JPH10281707A - Non-contact dislocation measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a non-contact dislocation measuring device wherein no random phenomenon occurs in the output signal of a differential expansion indicator for accurate measurement of differential expansion even in a rotation number region just before merge state wherein rotation axes of a turbine and a generator are combined together. SOLUTION: A detector magnetization AC power source 2a and synchronous rectification AC power sources 2b and 2c are not directly supplied with a voltage from a commercial AC power source 100 for plant facility, however, they are supplied with such AC voltage as of higher frequency than that of commercial AC power source 100 through an AC/DC conversion circuit 8 and a DC/AC conversion circuit 9. Therefore, no signal frequency approaches the turbine rotation frequency, even with a magnetism present at a disk surface for differential expansion detection while in the rotation number region just before merge state wherein the rotation axes of turbine and generator are combined together, thus, a random phenomenon in output signal of a differential expansion indicator due to the occurrence of beat signal is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a monitoring instrument used in a turbine power plant, and more particularly, to a non-contact displacement measuring device for non-contact measurement of the movement of an axle such as a turbine generator.

[0002]

2. Description of the Related Art Turbine generators generate electric power by rotating a turbine with steam and rotating the generator with the rotation of the turbine.
At this time, the steam expands the casing of the turbine and the rotating shaft, respectively, so that the inner wall of the casing and the blade provided on the rotating shaft do not contact with each other. Is provided with a non-contact type displacement meter for monitoring the displacement.

FIG. 3 is a diagram showing a circuit example of a non-contact type displacement measuring device used for monitoring the difference in extension between the above-mentioned cabin and the rotating shaft.

The non-contact type displacement measuring circuit shown in FIG. 1 is a transformer 10 having a displacement meter 101, an AC power supply 102a for excitation, and two AC power supplies 102b and 102c for synchronous rectification.
2, AC bridge circuit 103, synchronous rectifier circuit 105
, A transformer 106, a V / I conversion circuit 107, and an output generation circuit 108.

[0005] The non-contact type displacement measuring circuit is provided with a transformer 1 from a power supply 100 for equipment of a turbine power plant.
A signal output from the displacement meter 101 is extracted through an AC bridge circuit 103 while exciting the displacement meter 101 with an exciting AC power supply 102a generated through the AC power supply 102. Displacement meter 1 taken out from AC bridge circuit 103
01 are output from the synchronous rectification AC power supplies 102b, 10b.
The transformer 106 driven by the transformer 2c extracts the difference between the outputs of the coils 110a and 110b constituting the displacement meter 101 and converts the difference into a current signal by the V / I conversion circuit 107.

[0006] The signal converted into the current signal is converted into a plurality of signals by an output signal generation circuit 108 and output from the output signal generation circuit 108. Here, the equipment power supply 10
0 is a general commercial power supply, the voltage is AC100V, 1
It is a power supply of 10 V, frequency of 50 Hz, 60 Hz or the like.

The exciting AC power supply 102a generates an exciting AC voltage, and supplies the AC voltage to the middle point of the primary coil 111a constituting the transformer 111, and the coils 110a and 110b.
To the connection point.

The coils 110a, 110b of the displacement meter 101
Are mounted in pairs on a magnetic body such as a measurement flange provided on the turbine rotor so as to face each other. When the mounting gap between the turbine rotor and the ground portion changes, the inductance of each of the coils 110a and 110b decreases. Change. Then, using the excitation AC voltage output from the excitation AC power supply 102 as a power supply, two detection signals corresponding to changes in inductance are generated, and the two detection signals are generated by the coils 110a and 110a.
The signal is output from the midpoint of connection to 0b and the other end of each of the coils 110a and 110b and supplied to the AC bridge circuit 103.

The AC bridge circuit 103 includes a displacement meter 101
, And a difference voltage signal obtained by the extraction operation is supplied to each end of the primary coil 111a of the transformer 111 included in the transformer circuit 106.

[0010] AC power supplies 102b, 102c for synchronous rectification
Generates an AC voltage for synchronous rectification having a preset phase relationship using the common line 116 as a base potential, and supplies the AC voltage to the synchronous rectifier circuit 105.

The synchronous rectifier circuit 105 generates a synchronous rectified voltage from two AC voltages output from the synchronous rectifying AC power supplies 102b and 102c,
06 to perform synchronous rectification.

