JPH0618202A - Noncontact displacement measuring circuit - Google Patents

Abstract

PURPOSE:To prevent serious failure of turbine by detecting abnormality in AC power supply for synchronous rectification, AC power supply for excitation, displacement gauge, or the like, in its early stage. CONSTITUTION:A rectifying/smoothing circuit 40 and a comparator circuit 41 constituting an abnormality detecting circuit 8 rectify and smooth electrical signals outputted from an AC bridge circuit 3 and a transformer circuit 6. If a DC voltage thus produced has a magnitude deviating from a preset range, the DC voltage is detected and an abnormality detection signal is generated. On the other hand, a rectifying/smoothing circuit 42 and a comparator circuit 43 constituting an abnormality detecting circuit 8 rectify and smooth an AC voltage outputted from an AC power supply 2 for excitation. When a DC voltage thus produced has a magnitude deviating from a preset range, the DC voltage is detected and an abnormality detection signal is generated thus grounding a V/I converting circuit 7 on the output side thereof.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-contact type displacement measuring circuit used in a turbine monitoring instrument or the like, and more particularly to a non-contact type displacement measuring circuit for non-contactly measuring a moving amount of an axle of a turbine generator or the like. .

[0002]

2. Description of the Related Art Normally, in a turbine generator, steam is used to rotate a turbine, and the turbine is rotated to generate electricity.

In a normal turbine, a turbine rotor is arranged in the passenger compartment to guide high temperature steam to rotate the turbine rotor and rotate a generator connected to the turbine rotor to obtain electricity. There is.

In this case, in order to improve the power generation efficiency of the turbine, in a normal turbine, the tips of the blades provided on the turbine rotor and the ground portion of the turbine casing are attached at a very narrow interval. .

Therefore, when high-temperature steam is applied to the turbine, the turbine casing and the turbine rotor are exposed to high-temperature steam.
Due to the centrifugal force of turbine rotation, elongation occurs, and these elongations are not uniform.Therefore, the elongation difference between these blades and the gland is measured by measuring the difference between these elongations with a movement amount measurement and monitoring system that uses an inductance type displacement gauge or the like. I try not to touch them.

FIG. 3 is a circuit diagram showing an example of a non-contact type displacement measuring circuit used in such a movement amount measuring and monitoring system.

The non-contact type displacement measuring circuit shown in this figure is a displacement gauge 101, an exciting AC power source 102, an AC bridge circuit 103, and two synchronous rectifying AC power sources 104a and 10a.
4b, the synchronous rectification circuit 105, and the transformer circuit 106
, V / I conversion circuit 107, and output signal generation circuit 108
While exciting the displacement meter 101 by the exciting AC power supply 102, a signal output from the displacement meter 101 is taken out by the AC bridge circuit 103 and driven by the synchronous rectification AC power supplies 104a and 104b. After the difference is extracted by the transformer circuit 106 and converted into a current signal by the V / I conversion circuit 107,
The output signal generation circuit 108 converts into a plurality of signals,
Output this.

The exciting AC power supply 102 has coils 110a and 110 each having one power supply terminal constituting the displacement meter 101.
The primary coil 11 of the transformer 111 that is connected to the connection point of b and has the other power supply terminal that constitutes the transformer circuit 106.
A primary coil 1 that is connected to the midpoint of 1a, generates an alternating voltage for excitation, and uses this to form the transformer 111.
The voltage is applied to the midpoint of 11a and the midpoint of the displacement meter 101.

The displacement gauge 101 has one end connected to one end of each of the resistors 112 and 115 constituting the AC bridge circuit 103, and the other end connected to a midpoint to provide one power supply terminal of the exciting AC power supply 102. And the AC bridge circuit 1
03 is provided with two coils 110a and 110b connected to one end of the resistor 113, and when the mounting gap between the turbine rotor and the ground portion changes, a magnetic material such as a measurement flange provided on the turbine rotor. Each of the coils 110 attached to each other in pairs as opposed to each other.
The inductances of a and 110b change, and two detection signals corresponding to the change in the inductance are generated by using the excitation AC voltage output from the excitation AC power supply 102 as a power source. 110
It is output from the other end of b and supplied to the AC bridge circuit 103.

