JPH11257908A - Electromagnetic induction type sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To secure stable measuring performance independently of ambient temperature by providing an iron core interlocked with a probe. SOLUTION: An output voltage of an oscillator circuit 20 is input to a primary coil 12 of a transformer 10, and an output voltage of a secondary coil 13 united with the primary coil 12 through an iron core 11 interlocked with displacement quantity of a measurement element is detected with a diode 22 to input to a plus-input terminal of an operational amplifier 40. On the other hand, an output voltage of an oscillator 30 generating a constant voltage is detected with a diode 32 to input to minus-input terminal of the operational amplifier 40. Each input voltage differentially amplified at the operational amplifier 40 is output. An output voltage of a detection circuit obtained by detecting the output voltage of the secondary coil 13 with the diode 22 varies in accordance with temperature characteristics of the diode 22. However, variation quantity of the diode 22 by temperature characteristics is cancelled out and stable measuring is performed independently of ambient temperature by detecting the output voltage of the oscillator 30 with a constant voltage with the diode 32 having equal temperature characteristics and differentially amplifying.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electromagnetic induction type displacement sensor for measuring the amount of displacement by converting the amount of displacement of an object to be measured into an electric quantity using electromagnetic induction, and more particularly to a measurement error caused by a temperature change. The present invention relates to an improvement for reducing the influence of temperature and reducing the influence of temperature.

[0002]

2. Description of the Related Art Conventionally, as a displacement sensor of the electromagnetic induction type, a differential transformer in which two secondary coils are provided with an iron core displaced in accordance with the displacement amount of a tracing stylus for one primary coil. Was generally used. In a displacement sensor using this differential transformer, an AC voltage of an oscillation circuit is applied to a primary coil, a difference voltage of induced electromotive force of each secondary coil is detected, and a displacement amount is expressed based on the voltage. I have.
In a detection circuit for detecting the electromotive force of the secondary coil, a smoothing circuit using a diode is used.

[0003]

In the conventional electromagnetic induction type displacement sensor configured as described above, the induced electromotive force appearing in the secondary coil is detected by a diode as shown in FIG. At this time, the peak voltage decreases as shown in FIG. 6B due to the forward voltage drop of the diode. Since a forward voltage drop occurs in the diode used in the smoothing circuit of the secondary coil, the output voltage of the smoothing circuit becomes a voltage reduced by the forward voltage drop. However, since the forward voltage of the diode has a large temperature dependency as shown in FIG. 7, there is a problem that the output voltage easily changes according to the ambient temperature as shown in FIG. For this reason, the conventional electromagnetic induction type displacement sensor needs to be used under a constant temperature condition or a temperature correction circuit using a temperature detecting element such as a thermistor is required. For this reason, there was a problem that it could not be used for applications with a large temperature change.

[0004] The present invention is less sensitive to ambient temperature,
The purpose is to ensure stable measurement performance.

[0005]

According to a first aspect of the present invention, there is provided an oscillation circuit for generating an AC voltage, an iron core which is displaced in accordance with the amount of displacement of an object whose displacement is to be measured, and provided with the iron core interposed therebetween. A transformer comprising a primary coil and a secondary coil, wherein the degree of coupling between the primary coil and the secondary coil changes according to the displacement of the iron core; and a diode for generating an induced electromotive force generated in the secondary coil of the transformer. And a detection circuit that detects the output voltage of the fixed voltage generation circuit that generates a constant voltage value by using a diode having a temperature characteristic equivalent to that of the diode used in the detection circuit in the forward direction. A reference voltage generation circuit for generating a reduced reference voltage; and a differential amplifier for receiving an output voltage of the detection circuit and a reference voltage of the reference voltage generation circuit and outputting an operation value. And it features.

According to claim 2, in claim 1, the fixed voltage is a fixed DC voltage generated by a DC voltage generating circuit, and the reference voltage is a voltage obtained by dropping the fixed DC voltage by the diode. There is a feature. According to a third aspect, in the first aspect, the fixed voltage is an AC voltage generated by the oscillation circuit, and the reference voltage is a detection voltage obtained by detecting the AC voltage. According to a fourth aspect of the present invention, in the first aspect, the fixed voltage is a reference AC voltage generated by a reference AC generation circuit configured as a circuit different from the oscillation circuit, and the reference voltage detects the reference AC voltage. And a reference detection voltage.

