JPS6331734B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method and apparatus for continuously measuring changes in liquid properties, particularly changes in dielectric constant or conductivity, in a non-contact manner.

[Conventional technology]

BACKGROUND ART Conventionally, PH meters and conductivity measuring devices, which measure by bringing electrodes into direct contact with a measured object, have been used as continuous measuring devices for liquid quality.

Furthermore, as a non-contact measurement method, an electromagnetic induction method is used.

[Problems to be solved by the invention]

However, PH meters and conductivity measurement devices
Because the electrode is in direct contact with the object to be measured, chemical reactions between the electrode and the liquid, secondary contamination due to the production of hydroxide, reduction in measurement accuracy due to physical friction, etc., and contamination with substances that do not have conductivity, etc. There are problems such as the inability to measure changes in liquid quality due to

In addition, the electromagnetic induction method used as a non-contact liquid quality measurement method detects changes in magnetic flux caused by the primary coil.
Since detection is performed using a secondary coil linked to this, it has the disadvantage that solutions with low conductivity cannot be measured.

The present invention is intended to solve the above problems,
It is an object of the present invention to provide a continuous liquid property change measuring method and device that can measure changes in liquid property of a liquid having arbitrary permittivity and conductivity in a non-contact manner.

[Means for solving problems]

To this end, the continuous liquid quality change measuring method and device of the present invention transmits electromagnetic waves from an excitation ring electrode wound around a tube through which the liquid to be measured flows, and detecting coils wound around the tube at predetermined intervals. to detect electromagnetic waves, and to detect the dielectric constant or conductivity of the liquid to be measured using the detection output, and an excitation ring electrode for transmitting electromagnetic waves wound around the tube through which the liquid to be measured flows, and a ring electrode for transmitting electromagnetic waves. It is characterized by comprising a detection coil wound in one layer and arranged at a predetermined distance from the coil.

[Effect]

In the present invention, an electromagnetic wave is transmitted from an excitation ring electrode, the electromagnetic wave is detected by a detection coil at a position separated by a predetermined interval, and the dielectric constant or conductivity of the liquid to be measured can be detected from the detection output.

〔Example〕

Examples will be described below with reference to the drawings.

As shown in Fig. 1, an oscillator 2 that oscillates a high frequency into an insulating non-magnetic tube 6 such as a Teflon tube.
An alternating electric field from the ring electrode 1 is applied to the ring electrode 1, and the induced voltage in the detection coil 3, which is placed a little apart from the ring electrode 1, is detected independently from the alternating electric field. In the figure, 4 is an amplifier, and 5 is a recorder or meter. In this case, the detection coil is wound in one layer as shown. As a result, the stray capacity between each turn of the coil is large.

In such a system, the electromagnetic equation when an alternating electric field is applied to the ring electrode 1 is expressed as follows, as is well known.

rotH=i+eD/eT...(1) H is the magnetic field, D is the electric flux density. Here, the true current i is expressed as i=σE=σE ₀ e ^jwt ...(2) where the conductivity of the medium is σ. If the permittivity of is ε, then the electric flux density D
is expressed as D=εE=εE ₀ e ^jwt (3). Therefore, equation (1) is rotH=σE ₀ e ^jwt +jωεE ₀ e ^jwt = (σ+jωε)E = (σ−ε″ω+jωε′)E……(4) However, ε=ε′+jε″, ε′: Real part ε'' of the complex permittivity: This is the imaginary part of the complex permittivity, and a voltage proportional to √(-'') ² +(') ² ...(5) is obtained in the detection coil 3.

That is, the detection output from the detection coil 3 is expressed as a function of conductivity and permittivity, so if the permittivity is known, the permittivity can be measured, and if the permittivity is known, the conductivity can be measured. It becomes possible to do so. In this case, the detection coil 3 has a large stray capacitance, which changes depending on the liquid quality, that is, the dielectric constant and the conductivity, and a resonant circuit is formed by this and the inductance of the coil. The detection output is proportional to the Q value of the resonance system, and the Q value changes depending on the resistance and capacitance of the resonance system, that is, the permittivity and conductivity of the liquid, so the permittivity and conductivity can be detected from the detection coil output.

The liquid quality change is measured using the above detection principle, and the actually detected phenomenon will be explained below using resonance characteristics.

