JPH07280691A - Liquid leak detector - Google Patents

Abstract

(57) [Summary] [Purpose] To provide a liquid leak detector for an analyzer that can handle a wide variety of analysis samples. [Structure] A pulse waveform is input to an exclusive OR circuit as two input signals, and electrodes are connected to one of them. When liquid enters the electrode, the capacitance increases and the pulse waveform is delayed. This delay is detected by the exclusive OR circuit. Also, by taking the logical sum of the signal from the gas sensor, the liquid that cannot be detected by the electrostatic capacitance is also detected. [Effect] Stable detection can be performed with a simple structure, and a wide variety of solutions can be supported.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for analyzing a liquid such as a liquid chromatograph or a flow injection analyzer.

[0002]

2. Description of the Related Art Liquid leakage detection methods used in conventional analyzers include electric resistance measurement, electrostatic capacitance measurement, and gas sensor method. The method using electric resistance is one in which electrodes are provided and the electric resistance changes when a liquid enters between the electrodes. In the method of measuring electrostatic capacity, electrodes are provided, a high-frequency signal is applied between the electrodes, and when the liquid enters between the electrodes, the electrostatic capacity changes, so that the high-frequency current changes. The method using a gas sensor is a method in which the leaked liquid is vaporized and detected as gas, and the leak is detected depending on the presence or absence of gas. Figure 5
Is a conventional method used for liquid leak detection and liquid level detection. When the liquid enters between the electrodes 32 and 33, the impedance between the electrodes is lowered and the potential of the electrode 32 is lowered. For this reason, since it falls below the reference potential formed by the resistors 35 and 36,
It can be detected by the comparator 37. Although it has a characteristic that the configuration is extremely simple, it has a drawback that it cannot be detected depending on the type of liquid because of its low electrical conductivity.

[0003]

In the analyzer, many kinds of liquid samples are used depending on the purpose of analysis. Provided is a leak detection method applicable to a wide variety of samples for this purpose. In particular, it provides a simpler and more reliable method for detecting leaks, which can detect even a component that cannot be detected by a gas sensor in a sample having low volatility.

[0004]

The exclusive OR circuit used in a digital circuit is simple and suitable for detecting a phase shift of a pulse waveform. Further, a widely used microprocessor has a high versatility because a high frequency clock pulse can be easily taken out. When this pulse is applied to the electrode, the phase of the pulse can be changed according to the magnitude of the electrostatic capacitance of the electrode. The presence or absence of liquid between the electrodes can be detected by detecting the delay of this pulse with an exclusive OR circuit.

Further, when used in combination with a gas sensor, it is possible to detect a wide range of samples from aqueous systems to organic solvents.

[0006]

When the sample enters between the electrodes, the capacitance of the electrodes changes, and when a pulse is applied to the electrodes, the phase of the pulse can be changed by the capacitance. The exclusive OR circuit in the logic circuit can detect the phase shift.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a liquid leakage detection circuit according to the present invention. A capacitor is formed between the electrode 8 and the base 9. This electrode 8 is arranged in the analyzer, at the position of the base of the analyzer which serves as a flow path when a liquid leaks, and normally air is provided between the electrode and the base. When liquid leakage occurs, the liquid flows through the base 9 of the spectroscope and flows under the electrode 8. While the liquid does not flow between the electrodes in the normal state, the capacitance of this capacitor is small, and almost the same signal is input to the exclusive OR circuit 7 at its input terminal and the exclusive OR circuit 7 does not output. However, when liquid enters between the electrode 8 and the base 9, the capacitance increases, and the pulse entering the exclusive OR circuit 7 from the resistor 6 is delayed due to the time constant determined by the resistor 6 and the capacitor formed by the electrode 8. Therefore, a phase difference occurs between the two signals entering the exclusive OR circuit 7, and a pulse signal appears at the output of the exclusive OR circuit 7.

FIG. 2 shows a signal waveform when there is no liquid leakage. The pulse waveform from the oscillator is and the signal directly input to the exclusive OR circuit 7. The signal connected to the cable 12 connected to the electrodes and simultaneously entering the exclusive OR circuit 7 is When there is no liquid, since the electrostatic capacitance is small and the delay of the waveform is small, the output signal of the exclusive OR circuit 7 does not appear as a pulse.

FIG. 3 shows a signal waveform when there is a liquid leak. As the capacitance of the electrode 8 increases due to the liquid, the waveform is distorted due to the phase delay. As a result, a pulse signal appears at the output of the exclusive OR circuit 7.

FIG. 4 shows another application example of the analyzer, which can be detected by inputting the logical sum of the signals from the capacitance type liquid leak detector 25 and the gas sensor 26 of the present invention to the control unit 29. Can also detect liquid leaks. As a result, it is possible to detect a wide range from water-based samples having low volatility but high permittivity to organic solvents such as hexane and benzene which have low permittivity but high volatility and are easily detected as gas.

[0011]

EFFECT OF THE INVENTION Since it is detected by capacitance, it is possible to detect a sample which is difficult to detect by electric conductivity such as pure water. Also, the structure is extremely simple because it is only the exclusive OR. In addition, when used in combination with a gas sensor, it is possible to detect a wide range of substances from water-based to organic solvents.

The clock pulse of a commonly used microprocessor can be used and can be simply constructed.

[Brief description of drawings]

FIG. 1 is a diagram showing a liquid leak detector of the present invention.

FIG. 2 is a signal waveform diagram when there is no liquid leakage in the electric circuit of the present invention.

FIG. 3 is a signal waveform diagram when the electric circuit of the present invention has liquid leakage.

FIG. 4 is a diagram showing an example of an analysis device in combination with a gas sensor according to the application of the present invention.

FIG. 5 is a diagram showing a conventional method using electric conductivity.

[Explanation of symbols]

1 ... Pulse waveform generator, 2, 3, 4 ... Buffer, 5,
6, 11, 31, 35, 36 ... Resistance, 7 ... Exclusive OR circuit, 8, 32, 33 ... Electrode, 9, 34 ... Analytical instrument base, 10 ... Leaked solution, 12 ... Electrode cable, 25 ...
Capacitance type liquid leak detector, 26 ... Gas sensor, 27 ... Logical sum circuit, 28, 38 ... Liquid leak detection signal, 29 ... Control unit, 30 ... Power supply, 37 ... Comparator.

Claims (4)

[Claims] 1. A liquid leak detector for an analyzer, which has an electrode to which a high frequency is applied, wherein the capacitance increases when the leaked liquid is touched and the phase of the high frequency waveform is delayed. Liquid leak detector characterized by. 2. A liquid leak detector according to claim 1, wherein a digital pulse waveform is used as the high frequency. 3. A signal according to claim 2, wherein signals from the same oscillator are inputted to the exclusive OR circuit as two signals via different resistors, and the liquid is supplied to one input terminal of the exclusive OR circuit. A liquid leak detector characterized by connecting a detection electrode. 4. An analyzer comprising a combination of the liquid leak detector according to claim 3 and a gas sensor, and configured to judge a liquid leak regardless of which detector outputs an abnormal signal.