JPS63210627A - Liquid-level meter - Google Patents

Abstract

PURPOSE:To perform accurate measurement, by applying high frequency voltage to a signal electrode and measuring the liquid level on the basis of the detection voltage of a detection electrode. CONSTITUTION:Only the AC component of the high frequency pulse from an oscillator 3 passes through a condenser 5 to be applied to a signal electrode 1 and the detection voltage of a detection electrode 2 is inputted to a discrimination circuit 4. The discrimination circuit 4 has the function for judging whether the lower end of the detection electrode 2 is present above or below a liquid level and is equipped with a variable resistor 6 for adjusting the amplitude of the detection voltage of the detection electrode 2, a condenser 7 permitting the passage only of the AC component of the output of the variable resistor 6, a reference voltage level control circuit 8 for adjusting the reference voltage level of the output of the condenser 7 and an inverter 9 inputting the output of the control circuit 8.

Description

[Detailed description of the invention] Industrial applications The present invention relates to a liquid level gauge.

Conventional technology and its problems Conventionally, two electrode rods are placed in a tank, a low frequency voltage of 50 to 60 Hz is applied to one electrode, and the height of the liquid level is determined based on the voltage appearing at the other electrode. Liquid level gauges that measure the level of water are known.

However, since the conductivity of the liquid and the conductivity of bubbles to low frequencies are not very different, it is difficult to accurately measure the height of the liquid level when there are bubbles, especially high-density bubbles, on the liquid surface. The problem is that it can't be done.

SUMMARY OF THE INVENTION An object of the present invention is to provide a liquid level gauge that can accurately measure the height of a liquid level even when bubbles are present on the liquid level.

Means for Solving the Problems The liquid level gauge according to the present invention includes a signal electrode placed in a liquid tank and to which a voltage is applied, and a detection electrode placed in the liquid tank. A high frequency voltage is applied to the signal electrode, and the height of the liquid level is measured based on the detection voltage of the detection electrode.

Embodiment FIG. 1 shows the configuration of a liquid level gauge. A liquid level gauge consists of a signal electrode (1) and a detection electrode (2) arranged in a tank (T) containing a liquid, such as milk, and a signal electrode (1).
Based on the high-frequency oscillator (3) for applying a high-frequency voltage to the sensing electrode (2) and the sensing voltage of the sensing electrode (2), the sensing electrode (
2) a discrimination circuit (4) which discriminates whether the lower end is above or below the liquid level;

The lower end of the signal electrode (1) is located at the lower part of the liquid so that it is always immersed in the liquid, and the lower end of the sensing electrode (2) is located at the upper part of the liquid. The signal electrode (1) has an oscillator (3
) is applied via a capacitor (5). Discrimination circuit (4)
a variable resistor (6) for adjusting the amplitude of the detection voltage (high frequency pulse) of the detection electrode (2), and a capacitor (7) that allows only the alternating current component of the output of the variable resistor (6) to pass through;
a reference voltage level adjustment circuit (8) for adjusting the reference voltage level of the output of the capacitor (7); and an adjustment circuit (8)
and an inverter (9) to which the output of is inputted. The adjustment circuit (8) includes a DC power supply (10) and a DC power supply (10).
The voltage dividing circuit (11) is composed of a variable resistor (12) and a fixed resistor (13).

Referring to Figures 1 and 2, from the oscillator 3),
For example, a high frequency pulse (signal a) with a voltage of 12v1 and a frequency of 300 KHz is output.

Only the alternating current component of this high frequency pulse a is transmitted through the capacitor (5
), it becomes a high-frequency pulse (signal b) having the same waveform as pulse a but a different reference voltage level, and this pulse b is applied to the signal electrode (1).

When the lower end of the sensing electrode (2) is located above the liquid level and above the bubbles on the liquid surface, the signal electrode (1)
Since no current flows from the sensing electrode (2) to the sensing electrode (2),
The voltage in 2) becomes zero. Therefore, the inverter (9)
, the voltage vO of the DC power supply (10) is connected to the voltage divider circuit (11).
The voltage VD (signal cl) divided by the voltage VD (signal cl) is input.

The DC voltage VD is set to be higher than the threshold voltage VS of the inverter (9), so the output (signal dl) of the inverter (9) becomes L level.

