JPH08304147A - Liquid-level measuring apparatus - Google Patents

Abstract

PURPOSE: To detect the liquid level in a liquid storing tank highly accurately and to decrease the number of cables by providing a tank selecting circuit, an oscillating circuit and the like on the side of each liquid sensor, and constituting a single signal line and a power supply line for an operating circuit, an instinsically safe power supply circuit and the like provided at a safe part. CONSTITUTION: Liquid level sensors 2A-2N are provided for every tank of a plurality of liquid storing tanks 1A-1N. Sensor-side units 14A-14N are provided in the manhole for the sensors. The sensor-side units 14A-14N comprise tank selecting circuits, switching circuits, oscillating circuits and the like. Furthermore, at a safe part, a single display-side unit 23 comprising an operating circuit 24, an intrinsically safe circuit 27, a specifying circuit 29 and the like is provided. When the liquid storing tank 1A is specified with the specifying circuit 29, the applicable sensor-side unit 14A is selected, the liquid level sensor 2A and a standard capacitor 12A are switched with the switching circuit and the oil level and the like are accurately measured based on the oscillating frequency from the oscillating circuit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid level measuring device capable of highly accurately measuring the remaining amount in a liquid storage tank installed in a gas station or the like.

[0002]

2. Description of the Related Art Generally, in an underground tank (reservoir tank) of a gasoline filling station or the like, in order to constantly monitor the remaining amount of oil, JP-A-58-106423 and JP-A-1-223319 are used. A liquid level measuring device as disclosed in the publication is used.

In this liquid level measuring device according to the prior art, a capacitance type liquid level sensor is inserted for each of a plurality of liquid storage tanks, and a switching circuit is provided in the vicinity of each liquid level sensor. Here, the switching circuit switches the oscillation circuit between a liquid level sensor and a standard capacitor that corrects the capacitance detected by the liquid level sensor. It is composed of a cylinder and a lower inner cylinder. By switching the switching circuit, not only the liquid level can be measured, but also the dielectric constant and the water level can be measured to detect the liquid level.

Further, since gas stations handle dangerous materials such as gasoline, electric safety equipment has an intrinsically safe explosion-proof structure.
The intrinsically safe barrier circuit) is provided in the gas station office, which is a safe place away from the liquid storage tank. At this time, the intrinsic safety barrier circuit is provided for each liquid level sensor in a one-to-one correspondence, and each liquid level sensor is connected to the oscillation circuit via each intrinsic safety barrier circuit and the tank selection circuit. There is. Then, the oscillation circuit generates a frequency signal having an oscillation frequency corresponding to the measured capacitance from the liquid surface sensor or the reference capacitance of the standard capacitor, and the calculation circuit of the next stage calculates based on the frequency signal. Then, measure the oil level of each storage tank.

Here, the tank selection circuit designates a liquid storage tank for measuring the liquid level among the liquid storage tanks, and the liquid level sensor of the designated liquid storage tank is located near each liquid storage tank. The provided switching circuit sequentially switches the upper inner cylinder, the lower inner cylinder, and the standard capacitor to the outer cylinder,
By connecting to the oscillation circuit, the liquid level height, the dielectric constant, the water level in the tank, etc. are measured.

[0006]

By the way, in the above-mentioned liquid level measuring device according to the prior art, the intrinsic safety barrier circuit is provided for each liquid level sensor at a safe place separated from the liquid level sensor. For example, in a 10-channel liquid level measuring device that has 10 liquid storage tanks at a gas station and a liquid level sensor for each liquid storage tank, 10 intrinsically safe barrier circuits must be provided in a safe place. Becomes Therefore, not only is the number of intrinsic safety barrier circuits increased and the cost is high, but also the panel in which the intrinsic safety barrier circuits are accommodated is large and the occupied area is large.

Further, the switching circuit provided near each liquid storage tank is arranged such that the liquid level height, the dielectric constant, the height of the stored water level, etc. in the liquid storage tank are upper and lower than the outer cylinder of the liquid level sensor. Inner cylinder,
To detect by switching a standard capacitor or the like, to transmit at least five power supply cables and control signal cables between the switching circuit and the intrinsic safety barrier circuit, and a detection signal for detecting electrostatic capacitance to the arithmetic circuit. At least 2
A signal cable consisting of two twisted wires is required, and in the case of 10 channels, about (5 + 2) × 10 cables, that is, a total of 70 cables are required. The cost of cable wiring materials and work involved in installation work There is a problem that labor is heavy and maintenance is expensive.