The AC bridge circuit 103 has a bridge-structured resistor 1 having one end connected to one end of the coil 110a.
12, a resistor 115 for bridge configuration, one end of which is connected to one end of the coil 110b, and one end of each of the coils 1
A resistor 113 for bridge configuration connected to the connection point (middle point) of 10a and 110b, one end connected to the other end of the resistor 112, the other end connected to the other end of the resistor 115,
A variable resistor 114 having a sliding configuration, the sliding end of which is connected to the other end of the resistor 113.
A bridge circuit is constructed together with the coils 110a and 110b of No. 1 to extract the difference between the detection signals output from the displacement meter 101, and the differential voltage signal obtained by this extraction operation is the transformer 111 that constitutes the transformer circuit 106. Of 1
It is supplied to each end of the next coil 111a.

Further, the AC power supplies 104a, 1 for synchronous rectification are provided.
04b has one power supply terminal connected to the reference voltage terminal of the V / I conversion circuit 107 through the ground line 116,
The other end of each resistor 11 constitutes the synchronous rectification circuit 105.
7 and 118 are respectively connected to one end of each of them, and the ground line 116 is used as a base potential to generate an AC voltage for synchronous rectification having a preset phase relationship and the AC voltage is supplied to the synchronous rectification circuit 105. To do.

The synchronous rectification circuit 105 includes four resistors 120-
123 and four diodes 124 to 127, and a resistor 11 having one end connected to one end of the bridge circuit 119 and the other end connected to the other power supply terminal of the synchronous rectification AC power supply 104a.
7 and a resistor 118 having one end connected to one end of the bridge circuit 119 and the other end connected to the other power supply terminal of the synchronous rectification AC power supply 104b, the synchronous rectification AC power supply 104a, 2 output from 104b
Synchronous rectification voltage is generated by one AC voltage and is supplied to the transformer circuit 106 to perform synchronous rectification.

The transformer circuit 106 has one end connected to each end of the variable resistor 114 and a middle point connected to the other power supply terminal of the exciting AC power supply 102.
The transformer 111 having 1a and the transformer 11 at one end
The bridge circuit 119 that is connected to one end of the secondary coil 111b of No. 1 and has the other end that constitutes the synchronous rectification circuit 105.
A resistor 130 connected to one end of the bridge circuit 1 having one end connected to one end of the secondary coil 111b of the transformer 111 and the other end constituting the synchronous rectification circuit 105.
The synchronous rectifier circuit 105 includes a resistor 131 connected to one end of the resistor 19 and a capacitor 132 having one end connected to the other end of the resistor 130 and the other end connected to the other end of the resistor 131. The differential voltage signal output from the AC bridge circuit 103 is synchronously rectified using the output synchronous rectified voltage and converted into a DC signal, which is supplied to the input terminal of the V / I conversion circuit 107.

The reference voltage terminal of the V / I conversion circuit 107 is connected to the other power supply terminal of the AC power sources 104a and 104b for synchronous rectification, and the input terminal is connected to the middle point of the secondary coil 111b constituting the transformer 111. And a constant voltage circuit 13 whose output terminal constitutes the output signal generating circuit 108.
3 is connected to the positive voltage terminal and is connected to the ground line 11
The DC signal output from the transformer circuit 106 is taken in with the potential of 6 as a reference, and this is V / I converted to generate a current signal, which is output from the output terminal and supplied to the output signal generation circuit 108. .

The output signal generation circuit 108 has a constant voltage circuit 133 having a positive voltage terminal connected to the output terminal of the V / I conversion circuit 107, and a resistor 134 having one end connected to the negative voltage terminal of the constant voltage circuit 133. And a resistor 135 having one end connected to the other end of the resistor 134 and the other end connected to a ground point.
And takes in the current signal output from the V / I conversion circuit 107, outputs it as it is, and converts it into two voltage signals for output.

[0016]

However, in the above-mentioned conventional non-contact type displacement measuring circuit, the displacement meter 10 is used.
1, excitation AC power supply 102, synchronous rectification AC power supply 104
When a, 104b, the synchronous rectification circuit 105 and the like are normal, the voltage at the point A becomes as shown in FIG. 4 (a) in the measurement range of 0% to 100%, and the output voltage becomes 1 to 4% as shown in FIG. 5VD
The constants of each element are determined so as to fall within the range of C.

However, the displacement gauge 101, the excitation AC power supply 102, and the synchronous rectification AC power supplies 104a and 104 are used.
b, when one of the synchronous rectification circuit 105 and the like, for example, the synchronous rectification AC power supplies 104a and 104b becomes abnormal and the AC voltage for synchronization is lost, the differential voltage signal output from the AC bridge circuit 103 is output by the transformer 111. The voltage at the point A becomes a sine wave in the measurement range 0% to 100% after being amplified by the turns ratio.

