JPS6316707B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ion concentration measuring device comprising an ion measuring electrode and a reference electrode immersed in a sample solution, and a circuit system for measuring the potential between the two electrodes. The present invention relates to the ion concentration measuring device having a function of checking whether the circuit resistance is normal or not.

In this type of device, the ion measurement electrode generates a potential corresponding to the concentration of the ion to be measured, whereas the comparison electrode is required to detect a constant potential regardless of the state of the ions in the sample. If the reference electrode becomes defective, the potential will fluctuate, causing measurement errors. The main cause of defects in the reference electrode is that the diffusion of the internal liquid is hindered. These problems include clogging of the liquid junction, formation of a coating from the outside that impedes the diffusion of the internal liquid, and furthermore, sample water flowing back and contaminating the internal liquid.

In order to eliminate such problems and maintain correct measurement conditions, inspection and calibration, including regular replenishment and replacement of the internal liquid and cleaning of the liquid junction, are required, but the necessary inspection items may vary depending on the properties of the sample water. However, the content and inspection frequency are different, inspection and calibration are troublesome, and there is also a drawback that appropriate measures cannot be taken against the temporal failure of the electrode itself, especially sudden measurement failures. Therefore, since there is generally a certain relationship between the amount of leakage of the internal liquid of the reference electrode and the liquid junction resistance, it is necessary to measure the internal resistance frequently and observe changes in the value over time for comparison. It can be said that it is effective to check the diffusion state of the internal liquid of the electrode.

However, in the past, liquid junction resistance was measured by connecting the reference electrode to an impedance measuring device using the AC bridge method, which made it impossible to measure liquid junction resistance frequently. Therefore, this method was not suitable for checking the diffusion state of the internal liquid.

In this respect, the present invention makes it possible to monitor the liquid junction resistance of the reference electrode while the reference electrode remains immersed in the sample solution, and therefore enables frequent inspection during continuous measurement. This provides a new and useful means of achieving this goal.

That is, in the ion concentration measurement device of the present invention, in addition to the ion measurement electrode and the reference electrode, a third electrode is immersed in the sample solution, and in the inspection mode, an alternating current is applied between the reference electrode and the third electrode. is applied to obtain an alternating voltage between the reference electrode and the third electrode according to the liquid junction resistance, and by applying this to the circuit system via the DC conversion circuit, the reference electrode is immersed in the sample solution. The gist is that the liquid junction resistance can be inspected. Here, in addition to the liquid junction resistance, between the reference electrode and the third electrode, there is the resistance of the internal liquid of the reference electrode and the resistance of the sample liquid that exists between the liquid junction and the third electrode. However, the resistance of the internal liquid of the reference electrode is sufficiently small compared to the liquid junction resistance, and the resistance of the sample liquid can be made smaller than the liquid junction resistance by increasing the surface area of the third electrode and bringing it closer to the reference electrode. Since these resistances can be made sufficiently small, they do not pose a problem when inspecting the liquid junction resistance. In addition, the liquid junction resistance when there is a problem with the diffusion of the internal liquid, such as when the liquid junction is clogged or the sample liquid has entered, will vary depending on the conductivity of the sample liquid, but the liquid junction resistance will vary depending on the conductivity of the sample liquid, but the In this case, the liquid junction resistance will be about 10 times higher than when the internal liquid is normally diffused. Therefore, it is not necessary to use a precise resistance measurement circuit to check the liquid junction resistance, and therefore, a commonly used and well-known circuit can be used as a DC conversion circuit.

Next, one embodiment of the present invention will be described based on the drawings. In the figure, 1 is an ion electrode, for example, a glass electrode, 2 is a reference electrode, and 3 is a third electrode. Both electrodes are immersed in a sample liquid 4 such as factory wastewater. The third electrode 3 may be made of any metal, for example stainless steel, which is resistant to rust due to the sample liquid. It is desirable that this electrode 3 has a large surface area and is located as close to the comparison electrode 2 as possible. Reference electrode 2
This is to make the resistance of the sample liquid between the liquid junction 2a and the third electrode 3 sufficiently smaller than the liquid junction resistance.
In the illustrated example, the third electrode 3 has a mesh shape so as not to obstruct the flow of the sample liquid.

Each of the electrodes 1, 2, and 3 has a mode switching interlock switch for switching between measurement mode and inspection mode.
connected to S ₁ , S ₂ , S ₃ , the switches S ₁ ,
When S ₂ and S ₃ are switched to the measurement mode (the state shown in the figure), the ion electrode 1 and the comparison electrode 2 are connected to a circuit system 5 that measures the potential generated between them. At this time, the third electrode 3 is grounded through the inductive noise passing capacitor C.
On the other hand, when the switches S ₁ , S ₂ , and S ₃ are switched to the inspection mode, the comparison electrode 2 and the third electrode 3 are connected to a circuit system 6, which will be described later, and the output signal of this circuit system 6 is transmitted to the circuit system 6. It is configured to be input to system 5.

The circuit system 5 comprises a high input resistance amplifier OP1, a meter M, an asymmetric potential adjustment mechanism A, and a sensitivity adjustment mechanism B. The output end of this circuit system 5 is provided with a connection terminal t to a recorder (not shown) or the like.