Furthermore, since the capacitance signal output from the liquid level sensor or the standard capacitor is connected to the intrinsic safety barrier circuit, the tank selection circuit and the oscillation circuit provided in the gas station office through the cable, A cable having a stray capacitance exists between the oscillation circuit and the liquid level sensor in a long dimension. Therefore, there is a problem in that the oscillation frequency output from the oscillation circuit fluctuates due to the external environment (temperature, humidity, etc.) due to the stray capacitance of the cable, which causes a measurement error.

The present invention has been made in view of the above-mentioned problems of the prior art, and a first object of the present invention is to reduce the number of cables used and to accurately measure the remaining amount in the liquid storage tank. An object of the present invention is to provide a liquid level measuring device capable of detecting.

[0010]

In order to solve the above-mentioned problems, the liquid level measuring device adopted by the invention of claim 1 is
In a liquid level measuring device for measuring the liquid level of oil liquid stored in at least one liquid storage tank, in order to detect the capacitance of the oil liquid stored in each of the liquid storage tanks A coaxial cylindrical liquid level sensor composed of an outer cylinder and an inner cylinder to be inserted respectively, a standard capacitor provided in each of the liquid storage tanks in the vicinity of each liquid level sensor, and having a known reference capacity, A tank selection that is provided in the vicinity of each of the liquid storage tanks, stores a preset own liquid storage tank number, and starts a detection operation when a designation signal for designating the own liquid storage tank number is input. A circuit and the next stage of each tank selection circuit. When the own liquid storage tank number is designated by each tank selection circuit, the state in which the liquid level sensor is connected between the inner cylinder and the outer cylinder of the liquid level sensor. And connected to a standard capacitor A switching circuit for sequentially switching in a fixed order, and a switching circuit provided in the vicinity of each liquid storage tank in the vicinity of each switching circuit and formed between the inner and outer cylinders of each liquid level sensor by switching of each switching circuit. The oscillation circuit that oscillates a frequency signal having an oscillation frequency corresponding to the reference capacitance of the electrostatic capacity or the standard capacitor and the liquid storage tank are provided in a safe place, and the liquid level corresponding to the frequency signal is provided. A single arithmetic circuit for calculating the height and a single arithmetic circuit whose one end side is connected to each oscillating circuit and the other end side is connected to the arithmetic circuit in order to output the frequency signal from each oscillating circuit to the arithmetic circuit. Of the signal line and the liquid storage tank are provided in a safe place separated from each other, the intrinsically safe power supply circuit for outputting the intrinsically safe power supply, and the intrinsically safe power supply from the intrinsically safe power supply circuit, the oscillation circuits,
In order to supply the tank selection circuit and the switching circuit, one end side is connected to the intrinsically safe power supply circuit, and the other end side is connected to the oscillation circuit, the tank selection circuit and the switching circuit. In order to specify a desired liquid storage tank among the liquid tanks, it is characterized by comprising a tank designating means for outputting a designating signal to each of the tank selection circuits using the power supply line.

According to a second aspect of the present invention, each of the switching circuit, the tank selection circuit and the oscillation circuit is provided in a manhole into which a sensor is inserted in each of the liquid storage tanks.

According to the third aspect of the present invention, it is detected that the supply of the intrinsically safe power supply is started near the tank selection circuit and the switching circuit using the power supply line for measuring the liquid level. At this time, a reset circuit for outputting a reset signal is provided to each tank selection circuit and the switching circuit.

[0013]

According to the structure of claim 1, in order to measure the liquid level of a desired liquid storage tank, the designation signal from the tank designating means is superimposed on the intrinsically safe power source output from the intrinsically safe power source circuit, and the power line is provided. When input to each tank selection circuit using, the tank selection circuit determines whether or not the input designation signal matches the preset number of its own liquid storage tank, and Only the selection circuit starts the detection operation. Then, when the own tank selection circuit determines that it is the own liquid storage tank, the switching circuit provided in the next stage is connected between the inner and outer cylinders of the liquid level sensor and connected to the standard condenser. Are sequentially switched in a predetermined order, and are sequentially connected to an oscillation circuit provided near the switching circuit. The oscillation circuit outputs a frequency signal having an oscillation frequency corresponding to each capacitance to an arithmetic circuit provided in a safe place using a single signal line, and the arithmetic circuit oscillates this frequency signal. Liquid level height, remaining amount, etc. are calculated based on the frequency.

