JPH1096660A - Capacitive level-measuring apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correctly measure a level of a liquid in spite of an environmental change such as a temperature change or the like in a capacitive level-measuring apparatus. SOLUTION: A main electrode 5 is inserted and immersed in a liquid 1 in a metallic bath 3 storing the liquid 1. An electrode of the same potential 29 is arranged below a leading end of the main electrode 5 at a slight interval. The main electrode 5 and the electrode 29 are connected to an OP amplifier (operational amplifier) 33 via a shielded cable 31. The OP amplifier 33 sets the electrode 29 at the same alternating potential as the main electrode 5. A rectifying smoothing part 1 rectifies and smooths an output signal from the main electrode 5 via the OP amplifier 33, and an adjusting part 13 adjusts the signal and outputs a measurement signal.

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 liquid level of an insulating and conductive liquid.

[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, this type of capacitance-type level measuring device inserts an elongated main electrode 5 from the liquid level into a metal tank 3 containing a liquid 1 to be measured, as shown schematically in FIG. It is well known that an alternating current applied from a signal source 7 to the tank 3 is output through the main electrode 5 and the level of the liquid 1 to be measured is measured from the output current.

[0003] That is, if the distance between the metal bath 3 and the main electrode 5 is constant, the capacitance value generated between the metal bath 3 and the main electrode 5 is proportional to their area and the dielectric constant of the intervening substance. Therefore, the capacitance value changes in proportion to the change in the liquid level of the liquid 1 to be measured, due to the gas interposed between the metal tank 3 and the main electrode 5 and the difference in the dielectric constant of the liquid 1 to be measured. An alternating current accompanying the change in the capacitance value is output from the main electrode 5. Therefore, the AC current output from the main electrode 5 is converted into an AC voltage by the conversion unit 9, rectified and smoothed by the rectification and smoothing unit 11, and the adjustment unit 13 adjusts the reference point (zero level point) and the output gradient (full level). By adjusting the scale, 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 metal tank 3 and the main electrode 5 are short-circuited at the moment when the main electrode 5 touches the liquid 1 to be measured, so that the liquid level measurement is difficult. Therefore, as shown by a broken line in FIG. 8, the outer periphery of the main electrode 5 is covered with a covering insulating layer 15 having a uniform thickness. Note that the capacitance type level measuring device using the main electrode 5 covered with the coating insulating layer 15 can be used for measuring the liquid level of the above-mentioned insulating liquid 1 to be measured. Used for

The concept of measuring the liquid level in a capacitance type level measuring apparatus using the main electrode 5 covered with the covering insulating layer 15 will be described with reference to FIG. FIG. 9 shows an example of measuring the liquid level of the conductive liquid 1 to be measured.
When the length inserted into the metal tank 3 is Lo and the length of the main electrode 5 immersed in the liquid 1 to be measured is L, the distance between the main electrode 5 and the metal tank 3 at the length Lo is If the capacitance due to gas (air) is Cao, the capacitance due to gas between the main electrode 5 and the metal tank 3 is Ca, and the capacitance of the coating insulating layer 15 at the length Lo is Clo, The capacitance Ca due to the gas between the metal tanks 3 and the capacitance Cl due to the coating insulating layer 15 interposed between the main electrode 5 and the liquid 1 to be measured are as follows: Ca = [(Lo−L) / Lo] × Cao Cl = (L / Lo) × Clo.

The capacitance Ce of the coating insulating layer 15 surrounded by the gas is expressed as Ce = [(Lo−L) / Lo] × Clo. Further, the capacitance between the tip of the main electrode 5 and the bottom of the metal tank 3 is Cs, the resistance value of the liquid 1 to be measured in the horizontal direction between the main electrode 5 and the metal tank 3 is R1, the tip of the main electrode 5 and the metal Tank 3
Assuming that the resistance values of the liquid 1 to be measured in the vertical and diagonal directions between the bottoms are Rs, these resistance values R1 and Rs are generally 1 / ωC
Since the relation of l >> R1, l / ωCs >> Rs holds, it is considered that the state is 0Ω (short circuit) as shown in FIG.