Ring electrode 1 when the electrolyte concentration of the liquid is low.
A parallel resonance system is formed between and the detection coil 3, and if the resonance frequency ω, the sum of the solution capacitance and the stray capacitance between the lines of the detection coil 3 is C ₁ , and the electrical resistance of the liquid is R ₁ , then , the resonance Q is expressed as Q ₁ =ω ₁ C ₁ R ₁ (6).

On the other hand, when the electrolyte concentration of the liquid is high, series resonance is formed, and the resonance Q is Q ₂ = 1/ω ₂ C ₂ R ₂ ...(7), and generally V = Q ₁ + Q ₂ = ω. It is expressed as ₁ C ₁ R ₁ +1/ω ₂ C ₂ R ₂ .

FIG. 4 shows the results of actual measurement using the measuring device shown in FIG. 1 while gradually increasing the amount of electrolyte starting from pure water. In the figure, C ₁ is the measurement result for pure water, and as with C ₂ and C ₃ , by increasing the electrolyte concentration, the resonant voltage decreases while the resonant frequency ω ₁ remains almost constant. However, above a certain concentration, the resonant frequency decreases and shifts to ω ₂ , and as the concentration increases, the resonant voltage increases to Cn _-2 , Cn _-1 , and Cn. This conduction band of resonance frequency ω ₂ is a region where the resonance state is mainly determined by conductivity, and is a region that can be measured even with a conventional electromagnetic densitometer.

On the other hand, the dielectric band with the resonant frequency ω ₁ is a region in which the resonance state is mainly determined by the dielectric constant ε, and is a region that can be measured for the first time by the present invention.

The above was verified from changes in the resonant frequency and resonant voltage when the coupling mode between the ring electrode 1 and the detection coil 3 was replaced with an equivalent circuit as shown in FIG. 5, and the resistance R was changed. In the figure, a corresponds to the dielectric band, and b corresponds to the conduction band.

The measuring device of the present invention is characterized in that a change in stray capacitance between coil windings occurring in a detection coil is captured as a change in resonant voltage or resonant frequency.
As mentioned above, the detector coil 3 needs to be wound in a single layer as shown in FIG. 1, and it is necessary to make the Sotolay capacity between the wires as large as possible. Alternatively, as shown in FIG. 2, one turn of ring electrodes 2 and 3 may be connected in parallel, and a coil 4 may be connected to the outside.

Figure 3 shows an example of measurement using the above-mentioned measuring device.As a sensor for liquid chromatography, a mixture of 80% acetonitrile and 20% water was poured into a Teflon tube with an inner diameter of 0.5 mm, and the liquid was instantaneous. Purified water (1), propylene carbonate
(2), shows the change in resonance voltage when methanol (3), acetone (4), xylene (5), and tap water (6) are injected into the mobile phase. In this way, a change in detection voltage is detected as a difference in dielectric constant of each solvent, and changes in liquid quality can be continuously detected in a non-contact manner even for liquids with small dielectric constants.

Furthermore, since the excitation electrode is a ring electrode 1, the electrode width is extremely small, making it possible to induce an extremely sharp peak voltage even in response to minute changes in liquid quality.

〔Effect of the invention〕

As described above, according to the present invention, an electromagnetic wave is transmitted from an excitation coil, the electromagnetic wave is detected by a detection coil at a predetermined distance apart, and the detection output indicates the dielectric constant or conductivity of the liquid to be measured through which the electromagnetic wave propagated. rate can be detected.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing one embodiment of the present invention, FIG. 2 is a diagram showing another embodiment of the present invention, and FIG. 3 is a diagram showing detection output when the present invention is applied to a liquid chromatograph. FIG. 4 is a diagram showing resonance characteristics, and FIG. 5 is an explanatory diagram of the device shown in FIG. 1 in an equivalent circuit format. DESCRIPTION OF SYMBOLS 1... Ring electrode, 2... Oscillator, 3... Detection coil, 4... Amplifier, 5... Recorder or meter.

Claims (1)

[Claims] 1. Electromagnetic waves are transmitted from an excitation ring electrode wound around a tube through which a liquid to be measured flows, and the electromagnetic waves are detected by a detection coil wound around the tube at a predetermined distance apart, and a detection output is generated. A continuous liquid property change measuring method characterized by detecting the dielectric constant or conductivity of a liquid to be measured. 2 Equipped with an excitation ring electrode for electromagnetic wave transmission wound around the tube through which the liquid to be measured flows, and a detection coil wound in a single layer arranged at a predetermined distance from the transmission coil. Continuous liquid quality change measuring device.