RU2109258C1 - Piezooptical meter of mechanical values - Google Patents

Abstract

FIELD: measurement technology. SUBSTANCE: meter has light source, polarizer, photoflexible sensing element, two phase plates, analyzer, amplifier, two photoreceivers connected differentially to amplifier, two comparators and analog-to-digital converter, digital-to-analog converter the inputs of which are connected to outputs of analog-to-digital converter, voltage-to-current converter connected to output of digital-to-analog converter, current-to-force magnetoelectric transducer, force summing lever with area for application of measured value to it. Force summing lever is hinge-connected at one point, at another point it is brought in contact with photoflexible element, and at third point it is connected to coil of magnetoelectric transducer. Coil is connected to output of voltage-to-current converter. Analog-to-digital converter is made as reversible counter, the inputs of which are connected to outputs of comparators. Noninverting input of first comparator and inverting input of second comparator are connected to amplifier output, and the other input of each comparator is connected to reference voltage source of its own. EFFECT: higher measurement results. 3 dwg ЫЫЫ1

Description

 The invention relates to measuring equipment and can be used to measure force, pressure, acceleration, displacements, etc.

 Known piezoelectric meters of mechanical quantities containing a light source, a polarizer, a photoelastic sensor, phase plates, an analyzer, photodetectors and an amplifier [1]. The disadvantage of these meters is the narrowness of the dynamic range of measurements, since they work only in the first section of the characteristics of the conversion of force to electric voltage, since the transition to the second, third, etc. sections accompanied by an ambiguity countdown. The second disadvantage of these meters is the instability (drift, creep) of the readings due to the fluidity of the adhesive layer of the fastening of the photoelastic element. The fluidity of the adhesive layer and the creep of the meter readings caused by it, the greater, the more the force and its changes are measured [2].

 Closest to the proposed technical essence is a piezo-optical meter of mechanical quantities, containing sequentially located and optically conjugated light sources, a polarizer, a photoelastic sensor, phase plates, an analyzer, photodetectors, amplifiers, comparators, a triangular voltage driver and an analog-to-digital converter [3] . This meter also has the disadvantage of instability of creep type indications due to the fluidity of the adhesive fastening of the photoelastic sensing element. In addition, this meter has an insufficiently accurate conversion characteristic due to errors in the formation of a triangular voltage.

 The aim of the invention is to improve accuracy by reducing the creep of the meter.

 The essence of the invention lies in the fact that in a piezoelectric meter of mechanical quantities, containing sequentially located and optically conjugated light source, a polarizer, a photoelastic sensing element, two phase plates, an analyzer, an amplifier, two photodetectors differentially connected to the amplifier, as well as two comparators and analog -digit converter, a digital-to-analog converter is introduced, the bit inputs of which are connected to the bit outputs of the analog-to-digital converter, the converter For electric voltage to the current connected to the input of the digital-to-analog converter output, a magnetoelectric current converter into force, a permanent magnet of which is fixed motionless, a force-summing arm with a pad prepared for application of a measurand to it, articulated at one point, brought into contact at another point with a photoelastic element, and at a third point fastened to a magnetoelectric transducer coil, which is connected to the output of the voltage-to-current converter, at The analog-to-digital converter is made in the form of a reversible counter, the direct counting input of which is connected to the output of the first comparator, and the counting input is connected to the output of the second comparator, while the non-inverting input of the first comparator and the inverting input of the second comparator are connected to the output of the amplifier, and the inverting input the first and non-inverting inputs of the second comparators are each connected to its own voltage reference source.

The technical result of the invention is to increase the accuracy of the meter by reducing the instability of the type of "creep" of his readings, which is achieved by repeatedly reducing the force N _x acting on the photoelastic sensitive element and the adhesive layer fastening it: this force is equal in the proposed meter on the entire external measured force N (in the prototype), and the difference N _x = NN _{wasps, wasps} ≈I where N is the power at the output of the feedback circuit, namely the output current in the power of the magnetoelectric transducer, i.e. the force developed by the coil in the magnetic field of the magnet when a current I flows through it, proportional to the output voltage of the digital-to-analog converter. Due to the decrease in the force N _x (compared to N), the load on the adhesive layer of the fastening of the photoelastic element and the differences in this load are reduced, and hence the creep of the adhesive layer and the meter as a whole. Compared with counterparts of type [1], the ambiguity of reports is eliminated.

 The achievement of this technical result is provided by the totality of essential features.

 In FIG. 1 shows a diagram of the proposed meter; in FIG. 1 - diagrams explaining the operation of the meter; in FIG. 3 - one of the possible options for the converter of electric voltage to current.