[0007] The total capacitance C formed between the main electrode 5 and the metal bath 3 is the capacitance Cl, Ce, Ca, C
C = Cl + [(Ce × Ca) / (Ce + Ca)] + Cs = [(L / Lo) × Clo] + ｛[(Lo−L) / Lo] × Clo × [(Lo −L) / Lo] × Cao / [(Lo−L) / Lo] × Clo + [(Lo−L) / Lo] × Cao｝ + Cs = L / Lo ｛Clo − [(Clo × Cao) / (Clo + Cao) ]｝ + [(Clo × Cao) / (Clo + Cao)] + Cs.

Here, [Clo− (Clo × Cao) / (Clo + Cao)]
= Cf (Clo x Cao) / (Clo + Cao) = Cg, then C = (L / Lo) x Cf + Cg + Cs ...

On the other hand, when measuring the liquid level of the insulating liquid 1 to be measured, as shown in FIGS. 11 and 12, in addition to the above-mentioned capacitances Cao and Ce, the length Lo and the length L
Assuming that the capacitance between the main electrode 5 and the metal bath 3 due to the liquid 1 to be measured is Cbo and Cb, the capacitance Cl and the capacitance Ce due to the covering insulating layer 15 at the length L are Cl = (L / Lo) × Cbo Ce = [(Lo−L) / (Lo)] × Clo, and the series value of the capacitances Cs ₁ and Cs ₂ in the vertical and oblique directions at the tip of the main electrode 5 is Cs = (Cs ₁ × Cs ₂ ) / (Cs ₁ + Cs ₂ ).

The total capacitance C formed between the main electrode 5 and the metal tank 3 is, as shown in FIG. 12, a series composite value of the capacitances C1 and Cb, and the sum of the capacitances Ce and Ca. Since the sum of the series combination value and the series combination value of the capacitances Cs ₁ and Cs ₂ is as follows. C = [(Cl × Cb) / (Cl + Cb)] + [(Ce × Ca) / (Ce + Ca)] + [(Cs ₁ × Cs ₂ ) / (Cs ₁ + Cs ₂ )] = (L / Lo) ｛[ ((Clo × Cbo) / (Clo + Cbo))] − [((Clo × Cao) / (Clo + Cao)]} + [((Clo × Cao) / (Clo + Cao)] + Cs ...

Here, [(Clo × Cbo) / (Clo + Cbo)]-[(C
lo * Cao) / (Clo + Cao)] = Cf If (Clo * Cao) / (Clo + Cao) = Cg, then C = (L / Lo) * Cf + Cg + Cs.

As described above, the entire capacitance C formed between the main electrode 5 and the metal tank 3 has the same structural formula [C = (L / Lo) in both the conductive and insulating liquids 1 to be measured. × C
f + Cg + Cs]. Note that Cf
Is a constant having a different configuration depending on whether the liquid 1 to be measured is conductive or insulating. Accordingly, the difference between the constant (Cg + Cs) and the constant (Cg + Cs) is calculated by the adjusting unit 13 in FIG. The liquid level L of the liquid 1 to be measured can be measured based on the AC current to be measured.

[0013]

However, in the above-mentioned capacitance type level measuring device, the constants Cf and Cs
Are literally fixed values, and in fact they tend to be variable factors, and there is room for improvement to achieve accurate liquid level measurement. That is, the constant Cf
Is a composite value of the capacitance formed by the coating insulating layer 15 and the liquid 1 to be measured, and is easily affected by fluctuations due to temperature and the like. When the liquid 1 to be measured is insulative, it is sensitive to a change in the dielectric constant of the liquid 1 to be measured.

The constant Cs is a composite value of the capacitance formed by the coating insulating layer 15 and the liquid 1 to be measured, and is distributed at the tip of the main electrode 5. If the liquid 1 to be measured is conductive,
13 and the gap d between the tip of the main electrode 5 and the coating insulating layer 15 as shown in FIG. It sensitively affects changes in the dielectric constant of the liquid 1 to be measured and changes in the gap t between the coating insulating layer 15 and the bottom of the metal tank 3. Note that the constant Cg is
It becomes a synthetic value due to the gas between the coating insulating layer 15 and the main electrode 5 and the metal bath 3, and is relatively insensitive to fluctuations in temperature and the like.

