JPS6182117A - Direct current feedback type eddy current range finder - Google Patents

Abstract

PURPOSE:To eliminate oscillation due to a phase shift by detecting a difference voltage between a couple of secondary coils, applying a obtained DC signal to a DC amplifier, and controlling an AC signal in proportion to its output signal. CONSTITUTION:The difference voltage between voltages induced across secondary coils 1-2 and 1-3 of an eddy current sensor 1 is detected by a synchronous detecting circuit 14 in synchronism with an AC signal supplied to the primary coil 1-1. The DC signal ES obtained by the detection is fed back to a DC amplifier 13. Further, the output of an amplifier 13 is sent to a DC/AC converting circuit 10 to control the voltage level of the AC signal supplied to the coil 1-1. Consequently, the output voltage out of the amplifier 13 corresponds to the relative distance between the sensor 1 and a body 4 to be measured. Consequently, oscillation due to the phase shift of the feedback loop is eliminated and a high-precision DC feedback type eddy current range finder which operates stably and is effectively free of maintenance is obtained.

Description

[Detailed description of the invention] [Technical field of invention] The present invention relates to an improvement in a DC feedback type eddy current distance meter.

[Technical background of the invention]

Conventional techniques for measuring the distance to a measured object under non-contact conditions include distance meters that use Radhe light, ultrasonic waves, or eddy currents. Fig. 3 This eddy current sensor 1 is composed of a primary coil 1-1 and a pair of secondary coils 1-2, 1-3. The signal is fed through an amplifier 3ft. This eddy current sensor 1 is placed close to an object to be measured 4 such as a rolled metal plate or molten metal liquid. When the alternating current signal is supplied to the eddy current cell in this state, an alternating magnetic field is generated from the primary coil 1-1 and is directly connected to the object to be measured 4, thereby generating an eddy current on the bottom surface of the object to be measured 4. Occur. Due to this eddy current, a magnetic field is generated from the object to be measured 4 that is a reaction to the alternating current magnetic field generated by the primary coil 1-1. According to this, secondary coil 1-2.1
-3 and the magnetic field intersecting each secondary coil 1-2.1 changes.
-3, voltages with different values are induced. Here, the influence of magnetic field changes due to eddy currents is greater on the side of the secondary coil 1-2 that is closer to the object to be measured 4, so the difference between the pair of secondary coils 1-2 and 1-3 This differential voltage is amplified to a predetermined value by the signal amplifier 5 and fed back to the positive input terminal of the amplifier 3. The output voltage e of the amplifier 3 at this time. ut is a value corresponding to the relative distance between the eddy current sensor 1 and the object to be measured 4.

Here, the output voltage e. ut is expressed by the following equation.

1-G, ・G2 (eout/zpXM1-M2)
G is the open amplification degree of the amplifier 3, ein is the output voltage of the oscillator 2, G2 is the amplification degree of the signal amplifier 5, 2 is the impedance of the primary coil 1-1, Ml and M2 are the primary coils 1-1 and 1 These are the mutual impedances between the pair of secondary coils 1-2, 1-3.

Therefore, the output voltage e of the amplifier 3. Relative distance can be indirectly determined by measuring ut tri.

[Problems with background technology]

By the way, in the denominator of equation (1), the difference between each mutual impedance M1#M2 is multiplied by (eout/z,), but in this case, each mutual impedance M1 +
If the imaginary parts of M2 are not equal, the output voltage e. ut
can be expressed as an expression with an imaginary part. Having an imaginary part in this way is the actual output voltage e. At U, a phase deviation occurs at 0.The following factors can be considered as factors for this phase deviation. That is, (1) unbalance of each impedance of the pair of secondary coils 1-2, 1-3;

■ Electrical characteristics and magnetic characteristics of the object to be measured 4.

■ Frequency of the alternating current signal (alternating current) supplied to the primary six coils 1-1.

■ Diameter and shape of the entire eddy current sensor 1.

■ Input impedance value of signal amplifier 5 and its fluctuation.

■ Unbalance in the distributed capacitance of the coaxial cable that connects the excess current sensor 1 and the main unit of the device, that is, the amplifier 63 and the signal amplifier 5, and fluctuations in the distribution d due to temperature fluctuations.

■ These include the phase error of the device body (IC) and the distributed capacitance of the glint board.

By the way, when the phase deviation becomes large, the amplifier 3 cannot operate normally, and as a result, the output voltage e. ut
As shown in FIG. 4, the output characteristic (b) contains a very large error compared to the output characteristic (a) during normal manufacturing. Furthermore, it is also possible that it may be in a feedback loop and self-destruct.

[Purpose of the invention]

The present invention has been made based on the above-mentioned circumstances, and its purpose is to provide a DC feedback type eddy current distance meter that can eliminate the excavation phenomenon caused by phase deviation, operates stably, and has high accuracy. be.