The transformer circuit 106 includes a transformer 111
, A resistor 130, a resistor 131, and a capacitor 132. The transformer circuit 106 uses the synchronous rectified voltage output from the synchronous rectifier circuit 105 to synchronously rectify the difference voltage signal output from the AC bridge circuit 103 and converts it into a DC signal. Circuit 10
7 input terminal.

The V / I conversion circuit 107 is connected to the common line 1
The DC signal output from the transformer circuit 106 is taken in with reference to the 16 potentials, and the taken DC signal is V / I converted to generate a current signal. And V / I
The conversion circuit 107 outputs the generated current signal from the output terminal and supplies the output current signal to the output signal generation circuit 108.

The output signal generation circuit 108 is a constant voltage element 1
33, a resistor 134, and a resistor 135. Then, the output signal generation circuit 108 is connected to the V / I conversion circuit 107.
And outputs the current signal as it is, and converts it into two voltage signals by the resistors 134 and 135 and outputs it.

[0015]

However, when the above-mentioned conventional non-contact type displacement measuring circuit measures and monitors the difference in extension between the casing of the turbine and the rotating shaft, a magnetic disk is provided on the disc surface for detecting the difference in extension. Is present, and in the rotation speed region immediately before the combined state where the rotating shafts of the turbine and the generator are coupled to each other when the power plant is started and stopped, the differential expansion meter output signal has a true value. There is a drawback that a random point phenomenon occurs without showing a difference.

Hereinafter, the above-described random point phenomenon will be described with reference to the principle diagram of the non-contact type displacement meter shown in FIG. In FIG.
A pair of two differential expansion detectors 101a and 101b are provided with a differential expansion detection disk 2 provided on a rotating shaft 200 of the turbine.
01 are arranged on both sides of the disc 101 so as to face each other with the disk 201 therebetween. These detectors 101a, 101b
As shown in FIG. 3, the coils 110a and 110b form an AC bridge circuit with the primary winding 111a of the transformer 111, and include a connection point between the coils 110a and 110b and the primary winding 111a of the transformer 111. The excitation AC power supply 102a is applied between the points.

In the differential elongation detecting circuit thus constructed, the gap d1 between the disk 201 and the detector 101a is set.
And the difference between the gap d2 between the disk 201 and the detector 101b operates such that the bridge output voltage e of the primary winding 111a of the transformer 111 changes. Gap d1
When the difference between d2 and d2 is equal, the output voltage e becomes 0V,
When the difference between the gaps d1 and d2 increases, the output voltage e
Increase. Then, the synchronous rectifier circuit 10 shown in FIG.
5. The DC voltage signal is output through the V / I conversion circuit 107 and the output generation circuit 108.

Here, the frequency of the bridge output voltage e is
The frequency is 50 Hz or 60 Hz, which is the same as the frequency fb of the exciting AC power supply 102a, but if magnetism exists on the surface of the disk 201, the coils 110a and 110
0b, an AC noise voltage having a turbine rotation frequency ft is generated and superimposed on the signal frequency fb.

Assuming that the output voltage for the signal is eb and the noise output voltage due to the magnetism present in the disk 201 is et, the combined output voltage e and the frequency difference Δf are expressed by the following equations (1) and (2). . e = eb + et = maximum (Eb + Et) to minimum (Eb-Et) --- (1) Δf = fb-ft-(2) where, in the above equation (1), eb = Ebsin (ω
b) t, et = Et sin (ωt) t.

By starting the turbine, the frequency ft of the rotating shaft is
Is from 0 rpm to the rated rotation speed 3000 rpm (50H
z) or 3600 rpm (60 Hz), but it is combined with the generator near 150 to 180 rpm before the rated speed, so that ft = fb after the combination.

FIG. 5 shows the change in the frequency difference Δf due to the change in the turbine speed. Δf in the process of increasing the turbine speed is from 50 Hz (or 60 Hz) to 0 Hz.
In a region where Δf is as large as several Hz or more, noise other than the signal component eb is removed by the synchronous rectification circuit 105 in the subsequent stage, and the indicated value is not adversely affected.

However, Δf up to coupling with the generator is several H
In a region less than z, synchronous rectification cannot be performed, and a beat signal having a frequency Δf is generated, which causes a random point phenomenon in an output signal of the extensometer. This causes a similar random point phenomenon immediately after the turbine rotating shaft is disconnected from the generator when the turbine is stopped. At the time of the rated rotation speed after coupling with the generator, no beat signal is generated because fb = ft.