Therefore, in the above-mentioned conventional capacitance-type level measuring device, each variable element is used as it is at present. At present, the error range is widened in consideration of the variable element, or the measurement is performed. The measurement range is limited by lengthening the range Lo or ignoring the change in the capacitance Cs. However, a configuration for correcting each of the above-described variable elements in the capacitance-type level measurement device has also been proposed.

For example, as shown in FIG. 14, the main electrode 5 is inserted into the center of the inside of a cylindrical cylindrical electrode (surrounding electrode) 17, and the main electrode 5 is spaced apart from the tip of the main electrode 5 in the cylindrical electrode 17. A small reference electrode 19 is coaxially arranged, and the main electrode 5 and the reference electrode 19 are surrounded by the cylindrical electrode 17.

In such a configuration, the capacitance between the main electrode 5 and the cylinder electrode 17 and the capacitance due to the liquid to be measured 1 at the length Lo are represented by Cao and Clo, and the capacitance between the main electrode 5 and the cylinder electrode 17 by the gas. The capacitance is Ca, the capacitance of the liquid L between the main electrode 5 and the cylindrical electrode 17 at the length L is Cl, and the capacitance of the liquid 1 between the reference electrode 19 and the cylindrical electrode 17 is C.
Assuming that r, Ca = [(Lo−L) / Lo] × Cao Cl = (L / Lo) × Clo Cr = (Lr / Lo) × Clo

Here, the capacitance Clo of the main electrode 5
For example, if the capacitance Cl is divided by the capacitance Cr in order to suppress the influence of the fluctuation of the capacitance, Cl / Cr = [(L / Lo) × Clo] / [(Lr / Lo) × Clo] = L / Lr , And the capacitance Clo of the main electrode 5 is offset. As shown in FIG. 15, these are completely the same even when the main electrode 5 and the reference electrode 19 are covered with the coating insulating layer 15, and the capacitances Ca, Cl, and Cr are respectively insulated from the liquid 1 or gas to be measured by the coating insulation. Using the combined capacitance between layers 15 yields the above equation.

Therefore, the capacitance Clo of the main electrode 5 is
Are offset, the influence of a change in the dielectric constant or thickness of the liquid 1 to be measured or the coating insulating layer 15 on a temperature change or the like is suppressed, and an accurate liquid level can be obtained. In addition,
As a configuration for performing the signal processing as shown in the equation, as shown in FIG. 16, a conversion unit 21 and a rectification smoothing unit 23 similar to the conversion unit 9 and the rectification smoothing unit 11 shown in FIG. The calculation unit 25 divides the output signal S1 from the main electrode 5 by the output signal S2 from the reference electrode 19 (S1
/ S2), and the measurement signal is output after being adjusted by the adjustment unit 27.

However, even if the capacitance type level measuring device is configured as shown in FIG. 14 or FIG. 15, the capacitance formed between the main electrode 5 and the cylindrical electrode 17 is actually C.
Not only l but also the above-mentioned formula [C = (L / Lo) Cf
+ Cg + Cs]. With respect to this equation, the total capacitance Cm formed between the main electrode 5 and the cylindrical electrode 17 having the configuration shown in FIG. 14 or 15 is as follows: Cm = [(L / Lo) (Clo−Cao)] + Cao Since the reference electrode 19 is provided, it is difficult to form the capacitance Cs on the main electrode 5. However, Cf = Clo-Ca
o.

The capacitance of the reference electrode 19 becomes Crm including the capacitance Cs (Cs1, Cs2) between the reference electrode 19 and the metal tank 3 not shown in FIGS.
rm is expressed as Crm = (Lr / Lo) Clo + Cs.

Then, an equation in which the capacitance Cm is divided by the capacitance Crm is as follows: Cm / Crm = [(L / Lo) (Clo-Cao) + Cao] / [(Lr / Lo) (Clo) + Cs] = [L (Clo-Cao) + LoCao] / [LrClo + LoCs], and Cm / Crm = Cl / Cr is not satisfied. Cl / Cr = L / Lr, and there is a problem that the use is limited to a narrow range where the formula holds.

