JPH04301521A - Liquid level detector - Google Patents

Abstract

PURPOSE:To easily detect the liquid level from the outside of a tank without touching the liquid surface in the tank, by electrically detecting the difference of the electrostatic capacity based on the difference of the permittivity between a liquid and a gas. CONSTITUTION:This apparatus is provided with electrostatic capacity detecting parts 11, 12 which are detachably mounted at a predetermined position of the outer wall face of a plastic tank 21 containing a liquid thereinside and which detect the liquid level in accordance with the change of the electrostatic capacity of the liquid and a gas. Moreover, there are provided a high frequency oscillator 10 connected to the detecting parts 11, 12 oscillate a high frequency signal, an electrostatic capacity change detecting circuit 13 which detects the change of the electrostatic capacity corresponding to the difference of the detected electrostatic capacity of the liquid and gas, a and signal, generating circuit 15 which allows a light emitting diode to emit light based on the detecting result and outputs the result to a communication terminal device 16.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid level detector for detecting the level of liquid stored in a non-conductive tank such as a plastic tank.

0002

[Prior Art] Conventionally, some plastic tanks for storing water, waste water, chemicals, etc. cannot detect the level of the liquid inside from the outside, and it is difficult to detect the level of the liquid inside such a tank. Detectors include electrode type, reed switch type, and frit type, which detect the amount of liquid by inserting a sensor from the outside into the tank and bringing it into direct contact with the liquid, as well as communication tubes that connect the outside and inside of the tank. There are two types: one is a communicating tube type that detects the amount of liquid by installing an ultrasonic generator, and the other is an ultrasonic type that generates ultrasonic waves from an ultrasonic oscillator and measures the reflected waves to detect the level of the liquid.

0003

However, the above-mentioned detector has a drawback in that once a measurement point is set, the measurement point cannot be easily changed. In addition, when detecting the liquid level using an electrode type, reed switch type, or flint type detector, a flange for inserting the sensor is required at the top of the tank, and with existing equipment, it takes a lot of effort to install the above flange. The problem was that it was time consuming and costly. When detecting the liquid level using a communicating tube type detector, it is necessary to make a hole at the bottom of the tank to pass the communicating tube through, which makes it difficult to install while continuing work. The problem was that it took a lot of time and money. When detecting the liquid level using an ultrasonic detector, as with the above-mentioned detector, it takes a lot of time and money to install it, and the ultrasonic oscillator itself is expensive. There was a problem that equipment costs were high.

The present invention was made in view of the above circumstances, and it is an object of the present invention to provide a liquid level detector that can easily detect the liquid level from outside the tank without coming into contact with the liquid level inside the tank. With the goal.

[0005]

[Means for Solving the Problems] The present invention provides a static sensor that is detachably attached to a predetermined position on the outer wall surface of a container containing a liquid and that detects the liquid according to changes in capacitance between the liquid and gas. A liquid level detector is provided that includes a capacitance detection section, an oscillator that is connected to the capacitance detection section and oscillates a high frequency signal, and a capacitance change detection circuit that detects a change in the capacitance. .

[0006]

[Operation] The difference in capacitance based on the difference in dielectric constant between liquid and gas is electrically detected to detect whether a liquid level exists in the tank at the same position as the detector installation position. Therefore, the liquid level can be easily detected from the outside without installing a liquid level detector inside the tank.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be explained based on the drawings of FIGS. 1 to 5. FIG. 1 is a block diagram showing the configuration of a liquid level detector according to the present invention, and the liquid level detector is removably attached to a predetermined position on the outer wall of a plastic tank that detects the liquid level. .

In the figure, a high frequency oscillator 10 has a resistor R
1, R2, and R3, the capacitance detection unit 11, 1
2. It is connected to the capacitance change detection circuit 13, and oscillates a high frequency signal having a waveform of a predetermined amplitude. The capacitance detection units 11 and 12 are composed of sensing pattern circuits that detect capacitance on the atmosphere side and the tank side, and when combined with the high frequency oscillator 10, the high frequency oscillator 10 is activated according to the detected capacitance. The phase of the high-frequency signal oscillated from the oscillator is changed.

