JPH06331303A - Detection of quantity of displacement of core - Google Patents

Abstract

PURPOSE:To prevent the generation of an error due to the fluctuations of voltage by applying AC voltages having the same cycle and difference in phase to respective primary coils and detecting the quantity of displacement of a core on the basis of the phase change quantity of the output of a secondary coil accompanying the displacement of the core. CONSTITUTION:The output of a quartz oscillator 18 is divided in frequency by a frequency divider 19 and two square waves having 90 deg. phase difference are formed by a phase converter 20. One square wave is converted to a sin wave by a first active filter 21 to be inputted to a first coil 12 while the other square wave is converted to a cos wave by a second active filter 22 to be inputted to a second coil 13. The output of a detector 10, that is, the output of a secondary coil 16 (third coil 14) is binarized by a binarizing circuit 24 to be inputted to an AND circuit 25. The output from the phase converter 20 is inputted to the AND circuit 25 and the output of the AND circuit 25 is inputted to a counter 26. When the AND output is in an ON(high) state, the counter 26 counts the number of the output pulses of the quartz oscillator 18 and the count value is linearly corrected by a linear correction circuit 27 to be outputted as the quantity of displacement of the core 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a core displacement amount detecting method in a detector having a primary coil, a secondary coil, and cores inserted in these primary and secondary coils.

[0002]

2. Description of the Related Art For example, a differential transformer has been known as a detector incorporated in a device for measuring various physical quantities such as thickness, elongation, pressure, load, torque and acceleration (Japanese Patent Publication No. 39-3154). Gazette, Japanese Patent Publication No. 50-22904). In principle, this differential transformer has a primary coil 1, two secondary coils 2 and 3, and a core 4 inserted in these coils 1 to 3, as shown by an equivalent circuit in FIG. And a constant AC voltage Ep is applied to the primary coil 1 to generate an electromotive force Es of the secondary coil 2 due to the displacement of the core 4.
The potential difference Es between the electromotive force Es2 of the primary coil 3 and the secondary coil 3 is taken out as a secondary voltage, and the amount of displacement of the core 4 is detected by the secondary voltage Es.

[0003]

In the conventional differential transformer, since the displacement amount of the core 4 is detected by the secondary voltage Es, the change in the voltage of the circuit due to noise, temperature, etc. As it is, it appears as an error in the secondary voltage Es.
Similarly, the voltage drop due to the cable that connects the differential transformer and the measurement circuit that receives the output from the differential transformer and measures various physical quantities is a factor that causes an error in the secondary voltage Es as it is. .

Therefore, an object of the present invention is to provide a detector having a core inserted in the primary and secondary coils, such as a differential transformer, in order to prevent an error due to voltage fluctuation from occurring. It is to provide a detection method.

[0005]

In order to achieve the above technical object, according to the present invention, AC voltages having the same period and different phases are applied to each of the primary coils, which accompanies the displacement of the core. The structural feature is that the displacement amount of the core is detected based on the phase change amount of the output of the secondary coil.

[0006]

The primary coil has a phase difference of 90 °, for example.
The operation of the present invention will be described assuming that an in wave and a cos wave are added. Between the primary coil to which the sine wave and the cos wave are added and the secondary coil, the impedance changes according to the displacement of the core. The voltage V of the secondary coil can be expressed by the following equation.

V = (K−a) · sin (wT) + (K + a) · cos (wT) = Z · sin (wt + x) where K is the magnetic permeability of the detector, and a is the displacement of the core. It is a change in magnetic permeability efficiency due to. As understood from the above equation, the potential V of the secondary coil is the phase change amount x of the output voltage of the secondary coil, and therefore the displacement amount of the core is detected as the phase change amount x of the output of the secondary coil. It is possible. In other words, the displacement amount of the core can be detected by knowing the phase change amount x of the output of the secondary coil. Further, since the displacement amount of the core is detected by the phase change, not by the voltage of the output of the secondary coil as in the conventional case, there is no influence by the voltage fluctuation in the detection of the displacement amount of the core.

Further, since the detector used in the present invention has the same basic structure as that of the conventional differential transformer, the present invention can be constructed by using the differential transformer as it is.

[0009]

Embodiments of the present invention will be described below with reference to the accompanying drawings. First Embodiment (FIGS. 1 to 3) In FIG. 1, reference numeral 10 is a displacement detector.
Is installed in a balance measuring machine (not shown) for automobile tires, which requires micron-order detection accuracy. The detector 10 comprises three coils 12 arranged around a core 11.
It has the same mechanical structure as the conventional 6-wire type differential transformer including .about. Here, the primary coil 15 is composed of two first and second coils 12 and 13, and a secondary coil 16
Is composed of one third coil 14.

In the figure, reference numeral 18 is a high-frequency crystal oscillator, and the output of the crystal oscillator 18 is divided by a frequency divider 19 and then two square waves having a phase difference of 90 ° are formed by a phase converter 20. To be done. The one square wave is converted into a sin wave by the first active filter 21 and input to the first coil 12, and the other square wave is cos by the second active filter 22.
It is converted into a wave and input to the second coil 13.

