JPH0121605B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a potentiometer using a magnetoresistive element that changes the resistance value according to the amount of intersecting magnetic flux, that is, a non-contact potentiometer. The object is to provide a non-contact potentiometer that outputs accurate measured values despite changes in temperature.

A non-contact potentiometer that uses a magnetoresistive element that changes its resistance according to the amount of intersecting magnetic flux has extremely low sliding resistance in its moving parts, making it extremely advantageous for detecting and measuring minute displacements. It is now widely used in the detection parts of level meters, inclinometers, and other precision instruments.

In this way, non-contact potentiometers have excellent measurement capabilities, but with current magnetoresistive element manufacturing technology, it is almost impossible to obtain magnetoresistive elements with exactly the same resistance-temperature characteristics. Therefore, there is a problem in that a change in the ambient temperature of a non-contact potentiometer using this magnetoresistive element causes a large error in the measured value.

That is, in principle, a contactless potentiometer using a magnetoresistive element has a first magnetoresistive element MR ₁ and a second magnetoresistive element between both electrodes of a DC constant voltage source E, as shown in FIG. A series circuit with magnetoresistive element MR ₂ is inserted _, and both magnetoresistive elements MR ₁ and MR ₂ are arranged facing a permanent magnet Mg assembled so as to be able to reciprocate. Both terminals a, b
is configured as an output terminal.

The output characteristics of a potentiometer with such a configuration are as shown in Fig. 2 when the permanent magnet Mg is displaced relative to both magnetoresistive elements MR ₁ and MR ₂ while keeping the ambient temperature T constant. The detectable displacement range that can be used effectively as a potentiometer is set in the range from point A to point B with good linearity.

Now, assuming that the resistance-temperature characteristics of both magnetoresistive elements MR ₁ and MR ₂ are completely equal, the temperature change characteristics at the lower limit point A, upper limit point B, and middle point C of the effective range shown in FIG. As shown in Figure 3, the characteristic curve C at the middle point C is parallel to the temperature axis, and the characteristic curve d ₁ at the lower limit point A and the characteristic curve d ₂ at the upper limit point B are the characteristics of the magnetoresistive element MR ₁ used. , MR ₂ is a curve that is approximately line symmetrical with respect to the straight line c determined according to the temperature characteristics.

That is, from the temperature characteristic curve shown in Fig. 3, although the measurable displacement of the permanent magnet Mg of the potentiometer used decreases in the high temperature range, Since it is parallel to the temperature axis, there are no temperature errors in the measured values, and accurate measurements can be achieved.

However, as mentioned above, it is almost impossible to select magnetoresistive elements MR ₁ and MR ₂ that have exactly the same resistance-temperature characteristics.
A combination of MR ₁ and MR ₂ is used.

In this way, when two magnetoresistive elements MR ₁ and MR ₂ with different resistance-temperature characteristics are used, the output temperature characteristic of the potentiometer shown in FIG. 1 becomes as shown in FIG. 4, for example, and the midpoint is The characteristic curve c will be inclined with respect to the temperature axis, and the measured value will include an error corresponding to the inclination of the characteristic curve c with respect to the temperature axis.

As mentioned above, potentiometers using conventional magnetoresistive elements produce temperature errors due to changes in ambient temperature, so they must always be used within a set constant temperature atmosphere. For this reason, temperature control is troublesome, and the mechanism for maintaining the temperature at a constant temperature is troublesome.

In addition, since the ambient temperature that can be used is limited to a certain value, not only can it not be installed on portable equipment, but it is also necessary to adjust and set the zero point of the equipment depending on the installation location. For this reason, the scope of use is extremely limited, and handling is troublesome and requires specialized skills.

The present invention was devised to eliminate the disadvantages and shortcomings of the conventional example described above, and one embodiment of the present invention will be described below with reference to FIGS. 5 and 6.

The potentiometer according to the present invention includes a series circuit of a first magnetoresistive element MR ₁ and a first series resistance Q ₁ in which a first parallel resistance P ₁ is connected in parallel between both electrodes of a DC constant voltage source E. and a series circuit of a second magnetoresistive element MR ₂ in which a second parallel resistance P ₂ is connected in parallel and a second series resistance Q ₂ are connected in series and inserted,
The first and second magnetoresistive elements MR ₁ , MR ₂
are arranged opposite to a permanent magnet Mg which is provided so as to be able to reciprocate, and both magnetoresistive elements MR ₁ ,
According to the temperature characteristics of MR ₂ , each resistor P ₁ , P ₂ , Q ₁ ,
Set the numerical relationship for _Q2 .

In other words, the numerical relationship between the resistors P ₁ , P ₂ , Q ₁ , and Q ₂ is expressed as temperature characteristic data in the case of the basic configuration shown in Figure 1, which is composed only of both magnetoresistive elements MR ₁ and MR ₂ . Calculate based on the first series circuit and the second series circuit.
This is to match the magnetic force-temperature characteristics with the series circuit.

