JPS61151402A - Differential mutual induction type eddy current measuring sensor - Google Patents

Abstract

PURPOSE:To measure distance accurately evn if it is for from a metallic plate, by arranging two secondary coils facing against each other with the primary coil in between, the secondary coils being of the specified clearance and number of windings. CONSTITUTION:The No.1 secondary coil S1 and the No.2 secondary coil S2 are arranged opposedly with primary coil P of number of coils N1 in between in such a way that a distance between the coil S1 and the primary coil B is larger than that between the coil S2 and the primary coil P. Further, the number of windings N2 of the coil S1 is larger than that N2'. By this arrangement, when a metallic plate MP is located on the secondary coil S1 side, a displace ment sensitivity DELTAM2 of the mutual inductance M2 of the primary coil P and the secondary coil S2 and even if a distance between the secondary coil S1 and the metallic plate MP significant, the displacement sensitivity of the differen tiated connection of the S1 and S2 coies is not weakened by the DELTAM2.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a differential mutual induction eddy current measuring sensor, and more particularly to a differential mutual induction eddy current measuring sensor having two secondary coils.

[Conventional technology]

Eddy current measurement is widely put into practical use, for example, to measure the distance between a coil, which is a sensor for eddy current measurement, and a metal plate. This is done by measuring the self-inductance of the coil, whose size corresponds to the distance from the metal plate. Furthermore, by arranging the primary coil and a metal plate facing each other with the secondary coil in between, and measuring the mutual inductance between the primary coil and the secondary coil, a measurement result with higher accuracy than the measurement of self-inductance can be obtained. . Furthermore, as a highly accurate eddy current measurement method, there is a method in which first and second secondary coils are disposed opposite to each other with a primary coil sandwiched therebetween.

FIG. 2 is a schematic diagram of a conventional differential mutual induction eddy current measuring sensor equipped with such two secondary coils. Number of turns N1
The first secondary coil S1 and the second secondary coil S2, which are arranged opposite to each other with the primary coil P in between, have the same length 11 in the arrangement direction, and have the same distance from the primary coil P. Furthermore, the number of windings is N2. therefore,
A metal plate MP is placed near these coils p, si and S2.
When there is no mutual inductance M1 between the primary coil P and the first secondary coil S1 and mutual inductance M2 between the primary coil P and the second secondary coil S2 are equal, M 1 = M 2 (1 ) holds true. When a metal plate MP is placed near the first secondary coil S1, since the first secondary coil S1 is closer to the metal plates M and P than the primary coil, mutual inductance M1. M2 satisfies M 1 < M 2 (2). Therefore, the displacement sensitivity ΔM1. of mutual inductance M1, M2. ΔM2 is larger than the displacement sensitivity ΔM1, and becomes 6M1)6M2 (3). In addition, as shown in FIG. 6, the first and second secondary coils S
1 and S2 are differentially connected, the displacement sensitivity becomes Δ(Ml−M21 =ΔM1−ΔM2 (4).

[Problem that the invention seeks to solve]

By the way, as the distance h1 between the first secondary coil S1 and the metal plate MP increases, the difference between the displacement sensitivities ΔM1 and 6M2, that is, the value of the displacement sensitivity shown in equation (4), decreases. This was problematic because the distance between the first secondary coil S1 and the metal plate MP measured based on mutual inductance contained a large error. Also,
In some cases, there was a problem in that it became impossible to measure distance.

The present invention was made for the purpose of solving the above problems.
To provide a differential mutual induction amount eddy current measuring sensor that can accurately measure the distance to a metal plate even if the distance to the metal plate is far.

[Failure to solve the problem]

Therefore, in the present invention, the primary coil is sandwiched between the first and second coils.
The secondary coils are arranged to face each other, and the interval between the primary coil and the first secondary coil is made larger than the interval between the primary coil and the second secondary coil, and the winding of the first secondary coil is A differential mutual induction eddy current measurement cell is constructed in which the number of wires is greater than the number of turns of the second secondary coil.

[Effect]

The sensor for differential mutual induction eddy current measurement with the above configuration connects the first secondary coil and the second secondary coil differentially, and connects one terminal of the primary coil to the first or second secondary coil. Connect one terminal of the coil to supply an alternating current to the primary coil, measure the voltage induced in the differentially connected first and second secondary coils, and measure these currents. Mutual inductance is determined from the voltage value, and based on this mutual inductance, the distance to the metal plate placed on the first secondary coil side is calculated.

