JPH0370773B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a liquid level measuring device, and particularly to a capacitive liquid level measuring device for measuring the amount of liquid, such as fuel oil, contained in a tank. Related to equipment.

(Prior art) Two metal plates constituting a positive electrode and a negative electrode are placed facing each other in a container, and when a liquid such as gasoline is introduced into the container, the capacitance value between the two electrodes increases to the level of the liquid level. It is well known that it changes depending on the situation. This is because the dielectric constant of the air, which is not immersed in the liquid, is approximately 1.0.
, while the dielectric constant of gasoline is approximately 2.1. In other words, the capacitance value increases as the height of the liquid level increases.

A liquid level measuring device that uses the above principle, that is, a measuring electrode with a positive electrode and a negative electrode is placed inside the tank, measures the capacitance value between the two electrodes, calculates the liquid level height from this, and also takes tank dimensions into consideration. Conventional equipment for measuring liquid volume uses an LC oscillator to convert the capacitance measured by a liquid depth measuring electrode and a reference electrode placed in a position that is constantly immersed in the liquid into a frequency. The liquid level is calculated based on both frequencies, and the liquid volume is calculated from the liquid level and the calculated liquid volume is displayed.

In this liquid level measuring device, the capacitance of the electric wire between the measuring electrode and the LC oscillator (frequency conversion means) is added to the capacitance measured by the measuring electrode. In order to reduce this, an LC oscillator is installed near the measurement pole.

(Problem to be solved by the invention) By installing the LC oscillator near the measurement pole in this way, the influence of capacitance due to the electric wire is reduced, but on the other hand, the influence of the capacitance due to the electric wire is reduced. There is a disadvantage that mechanical stress from the LC oscillator acts on the LC oscillator and affects the frequency conversion.

Therefore, an object of the present invention is to enable accurate frequency conversion without being affected by gas or mechanical influences as described above when an LC oscillator is provided near a measurement pole.

(Means for Solving the Problems) According to the present invention, the above object is to change the capacitance measured by the liquid depth measuring electrode and the comparison electrode provided at a position constantly immersed in the liquid through a switching means. In a capacitive liquid volume measuring device that converts each frequency into a frequency using a single LC oscillator, calculates the liquid level based on both frequencies, calculates the liquid volume from the liquid level, and displays the liquid volume. The liquid depth measurement electrode has two hollow cylindrical members arranged concentrically to constitute a positive electrode and a negative electrode, and is configured such that the object to be measured can freely flow in and out between these two electrodes, and the comparison electrode is A larger number of hollow cylindrical members than the liquid depth measurement electrode are arranged concentrically to form a positive electrode and a negative electrode, and the object to be measured is configured to freely flow in and out between these two electrodes, and the comparison electrode is A hollow cylindrical column in which a level transmitter is arranged at the lower end of the liquid depth measuring electrode, and the switching means, the LC oscillator, and a board on which they are mounted are embedded in an insulating resin, and the level transmitter is arranged above the liquid depth measuring electrode. This is achieved by housing it in a shaped member.

(Example) FIG. 1 shows an outline of a liquid amount measuring device according to the present invention, which is applied to measuring the amount of liquid, especially gasoline, contained in a tank buried underground. Although only one underground tank RS containing fuel oil F is shown in this figure, in reality, a plurality of underground tanks RS may be installed. A detector DT belongs to each underground tank RS. This detector DT, which will be described in detail later in connection with FIGS. 2 and 3, is constructed as a capacitance measuring rod, is inserted upright in an underground tank RS, and includes a water sensing pole. A comparison electrode CP, which is constantly immersed in the liquid, and a liquid depth measurement electrode MP, which is placed above the comparison electrode and measures the capacitance value according to the oil level.
and a level that has a built-in reference electrode and converts the capacitance values measured with the comparison electrode and liquid depth measuring electrode and the capacitance values measured with the built-in reference electrode into frequencies and sends them out as output. It is equipped with a transmitter LF. The output from the level transmitter LF dedicated to each underground tank RS is inputted via a signal line A to a control box CB installed in an office or the like. The control box CB includes a numerical display 1 that is common to each tank and displays the tank number, liquid level, etc., an upper limit indicator lamp 2 for the liquid level in each tank, and a lower limit indicator lamp 3 for each tank.
, a tank water level notification lamp 4, a tank selection button 5, a printer 6 and its operation button 7, a notification buzzer 8 for making this into audible information when the notification lamps 2, 3, and 4 are activated, and a control. A data input key 9 is provided inside the lower cover of the box CB. Further, an alarm device 10 installed at a desired location is connected to a control box CB by a signal line 11, and its operation button 7' is provided in the control box CB.

