RU2208762C1 - Amplitude-phase differential-transformer displacement sensor with phase output - Google Patents

Abstract

FIELD: control and measurement technology; measurement of displacements. SUBSTANCE: proposed sensor is provided with additional circuit including phase-shifting and scaling sections, armature and closing plate made from conducting diamagnetic material for modulation of output voltages in amplitude due to eddy current effect formed by armature and closing plate. Sections of excitation winding are connected to AC source , signal output of working section of measuring winding is connected to first input of adder, signal output of compensating section of measuring winding is connected to first input of phase meter and to second input of adder through additional circuit, output of adder is connected to second input of phase meter. EFFECT: extended field of measurements. 2 dwg

Description

 The invention relates to instrumentation and can be used to measure the movements of objects.

 A device [1] is known for moving-phase, containing an alternating voltage source, a converter, a scaling circuit in the form of a phase shifter and a scaling link connected in series, an adder and a phase meter.

 The disadvantage of this device is the low accuracy of the conversion, due to the small increment of the phase of the total signal per unit of displacement, since the change in amplitude occurs only due to a change in one of the geometrically summed signals.

 Closest to the proposed technical essence is a transformer displacement transducer with a phase output [2], comprising: a ferromagnetic core of the L-shaped cross section, an armature made of ferromagnetic material and connected during the measurement with a controlled object, symmetrical plate made of ferromagnetic material, two sections of the field winding and two sections of the measuring winding, resistor, selective amplifier, phase meter.

 The disadvantage of the above sensors is the small measurement range, because when using a ferromagnetic armature and a ferromagnetic closing plate in these sensors, the amplitude modulation of the output voltages is carried out due to a change in the mutual-inductive coupling between the field windings and the measurement windings when the armature is moved from the sensor by a small distance not exceeding 0.2 diameter of the sensor [3].

 The proposed sensor design will significantly expand upward the range of measurement of displacements. According to the proposed design, the expansion of the measuring range is achieved due to the fact that an additional circuit consisting of a phase-shifting circuit and a scaling link, an adder, and the electrically conductive armature and the closing plate located at the ends of the L-shaped core of the working and compensation windings, are made of diamagnetic material to provide modulation of the output voltage in amplitude due to the eddy current effect. The sections of the field winding are connected to an AC voltage source, the signal output of the working section of the measuring winding is connected to the first input of the adder, the signal output of the compensation section of the measuring winding is connected to the first input of the phase meter and through an additional circuit to the second input of the adder, while the output of the adder is connected to the second phasometer input.

 The amplitude-phase transformer displacement transducer with phase output (Fig. 1) contains: 1 - an alternating voltage source, 2 - a working one and 3 - compensation transformers with open magnetic circuits; 4 - working anchor, connected during the measurement with the controlled object and 5 - the closing plate, placed at the open ends of the transformers and made of diamagnetic, having a large electrical conductivity of the material; 6 - an additional circuit, made in the form of series-connected 7 - phase-shifting circuit and 8 - scaling link, 9 - adder, 10 - phase meter.

On the central rod of the L-shaped ferromagnetic core of the working and compensation transformers, sections W _1p and W _1k for the field winding, sections W _2p and W _{2k for the} measuring coil are placed.

The sections W _1p and W _{1k are} electrically interconnected in series according to and connected to the output of the AC voltage source 1, the signal output of the working section of the measuring winding is connected to the first input of the adder 9, and the signal output of the compensation section of the measuring winding is connected to the first input of the phase meter 10 and through an additional circuit to the second input of the adder 9, the output of the adder is connected to the second input of the phase meter 10.

 Amplitude-phase transformer displacement sensor with phase output works as follows.

When a sinusoidal voltage U _{n ~ is} supplied from the output of a power source 1 having a low internal resistance to the working W _1p and compensation W _1k sections of the field winding in the sections W _2p and W _{2k of the} measuring windings, voltages U _{p (x)} and U _{k (x )}

 When moving the controlled object and the associated working armature 4 in the direction of increasing the gap X (shown in figure 1 by an arrow) in the diamagnetic electrically conductive armature 4, eddy currents varying in magnitude are induced, creating a magnetic field directed opposite to the magnetic field generated by the current flowing along field winding of the working transformer 2.

As a result of the interaction of two magnetic fields, the exciting magnetic field of the working transformer 2 increases, because the action of the counter-directional magnetic field created by eddy currents becomes smaller with increasing measured displacement and, as a result, the excited voltage U _{p (x)} in the measuring transformer winding section W _2p increases, and the voltage U _{к (x)} in the compensating winding section W _2k the transformer is reduced due to the redistribution of voltages in the sections W _1p and W _{1k of the} field winding, powered by a voltage source having a low internal resistance.

The stresses U _{p (x)} and U _{к (х) are} connected with the movement of X by a dependence close to exponential:
U _(x) = U ₀ • e ^{± αx} , (1)
where U ₀ is the voltage from the signal output of the working section W _{2p of the} measuring winding or from the signal output of the compensation section of the measuring winding at X = 0 mm;
α is the exponent of the exponential function (taken with the “+” sign for the increasing function and with the “-” sign for the decreasing function).