According to a second aspect of the present invention, the tank selection circuit, the switching circuit and the oscillating circuit are provided in the manholes surrounding the sensor insertion openings of the respective liquid storage tanks. The oscillating circuit can be brought closer to the standard capacitor located at the position via the switching circuit, and the signal line connecting the oscillating circuit to the liquid level sensor and the standard capacitor can be shortened. This allows
The stray capacitance added to the capacitance output from the liquid level sensor or standard capacitor is only the stray capacitance on the board,
The stray capacitance can be reduced, and the capacitance error added to the oscillation frequency output from the oscillation circuit can be reduced.

According to the third aspect of the present invention, since the tank selection circuit and the switching circuit are provided with a reset circuit for outputting a reset signal when the supply of the intrinsically safe power supply is started using the power supply line, The tank selection circuit and the switching circuit can be set to the initial state by using the power supply line before the designation signal is input to the tank selection circuit together with the main power supply.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A case where a liquid level measuring device according to an embodiment of the present invention is used in a gas station will be described below with reference to FIGS.

In the figure, 1A, 1B, ..., 1N are N storage tanks (collectively referred to as storage tank 1), 2A, 2
B, ..., 2N denote liquid level sensors (collectively referred to as liquid level sensors 2) inserted into the respective liquid storage tanks 1, and the liquid level sensors 2 are used to store the oil liquids stored in the liquid storage tanks 1. It detects electrostatic capacitance.

Here, the N liquid level sensors 2 are shown in FIG.
As shown in FIG. 2, the outer cylinder 3 is formed in a coaxial cylindrical shape and is composed of a single cylinder, and the inner cylinder 4 is inserted coaxially into the outer cylinder 3. A cylinder 4A, a lower inner cylinder 4B,
The lower inner cylinder 4B is composed of three cylinders including a water detecting inner cylinder 4C located below, and the lower end of the upper inner cylinder 4A and the upper end of the lower inner cylinder 4B are connected via an insulating member 5A. In addition, the lower end of the lower inner cylinder 4B and the upper end of the water detecting inner cylinder 4C are also connected via an insulating member 5B.

The liquid level sensor 2 includes an upper liquid sensor section 6 between the upper inner cylinder 4A and the outer cylinder 3, a lower liquid sensor section 7 between the lower inner cylinder 4B and the outer cylinder 3, and water detection. A water sensor unit 8 is formed between the inner cylinder 4C and the outer cylinder 3, and the sensor units 6, 7, 8 detect the electrostatic capacitances C1, C2, C3, respectively, and the sensor units 6, 7, 8 is a switch 9,1
It is connected to an oscillation circuit 21 described later via 0 and 11 (see FIG. 4). 3A, 4A1, 4B1 and 4C1 respectively indicate signal lines connected to the sensor side unit 14.

, 12N are standard capacitors (collectively referred to as standard capacitors 12) provided in the vicinity of the liquid level sensors 2A, 2B, ..., 2N, and the standard capacitors 12 have a reference capacitance C0. The reference capacitance C0 is set to, for example, a value approximately in the middle of the change range of the electrostatic capacitance C2 of the lower liquid sensor section 7, and the standard capacitor 12 is provided for the external environment such as temperature and humidity received by the liquid level sensor 2. By receiving the same condition as the condition, a capacitor with good stability that does not change the reference capacitance C0 is used, and the capacitances C1, C2, C3 detected by the liquid level sensor 2 are corrected for the influence of temperature. I go without receiving it. Further, the standard capacitor 12 is connected to the oscillation circuit 21 via the switch 13 (see FIG. 4).

, 14N are sensor-side units (collectively referred to as sensor-side unit 14) provided near the liquid storage tanks 1A, 1B, ..., 1N, respectively. As shown in FIG. 2, the sensor-side unit 14 includes a tank selection circuit 15, a switching circuit 20,
It is composed of an oscillation circuit 21 and a reset circuit 22 (see FIG. 4).

Here, the sensor side unit 1 consisting of N pieces
4 will be described with reference to FIG.

In the figure, reference numeral 15 denotes a tank selection circuit. The tank selection circuit 15 has a number setting circuit 16 constituted by a DIP switch or the like for preset setting and storing its own storage tank number, and a power supply line 28 described later. Is connected to the counter circuit 17 and extracts a designation signal which is superimposed and input to the intrinsically safe power supply through the power supply line 28, and the designation signal extracted by the counter circuit 17 and the number setting circuit 16 are set. It is composed of a match determination circuit 18 for determining whether or not the tank numbers match. When the tank number matches the designated signal in the coincidence determination circuit 18, the coincidence signal is transmitted to the switching circuit 20 and the switch 19 that restricts power supply to the oscillation circuit 21, and the switching circuit 20 and the oscillation circuit 21. The operation of is started at the same time.