FIG. 2 shows in detail the structure of the detector DT section shown schematically in FIG. The lower part of this detector DT is placed against the inner bottom of the underground tank RS to prevent the inflow of fuel oil F or water that has been separated from the fuel oil or has entered the tank for some reason. A cannula 12 of electrically insulating material is disposed with an enabling opening 121 formed therein. Above this mantle 12 are metal concentric multiple pipes 13, 1.
3', 13'', 14, 14', 14'', with the outermost pipe as the negative electrode, and the electrodes are arranged alternately like positive electrode - negative electrode - positive electrode, etc., and the positive electrodes 14, 14', 14'' are made of an insulating material support member. A comparative electrode CP is disposed, which is supported by a conductive member 15 and connected to a conductive member 16, and whose negative electrodes 13, 13', 13'' are supported by a support member 17 made of conductive material. The concentric multiple pipes constituting the comparison pole CP are connected to the inside of the mantle 12 through an opening (not shown) formed in the support member 17, and are constantly filled with fuel oil F. Moreover, it is preferable that the comparison electrode CP has a built-in water detection electrode 19 in its lower part. Above the comparison electrode PC, an outer pipe 20 composed of a double metal pipe is used as a negative electrode, and an inner pipe 21 is used as a positive electrode, so that heating oil F enters between the two pipes through the comparison electrode CP. A liquid depth measurement pole MP is installed. This liquid depth measuring pole
The negative electrode of MP, that is, the lower end of the outer pipe 20 is electrically connected to the negative electrode 13 of the comparative electrode CP by a conductive support member 22, and the upper end is supported by a conductive support member 23. On the other hand, the lower end of the positive electrode, that is, the inner pipe 21 is connected to the supporting member 15 (this member has an opening (not shown) between the multiple pipes constituting the comparative electrode CP and the inner and outer parts of the liquid depth measuring pole MP. The inner and outer pipes 20 and 21 are connected to each other so that the fuel oil F can enter between the inner and outer pipes 20 and 21 from below, and the upper end is made of an insulating material. It is supported by a support member 24 made of aluminum. There is a comparison electrode inside the inner pipe 21.
A conducting wire 25 connected to the positive electrode of the CP is arranged to transmit capacitance information measured at the comparison electrode CP including the water sensing electrode 19. An opening 201 is bored near the upper end of the outer pipe 20, so that the fuel oil can easily enter between the inner and outer pipes 20, 21. Above the liquid depth measurement pole MP, there is a level transmitter LF disposed in a metal pipe 26, a joint pipe 29 connected above the pipe 26 via a conductive support member 27, and a joint pipe 29 connected above the pipe 26 via a conductive support member 27. A head box 30 is provided to maintain the water detection electrode 19 in a vertical position and to conveniently maintain the comparison electrode CP including the water detection electrode 19, the liquid depth measurement electrode MP, and the level transmitter LF.
and are arranged. Comparative pole CP with the above mantle 12
The outermost pipe to the pole 13, the outermost pipe 13
and the outer pipe 20 of the liquid depth measuring pole MP, the outer pipe 20 and the metal pipe 26 in which the level transmitter LF is installed, and the metal pipe 26 and the joint pipe 29.
The detector DT is connected to the detector DT by an appropriate fixing means such as a screw. Therefore, by removing the fixing member, the detector DT can be disassembled, and parts can be easily replaced. A net-like member 31 is provided at the upper part of the sleeve 12 to prevent dust, etc., which may be suspended in the liquid in the tank, from reaching the comparison electrode or the liquid depth measuring electrode. There is. The comparison electrode CP is constructed as a concentric multiple pipe, which increases the electrode plate area without increasing its height or length, and the capacitance value is almost the same as that measured by the liquid depth measurement electrode. This is to enable accurate measurement of changes in capacitance depending on liquid type and liquid temperature. The level transmitter LF is connected to the pipe 26, which is a negative electrode, by a signal line 32,
Capacitance value measured at comparison electrode CP including water detection electrode 19 sent from signal line 25 and signal line 3
The capacitance values measured by the measuring electrode MP sent from 3 are converted into frequencies, and the capacitance values measured by the reference electrode, which has a reference electrode, are converted into frequencies, and these It transmits the frequency as an output to the control box CB (see Fig. 1) via the signal line 34, and is equipped with various elements as described later in connection with Fig. 3. The upper and lower sides are attached to a substrate 37 supported by insulating support members 35 and 36, and the substrate 37 is disposed within the metal pipe 26 and is embedded in an insulating synthetic resin, such as an epoxy resin 38. The joint pipe 29 serves as a so-called mounting pipe provided for convenience in installing the comparison electrode (including the water detection electrode), the liquid depth measurement electrode, and the level transmitter, which are measurement units. In other words, each underground tank RS has a different burial depth and a different diameter size.On the other hand, the comparison electrode including the water detection electrode must be placed near the bottom of the tank due to its nature, and the liquid depth measurement electrode must be placed inside the tank. In addition, the level transmitter converts the capacitance value, which is analog information, into frequency, which is digital information, and since the capacitance value changes depending on temperature changes, it must be located close to the measurement pole. must be placed. For this purpose, a joint pipe 29 is provided, and the joint pipe is set to be relatively long and can be cut at the time of construction according to the buried depth of the tank and the tank diameter.