The output of the detector 10, that is, the secondary coil 16
The output of the (third coil 14) is binarized by the binarization circuit 24 and then input to the AND circuit 25. AND circuit 2
The output from the phase converter 20 is also input to 5, and A
The output of the ND circuit 25 is input to the counter 26. The counter 26 counts the number of output pulses of the crystal oscillator 18 while the AND output is ON (high), and this count value represents the amount of displacement of the core 11 after the linear correction is performed by the linear correction circuit 27. It is output as a value.

In the above structure, when the core 11 is displaced from the center position, the amount of core displacement, as described above, appears as the phase change amount x, that is, the length of the ON (high) state of the AND output. Counter 26 with crystal oscillator 18
It is quantified based on the number of output pulses of. The above state is shown in FIG. FIG. 2 shows the output of the oscillator 18, the output of the binarization circuit 24, and the AND output.

According to the above embodiment, since the same high frequency oscillator 18 drives the detector 10 and detects the amount of phase change, the error caused by the frequency fluctuation is extremely small. Further, the AND output is, as shown in FIG.
Although it does not show perfect linear characteristics, the linear correction circuit 27 applies linear correction to this, so the core 1
An output linearly corresponding to the displacement amount of 1 can be obtained. Second Embodiment (FIGS. 4 and 5) In the description of the second embodiment, the same elements as those in the first embodiment are designated by the same reference numerals, and the description thereof will be appropriately omitted.

In FIG. 4, the oscillator 18 is
The frequency is set to 20 MHz, and the output from the oscillator 18 is input to the counter 30. The counter 30 counts the output of the oscillator 18, and the count value is input to the address side of the first and second ROMs 31 and 32. In the first and second ROMs 31 and 32, instantaneous value data of sin waves are written respectively, and the first ROM 3
The sin wave data of 1 and the sin wave data of the second ROM 32 have different phases. Here, the phase difference between these data is set to 155 ° to 165 °. this is,
This is because it has been experimentally found that it is optimum for obtaining high resolution from the relation using the 20 MH oscillator 18.

The digital signals from the first and second ROMs 31 and 32 are input to the first and second D / A converters 33 and 34, respectively, converted into analog signals, amplified by the amplifiers 35 and 36, and then, respectively. It is input to the first and second coils 12 and 13. The output of the detector 10, that is, the output of the secondary coil 16 (third coil 14) is binarized by the binarization circuit 24 as in the first embodiment, and the binarized signal S1, that is, the rectangular wave is generated. It is input to the center detector 38.

The center detector 38 detects the midpoint between the rising edge and the falling edge of the binarized signal and outputs a pulse signal S2 (referred to as a midpoint pulse signal) representing the midpoint to a flip-flop (F / F). ) Send to circuit 39. On the other hand, for example, each time the highest address value (MBS) from the counter 30 becomes "1", it is input to the F / F circuit 39 as a clock pulse S3 every 360 °. The F / F circuit 39 generates an "ON (high)" state by the clock pulse and holds it, and generates an "OFF (low)" state which is inverted by the midpoint pulse signal.

The signal S5 generated by the F / F circuit 39 is input to the counter 40, and while the output S5 of the F / F circuit 39 is in the "ON" state, the number of output pulses of the oscillator 18 is counted. Similar to the first embodiment, the value S6 is output as a value representing the amount of displacement of the core 11 after being corrected by the linear correction circuit 27. The above state is shown in FIG.

According to this embodiment, the primary coils 12, 1
Since digitalization is performed once on the 3 side, a stable waveform can be supplied to the primary coils 12 and 13, and a stable detector without distortion or phase change can be obtained.
In addition, since the phase difference of the sin wave supplied to the primary coils 12 and 13 is set to a large value, it is possible to increase the “ON” output time of the F / F circuit, and it is possible to use the oscillator 18 of 20 MH. Nevertheless, sufficient resolution can be secured.

[0019]

As is apparent from the above description, according to the present invention, the displacement of the core is detected by the change of the phase, so that the error due to the voltage fluctuation does not occur. Also,
Since the mechanical structure is the same as the conventional differential transformer, it can be used as it is.

[Brief description of drawings]

FIG. 1 is an equivalent circuit diagram of a core displacement amount detecting device according to a first embodiment.

FIG. 2 is a diagram showing various outputs with time for explaining the operation of detecting a core displacement amount in the first embodiment.

FIG. 3 is a diagram showing output characteristics before linear correction is applied in the first embodiment.

FIG. 4 is an equivalent circuit diagram of the core displacement amount detecting device according to the second embodiment.

FIG. 5 is a diagram showing various outputs with time in the second embodiment.

FIG. 6 is an equivalent circuit diagram of a conventional differential transformer.

[Explanation of symbols]

 10 Displacement Detector 11 Core 15 Primary Coil 16 Secondary Coil 18 High Frequency Crystal Oscillator 20 Phase Converter 26 Counter

Claims (1)

[Claims] 1. A detector having at least two primary coils, a secondary coil, and a core inserted in the primary and secondary coils, wherein each of the primary coils has the same cycle. Further, a core displacement amount detecting method is characterized in that the displacement amount of the core is detected based on the phase change amount of the output of the secondary coil due to the displacement of the core by applying AC voltages having different phases.