RU152930U1 - DIFFERENTIAL-TRANSFORMER LINEAR MOVEMENT SENSOR - Google Patents

Abstract

A differential transformer linear displacement sensor containing a coaxially arranged magnetic core, duplicated field windings, duplicated measuring windings consisting of equal sections symmetrically located relative to their center, and a ferromagnetic core moving inside the windings, in which the information about the movement of the core is a dimensionless value from the division of the voltage difference sections of measuring windings for their sum, characterized in that the lengths of its core, magnetic cores ode, field windings, the total length of the measuring windings are equal to each other.

Description

The differential transformer linear displacement sensor belongs to the field of instrumentation and can be used to measure linear displacements of the working bodies of mechanisms.

There are known differential transformers containing a coaxially located field winding and a working winding and a ferromagnetic core moving inside the windings, with very high accuracy with stable input and output parameters (load) and when using the initial section of the output characteristic [Shidlovich A.Kh. Differential transformers and their application. L., "Energy", 1966].

In the known differential transformer linear displacement transducer containing a cylindrical magnetic circuit, coaxially placed inside it and connected in series with the opposite sections of the measuring winding, the excitation winding placed between them and mounted on their axis with the possibility of moving the ferromagnetic armature, an increase in accuracy is proposed by reducing non-linearity with by means of a correcting winding, which is connected sequentially counter to the field winding and has a length equal to the total th length of the field windings and measuring windings [A.S. USSR No. 1569525, M., 06/07/90. BI No. 21].

The main disadvantage of the above sensors is the relatively low accuracy in harsh operating conditions when fluctuating supply voltage, frequency, temperature, pressure (deterioration of heat transfer in a vacuum), typical, for example, for aviation and astronautics and, what is especially important, under the indispensable condition of minimum dimensions and mass .

In the known inductive linear displacement sensor due to the destruction of capacitive coupling in the secondary coils, the sensor becomes self-controlled and less dependent on the supply frequency. In one of the versions, sensitivity adjustment is provided due to the mutual movement of two frames on which the secondary windings are wound. Each secondary winding contains a winding with a constant number of turns along the winding and a winding with a linearly varying length of the number of turns wound in the "ladder" connected in series [Patent No. 2587.795, France, 03/27/1987., "Inductive linear displacement sensor"].

A converter is known comprising a primary winding wound around a first cylindrical frame, in which a channel with an axially movable core is located, a first secondary winding wound around a primary winding and a second secondary winding wound on a second cylindrical frame, and which encompasses a first secondary winding.

The first secondary winding consists of two parts: a part with an ordinary winding (coil to coil along the entire length of the frame) and a stepped part that are electrically connected to each other in phase, and the second secondary winding consists of two similar parts that are electrically connected to each other in out of phase.

The output signals of the secondary windings are combined so as to obtain the resulting signal of the ratio of their sum to the difference.

The location of the secondary windings on the individual frames allows you to change their relative position along the axis to adjust the output characteristics of the Converter.

The sections of the secondary windings forming the first secondary output are interconnected in series - in accordance, while the sections forming the second secondary output are interconnected in series - in the opposite direction. Thus, when power is supplied to the primary winding, the resulting voltages of the first and second secondary outputs change in a linear functional dependence on the movement of the core and are dependencies that are parallel and shifted relative to one another. The voltages of the secondary outputs are combined into the resulting signal r = (v1 + v2) / (v1-v2), which depends only on the coordinate of movement and is very insensitive to temperature changes and voltage fluctuations applied to the primary winding.

When one of the secondary windings breaks (v1 or v2 = 0), the converter is self-monitoring, failure is detected [Patent No. 4,694, 246, USA, 09/15/1987., "Displacement transducer"].

The disadvantage of this sensor is the increased overall dimensions associated with the use of mutually moving frames with windings covering each other.

In the above sensors, winding with a changing density of the distribution of turns to ensure high linearity of the output characteristic prevents the reduction of the diametrical size of the case.

To achieve measurement accuracy in harsh operating conditions, an invariant sensor construction scheme is used when the output characteristic is the ratio of the voltage difference of the output semi-windings U ₂₁ and U ₂₂ to their sum (U ₂₁ + U ₂₂ ):

It can be seen from expression (1) that Y is a dimensionless quantity and any change in U ₂₁ or U ₂₂ from external factors (supply voltage, temperature, frequency, etc.) does not lead to a change in Y as a quotient of the division of these values. In addition, the expression (1) does not include the supply voltage U ₁ , as a result of which the change in the active resistance of the field winding also does not affect the value of Y.

When implementing an invariant scheme, the measurement error of the sensor is determined only by the nonlinearity and technological spread of the steepness of the output characteristic.

In the general case, both (U ₂₁ -U ₂₂ ) and (U ₂₂ + U ₂₁ ) in the displacement function are non-linear quantities. To obtain a linear value of Y, it is necessary to wind sections of the measuring winding with a variable density of turns along the length, i.e. it is necessary to find such a law of variation of w ₂ (x) so that the quotient Y of the division of two nonlinear functions (U ₂₁ -U ₂₂ ) and (U ₂₁ + U ₂₂ ) is linear.

For all of the above sensors, the length of the movable part is not more than the length of the measuring winding section. The variable density of the distribution of turns along the length of the winding sections of the measuring windings allows you to get a high linearity of the output characteristics, but does not allow you to radically solve the problem of reducing the diametrical dimensions of the sensors.