[Summary of the invention]

The present invention provides an eddy current sensor that includes a primary coil to which an alternating current signal of a predetermined frequency is supplied and a pair of secondary coils that output a voltage difference between respective induced voltages on an object to be measured. The differential voltage output from the next coil is detected by a synchronous detection circuit in synchronization with the AC signal and output as a DC signal, and this DC signal is applied to a differential amplifier circuit to which a DC signal of a preset level is added. The level t-side of the AC signal supplied to the primary coil is controlled in accordance with the output signal of this differential amplifier circuit, and a signal corresponding to the distance between the eddy current sensor and the object to be measured is output from this differential I/lh amplifier circuit. This is a DC feedback type eddy current distance meter with output.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of the DC feedback type eddy current distance needle of the present invention. Note that the same parts as in FIG. 3 are given the same reference numerals. That is, 1 is an eddy current sensor, 1-1 is a primary coil, 1-2.1-3 is a pair of secondary coils,
2 is an oscillator, 4 is a technique for molten metal liquid, rolled plate, etc., DC
An alternating current signal is supplied through a power amplifier (referred to as a ZAC conversion circuit) and a power amplifier (referred to as a ZAC conversion circuit) and a power amplifier (referred to as a ZAC conversion circuit), which is set to amplification of 1fil, and a secondary coil (referred to as a ZAC conversion circuit); , 1-3 are connected to the input terminals of the differential signal amplifier @12. In addition,
The DC/AC conversion circuit 10 receives the signal E output from the DC amplifier 13. u, t-receive the voltage level of the alternating current signal from oscillator 2 as signal E; It has a function of controlling proportionally to ut and sending it to the power amplifier 11.

Further, the output terminal of the differential signal amplifier 12 is connected to the synchronous detection circuit 1.
Connected to 4. This synchronous detection circuit 14 detects the frequency i! of a predetermined frequency output from the oscillator 2! The output signal of the differential signal amplifier 12 is detected in synchronization with the signal, and the DC signal E obtained by this detection is supplied to the positive input terminal of the DC amplifier 13. This DC amplifier 13 has a DC reference voltage ER of a preset level applied from the DC reference voltage generation circuit 15 to the negative input terminal of the 0 output terminal.
It outputs the difference voltage "out" between this DC reference voltage EIL and the DC signal Es obtained from the synchronous detection circuit 14, and this difference voltage E.ut is the difference between the eddy current sensor and the object to be measured 4.
The value corresponds to the distance from

Next, the operation of the distance hand configured as described above will be explained. An eddy current sensor is placed close to the object to be measured 4, and an alternating current signal of a predetermined frequency is supplied from the oscillator 2 to the primary coil 1-1 of the eddy current sensor via the DC/ACi conversion circuit 102 and the power amplifier 11t. Then, an alternating current magnetic field is generated from the first coil 1-1, and this alternating magnetic field intersects with the object to be measured 4. Then, an eddy current is generated on the surface of the object to be measured 4, and this eddy current generates a magnetic field that acts as a reaction to the alternating current magnetic field generated from the primary coil 1-1.

Due to the reaction of this magnetic field, the alternating current magnetic field intersecting the secondary coil 1-2, 1-3 changes, and the change becomes larger for the coil 1-2 closer to the metal object 4 to be measured.

Therefore, the respective electromotive voltages of the secondary coils 1-2, 1-3 have different voltage values. Therefore, if the induced voltage t"e of the secondary coil 1-2 and the induced voltage te of the secondary coil 1-3 are □, then the differential signal amplifier 12 outputs (
e, "s2)" A signal Gb=e is output. Note that Gb is the amplification degree of the differential type signal amplification@612.

This signal e is applied to the synchronous detection circuit 14 and detected by the synchronous detection circuit 14. That is, the synchronous detection circuit 14 detects the signal e,'t- in synchronization with the AC signal output from the generator IJi device 2, and outputs the DC signal E,=e,asθ obtained by this detection. Therefore, even if the output signal e of differential signal amplifier #12 has a phase deviation,
This phase deviation component is removed.

