JPH11248516A - Capacitive level measuring apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately and linearly measure the liquid level of liquid to be measured, with a simple and small structure, in a capacitive level measuring apparatus. SOLUTION: An auxiliary electrode 5 and a main electrode 7 are arranged in parallel. An equal potential electrode 29 is arranged in the lower tip parts of the electrodes 5 and 7, maintaining intervals from them. A reference electrode 39 is arranged between the electrodes 7 and 29, maintaining intervals from them. The electrodes 7, 29 and 39 are accommodated in a cylindrical insulation layer 19 having a bottom. The layer 19 in which the electrodes are collectively accommodated is inserted in an insulation vessel 3 containing liquid 1 to be measured. An AC signal is applied to the auxiliary electrode 5 from a signal source 9. The main electrode 7, the equal potential electrode 29 and the reference electrode 39 are connected with equal potential forming parts 37, 49 through shielded-conductor cables 31, 41. The equal potential forming parts 37, 49 maintain the main electrode 7, the reference electrode 39 and the equal potential electrode 29 at equal potentials.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a capacitance-type level measuring device, and more particularly to an improvement in a capacitance-type level measuring device for measuring a conductive and insulating liquid level (liquid level).

[0002]

2. Description of the Related Art For example, a capacitance type level measuring device is used for measuring a chemical level in a cleaning tank of a semiconductor manufacturing apparatus, measuring a level of a liquid food in a food processing apparatus, and measuring a liquid level in a general factory. Conventionally, as shown in FIG. 9, a capacitance type level measuring device of this type inserts a long and thin auxiliary electrode 5 and a main electrode 7 into an insulating tank 3 containing a liquid to be measured 1 from above the liquid level, and It is well known that a source 9 outputs, for example, an AC signal applied to the auxiliary electrode 5 through the main electrode 7 and the level of the liquid 1 to be measured is measured from the output signal.

Generally, the capacitance value generated between the auxiliary electrode 5 and the main electrode 7 is proportional to the area of the auxiliary electrode 5 and the dielectric constant of the intervening substance if the distance between the auxiliary electrode 5 and the main electrode 7 is constant. From the above, the change in the dielectric constant of the gas or the liquid 1 to be measured interposed between the auxiliary electrode 5 and the main electrode 7,
The capacitance value changes in proportion to the change in the liquid level, and an AC signal accompanying the change in the capacitance value is output from the main electrode 7. Therefore, the AC signal output from the main electrode 7 is converted into a voltage by the conversion unit 11, rectified and smoothed by the rectification and smoothing unit 13, and the reference unit (zero level point) and the output gradient (full scale) are adjusted by the adjustment unit 15. If adjusted, it is possible to output a measurement signal corresponding to the liquid level of the liquid 1 to be measured.

However, when the liquid 1 to be measured is conductive, the auxiliary electrode 5 and the main electrode 7 are short-circuited at the moment of touching the liquid 1 to be measured, making it difficult to measure the liquid level. The outer circumferences of the electrode 5 and the main electrode 7 are covered with insulating layers 17 and 19 to a uniform thickness. The capacitance type level measuring device using the auxiliary electrode 5 and the main electrode 7 covered with the insulating layers 17 and 19 can be used for measuring the liquid level of the insulating liquid 1 to be measured. Therefore, the insulating layer 1
The concept of measuring the liquid level in a capacitance-type level measuring device using the auxiliary electrode 5 and the main electrode 7 covered with the electrodes 7 and 19 will be described with reference to, for example, a conductive object to be measured.

In FIG. 9, the capacitances of the insulating layers 17 and 19 surrounded by gas (air) are Ce1 and Ce2, and the capacitances of the insulating layers 17 and 19 surrounded by the liquid 1 to be measured are C11 and C1.
l2, insulating layer 1 at the lower end of auxiliary electrode 5 and main electrode 7
Assuming that the capacitances formed by the electrodes 7 and 19 are Cs1 and Cs2, an equivalent circuit between the auxiliary electrode 5 and the main electrode 7 is shown in FIG.
become that way.