The capacitance change detection circuit 13 detects the presence or absence of liquid in the tank as a change in the capacitance by detecting the high frequency signal changed by the capacitance detection sections 11 and 12, In this embodiment, the detection result is output to a hysteresis generating circuit 14 that prevents chattering of the liquid level. The hysteresis generating circuit 14 is a circuit that prevents chattering of the liquid level, removes unnecessary pulses, and outputs the detection result to the signal generating circuit 15.

The signal generating circuit 15 causes a light emitting diode (described later) to emit light in accordance with the detection result, and also outputs the detection result to the communication terminal 16. FIG. 2 is a circuit diagram showing the circuit configuration of FIG. 1, and the operation of the liquid level detector according to the present invention will be explained based on FIG. 2. In addition, in the above detector, in order to eliminate the influence of noise around the detector, a grounding circuit is provided around the sensing pattern circuit, and a copper cover is provided.

In the figure, a high frequency oscillator 10 oscillates a high frequency signal A having a waveform as shown in FIGS. 3 and 4 (a). The capacitance detection units 11 and 12 are sensing pattern circuits consisting of capacitors printed in a comb-shaped pattern on both sides of a predetermined printed circuit board, and can perform compact sensing. , When there is no liquid at the detector installation position, a waveform signal having the same phase as the high frequency signal A is generated at the positions ■ and ■, as shown in FIGS. 3(b) and 3(c). Since each of the above waveform signals is based on the capacitance depending on the dielectric constant of the atmosphere, which is a gas, they are outputted to the capacitance change detection circuit 13 with the same phase and amplitude. In addition, if there is liquid at the detector installation position, the
As shown in (b) of Fig. 4, a waveform signal having the same phase as the high-frequency signal A is generated, and at the position (■), as shown in (c) of Fig. 4, a waveform signal whose phase is delayed from the high-frequency signal A by t time is generated. occurs. The capacitance change detection circuit 13 includes a resistor R1,
A plurality of inverters 13a to 13e connected to R2
As shown in FIGS. 3 and 4 (d), a waveform signal obtained by inverting the signal in (b) is output at the position (■),
As shown in Figures 3 and 4 (e), there is a (
c) The same waveform signal as in is output. Both signals at positions ■ and ■ are connected to diode D and resistor R4.
, R5, the waveform is converted into a waveform as shown in (f) of FIGS. 3 and 4, and reaches the position (■). Furthermore, Figure 4
The waveform of (f) in Fig. 4 has a phase of (d) of (e).
This is a low-level trigger voltage that is generated when there is a delay of t time with respect to the high-frequency signal A, and the amplitude has been changed to be different from that of the high-frequency signal A. That is, the capacitance change detection circuit 13 detects that when both the signals at the positions ■ and ■ are at high level,
If a high level signal is output and both signals are low level, a low level signal is output, and if one of both signals is high level and one is low level, then , a high level signal is output.

In the capacitance change detection circuit 13, when a high level voltage is applied to the inverter 14a,
A signal having a low level waveform is outputted according to its own threshold level, and the entire circuit 13 outputs a signal having a high level waveform to the hysteresis generating circuit 14. Furthermore, when the low-level trigger voltage is applied, the inverter 14a outputs a signal having a high-level waveform, and the circuit 13 as a whole outputs a signal having a low-level waveform to the hysteresis generating circuit 14.

In the signal generating circuit 15, when a high-level signal is input from the hysteresis generating circuit 14, the inverter 15a operates as shown in the position ■ in (g) of FIG.
A signal consisting of a low level waveform is output, whereby the light emitting diode 15b turns off, and the transistor Tr
Since the communication terminal 16 is in the off state, the communication terminal 16 is in the (h) state of FIG.
As shown in the position (■), a high level signal indicating "no liquid" is obtained. In addition, the hysteresis generating circuit 14
When a low level signal is input from the inverter 15a
outputs a signal consisting of a high-level waveform, as shown at position ■ in (g) of FIG. The container 16 can obtain a low level signal indicating "liquid present" as shown at position (■) in FIG. 4(h).