The circuit system 6 includes an oscillator 7 that applies an alternating current to the comparison electrode 2 and the third electrode 3, and a circuit 8 that converts the alternating voltage generated between the electrodes 2 and 3 into direct current. The oscillator 7 is constituted by a well-known circuit that generates a voltage with a constant frequency, and the voltage generated by the oscillator 7 is applied between the electrodes 2 and 3 via a resistor R. Therefore, an alternating current flows between the electrodes 2 and 3, which is determined by the sum of the resistance R and the resistance between the electrodes 2 and 3. As a result, an alternating voltage proportional to the product of the resistance between the electrodes 2 and 3 and the alternating current is generated between the electrodes 2 and 3, and this alternating voltage is applied to the DC conversion circuit 8. Here, the resistance between the two electrodes 2 and 3 is the sum of the internal resistance of the reference electrode, the liquid junction resistance, and the resistance of the sample liquid, but as mentioned above, the internal resistance is small, and the resistance of the sample liquid is also the sum of the resistance of the sample liquid. Since the surface area of the electrode 3 of No. 3 can be made small by increasing the surface area and bringing it closer to the reference electrode 2, it can be regarded as approximately a liquid junction resistance. Therefore, the alternating voltage applied to the DC conversion circuit 8 is a voltage corresponding to the liquid junction resistance. The oscillation frequency of the oscillator 7 is desirably set to a value different from the power supply frequency at which sample liquid such as factory wastewater may be drawn from the power source in the factory. If the approximation is made, the situation will be similar to that where voltage is applied at the power frequency even though no voltage is applied from the oscillator 7 between the electrodes 2 and 3, resulting in a large error in measuring the liquid junction resistance. This is because it will result in However, even if the frequency of the oscillator 7 is close to the power supply frequency, measurement errors can be reduced by adopting a synchronous rectifier circuit synchronized with the phase of the oscillator 7 as the rectifier circuit of the DC converter circuit 8, which will be described later. Can be done.

The DC conversion circuit 8 includes a comparison electrode 2 and a third electrode 3.
Amplifier OP2 that amplifies the alternating voltage generated between
, rectifier circuits D ₁ and D ₂ that rectify the output voltage of this amplifier OP2, and an amplifier OP3 that amplifies the rectified output.
It is assembled from. This rectifier circuit D ₁ , D ₂
Using a FET switch instead of the diode,
A synchronous rectification method controlled by the signal of the oscillator 7 and its inverted signal may also be used. Further, a DC voltage V adjusted by a variable resistor VR is applied to the amplifier OP3, superimposed on the rectified output. The reason why the DC voltage is applied superimposed on the rectified output in this way is as follows. That is, the normal value and abnormal value of the liquid junction resistance differ significantly depending on the structure of the reference electrode. For this reason, if only the rectified output is applied to the circuit system 5, even if the liquid junction resistance is normal, the amount of deflection of the meter M will vary significantly depending on the reference electrode, and therefore the amount of deflection of the meter M will be It is difficult to determine whether resistance is normal or abnormal. For this reason, the DC voltage V can be adjusted according to the structure of the reference electrode,
By superimposing the adjusted voltage on the rectified output and applying it to the circuit system 5, no matter which reference electrode is used, if the amount of deflection of the meter M is larger than a certain point, the liquid junction resistance is abnormal or small. This makes it possible to determine that the condition is normal.

The rectified output on which the DC voltage V is superimposed is amplified by the amplifier OP3 and applied to the circuit system 5, causing the meter M to swing. The supervisor monitors the DC voltage V mentioned above.
By this action, it is possible to check whether the liquid junction resistance is normal or abnormal from the amount of deflection of the meter M. This inspection can be performed by simply switching the selector switches S ₁ , S ₂ , and S ₃ to inspection mode, without having to pull out the reference electrode from the sample solution and reconnect it to another resistance measuring device as in the conventional method. Therefore, the liquid junction resistance can be checked frequently during continuous measurements. In addition, the liquid junction resistance can be checked without depending on the amount of deflection of the meter M by connecting a recorder to the connection terminal t and using the recorded value of the recorder. This method is more effective for observing long-term changes in liquid junction resistance.

To summarize above, since the ion concentration measuring device according to the present invention is constructed as described above, it has the following effects.

Since it is possible to check whether the liquid junction resistance is normal or abnormal without having to pull out the reference electrode from the sample solution each time, it is possible to check whether the liquid junction resistance is normal or abnormal in the same state, so inspections can be performed frequently during continuous measurement.
Therefore, it is possible to quickly confirm that the reference electrode is normal and to discover that an abnormality has occurred.

Since the circuit system for measuring the potential between the ion electrode and the comparison electrode is used as is to check the liquid junction resistance of the comparison electrode, the number of components is small and the circuit configuration does not need to be too complicated. Therefore, due to the above-mentioned effects, it is extremely useful and has the advantage that it can be manufactured at low cost.

[Brief explanation of the drawing]

The figure is an electrical circuit diagram showing one embodiment of the present invention. 1... Ion electrode, 2... Reference electrode, 3... Third electrode, 4... Sample liquid, 5... Circuit system, 8...
DC conversion circuit.

Claims (1)

[Claims] 1. In an ion concentration measuring device consisting of an ion measuring electrode and a reference electrode immersed in a sample solution, and a circuit system for measuring the potential between the two electrodes, a third electrode is connected to the sample in addition to the ion measuring electrode and the reference electrode. When immersed in the liquid and in inspection mode, the reference electrode and the third
An alternating current is applied between the comparison electrode and the third electrode.
By obtaining an alternating voltage between the electrodes according to the liquid junction resistance and applying this to the circuit system through the DC conversion circuit, the liquid junction resistance can be checked while the reference electrode remains immersed in the sample liquid. An ion concentration measuring device characterized by: