JPH0442771Y2 - - Google Patents

Description

[Detailed Description of the Invention] A. Field of Application of the Technology The present invention relates to a deterioration detection circuit for an ion selective electrode in an ion concentration measuring device.

(b) Prior art Ion concentration measuring devices tend to have impurities deposited on the surface of the ion-selective electrode due to long-term use.
As shown in the figure, a decrease in response speed, linearity, and reproducibility result in analysis errors.

For this reason, a method has been adopted in which deterioration of the ion-selective electrode is detected by comparing the output potential from the ion-selective electrode with a preset reference value such as a theoretical value.

However, since this method detects steady-state values from an ion-selective electrode, it is only possible to detect deterioration at a fairly advanced stage, and there is a problem in that the analytical values include errors.

Of course, this kind of problem can be solved by converting the output from the electrodes into a digital signal and calculating the response speed, but this requires an expensive high-speed A/D converter, which makes the equipment difficult to use. There is a new problem of increasing costs.

C. Purpose In view of these problems, the present invention aims to provide an inexpensive ion-selective electrode deterioration detection circuit that can detect deterioration at an early stage.

D. Structure of the invention In other words, the feature of the present invention is that the potential differences between the electrodes are compared after a certain time difference.

E. Embodiments Therefore, details of the present invention will be explained below based on illustrated embodiments.

FIG. 1 shows an embodiment of an ion concentration measuring device to which the present invention is applied, and the reference numeral 1 in the figure is
This is a differential amplifier that outputs an inter-electrode potential difference proportional to the ion concentration.One input terminal is connected to an ion-selective electrode 3 via a preamplifier 2, and the other input terminal is connected to a reference electrode 5 via a preamplifier 4. is connected to.
Reference numeral 6 denotes an ion-selective electrode deterioration detection circuit, which is a characteristic part of the present invention, and is composed of a voltage dividing circuit 7, a delay circuit 8, and a differential amplifier 9. The differential amplifier 9 has one input terminal set to the deterioration judgment level. divider resistor to set
The other input terminal is connected to the output terminal of the differential amplifier 1 via R _{1 and} R 2 via a delay circuit 8 having a delay time Δt and consisting of a resistor R ₃ and a capacitor C.

In this embodiment, when the ion-selective electrode 3 and the comparison electrode 5 are each immersed in a sample, a potential difference between the electrodes is output from the differential amplifier 1 compared to the ion concentration of the sample. In this way, when the output from the differential amplifier 1 reaches a steady state after a certain period of time has elapsed, the output from the differential amplifier 1 is input to an indicating circuit (not shown) to display the ion concentration, and the ion selectivity. It is input to the electrode deterioration detection circuit 6.

At this point, the ion-selective electrode has not deteriorated, and the interelectrode potential difference output A' (FIG. 2 A) via the delay circuit 8 has already reached a steady state, and Higher than the entered setting level L ₁ . Therefore, the differential amplifier 9 cannot output a signal.

When the surface of the ion-selective electrode 3 becomes contaminated due to long-term analysis and the response speed decreases, the period of the transient state becomes longer, and the inter-electrode potential difference outputs B' and C' (Fig. C) is lower than the set levels L ₂ and L ₃ inputted via the voltage dividing circuit 7. As a result, the differential amplifier 9 outputs a signal to activate an alarm (not shown), prompting cleaning or replacement of the ion-selective electrode 3 (see B and C in the figure).

In addition, in the above-mentioned embodiment, the output difference is calculated based on the measurement start point, but
It goes without saying that deterioration can be similarly detected using the response start time as a reference.

Effects As explained above, the present invention includes a delay circuit that delays the potential difference between the ion selective electrode and the comparison electrode, a voltage divider circuit that divides the signal from the delay circuit to generate a reference voltage, Since it is equipped with a differential amplifier that compares the signals from the delay circuit and the voltage divider circuit, the response speed of the ion-selective electrode, which is easily affected by the degree of deterioration, can be detected with a simple circuit configuration. deterioration can be reliably detected at an early stage.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an apparatus showing an embodiment of the present invention, FIG. 2 A to C are waveform diagrams showing the operation of the same device, respectively, and FIG. FIG. 1...Differential amplifier, 3...Ion selective electrode,
5... Reference electrode, 6... Ion selective electrode deterioration detection circuit, 7... Voltage dividing circuit, 8... Delay circuit, 9...
...Differential amplifier.

Claims (1)

[Scope of utility model registration request] A delay circuit that delays the potential difference between the ion-selective electrode and the comparison electrode, a voltage divider circuit that divides the signal from the delay circuit to generate a reference voltage, and compares the signals from the delay circuit and the voltage divider circuit. Ion selective electrode deterioration detection circuit consisting of a differential amplifier.