JPH0133777B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to gas bubbles (bubbles) generated in a liquid.
The present invention relates to a method for detecting liquid level and a method for detecting liquid level.

If you leave the bubbles that form in the liquid as is,
This may lead to serious accidents. For example, if a liquid intended for cooling fuel rods, such as cooling water in a nuclear reactor, generates bubbles due to overheating of the fuel rods, it is necessary to immediately detect the bubbles and add cooling water. If the gas bubbles generated in the tank are not removed, thermal runaway or tank destruction may occur, leading to a serious accident.

As shown in Figure 1, one of the typical methods conventionally used to detect bubbles generated in a liquid is to use an internal electrode 1 with an exposed tip and an insulated A probe 4 equipped with an external electrode 3 insulated by a body 2 is immersed in a liquid, and a direct current source 5 is connected to both electrodes of the probe 4 to drive it, and changes in the current flowing through the circuit are inserted and connected into the circuit. It is extracted as a change in the potential difference across the resistor 6, amplified by an amplifier 7, and displayed on a display 8 such as a meter.
It is known that it is displayed as .
In this method, the electrical resistance between the electrodes 1 and 3 of the probe 4 immersed in the liquid changes due to the generation of bubbles, so the potential difference between both ends of the resistor 6 changes, which causes the display 8 to change. Bubble formation is displayed.

In such a conventional method, since the change in electrical resistance due to bubble generation is minute, it not only has the drawback of low detection sensitivity, but also requires the use of a high-gain DC amplifier as the amplifier 7, which requires high stability. However, it becomes expensive.

Another known method is to connect a probe similar to that shown in Figure 1 to one side of a resistive bridge, and detect air bubbles based on the unbalance of the bridge due to changes in electrical resistance between both electrodes of the probe due to air bubble generation. However, this method also has the drawback of poor detection sensitivity.

Furthermore, in the above two methods, a sine wave AC power source is used instead of a DC power source, but even in this case, bubbles are still detected based on the change in electrical resistance caused by bubble generation. ,
It still has the drawback of low detection sensitivity.

Note that the conventional bubble detection method described above is also used for liquid level detection. That is, since a bubble rate of 100% means that there is no liquid, it is possible to detect whether the liquid level is above or below the probe.

SUMMARY OF THE INVENTION In view of the drawbacks of the conventional methods described above, it is an object of the present invention to provide a bubble detection method and a liquid level detection method that are highly sensitive, stable, and can be realized at low cost.

The present invention applies an alternating rectangular wave as a power supply to both electrodes of the probe, and thereby detects not only a signal due to a change in resistance between both electrodes of the probe, but also a signal due to a change in capacitance between the two electrodes of the probe. They are taken out at the same time to improve detection sensitivity.

Hereinafter, the present invention will be explained in detail with reference to embodiments shown in the drawings.

FIG. 2 is a block diagram showing an embodiment of the present invention, in which a rectangular wave power source 9 is connected between both electrodes 1 and 3 of a probe 4 similar to the conventional one, and an amplifier 1 is connected in the middle.
0 is connected.

Here, the equivalent circuit between the electrodes 1 and 3 of the probe 4 is as shown in FIG. It is represented by a parallel circuit with a capacitance C determined by the dielectric constant of the liquid around the electrode and the dielectric constant of the liquid around the electrode.

By the way, when a rectangular wave is applied to both ends of such a CR parallel circuit, the waveform changes due to a transient phenomenon. That is, it is well known that the differential wave due to C and R is added. If either R or C changes, a change will appear in the waveform, and if both change, it will also change.

Therefore, in FIG. 2, applying a rectangular wave to both electrodes 1 and 3 of the probe 4 is equivalent to applying a rectangular wave to the CR parallel circuit as shown in FIG. The generation of bubbles in the immersed liquid is equivalent to a change in the resistance R and capacitance C shown in FIG. , bubble generation can be detected.

Here, the change in bubble generation in the signal wave input to the amplifier 10 is due to the change in both C and R, that is, the change due to the change in resistance R, and the change in the differential wave due to the change in capacitance C. The amount of change is added. On the other hand, when direct current or sine wave alternating current is used, as in the past, only the change in resistance is detected, so using transient phenomena, in addition to the change in resistance, the change in capacitance is detected. It is clear that in the present invention, the detection sensitivity is significantly improved compared to the conventional method.

Even with the conventional method, the equivalent circuit between both electrodes of the probe immersed in the liquid is expressed as shown in Figure 3, but when direct current is applied as in the conventional method, it is impossible to extract the change in C. be. Furthermore, even when a sinusoidal alternating current is applied, the capacitance C affects the phase and does not significantly affect the change in signal amplitude. However, according to the present invention, since changes in resistance and capacitance can be detected as changes in the amplitude of the signal wave, detection sensitivity can be significantly improved. In addition, in the present invention, since the resistance change and the capacitance change are extracted using the transient phenomenon caused by the application of a rectangular wave, the S/N ratio is not particularly deteriorated compared to the conventional example.

This bubble detection method can of course be used for liquid level detection as well as conventional methods.

In this way, high detection sensitivity can be obtained by using a rectangular wave as the drive source for the probe.

Furthermore, in the present invention, since the rectangular wave is an alternating rectangular wave, the two electrodes of the probe alternately have positive and negative potentials, which has the effect of reducing electrolytic corrosion of both electrodes.

It should be noted that, as an amplifier for the detection signal, there is no need to use a high gain DC amplifier that requires high stability as in the conventional case, and an inexpensive AC amplifier has the advantage of being sufficient.

Furthermore, since the method according to the present invention detects not only resistance changes but also capacitance changes, it is also possible to detect bubbles generated in an insulating liquid (for example, insulating oil), which was impossible with conventional methods.

As described above, the method of the present invention, which drives the probe with an alternating square wave and adds and detects changes in capacitance, can be realized by simple modification of conventional equipment, so it is possible to improve the sensitivity of conventional equipment. Since it is easy to use and an AC amplifier can be used, an inexpensive system can be realized.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a conventional bubble detection method, FIG. 2 is a block diagram showing an embodiment of the present invention, and FIG. 3 is a diagram showing an equivalent circuit of a probe immersed in liquid. DESCRIPTION OF SYMBOLS 1...Internal electrode, 2...External electrode, 3...Insulator, 4...Probe, 9...Square wave power supply, 10...
…amplifier.

Claims (1)

[Claims] 1. A probe having two mutually insulated tip electrodes exposed to the outside is placed in a liquid, and electric power is supplied to the two electrodes of the probe to detect electrical changes caused by bubble generation. - A bubble/liquid level detection method characterized in that an alternating square wave power source is used as the power source in the liquid level detection method.