JPS5846681B2 - thickness measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thickness measuring device, in particular, a sensor electrode portion is disposed facing a thin plate-shaped object to be measured, and the sensor electrode portion is electrically connected to a signal detection electric circuit. In addition to combining it with
The present invention relates to a non-destructive thickness measuring device that measures and displays fluctuations in the output voltage of the electrical circuit.

Conventionally, as a plate thickness measuring device capable of non-destructively measuring the thickness of a plate, there is a plate thickness measuring device using ultrasonic waves, that is, an ultrasonic thickness gauge.

However, ultrasonic thickness gauges are suitable for measuring the thickness of relatively dense materials such as metals, but they are suitable for measuring the thickness of relatively low-density materials such as wood, paper, plastic, or FRP, which have high ultrasonic attenuation. However, it is difficult to accurately measure the plate thickness, and due to limitations on the wavelength of ultrasonic waves, it is extremely difficult to measure thickness on the order of 1/10 to 1/100 mm. The inherent problem is that it is impossible to measure plate thickness unless the vibrating surface of the transducer is pressed against the object to be measured, or an ultrasonic propagator is interposed between the object and the ultrasonic transducer to eliminate an air layer. always has the disadvantages of

On the other hand, although there are some examples of techniques for measuring the thickness of dielectric materials such as plastics, most of these conventional techniques have complicated structures, are difficult to operate, and have a high failure rate. It was always accompanied by this inconvenience.

In addition, in many conventional technologies, the sensor part and the main body are integrated, which makes it impossible to effectively measure the thickness of objects whose shape or size changes in a complex manner. This caused an inconvenience.

The purpose of the present invention is to improve the inconveniences of the prior art, and in particular to significantly improve the reliability of measured values by constantly setting optimal measurement conditions in response to changes in the thickness and shape of the object to be measured. The object of the present invention is to provide a thickness measuring device that has the same characteristics.

Therefore, in the present invention, the sensor electrode section is detachably attached to the measuring instrument body via the signal cable, and
The sensor electrode section is provided with a fine adjustment section that shifts the resonance point of the signal detection electric circuit to always set the variation range of the output voltage in an optimal state corresponding to the object to be measured, thereby achieving the above purpose. This is what I am trying to do.

Embodiments of the present invention will be described below with reference to the drawings.

In Figure 1, a high frequency oscillator 1 that oscillates a reference frequency.
The output of is applied to a signal detection device 2 consisting of an electrical resonant circuit.

Sensor electrodes 3 and 4 are provided at the signal detection end of this signal detection device 2.
When connected, the sensor electrodes 3 and 4 are electrically (electrostatically or magnetically) coupled to an object to be measured 5 having a certain thickness.

A detector 6 is connected to the signal detection device 2.
detects (rectifies) the output voltage of the signal detection device 2 and sends the output to the amplifier 7.

An amplifier 7 amplifies the output signal of the detector 6 and drives a display 8.

Here, the display 8 may be either a digital display or an analog display such as a meter.

Here, in the thickness measuring device configured as described above, the principle of measuring the thickness of the object to be measured 5 and the sensor electrodes 3 and 4 will be described.
The relationship between the output voltage of the signal detection device 2 and the electrode surfaces 3A and 4A will be explained.

It is generally known that when an electric field is applied to a dielectric, polarization within the dielectric is proportional to the dielectric constant of the dielectric.

Polarization is also proportional to the number of molecules in the dielectric, so when considering unit area, it is naturally proportional to the thickness of the dielectric.

Therefore, since the amount of electricity generated within the dielectric by the electric field is proportional to the polarization, the amount of electricity is ultimately proportional to the dielectric constant and thickness of the dielectric.

Now, assuming that the object to be measured 5 is a dielectric and its relative dielectric constant is known, the change in capacitance due to the object to be measured 5 being placed close to the sensor electrodes 3 and 4 (i.e. If the signal detection device 2 detects a change in the amount of electricity generated within the object to be measured 5, the thickness of the object to be measured 5 can be measured from the amount of change.

Conversely, if the origin of the object to be measured 5 is known, the dielectric constant can be determined from the amount of change.

In this case, the change in capacitance can be interpreted as a change in the resonant frequency of the resonant circuit that constitutes the signal detection device 2.

That is, since the resonant voltage of the resonant circuit of the signal detection device 2 changes with respect to the reference frequency of the high frequency oscillator 1, this is detected by the detector 6 and taken out as a voltage change, amplified by the amplifier 7, and applied to the display 8. , the thickness or dielectric constant of the object to be measured 5 is measured.

