Magnetic field sensing apparatus

© Start of patent term: 1977 09 15

Longest possible duration:

© Issued on: 1978 05 10 © inventor:

© dependence:

© Pamphlets considered to delineate the prior art:

No.343209

This invention relates to a device which generates an output signal upon sensing a magnetic field. In particular, it relates to the use of such a device as a non-contact switch which is actuated upon the approach of a magnetic field.

In many applications, a switching function is to be generated as a function of a mechanical component without the use of mechanical contacts which are actuated by a mechanical component and thereby physically closed. Such activity can generally be achieved with a non-contact switch. This means that, depending on the position of the mechanical component in question, a switching function, eg the actuation of an electronic switching element takes place. In general, various types of non-contact switches are known. Among them, there are photoelectronic, electrostatic and magnetic sensitive components with all of which a switching function can be made without actual physical engagement of mechanical contacts.

A typical magnetosensitive non-contact switching element heretofore used has been the known magnetic head commonly used as an electromagnetic transducer in recording and reproducing operation of magnetic tapes. If it is used as a non-contact Sehalter an electrical output signal is generated as a function of a magnet adjacent to the magnetic head. When the relative position of the magnetic head and the magnetic pole is changed, this change in position produces the electrical output signal. Accordingly, in this particular application, the magnetic head can be used to generate various switching functions.

However, the use of the magnetic head as a non-contact switch suffers from various disadvantages. A disadvantage lies in the relatively large structure which is necessary. The magnetic head requires an electromagnetic coil, a suitable support core and a bias signal oscillator for the head to detect the presence and proximity of an external magnetic field. Further, when the magnetic head is used as a non-contact limit switch, a high-sensitivity output can not be obtained unless the head is placed very close to the magnetic field source, ie, the magnet. Such a small distance, however, restricts the scope of application of these heads as non-contact switches. The magnetic head is thus unsatisfactory in several applications and not overwhelmingly successful in many commercial designs.

An object of this invention is therefore to provide a device which generates an output signal in response to the sensing of a magnetic field.

Another object of this invention is to provide a magnetically actuated non-contact switch that does not suffer from the disadvantages of the prior art devices.

Yet another object of this invention is to provide a magnetic field detector having a magnetic resistance element capable of producing an output signal in response to the proximity of a magnetic field source.

Yet another object of this invention is to provide a non-contact switch having a magnetic resistance element.

Another object of this invention is to provide a small, high sensitivity magnetic field sensing device that can be used as a non-contact switch.

An additional object of this invention is to provide a device with which the relative position of a generator magnet can be displayed.

Another object of this invention is to provide a device which can be seen when a movable part has been deflected beyond tolerable limits.

It is another object of this invention to provide a device capable of coded encircling a rotatable member.

Yet another object of this invention is to provide a magneto-sensitive card reader for information cards.

Various other objects and advantages of this invention will become apparent from the following detailed description, the novel aspects of which are pointed out with particularity in the appended claims.

The device serves to generate an output signal when it senses the proximity of a source of magnetic field, comprising: a magnetic resistance element having an insulating support and two ferromagnetic strips on the support forming two main lines facing each other, the strips being connected in series about a connection point therebetween set; Impedance elements parallel to the series-connected strips to form a bridge circuit, the connection point between the strips including a bridge output terminal; a generator magnet for generating a magnetic field whose surface is in a plane spaced from the magnetoresistor element to produce an output signal from the bridge circuit as a function of the relative positions of the leading and trailing edges of the generator magnet to a leading edge of the magnetoresistive element.

The invention will now be described with reference to the drawings, in which: Fig. 1 is a plan view of a

No . 343209

Magnetic resistance element which can be used in an embodiment of this invention; Fig. 2 is a schematic view showing the working principle of a magnetic resistance element used in this invention; Fig. 3 is a diagram in which the ratio of the change of the output signal of a magnetic resistance element is shown to the direction of a magnetic field applied to it. Eig. 4 is an equivalent circuit diagram for FIG. 2; FIG. 5A to 5C are schematic diagrams showing how the magnetic resistance element generates output signals as a function of a nearby magnetic field; Figures 6 and 7 are schematic diagrams showing how the output signals produced by the magnetic resistance elements are processed to obtain another output; Figures 8A to 8C are graphical representations of the output signals derived from the apparatus of this invention; FIG. 9 A to 9 C show further arrangements in which an output signal is reproduced as a function of the proximity of a magnetic field; Fig. 10 is a graph showing how the output from the magnetic resistance element of this invention changes as a circuit parameter changes; Figures 11A and 11B illustrate how this invention can be used to generate a modified output signal; FIG. 12 and Figure 13 shows schematic representations of the temperature compensation technique that may be used in this invention; Fig. 14 is a schematic diagram of another embodiment of this invention; Fig. 15 is a schematic view showing how the magnetic resistance element used in this invention is provided with a composite magnetic field; FIG. 16 Figures A and 16B show in a schematic representation how this invention can be used as a non-contact switch; Figures 17A and 17B are schematic illustrations of how this invention can be used to determine angular displacement of a rotatable member; Figs. 18A and 18B are a schematic illustration of how this invention can be used to determine a linear displacement of a movable member; FIG. 19 Fig. 20 is a schematic illustration showing how this invention can be used to read coded information from a data card, for example.