When the lower end of the sensing electrode (2) is located below the liquid level and immersed in the liquid, current flows from the signal electrode (1) through the liquid to the sensing electrode (2), so the sensing electrode A high frequency pulse appears in (2). This high frequency pulse is sent to the reference voltage level adjustment circuit (8) via the variable resistor (6) and capacitor (7), so the inverter (9) receives the reference voltage of the high frequency pulse that has passed through the capacitor (7). The signal C2 whose level has been shifted by the DC voltage VD is manually input. The lower limit value of this signal C2 is set so that it is lower than the threshold voltage VS of the inverter (9).
) (12), and the inverter (9)
A positive high frequency pulse (signal d2) is output from.

When the lower end of the sensing electrode (2) is above the liquid level and immersed in bubbles above the liquid surface, current flows from the signal electrode (1) through the bubbles to the sensing electrode (2). Detection electrode (2
) a high-frequency pulse appears. The electrical conductivity of foam for low frequencies and the electrical conductivity of liquid for low frequencies are not much different, but the electrical conductivity of foam for high frequencies is lower than the electrical conductivity of liquid for high frequencies, and the difference is significant. therefore,
The amplitude of the high frequency pulse appearing on the sensing electrode (2) is smaller than when the sensing electrode (2) is immersed in the liquid. The detection voltage of the detection electrode (2) is sent to the adjustment circuit (8) via the variable resistor (6) and the capacitor (7) to the reference voltage level, so the inverter (9) is connected to the capacitor (7). A signal c3 in which the reference voltage level of the passed high-frequency pulse is shifted by the DC voltage VD is input. The amplitude A3 of the high frequency pulse that passed through the capacitor (7) is
When the sensing electrode (2) is immersed in the liquid, the capacitor (
7), the lower limit value of the signal C3 is larger than the lower limit value of the signal C2. The lower limit value of the signal C3 is set so that it is larger than the threshold voltage ■S of the inverter (9).
) (12), and the inverter (9
) output (signal d3) becomes L level.

In the above liquid level gauge, if the lower end of the detection electrode (2) is above the liquid level and immersed in bubbles on the liquid level, or if it is located above the bubbles on the liquid level, the inverter The output of (9) becomes L level, and when the lower end of the detection electrode (2) is located below the liquid level, a high frequency pulse is output from the inverter (9), so bubbles are generated on the liquid surface. Even if the detection electrode (2) is located above the liquid level or below the liquid level, it can be accurately determined whether the lower end of the sensing electrode (2) is located above or below the liquid level.

In the above embodiment, it is determined whether the liquid level is above or below the lower end of the sensing electrode (3).
) is a value that depends on the length of the detection electrode (3) immersed in the liquid surface, so the variable resistance (G) (12)
By adjusting the resistance value, it is also possible to determine whether the liquid level is above or below with respect to an arbitrarily determined length position (height position) of the sensing electrode (3). .

Therefore, for one sensing electrode (3), the discrimination circuit (
By providing a plurality of 4), it becomes possible to determine whether the liquid level is above or below at a plurality of different height positions. In this case as well, since the conductivity of the bubbles is lower than that of the waves, the height of the liquid level can be accurately detected. By arranging a plurality of sensing electrodes so that the lower ends of each sensing electrode are located at different heights, and connecting a discrimination circuit (4) like the above embodiment to each sensing electrode, a plurality of sensing electrodes can be arranged at different heights. It is also possible to determine whether the liquid level is above or below with respect to the position.

Effects of the Invention In the liquid level gauge according to the present invention, a high frequency voltage is applied to the signal electrode. The conductivity of liquid to high frequencies is higher than that of foam to high frequencies, and the difference is significant. Therefore, even when bubbles are generated on the liquid surface, the height of the liquid level can be accurately measured.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing an embodiment of this invention, and FIG.
5 is a time chart showing waveforms at various parts in the figure. (1)...Signal electrode, (2)...Detection electrode, (3)
... High frequency oscillator, (4) ... Discrimination circuit, (T).
··tank. that's all

Claims (1)

[Claims] In a liquid level gauge that includes a signal electrode placed in a liquid tank and to which a voltage is applied, and a detection electrode placed in the liquid tank, a high frequency voltage is applied to the signal electrode, and a high frequency voltage is applied to the signal electrode, and A liquid level gauge characterized in that the height of the liquid level is measured.