In such a configuration, the correction division (S
1 / S2) Capacitance Cr related to denominator reference electrode 19
Is always in the liquid 1 to be measured and is sensitive to the fluctuation of the dielectric constant and the coating insulating layer 15, whereas the capacitance Cm of the main electrode 5 of the molecule is the capacitance of the liquid 1 to be measured. Due to the difference between the capacitance and the capacitance of the gas, deviations in the denominator and the numerator tend to shift, and the correction range is narrow from this viewpoint. In addition, the capacitance Cs of the reference electrode 19 includes the capacitance Cs between the metal tank 3 and the capacitance Cs with respect to a temperature change.
In addition, there is a limit to accurate liquid level measurement due to fluctuations in the temperature, and it is difficult to reduce the size of the reference electrode 19, and there is still room for improvement.

The present invention has been made under such a circumstance, and provides a capacitance type level measuring apparatus capable of accurately measuring the liquid level of a liquid to be measured even when the environment such as temperature changes. Aim.

[0025]

In order to solve such a problem, the present invention provides an elongated main electrode which is immersed downward into a liquid to be measured, and a space provided at the tip of the main electrode. An equipotential electrode disposed, an enclosing electrode surrounding the outer periphery of the main electrode and the equipotential electrode at an interval, a signal source for applying an AC signal between the enclosing electrode and the main electrode, An equipotential forming section for forming an ac equipotential state between the electrodes; the liquid level of the liquid to be measured is measured by an output signal from the main electrode or the surrounding electrode.

According to the present invention, a reference electrode for outputting a signal for correcting the output signal is disposed between the tip of the main electrode and the same-potential electrode, and the main electrode, the same-potential electrode, It is also possible to form the same potential forming section so that the electrodes have the same AC potential. In addition, the present invention covers these electrodes with a coating insulating layer,
It is preferable to form the surrounding electrode by a cylindrical electrode in which the main electrode and the same potential electrode are coaxially arranged.

[0027]

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 an embodiment of a capacitance type level measuring device according to the present invention, and FIG. 2 is an equivalent circuit diagram thereof. In FIG. 1, a metal tank 3 is a well-known container formed of a well-known conductive material, in which an insulative liquid to be measured 1 is put, and a level of, for example, 4
A signal source 7 for oscillating and outputting a 0 KHz AC signal is connected.

The main electrode 5 has an elongated cylindrical shape, and the metal tank 3
Is inserted downward into the liquid to be measured 1 from the opening side thereof, is held at a central portion thereof by a suitable holding means (not shown), and an upper portion thereof slightly protrudes from the metal tank 3. In the liquid 1 to be measured in the metal bath 3, a small equipotential electrode 29, which is slightly spaced from the main electrode 5, is coaxially held by a suitable holding means (not shown). .

The main electrode 5 is connected to an inverting input terminal of an operational amplifier (OP) 33 via a core 31a of the shielded cable 31. The same potential electrode 29 is connected to the main electrode 5
Hollow part and shield part 31 of shielded cable 31
It is connected to the non-inverting input terminal of the OP amplifier 33 via b. The non-inverting input terminal of the OP amplifier 33 has a potential of 0 (0
V), the output terminal of which is connected to a non-inverting input terminal via a feedback circuit 35, while the rectifying / smoothing unit 1
1 connected.

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 are changed. The same potential is obtained in an AC manner.
9 has a function of converting the output current from the main electrode 5 into a voltage, while functioning as an equipotential forming unit 37 for setting the same 9 in an alternating potential state. The rectifying / smoothing unit 11 rectifies and smoothes an output signal from the OP amplifier 33 and is connected to the adjusting unit 13. The rectifying / smoothing unit 11 and the adjusting unit 1
The function of No. 3 is the same as the conventional example.

Next, the operation of the capacitance type level measuring device having such a configuration will be described. 1 and 2,
In addition to the above-mentioned capacitances Ca and Cl, a capacitance Ck between the main electrode 5 and the same potential electrode 29, a capacitance Ch between the same potential electrode 29 and the horizontal metal tank 3, , The capacitance Cs is formed between the bottom of the metal tank 3 and the capacitance Cs formed between the main electrode 5 and the bottom of the metal tank 3 is negligible.

Here, the AC current i2 flowing through the same potential electrode 29 becomes i2 = ωV (Ch + Cs) as shown in FIG. 2, and this AC current i2 flows to the non-inverting input terminal of the OP amplifier 33. On the other hand, the AC current i1 output from the main electrode 5 becomes il = ωV (Ca + Cl), which flows to the inverting input terminal of the OP amplifier 33, and the capacitance (Ca) in proportion to the liquid level of the liquid 1 to be measured.
+ Cl) changes, the AC current i1 becomes an output value proportional to the liquid level of the liquid 1 to be measured.

Although a capacitance Ck is formed between the main electrode 5 and the same potential electrode 29, the potential difference between the same potential electrode 29 and the main electrode 5 is always controlled to the same potential (0 V), and during this time the current is reduced. Does not flow, the existence of the capacitances Ck, Ch, Cs formed by the same potential electrode 29 is removed, and the capacitance Cm formed between the main electrode 5 and the metal tank 3 is as follows. Cm = (L / Lo) × (Clo−Cao) + Cao Then, the AC voltage from the output terminal of the OP amplifier 33 is rectified and smoothed by the rectification and smoothing unit 11 and adjusted by the adjustment unit 13 to adjust the liquid level of the liquid 1 to be measured. Is output in proportion to.

As described above, in the capacitance type level measuring device of the present invention, the metal tank 3 containing the liquid 1 to be measured and the liquid 1
An AC signal is applied to the main electrode 5 which is inserted vertically and outputs a current proportional to the liquid level, an equipotential electrode 29 which is arranged at an end of the main electrode 5 at an interval, and the metal tank 3. Since there is a signal source to be applied and an equipotential forming section 37 that sets the same potential electrode 29 to the same potential in an AC manner with respect to the main electrode 5,
The capacitance Cs is provided between the lower end of the main electrode 5 and the bottom of the metal tank 3.
And the capacitance Cs is formed between the same potential electrode 29 and the bottom of the metal tank 3, but the main electrode 5 and the same potential electrode 29 become the same potential in an alternating current, and a current flows between them. Since the current does not flow, the change in the capacitance Cs hardly affects the output AC current i1 from the main electrode 5. Therefore, accurate liquid level measurement is possible even if there is an environmental change due to a temperature change or the like.

Next, another embodiment of the capacitance type level measuring apparatus according to the present invention will be described. The configuration shown in FIG. 3 is different from the configuration of FIG.
It is covered with a coating insulating layer 15 made of an insulating material having good corrosion resistance, and is suitable for measuring the liquid level of the conductive liquid 1 to be measured. The other configuration is the same as that of FIG.

In this configuration, the capacitance C formed between the metal electrode 3 and the main electrode 5 or the same potential electrode 29 shown in FIG.
If the capacitance obtained by combining the capacitances formed between the coating insulating layer 15 and the liquid 1 to be measured or between the coating insulating layer 15 and the gas is used for a, Cl, Ck, Ch, and Cs, respectively. The equivalent circuit configuration is the same as in FIG. 2, and the operation is also the same. In addition, in the configuration shown in FIG. 3, in addition to the effect of the configuration shown in FIG. 1, as shown in FIG. 13, the distance between the tip of the main electrode 5 and the coating insulating layer 15 due to a temperature change or the like. Even if d or the interval t between the coating insulating layer 15 and the bottom of the metal tank 3 changes, accurate liquid level measurement can be performed without being affected by them.

Further, the configuration shown in FIG. 4 is different from the configuration shown in FIG. 1 in that a cylindrical reference electrode 19 and a same potential electrode 29 smaller than the main electrode 5 are coaxially arranged at a slight distance from each other. And the core wire 31a of the shielded cable 31
The main electrode 5 is connected to the OP amplifier 33 via the OP, and the reference electrode 19 is connected to the OP via the core 31a of the shielded cable 31.
The amplifier 39 is connected to the rectifying / smoothing unit 11
And the operational amplifier 25 is connected to the arithmetic unit 25 via the rectifying / smoothing unit 23. Reference numeral 41 denotes a feedback circuit similar to the feedback circuit 35.
As shown in FIG. 5, in the capacitance type level measuring device having this configuration, the alternating current i1 as an output signal for measuring the liquid level is supplied to the capacitances Ca and Cl and the core wire 3 of the shielded cable 31.
1a flows to the OP amplifier 33, the AC current i3 as a correction signal flows to the OP amplifier 39 via the capacitance Cr and the core wire 31a of the shielded cable 31, and the AC current i4 flows to the capacitance Ch, Cs and the shield. It flows to the OP amplifier 39 via the shield part 31b of the cable 31.