In general, it is inevitable that the elongation difference detecting disk 201 generates magnetism due to thermal stress generated during processing. Also, at the time of periodic inspection of the plant, demagnetization is performed. Even if demagnetization is performed, magnetism is accumulated in the differential expansion detection disk 201 due to the axial current from the generator,
Again, the above-mentioned random point phenomenon occurs.

As described above, the existence of magnetism in the disc 201 for detecting the difference in extension of the actual power generation plant is inevitable. Therefore, in the conventional non-contact type displacement measuring circuit, the rotating shaft between the turbine and the generator at the time of start and stop is stopped. In the rotation speed region just before the merged state where the two are combined, the output signal of the differential extensometer does not show a true differential expansion, causing a random point phenomenon, which makes it impossible to perform accurate measurement. Was.

In view of the above circumstances, an object of the present invention is a case where magnetism is present on the surface of a disc for detecting difference in elongation, which is just before the combined state where the rotating shafts of the turbine and the generator are coupled to each other. An object of the present invention is to realize a non-contact type displacement measurement device capable of accurately measuring a difference in extension without causing a random point phenomenon in an output signal of the difference measuring device even in a rotation speed region.

[0026]

[Means for Solving the Problems]

(1) The present invention is configured as follows to achieve the above object. That is, it has an exciting AC power supply that generates an exciting AC voltage, and two coils whose inductance changes according to the amount of movement of the object to be measured, and supplies the AC voltage obtained by the exciting AC power supply. A displacement meter that generates an electric signal corresponding to the inductance of each of the two coils; an AC bridge circuit that extracts a difference voltage between the electric signals output from each of the two coils of the displacement meter; A synchronous rectification AC power supply for generating an AC voltage for rectification, and, based on an AC voltage output from the synchronous rectification AC power supply, synchronously rectify a difference voltage output from the AC bridge circuit to generate a DC voltage signal. An AC / DC conversion circuit for generating a DC voltage from a commercial AC power supply in a non-contact displacement measuring device having a synchronous rectifier circuit for generating and outputting As input the DC voltage, and, 1 Hz from the power source frequency of the commercial AC power source
A DC / AC conversion circuit for generating an AC voltage having a frequency higher than the above, an AC voltage having a frequency higher than the power supply frequency by 1 Hz or more as a primary winding voltage, and a secondary winding voltage as the excitation AC power supply and the synchronous rectification AC. A transformer for setting the output voltage of the power supply.

The AC power supply for excitation of the detector and the AC power supply for synchronous rectification are not supplied with a voltage directly from the commercial AC power supply, but are supplied from the commercial AC power supply frequency via the AC / DC conversion circuit and the DC / AC conversion circuit. A high frequency AC voltage is generated and supplied. As a result, the signal frequency is close to the turbine rotation frequency even in the rotation speed region immediately before the combined state in which magnetism exists on the differential expansion detection disk surface and the rotation shafts of the turbine and the generator are coupled to each other. This does not occur, and no random point phenomenon occurs in the differential expansion meter output signal.

(2) Preferably, in the above (1),
The DC / AC conversion circuit generates an AC voltage having a frequency higher than the power supply frequency of the commercial AC power supply by 1 Hz or more and not being an integral multiple of the power supply frequency.

By configuring the DC / AC conversion circuit to generate an AC voltage having a frequency that is not an integral multiple of the power supply frequency, the influence of a disturbance point caused by a harmonic of the commercial frequency is prevented, and the detection accuracy is improved. can do.

[0030]

FIG. 1 is a circuit diagram of a non-contact displacement measuring device according to an embodiment of the present invention. The circuit of the non-contact displacement measuring device shown in FIG. 1 includes an AC / DC conversion circuit 8, a DC / AC conversion circuit 9, and a power transformer circuit 2.
, A displacement meter 1, an AC bridge circuit 3, a synchronous rectifier circuit 4, a transformer circuit 5, a V / I conversion circuit 6, and an output signal generation circuit 7.