The same reference numerals are used throughout the drawings. Fig. 1 shows the schematic representation of a magnetic resistance element -10- which can be used with this invention. On an insulating support, a thin layer of ferromagnetic material is applied at a thickness of 600 to 1000 Å, for example, by a conventional vacuum evaporation method. As typical carriers, glass slides, photo-dry plates or the like. but other suitable materials can be used. The thin layer is then etched to zigzag the ferromagnetic strips -A and B- as shown here in a serpentine pattern or in strips together with the terminals -5, 7A and 7B-. The ferromagnetic strips -A and B- include a plurality of main flow paths - 2A and 2B- with the associated connectors -3A and 3B-, respectively. The main flow paths - 2A and 2B - are substantially perpendicular to each other.

In the position shown in FIG. 1, the strips -A- can guide the stream predominantly in a vertical direction and the strip B in a horizontal direction. Of course, other mutually perpendicular directions can be used for the power supply. The last path -4A- of the main flow path -2A- is in series with the first path -4B-- of the main flow path -2B-. The connection point of the last path -4A- to the first path -4B- is connected to the connection -5-. The terminals -7A and 7B- serve as power supply terminals for the magnetic resistance element, they are connected via the parts -6A and 6B- with the paths -2A and 2B-.

Magnetic resistance element -10- is disclosed in co-pending patent application Ser. No. 487,282 of

10th In July 1974, in more detail. Further, the use of this magnetic resistance element for detecting the direction of a magnetic field is disclosed in another pending patent application.

As shown in the latter, it is better to use the magnetic resistance element -10- in a magnetic field which is large enough to saturate the ferromagnetic strips -A and B- to provide a self-limiting effect on the output signal by which the output signal is substantially insensitive to field strength variations becomes.

In Fig. 2 is shown schematically how the strip A and B are electrically in series. The power supply terminals -7A and 7B- are at the opposite ends of the strips -A and B-, and the output -5- is connected to the connection point of the serial strips. Between the power supply terminals -7A and 7B ~ is a voltage source -8-. A power supply terminal -7- is connected to a reference potential, eg ground. The resulting magnetic resistance element forms a sampling circuit for detecting magnetic fields.

Let it be assumed that a magnetic field H is applied at an angle Θ relative to the longitudinal direction of the strip A with a field strength to the strips A and B which is sufficient to saturate the strips.

Generally, the resistance of a saturated ferromagnetic material is anisotropic. That is, the

No.343209

Resistance of such a substance is greater in the magnetization direction than perpendicular thereto. Accordingly, the resistances pa^un5 PB strips -A and B- are represented by the Voight-Thomson formula:

PA (Θ) = PJ. sin "© + p |, cos²© ρ-θ (Θ) = PJ. cos²© + p μ sin²© (1) (2)

Where pj_ is the resistance of a ferromagnetic strip -A or B- which is saturated with a magnetic field perpendicular to the longitudinal direction of the strip and pn is the resistance of a ferromagnetic strip saturated with a magnetic field parallel to the longitudinal direction of the strip.

Fig. 4 shows an equivalent circuit of the magnetic resistance element shown in Fig. 2. The voltage division gives at output -5- a voltage V (©) which is given by:

Where V is_O the voltage of the voltage source -8-.

Substituting equations (1) and (2) into equation (3) and ordering them to obtain:

<img file="AT343209B_D0001.tif" />

Δ p cos 2 ©

2 (pii + pj,) ' ^V° (4) with

Δρ = p, | - pj. ,

In equation (4), the first term represents a constant voltage Vs, which is a function of the span

<img file="AT343209B_D0002.tif" />

Voltage due to the influence of the magnetic field -H-. This change of the output voltage is denoted by ΔV (Q). When the resistance of the ferromagnetic strip -A or B-- when

Absence of a field -H- denoted by θ and is 2 p_Q = p «+ ρχ, so you can ^Δν(Θ) ^al^s

<img file="AT343209B_D0003.tif" />

(5) write.

From equation (5) it can be seen that Δν ^ θ ^ assumes a maximum positive or negative value, i. E.

the absolute value of the output voltage change increases at an angle © of 0 °, 90 °, 180 ° and 270 ° -the cos θ ± 1 - is maximum.

Fig. 3 shows the graph of equation (4). It can be seen that the output V (Q) of the MaV_O If the magnetic field - H ~ at an angle © = 45 ° to the

Strip lies. This means: AV ^ = 0, since θ = 45θ, cos 2 © = 0, Furthermore, the output voltage ν ^ θ ^ becomes a minimum or a maximum at an angle φ = oo and 900.

It will now be described how the magnetic resistance element shown in Fig. 1 and described above mathematically is applied in this invention. Figs. 5A to 5C show the mutual position between a magnetic field source -11 and a magnetic resistance element -10. Preferably, the generator magnet -11 is magnetized in the direction of its thickness -t-. That is, one surface of the magnet carries the south pole -S-, the opposite surface the north pole -N-. For the description of this invention, it shall be assumed that the pole face -S- lies in a plane which is spaced from the magnetic resistance element -10- by the distance -d-. In Fig. 5A, the support surface of the magnetoresistive element -10- - in the sequence the plane of the magnetoresistive element - is substantially perpendicular to the S-pole face.