 The piezoelectric meter (Fig. 1) consists of sequentially located and optically conjugated light source 1, a polarizer 2, a photoelastic sensing element 3 (for example, a gallium phosphide crystal in the form of a prism) glued to a fixed base 4, two quarter-wave phase plates 5 and 6, analyzer 7, amplifier 8, photodetectors 9 10, differentially connected to the inputs of amplifier 8, two comparators 11 and 12, analog-to-digital Converter 13, made in the form of a reversible counter, input 14 direct count which connected to the output of the first comparator 11, and a countdown input 15 of which is connected to the output of the second comparator 12, a digital-to-analog comparator 16, the bit inputs of which are connected to the bit outputs of the analog-to-digital converter 13, the voltage-to-current converter 17, connected to the output of the digital-to-analog converter 16, a magnetoelectric current transducer in force, comprising a permanent magnet 18 that is fixedly mounted, and a coil 19 connected at the output of the voltage transducer voltage into the current 17, the silo-summing lever 20 with the platform 21, prepared for the application of a measurable quantity, for example, the force N, pivotally fixed at one point (for example, the left end, as in FIG. 1), at another point (for example, under platform 21) brought into contact with the photoelastic element, and at the third point (for example, the right end) fastened to the coil 19 (or its frame) of the magnetoelectric transducer, the non-inverting input of the first comparator 11 and inverting the input of the second comparator 12 is connected to the output of the amplifier 8, the inverting input of the first comparator 11 and the non-inverting input of the second comparator 12 are each connected to one of the voltage sources 22 and 23. The optical axes of the quarter-wave plates 5 and 6 are oriented so that the plate 5 increases, and the plate 6 reduces the phase difference of the rays passing through them by π / 2. . The optical axis of the polarizer 2 and the analyzer 7 are crossed. The composition of the meter may include an adder 24 of electrical voltages, one input of which is connected to the output of the digital-to-analog converter 16, and the other input is connected to an additional bias voltage source 25, and the output of the adder is connected to the input of the voltage-to-current converter 17.

 The piezoelectric measuring device of mechanical quantities works as follows.

,
где

; I - длина рычага; I₁ - расстояние от оси шарнирного закрепления рычага до точки приложения измеряемой силы N и контакта рычага с фотоупругим элементом. При отключенной обратной связи, например, отключением катушки 19 от входа преобразователя 17, N_x представляет собой только измеряемую силу N.According to the circuit of FIG. 1 and the formula of the lever of the second kind on the photoelastic element 3, the lever 21 transmits the force

,
Where

; I is the length of the lever; I ₁ is the distance from the axis of articulation of the lever to the point of application of the measured force N and the contact of the lever with the photoelastic element. When feedback is disabled, for example, by disconnecting the coil 19 from the input of the transducer 17, N _x represents only the measured force N.

Under the action of the force N _{x, the} photoelastic element 3 is deformed and acquires anisotropy with respect to the propagation of light in it.

The light from the source 1 passes through the polarizer 2 and linearly polarized falls on the photoelastic element 3 at an angle to the direction of the uniaxial voltage in it. In a photoelastic element 3, a light wave splits into two components, between which, due to the birefringence effect [4], a phase difference arises (see (1) in [1] on page 45 and (4.5) and [4] on page 123)
Δα = 2πΔnt / λ = 2πRεt / λ,
Where
Δn -n ₁ -n ₁₁ , n ₁ and n ₁₁ is the refractive index of the components of the light wave, respectively, perpendicular and parallel to the deformation of element 3 under uniaxial stress: t is the path length of the rays in element 3: λ is the wavelength of light: R is the optical constant system: ε -deformation of element 3. Thus, the elastic deformation of element 3 leads to phase modulation of polarized light.

 The quarter wave plate 5 increases the phase difference Δα by π / 2, and the plate 6 reduces Δα by the angle π / 2. .

The analyzer 7 extracts from the optical radiation components that oscillate in the transmission plane of the analyzer. As a result of the interference of these components, the radiation intensity after the analyzer changes, i.e. phase modulation is converted to amplitude. With a change in the force N _x and Δα, the intensities of the light rays incident on the photodetectors 9 and 10 change by the same values, but with opposite signs, which leads to equal but opposite sign changes in the photo emf of the photodetectors. Amplifier 8 amplifies the differential components of these changes and at its output
U = KU _{O 0 0} sinΔα = KU sinkε, (1),
Where
K and U _о are the constants of the system.

On the linear section of the transformation function (1) is performed
U _o = KU ₀ Δα = KU ₀ kε = KU ₀ mΔN _x
Where
ΔN _x is the increment of force; m is a constant; in this linear section, the sensitivity of the meter to ΔN _{x is} maximum.

, создаваемая катушкой 19 вследствие взаимодействия тока в ней с полем магнита 18, отслеживает изменение измеряемой силы N (фиг. 2, а). При этом сила N_x , воздействующая на фотоупругий элемент 3, изменяется как показано на фиг. 2, б. Формирование ступенек (квантов) N_Δ силы обратной связи осуществляется цифроаналоговым преобразователем 16, преобразователем напряжения в ток 17 и магнитоэлектрическим преобразователем 18-19 по сигналам компараторов 11 (фиг. 2, в) и компаратора 12 (фиг. 2, г), соответственно увеличивающим и уменьшающим число в реверсивном счетчике (аналого-цифровом преобразователе) 13. Уровня силы N_П1 и N_П на фиг. 2, в, г соответствуют опорные напряжения U_П1 и U_П2 источников 22 и 23 соответственно, согласованные с диапазоном рабочих напряжений U_вых усилителя 8. Срабатывание компаратора 12 в момент включения системы или приложения к рычагу 20 измеряемой силы N не приводит к ложному формированию кванта - N_Δ , так как реверсивный счетчик 13 при этом пуст и не реагирует на сигнал обратного счета (вычитания).With closed feedback, the force

created by the coil 19 due to the interaction of the current in it with the field of the magnet 18, monitors the change in the measured force N (Fig. 2, a). In this case, the force N _x acting on the photoelastic element 3 changes as shown in FIG. 2, b. The formation of steps (quanta) N _{Δ of} the feedback force is carried out by a digital-to-analog converter 16, a voltage to current converter 17, and a magnetoelectric converter 18-19 according to the signals of comparators 11 (Fig. 2, c) and comparator 12 (Fig. 2, d), respectively increasing and decreasing the number in the reversible counter (analog-to-digital converter) 13. The power level N _P1 and N _P in FIG. 2, c, d correspond to the reference voltages U _P1 and U _{P2 of} sources 22 and 23, respectively, consistent with the operating voltage range U of the _output amplifier 8. The operation of the comparator 12 when the system is turned on or the measured force N is applied to the lever 20 does not lead to false quantum formation - N _Δ , since the reverse counter 13 is empty and does not respond to the signal of the countdown (subtraction).

To offset the operating point of the meter to the region of the conversion characteristic (1) with maximum slope and sensitivity, a bias force N _cm , determined by the voltage E _{cm of the} source 25, can be set on the photoelastic element 3 through the feedback loop. Using the bias also allows you to hold the photoelastic element in a fixed position without gluing it to the base 4, i.e. completely eliminate the source of instability such as creep.

As can be seen from FIG. 2b, the force N _x acting on the sensitive element 3 (and the adhesive layer, if the element 3 is still glued) can be made (by choosing the values of the quantum N _Δ and the threshold N _П1 very small - there is much less difference in the measured force N than provides a decrease in "creep" of the adhesive layer and the meter as a whole.

,
как показано в [6], ток не зависит от величины R_Н и определяется величинами резисторов
I = UR₀/R₁R₃ .Circuitry embodiments of the Converter of electrical voltage to current 17 are described in the literature, for example [5], Art. 186-188, fig. 6.6, tab. 6.1; [6], p. 377, fig. 11.8, a, (reproduced in FIG. 3), p. 380, fig. 11.9, b. In the circuit shown in figure 3, the negative feedback through the resistor R _about maintains the current I in the load R _{N is} strictly proportional to the input voltage U, and when the condition

,
as shown in [6], the current does not depend on the value of R _N and is determined by the values of the resistors
I = UR ₀ / R ₁ R ₃ .

Sources accepted
1. Slezinger II Piezoelectric transducers. Measuring equipment, N11, 1985, p. 46, fig. 1a.

 2. Serious A. Strength tests of aircraft structures. - M.: Mechanical Engineering, 1976.

 3. Copyright certificate of the USSR N 1446496 A1, cl. G 01 L 1/24, 1988.

 4. Frocht M.M. Photoelasticity. t. 1. M.-L., OGIZ, 1948.

 5. Aleksenko A.G., Colombet E.A., Starodub G.I. The use of precision analog microcircuits. -M .: Radio and communications, 1985.

 6. Aleksenko A. G. Shagurin I.I. Microcircuitry. -M.: Radio and communication. 1982.

Claims (1)

 A piezoelectric mechanical quantity meter containing a sequentially located and optically conjugated light source, a polarizer, a photoelastic sensor, two phase plates, an analyzer, an amplifier, two photodetectors differentially connected to the amplifier, as well as two comparators and an analog-to-digital converter, characterized in that a digital-to-analog converter is introduced into it, the bit inputs of which are connected to the bit outputs of the analog-to-digital converter, the converter is electrically voltage to current connected to the input of the output of the digital-to-analog converter, a magnetoelectric current converter into force, a permanent magnet of which is fixed motionless, a force-summing arm with a pad prepared for application of a measurable quantity, articulated at one point, brought into contact with another photoelastic element, and at a third point bonded to the coil of the magnetoelectric transducer, which is connected to the output of the voltage to current transducer, and analog The front-end converter is made in the form of a reversible counter, the input of the direct count of which is connected to the output of the first comparator, and the input of the countdown to the output of the second comparator, while the non-inverting input of the first comparator and the inverting input of the second comparator are connected to the output of the amplifier, and the inverting input of the first and non-inverting input of the second comparators are each connected to its own source of reference voltage.

Images