Let me explain in more detail. The resistance-temperature characteristics of the magnetoresistive element MR are shown in the seventh graph, which shows the temperature-resistance ratio characteristic, where the horizontal axis is the temperature axis, and the vertical axis is the ratio of the resistance value at other temperatures to the resistance value at room temperature of 25°C. This is the a curve in the figure. When a resistor P (preferably the resistance value at room temperature is larger than that of the magnetoresistive element MR) is connected in parallel to the magnetoresistive element MR having such resistance-temperature characteristics, in a range of low ambient temperature, the magnetoresistive element MR Since the resistance value of magnetoresistive element MR becomes larger, the ratio of this magnetoresistive element MR to parallel resistance P becomes smaller, so that the combined resistance temperature characteristic becomes curve b in FIG. 7, and the rate of change of the characteristic becomes smaller. Similarly,
When a resistor Q (preferably the resistance value at room temperature is smaller than that of the magnetoresistive element MR) is connected in series with the magnetoresistive element MR, in a high ambient temperature range,
Since the resistance value of the magnetoresistive element MR becomes smaller, the ratio between the magnetoresistive element MR and the series resistance Q becomes smaller, and the resultant resistance temperature characteristic becomes the seventh
The curve becomes curve c in the figure, and the rate of change in characteristics becomes smaller.

Utilizing this principle, in a combination circuit of magnetoresistive element MR, parallel resistance P, and series resistance Q, by adjusting the resistance values of parallel resistance P and series resistance Q, the resistance temperature characteristic of the composite circuit of this combination circuit is of,
It can be set to change arbitrarily from low temperature to high temperature.

Therefore, by adjusting and setting the resistance values of both parallel resistors P1 and P2 and both series resistors Q1 and Q2, it is possible to match the combined resistance temperature characteristics of the first series circuit and the second series circuit, By matching the combined resistance-temperature characteristics of both series circuits in this way, the combined resistance-temperature characteristics of both circuits are canceled out, and the output temperature characteristics become parallel to the temperature axis at the output midpoint C. be.

In this way, the present invention makes it possible to make the characteristic curve c at the midpoint C parallel to the temperature axis, so that there is no temperature error included in the detected value despite changes in the ambient temperature. , accurate measurements can be achieved despite temperature changes.

In addition, the resistance P ₁ , which is calculated and determined according to the temperature characteristics of the magnetoresistive elements MR ₁ and MR ₂ used, is
By setting the values of the resistors P ₁ and P ₂ or Q ₁ and Q ₂ to be large or small without changing the resistance value ratio of P ₂ and the resistances Q ₁ and Q ₂ , the characteristic curve c can be adjusted along the temperature axis. The displacement point of both characteristic curves d ₁ and d ₂ can be freely moved from the low temperature region to the high temperature region while maintaining the attitude parallel to , so if this displacement point is located in the low temperature region, It is possible to use a potentiometer with a large amount of displacement that can be detected in this low temperature range.On the other hand, if the displacement point is located in a high temperature area, a potentiometer that can detect a large amount of displacement in this high temperature area can be used. Can be done.

In this way, the present invention allows the characteristic curve c at the midpoint C of the output Vab as a potentiometer to be set on the temperature axis even if the temperature characteristics of the two magnetoresistive elements MR ₁ and MR ₂ used are different. Since the potentiometer can be made parallel to the current value, it is possible to obtain a detected value without temperature error as a potentiometer.

Moreover, the setting of the characteristic curve c is simply done by each resistance P ₁ ,
Since it is only necessary to set the values of P ₂ , Q ₁ , and Q ₂ , this can be achieved easily and accurately.

Furthermore, by setting the values of each of the resistors P ₁ , P ₂ , Q ₁ , and Q ₂ , the potentiometer can be made to have a capability that is compatible with the temperature and environmental conditions in which it is used.

As is clear from the above description, the present invention can obtain accurate detected values without temperature errors even when using magnetoresistive elements with different temperature characteristics, and the setting is such that the characteristic curve c is parallel to the temperature axis. It is extremely easy to set the values of each resistor P ₁ , P ₂ , Q ₁ , and Q ₂ so that the values match the temperature and environmental conditions in which the potentiometer is used. It has many excellent effects, such as being able to set the detection capability range.

[Brief explanation of drawings]

FIG. 1 is a basic circuit diagram of a non-contact potentiometer using two magnetoresistive elements.
FIG. 2 shows an output change curve with displacement of the permanent magnet of the potentiometer shown in FIG. FIG. 3 shows ideal temperature characteristic curves at the upper limit, lower limit, and midpoint of the potentiometer shown in FIG. FIG. 4 shows temperature characteristic curves at the upper limit, lower limit, and midpoint of the output when the circuit shown in FIG. 1 is constructed using magnetoresistive elements having different temperature characteristics. FIG. 5 is a circuit diagram showing one embodiment of the present invention. FIG. 6 is a diagram showing an example of a temperature characteristic curve at the upper limit, lower limit, and middle point of the output according to the present invention. FIG. 7 is a diagram showing the combined resistance temperature characteristics of a series circuit composed of a magnetoresistive element, a magnetoresistive element, a parallel resistance, and a series resistance. Explanation of symbols E…DC constant voltage source, MR ₁ , MR ₂
...magnetic resistance element, Mg...permanent magnet, P ₁ , P ₂ , Q ₁ ,
Q ₂ ...Resistance.

Claims (1)

[Claims] 1. A potentiometer using a magnetoresistive element that changes the resistance value according to the amount of intersecting magnetic flux, the first magnetoresistive element having a first parallel resistance connected in parallel between both electrodes of a DC voltage source. and a first series resistor, and a second series circuit of a second series resistor and a second magnetoresistive element in which a second parallel resistor is connected in parallel. , wherein both the magnetic resistance elements are arranged opposite to a permanent magnet arranged to be able to reciprocate, and the temperature coefficient at the midpoint of the output output between both terminals of the first series circuit is zero. A potentiometer using a magnetoresistive element, which is configured to set the values of each of the resistances as described above.