Then, while exciting the displacement meter 1 by the exciting AC power supply 2a, a signal output from the displacement meter 1 is taken out by the AC bridge circuit 3, and is driven by the synchronous rectification AC power supplies 2b, 2c. The coils 10a and 10a constituting the displacement meter 1 are
The difference between the output from b and the output is extracted, and this is converted into a current signal by the V / I conversion circuit 6. The signal converted into the current signal is converted into a plurality of signals by the output signal generation circuit 7, and a DC signal corresponding to a difference in extension between the vehicle compartment and the rotating shaft is output.

The voltage from the commercial AC power supply 100 for plant equipment is applied to the input terminal of the AC / DC conversion circuit 8, and the + output terminal of the AC / DC conversion circuit 8 is the + input terminal of the DC / AC conversion circuit 9. The negative output terminal is connected to the negative input terminal of the DC / AC conversion circuit 9. And this DC /
The AC conversion circuit 9 converts the AC voltage into an AC voltage having a frequency higher than that of the commercial AC power supply 100. The AC voltage converted by the DC / AC conversion circuit 9 is applied to the primary winding of the power supply transformer circuit 2 as an output AC voltage, and one secondary winding voltage becomes the excitation AC power supply 2a and the other 2 The secondary winding voltage becomes the synchronous rectification AC power supplies 2b and 2c.

One terminal of the exciting AC power supply 2a is connected to a connection point between the coils 10a and 10b, and the other terminal of the exciting AC power supply 2a is connected to the primary coil 11a of the transformer 11 constituting the transformer circuit 5. Connected to midpoint. Then, the exciting AC power supply 2a generates an exciting AC voltage, and applies the AC voltage to the middle point of the primary coil 11a constituting the transformer 11 and the connection point of the coils 10a and 10b.

One end of a coil 10a of the displacement meter 1 is connected to one end of the coil 10b, and the other end of the coil 10a is connected via a resistor 12, a variable resistor 15, and a resistor 14 constituting the AC bridge circuit 3. To the other end of the coil 10b. One end of the resistor 13 is connected to a connection point between the coils 10a and 10b, and the other end, which is a sliding end of the resistor 13, is connected to a middle point of the variable resistor 15.

The coils 10a and 10b of the displacement meter 1 are mounted on a magnetic body such as a measurement flange provided on the turbine rotor in pairs, and are opposed to each other, and the mounting gap between the turbine rotor and the ground portion changes. Then, the inductance of each of the coils 10a and 10b changes. Then, using the excitation AC voltage output from the excitation AC power supply 2 as a power supply, two detection signals corresponding to the change in inductance are generated, and the two detection signals are connected to the midpoint of connection between the coils 10a and 10b and the other ends of the coils 10a and 10b. And supplies it to the AC bridge circuit 3.

The AC bridge circuit 3 includes a bridge-forming resistor 12, a resistor 14, a resistor 13, and a variable resistor 15, and constitutes a bridge circuit together with the coils 10a and 10b of the displacement meter 1. Then, the AC bridge circuit 3 extracts the difference between the detection signals output from the displacement meter 1 and converts the difference voltage signal obtained by the extraction operation into each of the primary coils 11a of the transformer 11 constituting the transformer circuit 5. Feed to the end.

Each of the synchronous rectifying AC power supplies 2b, 2c
Has one power supply terminal connected to a reference voltage terminal of the V / I conversion circuit 6 via a common line 16. The other ends of the synchronous rectification AC power supplies 2b and 2c are respectively connected to one ends of resistors 17 and 18 constituting the synchronous rectification circuit 4, and are set in advance using the common line 16 as a base potential. The AC voltage for synchronous rectification having the phase relationship is generated and supplied to the synchronous rectifier circuit 4.

The synchronous rectifier circuit 4 includes a bridge circuit 19,
A resistor 17 and a resistor 18 are provided. The bridge circuit 19 includes four resistors 20 to 23 and four diodes 24 to 27. One end of the resistor 17 is connected to one end of the bridge circuit 19, that is, a connection point between the resistors 20 and 21, and the other end of the resistor 17 is connected to the other power terminal of the AC power supply 2b for synchronous rectification. . One end of the resistor 18 is connected to the other end of the bridge circuit 19, that is, a connection point between the resistors 22 and 23, and the other end of the resistor 18 is connected to the other power supply terminal of the synchronous rectification AC power supply 2c. You.

The synchronous rectifier circuit 4 generates a synchronous rectified voltage from the two AC voltages output from the synchronous rectifier AC power supplies 2b and 2c, and supplies the synchronous rectified voltage to the transformer circuit 5 to perform synchronous rectification. .