Figure 3 is a block diagram of the level transmitter LF, which includes two relays (contact relays) RF ₁ and RF ₂ ,
LC oscillation circuit OSC and reference pole (reference capacitor)
It consists of RC. The reference capacitor that makes up the reference electrode RC is a high-grade capacitor whose capacitance value does not change much due to temperature changes or aging, and its capacitance value is approximately the same as the value measured by the comparison electrode and liquid depth measuring electrode. Those of similar quality are selected. In this level transmitter, line 33 is the measuring pole
The line 25 is connected to the positive electrode or inner pipe 21 of the MP, the line 25 is connected to the positive electrode of the comparison electrode CP, and the line 32 is connected to the common outer electrode or negative electrode of the measurement electrode and the comparison electrode. The LC oscillator circuit OSC is equipped with a coil and a capacitor, and has the function of oscillating into a frequency signal based on capacitance signals sent from the liquid depth measuring pole, comparison pole, and reference capacitor RC. Note that lines a and b of the level transmitter LF are relay lines, f is a transmission line for the measured frequency signal, and line g is a ground line.

Figure 4 is a block diagram showing the control box CB part shown in Figure 1 in slightly more detail in connection with the case where multiple tanks (5 in Figure 4) are provided. be. In this figure,
TDSC is a switching circuit, and lines A ₁ to _{A 5} are the first
This is a signal line from the level transmitter of tank No. 5 to the level transmitter of tank No. 5, and is connected to the control circuit CPU.
The switching circuit TDCS is sequentially switched by signals from the TDCS. The signal from the switching circuit is sent to the memory circuit MEC via the receiving circuit REC.
The memory circuit MEC calculates the liquid depth from the frequency converted by the LC oscillation circuit based on the capacitance values measured at the reference electrode, comparison electrode, and liquid depth measurement electrode, and calculates the liquid volume from the liquid depth. The calculation formula, upper and lower limit liquid volume values for each tank, etc. are stored, and each tank has a liquid volume storage area. Arithmetic circuit
OPC is the signal from the receiving circuit REC and the memory circuit MEC
Calculate the liquid volume using the calculation formula signal stored in the
It is also determined whether the liquid volume corresponds to the upper limit or lower limit liquid volume value stored in the memory circuit MEO. The signal from this arithmetic circuit OPC is then sent to a display-printer (IDC=PTC).
The circuit (IDC+PTC) is connected to a notification buzzer 8, notification lamps 2, 3, 4 display meter 1, and a printer 6. Tank selection button 5, printer operation button 7, timer TM, input key 9, alarm button 7', alarm circuit
The AR and each of the above-mentioned circuits are connected to a control circuit CPU.

Next, the device of the present invention will be explained in relation to its operation.

Switching circuit by signal from control circuit CPU
When the TDSC is connected to the signal line A ₁ from the level transmitter LF of the No. 1 tank, a signal is first sent to the relays RE ₁ and RE ₂ of the level transmitter, and these relays are switched to become the standard. pole (reference capacitor)
A frequency signal connected from the RC to the LC oscillator OSC and responsive to the capacitance value measured by the reference pole is stored in the storage circuit MEC via the receiving circuit REC. Next, the signal to relay RE ₂ disappears, and the signal line 25 from the comparison pole CP is connected to the LC oscillator OSC, and the signal line 25 from the comparison pole CP is connected to the comparison pole CP.
A frequency signal responsive to the capacitance value measured by the CP is stored in the storage circuit MEC via the receiving circuit REC. Finally, the signal to relay RE ₁ disappears, and the signal line 33 from the liquid depth measuring pole MP is connected to the LC oscillator OSC, and the frequency signal responsive to the capacitance value measured by the measuring pole MP is transmitted to the receiving circuit.
It is stored in the memory circuit MEC via REC. These frequency signals stored in the memory circuit MEC are converted into liquid volume in the arithmetic circuit OPC using a liquid volume calculation formula already stored in the memory circuit, and this calculated liquid volume is also stored in the memory circuit. It is compared with the upper and lower limit liquid volume values of the tank, and if it is above the upper limit, the notification lamp 2 is turned on and the buzzer 8 emits an alarm, and if it is below the lower limit, the notification lamp 3 is turned on and the buzzer 8 is turned on. sounds an alarm.

