JPS6212862B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic detector using a differential transformer method.

Such magnetic detectors are used to detect minute magnetic changes such as the earth's magnetic field, and conventionally the first
The configuration shown in the circuit diagram in Figure was used.

That is, each has a primary winding P and a secondary winding S
The first and second transformers T ₁ and T ₂ have the same winding ratio and use high magnetic permeability iron cores such as permalloy.
and the second transformer _T1 is connected to the primary winding _P1 of the first transformer
The primary winding P ₂ of transformer T ₂ is connected in series with opposite polarity, and the secondary windings of each transformer T ₁ and T ₂ are connected in series.
S ₁ and S ₂ are connected in series with the same polarity, and a resistor is connected to both ends of the series circuit formed by each secondary winding S ₁ and S ₂ through a prism circuit consisting of diodes D ₁ to D ₄ as a detector. A transformer R is connected to the transformer R, and each transformer is connected to both ends of the series circuit formed by each primary winding P ₁ and P ₂
An alternating current power supply G of a specific frequency is connected which passes the peak current just before the iron cores of T ₁ and T ₂ are saturated.

Therefore, currents i 1 , i ₂ of the polarities indicated by the arrows flow through the respective primary windings P ₁ , P ₂ , and thereby the currents i 1 , i ₂ having the polarities indicated by the arrows flow through the respective secondary windings S ₁ , S ₂ . voltages of opposite polarity e ₁ , e ₂
is induced, and since each transformer T ₁ and T ₂ have the same number of windings, e ₁ =e ₂ , and the combined voltage E is zero as shown in the following equation.

E=e ₁ -e ₂ = 0...(1) However, when the magnetic change H to be detected from the direction indicated by the large arrow is given, as shown in Figure 1A,
In the positive half cycle A by AC power supply G,
Currents i _1A , i _2A pass through each primary winding P ₁ , P ₂ , and the first
In the transformer T _{1 ,} the direction of excitation by the current i _1A and the direction of the magnetic change H are opposite to each other, and its iron core is excited in the non-saturation direction _. The mutual induction coefficient M ₁ changes in the increasing direction, and the voltage e ₁ of the secondary winding S ₂ increases by the amount of change Δe ₁ accordingly.

On the other hand, in the second transformer T ₂ , the direction of excitation by the current i _2A and the direction of the magnetic change H are the same, the iron core of this is excited in the saturation direction, and the primary windings P ₂ and 2
The mutual induction coefficient M ₂ with the secondary winding S ₂ changes in the decreasing direction, and accordingly, the voltage e ₂ of the secondary winding S ₂ changes by the amount Δ
The resultant voltage decreases by e ₂ , and the combined voltage E at this time is given by the following equation, assuming the conditions e ₁ = e ₂ = e and Δe ₁ = Δe ₂ = Δe, and assuming that the direction of e ₁ is positive. Become something.

E=(e ₁ +Δe ₁ )+(−e ₂ +Δe ₂ )=(e+Δe)+(−e+Δe)=2Δe…(2) Therefore, the voltage change due to magnetic change H is 2
It is obtained as Δe.

Furthermore, as shown in FIG. 1B, in the negative half cycle B of the AC power supply G, the combined voltage E at this time is given by the following equation based on the same principle.

E = (-e ₁ + Δe ₁ ) + (e ₂ + Δe ₂ ) = (-e ₁ + Δe) + (e + Δe) = 2Δe...(3) Therefore, the magnetic change H occurs every positive and negative half cycle of the AC power supply G. A voltage change of 2Δe is obtained.

Therefore, if the combined voltage E shown by equations (2) and (3) is detected by the diodes D ₁ to D ₄ , the detected output will be a DC voltage _{E d} proportional to 2Δe.
is obtained, and thereby the magnetic change H can be detected.

However, the forward voltage of diodes D ₁ to _{D 4} is generally about 0.6 V, and unless a forward voltage higher than this is applied, forward current will not flow, so they are turned off for a small composite voltage E. The problem was that the weak magnetic change H could not be detected.

The present invention has an object of solving the conventional drawbacks at once, and has a primary winding and a secondary winding, and the mutual induction coefficient between the primary winding and the secondary winding is the magnetic field to be detected. It has a first transformer that changes according to the change in temperature, a primary winding and a secondary winding having the same turns ratio as the first transformer, and a mutual induction coefficient between the primary winding and the secondary winding. a second transformer whose magnetic flux changes in a direction opposite to that of the first transformer in response to the magnetic change; and an AC power supply connected to both ends of a series circuit formed by the respective primary windings of the first and second transformers. In the magnetic detector provided, the first
A second transformer is connected in series with the primary winding of the transformer with the primary winding having opposite polarity, and is connected in series with the secondary winding of the first transformer with the secondary winding having opposite polarity. , a detector connected to both ends of the series circuit formed by the secondary windings of the first and second transformers to detect the alternating current voltage generated between the ends, and mutually equal resistors connected to the detection output of the detector. A voltage divider circuit consisting of first and second resistors of different values is provided, and a detection output is extracted from the connection point of each secondary winding and the connection point of each resistor in the voltage divider circuit and applied to the detector. The present invention provides an extremely effective magnetic detector that can reliably detect even weak magnetic changes by always maintaining a sufficient combined voltage.

