JPH035899Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for detecting a change in concentration of a solution (eg, saline solution), and more particularly to a device for detecting a change in concentration based on a change in impedance of the solution.

FIG. 1 shows a conventional solution concentration change detection circuit, in which 1 is a square wave oscillator, 2 and 3 are electrodes, 4 is a cylindrical container, 5 is a solution, 6 is a resistor,
7 is an amplification/detection device, and 8 is an output meter.

FIG. 2 shows an equivalent circuit on the input side of the amplification/detection device 7, where C ₁ and R ₁ represent the capacitance and resistance value between the electrodes 2 and 3, respectively, and R ₂ represents the resistance value of the resistor 6. Indicates resistance value.

FIG. 3 is a diagram showing waveforms related to the conventional device shown in FIG. 1, and FIG. This is to prevent specific substances from collecting on one electrode due to electrolysis of the solution.
Figure 3b shows the voltage across the resistor 6, that is, the amplification voltage.
The waveform of the input voltage of the detection device 7 is shown. As shown in the figure, due to the influence of the interelectrode capacitance C ₁ , the voltage waveform across the resistor 6 is slightly larger at the leading edge than at the trailing edge. In other words, as the capacitor _C1 is charged, the voltage across the resistor 6 changes to the resistance value.
The current value (1/R ₁ + R ₂ × E (input voltage)) determined by R ₁ and R ₂ decreases toward the voltage value (E × R ₂ /R ₁ + R ₂ ) multiplied by the resistance value R ₂ . , is inverted at the trailing edge as shown in the figure according to the period of the rectangular wave from the oscillator 1. Figure 3c shows the resistor 6 when the concentration is higher than that in Figure 3b.
In the equivalent circuit of Figure 2, the increase in concentration means that the capacitance C ₁
This corresponds to a case where the resistance value R ₁ decreases as the resistance value R 1 increases. In the case of Fig. 3c, the leading edge becomes larger than the trailing edge due to the effect of capacitance _C1 , but as a result of the capacitance _C1 becoming larger and the resistance value _R1 becoming smaller,
As shown, the voltage across the resistor 6 (ExR ₂ /R ₁ +R ₂ ) rises higher than in the case of FIG. 3b, and the charging waveform becomes gentler than in the case of FIG. 3b.

On the other hand, the amplification/detection device 7 amplifies the input waveform and performs half-wave rectification, and outputs a voltage proportional to the peak value of the input voltage, causing the output meter 8 to swing. Therefore, if the change in the voltage across the resistor 6 when the concentration changes is smaller between peak values than the change between average values, then the change in concentration will have a smaller effect on the output meter 8. However, in order to increase this size, necessary parts must be added to the amplification/detection device 7, which has the drawback of increasing the cost.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a solution concentration change detection device that improves the detection sensitivity of concentration changes, that is, impedance changes, without increasing the cost substantially.

In order to achieve this objective, the present invention includes a pair of electrodes arranged in isolation in a solution, a rectangular wave oscillator connected in series to the pair of electrodes via a resistor, and amplifying and detecting the voltage across the resistor. an amplification/detection device connected to the resistor to output a voltage proportional to the peak value of the input voltage from the resistor;
In a solution concentration change detection device equipped with an output meter connected to a detection device, a capacitor of a predetermined capacitance is connected in parallel with the resistor, and the predetermined capacitance C ₂ and the capacitance between the electrodes are C _1. Where the resistance value between the electrodes is R ₁ and the resistance value of the resistor is R ₂ , the predetermined capacitance C ₂ has a relationship of C ₁ R ₁ ≧C ₂ R ₂ . It is.

Hereinafter, the present invention will be explained along with preferred embodiments of the present invention.

FIG. 4 is a circuit diagram showing a preferred embodiment of the solution concentration change detection device according to the present invention. The only difference from the conventional device shown in FIG. 1 is that a capacitor 9 is connected in parallel to a resistor 6. be.

Figure 5 is an equivalent circuit diagram of the detection device shown in Figure 4, and by adding a capacitor 9 with a capacitance of _C2 ,
At the leading edge of the rectangular wave input voltage shown in FIG. 3a, a change occurs in the phase of the harmonic component included in the rectangular wave, and as shown in FIGS. Contains. The amplitude of these vibration parts decreases as the interelectrode resistance value R ₁ decreases, and the amplitude increases as the interelectrode capacitance C ₁ increases, so they tend to cancel each other out, and the vibration parts due to concentration changes decrease. The change in the amplitude of is almost negligible.