The output signal S1 from the rectifying / smoothing unit 11 and the output signal S2 from the rectifying / smoothing unit 23 are divided (S1 / S2) by the arithmetic unit 25 and output as a measurement signal. Since the op-amps 33 and 39 have the same potential between the main electrode 5 and the reference electrode 19 and between the reference electrode 19 and the same potential electrode 29, the main electrode 5 and the reference electrode 19 have the same potential.
No alternating current flows through the capacitances Ck1 and Ck2 formed between the reference electrode 19 and the same potential electrode 29, and the existence of the capacitances Ck, Ch and Cs formed on the same potential electrode 29 is removed. You. That is, the OP amplifier 39 also functions as the same potential forming unit 43.

The capacitance Cm formed by the main electrode 5
And the capacitance Crm formed by the reference electrode 19 is as follows: Cm = Ca + Cl = (L / Lo) × (Clo−Cao) + Cao... Crm = (Lr / Lo) × Clo = Cr. By forming the same potential electrode 29, the capacitance Crm
And the capacitance Cs is removed from the
Crm = Cr, and the liquid level measurement conditions are not limited.

Further, the capacitances Cm and Crm when the liquid 1 to be measured in the metal tank 3 is completely empty are as follows: Cm = Cao Crm = (Lr / Lo) × Cao , The output signals S1 and S2 from the main electrode 5 and the reference electrode 19 are measured at the output terminals P1 and P2, and compensation signals such that the output signals S1 and S2 become “zero” are supplied from the compensation units 45 and 47 to the rectifying / smoothing unit. When output to the output terminals 11 and 23, the expressions are as follows: Cm = Cao−Cao = 0 Crm = [(Lr / Lo) × Cao] − [(Lr / L)
o) × Cao] = 0. Here, [Cao] and [(Lr / Lo) ×
Cao] is a compensation capacitance corresponding to compensation signals from the compensation units 47 and 45.

Therefore, if the compensation signal value corresponding to the compensation capacitance in the empty state is stored in the compensation units 45 and 47, when the liquid 1 to be measured is put into the metal tank 3 after the empty adjustment,
The capacitances Cm and Crm formed by the main electrode 5 and the reference electrode 19 viewed from the output terminals P1 and P2 are as follows: Cm = (L / Lo) × (Clo−Cao) + Cao−Cao = (L / Lo) × (Clo−Cao) Crm = (Lr / Lo) × Clo− (Lr / Lo) × Cao = (Lr / Lo) × (Clo−Cao)

Thus, the division calculation force from the arithmetic unit 25 is: S1 / S2 = [(L / Lo) × (Clo-Cao)] / [(Lr / Lo) × (Clo-Cao)] = L / Lr As a result, each capacitance term is deleted. That is, Cm
/ Crm = Cl / Crm = L / Lr, and it can be seen that almost complete correction has been achieved.

As described above, the main electrode 5 and the same potential electrode 2
9, the capacitances Ck (Ck2), Ch, and Cs formed on the same potential electrode 29 are provided.
Can be removed, and the capacitance which is a variable element in the main electrode 5 can be removed, so that a more accurate liquid level measurement can be performed. Moreover, in the conventional configuration without the empty adjustment function, for example, as the measurement target liquid 1 decreases, the measurement signal (S1 / S2) from the calculation unit 25 decreases substantially linearly, but the main electrode 5 and the reference electrode 19 are not. When exposed, the output signal S2 from the rectifying and smoothing unit 23 is minimized,
On the contrary, there is a possibility that an output inversion phenomenon in which the measurement signal (S1 / S2) becomes larger in the opposite direction may occur.