The generator magnet has a length - L- and a height -h-, it can be moved in the ± x direction to both sides. In the embodiment shown here, the magnetic field -Hg- is substantially parallel to the plane of the magnetic resistance element. Assuming that the generator magnet

No. 343209 nearest edge of the magnetoresistive element the leading edge of the element and the outermost right edge of the magnet 11 and the leftmost edge of the magnet the front and If the magnet is moved in the ± x direction, it will be seen that the magnetic resistance element at the output produces a signal which is a function of the relative positions of the leading and trailing edges of the generator magnet -11- to the leading edge of the magnetic resistance element -10- is,

Fig. 5B shows another arrangement in which the magnetic resistance element -10- is adjacent to the generator magnet -11. Similar to the embodiment of Fig. 5A, the magnetoresistance element -10- is spaced from the S-pole surface by a distance -d-, and the generator magnet -11- can be moved in both directions in the ± x direction. However, it can be seen that the magnetic resistance element -10- has been rotated clockwise by 90 ° C. In this position, the leftmost edge of the magnetoresistive element -10- can be regarded as the leading edge of the magnetoresistance element in the embodiment of FIG. 5B. This gives an output signal depending on the ratio between the leading and trailing edges of the generator magnet -11- to the leading edge of the magnetic resistance element -10- at the output -5- of the element.

In the embodiment shown in Fig. 5C, the S-pole face of the generator magnet -11- is substantially parallel to the plane of the magnetic resistance element -10- and spaced therefrom by the distance -d-.

As will be described in detail below in connection with FIGS. 8A to 8C, in the embodiment shown in FIG. 5, the magnetic resistance element -10- generates an output signal which represents a function of the magnetic field detected by the element. Preferably, the magnetic field Hg-- generated by the generator magnet 11 - should have a component which is parallel to the plane of the magnetic resistance element.

From Figs. 5A and 5B, it can be seen that the major component of field-H₂Parallel to this direction. In the embodiment shown in Fig. 5C, only a minor component of field -H - is parallel to the plane of element -10-, yet this minor component at output -5- also provides an output signal. The nature of the generated output signal and the mutual position between the element -10 and the magnet -11 which is decisive for the output signal will be described later.

Fig. 6 shows a schematic circuit diagram in which then an output signal e₀ is generated when the magnetic resistance element -10-scans the rectilinear motion of the generator magnet -11-. It should be noted that the mutual position between the element -10 and the magnet -11- corresponds to the embodiment previously described in connection with FIG. 5,

The series-connected resistors -R ^ and Rg- are connected to the power supply terminals -7A and 7B- of the magnetic resistance element, forming a bridge circuit with the 35 outputs -5 and 5 '- respectively. This bridge circuit is supplied by the voltage source -8-one

Preload V_O supplies.

The outputs -5 and 5'- of the bridge are connected to the inputs of a differential amplifier -12- whose output is connected to a circuit output -13- which is the output signal e₀ supplies. The differential amplifier -12- is conventionally constructed and may include an operational amplifier 40 whose positive input is connected to the bridge output -5 '- and whose negative input is connected to the bridge output -5-. Of course, if desirable, these input terminals of the differential amplifier may also be reversed.

The bridge circuit is set by setting the resistor "" Hg^{- a}kS^eGüchen of a potentiometer, a rheostat or the like was included.

Assume that the magnetic resistance element -10- produced an output that was a function of the relative position between the generator magnet -11- and the element -10-. This position-dependent output signal should be denoted by V (x). This signal V (x) corresponds to the signal V (G) of the above-mentioned equation (5). Consequently, the output signal e "at the output -5- of the magneto-resistance element -10- came with e = 1 / 2V_O + V (x) are shown. The output signal e ^ appearing at the bridge output is only e ^ = 1/2. The differential amplifier -12- pulls the signal e₂ from the signal e ^ and amplifies this difference signal in a suitable manner. Thus, the output signal e lying at the terminal 13 is₀ = ο: (β ^ -β₂) = a: V (x), whom the diferential amplifier -12- has the spam gain a. The output signal eo generated by the illustrated circuit is thus a direct representation of the mutual position between the magnetic resistance element -10 and the generator magnet -11-. A relative movement between the two results in a corresponding change of the output signal e₀, As will be shown, in many applications a stationary magnetic resistance element -10- is preferred,

In Fig. 7, another embodiment of the circuit shown schematically in Fig. 6 is shown. In this alternative embodiment, the bridge output 5 is connected across the resistor Rg-

Nr.343209

Input of the differential amplifier -12- placed. To connect the differential amplifier output to the input a Rüekkoppelwiderstand Κθ is provided. Furthermore, the bridge output -5'- Uber one from the series connection of the resistors R_G and R ^ existing voltage divider connected to the other input of the differential amplifier.

In the representation shown in FIG. 7, therefore, the bridge output signal from the resistors R_G and R ^ and the bridge output e₂ from the resistors R_G and R_G divided. The differential amplifier -12- is constructed in a conventional manner, the output signal e₀ can be represented as:

_ ^{+ R}ü) ^r4 θ ^R6 (R₃ + R₄) 'r₅ '1 R

Is Rg = Rg and R₄ = R_G this simplifies the equation too

It can thus be seen that in the embodiment of FIG. 7, the output signal e₀ is a direct representation of the relative position between the generator magnet -11- and the magnetic resistance element -10-. Changes in the position of the magnet to the element, ie, changes in the relative positions of the leading and trailing edges of the magnet 11 to the leading edge of the magnetic resistance element 10, produce a corresponding change in the output signal e₀,

FIGS. 8A to 8C show a graphical representation of the output signal e₀ which is then produced by the embodiments of FIGS. 6 and 7, when changing the relative position between the generator magnet -11- and the magnetic resistance element -10-. In all of these graphs, let it be assumed that the generator magnet -11- has a length -L- in the ± x direction, a height -h-, and a thickness -t-. Furthermore, it is assumed that the surface of the generator magnet closest to the magnetoresistive element lies in a plane which is spaced from the element by the distance -d-.