Further, if the auxiliary electrode 5, the main electrode 7, and the insulating layers 17 and 19 have the same dimensions, Cl1 = Cl2 = Cl, Cs1 = Cs2 = Cs, and a series circuit of capacitances Ce1, Ca and Ce2. To C
If A, it is simplified as shown in FIG. 10B.

Here, the liquid to be measured 1 in the insulating tank 3 in FIG.
Is empty, let CAo be the capacitance due to gas between the auxiliary electrode 5 and the main electrode 7, and Clo be the capacitance of each of the insulating layers 17 and 19 with respect to the length Lo of the auxiliary electrode 5 and the main electrode 7. Cl = (L / Lo) Clo CA = [(Lo−L) / Lo] CAo, and the combined capacitance C between the auxiliary electrode 5 and the main electrode 7 is C = [(Cl + Cs) / 2] + CA = ｛ [(L / 2Lo) Clo] + [(Lo-L) / Lo) CAo] + (Cs / 2)]｝ = {(L / Lo) [(Clo / 2) -CAo]} + CAo + (Cs / 2 ).

If the positions and dimensions of the auxiliary electrode 5 and the main electrode 7 are constant including the insulating layers 17 and 19, the capacitances CAo and Cs / 2 become constants. By electrically calculating [CAo + (Cs / 2)], C = {(L / Lo) [(Clo / 2) -CAo]} + CAo + (Cs / 2)-[CAo + (Cs / 2) )] = (L / Lo) [(Clo / 2) −CAo], and an electrostatic capacity proportional to the liquid level of the liquid 1 to be measured can be obtained.

[0009]

However, in the capacitance-type level measuring device having the above-described structure, the independent auxiliary electrode 5 and the main electrode 7 are separately separated in the biaxial state while maintaining the parallel positional relationship. Since it is necessary to insert it inside and hold it by an appropriate holding means, the structure becomes complicated and downsizing tends to be difficult. further,
As shown in FIG. 9, the capacitance-type level measuring device is generally arranged such that the insulating tank 3 is arranged on the ground 21 via the insulating base 23, so that an accurate liquid level can be measured. It is not sufficient to consider only the capacitance distribution between the auxiliary electrode 5 and the main electrode 7 in the insulating tank 3, and the capacitances Cx 1, Cx 2 between the side and bottom of the insulating tank 3 and the ground 21 are not enough. In addition, it is necessary to consider the capacitance Cg between the conversion unit 11 and the ground 21.

Further, as shown in FIG. 11, the insulating tank 3 is arranged on the high insulating base 23, and the valve 2
5 is connected to the insulating tank 3, the liquid 1 to be measured in the pipe 27 before and after the valve 25 is connected.
It is also necessary to consider the capacitances Cx3 and Cx4 between the ground and the ground 21. Then, each capacitance Cx1, Cx2, Cx3, Cx4 between the insulating tank 3 and the ground 21, the conversion unit 11 and the ground 2
FIG. 12 shows an equivalent circuit in which the capacitance Cg between the two is considered.

Here, the alternating current input from the auxiliary electrode 5 is the current ix flowing through the capacitances Cx1 to Cx4 and Cg.
In order to output a linear measurement current im corresponding to the liquid level fluctuation from the main electrode 7, the voltage VM across the series-parallel circuit of the capacitances Cx1 to Cx4 and Cg is lost.
Needs to be constant.

Furthermore, to make the voltage VM between both ends constant with respect to the fluctuation of the liquid level, it is necessary to obtain [(L / Lo) Clo] + Cs = α ｛[(Cx1 + Cx
2 + Cx3 + Cx4) Cg] / (Cx1 + Cx2 + Cx
3 + Cx4 + Cg)｝ [α is a constant of proportionality], but it is not true at all, and the liquid level change cannot be obtained in a linear state. However, in order to measure the liquid level change in a linear state, as shown in the equivalent circuit diagram of FIG.
A method has been proposed in which the output of the signal source 9 is grounded for measurement.

In the equivalent circuit in which the output of the signal source 9 is grounded, for example, (Cl1 + Cs1) << (Cx1 +
Cx2 + Cx3 + Cx4) and (Cl2 + Cs2) <
In the case of <(Cx1 + Cx2 + Cx3 + Cx4), FIG.
It is considered that Cl1 + Cs1 + (Cx1 to Cx4) is in a short-circuit state when viewed from Cl2 + Cs2, and a linear change in capacitance with respect to a change in the liquid level of the test liquid 1 is considered to be obtained.