Reference numeral 20 denotes a switching circuit connected to the next stage of the tank selection circuit 15. The switching circuit 20 is composed of, for example, a shift register, and the tank selection circuit 1 is provided on the input side thereof.
5 are connected to the output side, and switches 9, 10, 11 for connecting the upper side liquid sensor section 6, the lower side liquid sensor section 7 and the water sensor section 8 of the liquid level sensor 2 to the oscillation circuit 21 and the standard condenser 12 are connected. The switch 13 connected to the oscillation circuit 21 is connected to each.

When a coincidence signal is input from the tank selection circuit 15 to the switching circuit 20, that is, when the own liquid storage tank 1 (liquid level sensor 2) is designated by the designation signal, FIG. As shown, the predetermined time t (for example, 10
The drive signal is sequentially switched every 0 mS).
It is automatically output to the liquid level sensor 13, and the upper liquid sensor unit 6, the lower liquid sensor unit 7, the water sensor unit 8 and the standard capacitor 12 of the liquid level sensor 2 are sequentially connected to the oscillation circuit 21. .

Reference numeral 21 denotes an oscillating circuit, which is composed of a coil having a predetermined inductance L,
Capacitance C1 detected by the upper liquid sensor unit 6, the lower liquid sensor unit 7, and the water sensor unit 8 of the liquid level sensor 2 described above.
, C2, C3 and the reference capacitance C0 of the standard capacitor 12
The inductance L is
Then, a frequency signal having an oscillation frequency f is generated by the capacitance C and the frequency signal is output to the arithmetic circuit 24 using a signal line 26 described later. Since the inductance L is fixed, the oscillation frequency f causes oscillation corresponding to the change in the capacitance C.

Reference numeral 22 denotes a reset circuit built in the sensor side unit 14. The reset circuit 22 sends a reset signal to the counter circuit 17 of the tank selection circuit 15 when the intrinsically safe power is supplied through the power line 28. And the switching circuit 20. The reset signal sets the tank selection circuit 15 and the switching circuit 20 to the initial state, and the counter circuit 17 determines the waveform of the intrinsically safe power supply when the power is turned on.
In order to prevent accidental reading as a designated signal.

The sensor side unit 1 configured as described above
In FIG. 4, as shown in FIG. 5, the coincidence determination of the tank selection circuit 15 is performed only when the designating signal superimposed on the intrinsically safe power supply supplied using the power supply line 28 designates the own liquid storage tank 1. From the circuit 18 to the switching circuit 20 and the oscillation circuit 2
The coincidence signal is transmitted toward 1. Also, the switching circuit 2
At 0, the drive signals of the switches 9, 10, 11, and 13 are sequentially output at predetermined time t based on the input coincidence signal, and the sensor units 6, 7, and 8 and the standard capacitor 12 are output. The oscillator circuits 21 are sequentially connected. Then, the oscillation circuit 21 outputs a frequency signal having an oscillation frequency based on the electrostatic capacitances of the sensor units 6, 7, 8 and the standard capacitor 12 to the display side unit 23 via the signal line 26. .

Reference numeral 23 denotes a single display side unit provided in a gas station office or the like (not shown) which is a safe place. The display side unit 23, as shown in FIG.
And a designating circuit 29, which will be described later, which is connected to the input side of the computing circuit 24 and outputs a designating signal, and the designating circuit 29 which is connected to the output side of the computing circuit 24 and which supplies a designating signal based on the power supply signal from the computing circuit 24. Sensor side unit 14
Intrinsically safe power supply circuit 27 for outputting to
4 is connected to the output side and the liquid level in the arithmetic circuit 24 is
It is composed of a display unit 25 for calculating the water surface height, the dielectric constant and the like and displaying the result.

Here, the arithmetic circuit 24 is constituted by a microcomputer or the like, and comprises a processing circuit (CPU), an input / output circuit and a memory circuit (none of which is shown), and the arithmetic circuit 24 comprises the liquid level sensor 2 Detectors 6, 7,
From the oscillation frequency based on the electrostatic capacitances C1, C2, C3 and the oscillation frequency based on the reference capacitance C0 of the standard capacitor 12 sequentially detected by 8, the liquid level height in the liquid storage tank, the dielectric constant, and the storage in the tank The calculation is performed in a state where the water surface height and the like are corrected by the standard condenser 12, and the result is displayed on the display 25.