Finally, suppose that each of the strips -A and B- on the support layer of the magnetoresistive element covers an equal area having a length -1- measured from the center of the element to an opposite edge.

In Fig. 8A, the output signal e₀ represented with the following parameters:

1 = 1 mm L = 20 mm h = 6 mm d = 1 mm

As can be seen, the generator magnet is magnetized in the direction of its thickness -t- and for this embodiment it is assumed that the S-pole face is closest to the magnetoresistive element -10- and the N-pole face lies on the opposite face of the magnet -11-. The magnetic field -H₂Thus starts from the N pole face and is directed to the S pole face. The main component of this field is parallel to element -10-,

Initially, suppose that the generator magnet -11- is spaced very far to the left of the element, although it is spaced apart from the magnetoresistor element-10 at the constant distance. The distance -x can therefore be considered as infinite. At this distance, substantially no field H is produced by the magnetoresistor element-10₂ sampled. One can therefore assume that the component V (x) is equal to zero. If the magnet -11- is now moved closer to the magnetic resistance element -10- in the + x direction, the element will soon detect part of the flux generated by the magnet. In the graph, this part is labeled E. The polarity of this sampled flow can be attributed primarily to one or the other pole. In any case, the sensed flux increases as the generator magnet -11- is moved closer to the magnetic resistance element -10-, and the curve E increases accordingly. However, a point is reached where the dominant polarity of the flow determined by the element is reversed. If the element has detected a flux associated with the North Pole, then at point G, the flux due to the South Pole suddenly prevails.

Because of this sharp change in the flux polarity detected by the element 10, therefore, the output signal e also changes₀ accordingly. As you can see with the above assumed parameters this sharp change of the output signal e_Q at point G, when the leading edge -11a of the generator magnet -11- is about 12 mm from the leading edge of the magnetic resistance element -10-.

The output signal e_Q now remains at the indicated level, eg between -3 and -4 volts, until the

No.343209

Trailing edge -11b- of the generator magnet -11- is about 10 mm across the edge of the magnetic resistance element -10- across. At this point, the output signal e increases_Q by a further sharp reversal of the sampled Flußpolarität suddenly to the point H. If the generator magnet -11 further moves in the + x direction, the output signal e appears_Q as a curve I. As you can see, this curve suddenly falls below the zero level and then increases asymptotically when the magnet moves farther away.

It can be seen that an output signal e_Q with the curve shown in Fig. 8A for indicating the approach of the generator magnet -11- to the magnetic resistance element -10-. Furthermore, the characteristic curve shown can be used as a switching function in a non-contact switch.

Before typical applications of the magnetoresistive element -10- with the generator magnet -11- are described, additional output characteristics of the supplied contact signal e₀ be set out. In Fig. 8B are graphs of the output signal e₀ for the arrangement of Fig. 5B. The following parameters were used for the illustrated curves:

1 = 1 mm

L = 6mm h = 6mm d = 1mm, 3mm

The graphical representation of the output signal e_Q Fig. 8B is somewhat similar to the one described above in Fig. 8A. If the generator magnet 11 is located very far to the left of the magnet 20 resistance element, then the flux provided by the magnet has essentially no effect on the element. When the magnet is moved in the + x direction, a flux of one polarity is sampled which is the output e shown_Q entails. When the leading edge -11a- of the generator magnet -11- approaches the leading edge of the magnetic resistance element -10-, the output signal e decreases₀ to. As already described above, a point is reached at which the flux polarity sensed by the magnetic resistance element suddenly reverses. In a further movement of the generator magnet in the + x direction away from this point, the output signal e falls₀ below the zero axis until a maximum peak voltage of about -3.5V is reached. This maximum peak voltage is obtained when the generator magnet -11- and the magnetoresistance selement -10- are substantially symmetrical. By further movement of the generator magnet in the + x direction, the output signal e increases_O over the zero axis until a point is reached at which the polarity of the sensed flow changes again. Upon further movement of the generator magnet away from this point, the output signal e approaches₀ the zero axis asymptotic.

From the graph of Fig. 8B, it can be seen that the maximum peak voltage, which is the output e₀ irrespective of whether the generator magnet -11- is spaced from the magnetoresistance element -10-by a distance - d- of 1 mm or 3 mm. However, this change in the distance -d- has a decisive influence on the zero crossings of the output signal.

FIG. 8C shows a graphical representation of an output signal e₀ generated by the arrangement of the magnetic resistance element -10- and the generator magnet -11- shown in Fig. 5C. The parameters for the illustrated output signal are:

1 = 1 mm

L = 20 mm h = 6 mm t = 3 mm d = 2.5 mm

As can be seen, the general shape of the curve shown in Fig. 8C is similar to that of the previously described curves of Figs. 8A and 8B. However, the transitions of the curve of Fig. 8C are not as sharp as in the curves described above.