However, in the case where the equivalent circuit of FIG. 14 is established in the capacitance type level measuring device, FIG.
As shown in FIG. 5, it is necessary to satisfy the conditions that the bottom of the insulating tank 3 is thin, the bottom area of the insulating tank 3 is large with respect to the ground 21, and the interval between the ground 21 and the insulating tank 3 is narrow. It is necessary to place the insulating tank 3 having a large bottom area directly on the ground 21. In addition, the actual use state of the capacitance type level measuring device is, for example, as shown in FIG. 11, through the pipe 27 in which the insulating tank 3 is placed on the supporting columnar insulating stand 23 and the valve 25 is arranged in the middle. In general, the liquid 1 to be measured flows into and out of the insulating tank 3 with the condition that the capacitance is (Cl1 + Cs
1) >> (Cx1 + Cx2 + Cx3 + Cx4)

Therefore, even if a person approaches the insulating tank 3, the capacitances Cx 1 and Cx 2 increase rapidly and become unstable, and the liquid 1 to be measured is transferred between the insulating tank 3 and the outside by opening and closing the valve 25. When they flow in and out, their capacitance C
x3 and Cx4 change and the output becomes unstable. As described above, in the capacitance type level measuring device of FIG.
In the configuration in which the auxiliary electrode 5 is grounded to the ground 21 as shown in FIG. 15, the insulating tank 3 having a large bottom area is connected to the ground 21 as shown in FIG.
The effect is expected only when measuring directly by placing
Other configurations have little effect, are not practical, and have large errors.

The present invention has been made in order to solve such a conventional drawback, and has a simple structure, easy miniaturization, and irrespective of the installation form and shape of the container storing the liquid to be measured. It is an object of the present invention to provide a capacitance type level measuring device capable of accurately and linearly measuring a liquid level of a liquid to be measured.

[0017]

In order to solve such a problem, the present invention provides an elongated main electrode which is inserted downward into a liquid to be measured and outputs an output signal corresponding to the level of the liquid to be measured. An elongated auxiliary electrode which is inserted downward into the liquid to be measured in a parallel positional relationship with the main electrode, and is disposed at least at the tip of the main electrode among the main electrode and the auxiliary electrode. The same potential electrode, a reference electrode which is arranged along the auxiliary electrode with a space between the main electrode and the same potential electrode and outputs a correction signal for correcting the output signal, and an AC signal is supplied to the auxiliary electrode. An electrostatic capacitance level measuring device comprising: a signal source to be applied; and an equipotential forming section that forms an ac equipotential state between the main electrode, the equipotential electrode, and the reference electrode. Electrode, same potential electrode Fine reference electrode is formed by arranging the rod-like insulating body.

In the present invention, an electrostatic shielding member may be provided between the main electrode and the reference electrode and the auxiliary electrode. Further, according to the present invention, it is preferable that the electrostatic shielding member is formed to extend from the same potential electrode with a rod having a width equal to or larger than the width of the main electrode and the auxiliary electrode.

[0019]

Embodiments of the present invention will be described below with reference to the drawings. Note that the same reference numerals are given to portions common to the conventional example.

FIG. 1 is a diagram showing a capacitance type level measuring device according to the present invention, FIG. 2 is a schematic diagram for explaining the operation, and FIGS. 3 and 4 are equivalent circuit diagrams. In FIG. 1, an insulating tank 3 is a container formed of a known insulating material, for example, contains a conductive liquid 1 to be measured, and the insulating tank 3 is placed on the ground 21 via an insulating table 23. ing.

The rod-shaped auxiliary electrode 5 and the main electrode 7 are arranged in parallel at a predetermined interval in the vertical direction, and a plate-shaped equipotential electrode is provided at a lower end of the auxiliary electrode 5 with a small interval. 29 are arranged. Between the lower end of the main electrode 7 and the same potential electrode 29, a thin and small reference electrode 39 is arranged along the auxiliary electrode 5 at a slight distance from each other. The main electrode 7 and the reference electrode 39 are arranged along the auxiliary electrode 5 so as to be substantially equal in length to the extension of both lower ends of the electrode 7.