Using the phase-shifting circuit 7 between sinusoidal voltages U _{p (x)} and U _{to (x)} set the phase angle фаз ₀ greater than 90 ^o , but less than 180 ^o . The voltages U _{p (x)} and U ' _{k (x) are} geometrically summed on the adder 9, and the resulting (total) voltage U _{Σ (x)} and voltage U _{k (x)} are supplied to the inputs of the phase meter 10, from the output of which the phase dependence of the output resulting U _{Σ (x)} from displacement, i.e. the phase φ _out = f (x) of the vector of the resulting voltage U _{Σ (x)} changes from the value of φ ₂ to the value of φ ₁ (figure 2).

где φ_вых - фаза результирующего сигнала U_Σ(x) относительно вектора напряжения U_к(х);
ψ₀ - угол сдвига фаз между векторами напряжений U_p(x) и U_к(х), устанавливаемый с помощью фазосдвигающей цепи 7.The sensor conversion function is defined by the following expression:

where φ _o is the phase of the resulting signal U _{Σ (x)} relative to the voltage vector U _{k (x)} ;
ψ ₀ - phase angle between the stress vectors U _{p (x)} and U _{to (x)} , set using the phase-shifting circuit 7.

To obtain optimal linearity of the output characteristic of the sensor, the required phase angle ψ _{0 is set} between the voltages U _{p (x)} and U _{к (x)} using the phase-shifting circuit 7 and the signal amplitude U _{к (x) is} changed using the scaling link 8 to the value U ' _{k (x)} at which the ratio U _{p (x)} / U _{k (x)} at the end point of the measuring range takes a value close to 1, and as the control object and the associated working armature 4 approaches the starting point of the measuring range attitude should decrease.

Thus, when the modulated voltages U _{p (x)} and U _{k (x)} change on the sections of the measuring windings in the displacement function X, the phase of the output voltage U _{Σ (x)} also changes by | φ ₁ -φ ₂ |.

In the vector diagram of the sensor output voltages (FIG. 2), the index “K” denotes the voltage corresponding to the maximum value of the measured displacement X _max , and the index “H” denotes the voltage corresponding to the minimum value of the displacement X _min .

The extension of the measuring range of the sensor is achieved by increasing the conversion sensitivity at the end of the measuring range due to the fact that the amplitude modulation of the output voltages U _{p (x)} and U _{к (x) is} carried out by using the eddy current effect created by the diamagnetic conductive anchors 4 and 5 made from a material with a magnetic permeability equal to 1, and having high electrical conductivity (copper, aluminum, etc.).

The modulation of the output voltages U _{p (x)} and U _{k (x)} in amplitude in the displacement function due to the use of the eddy current effect is carried out as a result of the interaction of the magnetic field generated by the excitation winding of the transformer with an open end and the magnetic field created by eddy currents in an electrically conductive armature when it moving a distance from 0 to a value reaching a value (0.5 ÷ 0.6) from the outer diameter of the sensor, which, in accordance with expression (2), determines the phase change of the resulting signal as a function of room φ _out = f (x) in the measuring range from 0 to (0.5 ÷ 0.6) D, where D is the outer diameter of the sensor.

In the prototype sensor, the amplitude modulation of the output voltage is carried out by changing the mutually inductive coupling between the field winding and the measuring winding of the transformer with an open end due to the movement of the ferromagnetic armature associated with the control object by a maximum distance not exceeding the value (0.15 ÷ 0, 3) from the outer diameter of the sensor. This is due to the fact that in the prototype sensor, the modulation of the output voltages is caused by two phenomena: a change in the mutually inductive coupling due to the magnetic properties of the moving ferromagnetic armature (μ is much greater than 1) and the current-curling effect (the ferromagnetic armature has electrical conductivity), which counteracts ("parasitic" action ) to change the amplitude of the output voltages, i.e. if when approaching the ferromagnetic armature sensor due to the first phenomenon, the output voltage U _{p (x)} increases, then due to the second phenomenon U _{p (x)} decreases.

Thus, the use of the proposed amplitude-phase transformer displacement transducer with phase output will increase the conversion sensitivity at the end of the measurement range by using the eddy current effect to modulate the geometrically summed voltages U _{p (x)} and U _{к (x)} in amplitude by 2 times larger than in the prototype sensor, and therefore expand the measurement range 2 times, and increase the ratio X _g / D 2 times (where X _g is the measurement range; D is the outer diameter of the sensor), i.e. and reduce the overall dimensions of the sensor.

Sources of information
1. SU, patent 1260664, G 01 B 7/00, 09/30/1986. Bull. 36.

 2. SU, patent 1627820, G 01 B 7/00, 02.15.1991. Bull. 6.

 3. V. I. Seredenin "Measuring instruments with high-temperature transformer displacement sensors". Energy. L. 1968.2

Claims (1)

 An amplitude-phase transformer displacement sensor with a phase output, containing a L-shaped ferromagnetic core with a two-section excitation winding on the central part of the core, connected in series according to, and with a two-section working measuring winding, consisting of working and compensation sections interconnected in series, selective amplifier and phase meter, characterized in that an additional circuit is introduced into it, consisting of a phase-shifting circuit and a scaling link, sum a mator, wherein the electrically conductive anchor and the closing plate are placed at the ends of the L-shaped core from the side of the working and compensation windings and are made of diamagnetic material, and the excitation winding sections are connected to an alternating voltage source, while the signal output of the measuring winding working section is connected to the first input of the adder , the signal output of the compensation section of the measuring winding with the first input of the phase meter and through an additional circuit with the second input of the adder, and the output of the adder with second th input of the phase meter.

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