However, in this case as well, FIG.
As shown in, the output voltage falls within the range of 1 to 5 VDC.

Further, when one of the coils 110a and 110b constituting the displacement meter 101 is disconnected, the coil 11
Measuring range 0% depending on the inductance of 0a and 110b
At ~ 100%, the voltage at point A becomes a sine wave that is larger than the full-wave rectified voltage under normal conditions, as shown in Figs. 6 (a) and 6 (b).
Also in this case, the output voltage falls within the range of about 1 to 5 VDC as shown in FIGS. 6 (c) and 6 (d).

As can be seen from the above, in the conventional non-contact type displacement measuring circuit, the displacement gauge 101, the exciting AC power source 102, the synchronous rectifying AC power sources 104a, 1
04b, even if one of the synchronous rectification circuit 105 or the like becomes abnormal, the output voltage falls within the range of approximately 1 to 5 VDC, and these abnormalities cannot be detected from the value of the output voltage.

Therefore, the synchronous rectification AC power supply 104a,
Even if the actual measurement becomes impossible due to the abnormality of 104b, the excitation AC power supply 102, the abnormality of the displacement gauge 101, etc., the turbine operation is continued without noticing this and a serious accident occurs. There was a risk of being lost.

In view of the above circumstances, the present invention detects an abnormality of the AC power supply for synchronous rectification, an abnormality of the AC power supply for excitation, an abnormality of the displacement gauge, or the like early to detect a serious turbine accident. It is an object of the present invention to provide a non-contact type displacement measuring circuit which can be prevented.

[0023]

In order to achieve the above object, a non-contact type displacement measuring circuit according to the present invention includes an exciting AC power source for generating an exciting AC voltage and an object moving amount to be measured. A displacement meter that has two coils whose inductance changes in accordance with the displacement, and generates an electric signal according to the inductance of each coil by using an AC voltage obtained by the excitation AC power source as a power source; An AC bridge circuit that extracts a differential voltage of an electric signal output from a coil, an AC power supply for synchronous rectification that generates an AC voltage for synchronous rectification, and an AC voltage output from the AC power supply for synchronous rectification A non-contact displacement measurement circuit having a synchronous rectification circuit for synchronously rectifying a differential voltage output from an AC bridge circuit to generate a DC voltage signal and outputting the DC voltage signal. A DC voltage value obtained by rectifying and smoothing the electric signal output from the latch circuit is out of a preset range, a differential voltage abnormality detection unit that generates an abnormality detection signal, and the excitation An exciting voltage abnormality detection unit that generates an abnormality detection signal when the value of the DC voltage obtained by rectifying and smoothing the AC voltage output from the AC power supply is out of a preset range is provided. It has a feature.

[0024]

In the above structure, the differential voltage abnormality detecting section rectifies and smoothes the electric signal output from the AC bridge circuit, and the value of the DC voltage obtained by this rectifying and smoothing operation is within a preset range. When it is out, an abnormality detection signal is generated, and the excitation voltage abnormality detection unit rectifies and smoothes the AC voltage output from the excitation AC power supply, and the value of the DC voltage obtained by this rectification and smoothing operation is set in advance. When it is out of the set range, the abnormality detection signal is generated and output to the outside.

[0025]

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

The non-contact type displacement measuring circuit shown in this figure comprises a displacement gauge 1, an exciting AC power supply 2, an AC bridge circuit 3 and
It is equipped with two AC power supplies 4a and 4b for synchronous rectification, a synchronous rectification circuit 5, a transformer circuit 6, a V / I conversion circuit 7, an abnormality detection circuit 8 and an output signal generation circuit 9 for excitation. While exciting the displacement meter 1 with the AC power supply 2, the signal output from the displacement meter 1 is taken out by the AC bridge circuit 3 and the difference is taken by the transformer circuit 6 driven by the AC power supplies 4a and 4b for synchronous rectification. Is converted into a current signal by the V / I conversion circuit 7, and then converted into a plurality of signals by the output signal generation circuit 9 and output. When an abnormality occurs in the synchronous rectification AC power supplies 4a and 4b, an abnormality in the excitation AC power supply 2, an abnormality in the displacement gauge 1 or the like, this is detected to set the values of the output current signal and the output voltage signal to zero. Notify the operator that an abnormality has occurred.