Reference numeral 26 denotes a signal line composed of a single twisted pair twisted wire. One end of the signal line 26 is one unit of the sensor side unit 14, for example, the tank number is NO. It is connected to the oscillating circuit 21A of the sensor side unit 14A which becomes 1, and the other end side is connected to the arithmetic circuit 24 of the display side unit 23. The other sensor side units 14B, ..., 14N are connected in parallel via branch signal lines 26A, 26A, ... Connected to one end of the signal line 26, respectively.

Reference numeral 27 denotes a single intrinsically safe power supply circuit built in the display side unit 23. The intrinsically safe power supply circuit 27 is, for example, an intrinsically safe transformer, an intrinsically safe resistor, a thyristor or an optical element (all of which are not shown). It is configured as a safety intrinsic safety barrier circuit consisting of (1), and has a circuit configuration that suppresses the power supplied to the sensor side from becoming larger than the ignition energy. Further, the intrinsically safe power output from the intrinsically safe power supply circuit 27 is supplied toward the sensor side unit 14 using a power supply line 28.

Reference numeral 28 denotes a power supply line composed of a single twisted pair twisted wire, one end of the power supply line 28 is connected to the intrinsically safe power supply circuit 27, and the other end has a tank number N.
O. It is connected to the tank selection circuit 15 (counter circuit 17, coincidence determination circuit 18), switching circuit 20 and reset circuit 22 of the sensor-side unit 14A which becomes 1. Further, the other sensor side units 14B, ..., 14N are connected to the other end side of the power supply line 28 by a branch power supply line 28A,
28A, ... Are connected in parallel.

Reference numeral 29 indicates a designation circuit as a tank designation means for designating a desired liquid storage tank 1. The designation circuit 29 is constituted by including a keyboard, a push switch or the like, and a tank number for confirming the remaining amount of oil liquid. If you enter
A designation signal based on this tank number is input to the arithmetic circuit 24, and the arithmetic circuit 24 superimposes this designation signal on the power supply signal. Then, when the power supply signal is supplied to the sensor side unit 14 using the intrinsically safe power supply circuit 27, the designation signal is also transmitted to the sensor side unit 14.

Next, the arrangement of the sensor side unit 14 near the liquid storage tank 1 will be described with reference to FIG.

In FIG. 2, reference numeral 31 denotes a site of a gas station, in which the liquid storage tank 1 is embedded, and a plurality of holes (only one is shown) are formed in the liquid storage tank 1. One of them is provided with a manhole 32 for inserting the liquid level sensor 2, and the opening of the manhole 32 is covered by a lid 33.

Here, the above-mentioned sensor side unit 14
Are arranged on the bottom side of the manhole 32.

The liquid level measuring apparatus according to this embodiment is constructed as described above, and its operation will be described below.

First, in the power supply, the power is turned on by closing the main switch (not shown) of the display unit 23 in the building, and the display unit 2 is turned on.
Arithmetic circuit 24, indicator 25, intrinsically safe power supply circuit 2 in 3
7 and the designation circuit 29 are turned on.

On the other hand, in the sensor-side unit 14, the tank selection circuit 15 (counter circuit 1) is operated by the intrinsically safe power source supplied from the intrinsically safe power source circuit 27 through the power supply line 28.
7, the coincidence determination circuit 18), the switching circuit 20 and the reset circuit 22 are turned on. At this time, the reset circuit 2
2, the reset signal is output to the counter circuit 17 and the switching circuit 20 by inputting the intrinsically safe power source as shown in FIG. Here, the counter circuit 17 and the switching circuit 20
The reset signal is input to erase the stored designated signal and the coincidence signal in the previous measurement and restore the initial state, and the counter circuit 17 erroneously detects the waveform at power-on as a designated signal. I try to prevent this.

Next, the operator inputs a tank number to the designating circuit 29 of the display side unit 23 in the office of the gas station in order to designate the liquid storage tank 1 to be measured. It is superposed on the intrinsically safe power source output from the intrinsically safe power source circuit 27 via. Then, this intrinsically safe power source is supplied to the sensor side unit 14 via the power source line 28.

Here, the designation signal to be superimposed on the main safety power source becomes a pulse signal after the main pressure power source has risen, as shown in FIG. There are two pulses for the tank 1B, and N pulses for the liquid storage tank 1N.