The technical result of the proposed utility model is:

- obtaining a linear portion of the output characteristics of the sensor with an invariant construction scheme and duplicated windings for measuring displacement with increased accuracy both in normal conditions and in harsh operating conditions (from fluctuations in supply voltage, frequency, temperature, pressure, from vibration, shock, linear accelerations and others) with a minimum diameter of the body, which allows the sensor to be embedded inside the stem of the drive mechanism in order to measure the movement of the rod.

The improvement of linearity with a minimum diameter of the housing is associated with obtaining the necessary law of distribution of the magnetic field lines generated by the sensor in the range of its working stroke for uniform distribution of turns in the layers of the windings of the primary and secondary circuits. The necessary law of the distribution of the field lines depends on the ratio of the length of the core, the external magnetic circuit, the length and height of the windings of the primary and secondary circuits. With a uniform distribution of the turns, the number of layers of the secondary windings is minimized, which makes it possible to approximate the average field line of the magnetic flux generated by the field windings to the axis of the core and improve the uniformity of the distribution of the magnetic field lines within a given sensor travel, and therefore the linearity of the output characteristics.

The specified technical result is achieved by minimizing the number of steps in the measuring windings and the number of turns in the field windings by choosing a core length equal to the length of the external magnetic circuit and the length of the primary and secondary windings. An increase in the length of the core to the length occupied by the windings causes a decrease in the resistance of the magnetic system of the sensor, which leads to a decrease in the magnetizing force necessary to provide a given current consumption, and, as a consequence, to a decrease in the number of turns in the field windings.

In FIG. 1 shows a structural diagram of the proposed sensor. The sensor (Fig. 1) contains a housing 1 made of non-magnetic steel, an external magnetic circuit 2 made of ferromagnetic steel, which serves to reduce energy consumption and protect against external magnetic fields, a pressed plastic frame 5, on which are equal sections of two duplicated measuring windings 4 and duplicated windings excitation 3, core 6, rod 7, which serves to communicate with the object, the movement of which is measured.

Duplicate field windings are made in two wires by ordinary winding coil to coil along the entire length of the frame, so that each coil of one winding follows the coil of the other.

Each measuring winding occupies the entire length of the frame and consists of two equal-sized sections symmetrically located relative to its center, connected in series with each other. Sections of different measuring windings located on the same parts of the frame are made in pairs by ordinary winding, so that each turn of the section of one winding follows the turn of the section of the other.

The measuring windings do not have a galvanic connection between themselves.

The sensor operates as follows.

An ac voltage is applied to the field windings. A current flows in the circuit of these windings, which creates a magnetizing force. Under the action of a magnetizing force, a magnetic flux occurs, interacting with the turns of the sections of the measuring windings and closing around the field winding. Part of the flow passes through the core, and part through the air. When the core is located on electrical neutral, the flow is symmetrical relative to the sections of the measuring windings, the EMF induced in the sections are equal. Moving the core to the left or right of the electrical neutral causes an increase in flux linkage of one pair of sections and a decrease in the other pair. Correspondingly, the output voltages of the sections also change, which increase or decrease depending on the direction of movement of the core. Moreover, as shown in FIG. 3, for a sensor with a stroke of ± 5 mm, with a linear nature of the change in U ₂₁ and U ₂₂ , and therefore {U ₂₁ -U ₂₂ ) and (U ₂₁ + U ₂₂ ) from the movement of the core x, the current values of the output characteristic Y according to the expression ( 1) increase in proportion to movement.

The ratio of the current value of the output characteristic Y to the corresponding movement of the core determines the slope of the output characteristic of the sensor.

The measuring windings provide two identical output characteristics or two sensor outputs (first and second) that duplicate each other during operation of the sensor. In the event of a malfunction in one of the measuring windings (open circuit or short circuit), one of the outputs remains operational.

The output characteristics of the sensor with two measuring windings and a stroke of ± 5 mm were experimentally verified. The length of the sensor core is equal to the lengths occupied on the frame by the field winding and measuring windings, and the length of the outer magnetic circuit. The characteristics were tested at a supply voltage of 2 V and an ac frequency of a sinusoidal shape of 4000 Hz and a load resistance in each section of the measuring windings of 20 kOhm. The current consumption of the sensor was not more than 0.02 A.

The dependences of U ₂₁ and U ₂₂ , Y on the movement of the core for one of the two sensor outputs with a stroke of 5 mm are presented in FIG. 2, and the dependence n (non-linearity of the output characteristic as the relative error in measuring the position of the core) on the movement of the core — in FIG. 3.

Similar dependencies has another sensor output.

The mass of the sensor was 35 g, the diameter of the case was 11 mm, and the length of the case was 47 mm.

The obtained test results make it possible to use the sensor inside the rods of the drive mechanisms with a diameter of 15 mm or more to measure their movement within ± 5 mm.

Claims (1)

A differential transformer linear displacement sensor containing a coaxially arranged magnetic core, duplicated field windings, duplicated measuring windings consisting of equal sections symmetrically located relative to their center, and a ferromagnetic core moving inside the windings, in which the information about the movement of the core is a dimensionless value from the division of the voltage difference sections of measuring windings for their sum, characterized in that the lengths of its core, magnetic cores ode, field windings, the total length of the measuring windings are equal to each other.

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