In this regard, in the configuration of FIG. 4, the output signal S2 is set to substantially "0" as described above, and the measurement signal (S1 / S
2) can also be substantially "0", and after the main electrode 5 and the reference electrode 19 are exposed, the output inversion phenomenon is suppressed and the measurement signal (S1 / S2) is leveled off or reduced until it reaches "0". It becomes possible. Although not shown, in the configuration shown in FIG. 4, the main electrode 5, the reference electrode 19, and the same potential electrode 29 are covered with the coating insulating layer 1 as shown in FIG.
5, the liquid level of the conductive liquid 1 to be measured can be measured, and the distance between the tip of the same potential electrode 29 and the coating insulating layer 15 or the coating insulating layer 15 and the metal tank can be measured due to a temperature change or the like. Even if the distance between the bottoms of the bases 3 changes, they are not affected as in the above-described example.

In the present invention, FIGS. 1, 3 and 4
In the configuration shown in FIG. 16, as shown in FIG. 16, a configuration in which the outer circumferences of the main electrode 5, the reference electrode 19, and the same potential electrode 29 are surrounded by the cylindrical electrode 17 at a predetermined interval is also possible. The cylindrical electrode 17 functions as a surrounding electrode.
Further, the capacitance type level measuring device according to the present invention is not necessarily limited to the configuration using the metal tank 3 or the cylindrical electrode 17 as the surrounding electrode. It is sufficient that the main electrode 5 and the metal tank 3 are kept at a constant interval in the liquid level direction (normally the height direction). For example, as shown in FIG. It is possible to use a metal tank such as a square or an ellipse.

In the embodiment described above, the same potential formation 37, 43 is formed by the OP amplifiers 33, 39, but in the present invention, the AC potential difference between the main electrode 5, the same potential electrode 29 and the reference electrode 19 is reduced. The object of the present invention can be achieved by a circuit that suppresses the generation. Further, in the present invention, an AC signal is applied from the metal tank 3 to
The AC signal is applied to the same potential electrode 29 and the main electrode 5 side as shown by a broken line in FIG. The present invention can be applied to a configuration in which output is performed, and any configuration may be used as long as an AC signal is applied between the main electrode 5 and the surrounding electrodes (the metal tank 3 and the cylindrical electrode 17).

In each of the embodiments described above, the same potential electrode 29 is arranged at the lower end of the main electrode 5. However, in an actual capacitance type level measuring device, for example, Is used as a measurement dead zone,
It is common to configure to prevent malfunction due to contact. Therefore, in the capacitance type level measuring device of FIG.
For example, as shown in FIG. 7A, an upper equipotential electrode 49 is arranged coaxially at a slight interval above the main electrode 5, and the same potential electrode 49 is alternately and equipotentially arranged with respect to the main electrode 5. It is possible to provide a shield function as well as a state in which the main electrode 5 and the same potential electrode 29 are surrounded by the cylindrical electrode 17, as shown in FIG. 7B. The upper equipotential electrode 49 at an interval
Can be arranged coaxially.

Further, the tip of the main electrode 5 and the same potential electrode 29
7C, the same potential electrode 49 on the upper side is coaxially arranged at an interval above the main electrode 5 as shown in FIG. 7C, or as shown in FIG. 7D. , The upper equipotential electrode 4 above the main electrode 5 in the cylindrical electrode 17.
A configuration in which 9 are arranged coaxially is possible. In order to make the same potential electrode 49 on the upper side AC and the same potential state with respect to the main electrode 5, the same potential forming parts 37 and 43 composed of the above-mentioned feedback circuits 35 and 41 are connected to the same potential electrode 49. The configuration may be such that

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 metal tank 3 as in the above-described embodiments, but may be a widely used container, a water storage such as a water treatment or the like. It is applicable to liquid level measurement of tanks, natural dams and rivers.