On the other hand, in the sensor side unit 14, the counter circuit 17 extracts only the designated signal from the intrinsically safe power supplied to the tank selection circuit 15 through the power supply line 28, and is preset by the number setting circuit 16. The coincidence determination circuit 18 determines whether or not the coincidence with the number of the liquid storage tank 1 is made, and only when they coincide with each other, the coincidence determination circuit 18 outputs a coincidence signal. Therefore, only the sensor-side unit 14 corresponding to the number of the liquid storage tank 1 designated by the operator operates,
For example, NO. When the liquid storage tank 1A of No. 1 is designated, as shown in the upper part of FIG. 5, the sensor side unit 14A provided in the liquid storage tank 1A operates to supply the coincidence signal to the switching circuit 20 and the oscillation circuit 21. Then, the circuits 20 and 21 are turned on, and as shown in FIG. 6, the sensor units 6, 7 and 8 of the liquid level sensor 2 and the standard capacitor 12 are sequentially switched to be connected to the oscillation circuit 21 so as to be driven. A signal is output every predetermined time t to start the detection operation.

As a result, the oscillation circuit 21 outputs a frequency signal having an oscillation frequency based on the electrostatic capacitances C1, C2, C3 of the sensor units 6, 7, 8 of the liquid level sensor 2 and the reference capacitance C0 of the standard capacitor 12. It can be transmitted to the arithmetic circuit 24 of the display side unit 23 using the line 26. In the arithmetic circuit 24, the capacitances C1, C2, C3 of the sensor units 6, 7, 8 are determined by the oscillation frequency of this frequency signal.
Then, the reference capacity C0 of the standard capacitor 12 is calculated, and based on this electrostatic capacity, a calculation as shown in Japanese Patent Laid-Open No. 1-234320 is performed to obtain the liquid storage tank 1A.
Standard capacitor for liquid level, water level, dielectric constant, etc. inside 1
It can be measured in the state corrected by 2.

Furthermore, if the worker is NO. 2 storage tanks 1
When B is designated, the designation signal as shown in the middle part of FIG. 5 is supplied to the sensor side unit 14, and only the sensor side unit 14B provided in the designated liquid storage tank 1B operates, and By repeating the operation, the liquid level and the water level in the liquid storage tank 1B are measured.

However, in the liquid level measuring device according to the present embodiment, the sensor side unit 14 including the tank selection circuit 15, the switching circuit 20, the oscillation circuit 21 and the reset circuit 22 is provided near the liquid storage tank 1. Therefore, the distance between the oscillation circuit 21 and the liquid level sensor 2, the distance between the oscillation circuit 21 and the standard capacitor 12, etc. can be significantly shortened. As a result, the stray capacitance existing in the signal line connecting between them can be reduced, and the capacitance C1 of the upper liquid sensor unit 6 of the liquid level sensor 2 output to the oscillation circuit 21 and the lower liquid sensor unit 7 can be reduced. Capacitance C2 of the water sensor unit 8
Also, the reference capacitance C0 of the standard capacitor can be accurately detected, and the error in the oscillation frequency generated from the oscillation circuit 21 can be surely reduced. Further, by shortening the signal line, the influence of external conditions such as temperature and humidity can be reduced.

As a result, the oscillation frequency of the frequency signal transmitted to the arithmetic circuit 24 of the display-side unit 23 via the signal line 26 is the oscillation frequency corresponding to the electrostatic capacitance with a small error. In 24, the liquid level height and the water amount in the liquid storage tank 1 can be accurately measured, and the measurement accuracy can be improved.

Further, the tank selection circuit 15 provided in the sensor side unit 14 includes a number setting circuit 16 for storing a preset own storage tank number and a counter circuit for extracting a designation signal superimposed on the intrinsically safe power source. 17 and a coincidence determination circuit 18 for determining whether or not the own storage tank number set by the number setting circuit 16 and the designated signal match. As a result, it is possible to supply the designation signal via the power supply line 28, and it is possible to cause the tank selection circuits 15 of the sensor side units 14A to 14N to perform the determination processing substantially at the same time.

Therefore, as in the prior art, a number of signal lines for connecting a plurality of sensor sides in a safe place, which were necessary when transmitting a signal for starting the detection operation only from the sensor side designated from the outside. Can be abolished, and the display side unit 23 and the sensor side unit 14A are connected by using one signal line 26 composed of a twisted wire, and the other sensor side units 14B to
14N can be connected by branch signal lines 26A, 26A, ....