The exciting AC power supply 2 has one power supply terminal connected to a connection point of the coils 10a and 10b constituting the displacement meter 1 and one input terminal of a rectifying / smoothing circuit 42 constituting the abnormality detecting circuit 8. , The other power source terminal is the primary coil 11a of the transformer 11 which constitutes the transformer circuit 6.
Connected to the middle point and the other input terminal of the rectifying / smoothing circuit 42, and generates the AC voltage for excitation, which is the middle point of the primary coil 11a constituting the transformer 11.
It is applied to the midpoint of the displacement meter 1 and to each input terminal of the rectifying and smoothing circuit 42 of the abnormality detection circuit 8.

The displacement gauge 1 has one end connected to one end of each of the resistors 12 and 14 constituting the AC bridge circuit 3 and the other end connected to a midpoint, and one power supply terminal of the excitation AC power supply 2 And a resistor 1 constituting the AC bridge circuit 3
3 is provided with two coils 10a and 10b connected to one end, and when the mounting gap between the turbine rotor and the ground portion changes, two sets are provided for the magnetic material such as the measurement flange provided on the turbine rotor. The inductance of each of the coils 10a and 10b mounted in opposition to each other changes according to the inductance change using the exciting AC voltage output from the exciting AC power supply 2 as a power source.
Two detection signals are generated and output from the midpoint and the other ends of the coils 10a and 10b to generate the AC bridge circuit 3
Supply to.

One end of the AC bridge circuit 3 is the coil 1
A resistor 12 for bridge configuration connected to one end of 0a,
A resistor 14 for bridge construction having one end connected to one end of the coil 10b, and one end of each of the coils 10a and 10b.
Resistor 1 for bridge configuration connected to the connection point (middle point) of
3 and a variable resistor 15 for bridge configuration, one end of which is connected to the other end of the resistor 12, the other end of which is connected to the other end of the resistor 14, and the sliding end of which is connected to the other end of the resistor 13. A bridge circuit is formed together with the coils 10a and 10b of the displacement meter 1 to extract the difference between the detection signals output from the displacement meter 1 and the difference voltage signal obtained by this extraction operation Transformer 1 that constitutes the transformer circuit 6
It is supplied to each end of one primary coil 11a.

Each of the AC power supplies 4a and 4b for synchronous rectification has one power supply terminal connected to the V / I via the ground line 16.
It is connected to the reference voltage terminal of the conversion circuit 7, and the other end is connected to one end of each of the resistors 17 and 18 of the synchronous rectification circuit 5, and the ground line 16 is used as the base potential.
An AC voltage for synchronous rectification having a preset phase relationship is generated and supplied to the synchronous rectification circuit 5.

The synchronous rectification circuit 5 has a bridge circuit 19 composed of four resistors 20 to 23 and four diodes 24 to 27, one end of which is connected to one end of the bridge circuit 19, and the other end of which is the AC for synchronous rectification. A resistor 17 connected to the other power supply terminal of the power supply 4a and a resistor 18 having one end connected to one end of the bridge circuit 19 and the other end connected to the other power supply terminal of the synchronous rectification AC power supply 4b. The synchronous rectification voltage is generated by the two AC voltages output from the synchronous rectification AC power supplies 4a and 4b and is supplied to the transformer circuit 6 to perform the synchronous rectification.

The transformer circuit 6 has the variable resistor 1 at one end.
5, a transformer 11 having a primary coil 11a connected to each one end of the transformer 5, the middle point of which is connected to the other power supply terminal of the exciting AC power supply 2, and one end of the secondary coil 1 of the transformer 11.
A resistor 3 connected to one end of 1b and the other end connected to one end of the bridge circuit 19 that constitutes the synchronous rectification circuit 5.
0, a resistor 31 having one end connected to one end of the secondary coil 11b of the transformer 11 and the other end connected to one end of the bridge circuit 19 constituting the synchronous rectification circuit 5, and one end of the resistor 30. It is connected to the other end and the other end is the resistor 3
And a capacitor 32 connected to the other end of 1.
Using the synchronous rectification voltage output from the synchronous rectification circuit 5, the differential voltage signal output from the AC bridge circuit 3 is synchronously rectified and converted into a DC signal, which is an input terminal of the V / I conversion circuit 7. And the input terminal of the rectifying / smoothing circuit 40 that constitutes the abnormality detection circuit 8.

