JPS6018701A - Displacement measuring device - Google Patents

Abstract

PURPOSE:To prevent the deterioration in measuring accuracy due to temperature change, by taking out a sum voltage signal from the output signals of the secondary coils of a differential transformer, and compensating the fluctuation of the measured value based on said signal. CONSTITUTION:A primary coil 12b of a differential transformer 12 is excited by the oscillating signal from an oscillating circuit 11. The output voltages e1 and e2 of secondary coils 12c and 12d are changed approximately linearly in correspondence with the displacement of a core 12a. When the output voltages e1 and e2 of the differential transformer 12 are fluctuated by the temperature change and the like, the differential voltage e1-e2 and the average voltage (e1+e2)/2 are also fluctuated. The voltages e1 and e2 are increased in proportion to the displacement of the core. Therefore the fluctuation in the differential voltage is eliminated when the control is performed so that the fluctuation width (c) of the average voltage becomes zero even though the temperature is changed. Thus the displacement signal with few error is obtained. Therefore the deterioration in measuring accuracy due to the temperature change and the like can be prevented.

Description

[Detailed description of the invention] The present invention relates to a displacement measuring device using a differential transformer.

In devices that use a differential transformer, such as length measuring machines and weighing machines, the core of the differential transformer is displaced in a linear direction in proportion to the length to be measured, the mold needle, etc., and this amount of displacement is converted into an electrical signal. Conversion l- is used to measure length, weight, etc. However, since extremely high measurement accuracy is required in such measuring devices, changes in the characteristics of the differential transformer and other electronic circuits due to changes in temperature, etc., have caused large measurement errors.

As a countermeasure against this problem, conventional methods have been used, for example, as shown in Figure 1, to insert a thermistor 2 in series on the primary coil side of the differential transformer 1 to offset changes in sensitivity due to temperature of the differential transformer 1. . However, with this method, it is difficult to match the characteristics of the differential transformer 1 and the thermistor 2, and sufficient temperature compensation cannot be achieved.
The oscillation circuit generator that applies the oscillation signal to the primary side of the oscillator, and the subsequent electronic circuit 3 of the displacement detection device that performs processing such as amplification, detection, or A/D conversion on the output signal, do not compensate for sensitivity changes due to temperature. As a result, measurement accuracy could not be maintained sufficiently. (Note that 5 in the figure is a display that displays the amount of displacement using the output signal of the electronic circuit 3.) Conventionally, as shown in FIG. 2, the output of the differential transformer 1 is amplified, detected, and A/D converted. The detection circuit 6 is taken out to a separate system from the electronic circuit 3 for detecting displacement in the subsequent stage.
A method is also used in which the oscillation voltage is controlled by detecting the DC voltage, comparing it with a preset reference voltage E in the comparator circuit 7, and outputting a control signal to the oscillation circuit so that the two match. There is.

However, this method cannot compensate for changes in the sensitivity of the electronic circuit 3 used to detect the amount of displacement, and therefore measurement accuracy cannot be maintained sufficiently.

SUMMARY OF THE INVENTION An object of the present invention is to improve the above-mentioned drawbacks and provide a displacement measuring device that can perform sufficient sensitivity compensation.

Hereinafter, one embodiment of the present invention will be described based on the drawings.

FIG. 3 is a block diagram showing an embodiment of the displacement measuring device of the present invention.