The auxiliary electrode 5, the main electrode 7, and the reference electrode 3
The electrode 9 and the same potential electrode 29 are housed and supported in a corrosion-resistant insulating layer 19 (17), which is formed of, for example, a quartz material and has a cylindrical bottom with an outer periphery coated with a fluororesin, in the above-described positional relationship, and is uniaxial. A composite electrode is formed, and the insulating layer 19 is held by holding means (not shown). If the shapes of the auxiliary electrode 5, the main electrode 7, the reference electrode 39, and the same potential electrode 29 are specifically illustrated, FIG.
A and B are as shown.

That is, the configuration shown in FIG. 5A comprises an auxiliary electrode 5 and a main electrode 7 each having a shape obtained by dividing a cylindrical rod into two in a half along the axial direction. 5 and a disk-shaped equipotential electrode 2 at the lower end of the main electrode 7.
9, and a semi-circular reference electrode 39 is arranged between the main electrode 7 and the same potential electrode 29. The configuration in FIG. 5B includes an arc-shaped auxiliary electrode 5, a main electrode 7, and a reference electrode 39 obtained by dividing a cylindrical rod into two halves along the axial direction.
It is composed of a disc-shaped same potential electrode 29.

Returning to FIG. 1, a signal source 9 for oscillating and outputting an AC signal of, for example, 40 KHz having a stable output level is connected to the upper end of the auxiliary electrode 5, and the oscillation output of the signal source 9 is ground 21. Is also connected. Of course, it is not necessary to connect the signal source 9 to the ground 21, but it is preferable from the viewpoint of safety, and has a merit that the correction operation range is narrow and easy to use. The upper end of the main electrode 7 is connected to an OP (operation) amplifier 33 through a core 31 a of the shielded cable 31.
The inverting input terminal of the OP amplifier 33 has a non-inverting input terminal.
b is connected.

The non-inverting input terminal of the OP amplifier 33 is fixed at 0 potential (0 V), and its output terminal is connected to the feedback circuit 3.
5 is connected to the non-inverting input terminal, while being connected to the rectifying / smoothing unit 13. Therefore, a voltage having a polarity opposite to that of the voltage applied to the inverting input terminal is output to the output terminal of the OP amplifier 33. By appropriately selecting the feedback circuit 35, the non-inverting input terminal and the inverting input terminal become It has the same potential.

Therefore, the OP amplifier 33 is provided with a feedback circuit 35
Together with the main electrode 7 to function as an equipotential forming section 37 for alternately bringing the main electrode 7 into the same potential state as the zero potential.
A converter for converting the output current from the converter into a voltage (for example, FIG.
11). Rectifying smoothing unit 13
Is for rectifying and smoothing the output signal from the OP amplifier 33, and is connected to the adjusting unit 15. These rectifying and smoothing units 1
The functions of 3 and the adjusting unit 15 are the same as in the conventional example.

The reference electrode 39 is the main electrode 7 or the auxiliary electrode 5
Is connected to the inverting input terminal of the OP amplifier 43 via the core wire 41a of the shielded cable 41 passing through the vicinity of the same, and the same potential electrode 29 is connected to the non-inverting input terminal of the OP amplifier 43 via the shield portion 41b of the shielded cable 41. The non-inverting input terminal is fixed at 0 potential (0 V).
The output terminal of the OP amplifier 43 is connected to an inverting input terminal via a feedback circuit 45 similar to the feedback circuit 35 and to a rectifying / smoothing unit 47 similar to the rectifying / smoothing circuit 13. 45 forms the same potential forming part 49 similar to the same potential forming part 37 described above.

The rectifying / smoothing units 13 and 47 are connected to the calculating unit 51 and to the compensating units 53 and 55, respectively.
Output terminals P are provided between the rectifying and smoothing units 13 and 47 and the arithmetic unit 51, respectively.
1, P2 are formed. The compensation units 53 and 55 store compensation values corresponding to compensation capacitances when the liquid 1 to be measured in the insulating tank 3 is empty.