The details of the present invention will be explained below with reference to the circuit diagram of FIG. 2 showing an embodiment.

In the same figure, the secondary winding S ₂ of the second transformer T ₂ is also connected in series with the secondary winding _{S 1} of the first transformer T 1 with opposite polarity, and each winding S ₁ , A diode is installed at both ends of the series circuit using _S2 as a detector to detect the alternating current voltage generated between the two ends.
A bridge circuit consisting of D ₁ to _{D 4} is connected, and a voltage divider circuit consisting of first and second resistors R ₁ and R ₂ having the same resistance value is connected to the detection output of this bridge circuit, and each secondary winding A load resistor Rs is connected between the connection point of the wires S ₁ and S ₂ and the connection point of the first and second resistors R ₁ and R ₂ , and the detection output E _p is obtained by the terminal voltage of this. ing.

Note that the capacitors C ₁ and C ₂ cause the respective secondary windings S ₁ and S ₂ to resonate at a specific frequency of the AC power supply G, thereby improving detection sensitivity.

Therefore, the composite voltage E is the sum of the voltages e ₁ and e ₂ and is expressed by the following equation.

E=e ₁ +e ₂ =e+e=2e...(4) That is, the combined voltage E is larger than the equations (2) and (3), and is sufficiently higher than the forward voltage of the diodes D ₁ to D ₄ . is always on, so the loss of diodes D ₁ to _{D 4} can be ignored.

Figure 3 is an equivalent circuit of Figure 2, ignoring the loss of diodes D ₁ to _{D 4.} This constitutes a bridge circuit including a general transformer, and is indicated by the large arrow in Figure 2. When a magnetic change H is applied from the direction shown, the combined voltage is expressed by the following equation based on the same principle as in FIG.

E = (e ₁ + Δe ₁ ) + (e ₂ - Δe ₂ ) = (e + Δe) + (e - Δe) = 2e (5) In addition, the current Δi flowing to the load resistor Rs is Current i _S1 flowing to the devices R ₁ and R ₂ ,
i _S2 and ignoring diodes D ₁ to D ₄ , Δi = i _S1 − i _S2 i _S1 = (e ₁ + Δe ₁ )/R ₁ i _S2 = (e ₂ − Δe ₂ )/R ₂ , e ₁ = e ₂ = e, Δe ₁ = Δe ₂ = Δe, R ₁ =
Since the condition is R ₂ , Δi=e+Δe/R−e−Δe/R=2Δe/R…(6
) E _p =Δi・R ₃ =2Δe/R・R ₃ …(7) Therefore, in addition to turning on the diodes D ₁ to _{D 4} , the detection output voltage E proportional to the magnetic change H
Since _p can be taken out, even weak magnetic changes H can be reliably detected without being affected by forward voltage characteristics.

In addition, depending on conditions, capacitors C ₁ and C ₂
may be omitted, or other directional elements may be used as the detector, or other detection circuits other than _the diode bridge circuit may be _used . Various modifications can be made, such as inserting a potentiometer to enable balance adjustment.

As is clear from the above explanation, according to the present invention, weak magnetic changes can be sufficiently and reliably detected without using a diode with a particularly low forward voltage, so that it can be highly effective as a magnetic detector for various uses. It will be done.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a conventional example, FIG. 2 is a circuit diagram showing an embodiment of the present invention, and FIG. 3 is an equivalent circuit of FIG. T ₁ ...first transformer, T ₂ ...second transformer, P ₁ ,
P ₂ ...Primary winding, S ₁ , S ₂ ...Secondary winding, D ₁ to _{D 4}
...Diode (detector), R ₁ ...First resistor,
R ₂ ... Second resistor, G ... AC power supply, E _p ... detection output.

Claims (1)

[Claims] 1. A first transformer having a primary winding and a secondary winding, in which a mutual induction coefficient between the primary winding and the secondary winding changes in accordance with a magnetic change to be detected, and the first transformer. has a primary winding and a secondary winding with the same winding ratio, and the mutual induction coefficient between the primary winding and the secondary winding is in the opposite direction to that of the first transformer in response to the magnetic change. A magnetic detector comprising a second transformer that changes, and an AC power source connected to both ends of a series circuit formed by primary windings of the first and second transformers, wherein the primary winding of the first transformer the second transformer, the second transformer having a primary winding connected in series to the line with a reverse polarity, and a secondary winding connected in series to the secondary winding of the first transformer with a secondary winding having a reverse polarity; and a detector connected to both ends of the series circuit formed by each secondary winding of the second transformer to detect the alternating current voltage generated between the ends, and a detector having equal resistance values connected to the detection output of the detector. a voltage divider circuit consisting of a first and second resistor; a point connecting each secondary winding of the first and second transformers and a connection point of the first and second resistors of the voltage divider circuit; A magnetic detector characterized by obtaining detection output from.