JPH0648254B2 - Capacitance measurement method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method of measuring capacitance, and more particularly to a method of capacitance measurement with improved measurement reliability.

[Prior Art] As shown in FIG. 8, an AC bridge having a capacitance formed by parallel plate electrodes A and B on one side is formed, and an object to be measured I is interposed between the electrodes A and B with a gap. As a matter of fact, the physical properties of the object to be measured I are conventionally measured by measuring the electrostatic capacitance between the electrodes A and B.

As a specific example, there is one in which a damp cloth or paper is used as the object I to be measured, and the moisture content of the cloth or paper is measured from the capacitance between the electrodes A and B.

[Problems to be Solved by the Invention]

Between the parallel plate electrodes A and B, a plate-shaped object to be measured I is placed between the electrodes A and
When placed in parallel with B, theoretically the electrodes A, B
The position of the object I to be measured between the electrodes is irrelevant to the capacitance between the electrodes A and B.

However, in reality, due to various causes, the non-grounded electrode A
The capacitance between the electrodes A and B changes depending on the distance x from. The change may be linear as shown in FIG. 9 or may be inversely proportional as shown in FIG.

Therefore, when it is difficult to keep the distance between the electrode A or B and the non-measurement object I constant, there is a problem that the reliability of the capacitance measurement is reduced.

As such a specific example, when a wet cloth or paper is continuously run between the electrodes A and B to measure the moisture content of the cloth or paper, the position of the cloth or paper is accurately maintained. However, the reliability of measurement may decrease.

[Means for Solving the Problems]

The capacitance measuring method of the present invention is characterized in that an object to be measured is interposed between a first electrode and a second electrode facing each other with a space between them and a gap, and the capacitance between the two electrodes is measured. In the measuring method of the capacitance to be measured, the first electrode is not grounded and the second electrode is grounded to obtain a measured value, and then the first electrode is grounded and the second electrode is grounded.
The configuration is characterized in that the electrodes are not grounded, the measured values are obtained, and then these measured values are calculated to obtain the capacitance.

〔Example〕

Hereinafter, the present invention will be described in more detail based on the embodiments shown in the drawings. Here, FIG. 1 is a conceptual diagram of a main part configuration of an apparatus for carrying out the present invention, FIG. 2 is a graph for explaining a result of measurement using the apparatus shown in FIG. 1, and FIG. Another graph for showing results measured by using the apparatus shown in the figure, FIG. 4 is a detailed circuit diagram of an example of the apparatus for carrying out the method of the present invention, and FIG. 5 is a method of the present invention continuously. FIG. 6 is a graph for explaining the state of carrying out the above, and FIG.
FIG. 7 is a graph showing the relationship between the capacitance variation rate and the distance from the electrode. The present invention is not limited to the embodiments shown in the drawings.

In FIG. 1, the first electrode A and the second electrode B are parallel plate electrodes, which are installed facing each other with a space of a distance d.

The object I to be measured is interposed between the electrodes A and B with a gap. The size of the gap between the first electrode A and the object to be measured I is x.

The first electrode A and the second electrode B are respectively connected to the first switch S ₁
And the second switch S ₂ . These switches S ₁ and S ₂ are interlocked, and at the same time, they are in the positions indicated by the solid line in the figure or the positions indicated by the broken line in the figure.

Now, when the switches S ₁ and S ₂ are in the positions shown by the solid lines in the figure, the state is the same as that shown in FIG. 8, and the relationship between the capacitance between the electrodes A and B and the distance x is The relationship is the same as that shown in FIG. 10 and FIG. 10 and is linear as shown by the solid line in FIG. 2 or inversely proportional as shown by the solid line in FIG.

On the other hand, if the switches S ₁ and S ₂ are set to the positions indicated by broken lines in the figure,
The relationship between the electrostatic capacitance between the electrodes A and B and the distance x is such that the relationship shown by the solid line in FIGS. 2 and 3 is folded back at x = d / 2, that is, the relationship shown in FIG. The relationship is as shown by the broken line in FIG.

As shown in FIG. 2, when the relationship between the capacitance and the distance x is linear, the present invention is carried out as follows.

That is, first, the capacitance is measured by setting the switches S ₁ and S ₂ to the positions indicated by solid lines. If the distance x at this time is x _a , the measured value c _a1 is obtained.