The transformer circuit 5 includes a transformer 11, a resistor 30, a resistor 31, and a capacitor 32.

Both ends of the transformer 11 are connected to both ends of the variable resistor 15, respectively, and the middle point of the primary coil 1 is connected to the other power supply terminal of the exciting AC power supply 2a.
1a and a secondary coil 11b. One end of the resistor 30 is connected to one end of the secondary coil 11b of the transformer 11, and the other end of the resistor 30 is connected to one end of the bridge circuit 19 (the anode of the diode 24 and the diode 26). (Connection point with the cathode).

One end of the resistor 31 is connected to one end of the secondary coil 11b of the transformer 11, and the other end of the resistor 31 is connected to one end of the bridge circuit 19 (the anode of the diode 27). (A connection point with the cathode of the diode 25). One electrode of the capacitor 32 is connected to the other end of the resistor 30, and the other electrode of the capacitor 32 is connected to the other end of the resistor 31.

The transformer circuit 5 uses the synchronous rectified voltage output from the synchronous rectifier circuit 4 to synchronously rectify the difference voltage signal output from the AC bridge circuit 3 and converts it into a DC signal. It is supplied to the input terminal of the / I conversion circuit 6.

A reference voltage terminal of the V / I conversion circuit 6 is connected to the other power supply terminals of the AC power supplies 2b and 2c for synchronous rectification, and an input terminal of the V / I conversion circuit 6 is a secondary It is connected to the midpoint of the coil 11b. And
An output terminal of the V / I conversion circuit 6 is connected to a positive voltage terminal of a constant voltage element 35 included in the output signal generation circuit 7.

The V / I conversion circuit 6 takes in the DC signal output from the transformer circuit 5 on the basis of the potential of the common line 16, and V / I converts the taken DC signal to generate a current signal. Then, the V / I conversion circuit 6
Outputs the generated current signal from the output terminal and supplies it to the output signal generation circuit 7.

The output signal generation circuit 7 includes a constant voltage element 35
, A resistor 36, and a resistor 37. The positive voltage terminal of the constant voltage element 35 is connected to the output terminal of the V / I conversion circuit 6, and the negative voltage terminal of the constant voltage element 35 is connected to a resistor 36.
And a resistor 37 connected to the ground point.

The output signal generation circuit 7 takes in the current signal output from the V / I conversion circuit 6 and outputs it as it is, and converts it into two voltage signals by resistors 36 and 37 and outputs it. I do.

Here, as described above, in the conventional non-contact type displacement measuring device, when the power plant is started and stopped, the rotating shafts of the turbine and the generator are connected to each other just before the combined state. In a few regions, that is, in a region where the frequency difference Δf until coupling with the generator is less than several Hz, synchronous rectification cannot be performed, a beat signal of the frequency difference Δf is generated, and the output signal of the differential extensometer indicates a true expansion difference. It does not show and causes a random point phenomenon.

Therefore, in the non-contact type displacement measuring device according to one embodiment of the present invention, the DC / AC conversion circuit 9
It is configured to generate an AC voltage having a frequency higher than the voltage frequency of the commercial power supply 100 for plant equipment.

That is, the DC / AC conversion circuit 9 theoretically provides the power supply frequency f of the commercial power supply 100 for plant equipment.
An AC voltage having a frequency fc higher than b by 1 Hz or more may be generated. Therefore, for example, when the power supply frequency fb is 50 Hz
Then, the DC / AC conversion circuit 9 only needs to generate an AC voltage having a frequency of 51 Hz or more. However, in practice, a frequency higher than the power supply frequency fb by 10 Hz or more (when the power supply frequency is If 50Hz, 60Hz
Above) is generated.

As described above, in one embodiment of the present invention, the AC power supply 2a for the detector excitation and the AC power supplies 2b and 2c for the synchronous rectification are connected to the commercial AC power supply 10 for the plant equipment.
The voltage is not supplied directly from 0, but is accelerated to an AC voltage having a frequency higher than the frequency of the commercial AC power supply 100 through the AC / DC conversion circuit 8 and the DC / AC conversion circuit 9 once. AC power supply 2a and synchronous rectification AC power supply 2b, 2
c.