[0050]

As described above, according to the capacitance type level measuring apparatus of the present invention, the same potential electrodes are arranged at the tip of the main electrode inserted into the liquid to be measured at a distance from the main electrode. An AC signal is applied between the surrounding electrode surrounding the electrode and the same potential electrode and its main electrode to form an AC same potential state between the same potential electrode and the main electrode. A measurement signal can be output in accordance with the liquid level of the measurement liquid.Also, the influence of the fluctuation of the capacitance formed mainly at the tip of the main electrode is eliminated, and the liquid to be measured is protected against environmental changes such as temperature. Accurate liquid level measurement becomes possible. Then, a reference electrode for outputting a signal for correcting the measurement output signal is arranged at an interval between the tip of the main electrode and the same-potential electrode, and the AC electrode between the main electrode, the same-potential electrode and the reference electrode is separated from each other. In the configuration for forming the potential state, in addition to the effects described above,
There is an advantage that empty adjustment can be performed in an empty state of the liquid to be measured. In a configuration in which the electrodes arranged coaxially are covered with an insulating layer, even if the dimensions between the insulating layer and the main electrode or the same potential electrode change due to changes in environmental conditions such as temperature, the change is not affected. The effect can be suppressed. Furthermore, in a configuration in which a cylindrical electrode in which the main electrode, the same potential electrode, and the reference electrode are disposed in the inner hollow portion is used as the surrounding electrode, the capacitance formed between the lower end of the main electrode and the reference electrode and the bottom of the container is reduced. Since there is almost no liquid level, a more 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 an equivalent circuit diagram of the capacitance type level measuring device of FIG.

FIG. 3 is a diagram showing another embodiment of the capacitance type level measuring device according to the present invention.

FIG. 4 is a diagram showing another embodiment of the capacitance type level measuring device according to the present invention.

FIG. 5 is an equivalent circuit diagram of the capacitance type level measuring device of FIG.

FIG. 6 is a schematic view of a main part showing still another embodiment of the capacitance type level measuring device of the present invention.

FIG. 7 is a schematic diagram schematically showing still another embodiment of the capacitance type level measuring device of the present invention.

FIG. 8 is a diagram showing a conventional capacitance-type level measuring device.

FIG. 9 is a diagram for explaining the operation of the capacitance type level measuring device according to FIG. 8;

FIG. 10 is a view for explaining the operation of the capacitance type level measuring device according to FIG. 8;

FIG. 11 is a view for explaining the operation of the capacitance type level measuring device according to FIG. 8;

FIG. 12 is a view for explaining the operation of the capacitance type level measuring device according to FIG. 8;

FIG. 13 is a view for explaining the operation of the capacitance type level measuring device according to FIG. 8;

FIG. 14 is a diagram illustrating a correction operation of the capacitance-type level measurement device.

FIG. 15 is a diagram illustrating a correction operation of the capacitance type level measuring device.

FIG. 16 is a diagram illustrating a capacitance type level measuring device according to FIG. 14 or FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Measurement liquid 3 Metal tank 5 Main electrode 7 Signal source 9, 21 Conversion part 11, 23 Rectification smoothing part 13, 27 Adjustment part 15 Coating insulating layer 17 Cylindrical electrode 19 Reference electrode 25 Operation part 29, 49 Same potential electrode 31 Shield Cable 31a Core 31b Shield 33, 39 OP amplifier (same potential forming part) 35, 41 Feedback circuit 37, 43 Same potential forming part 45, 47 Compensation part

Claims (4)

[Claims] 1. An elongated main electrode immersed downward into a liquid to be measured, an equipotential electrode disposed at an end of the main electrode at an interval, and the main electrode and an electrode at an interval. A surrounding electrode surrounding the outer periphery of the potential electrode; a signal source for applying an AC signal between the surrounding electrode and the main electrode; and a same potential forming section for forming an AC same potential state between the same potential electrode and the main electrode. And a liquid level of the liquid to be measured is measured by an output signal from the main electrode or the surrounding electrode. 2. A reference electrode which is arranged at an interval between a tip of the main electrode and the same-potential electrode and outputs a signal for correcting the output signal, and wherein the same-potential forming part is provided with the main-potential forming part. 2. The capacitance-type level measuring device according to claim 1, wherein an alternating-current same potential state is formed between the electrode, the same potential electrode and the reference electrode. 3. The capacitance type level measuring device according to claim 1, wherein the electrode is covered with an insulating layer. 4. The capacitance type level measuring device according to claim 1, wherein the surrounding electrode is a cylindrical electrode in which the main electrode, the same potential electrode, and a reference electrode are arranged.