On the other hand, when the object to be measured 5 is a metal, especially a magnetic material,
The sensor electrodes 3 and 4 are made of a magnetic material, and are coupled to the coil part of the resonant circuit of the signal detection device 2, and are magnetically coupled to the object to be measured 5 to detect the signal. Since the inductance of the resonant circuit of the device 2 responds to changes in the thickness or relative permeability of the object to be measured 5, the output voltage of the signal detection device 2 changes.

If this change is taken out to the outside and shown on the display 8 via the detector 6 and the amplifier 7, the thickness can be determined when the relative magnetic permeability is known, and the relative magnetic permeability can be determined when the thickness is known.

Here, the area 3 of the sensor electrodes 3 and 4 facing the object to be measured 5
The magnitude of A and 4A directly affects the fluctuation of the resonant voltage of the resonant circuit of the signal detection device 2.

That is, the larger the electrode surfaces 3A and 4A of the sensor electrodes 3 and 4 are for the same object to be measured 5, the larger the capacitance component of the resonant circuit portion becomes.

Furthermore, in the case of measuring the thickness, etc. of the magnetic material mentioned above, the inductance component becomes large.

Focusing on this point, the electrode surface 3A of the sensor electrode 3.4,
By appropriately setting the size and shape of 4A, it becomes possible to detect the optimum thickness signal etc. for a specific object to be measured 5.

In the above embodiment, an electric resonant circuit is used as an example of the signal detecting circuit of the signal detecting device 2, but it is not limited to a resonant circuit, but is simply an inductance circuit, and the change in the output voltage value due to the change in impedance is detected by the detector. The configuration may be such that the wave is detected and extracted at step 6.

FIG. 2 shows a specific configuration of the signal detection device 2 when the object to be measured 5 is a dielectric.

Here, the high frequency oscillator 1 is represented equally parsimoniously by a signal source 10 and its internal impedance 11.

The signal detection device 2 includes a primary coil 12 and a secondary coil 13.
The variable capacitor 14 is connected in parallel to the secondary coil 13 and serves as a fine adjustment section.

It is assumed that the primary coil 12 and the secondary coil 13 are matched.

The output of the high frequency oscillator 1 is applied to the primary coil 12.

Sensor electrodes 3 and 4 made of rod-shaped or plate-shaped metal are connected to both ends of the secondary coil 13.

Both ends of the primary coil 12 are connected to a detector 6, and voltage changes appearing at both ends of the primary coil 12 are detected by a diode 15 within the detector 6.

The sensor electrodes 3 and 4 together with the secondary coil 13 of the matching transformer and the variable capacitor 14 constitute an electrical resonance circuit having a resonance frequency f1.

Now, the reference frequency of oscillator 1 is f. Then, the resonant voltage E across the secondary coil 12 (that is, the voltage applied to the detector 6) becomes maximum when f, = fo.

If the capacitance at this time is defined as C8 and the change in voltage E with respect to any capacitance C is displayed, a resonance curve as shown in FIG. 3 will be obtained.

Therefore, the capacitance when there is no object to be measured 5 is Co-J
If it is set to Cl, the inclined portion of the resonance curve that approximates a straight line can be used, so the object to be measured 5 can be connected to the sensor electrodes 3 and 4.
The increase in capacitance due to the proximity of the measured object 5 by a predetermined distance, that is, the relationship between the thickness or dielectric constant of the object to be measured 5 and the voltage E can be made into a substantially linear relationship within a certain range.

This fixed operating range (T1 or T2 in FIG. 3) is the electrode surface 3A of the sensor electrodes 3, 4.

It is specified by the size of 4A.

FIG. 4 shows a specific configuration of the signal detection device 2 when the object to be measured 5 is a magnetic material.

Here, the high frequency oscillator 1, detector 6, etc. are the same as in the case of FIG.

Here, the signal detection device 2 includes a magnetic core 31
It has an electrical parallel resonant circuit consisting of a coil 30 wound around the coil 30 and a variable capacitor 32 as a fine adjustment section connected in parallel to the coil 30.

Both ends of the core 31 protrude outside the detection device 2 to form sensor electrodes 33, 34, and the electrode surfaces 33A, 34A
are arranged on the same plane facing the object to be measured 5.

This sensor electrode surface 33A. When the object to be measured 5 made of a magnetic material approaches 34A, the magnetic resistance of the magnetic circuit made up of the core 31 and the coil 30 changes, and the impedance of the coil 30 changes.

Therefore, the resonant voltage E of the parallel resonant circuit formed together with the variable capacitor 32 changes, and this change is detected by a detector.