Therefore, even in a region where magnetism is present on the surface of the disk for detecting difference in elongation and the rotating shafts of the turbine and the generator are connected to each other, the turbine rotating speed of FIG. As shown in the graph showing the relationship with the frequency difference Δf, the signal frequency does not approach the turbine rotation frequency, and the occurrence of a beat signal prevents the output signal from the extensometer from being disturbed, thereby achieving accurate expansion. A non-contact displacement measurement device capable of measuring a difference can be realized.

Here, in the above-described example, the DC / AC conversion circuit 9 accelerates the AC voltage to a frequency higher than the commercial AC power supply frequency, and uses the AC power for detector excitation and the AC power for synchronous rectification. Set the acceleration frequency to commercial frequency 50.
In some embodiments, the frequency is set to a frequency that does not become an integral multiple such as 2 times, 3 times,... N times of 60 Hz or 60 Hz, for example, 220 Hz.

By adopting such an embodiment, it is possible to prevent the influence of the disturbance point due to the harmonics of the commercial frequency of 50 Hz and 60 Hz, to obtain the effect of the above-described embodiment, and to further improve the detection accuracy. There is an effect that can be.

[0055]

Since the present invention is constructed as described above, the following effects can be obtained. The AC power supply for excitation of the detector and the AC power supply for synchronous rectification are not supplied with a direct voltage from the commercial AC power supply, but are supplied with a frequency higher than the commercial AC power supply frequency via the AC / DC conversion circuit and the DC / AC conversion circuit. It is configured to generate and supply an AC voltage.

Thus, the signal frequency is maintained at the turbine rotational frequency even in the rotational speed range immediately before the combined state in which magnetism exists on the differential expansion detection disk surface and the rotating shafts of the turbine and the generator are coupled to each other. Therefore, a non-contact type displacement measuring device capable of accurately measuring the difference in elongation without realizing a random point phenomenon in the output signal of the difference elongation meter can be realized.

Further, by configuring the DC / AC conversion circuit to generate an AC voltage having a frequency that is not an integral multiple of the power supply frequency, it is possible to prevent the influence of a disturbance point caused by a harmonic of the commercial frequency, thereby improving the detection accuracy. Can be improved.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a non-contact type displacement measuring device according to an embodiment of the present invention.

FIG. 2 is a graph showing a relationship between a turbine speed and a frequency difference Δf according to the present invention.

FIG. 3 is a circuit diagram of an example of a conventional non-contact type displacement measuring device.

FIG. 4 is a principle diagram of a non-contact displacement meter.

FIG. 5 is a diagram showing a conventional example of turbine speed and frequency difference Δf.
It is a graph which shows a relationship.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Displacement meter 2 Power transformer circuit 2a AC power supply for excitation 2b, 2c AC power supply for synchronous rectification 3 AC bridge circuit 4 Synchronous rectifier circuit 5 Transformer circuit 6 V / I conversion circuit 7 Output signal generation circuit 8 AC / DC conversion circuit 9 DC / AC conversion circuit 10a, 10b Detection coil 100 Commercial power supply for plant equipment

Claims (2)

[Claims] An AC power source for generating an AC voltage for excitation, and two coils whose inductance changes according to the amount of movement of an object to be measured, the AC power source being provided by the AC power source for excitation. A displacement meter that is supplied with a voltage and generates an electric signal corresponding to the inductance of each of the two coils, and an AC bridge circuit that extracts a difference voltage between the electric signals output from each of the two coils of the displacement meter A synchronous rectification AC power supply that generates an AC voltage for synchronous rectification; and an AC voltage output from the synchronous rectification AC power supply. A non-contact type displacement measuring device having a synchronous rectifier circuit for generating and outputting a voltage signal, comprising: an AC / DC conversion circuit for generating a DC voltage with a commercial AC power supply as an input. A DC / AC conversion circuit that receives the DC voltage as input and generates an AC voltage having a frequency higher than the power supply frequency of the commercial AC power supply by 1 Hz or more; A winding voltage, and a transformer using the secondary winding voltage as an output voltage of the excitation AC power supply and the synchronous rectification AC power supply,
A non-contact type displacement measuring device comprising: 2. The non-contact type displacement measuring device according to claim 1, wherein the DC / AC conversion circuit has an AC power having a frequency higher than a power supply frequency of the commercial AC power supply by 1 Hz or more and not being an integral multiple of the power supply frequency. A non-contact displacement measuring device characterized by generating a voltage.