In the V / I conversion circuit 7, the reference voltage terminal is connected to one of the power supply terminals of each of the synchronous rectification AC power supplies 4a and 4b, and the input terminal is at the middle point of the secondary coil 11b constituting the transformer 11. The output terminal is connected to the positive voltage terminal of the constant voltage circuit 35 constituting the output signal generation circuit 9, and the DC signal output from the transformer circuit 6 is taken in with the potential of the ground line 16 as a reference. At the same time, this is V / I converted to generate a current signal, which is output from the output terminal and supplied to the output signal generation circuit 9.

The output signal generation circuit 9 has the positive voltage terminal V
Constant voltage circuit 35 connected to the output terminal of the I / I conversion circuit 7
A resistor 36 having one end connected to the negative voltage terminal of the constant voltage circuit 35, and one end connected to the other end of the resistor 36,
The other end of the V / I conversion circuit 7 is connected to the ground, and the current signal output from the V / I conversion circuit 7 is taken in and output as it is, and converted into two voltage signals and output. .

Further, the abnormality detection circuit 8 takes in a DC signal inputted to the reference voltage terminal and the input terminal of the V / I conversion circuit 7, and rectifies and smoothes this DC signal.
When the value of the DC signal output from the rectifying / smoothing circuit 40 is larger than a preset value, the AC voltage from the synchronous rectifying AC power supplies 4a and 4b is no longer output and the displacement meter 1 Each coil 10a, 1 that composes
0b of the synchronous current source, which indicates that at least one of 0b has been disconnected, and a comparator circuit 41 for generating a displacement meter disconnection detection signal, and the AC voltage output from the excitation AC power supply 2 are taken in and rectified and smoothed. Rectifying / smoothing circuit 42, and when the value of the DC signal output from the rectifying / smoothing circuit 42 is smaller than a preset value, an exciting current indicating that the AC voltage from the exciting AC power supply is no longer output. When a synchronous current source loss / displacement meter disconnection detection signal or an exciting current source loss detection signal is output from the comparator circuit 43 that generates a source loss detection signal, the comparator circuits 41 and 43 detect the loss. V /
Output short circuit 44 for short-circuiting the output terminal of the I conversion circuit 7
It has and.

The synchronous rectification AC power supplies 4a, 4
When the abnormality of b or the abnormality of the displacement meter 1 occurs, this is detected by the comparator circuit 41, and the output terminal of the V / I conversion circuit 7 is grounded by the output short circuit 44, whereby the output current signal or the output voltage signal is generated. Value is set to zero to inform the operator that an abnormality has occurred, and when an abnormality has occurred in the excitation AC power supply 2, the comparator circuit 43 detects this and the output short circuit 44 causes the V / I conversion circuit. The output terminal of 7 is grounded, whereby the value of the output current signal or the output voltage signal is set to zero, and the operator is informed that an abnormality has occurred.

As described above, in this embodiment, while exciting the displacement meter 1 by the exciting AC power supply 2, the signal output from the displacement meter 1 is taken out by the AC bridge circuit 3 and is used for synchronous rectification AC. The difference is extracted by the transformer circuit 6 driven by the power supplies 4a and 4b, converted into a current signal by the V / I conversion circuit 7, and then converted into a plurality of signals by the output signal generation circuit 9 and output. On the other hand, when an abnormality occurs in the synchronous rectification AC power supplies 4a and 4b, an abnormality in the excitation AC power supply 2, an abnormality in the displacement meter 1, or the like, the abnormality detection circuit 8 detects this and outputs the output current signal or the output voltage signal. Since the value is set to zero to notify the operator etc. that an abnormality has occurred, when an abnormality in the AC power supply for synchronous rectification, an abnormality in the AC power supply for excitation, an abnormality in the displacement gauge, etc. It is possible to early detect and prevent turbine of the serious accidents a.

FIG. 2 is a circuit diagram showing another embodiment of the non-contact type displacement measuring circuit according to the present invention. In this figure, the same parts as those in FIG. 1 are designated by the same reference numerals.

The non-contact type displacement measuring circuit shown in FIG.
The point different from the circuit shown in (1) is that when the synchronous current source loss / displacement meter disconnection detection signal is output from the comparator circuit 41,
A switch circuit 45 that detects this and generates a contact signal (or open collector output) and outputs this to the outside.
And when the exciting current source loss detection signal is output from the comparator circuit 43, this is detected and the contact signal (or,
A switch circuit 46 for generating an open collector output) and outputting this to the outside, and each of these switch circuits 45,
This is to add an abnormality display lighting circuit 47 which detects a contact signal (or an open collector output) when any of the 46 outputs, and lights an indicator lamp for abnormality display.