(3) In the figure, 11 is an oscillation circuit that outputs an oscillation signal of a predetermined frequency, 12 is a differential transformer whose core 12a is displaced in proportion to the linear displacement to be measured, and the oscillation circuit 11 oscillates. The primary coil 121) is excited by the signal, and the two secondary coils #12C, 12'' connected with opposite polarity
output voltages e4 and θ2 corresponding to the displacement of the core 12a, respectively. 13 is the difference voltage e1- between the output voltages θ1 and θ2 of the secondary coil 12C112d of the differential transformer 12.
02 to the secondary coil 13b, and an average voltage (e1+02)/2 of θ1 and 02 is taken out from the intermediate tap of the primary coil 13a of the input quadrangle 13. 14 is a first changeover switch, which connects the output terminal (A) from the secondary coil 131) of the input transformer 13 and 1
This is for switching between the output terminal (b) from the middle tap of the next coil 13a. 15 is an AC amplifier that amplifies the output signal from the terminal (a) or (b) via the changeover switch 14; 16 is a detector that detects the output signal of the AC amplifier 15 and converts it into a DC signal; 17 is a detector 16 The output f51 A (4) is a DC amplifier that amplifies the signal, and 18 is an A/D converter that converts the output signal of the DC amplifier 17 into a digital signal. Reference numeral 19 denotes a second changeover switch, which distributes the output signal of the A/D converter 18 to terminals (A) and (B) in conjunction with the first changeover switch 14-. A displacement output circuit 20 is connected to the terminal (a) and outputs the output signal of the A/D converter 18 as a displacement signal. A D/A converter 21 is connected to the terminal (b) and converts the output signal of the A/D converter 18 into an analog signal. 22 is D/A
A comparison circuit 23 compares the output signal of the converter 21 with a preset reference voltage E and outputs a control signal so that the two become equal. 23 stores the control signal of the comparison circuit 22 and sends the control signal to the oscillation circuit 11. This is a control signal storage circuit that controls the amplitude of the oscillation signal of the oscillation circuit 11 by outputting the oscillation signal.

Next, the operation of the above embodiment will be explained.

The primary coil 121) of the differential transformer 12 is the oscillation circuit 11
is excited by the oscillation signal from the secondary coil 12 (!
, 12'' (7) The output voltages 81 and e2 change in accordance with the displacement of the core 12a.The output voltage θ1-82 is generated in the input quadrature transformer (6) (secondary coil 131) of the primary coil 13a. For the middle tap (e1+02)
'2 occurs.

The output signal obtained from the terminal (a) or (b) via the first changeover switch 14 is amplified by the AC amplifier 15, detected by the detector 16 to become a DC signal, and amplified by the DC amplifier 17. , is converted into a digital signal by the A/D converter 18. First and second changeover switches 14, 19
is connected to the (a) side, the differential voltage θ1-8
The AC signal of 2 is amplified and detected as above, and A /
The D-converted signal is output from the displacement output circuit 20 as a displacement signal.

When the first and second changeover switches 14 and 19 are connected to the (b) side, the average voltage (e1+82)A! The alternating current signal passes through the same circuits 15 to 18, is converted into an analog signal by a D/A converter 21, is compared with a reference voltage E by a comparator circuit 22, and a control signal is outputted so that the two become equal. This control signal is stored in the control signal storage circuit 23 and output to the oscillation circuit 11 to control the amplitude of the oscillation signal and generate the oscillation voltage e.

control.

As is well known, the secondary coil 12C, 1 of the differential transformer 12
2d(7) The output voltages e1 and e2 change approximately linearly in response to the displacement of the core 12a of the differential transformer 12, as shown in FIG. That is, when the core 12a is displaced upward from the zero point (to the + side of the horizontal axis), the output voltage e1 of the secondary coil 12C increases, and the output voltage θ2 of the secondary coil 12d decreases. When the core 12a is displaced downward, 81 decreases and e
2 increases.

Therefore, the differential voltage e, -82 increases approximately in proportion to the upward and downward displacement from the zero point, but the average voltage (e1+02
)/2 remains approximately constant regardless of the displacement of the core 12a.

However, if the output voltages θ1 and e2 of the differential transformer 12 fluctuate due to temperature changes, the differential voltage e1-02
and the average voltage (θ1+02)/2 also vary.

As shown by the chain line in FIG. 4, since 01 and e2 increase in proportion to the displacement of the core, the fluctuation range a of el and e2 also increases in proportion to the displacement of the core, and therefore the differential voltage e1- 0
The fluctuation width C of the average voltage (e 1 + e 2 )/2 increases in proportion to the displacement of the core, but the fluctuation width C of the average voltage (e 1 + e 2 )/2 remains almost constant regardless of the displacement of the core. Therefore, even if a change in temperature occurs, if the variation width C of the average voltage (e1+02)/2 is controlled to zero, the variation of the differential voltage θ, -02 will also disappear, and a displacement signal with less error can be obtained. In addition to the differential transformer 12, the oscillation circuit 11, input transformer 13,
AC amplifier 15, detector 16, DC amplifier 17, A/
The sensitivity of the D converter 18 etc. also changes due to temperature changes, etc., but the average voltage signal (e 1 + e 2 ) /
2 and the differential voltage signal θ1 '2 pass through exactly the same circuit, so that the average voltage and the differential voltage will fluctuate at the same ratio.