A comparison of these curves with one another shows that the zero crossings, correspondingly shift, when the length -L- of the generator magnet -11- is changed. Taking the distance between the 50 zero crossings, i. the distance between the negative and positive transitions through the zero axis as an indication of the driving range of the scanning operation of the magnetic resistance element -10, it is recognized that this driving range can be set arbitrarily in accordance with a specific length of the generator magnet. Furthermore, the generator magnet may be spaced from the magnetoresistor element-10 by a correspondingly greater distance -d- as the thickness -t- of the rotor magnet -11- is increased.

No . 343209

The graphs of Figs. 8A and 8C show that the maximum peak of the output e₀ has a negative polarity. Since this output signal e_Q is generated by a Differentlaiverstärker which in turn is supplied with the originating from the bridge circuit output signals βχ and it is seen that the maximum peak value of the output signal e_Q may also have the opposite polarity (eg, positive polarity), when the inputs of the differential amplifier, where the output signals of the bridge circuit are interchanged. With regard to the circuit of Fig. 6, this means that the output signal of the differential amplifier e shown in Figs. 8A to 8C₀ is inverted when the bridge output signal and the negative input of the differential amplifier and the bridge output signal β2 are applied to the positive input.

In order to obtain the graphs shown graphically in FIGS. 8A to 8C, it was assumed that the longitudinal axis of the generator magnet -11- is perpendicular to the longitudinal axis of the magnetic resistance element -10- (FIG. 8A) or parallel thereto (FIGS. 8B and 8B) 8C). If the arrangement shown in Fig. 5B is modified so that one inclines the longitudinal axis of the generator magnet until, as shown in FIG. 9A and 9B, with the longitudinal axis of the magneto-resistive element -10- including an angle of about 300, the resulting output signal e corresponds₀ the graph shown in Fig. 9C. Although the general shape of this curve is similar to the curves described above, the control yield has been increased. This can easily be seen by comparing the curve of FIG. 9C with the curve of FIG. 8B, both of which originate from the same arrangement of magnet and element, except that an angular position was assumed in FIG.

The size of the voltage applied to the magnetic resistance element supply voltage has a significant influence of the in the output voltage e₀ characterizing, superimposed curves of Fig. 10 is shown. For example, the topmost curve is from an embodiment of FIG. 5B with a 5.75V supply voltage. If this supply voltage decreases, then it will be seen that the general shape of the output voltage curves remain substantially the same but the actual output voltage levels are changed.

Furthermore, the zero crossings of these curves change accordingly. As a result, the modulation range of the magnetic resistance element and thus also its sensing sensitivity change when the supply voltage V_Q will be changed. Thus, these factors can be arbitrarily set only by supplying the magnetic resistance element with an appropriate voltage.

In the embodiments described above, it has been assumed that the magnetic resistance element is disposed opposite to a pole face of the generator magnet. However, if the element -10- is oriented with respect to the direction of the thickness of the magnet so that the flux generated by the magnet is substantially parallel to the plane of the magnetic resistance element, as shown in FIG. 11A, the resulting output signal shown in FIG. 11B is obtained e₀ which occurs when the generator magnet is moved in the ± x direction. This omega-shaped curve allows for various designs and can be used to determine accurate relative positions of the generator magnet.

In the bridge circuit shown in Figs. 6 and 7, it can be seen that the temperature coefficients of the resistors -R ^ and Rg- are different from the temperature coefficients of the ferromagnetic strips -A and B- of the magnetic resistance element -10. The bridge circuit can thus come out of balance as a function of the ambient temperature during operation and must be re-calibrated. In addition, an unbalanced bridge can provide incorrect output signals. To prevent this, another embodiment of this invention has two magnetic resistance elements -10a and 10b-which, as shown in FIG. 12, are connected as a bridge. If the resistance characteristics of these respective elements are not equal, one can provide an adjustable resistor, for example a potentiometer -VR-, for balancing the bridge. As can be seen, the supply of the supply voltage -8- to the magnetic resistance elements -10a and 10b- takes place via the adjustable resistor --VR-.

The bridge output signals e₂ and e ^ is obtained from the respective outputs -5a and 5b- of the magnetic resistance element; they are processed in the same way as previously described with reference to Figs. 6 and 7 to provide an indication of the mutual position between the generator magnet -11 and the magnetic resistance element -10a-.

The effect of the flux originating from the generator magnet -11- on the magnetic resistance element -10b-originating output signal βχ can be substantially minimized when the field is applied to the magneto-resistive element with respect to the strip -Δ- at an angle of 45 ° becomes. From equations (4) and (5), it can be seen that when Θ = 45 °, the cos 2 Θ becomes zero and the fraction AV (Q) of the equation (5) reduces to zero. Thus, the output signal βχ becomes substantially equal to ^ · regardless of the movement of the generator magnet -11-. The temperature dependence of the sensing element of FIG. 12 is thereby substantially stabilized, so that the output signal e₀ is not affected by temperature changes.

In Fig. 13, another embodiment of a temperature-compensated magnetoresistor belt 9 is shown

No . 343209 tes shown. As you can see here are the corresponding magnetic resistance elements -10a and 10b- mounted on the same support and have the same temperature coefficient. With this arrangement, an applied magnetic field can be determined. In the embodiment shown in Fig. 13, the output signals produced at the outputs 5 and 5 'of the magnetic resistance element are of opposite polarity. Therefore, if one of these output signals is first inverted and then added to the other output signal, it can be seen that the resulting sensitivity of the illustrated device has increased by a factor of two.