[0007]

According to the present invention, when an AC voltage generated in the oscillation circuit is applied to the primary coil of the transformer, a secondary voltage is generated in the secondary coil by electromagnetic induction of the transformer.
In a transformer, the degree of coupling between the primary coil and the secondary coil changes according to the amount of displacement of the iron core that is displaced according to the displacement of the stylus, so the secondary voltage of the secondary coil is Appears accordingly. As shown in FIG. 1, the secondary voltage is detected by a detection circuit 102 using a diode 101 to become a DC voltage. However, the forward voltage drop in the diode 101 is affected by the ambient temperature, and Output voltage Vin changes with a temperature change. On the other hand, in the present invention, there is provided a reference voltage generating circuit 105 for dropping the output voltage of the fixed voltage generating circuit 103 for generating a constant voltage value by using the diode 104 having the same temperature characteristic as the diode in the forward direction. And fixed voltage generation circuit 1
The output voltage Vr of the reference voltage generation circuit 105 appears as a voltage obtained by lowering the output voltage of the reference voltage generator 03 by the voltage drop corresponding to the characteristics of the diode 104.

The output voltage Vin of the detection circuit 102 is
Appears as a voltage drop by the voltage based on the characteristic of the diode 101 corresponding to the ambient temperature, and the output voltage Vr of the reference voltage generating circuit 105 also increases by the voltage corresponding to the temperature characteristic of the diode 104. The dropped voltage appears as an output voltage. Therefore, as shown in FIG. 2, of the voltage drop value on the secondary coil side input to the differential amplifier 106, the change of the diode 101 that changes according to the ambient temperature is input from the reference voltage generation circuit 105 side. Only the voltage component that has been subtracted by the change in the reference voltage Vr and is free from the influence of temperature appears as the output of the differential amplifier 106. As a result, by displaying the displacement of the tracing stylus using the output of the differential amplifier 106, an output voltage corresponding to only the position of the iron core can be obtained regardless of the surrounding temperature at the time of measuring the displacement. In addition, a value that does not include an error due to the ambient temperature can be displayed as a displacement measurement value.

As described above, according to the present invention, even if the ambient temperature changes, the output of the differential amplifier does not show a change due to the temperature change. Can be measured well.

[0010]

FIG. 3 shows the configuration of an electromagnetic induction type displacement sensor 100 according to a first embodiment of the present invention. Reference numeral 10 denotes a transformer having an iron core 11 interlocked with a tracing stylus that is displaced in accordance with the displacement of the measurement target. The transformer 10 includes a primary coil 12 and a secondary coil 13 connected by the iron core 11. An oscillation circuit 20 generates an AC voltage having a constant frequency.
The output voltage of 0 is input to the primary coil 12 of the transformer 10 via the capacitor 21. 22 is a diode for detecting the induced electromotive force of the secondary coil 13 of the transformer 10,
23 is a capacitor constituting a smoothing circuit for smoothing the pulsating flow detected by the diode 22, and 24 and 25 are voltage dividing resistors for dividing the voltage of the smoothing circuit.

Reference numeral 30 denotes an oscillator provided as a fixed voltage generating circuit, which generates a constant AC voltage as in the case of the oscillation circuit 20. Reference numeral 31 denotes a variable resistor for adjusting the output voltage of the oscillator 30. Reference numeral 32 denotes a diode having a forward voltage-ambient temperature characteristic equivalent to that of the diode 22, and reference numeral 33 denotes a capacitor constituting a smoothing circuit for smoothing a pulsating current detected by the diode 32, which constitutes a reference voltage generating circuit.

Reference numeral 40 denotes an operational amplifier, which constitutes a differential amplifier that inputs a voltage on the oscillation circuit 20 side and a voltage on the DC voltage generator 30 side and outputs a difference voltage between the resistors 41 and 42. An operational amplifier 50 includes resistors 51 and 5.
2 and the variable resistor 53 for gain adjustment constitute a non-inverting amplifier circuit. A resistor 61 and a capacitor 62 are provided on the output side of the operational amplifier 50, and a voltage corresponding to the displacement of the tracing stylus is output to an output terminal 63.