Then, the output signal E of the synchronous detection circuit 14 is sent to the DC amplifier 13, that is, it is positively fed back, and the difference voltage between the DC reference voltage E and the output signal E8 is amplified from the DC amplifier 13, and the DC/ It is added to the AC conversion circuit 10. Then, the DC/AC conversion circuit 10 controls the voltage value of the AC signal from the oscillator 2 in proportion to the voltage value of the input signal, and passes the AC signal to the primary coil 1 through the power island width converter 11. -1. The output voltage E of the DC amplifier 13 at this time. ut is the distance t between the eddy current sensor and the object to be measured 4
. I regret that this corresponds to this. Here, the output voltage E. ut is expressed by the following formula. Here, K is the conversion efficiency of the DC/ACi converter M10, G8 is the open amplification degree of the DC amplifier 13, G is the amplification degree of the differential signal amplifier 12, and N is the synchronous detection circuit. 14
The conversion efficiency of , e is the output voltage of the power amplifier p11. Therefore, from equation (2), E
If the six values of RlG, G, Kp and N are fixedly set, the output voltage E of the DC amplifier 13. It can be seen that U is a value corresponding to the relative distance between the eddy current sensor and the object to be measured 4.

FIG. 2 is an output characteristic diagram obtained by the rangefinder shown in FIG. 1. Note that the eddy current sensor used has a diameter of 30 mφ.

In this way, in the distance meter of the present invention, the difference voltage between the induced voltages of the secondary coils 1-2, 1-3 of the eddy current sensor is converted into an AC signal supplied to the primary coil 1-1 by the synchronous detection circuit 14. The DC signal E obtained by this detection is fed back to the DC amplifier 13, and further to the DC amplifier 1.
Send the output voltage of 3 to the DC/AC conversion circuit 10 and convert the output voltage of 1
The voltage level of the AC signal supplied to the next coil 1-1 is controlled, thereby increasing the output voltage E of the DC amplifier 613. Since the distance ut' corresponds to the distance pmto, the output voltage E due to the phase deviation. The operation of the rangefinder as a whole is stabilized without causing ut to become a single shift containing errors or causing oscillation in the feedback loop. Therefore, the object to be measured 4
For example, if the eddy current sensor 1 is disposed at the M-m boundary when the solution is at a certain temperature, the impedances of the secondary coils 1-2, 1-3 of the eddy current sensor 1 become unbalanced VC.
However, the distance ai't of the present invention
- If applied, the synchronous detection circuit 14 converts it to direct current and returns it, so even under adverse conditions, no excavation occurs and distances can be measured with stable operation.

In addition, in conventional rangefinders, the phase g# of the output voltage in each circuit was adjusted and inspected using an oscilloscope, etc., but in the distance needle of the present invention, the feedback loop f is changed to DC, so it is not necessary to use a complicated m There is no need for regular inspections and maintenance is simplified.

According to the equation, a measurement span equal to or greater than that of a conventional feedback amplification type eddy current distance meter can be obtained.

〔Effect of the invention〕

According to the present invention, a differential voltage between a pair of secondary coils of an eddy current sensor is detected by a synchronous detection circuit in synchronization with an AC signal supplied to the primary coil of the eddy current sensor, and the DC signal obtained by this detection is Add the signal to a DC amplifier, then control all AC signals in proportion to the output signal of this DC amplifier, and calculate the distance l between the dual-current sensor and the object to be measured from the output signal of the DC amplifier obtained at this time. As a result, it is possible to provide a highly accurate DC feedback type eddy current distance meter that can eliminate oscillation caused by phase deviation in the feedback loop, operates stably, and is maintenance-free and effective.

[Brief explanation of drawings]

Fig. 1 is a configuration diagram showing an embodiment of a DC feedback type eddy current rangefinder according to the present invention, Fig. 2 is an output characteristic diagram of the distance needle shown in Fig. 1, and Fig. 3 is a diagram of a conventional eddy current rangefinder. The configuration diagram, FIG. 4, is an output characteristic diagram of the distance meter shown in FIG. 3. 1... Eddy current sensor, 1-1... Primary coil, 1-2
゜1″″3...Secondary coil, 2...Energy #, 4.
...Object to be measured, 10...DC/AC conversion circuit, 11.
...Power amplifier, 12...Differential plastic signal amplifier, 13.
...DC amplifier, 14...synchronous detection circuit, 15...
DC reference voltage generation circuit. Izuka's agent Patent attorney Takehiko Suzue Figure 1 Figure 2 Edge γE angle L Lo (mm) Figure 3 F Figure 4 Rule 5 t\Ii-JiJ (mm)

Claims (1)

[Claims] An eddy current sensor is provided with a primary coil that is placed close to an object to be measured and is supplied with an alternating current signal of a predetermined frequency, and a paired secondary coil that outputs a differential voltage between the respective induced voltages, and a secondary coil of this eddy current sensor. a synchronous detection circuit that detects the difference voltage between the voltages output from the coil in synchronization with the AC signal and extracts it as a DC signal; a differential amplifier circuit that calculates a level difference with a DC reference signal and outputs a signal corresponding to the distance between the eddy current sensor and the object to be measured; A DC feedback type eddy current distance meter comprising a supply control circuit that controls the voltage level of an AC signal supplied to a primary coil of the sensor.