In Fig. 14, another embodiment of this invention is shown in which the magnetic resistance element -10- is provided with a bias field derived from a biasing magnet -100-. Preferably, the bias magnet has the same temperature dependence as the generator magnet -11- and may be magnetized, for example, to barium ferrite. As can be seen, the bias magnet -100 is magnetically polarized so that the bias field Ηχ extends to the current path extending from the power supply terminal -7B to the terminal 7A- of the magnetic resistance element -10-, is mainly parallel. The bias field Ηχ stands on the field H supplied by the generator magnet -11₂ perpendicular.

The arrangement of the generator magnet -11- and the bias field magnetic resistance element -10- is similar to the embodiment described above in connection with FIG. 5A. The resulting composite field Ηθ is a function of the bias field and the field H₂ and has, for example, on the strips - B- related, the direction shown in Fig. 15.

If the bias field H ^ is substantially equal to the field H₂ Thus, it can be seen that the composite vector of the field H acting on the magnetic resistance element 10 acts₀ then includes an angle Θ of 45 ° when the leading edge of the generator magnet -11- passes the magnetic resistance element. The resulting output signal from element output -5 is in accordance with equations (4) and (5) above. As can be seen, the angle Θ is therefore a function of the intensity of the scanned field Hg, which in turn is a function of the distance between the magnetoresistance element and the generator magnet.

The embodiment shown in Fig. 14 has the advantage that the output signal from the terminal 5 of the magnetic resistance element is not adversely affected by different ambient temperatures. This is because the generator and bias magnet, as mentioned above, have the same temperature dependence. Further, the output signal from the magnetic resistance element, which is a function of the relative position between leading and trailing edges of the generator magnet -11- to the leading edge of the magnetic resistance element -10- will then have a larger drive range if the bias field generated by the bias magnet -100 is sufficiently strong to saturate the magnetic resistance element. Since the composite field vector H_O includes an angle Θ which can be selected in a large range, you will reach this large modulation range, even if a zero offset occurs due to temperature changes.

The result obtained by the use of the bias magnet -100 can be described with reference to Figs. 14A and 14B, and Fig. 14A is a graph of the control output in the output e_Q, shown as AV, and its relation to the composite magnetic field Ηθ which is applied to the magnetic resistance element -10- from the generator magnet -11- together with the bias magnet-100.

The point H_b represents the field strength that acts to saturate the ferromagnetic strips of the magnetic resistance element. The upper curve 120 indicates the change in the drive range due solely to the bias field H 1 generated by the bias magnet 100. Similarly, the curve 121 shows the change in the drive range derived solely from the field Hg generated by the generator magnet -11-,

Assuming initially that the generator magnet -11- is quite far from the magneto-resistive element, as shown in FIG. 14, it is fixedly connected to the bias magnet -100-, as can be seen in FIG. 14B, the field H₂ neglected compared to the bias field Ηχ. In the position shown in Fig. 15, the composite field vector θθ includes an angle θ - 0θ. If the bias field is sufficiently large to saturate the magnetic resistance element, the drive range has the value indicated by the point 122 in the graph of FIG. 14A.

When the generator magnet is moved in the + x direction as shown in Fig. 14B until the leading edge of the generator magnet is aligned with the leading edge of the magnetic resistance element -10 ~, the drive range of the output signal travels along the curve 125 to the point 123 Point, the composite field subtends an angle = = 450 when the Ηχ and H2 fields are equal and the composite field is strong enough to saturate the magnetic resistance element.

If the generator magnet moves further in the + x direction, it will reach a point at the center

- 10 no. 343209 of the generator magnet is equipped with the leading edge of the magnetic resistance element -10. If the Vorspannnngsfeld Ηχ far exceeds the field generated by the generator magnet H2, the Aussteuererbereich reached at this point the point 124. In the position shown in Fig. 15, the composite field H forms_Q here an angle Θ = 90 °.

If the field H2 is substantially stronger than the bias field Ηχ, it can be seen that the angle θ rotates from 0 ° to about 90 ° when the generator magnet -11- moves past the magnetic resistance element -10-.

Using no bias magnet -100, the curve 121 representing the relationship between the drive range and the field H2 supplied by the generator magnet 11 becomes dependent on the zero point change caused by temperature changes. That is, the curve 121 undesirably changes up and down from the shown position to narrow the drive range of the output signal accordingly. This is prevented by the use of the bias magnet -100-.

With respect to the foregoing, it should be noted that the curves described above in FIGS. 8A to 8C can be redrawn so that the abscissa is proportional to the angle Θ. The zero crossings generally occur when θ = 45θ and the ordinate can be drawn from the point where Θ = 90 °. The modulation range is thus represented as a change in the angle Θ from 0 ° to 90 °.

If the magnitudes of the respective fields Ηχ and H2 are appropriately selected or controlled accordingly and the relative directions of these fields are suitably selected or controlled, then it can be seen that the angle θ can be adjusted as desired. This means that some modulation range of the output signal e_Q easy to choose suitable. The magnetic fields H-_Land H 2 are determined by the dimensions of the magnets, temperature coefficients and the like can be easily selected or changed to achieve certain operating characteristics of the magnetoresistance element that correspond to the desired particular application.