The time required to measure the liquid volume per tank is approximately 1 second, and when the liquid volume measurement of the first tank is completed, the switching circuit TDSC switches according to the signal from the control circuit CPU, and the signal A ₂ from the second tank is switched. The liquid level in the second tank is measured in the same manner as described above. This liquid amount measurement operation is repeated up to the final tank, for example, the fifth tank, and the liquid amount from the first tank is measured again. In other words, the liquid volume measurement in each tank is always performed in a linked manner.

Here, the liquid level of the tank designated by pressing the tank designation button 5 is displayed on the display meter 1 together with the designated specific tank number, and if the tank designation button 5 is reset, the liquid volume of the tank designated by pressing the tank designation button 5 is displayed on the display meter 1. is a timer
The time signal from the TM is displayed, and in other words, the display meter 1 functions as a digital clock when it is not used to display the liquid amount.

If the printer button 7 is pressed while the tank designation button 5 is pressed, the printer 6 will print out the current time and the amount of liquid in the designated tank.

Furthermore, if the alarm button 7' is pressed at the end of the supply of liquid in the tank, for example when the gas station is closed, the amount of liquid in each tank at that time will be stored in the memory circuit MEC, and if there is any problem in the tank, for example. If the liquid level changes by more than a certain amount due to water intrusion or theft, an alarm signal is generated from the alarm circuit AR, and this signal activates an alarm 10 installed at a desired location, for example, at a security company. is being done. This liquid volume change signal is sent to the control circuit CPU and printer circuit PTC.
It is also possible to start the printer 6 via the printer 6 and print out the time and the changed liquid amount.

Note that when water accumulates up to the water detection electrode 19, the capacitance value increases rapidly because the dielectric constant of water is 81.6. Therefore, when the comparison electrode is connected to the LC oscillator, the oscillation frequency becomes abnormal. This causes the water alarm lamp 4 to light up and/or the buzzer 8 to notify the user audibly. Draining water in a tank is carried out using a conventional method, but in a tank where the device of the present invention is installed, the water surface height is usually at the level of the water detection electrode, and therefore the amount of water can be estimated, so the water draining operation is also easy. This can be done relatively easily.

(Effects of the Invention) As detailed above, the liquid level measuring device of the present invention includes a switching means and an LC oscillator (frequency conversion means).
A level transmitter with the circuit board on which these are mounted is embedded in insulating resin is installed above the measurement electrode, which not only avoids the influence of capacitance due to the electric wire from the measurement electrode to the LC oscillator. The influence of surrounding gas on the LC oscillator can also be avoided, and the level transmitter is made rigid, eliminating the influence of external mechanical stress. At the same time, the liquid depth measuring electrode is made into a double tube, and the comparison electrode, which must be immersed in the liquid at all times, is made into a multi-tube. The large surface area allows the liquid depth measurement electrode to be relatively long and the comparison electrode to be short, allowing it to detect changes in the liquid level in the tank over a wide range, and also detect liquid type. The value measured by the liquid depth measuring electrode is corrected in response to changes in the dielectric constant of the liquid to be measured due to disturbances such as temperature changes and other disturbances, thereby making it possible to always accurately measure the liquid volume.

[Brief explanation of drawings]

FIG. 1 is a drawing schematically showing a liquid level measuring device according to the present invention, which is applied to measuring the amount of liquid, especially fuel oil, in an underground tank, and FIG. 2 is a longitudinal sectional view showing the detector portion and details. 3 is a block diagram showing a level transmitter, and FIG. 4 is a block diagram schematically showing a control circuit and related auxiliary circuits. Liquid depth measurement electrode...MP, positive electrode (inner pipe)...
21, Negative electrode (outer pipe)...20, Liquid to be measured...F, Comparison electrode...CP, Level transmitter...LF,
LC oscillator...OSC, board...37, switching means...
...RE ₁ , insulating resin.

Claims (1)

[Claims] 1. The capacitance measured by the liquid depth measuring electrode and the comparison electrode provided at a position constantly immersed in the liquid is converted into a frequency by one LC oscillator via a switching means, respectively,
In a capacitive liquid level measuring device that calculates the liquid level based on both frequencies, calculates the liquid volume from the liquid level, and displays the liquid volume, the liquid depth measuring electrode is made of two hollow cylinders. The shaped members are arranged concentrically to constitute a positive electrode and a negative electrode, and the object to be measured is configured to freely flow in and out between these electrodes, and the comparison electrode has a larger number of hollow cylinders than the liquid depth measuring electrode. The shaped members are arranged concentrically to constitute a positive electrode and a negative electrode, and the liquid to be measured is configured to freely flow in and out between these electrodes, and the comparison electrode is arranged at the lower end of the liquid depth measuring electrode, The level transmitter, which is constructed by embedding the switching means, the LC oscillator, and the board on which they are mounted in an insulating resin, is housed in a hollow cylindrical member disposed above the liquid depth measuring electrode. Capacitive liquid level measuring device.