In the above configuration, as described above, when the induced electromotive force appearing in the secondary coil 13 is detected by the diode 22, as shown in FIG. As shown in FIG. 6B, the peak voltage appears lower. This forward voltage drop causes a change in the diode 22 in accordance with the ambient temperature, so that a voltage that has changed with temperature appears at the positive input terminal of the operational amplifier 40. However, when a constant AC voltage generated by the oscillator 30 is also detected by the diode 32 connected in the forward direction via the variable resistor 31, the diode 32 receives a similar forward voltage drop by the diode 32. , The voltage on the negative input terminal side of the operational amplifier 40 is also
Similarly, a voltage that changes according to the temperature appears. Therefore, the output voltage differentially amplified by the operational amplifier 40 always has a voltage value according to the displacement amount of the tracing stylus without being affected by the temperature. As a result, in the present invention, the displacement can be accurately measured without being affected by the temperature.

FIG. 4 shows a second embodiment of the present invention. In the second embodiment, a DC voltage generating circuit 70 for generating a constant DC voltage is provided instead of the oscillator 30 in the first embodiment. Also in this embodiment, the constant DC voltage generated by the DC voltage generating circuit 70 receives a forward voltage drop at the diode 32 via the variable resistor 31, and the voltage drop depends on the temperature around the diode 32. Therefore, the displacement amount of the tracing stylus can be accurately measured regardless of the temperature.

FIG. 5 shows a third embodiment of the present invention. In the third embodiment, the reference voltage is generated using the output voltage of the oscillation circuit 20 that generates the voltage to be applied to the primary coil 12 of the transformer 10 as it is.

In the above embodiment, the core is displaced with a tracing stylus in order to detect the amount of displacement of the object to be measured, but the core of the transformer 10 is directly in contact with the object to be measured. It may be one that is displaced.

[Brief description of the drawings]

FIG. 1 is a principle circuit diagram for explaining the principle of the present invention.

FIG. 2 is a characteristic diagram showing a position of an iron core of a transformer and an output voltage of a differential amplifier together with a forward voltage drop value of each diode under a plurality of temperature conditions for explaining the operation of the present invention. is there.

FIG. 3 is a circuit diagram of an electromagnetic induction type displacement sensor according to a first embodiment of the present invention.

FIG. 4 is a circuit diagram of an electromagnetic induction type displacement sensor according to a second embodiment of the present invention.

FIG. 5 is a circuit diagram of an electromagnetic induction type displacement sensor according to a third embodiment of the present invention.

FIG. 6 is a characteristic diagram illustrating a relationship between an AC voltage and a detection voltage detected by a diode.

FIG. 7 is a characteristic diagram of a forward voltage and a forward current of a diode for showing a temperature change of a voltage drop caused by the diode.

FIG. 8 is a characteristic diagram showing output voltages of a conventional electromagnetic induction type displacement sensor at a plurality of temperatures.

[Explanation of symbols]

 REFERENCE SIGNS LIST 100 electromagnetic induction type displacement sensor 10 transformer 11 iron core 12 primary coil 13 secondary coil 20 oscillation circuit 22 diode (detection circuit) 30 oscillator (fixed voltage generation circuit) 32 diode (reference voltage generation circuit) 50 operational amplifier (differential amplifier)

Claims (4)

[Claims] 1. An oscillation circuit for generating an AC voltage, an iron core displaced in accordance with the amount of displacement of an object to be measured for displacement, a primary coil and a secondary coil provided with the iron core interposed therebetween. A transformer in which the degree of coupling between the primary coil and the secondary coil changes according to the amount; a detection circuit for detecting an induced electromotive force generated in the secondary coil of the transformer by a detection circuit using a diode; The output voltage of the fixed voltage generator that generates the voltage value is
A reference voltage generation circuit that generates a reference voltage having a voltage dropped by using a diode having a temperature characteristic equivalent to that of the diode used in the detection circuit in a forward direction, and an output voltage of the detection circuit and a reference voltage generation circuit. An electromagnetic induction type displacement sensor, comprising: a differential amplifier that inputs a reference voltage and outputs a calculation value. 2. The method according to claim 1, wherein the fixed voltage is a fixed DC voltage generated by a DC voltage generating circuit, and the reference voltage is a voltage obtained by dropping the fixed DC voltage by the diode. 2. The electromagnetic induction type displacement sensor according to 1. 3. The electromagnetic induction displacement according to claim 1, wherein the fixed voltage is an AC voltage generated by the oscillation circuit, and the reference voltage is a detection voltage obtained by detecting the AC voltage. Sensor. 4. The fixed voltage is a reference AC voltage generated by a reference AC generation circuit configured as a circuit different from the oscillation circuit, and the reference voltage is a reference detection voltage obtained by detecting the reference AC voltage. The electromagnetic induction type displacement sensor according to claim 1, wherein: