RU2036413C1 - Displacement meter - Google Patents

Abstract

FIELD: instrumentation. SUBSTANCE: capacitors of optimum capacitance are used in equalizing arms of bridge measuring circuit to minimize measurement error of displacements by reduction of effects of instability of resistances of sensor windings. Signal indicator is built in agreement with circuit of phase-sensitive demodulator with supply of reference voltage from feeding transformer via phase inverter. Readings of phase-sensitive demodulator are proportional to reactive component of current in measurement diagonal of bridge circuit which with optimum selection of capacitance of capacitors in equalizing arms of bridge circuit is proportional to difference of inductive impedances of sensor windings, i.e. to measured displacement. Thus accuracy of measurement by inductive sensor placed in bridge circuit with big internal resistance of signal indicator in measurement diagonal can be raised. EFFECT: raised accuracy of measurements. 1 dwg

Description

 The invention relates to measuring technique and can be used for accurate measurement of displacements using a measuring device containing an inductive sensor.

 A device for measuring displacements is known, in which the inductive sensor is included in the bridge circuit, which in addition to the sensor windings also contains balancing active resistances, the magnitude of which is selected so that the active component of the current in the measuring diagonal of the bridge circuit is proportional to the change in the inductive resistances of the sensor windings [ 1] This device can be used with a signal indicator having a low internal resistance, which is much less than the output resistance The skeleton of the circuit from the terminals of the measuring diagonal. The signal indicator can be, for example, a wattmeter, the current winding of which, having low resistance, is included in the measuring diagonal of the bridge circuit, and the voltage winding is connected to the power source of the bridge circuit. Such a circuit is inoperative with a signal indicator having a large internal resistance, i.e., it loses its positive properties, providing a small error from changes in the active resistances of the sensor windings due to their heating by current during measurements.

 Closest to the proposed is a device for measuring displacement, containing an inductive sensor included in the bridge circuit with active balancing resistances, which also implements a method of reducing the temperature error [2] Using a phase shifter, the phase of the reference voltage of the phase-sensitive detector is experimentally controlled in such a way as to reduce the sensitivity of the device to changes in the active resistances of the sensor windings during its operation, while the ration is not mentioned flax choice of balancing resistors. However, the optimization of the parameters of balancing resistances, namely the use of capacitors of certain values of their capacitance instead of active resistances, can be crucial to further reduce the temperature error.

 To do this, in a displacement measuring device containing a supply transformer, a phase shifter and a bridge measuring circuit connected to it, two arms of which include balancing resistances, a differential inductive sensor, the windings of which are connected to the other two arms of the bridge circuit, an amplifier connected to its output diagonal, a phase-sensitive demodulator connected to it by one of the inputs, to the other input of which a phase shifter output is connected, using balancing resistances using Vanir capacitors, the capacitance of each of which is determined from the following relation.

 The drawing shows a diagram of the proposed device for measuring displacement.

 The device contains an inductive differential sensor, the windings 1 and 2 of which are included in two arms of the bridge circuit, capacitors 3 and 4 are included in the other two balancing arms. The transformer 5 is powered by the EMF source and the secondary winding is included in the diagonal of the bridge circuit power supply and phase shifter 6. In the measurement the diagonal of the bridge circuit includes an amplifier 7, after passing through which an informative signal is supplied to a phase-sensitive demodulator 8, which receives the reference voltage from the phase shifter.

 The device operates as follows.

+ j

, (1) где A X_c ² X_c(X₁ + X₂) + (X₁X₂ R₁R₂); (2)
B X_c(R₁ + R₂) (R₁X₂ + R₂X₁); (3)
U напряжение питания мостовой схемы;
Z_д сопротивление приемника сигнала в измерительной диагонали мостовой схемы;
Х₁, Х₂ индуктивные сопротивления обмоток датчика;
R₁, R₂ активные сопротивления обмоток датчика;
Х_с уравновешивающие сопротивления.In the equilibrium position of the sensor armature, when the resistance of its windings are equal, the bridge circuit is in a state of balance and the current in its measuring diagonal is zero. The action of the sensor is based on converting the movement of the armature into a change in the inductance of the sensor windings. In this case, the current value J _о in the measuring diagonal of the bridge circuit is determined by the following expression (for the case when the resistance of the informative signal receiver in the form of an amplifier and a phase-sensitive demodulator is much more, at least an order of magnitude, of the output resistance of the bridge circuit):
I _o

+ j

, (1) where AX _c ² X _c (X ₁ + X ₂ ) + (X ₁ X ₂ R ₁ R ₂ ); (2)
BX _c (R ₁ + R ₂ ) (R ₁ X ₂ + R ₂ X ₁ ); (3)
U supply voltage of the bridge circuit;
Z _{d the} resistance of the signal receiver in the measuring diagonal of the bridge circuit;
X ₁ , X ₂ inductive resistances of the sensor windings;
R ₁ , R ₂ active resistance of the sensor windings;
X _with balancing resistance.

The movement of the sensor armature mainly causes a change in the inductive resistances of the windings X ₁ and X ₂ , but there is also a change in active losses in the sensor windings, which is characterized by the presence of a difference (R ₁ R ₂ ) in formula (1) and leads to an error in the measurement of displacement.

(R₂ R₁) можно пренебречь ввиду его малости.The error can be reduced by choosing the values of balancing resistance X _s . When choosing such a value of X _c , at which A << B, at least 10 times or more, the reactive component of the current in the measuring diagonal of the bridge circuit is proportional to the difference (X ₂ X ₁ ), since the term

(R ₂ R ₁ ) can be neglected due to its smallness.

The initial equation for minimizing coefficient A is obtained from expression (2), equating it to zero
X _c ² X _c (X ₁ + X ₂ ) + (X ₁ X ₂ R ₁ R ₂ ) 0.

Solving the last equation with respect to X _c for the case of the middle position of the armature (balance position of the bridge circuit), i.e., for X ₁ X ₂ and R ₁ R ₂ , we have
X _c X _{1 (2)} + R _{1 (2)} .

 To further improve the accuracy of measurement when choosing the values of the balancing resistances of the bridge circuit in order to optimally minimize the coefficient A, it is recommended in formula (4) to use the resistance values of the sensor windings not in the equilibrium mode, but taking into account their most likely temperature changes during operation.

Claims (1)

A MOVEMENT MEASUREMENT DEVICE containing a supply transformer, a phase shifter and a bridge measuring circuit connected to it, two arms of which include balancing resistances, a differential inductive sensor, the windings of which are connected to the other two shoulders of the bridge circuit, an amplifier connected to its output diagonal, connected to it one input is a phase-sensitive demodulator, to the other input of which a phase shifter output is connected, characterized in that as balancing resistances spolzovat capacitors, the capacitive reactance X _c are selected from the equation
X $\genfrac{}{}{0ex}{}{\text{2}}{\text{c}}$ - X _with (X ₁ + X ₂ ) + (X ₁ X ₂ -R ₁ R ₂ ) = 0,
where X ₁ , X ₂ inductive resistance of the windings of the inductive sensor;
R ₁ , R _{2 the} active resistance of these windings.

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