The change in the resonant voltage E due to the change in the impedance of the coil 30 has a similar aspect to the relationship between the capacitor component and the resonant voltage shown in FIG. 3, and can have a substantially linear relationship within a certain range.

This fixed operating range corresponds to the electrode surface 3 of the center and center electrodes 33 and
3A.

It is specified by the size of 34A.

FIG. 5 shows another embodiment in which the object to be measured is an insulator.

In this figure, an output signal of a high frequency oscillator 1 generated by self-oscillation of a transistor such as a field effect transistor is applied to a signal detection device 2A via a cable 40 such as a coaxial cable.

This signal detection device 2A has a bridge circuit formed by combining series resonant circuits as a signal detection electric circuit.

That is, this bridge circuit consists of a parallel circuit of a coil 41, a coil 42, a variable capacitor 4'3 as a fine adjustment section, and sensor electrodes 3 and 4, and a parallel circuit of a variable capacitor 44 and a resistor 45. There is.

This resistor 45 allows the electrodes 3 and 4 to be connected through the object to be measured 5.
The effect of dielectric loss between the two is reduced.

This bridge circuit is supplied with a high frequency signal by the mutual inductance between the primary coil 46 connected to the cable 40 and the coils 41, 42.

The bridge circuit, except for the sensor electrodes 3 and 4, is housed within an electrostatic shield body 47.

The signal detection device 2A includes a detection circuit 6A using a transistor.
A display device 8A is connected via.

This display 8A shows the operational amplifier 73 and the operational amplifier 7.
The meter 75 is connected to the output end of the meter 75, and the zero point of the meter 75 can be adjusted by a variable resistor 76.

In such a configuration, first, the balance of the bridge circuit of the two signal detecting devices is determined with the object to be measured 5 kept away from the sensor electrodes 3.4.

Then, the potential difference between the connection point C between the coils 41 and 42 and the ground becomes zero.

In this equilibrium state, the zero point of the meter 75 is adjusted.

Next, when the object to be measured 5 is brought close to the sensor electrodes 3 and 4, the capacitance between the electrodes 3 and 4 changes, and as a result, the balance of the bridge line is disrupted and an alternating current voltage is generated at the connection point C.

This AC voltage increases as the degree of unbalance of the bridge circuit increases.

After this AC voltage is detected by the detection circuit 6A, the display 8
Added to A.

As a result, the display on the meter 75 of the display 8A is the connection point C.
The value corresponds to the voltage, that is, the value (change) corresponds to the thickness or dielectric constant of the object to be measured 5.

In the embodiment shown in FIG. 5 above, the signal detection electric circuit is constructed with a bridge circuit, so that even if the object to be measured 5 has a different thickness, etc., it is possible to simply change the reference frequency of the output of the high-frequency oscillator 1. The output voltage fluctuation range of the bridge circuit as a signal detection electric circuit can be arbitrarily set, and at the same time, the output of the bridge circuit can be obtained as a stable value independent of the reference frequency of the high-frequency oscillator 1.

On the other hand, even if the electrode surfaces 3A and 4A of the sensor electrodes 3 and 4 are changed to correspond to the object to be measured 5 having different thickness, etc., and the capacitance between the sensor electrodes 3 and 4 is changed, the above-mentioned By shifting the balance point of the bridge circuit, the output voltage fluctuation range can be set arbitrarily.

The configuration in FIG. 6 differs from that in FIG. 5 in that a series resonant circuit consisting of a coil 70 and a variable capacitor 71 as a fine adjustment section is directly utilized in the signal detection electric circuit 2B.

In the signal detection circuit 2B, the sensor electrodes 3 and 4 are connected in parallel to a resistor 72 connected in parallel to the series resonant circuit, and a detection circuit 6B made of a transistor is also connected.

The output of this detection circuit 6B is applied to the display 8B.

This display 8B is composed of a differential circuit of operational amplifiers 73 and 74, and a meter 75 is provided between the output terminals of both amplifiers.

Note that the variable resistor 76 is used to adjust the zero point of the meter 75.

In such a configuration, the object to be measured 5 is connected to the sensor electrode 3,
By approaching 4, the resonance frequency of the resonant circuit is shifted, and the voltage induced across the resistor 72 changes.

In addition, in the same configuration, the resonance point is shifted, and the electrodes 3 and 4 forming a capacitive circuit with the capacitor 71 are
It is also possible to use a series circuit between the electrodes 3 and 4 to detect voltage changes on the object to be measured between the electrodes 3 and 4.

This voltage change is then displayed on the meter 75 of the display 8B.

Also in the embodiment shown in FIG.
It can be set arbitrarily by changing the electrode surfaces 3A, 4A and changing the capacitance component of the fine adjustment section, that is, the resonant circuit.