Further, since the designation signal transmitted to the sensor side unit 14 is superposed on the safety power source inputted from the display side unit 23, the power source line inputted from the display side unit 23 to the sensor side unit 14A. Can be connected by only one power supply line 28, and the other sensor side units 14B to 14N can be connected to the sensor side unit 14A by branch power supply lines 28A, 28A, ....

Furthermore, the oscillation circuit 21 and the liquid level sensor 2
Upper liquid sensor unit 6, lower liquid sensor unit 7, water sensor unit 8
Since the operation of the switches 9, 10, 11, 13 for sequentially switching the connection with the standard capacitor 12 is automatically switched by the switching circuit 20, the cable for this switching operation can be eliminated.

As a result, in the prior art, the liquid storage tank has 10
In the case of 10 channels, the number of wirings for connecting the sensor side and the display side was at least 70, but in the present embodiment, not only in the case of 10 channels, but also in the signal line 26. Since only two cables of the power supply line 28 and the power supply line 28 are required, the number and length of the cables can be significantly reduced, the cost of wiring material can be reduced, and the labor for installation work can be surely reduced.

Further, since the gas station handles dangerous materials such as gasoline, it is necessary for the electric equipment to constitute intrinsically safe explosion-proof. However, in this embodiment, the sensor side unit 1
Since there are only two cables, the power supply line 28 and the signal line 26, which connect the 4 and the display side unit 23, only one intrinsically safe power supply circuit 27 needs to be provided in the display side unit 23. The number of intrinsic safety barrier circuits required for the number of liquid storage tanks can be reduced to one, and the display-side unit 23 can be downsized.

In the above embodiment, the liquid storage tank 1 is set to 1
Although the case of 10 channels provided with 0 pieces has been described, the present invention may have a single liquid storage tank 1. In this case, the tank number of the number setting circuit 16 of the tank selection circuit 15 is set to NO. It may be set as 1.

Further, in the above-described embodiment, the intrinsic safety power supply circuit 27, which is a safety intrinsic safety barrier circuit, is connected only to the power source side, but the intrinsic safety barrier circuit may be provided also on the signal line 26 side. Of course.

Further, although the coincidence determination circuit 18 and the switching circuit 20 constituting the tank selection circuit 15 are configured as hard circuits, the present invention is not limited to this, and may be processed by software by a CPU or the like.

Furthermore, although each liquid level sensor 2 is described as comprising the outer cylinder 3, the upper inner cylinder 4A, the lower inner cylinder 4B and the water detecting inner cylinder 4C, the upper inner cylinder 4A and the lower inner cylinder 4B are described. It may be configured as one inner cylinder, or the water detection inner cylinder 4
C may be provided as necessary, and the inner cylinder 4
C may be eliminated, and the liquid level sensor 2 may be a coaxial cylindrical sensor of various types as long as the liquid level can be detected.

[0058]

As described in detail above, according to the invention of claim 1, a tank selection circuit, a switching circuit and an oscillation circuit corresponding to the number of the respective tanks are provided on the liquid storage tank side, respectively.
Since a single arithmetic circuit, intrinsically safe power supply circuit and tank designating means are provided in a safe place away from each of the liquid storage tanks,
The cable that connects the safe place and the liquid storage tank side is based on the capacitance of the power supply line that supplies the safe power supply with the specified signal superimposed from the safe place to the liquid storage tank side and the oscillation circuit on the liquid storage tank side. Since only the signal line that transmits the frequency signal oscillated by a safe place is sent, the stray capacitance of a long cable can be significantly reduced as an electrostatic capacitance compared to the case where an oscillation circuit is installed in a safe place. The liquid level can be measured with high accuracy based on the oscillation frequency of the frequency signal input to the circuit. Also, the number and length of cables can be reduced,
The cost can be reduced.

According to the second aspect of the present invention, since the switching circuits, the tank selection circuit, and the oscillation circuit are respectively provided in the manholes into which the sensors of the liquid storage tanks are inserted, the liquid level sensor inserted into the liquid storage tanks and The standard capacitor located in the vicinity can be brought close to the oscillation circuit via the switching circuit, and the cable connecting the oscillation circuit, the liquid level sensor and the standard capacitor can be shortened. As a result, the stray capacitance of the cable added to the capacitance output from the liquid level sensor or standard capacitor can be made extremely small, and the cable error added to the oscillation frequency output from the oscillation circuit can be reduced. Can be measured with higher accuracy.