As a result, the synchronous rectification AC power supply 4a,
When an abnormality of 4b or an abnormality of the displacement gauge 1 occurs, the comparator circuit 41 detects this and the switch circuit 45
Generates a contact signal indicating an abnormality of the AC power supplies 4a and 4b for synchronous rectification or an abnormality of the displacement gauge 1 and outputs the contact signal to the outside to notify an operator or the like that an abnormality has occurred. When an abnormality occurs, the comparator circuit 4
This can be detected by 3 and the switch circuit 46 can generate a contact signal indicating an abnormality of the excitation AC power supply 2 and output this to the outside to notify the operator or the like that an abnormality has occurred.

By doing so, in this embodiment, when the abnormality of the synchronous rectification AC power supplies 4a and 4b, the abnormality of the excitation AC power supply 2, the abnormality of the displacement meter 1 and the like occur, the details of the abnormality are described. Can be transmitted to the outside, and when an abnormality occurs, the operator can be immediately notified of this by turning on the indicator light provided for the abnormality display.

Further, in each of the above-described embodiments, when any of the coils 10a and 10b constituting the displacement meter 1 is disconnected, the comparator circuit 41 detects this, but the V / I conversion circuit is used. 7 is provided with two comparator circuits, and each of these comparator circuits determines whether the value of the current signal output from the V / I conversion circuit 7 is 1 V or less or 5 V or more, and each of the coils 10a, 10b. It may be possible to determine which of the two is disconnected.

By doing so, the details of the abnormality can be known in more detail than in the above-described embodiments.

[0044]

As described above, according to the present invention, when an abnormality in the AC power supply for synchronous rectification, an abnormality in the AC power supply for excitation, an abnormality in the displacement gauge, etc. occur, they are detected early and the turbine It is possible to prevent serious accidents.

[Brief description of drawings]

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

FIG. 2 is a circuit diagram showing another embodiment of the non-contact type displacement measuring circuit according to the present invention.

FIG. 3 is a circuit diagram showing an example of a conventionally known non-contact type displacement measuring circuit.

FIG. 4 is a waveform diagram showing an operation example of the non-contact displacement measuring circuit shown in FIG. 3 in a normal state.

5 is a waveform diagram showing an operation example of the non-contact displacement measuring circuit shown in FIG. 3 when synchronous rectification current is lost.

FIG. 6 is a waveform diagram showing an operation example of the non-contact type displacement measuring circuit shown in FIG. 3 when the displacement gauge is disconnected.

[Explanation of symbols]

 1 Displacement meter 2 AC power supply for excitation 3 AC bridge circuit 4a, 4b AC power supply for synchronous rectification 5 Synchronous rectification circuit 6 Transformer circuit 7 V / I conversion circuit 8 Abnormality detection circuit 9 Output signal generation circuit 10a, 10b Coil 40 Rectification smoothing circuit (Difference voltage abnormality detection unit) 41 Comparator circuit (Difference voltage abnormality detection unit) 42 Rectification smoothing circuit (Excitation voltage abnormality detection unit) 43 Comparator circuit (Excitation voltage abnormality detection unit) 44 Output short circuit

Claims (1)

[Claims] 1. An alternating current obtained by the exciting alternating current power supply, comprising: an exciting alternating current power supply for generating an exciting alternating current voltage; and two coils whose inductance changes according to an amount of movement of an object to be measured. A displacement meter that uses a voltage as a power source to generate an electric signal corresponding to the inductance of each coil, an AC bridge circuit that extracts a differential voltage of an electric signal output from each coil of the displacement meter, and an AC for synchronous rectification An AC power supply for synchronous rectification that generates a voltage, and a differential voltage output from the AC bridge circuit is synchronously rectified based on the AC voltage output from the AC power supply for synchronous rectification to generate and output a DC voltage signal. In a non-contact type displacement measurement circuit having a synchronous rectification circuit, the value of a DC voltage obtained by rectifying and smoothing an electric signal output from the AC bridge circuit is preset. When the value is out of the range, the value of the DC voltage obtained by rectifying and smoothing the AC voltage output from the excitation AC power supply and the difference voltage abnormality detection unit that generates an abnormality detection signal is preset. A non-contact type displacement measurement circuit comprising: an excitation voltage abnormality detection unit that generates an abnormality detection signal when the output voltage is out of the range.