Although the bias magnet -100- of FIG. 14 may be mounted on the magnetic resistance element -10-, it is better to use a silicon spacer -101- or a rubber washer for connecting the element -10- to the magnet -100-. The purpose of the silicon spacer or rubber washer is to prevent damage to the magnetic resistance element -10- or the bias magnet -100 which may be caused by expansion of one towards the other. Indeed, if the temperature coefficients of these components are not equal, one may expand more or more rapidly than the other. The silicon spacer or rubber washer -101- prevents damage caused by the expansion differences.

In connection with Figs. 16A and 16B will now be described how the Magnetwider was selement -10- used together with the generator magnet -11- as a non-contact switch. As can be seen from Fig. 16, the arrangement of the magnetic resistance element and the generator magnet -11- can be made as described above in Fig. 5A. The output of the magneto-resistive element -10- is connected to a differential amplifier -14, which may comprise, for example, the resistors-Rx and Rg- of the bridge circuit or otherwise an additional magneto-resistive element -10b- connected to the element -10- in a bridge circuit. The output of the differential amplifier is above a Schwingungsformer circuit -15- and an additional amplifier -16- at an actuating stage -17-, To supply all these circuit elements, a voltage source -8- is provided.

The actuation stage -17- preferably includes a display position with which the relative position between the generator magnet -11- and the magnetic resistance element -10- is displayed. For example, the display posture -17- may include a relay.

As soon as the generator magnet -11- moves rectilinearly on a path along the magnetic resistance element -10-, as shown for example in FIGS. 5A and 8A, the signal generated by the magnetic resistance element is in operation at the differential amplifier -14- in which the output signal eq is generated. For the sake of simplicity, the graphical representation of the output signal e_Q in Fig. 16B reproduced again. The output signal e₀ is due to the Schwingformformerschaltung, which preferably includes a threshold detector. Any conventional threshold detector such as a Schmitt trigger or similar circuit may be used which will then generate an output pulse when the level of the output signal e_ö the strichhliert drawn in Fig.l6B, predetermined level threshold goes through. This output pulse P is amplified -16-further in the amplifier and applied to the relay -17-. In this example, the relay -17- is turned off with the positive edge of the output pulse Pein- and with the negative edge of the output pulse. Of course, if necessary, the relay can also be energized with the negative edge and switched off with the positive edge. In this case, the pulse P shown in Fig. 16B is inverted.

As you can see, the selective operation of the relay -17- can be used to any suitable

- 11 no. 343209 desired switching function to produce. The Sehaltungsanordnungder Fig, 16A therefore functions like a non-contact switch in which the switching function is carried out without the switching contact is physically touched example of a mechanical component.

Another application of this invention is illustrated in Figs. 17A and 17B. In this embodiment, the magnetic resistance element -10- together with the generator magnet -11- serves as a position detector for a probe. The generator magnet -11- is mounted on a rotor element -18- which has a rotation axis -19-. On the rotor -18- acting from the springs -20und21- equal, opposite spring forces to keep the rotor in a safe, characterized by the angular displacement 0 ° rest position, As can be seen, the Polfläohe the generator magnet -11- relative to the Magnetic resistance element -10- arranged symmetrically. As shown in Fig. 17B, the output signal e generated by the differential amplifier -14- has_Q then a maximum peak value, when acting on the rotor -18- no external forces and the rotor remains in its rest position of 0 °.

If, however, the rotor 18 is pivoted about the axis 19- when external forces are applied to it, then, as shown in FIG. 17B, the output signal e changes as a result of the resulting movement of the generator magnet 11 to the magnetoresistive element 10₀, If the angular displacement exceeds a predetermined value, the output signal e crosses_Q the x-axis. If the circuit arrangement described above in connection with FIG. 16A is used, then an indication is obtained when the rotor 18 is deflected from its rest position by more than a predetermined angle. This function can be suitably selected by merely using the threshold sample level with which the output signal e₀is compared, changes.

If necessary, the output of the differential amplifier -14- can also be connected to other than the devices shown in Fig. 16A, for example to a digital display, a computer or the like. Such devices may be used to process the information derived from the relative movement of the rotor to the magnetoresistance element.

The principles that apply to the embodiment shown in FIG. 17A can also be used for the embodiment of FIG. 18A. In the latter embodiment, the magnetic resistance element -10- together with the generator magnet -11- is used to detect the movement of a linearly displaceable member -22 beyond a predetermined value. The component -22- may be housed in a suitable housing and have opposite end pins -18a extending therefrom and further having springs -23 and 24- through which the component -22- is held symmetrically to the magnetoresistive element -10-. More specifically, the center of the generator magnet -11 attached to the movable member -22- is aligned with the magnetic resistance element.

When the component -22 is moved in the ± x direction, the differential amplifier -14- generates the output shown in Fig. 18B. As soon as the component 22 is moved beyond a certain value, the oscillation form e crosses_Q a reference or threshold level. Thus, a suitable device for determining the threshold value may be used to provide an indication when the rectilinearly movable component 22 is displaced from its rest position by more than a predetermined value. Any suitable devices can be connected to this threshold detector to evaluate this information and provide a suitable indication thereof.