FIG. 5 is a diagram showing an embodiment of an information transmission system for transmitting information on the liquid level detected by the liquid level detector shown in FIGS. 1 and 2 to a host computer. In the figure, a liquid level detector 20 is detachably attached to a tank 21, and as mentioned above, the liquid level detector 20 is equipped with a sensing device having capacitors for detecting capacitance printed on both sides of a printed circuit board. Pattern circuit 11, 12
is depicted. The sensing pattern circuit 11 is
The sensing pattern circuit 12 detects the capacitance of the atmosphere, which is a gas on the opposite side of the tank 21, and the sensing pattern circuit 12 detects the capacitance of the liquid in the tank 21. The liquid level detector 20 detects the liquid level in the tank using the difference in dielectric constant between the gas and liquid, and outputs a corresponding signal.

The communication terminal 16 detects the signal output from the detector 20 and transmits the signal to the host computer 25 via the modem 22, telephone line 23, and modem 24. Thereby, the host computer 25 can detect the liquid level, and can, for example, adjust the amount of liquid in the tank according to the detection. Therefore, in this embodiment, the difference in capacitance based on the difference in dielectric constant between liquid and gas is electrically detected to determine whether or not there is a liquid level in the tank at the same position as the detector installation position. Therefore, the liquid level can be easily detected from the outside without installing a liquid level detector inside the tank during improvement work or the like. Furthermore, since the liquid level detector of this embodiment is mounted externally, the detector can be easily attached and detached, and the measurement point can be easily changed. Further, in this embodiment, since a hysteresis circuit is provided, chattering due to liquid level waves, which is a problem in liquid level measurement, can be effectively prevented. Furthermore, in this embodiment, the liquid level detector can be made small and have a simple configuration, so that the structural cost can be reduced.

In this embodiment, the liquid level detector 20 is attached to a plastic tank, but the present invention is not limited to this. For example, ceramic containers, wooden containers (
It is also possible to apply it by attaching it to a sake barrel), etc.

[0017]

As explained above, in the present invention, the device is removably attached to a predetermined position on the outer wall surface of a container holding a liquid, and detects the liquid according to changes in capacitance between the liquid and gas. The present invention includes a capacitance detection section that detects a capacitance, an oscillator that is connected to the capacitance detection section and oscillates a high frequency signal, and a capacitance change detection circuit that detects a change in the capacitance.
The liquid level can be easily detected from outside the tank without touching the liquid level inside the tank.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of a liquid level detector according to the present invention.

FIG. 2 is a circuit diagram showing the circuit configuration of FIG. 1;

FIG. 3 is a diagram showing output waveforms at each position shown in FIG. 2;

FIG. 4 is a diagram showing output waveforms at each position shown in FIG. 2, similar to FIG. 3;

FIG. 5 is a diagram showing an embodiment of an information transmission system that transmits information on the liquid level detected by the liquid level detector shown in FIGS. 1 and 2 to a host computer.

[Explanation of symbols]

10 High frequency oscillator 11, 12 Capacitance detection section 13 Capacitance change detection circuit 14 Hysteresis generation circuit 15 Signal generation circuit 16 Communication terminal 20 Liquid level detector 21 Plastic tank 22, 24 modem 23　Telephone line 25 Host computer

Claims (1)

[Claims] 1. A capacitance detection section that is detachably attached to a predetermined position on an outer wall surface of a container that holds a liquid therein, and that detects the liquid according to changes in capacitance between the liquid and the gas; A liquid level detector comprising: an oscillator connected to a capacitance detection section to oscillate a high-frequency signal; and a capacitance change detection circuit to detect a change in the capacitance.