Next, the operation of the capacitance type level measuring device having such a configuration will be described. As shown in the schematic diagram of FIG. 2, the capacitance in the gas (air) between the auxiliary electrode 5 and the main electrode 7 is Ca, and the capacitance in the liquid around the auxiliary electrode 5 is as shown in the schematic diagram of FIG. The capacitance of the insulating layer 19 is CL1,
The capacitance of the insulating layer 19 in the liquid around the main electrode 7 is CL2,
The capacitance of the insulating layer 19 around the reference electrode 39 is Cr, the capacitance between the same potential electrode 29 and the reference electrode 39 is Ck1, the capacitance between the auxiliary electrode 5 and the same potential electrode 29 is Ck2, and the main electrode 7 is The capacitance between the reference electrode 39 and Ck3 is the same as that of the potential electrode 2
9, the capacitance of the insulating layer 19 at the tip is Cs, the capacitance between the side of the insulating tank 3 and the ground 21 is Cx1, the capacitance between the bottom of the insulating tank 3 and the ground 21 is Cx2, The capacitance in the electrode between the main electrodes 7 is Ck4, the auxiliary electrode 5 and the reference electrode 3
Assuming that the capacitance in the electrode between electrodes 9 is Ck5,
FIG. 3 shows an equivalent circuit in which the signal exceeds the reference electrode 39.

The capacitance Ca includes the capacitance of the auxiliary layer 5 and the insulating layer 19 around the main electrode 7 in the gas including the capacitance.
Detailed illustration is omitted. Then, the AC signal Vo applied from the signal source 9 to the auxiliary electrode 5 and the ground 21 is used as an AC current im for measuring the liquid level as the capacitances Ca, CL1, and CL.
2, Cx1, Cx2, Ck4, the main electrode 7, and the core cable 31a of the shielded cable 31 are output to the OP amplifier 33, while the capacitance C is output as a correction AC current ir.
L1, Cx1, Cx2, Cr2, Ck5, reference electrode 39
And OP via the core wire 41a of the shielded cable 41.
Output to the amplifier 43. The output signals S1 and S2 rectified and smoothed by the rectification smoothing units 13 and 47 are output to the calculation unit 51, divided (S1 / S2), and output as measurement signals.

Here, in the equivalent circuit of FIG. 3 in which the liquid 1 to be measured is stored to some extent, the alternating current im from the main electrode 7
The AC current ir from the reference electrode 39 is as follows, and flows to the inverting input terminals of the OP amplifiers 33 and 43.
The symbol VM is the potential of the liquid 1 to be measured, and the symbol ω is the angular velocity of the alternating current. im = ωCL2VM + ωCaVo + ωCk4Vo (1) ir = ωCrVM + ωCk5Vo (2)

When the liquid to be measured 1 is lower than the reference electrode 39 and is empty, the capacitance between the auxiliary electrode 5 and the main electrode 7 is Cao, and the capacitance between the auxiliary electrode 5 and the reference electrode 39 is Car, the capacitance between the same potential electrode 29 and the ground 21 is C
sa, the equivalent circuit is as shown in FIG.
The AC current imo from the main electrode 7 and the AC current iro from the reference electrode 39 are as follows. imo = ωCaoVo + ωCk4Vo (3) iro = ωCarVo + ωCk5Vo (4)

The values of these equations (3) and (4) are stored in advance in the compensating units 53 and 55 in FIG. 1 as empty adjustment values, and the rectifying / smoothing units 13 and 47 include these empty adjusting compensation values. The result obtained by performing the difference operation from Expressions (1) and (2) and substituting the input currents im and ir is as follows when the capacitance at the electrode length Lo of the insulating layer 19 around the main electrode 5 is Clo. become. im = [omega] CL2VM + [omega] CaVo- [omega] CaoVo + [omega] Ck4Vo- [omega] Ck5Vo = {([omega] L / Lo) CloVM} + [omega] [(Lo-L) / Lo {CaoVo- [omega] CaoVo = [[omega] (L / Lo)] (CloVM-CoVoVoCoVoVoCoVoCoVoCoVoVoCoVoVoCoVoVoCoVoVoCoVoVoCoVoVoCoVoVoCoVoVoVoVoVoCoVoVoCoVoVoCoVoVoCoVoVoCVo. = (ΩLr / Lo) CloVM− (ωLr / Lo) CaoVo = [ω (Lr / Lo)] (CloVM−CaoVo) However, CL2 is (L / Lo) Clo and Ca is [(L
o-L / Lo)] Cao and Cr are (Lr / Lo) Cl
For o and Car, their expressions are satisfied under conditions such as (Lr / Lo) Cao.

