JPH0334691Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic body detection sensor used in a balanced bridge circuit suitable for detecting magnetic bodies, particularly weak magnetic bodies.

When a weakly magnetic material (for example, magnetic impurities contained in metals such as aluminum or copper, or magnetic toner for dry copying machines) is brought close to an inductance element with an open magnetic path, a minute change in inductance is detected.

In order to detect this minute change in inductance with high sensitivity, a bridge circuit is usually used.

In order to increase the sensitivity (S/N ratio) in a bridge circuit, it is necessary to maintain a zero balance state (hereinafter simply referred to as balance) as much as possible.

It is well known that in order to maintain balance in a bridge circuit as shown in FIG. 1, the following relationship is required: Z ₁ .Z ₄ =Z ₂ .Z ₃ (1).

Now, if Z ₂ is a magnetic sensor inductance element, then Z ₁ , Z ₂ , Z ₃ are set so as to maintain the relationship of equation (1).
The elements to be used are selected and adjusted. however,
Due to the high sensitivity of bridge circuits, the balance is likely to be lost due to differences in the temperature characteristics and aging of each element used. In addition, as an inductance element for a sensor, a winding 2'a as shown in FIG.
If the U-shaped core 1'a is used, even if a ferromagnetic material other than the object to be detected approaches a surface other than the detection surface, the balance of the bridge will be lost. Furthermore, in a magnetic sensor using an inductance element, if an alternating magnetic field exists near the sensor, an induced voltage will be generated in the sensor winding, causing the bridge to become unbalanced.

Therefore, such sensors are
Restrictions were needed on the surrounding environment, etc.

The purpose of the present invention is to solve such drawbacks and provide a sensor for detecting magnetic substances that does not cause malfunctions due to magnetic substances that are close to the surface other than the detection surface or AC magnetic fields that exist near the sensor part. shall be.

In the present invention, an inductance element for a sensor formed by winding a magnetic core having an open magnetic path portion is used as one side of a bridge circuit, and a drive signal is applied between a pair of opposing vertices of the bridge circuit. In a sensor for detecting a magnetic body for use in a magnetic body detection device, the sensor for detecting a magnetic body is configured to obtain a detection output between the other pair of opposing vertices of the bridge circuit when a magnetic body approaches the open magnetic path portion of the inductance element for use. A sensor inductance element and a balancing inductance element used for the balancing side of the sensor inductance element in the bridge circuit are housed in one case having a detection surface, and the sensor inductance element and the balancing inductance element are housed in a single case having a detection surface. Both the elements are formed by winding a central columnar part of a pot-shaped core having the same shape and an open magnetic path part in only one direction, and the open magnetic path part is placed in the case. These magnetic substance detection sensors are characterized in that they are arranged in parallel facing the detection surface.

Note that a step may be provided at the housing position of the sensor inductance element and the balancing inductance element in the case.

Further, a three-terminal configuration can be adopted in which the sensor inductance element and the balance inductance element are wound in the same direction, and the beginning of one winding and the end of the other winding are commonly connected.

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

FIG. 3 shows a magnetic substance detection sensor 10 according to the present invention.
This is an example. With reference to the same figure, 1a, 2a
is a pot-shaped core (Mn
−Zn ferrite system μ1800), respectively.
300 turns of winding 1b around the central columnar part,
2b is applied to configure the inductance elements 1 and 2. The inductance element 1 is used as an inductance element for a sensor. On the other hand, the inductance element 2 is used as a balancing inductance element used on the balanced side of the bridge. The two inductance elements 1 and 2 are housed in one case 3 side by side with the open magnetic path direction facing the detection surface side with a difference in level. Moreover, the two windings 1b and 2b are
They are wound in the same direction, and the beginning of one winding and the end of the other winding are connected to a common terminal 4b, and the end of one winding and the beginning of the other winding are connected to terminals 4a and 4, respectively.
It is connected to C and has three terminals 4a, 4b, and 4c.

In the circuit shown in FIG. 1 described above, resistance elements (partially variable) are used for Z ₁ and Z ₃ , and inductance elements 1 and 2 of the sensor 10 of FIG. 3 are used for Z ₃ and Z ₄ . If the common terminal 4b of the sensor 10 is used as the ground terminal at the output end, a bridge circuit as shown in FIG. 4 will be obtained. L _{S and LB} indicate the inductance of the sensor inductance element 1 and the balancing inductance element 2, respectively.

In Fig. 4, an AC voltage with a frequency f8kHz input maximum change voltage Vp.p ₁ 10V is applied to the input terminal as a drive signal, and the sensor 10 when a magnetic body approaches from the detection surface direction of the sensor 10 from the balanced state of the bridge. FIG. 5 shows the change in the detected output maximum change voltage V _ppp corresponding to the change in inductance (ΔLs/Ls) of the inductance element Ls.

In this embodiment, since the two inductance elements 1 and 2 have a step in the direction of the detection surface, the change in inductance of the sensor inductance element 1 due to the approach of a magnetic body is due to the change in inductance of the other balancing inductance element 2. Always greater than change.