FIG. 7 shows another embodiment of the signal detection device 2. In FIG.

Here, the same components as in the first embodiment are designated by the same reference numerals.

The probe 51 includes a matching transformer 54 formed by a primary coil 52 and a secondary coil 53, a variable capacitor 55 as a fine adjustment section connected in parallel to the secondary coil 53 of the matching transformer 54, and a variable capacitor 55 connected in parallel to the secondary coil 53 of the matching transformer 54. It consists of a sensor electrode 56 connected to one end, and a probe box 57 housing the matching transformer 54, variable capacitor 55, and sensor electrode 56.

The sensor electrode 56 is arranged so as to approach and face the object to be measured 5 made of a dielectric material.

The secondary coil 52 is connected to the output end of the high frequency oscillator 1 via a coaxial cable 58 and a coupling capacitor 59.

A signal corresponding to the thickness or dielectric constant of the object to be measured 5 detected by the probe 51 is detected from the oscillator 1 side of the coaxial cable 58 via a detector 60.

The output of the detector 60 is sent to the display 8 via the amplifier 7 and displayed.

The other end of the variable capacitor 55 and the outer wire of the coaxial cable 58 are maintained at the same potential as the probe box body 57 and are grounded.

The measuring instrument main body 9 is composed of other parts except the probe 51 and the coaxial cable 58.

Even with this configuration, its operation is the same as that of the embodiments shown in FIGS. 1 and 2.

FIGS. 8 to 15 are examples of the shape of the electrode surface of the specified sensor electrode as viewed from the object to be measured side.

Among these, the ones shown in FIGS. 8 to 11 are suitable when the object to be measured is a dielectric material (particularly in the case of the embodiment shown in FIG. 7), and the divided ones shown in FIGS. This device can be used whether the object to be measured is a dielectric material or a magnetic material.

As described above, according to the present invention, the sensor electrode portion is formed by the sensor electrode disposed facing the object to be measured and the signal detection electric circuit including the coil electrically coupled to the sensor electrode. A measuring device body is provided which amplifies and displays an output voltage obtained by applying a reference signal of a constant frequency to the sensor electrode portion, and the sensor electrode portion is detachably attached to the measuring device body via a signal cable. At the same time, we have adopted a configuration in which the sensor electrode section is provided with a fine adjustment section for shifting the resonance point of the signal detection electric circuit in accordance with the object to be measured. This is an unprecedented and excellent thickness measuring device that allows you to easily set the optimal measurement conditions even for many different types of objects to be measured, and therefore significantly improves the reliability of measured values. can be provided.

[Brief explanation of drawings]

Figure 1 is a block diagram showing an embodiment of the thickness measuring device;
The figure is a circuit diagram of a signal detection device showing an embodiment of the thickness measuring device according to the present invention, and FIG. 3 is a change in the output voltage of the signal detection circuit that changes when the electrode area of the sensor electrode in FIG. 2 is changed. FIGS. 4 to 6 are circuit diagrams of signal detection devices showing other embodiments, FIG. 1 is a circuit diagram showing still other embodiments, and FIGS. Examples of specifying the shape of the sensor electrode as seen from the measurement object side are shown in Fig. 8 for a circular shape, Fig. 9 for an annular shape, and Fig. 10 for an angular shape.
Fig. 11 shows hollow square electrodes, and Fig. 12 and subsequent figures show examples of cases in which a plurality of electrodes are provided. FIG. 15 shows two small circular electrodes separated from each other, and FIG. 15 shows two rectangular electrodes separated from each other. Whistle 1 Bait 2.2A, 2B, 51... Sensor electrode part, 3°4.33, 34, 56, 57... Sensor electrode,
3A, 4A, 33A, 34A... Electrode part, 5.
...Object to be measured, 9...Measuring instrument body, 13
,30,41゜53.70... Coil of electric circuit for signal detection, 14.32,43,55.71...
...Capacitor as a fine adjustment part.

Claims (1)

[Claims] 1. A sensor electrode section is formed by a sensor electrode disposed facing the object to be measured, and a signal detection electric circuit including a coil electrically coupled to the sensor electrode, and a constant A measuring instrument body is provided which amplifies and displays an output voltage obtained by applying a frequency reference signal, and the sensor electrode portion is detachably attached to the measuring instrument body via a signal cable, and the sensor electrode portion is attached to the measuring instrument body via a signal cable. 1. A thickness measuring device, comprising: a fine adjustment section having a function of shifting the resonance point of the signal detection electric circuit in accordance with the object to be measured.