〔Example〕

Hereinafter, one embodiment of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a schematic diagram of a differential mutual induction sensor for measuring eddy current according to the present invention. In FIG. 1, the first secondary coil S
The first and second secondary coils S2 are such that the distance between the first secondary coil S1 and the primary coil B is such that the distance between the first secondary coil S1 and the primary coil B is the same as that of the second secondary coil S2.
The number of windings is N10 and the primary coil P is sandwiched between the coils and the primary coil P so that the distance between the coils and the primary coil P is larger than the distance between the coils P and the primary coil P. Further, the number of turns N2 of the first secondary coil S1 is larger than the number of turns "N2'" of the second secondary coil S2. Therefore, the metal plate is attached to the first secondary coil S1 side. When you place MP,
The displacement sensitivity ΔM1 of the mutual inductance M1 between the primary coil P and the first secondary coil S1 is
Displacement sensitivity Δ of mutual inductance M2 with the next coil S2
larger than M2, the first secondary coil S1 and the metal plate MP
Even if the distance h1 from the The temperature will not be lowered due to the sensitivity ΔM2.

Next, the measurement of the mutual inductance of the differential mutual induction eddy current measuring cell shown in FIG. 1 will be explained. When measuring mutual inductance, first, the first secondary coil S1 and the second secondary coil S2 are differentially connected as shown in FIG. That is, one terminal 1' of the first secondary coil S1 is connected to one terminal 2 of the 202nd secondary coil S2.

Still, one terminal 3 of the primary coil P is connected to one terminal 1 of the first secondary coil S1. In this connection state, when an alternating current of a predetermined frequency f is applied between both terminals 1 and 1' of the primary coil P, the differentially connected first and second terminals
The secondary coils S1 and S2 are in an open state, and terminal 4-
An induced voltage E is induced between 4' and 4'. At this time f, I, E
The following equation is obtained from the mutual intance (M2-Ml).

E=2πf (M2-M1) I
(6) Therefore, the mutual inductance (M2-Ml)
C, (M 2 - M 1 ) = E/2πt I
It is determined by (7).

When measuring mutual inductance using the above method, the equation (0) does not necessarily hold. If the equation (1) does not hold, M 1 < M 2 (8)
has been established. Therefore, the mutual inductance (M
2-Ml) is minimized when the metal plate MP is moved away from the first secondary coil S1, and when the metal plate MP is moved away from the first secondary coil S1.
As it approaches 1, it becomes maximum, so the change rate Δ(M2-M
It turns out that it is advantageous to consider l)/(M2-Ml).

Note that the differential mutual induction amount eddy current measuring sensor according to the present invention may be used without differential connection as described above, and connected to a measuring device with six terminals as is. In this case, the induced voltages of the first and second coils act in the measuring device in the same way as if they were operatively connected.

Furthermore, the conventional eddy current measurement sensor shown in Fig. 2 has a compensation effect for temperature changes in the coil that is the sensor;
Even with the sensor for measuring the differential mutual induction amount eddy current according to the present invention, the compensation effect is not lost.

In addition, in this example, distance measurement to a metal plate was explained, but conductivity measurement of a metal plate, flaw detection (flaw detection) of a metal plate, etc.
Alternatively, it can be applied to metal detection, etc., and is particularly effective when the distance to the object to be measured is long.

Furthermore, the object to be measured is not limited to a metal plate, but may be seawater, for example. However, in this case, the amount of change in mutual inductance is the number of multiple lines. Therefore, the present invention is also applicable to estimating the thickness of seawater. That is, the thickness of sea ice is estimated by passing a high frequency current through the primary coil and detecting the phase angle of the voltage induced in the secondary coil.

(For details, see ``Sea Ice Thickness Estimation Method'', JP-A-58-2
23704) [Effects of the Invention] As explained above, according to the present invention, the first and second secondary coils are arranged opposite to each other with the primary coil in between, and the primary coil and the first secondary coil are The interval between the primary coil and the second secondary coil is made larger than the interval between the primary coil and the second secondary coil, and the number of turns of the first secondary coil is also increased (than the number of turns of the second secondary coil). Additionally, even if the metal plate is located away from the first secondary coil, the displacement sensitivity does not decrease, allowing highly accurate measurement.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram of a differential mutual induction eddy current measurement sensor according to the present invention, Fig. 2 is a schematic diagram of a conventional differential/mutual induction eddy current measurement sensor, and Fig. 6 is a diagram showing a sensor for measuring mutual inductance. It is a differential connection diagram of a secondary coil. P...Primary coil, Sl...ith coil
o Secondary coil, S2... Second secondary coil.

Claims (1)

[Claims] The first and second secondary coils are arranged opposite to each other with the primary coil in between, and the distance between the primary coil and the first secondary coil is set to 1.
The differential type is characterized in that the distance between the primary coil and the second secondary coil is greater than the distance between the secondary coil and the second secondary coil, and the number of turns in the first secondary coil is greater than the number of turns in the second secondary coil. Sensor for measuring mutual induction amount eddy current.