If the length of the main electrode 7 immersed in the liquid 1 to be measured is L and the length of the reference electrode 39 in the axial direction is Lr, im / ir = L / Lr, and the alternating current im The liquid level of the liquid 1 to be measured can be measured from the ratio of the AC current ir.

In the present invention, the auxiliary electrode 5, the main electrode 7, the reference electrode 39, and the same potential electrode 29 are housed so as to be covered in the bottomed cylindrical insulating layer 19, and are integrated into one. Therefore, as compared with the conventional configuration in which the auxiliary electrode 5 and the main electrode 7 are separately provided at a distance from each other, the electrode structure is simplified, the size is reduced, and the handling becomes easier. Further, since the main amplifier 7, the reference electrode 39, and the same potential electrode 29 are brought into the same potential in an alternating current state by the OP amplifiers 33, 43, that is, the same potential forming parts 37, 49, the auxiliary electrode 5 and the same potential electrode are used. No alternating current flows through the capacitances Ck1, Ck2, Ck3 formed between the electrodes 29, the reference electrode 39 and the same potential electrode 29, and between the main electrode 7 and the same potential electrode 29.

Further, the capacitances CL1, Cx1, Cx2,
The change in Cs does not affect the ratio of the output alternating currents im and ir from the main electrode 7 and the reference electrode 39, and the liquid level of the liquid 1 to be measured can be measured accurately and linearly. Further, the output signal S from the main electrode 7 and the reference electrode 39 in the empty state
1, S2 are measured at the output terminals P1, P2, and the output signals S1,
The output AC currents im and ir can be compensated by the compensation values stored in the compensation units 53 and 55 such that S2 becomes “0 (zero)”.

For this reason, conventionally, for example, when the liquid to be measured 1 is reduced and the reference electrode 39 is exposed,
7 is minimized and the measurement signal (S1 / S
In contrast, in the configuration of FIG. 4, the output signal S1 is almost “0” when the liquid to be measured 1 is empty, and the measurement signal (S1) may be generated.
If / S2) is also set to approximately "0", it is possible to suppress the output inversion phenomenon and reduce the measurement signal (S1 / S2) to the level or to "0" after the reference electrode 39 is exposed. .

By the way, in the first configuration shown in FIG. 1, the dimensions of the auxiliary electrode 5, the main electrode 7, the reference electrode 39 and the same potential electrode 29 do not need to have the same cross-sectional shape, and the intervals are constant. I just want it. In the above-described embodiment of the present invention, the same potential electrode 29 is located on the extension of the lower end of both the auxiliary electrode 5 and the main electrode 7. The object of the present invention can be achieved even with a configuration in which the same potential electrode 29 is located only on the extension of the tip.

However, if the same potential electrode 29 is located on the tip side of both the auxiliary electrode 5 and the main electrode 7, more stable liquid level measurement becomes possible. The point is that the auxiliary electrode 5 and the main electrode 7 may be arranged at least at the tip of the main electrode 7 with an interval. In the capacitance type level measuring device of the present invention, as shown in FIG. 6, the same potential as the same potential electrode 29 in FIG. A configuration in which the electrodes 29 are arranged is also possible. As described above, in the configuration in which the same potential electrode 29 is disposed above the auxiliary electrode 5 and the main electrode 7, the auxiliary electrode 5 and the main electrode 7
There is an advantage that the liquid level of the liquid 1 to be measured can be measured accurately and linearly even if an object or an operator approaches the upper side of the liquid.

FIG. 7 is a schematic perspective view showing another embodiment of the capacitance type level measuring device according to the present invention. 5A and FIG. 5B, the main electrode 7 and the reference electrode 39 extend from the disk-shaped equipotential electrode 29 to the vicinity of the upper ends of the auxiliary electrode 5 and the main electrode 7 integrally with this outer diameter. A shield 57 is formed to extend in a gap between the auxiliary electrode 5, the auxiliary electrode 5, the main electrode 7, the same potential electrode 29, and the reference electrode 3.
9 is covered with an insulating layer (not shown) 19, and other configurations are almost the same as those in FIG.