On the other hand, it has been confirmed that when a ferromagnetic material (for example, a steel plate) is approached from other than the detection surface, the sensor 10 according to the present invention does not lose its balance because the open magnetic path is only in one direction. can.

In addition, in order to examine the influence of an external alternating magnetic field applied to the sensor, a 100 Hz alternating magnetic field was applied to the sensor 10, and the bridge detection output _V1 was measured.

As shown in FIG. 6, the vertical axis shows the change in V1 V _ppp (mV) with respect to the change H _pp (gauss) in the strength of the alternating current magnetic field (maximum magnetic field value) shown on the horizontal axis.

For comparison, the change in the strength of the alternating current magnetic field (maximum magnetic field value) of the detection output V2 when the two inductance elements 1 and 2 are separated and an alternating magnetic field is applied to only one of them, H _pp (gauss), is compared with the change in V2. Change V _ppp
(mV) is also shown.

When the sensor and balance inductance elements 1 and 2 are arranged side by side as in the present invention, the same degree of alternating current magnetic field is applied to both inductance elements 1 and 2, generating an induced voltage. Due to the wiring, the induced voltages cancel each other out, and the output voltage of the bridge can be made extremely small.
Therefore, restrictions on use in an alternating magnetic field can be reduced.

In the magnetic body detection sensor according to the present invention, since the sensor inductance element and the balancing inductance element have the same core and the same winding, the inductance value temperature characteristics and aging changes can be made almost the same.

Furthermore, since both inductance elements are arranged in parallel, there is almost no difference in inductance due to a difference in temperature. Therefore, the balance of the bridge can be well maintained even in the face of temperature fluctuations.

Furthermore, the cores of both inductance elements are pot-shaped cores with an open magnetic path in one direction, and the open magnetic path is placed toward one detection surface of the case, so even if a magnetic body approaches other than the detection surface, , it is not sensitive to this, and malfunctions are prevented.

As described above, according to the present invention, problems with temperature characteristics, aging, effects of ferromagnetic materials other than the one to be measured, or induced voltage due to alternating current magnetic fields, which have been problems with conventional sensors for detecting magnetic materials using inductance elements, can be solved. It was possible to prevent the balance from being disrupted due to this, and it was possible to significantly reduce restrictions on installation location and environment.

Furthermore, in the sensor for detecting magnetic substances according to the present invention,
The two inductance elements may be similar,
It is structurally simple, can be provided at low cost, and is industrially advantageous.

In addition to being used as a normal magnetic material sensor, specific examples of the use of this invention include non-contact detection of the remaining amount of magnetic toner for ordinary dry copiers, and output voltage based on the difference in the magnetism of the magnetic material. Suitable for coin sensors, magnetic toner concentration sensors, etc. that utilize different V _ppp .

[Brief explanation of the drawing]

Fig. 1 is a bridge circuit diagram used in a magnetic substance detection device, Fig. 2 is a perspective view of an example of an inductance element used in a conventional magnetic substance detection sensor, and Fig. 3a is a longitudinal cross-section of an embodiment of the present invention. Front view, Figure 3b
4 is an external view of the pot-shaped core used in the present invention.
The figure is a bridge circuit diagram using the sensor in Figure 3a,
Figure 5 is a relationship diagram between the inductance change rate of the sensor inductance element and the detection output voltage of the bridge circuit when a magnetic substance is close to the detection surface of the sensor, and Figure 6 is the relationship between the strength of the applied AC magnetic field and the detection of the bridge circuit. In the relationship diagram with the output voltage, V ₁ indicates the case of the present invention, and V ₂ indicates the case where an alternating magnetic field is applied only to either the sensor or balance inductance element. 1... Inductance element for sensor, 2... Inductance element for balance, 3... Case, 1a,
2a... pot-shaped core, 1b, 2b... winding, 4
a, 4b, 4c...Terminal, 10...Sensor for detecting magnetic material.

Claims (1)

[Claims for Utility Model Registration] A sensor inductance element formed by winding a magnetic core having a closed magnetic path portion is used as a part of a bridge circuit, and a drive signal is applied between a pair of opposing vertices of the bridge circuit. , a sensor for detecting a magnetic body for use in a magnetic body detection device, which obtains a detection output between another pair of opposing vertices of the bridge circuit when a magnetic body approaches the open magnetic path portion of the inductance element for the sensor. The sensor inductance element and the balancing inductance element used for the balancing side of the sensor inductance element in the bridge circuit are housed in one case having a detection surface, and the sensor inductance element and Both the balancing inductance element and the balancing inductance element each have the same shape and are formed by winding the same number of wires on the central columnar part of a pot-shaped core having an open magnetic path part in only one direction, and The open magnetic path portions are arranged in parallel with a step difference, with the open magnetic path portions facing the detection surface, and the winding directions of the sensor inductance element and the balancing inductance element are the same, and the winding direction of the sensor inductance element and the balancing inductance element are the same, and A magnetic substance detection sensor characterized by a three-terminal configuration in which the other end of the winding is connected in common.