Next, switch the switches S ₁ and S ₂ to the positions indicated by broken lines,
The capacitance between the electrodes A and B is measured. The switches S ₁ , S are switched within a time period sufficiently shorter than the time period in which the distance x changes.
_Since it can be considered that the distance x does not change when the switching of ₂ , the measured value c _a2 is obtained corresponding to the distance x _a .

Next, the arithmetic mean of the obtained measured values c _a1 and c _a2 is calculated, and the result (c _a1 + c _a2 ) / 2 is taken as the capacitance c.

As will be understood from FIG. 2, if the arithmetic mean value is used, the variation due to the distance x is canceled out, so that the electrostatic capacitance c independent of the distance x can be obtained.

On the other hand, as shown in FIG. 3, when the relationship between the capacitance and the distance x has an inversely proportional curve, the measured values c _c1 and c _c2 are similarly set.
The capacitance c that does not depend on the distance x can be obtained by the calculation of. The calculation method is not necessarily limited to the arithmetic mean.

Next, FIG. 4 is a circuit diagram showing in detail an apparatus capable of implementing the present invention. The device 1 is a device for measuring the moisture content of a cloth, and a damp cloth I continuously runs between opposing parallel plate electrodes A and B.

The electrodes A and B are connected to the switches S ₁ and S ₂ , respectively,
By switching the switches S ₁ and S ₂ , one becomes the ground side and the other becomes the non-ground side.

The switch S ₃ is a changeover switch that is interlocked with the switches S ₁ and S ₂ .

G _a and G _b are shields and perform active guard using an operational amplifier.

The switching cycle of the switches S ₁ , S ₂ , and S ₃ is set according to the moving speed of the cloth I, the material, the nonuniformity of dimensions, the state of external noise, and the like. To give a specific example, the moving speed of the cloth is 5
In the case of 0 m / sec, the switch cycle of the switches S ₁ , S ₂ , and S ₃ may be 1 msec. FIG. 5 shows a state in which the measured values C ₁ and C ₂ are alternately obtained by switching the switches S ₁ , S ₂ and S ₃ alternately.

FIG. 6 shows the relationship between the capacitance c and the distance x obtained by the method of the present invention, and the dependency on the distance x is small.

Further, FIG. 7 shows the result of measuring how much the capacitance c changes when the object to be measured at a certain distance x moves by 1 mm. B is the case of the present invention, and B is the case of the prior art. As understood from the figure, in the case of the present invention, the capacitance variation rate is remarkably reduced.

Therefore, according to the method of the present invention, when running a damp cloth between the opposing electrodes to measure the moisture content of the cloth,
It becomes possible to improve the reliability of the measurement.

Another example is a symmetrical arrangement of spherical electrodes.

〔The invention's effect〕

According to the present invention, the first electrode and the second electrode that face each other with a space therebetween are provided.
In the method of measuring the capacitance, in which an object to be measured is interposed between the electrodes by leaving a gap between the electrodes, and the capacitance between the electrodes is measured, the first electrode is not grounded and the second electrode is grounded. Capacitance measurement characterized by obtaining a measurement value, then obtaining a measurement value by grounding the first electrode and non-grounding the second electrode, and then computing these measurement values to obtain a capacitance. A method is provided which allows the capacitance to be measured regardless of the distance between the non-measured object and the electrode. Therefore, it becomes unnecessary to strictly define the position of the non-measurement object, in other words, the capacitance can be measured with high reliability even under the situation where the position cannot be precisely defined.

[Explanation of symbols]

A ...... first electrode B ...... second electrode I ...... DUT _{S 1, S 2, S 3} ...... switch 1 ...... water content degree measuring apparatus of the fabric.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-56-79962 (JP, A) Actual development: S59-183609 (JP, U)

Claims (1)

[Claims] 1. An electrostatic capacitance for measuring an electrostatic capacitance between both electrodes, wherein an object to be measured is interposed between a first electrode and a second electrode facing each other with a space between them and a gap. In the measurement method, the first electrode is not grounded and the second electrode is grounded to obtain a measurement value,
Then, the first electrode is grounded and the second electrode is not grounded to obtain measured values, and then these measured values are calculated to obtain the electrostatic capacitance.