As described above, the main electrode 7 and the reference electrode 39
When the shield 57 is arranged in the gap between the auxiliary electrode 5 and the main electrode 7 and the reference electrode 39 and the auxiliary electrode 5 is separated by the shield 57, the main electrode 7, the reference electrode 39, and the auxiliary electrode 5 are separated. 5, the capacitances Ck4 and Ck5 formed between them become almost zero, and more stable liquid level measurement can be performed. In addition, the shield 57 includes the main electrode 7 and the reference electrode 3.
8A and 8B, the width dimension S of the shielding body 57 is mainly set as shown in FIGS. 8A and 8B in order to secure the effect. Electrode 7
(Reference electrode 39) and the same width as the radial dimension s of the auxiliary electrode 5,
More preferably, it is preferable to select widely (S> s). The broken line in FIG. 8A is an example using the main electrode 7 and the auxiliary electrode 5 in FIGS. 5B and 7B.

Further, in the above-described embodiment, the auxiliary electrode 5 and the auxiliary electrode 5 are formed in the insulating layer 19 having a bottom formed in a cylindrical shape in advance.
Although an example in which the main electrode 7, the reference electrode 39, and the same potential electrode 29 are housed has been described, the present invention is not limited to this. For example, an elliptical shape, a square shape, and a polygonal shape can be implemented. 5, the main electrode 7, the reference electrode 39, and the same potential electrode 29 can be arranged so as to be embedded in the elongated columnar insulating layer 19, and the object of the present invention can be achieved if the main electrode 7, the reference electrode 39 and the same potential electrode 29 are housed and supported in a rod-shaped insulator. It is possible.

Further, the shield 57 disposed between the main electrode 7 (reference electrode 39) and the auxiliary electrode 5 is shown in FIGS.
It is not necessary to be in the shape of an elongated plate, a band, or a film as in FIG. 8B, and it is optional such as having a cross-sectional cylindrical shape as shown in FIG. 8B, and above the auxiliary electrode 5, the main electrode 7, and the shield 57,
A configuration in which a disk-shaped equipotential electrode 29 is arranged as shown in FIG. 5 is also possible. Further, in the above-described embodiment, the example in which the liquid level of the conductive liquid 1 to be measured is measured has been described.
The present invention is also suitable for measuring the liquid level of the insulating liquid 1 to be measured.

In the present invention, each of the same potential forming sections 37 and 43 described above is an example, and is not limited to the configuration including the OP amplifiers 33 and 43 and the feedback circuits 35 and 41. It can be implemented in a circuit as well. The capacitance type level measuring apparatus according to the present invention is not limited to the configuration in which the liquid to be measured 1 is stored in the insulating tank 3 as in each of the above-described embodiments, but is a widely used container, a water storage tank for water treatment, etc. It can be applied to liquid level measurement of dams and rivers.

[0045]

As described above, according to the present invention, an elongated main electrode and an elongated auxiliary electrode are arranged in a parallel positional relationship at intervals from each other, and the main electrode and the auxiliary electrode are arranged at least at the tip of the main electrode. Potential electrodes are arranged at intervals, reference electrodes are arranged between these main electrodes and the same potential electrodes along the auxiliary electrodes, and an AC signal is applied to the auxiliary electrodes from a signal source, and the same potential is applied. The forming section forms an AC equipotential state between the main electrode, the same potential electrode and the reference electrode, and corrects the output signal from the main electrode with a correction signal from the reference electrode to adjust the liquid level of the liquid to be measured. Since the main electrode, auxiliary electrode, same-potential electrode and reference electrode are arranged in the rod-shaped insulator in the capacitance type level measuring device to be measured, the structure, particularly the electrode structure, is simple and easy to miniaturize, and it is easy to use. Stores measurement liquid Regardless of the configuration or shape of the container, the liquid level of the liquid to be measured can be measured accurately and linearly, and the output signal according to the liquid level can be corrected.For example, accurate air conditioning of the liquid to be measured in the container There is an advantage that adjustment is possible. Further, in the configuration in which the electrostatic shielding member is arranged between the main electrode, the reference electrode, and the auxiliary electrode, more stable and accurate liquid level measurement can be performed. Further, in a configuration in which an electrostatic shielding member having a width equal to or larger than the width of the main electrode and the auxiliary electrode and extending from the same potential electrode is provided, more stable and accurate liquid level measurement can be performed.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of a capacitance type level measuring device according to the present invention.