Also, multiple magnetic resistance elements -10- with multiple generator magnets may be used to provide a coded output signal indicative of, for example, the angular position of a rotating shaft. This application is shown in FIG. 19. As can be seen, magnetoresistance elements -10- may be arranged rectilinearly on a suitable support or carrier. Opposite this rectilinear arrangement of the magnetoresistive elements, there may be provided a cylinder 25- with various generator magnets -26- disposed on its surface at selected locations. More specifically, the pole faces of the generator magnets form the cylindrical surface. For example, only S-pole surfaces may be provided on the outer cylindrical surface, whereas N-pole surfaces are arranged on the inner cylindrical surface, not shown here. These pole faces are arranged at predetermined locations in rows, each of which is aligned with one of the rectilinear magnetic resistance elements -10-. Preferably, all rows are the same width, but the size of the S-Polflächen varies from row to row depending on the information marked by her,

The cylinder provided on its outer surface with generator magnets is mechanically coupled to a rotatable shaft so that the cylinder rotates when the shaft is driven. As can be seen, different pole face patterns pass under the arranged elements as the cylinder rotates with respect to the magnetic resistance elements. Consequently, a coded output signal is generated by all the magnetic resistance elements in parallel depending on the instantaneous angular position of the rotatable cylinder. This coded information signal is a direct representation of the instantaneous angular position of the cylinder. The angular rotation can therefore be coded and, in the sequence, digital information can be supplied in order to identify the special position of the rotatable shaft.

- 12 No. 343209

Typical applications of the angular coder of FIG. 19 include a channel selector such as is conventional in television technology. For him, the coded information identified by the selected arrangement of the generator magnets on the surface of the cylinder - 25 - may be a direct indication of a television channel. If the shaft is rotated to change the channel to which the television receiver is tuned, the coded output of the magnetic resistance elements results in a corresponding indication of the channel selection. Other applications of the described embodiment include a rotary switch that may be used for other purposes. It should be mentioned again that the switching functions are performed without closing the contacts mechanically.

Yet another application of this invention is shown in FIG. In this case, a matrix arrangement of magnetic resistance elements-10 is provided with the selective bits of information can be read, which is characterized by the arrangement of selectively on a suitable carrier -28- attached generator magnets -29-. For example, the carrier -28- may include an information card and the arrangement of the generator magnets -29- may identify the information on the card.

As can be seen, the magnetic resistance elements -10-are arranged in matrix form with a plurality of rows and columns. The outputs of all magnetic resistance elements of a column are commonly connected to a differential amplifier. For example, in an embodiment where an information card has six readable information columns, the array of magnetoresistance elements contains six columns of elements and thus requires six differential amplifiers -12- ^ to 12θ- the resistors -Β.χ and R₂- Connected connection point connected. These resistors are connected to the magnetic resistance elements -10- so as to form a bridge circuit with each element.

In the embodiment shown in Fig. 20, the card information is read line by line when there is an information card -28 with information to be read from the magnetic resistance elements. This is done by applying all the power supply terminals of one row of the magnetic resistance elements -10- together to a power supply input. In the example shown here, for example, in which six rows of magnetic resistance elements are provided, six different power supply terminals 30χ to 30g are connected to the six rows of magnetic resistance elements, respectively. If a card -28- for the arrangement of the magnetoresistive elements -10- is in the correct position, then a current pulse R is first applied to the current input 30χ-.

This input pulse energizes the first row of magnetic resistance elements. The respective differential amplifiers -12 ^ to 12θ- produce at their outputs -31 ^ to 31g output signals e_Odepending on which elements are opposite the generator magnet 29-. Thus, at these outputs of the differential amplifiers, a coded output of selective bits is formed which identifies the information line contained in the first row of the information card.

As soon as the current pulse signal R at the current input -30 C - ends, a current pulse signal R is supplied to the second current input 30. At this time, the second line of the information encoded on the information card -28- is read out by the second row of the magnetic resistance elements -10-. At the outputs -31 ^ to 31g- the differential amplifier -12 to 12θ- one obtains in parallel a correspondingly coded output signal.

In turn, the current pulse R is applied to the other current inputs -30g to 30g-, one at a time, to obtain a line by line reading of the information contained on the information card-28 indicated by the selective arrangement of the generator magnets -29-.

However, the information reader shown in Fig. 20 may be modified to use only a linear array of magnetic resistance elements to read a matrix of selectively arranged generator magnets. This is accomplished by indexing the information card -28- to place each coded line of information one at a time beneath the rectilinear array of magnetoresistive elements so that each row can be read one at a time. On the other hand, it should be noted that, although here a 6x6 read matrix of magnetoresistance elements is shown, also a much larger range of information encoded on an information card -28- can be read out. The information card need only be indexed both horizontally and vertically to place the array of magnetoresistance elements 10- for reading across successive areas.

It can be seen that the pole face of the generator magnets -29-, eg, the S-pole faces, may be provided on the face of the information card -28- which faces the magnetoresistive elements -10-. The elements may be adjacent to these generator magnets in any of the above configurations has been described in connection with FIGS. 5A to 5C. To maximize the space and thereby a. To obtain as flat information reader, the in Fig. 5C can be used.

- 13 no. 343209

While this invention has been particularly shown and described in connection with certain preferred embodiments, it will be understood that various changes and modifications may be possible in arrangement and detail. For example, even if the magnetic resistance element 10-containing ferromagnetic film strips-A and B have non-identical characteristics, adequate compensation can be obtained. If the ferromagnetic strips -A and B- are applied to the carrier, then the magnetic powder in the film should first be oriented magnetically in the appropriate direction. This magnetic orientation during application to the carrier ensures substantially identical characteristics of the strips -A and B--.

It is therefore to be understood that the appended claims are to be construed to encompass all such changes or modifications as well as all other types of applications for which this invention is particularly well-suited.