On the other hand, the slope of the charging waveform from the leading edge of the rectangular wave to the trailing edge of the rectangular wave approaches the horizontal due to the addition of the capacitor 9, and the slope due to the concentration change from a to b in FIG. There will be less change.

As a result, even if the change in the output of the amplification/detection device 7 due to the change in concentration is proportional to the change in peak value, the change in the output of the amplification/detection device 7 due to the change in concentration will occur at the end of charging of the capacitor _C1 (the trailing edge of the pulse).
It is approximately proportional to the change in the voltage of , and is also proportional to the average value, so that the change given to the output meter 8 can be made larger than in the conventional case.

Furthermore, the size of the capacitance C ₂ of the capacitor 9 is:
Satisfy the relationship C ₁ R ₁ ≧ C ₂ R ₂ for C ₁ and R ₁ , which are determined by the concentration range of the solution to be measured (measured in advance based on a certain concentration) and the electrode structure. Choose as you like. If C ₁ R ₁ <C ₂ R ₂ , as shown in FIG. 7, the rise of the rectangular wave will be delayed and the waveform will be close to a triangular wave, making it impossible to achieve the purpose of detecting concentration changes.

In addition, the input terminal of the amplification/detection device 7
The impedance when looking at the detection device 7, that is, the input impedance, includes the capacitance (Ca),
This is an extremely small amplification/detection device used to detect the concentration of a solution, and it can detect changes in the concentration of saline solution used at concentrations in the range of about 0.5% to 5%. Various electrode structures are possible, but the interelectrode capacitance
C ₁ is 0.1 μF to 0.5 μF, interelectrode resistance R ₁ is several tens of Ω to several
It is approximately KΩ, and it is difficult to bring R ₂ Ca close to C ₁ R ₁ without adding the capacitance C ₂ of the capacitor 9. If the resistance value R ₂ is simply increased, the change in the voltage across the resistor 6 (E×R ₂ /R ₁ +R ₂ ) becomes small, and the intended purpose cannot be achieved. Interelectrode capacitance C ₁
Even if the resistance value _R1 exceeds the above value, by adding a capacitor 9 with an appropriate capacitance _C2 , the slope of the input waveform to the amplification/detection device 7 can be reduced and the change in output can be reduced. can be improved.

As described above, according to the present invention, the change in voltage with respect to the change in concentration of the solution can be made larger than that in the conventional device, so that the effect of simplifying the amplification mechanism can be obtained.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing a conventional solution concentration change detection device, Fig. 2 is an equivalent circuit diagram of a part of the device shown in Fig. 1, and Figs. 3 a to c are related to the device shown in Fig. 1. The obtained waveform diagram, Fig. 4 is a circuit diagram showing the solution concentration change detection device according to the present invention, Fig. 5 is a diagram showing an equivalent circuit of a part of the device in Fig. 4, and Fig. 6 a.
and b is a waveform diagram obtained for the apparatus of FIG. 4,
FIG. 7 is a waveform diagram when the rise of the rectangular wave is delayed. 1... Square wave oscillator, 2, 3... Electrode, 4...
Container, 5...solution, 6...resistor, 7...amplification/
Detection device, 8... Output meter, 9... Capacitor.
In addition, in the figures, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims for Utility Model Registration] A pair of electrodes arranged in isolation in a solution, a rectangular wave oscillator connected in series to the pair of electrodes via a resistor,
an amplification/detection device connected to the resistor for amplifying and detecting the voltage across the resistor and outputting a voltage proportional to the peak value of the input voltage from the resistor; In the solution concentration change detection device equipped with an output meter, a capacitor of a predetermined capacity is connected in parallel with the resistor, the predetermined capacitance is C ₂ , the capacitance between the electrodes is C 1 , and the capacitance between the electrodes is C ₂ . When the resistance value between the resistors is _R1 and the resistance value of the resistor is _R2 , the predetermined capacitance
A solution concentration change detection device characterized in that C ₂ satisfies the relationship C ₁ R ₁ ≧C ₂ R ₂ .