According to the third aspect of the invention, since the liquid level is measured, a reset circuit is provided for outputting a reset signal when it is detected that the supply of the intrinsically safe power source is started via the power source line. The tank selection circuit and the switching circuit can be set to the initial state before the designation signal is input to the tank selection circuit together with the intrinsically safe power supply via the power source, and malfunctions at power-on can be prevented.

[Brief description of drawings]

FIG. 1 is a system diagram showing an entire liquid level measuring device according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a state in which a liquid level sensor is inserted in a liquid storage tank.

FIG. 3 is an enlarged cross-sectional view showing a liquid level sensor used in an example.

FIG. 4 is a block diagram showing a sensor side unit, a liquid level sensor and a standard capacitor shown in FIG.

FIG. 5 is a waveform diagram showing the intrinsically safe power supply input to the tank selection circuit and the reset signal and the coincidence signal output.

FIG. 6 is a waveform diagram showing a coincidence signal input to the switching circuit and a drive signal output to the switching circuit.

[Explanation of symbols]

 1A, 1B, ..., 1N Storage tank 2A, 2B, ..., 2N Liquid level sensor 3 Outer cylinder 4 Inner cylinder 4A Upper inner cylinder 4B Lower inner cylinder 4C Water detection inner cylinder 6 Upper liquid sensor section 7 Lower liquid sensor Part 8 Water sensor part 12A, 12B, ..., 12N Standard capacitor 14A, 14B, ..., 14N Sensor side unit 15 Tank selection circuit 16 Number setting circuit 17 Counter circuit 18 Match determination circuit 20 Switching circuit 21 Oscillation circuit 22 Reset circuit 23 Display Side unit 24 Arithmetic circuit 25 Indicator 26 Signal line 27 Intrinsic power supply circuit 28 Power supply line 29 Designating circuit (tank designating means) 32 Manhole

Claims (3)

[Claims] 1. A liquid level measuring device for measuring the liquid level of an oil liquid stored in one or more liquid storage tanks, wherein the liquid level measuring device detects the electrostatic capacity of the oil liquid stored in each of the liquid storage tanks. A coaxial cylindrical liquid level sensor including an outer cylinder and an inner cylinder to be inserted into each liquid storage tank, and a known reference volume provided near each liquid level sensor in each liquid storage tank. And a standard capacitor having a storage unit for storing its own preset storage tank number, which is provided in the vicinity of each storage tank, and is detected when a designated signal for designating the own storage tank number is input. A tank selection circuit that starts operation, and a tank selection circuit that is provided in the next stage of each tank selection circuit, and when its own storage tank number is designated by each tank selection circuit,
A switching circuit for sequentially switching between a state in which the liquid level sensor is connected between the inner and outer cylinders and a state in which the liquid level sensor is connected to a standard capacitor, and a switching circuit of each of the liquid storage tanks in the vicinity of the switching circuit. Oscillation which is provided in the vicinity and oscillates a frequency signal having an oscillation frequency corresponding to the reference capacitance of the electrostatic capacitance formed between the outer cylinder and the outer cylinder of each liquid level sensor by switching of each switching circuit. A circuit, a single arithmetic circuit provided in a safe place separated from each of the liquid storage tanks, for calculating the liquid level height corresponding to a frequency signal, and the frequency signal from each of the oscillation circuits. A single signal line, one end of which is connected to each oscillation circuit and the other end of which is connected to an arithmetic circuit for outputting to Output of intrinsically safe power supply circuit In order to supply the intrinsically safe power from the intrinsically safe power supply circuit to the oscillation circuits, the tank selection circuit and the switching circuit, one end side is connected to the intrinsically safe power supply circuit and the other end side is the oscillation circuits and the tank selection circuit. A single power supply line connected to the circuit and the switching circuit, and to specify a desired liquid storage tank among the respective liquid storage tanks, the power supply line is used to output a designation signal to the respective tank selection circuits. A liquid level measuring device comprising a tank designating means. 2. The liquid level measuring device according to claim 1, wherein each of the switching circuit, the tank selection circuit, and the oscillation circuit is provided in a manhole into which a sensor is inserted in each of the liquid storage tanks. 3. When it is detected that the supply of the intrinsically safe power source is started near the tank selection circuit and the switching circuit by using the power supply line for measuring the liquid level,
3. The liquid level measuring device according to claim 1, further comprising a reset circuit for outputting a reset signal to each of the tank selection circuit and the switching circuit.