linked to the core 3OA, and this detection toroid 30 has two coils 30B□, :JOB2, each having a number of turns not n. Both ends of one of the coils 30B2 are connected to the hexagonal sides of an AC amplifier 41 with an extremely large voltage amplification degree A, and the other coil 30B2 is
Both ends of B1 are on the output side F of the AC amplifier 41.
・(26) becomes. Therefore, φ L:O...(27) From then on, the liquid 100
The output voltage E is proportional to the conductivity k. This is something that can be obtained.

Note that the amplifier that supplies the current I0 is not limited to the first and second embodiments described above, and various modifications can be made as long as the magnetic flux within the detection toroid can be canceled out to zero. .

(Effects of the Invention) As described above, according to the present invention, if a current that makes the magnetic flux in the detection toroid zero is supplied from the outside, the current is proportional to the conductivity of the liquid, so this current is converted into a voltage. The conductivity can be easily determined by converting to

At this time, since no magnetic flux exists in the core of the detection toroid, even if the magnetic permeability of the core changes due to changes in ambient temperature, it will not affect the output signal in any way. Furthermore, since the number of turns n0 of the coil of the detection toroid can be selected to a suitably low value, generation of unnecessary noise voltage due to mechanical impact can be prevented.

Furthermore, by selecting a high amplification degree of the amplifier, for example,
Since the resistance R on the output side can be selected to be large within the constraints of conditional expression (17) in the first embodiment and expression (25) in the second embodiment, a high level output voltage can be obtained. It becomes possible to significantly improve detection accuracy and detection sensitivity.

In addition, since the amplifier that supplies current from the outside can be realized with a simple circuit configuration, it is possible to provide a highly reliable conductivity measuring device at low cost.

[Brief explanation of the drawing]

FIG. 1 is an equivalent circuit diagram showing the configuration of the present invention, and FIGS. 2 and 3 are equivalent circuit diagrams showing the configuration of the present invention. FIG. 4 is an equivalent circuit diagram showing the second embodiment, and FIG. 4 is an equivalent circuit diagram showing the conventional example. 1.10... AC power supply 2... Excitation toroidal coil (excitation toroid) 3.3
0...Detection toroidal coil (detection toroidal 3A, 3
0A...Core 3B, 30B, 30B, 30B2・-+
Ile 4...Amplifier 41...AC amplifier 42,
44... Resistor 43... Operational amplifier 100...
・Liquid patent applicant Denki Kagaku Keiki Co., Ltd. Agent Patent attorney Mori 1) Connected to the male - (plow Ep mebunichi 9 Q-).Furthermore, the coil 30B is connected to the resistor 4.
2 are connected in series. Next, the circuit shown in FIG. 2 will be analyzed. As above, the power supply voltage E
Assuming that is a sine wave with an angular frequency ω, the input impedance of the AC amplifier 41 is sufficiently high, so the following simultaneous equations hold true for each closed circuit in FIG. ...(13) Here, L3 is the primary inductance of the detection toroid 30, Lo is the inductance of the coil 30B1, L is the inductance of the coil 30B2, and R is the resistance of the resistor 42. , fGT, and F weight indicate the mutual inductance due to each inductance. If the total magnetic flux of the core 30A of the detection toroid 30 is φ, and the input voltage of the AC amplifier 41 is V, then V=jωnφ= j (, + ( frmouth I, -f''
=I, l= (14), and from the previous equation (13), I2. I. By finding and substituting it into equation (14), we get: Here, IAI is sufficiently large, so if we omit terms that do not include A in the denominator, f7 = nL,, F
Since 70=noLa, appropriate n for liquid resistance r
. , R can be realized with a normal amplifier. If the above equation (17) is satisfied, the above equation (16) becomes V
Given O... (18) becomes. Therefore, from the previous equation (14), φ Cape 0
... (19), and the explanation in FIG. 1 and equation (12) holds true. Therefore, the voltage E across resistor 42 in FIG. Since it is possible to obtain an output voltage proportional to the conductivity k of the liquid 100, the conductivity k of the target liquid 100 can be calculated from the proportional relationship with the output voltage of a liquid whose conductivity is known. I can do it. Next, FIG. 3 shows a second embodiment of the present invention. In this embodiment, the voltage amplification degree A is used as the amplifier 4 in FIG.
It uses an operational amplifier 43 with extremely large 1],
In the figure, 44 is a feedback resistor, 30 is a detection toroid, and 3
0A indicates a core, and 30B indicates a coil. Note that the other configurations are the same as those of the first embodiment, so detailed descriptions will be omitted. In this embodiment, if the power supply voltage E is a sine wave with an angular frequency ω as described above, the following simultaneous equations hold true. Liquid electrician 2 and electrician. If the total magnetomotive force due to these is F, then F=I2X1+IoXn. ... (22) (21)
Solve the equation I2. I. Substituting into equation (22) yields. As above, if A is extremely large, then equation (23) is. becomes. In a normal operational amplifier, it is possible to achieve the following, so if equation (25) is satisfied, equation (24) becomes

Claims (1)

[Scope of Claims] An excitation toroidal coil connected to an AC power supply and a detection toroidal coil interlinked with a liquid current in the liquid generated by the excitation toroidal coil, and the liquid is detected from the current flowing through the detection toroidal coil. In a conductivity measuring device for measuring the conductivity of a sensor, a current that cancels the magnetic flux generated in the core of the detection toroidal coil by the liquid current flows into the coil of the detection toroidal coil from an external amplifier, and the inflow current at this time is A liquid conductivity measuring device characterized in that the conductivity of the liquid is determined by the value of .