FIG. 2 is a schematic diagram for explaining the operation of the capacitance type level measuring device of FIG.

FIG. 3 is an equivalent circuit diagram of the capacitance type level measuring device of FIG.

FIG. 4 is an equivalent circuit diagram of the capacitance type level measuring device of FIG.

FIG. 5 is a perspective view showing a schematic configuration of an auxiliary electrode, a main electrode, a reference electrode, and the same potential electrode used in the capacitance type level measuring device according to the present invention.

FIG. 6 is a diagram showing a schematic configuration of an auxiliary electrode, a main electrode, a reference electrode, and the same potential electrode used in the capacitance type level measuring device according to the present invention.

FIG. 7 is a perspective view showing a schematic configuration of an auxiliary electrode, a main electrode, a reference electrode, and the same potential electrode used in the capacitance type level measuring device according to the present invention.

FIG. 8 is a diagram showing a schematic configuration of an auxiliary electrode, a main electrode, a reference electrode, and an equipotential electrode used in the capacitance type level measuring device according to the present invention.

FIG. 9 is a diagram showing a conventional capacitance-type level measuring device.

FIG. 10 is an equivalent circuit diagram of the capacitance type level measuring device of FIG. 9;

FIG. 11 is a diagram illustrating an example of use of the capacitance type level measuring device of FIG. 9;

FIG. 12 is an equivalent circuit diagram of the capacitance type level measuring device of FIG.

FIG. 13 is an equivalent circuit diagram of the capacitance type level measuring device of FIG.

FIG. 14 is an equivalent circuit diagram of the capacitance type level measuring device of FIG.

FIG. 15 is a diagram illustrating an example of use of the capacitance type level measuring device of FIG. 9;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Measurement liquid 3 Insulation tank 3a Conductive tank (metal tank: auxiliary electrode) 5 Auxiliary electrode 7 Main electrode 9 Signal source 11 Conversion part 13, 47 Rectification smoothing part 15 Adjustment part 17, 19 Insulation layer 21 Ground 23 Insulation stand 25 Valve 27 pipe 29 equipotential electrode 31, 41 shield cable 31a, 41a core wire 31b, 41b shield part 33, 43 OP amplifier (op amp) 35, 45 feedback circuit 37, 49 equipotential forming part 39 reference electrode 51 arithmetic part 53, 55 compensation Part 57 Shielding member

Claims (3)

[Claims] 1. An elongated main electrode which is inserted downward into a liquid to be measured and outputs an output signal corresponding to the liquid level of the liquid to be measured, and said main electrode is spaced apart from said main electrode in a parallel positional relationship. An elongated auxiliary electrode that is inserted downward into the measurement liquid; and an equipotential electrode that is spaced apart at least at the tip of the main electrode among the main electrode and the auxiliary electrode; A reference electrode that is disposed along the auxiliary electrode with an interval therebetween and outputs a correction signal for correcting the output signal; a signal source that applies an AC signal to the auxiliary electrode; the main electrode and the same potential electrode And an equipotential forming unit that forms an ac equipotential state between the reference electrodes, and a capacitance type in which the output signal is corrected with the correction signal and the liquid level of the liquid to be measured is measured. A level measuring device, Electrode, the auxiliary electrode, the same potential and reference electrodes,
An electrostatic capacitance type level measuring device which is arranged in a rod-shaped insulator. 2. The electrostatic capacitance level measuring device according to claim 1, wherein an electrostatic shielding member is arranged between said main electrode and reference electrode and said auxiliary electrode. 3. The capacitance type level measuring device according to claim 2, wherein the electrostatic shielding member has a width equal to or greater than the width of the main electrode and the auxiliary electrode, and extends from the same potential electrode.