Therefore, if the average voltage signal passed through the second changeover switch 19 and the D/A converter 21 is compared with the reference voltage E set in advance by the comparator 22, and a control signal is output so that the two match, the first , the fluctuation of the differential voltage signal when the second changeover switch 14, 19 is switched to the (a) side is corrected and output to the displacement output circuit 20.

(9) Therefore, the first
By switching the second changeover switch 14, 19 to the (b) side and controlling the amplitude of the oscillation circuit 11, errors caused by temperature changes etc. can be significantly reduced.

Further, as shown in FIG. 5, when the displacement of the measurement target is extremely large and the displacement of the core 12a is large, el, θ2,
For both +311112 and (e1+02)/2, linearity deteriorates above a certain displacement. Therefore, even in such a case, if a control signal is outputted from the comparator circuit 22 so that the curved portion of (θ1+92)/2 shown by d in FIG. 5 becomes a straight line portion d', the difference voltage signal θ1-02 Since the curved part molecule of can be made to be the straight part molecule ′,
Compensation for errors due to measurement non-linearities is also possible.

In the above embodiment, the control signal is output to the oscillation circuit 11, but the same result can be obtained by performing closed loop control so that the output voltage from the second changeover switch 19 is constant. 15, a detector 16, a DC amplifier 17, and an A/D converter (10) 18.

As explained above, in the displacement measuring device of the present invention, a sum voltage signal is extracted from the output signal of the secondary coil of a differential transformer, and this sum voltage signal is passed through a circuit for displacement detection. Since fluctuations in measured values are compensated for, it is possible to prevent deterioration of measurement accuracy due to temperature changes, etc., and it is also possible to compensate for nonlinearity when the measured quantity is still large.

[Brief explanation of drawings]

1 and 2 are block diagrams showing a conventional displacement measuring device with a compensation circuit, FIG. 3 is a block diagram showing an embodiment of the present invention, and FIGS. 4 and 5 are block diagrams showing the core of a differential transformer. FIG. 3 is a diagram showing output characteristics with respect to displacement. 11... Oscillation circuit, 12... Differential transformer, 14...
...First changeover switch, 17...DC amplifier, 19
... second changeover switch, 20 ... displacement output circuit,
22... Comparison circuit, 23... Control signal storage circuit. Patent Applicant Anritsu Electric Co., Ltd. Agent Patent Attorney Makoto Hayakawa (11) Figure 1 Figure 2

Claims (1)

[Claims] An oscillation circuit that generates an oscillation signal of a predetermined frequency; a primary coil is excited by the oscillation signal of the oscillation circuit, and two secondary coils are excited.
A differential transformer in which the output voltage of the secondary coil changes in accordance with the displacement of the core; a differential voltage output circuit that outputs a differential voltage signal between the output voltages of the two secondary coils; and a sum voltage output circuit that outputs a sum voltage signal. a first circuit that switches and outputs the difference voltage signal and the sum voltage signal;
a changeover switch; an amplification detection circuit that amplifies and detects the output signal of the first changeover switch; a second changeover switch that switches the output signal of the amplification and detection circuit in conjunction with the first changeover switch; a displacement output circuit that outputs the differential voltage signal output from the second changeover switch as a displacement signal of the core, which is an output signal of the amplification/detection circuit; and the sum voltage signal outputted from the second changeover switch. a comparison circuit that compares the output signal of the amplification and detection circuit with a preset reference voltage and outputs it as a control signal; and a control signal storage that stores the control signal and outputs it to the oscillation circuit or the amplification and detection circuit. the oscillation circuit or the amplification and detection circuit based on the output signal of the amplification and detection circuit when the first changeover switch is switched to the sum voltage signal side and the control signal from the control signal storage circuit; A displacement measuring device characterized in that the output signal of the amplification/detection circuit is outputted as a core displacement signal when the first changeover switch is switched to the differential voltage signal side.