Strain-gauge converter

FIELD: measuring instrumentation.

SUBSTANCE: strain-gauge converter includes loading element attached to the monitored object, pieso-optic converter converting tension value in stress-optical element attached in preloaded state into electrical signal, and signal processing unit. Loading element is a plate with cylindrical hole where stress-optical element of cylindrical form is clamped adjustably in direction of measured deformations by two rods made of material with thermal expansion factor larger than respective factor of the plate. Rod length is designed so as to ensure independence of preloading compression from temperature.

EFFECT: enhanced measurement accuracy, simpler device design.

7 cl, 3 dwg

 

The technical field

The invention relates to the control and measurement technology, in particular, to measure the strain (stress) in various designs through the polarization-optical converters, and can be used in construction, transportation, industrial production, instrumentation.

The level of technology

It is known that piezooptical transducers used to measure deformations (strains)that have the greatest sensitivity in comparison with others, for example, piezoresistive transducers (Slesinger I.I. Piezooptical transducers. Measurement technology, 1985, No. 11, p.45-48) [1].

The closest in technical essence to the proposed strain sensor is piezooptical strain-gauge transducer (Patent No. 2422786 dated 23.04.2010) [2]. The Converter consists of a load element, mounted on a controlled object, piezooptical Converter that converts the magnitude of the stresses on the photoelastic element into an electrical signal and block signal processing. The load element is a plate that provides a stress concentration on a photoelastic element, a photoelastic element fixed in the plate in the notoriously Laden condition and thus is m, what action is the source of power of the load is carried out in two mutually perpendicular directions. Fixing a photoelastic element in the initially loaded condition allows to measure both strain compression and tensile strain. Action source power load in two mutually perpendicular directions provides temperature compensation of the transducer, as when the temperature of the plate photoelastic element is compressed equally in opposite directions, i.e. isotropic, that did not result in a false signal at the output piezooptical Converter.

The disadvantages of this strain transducer are: a) the consolidation of a photoelastic element in the plate is carried out using a cone Morse, which requires very high precision in manufacturing as a photoelastic element, and a taper hole in the plate, coinciding with the dimensions of the photoelastic element; b) plate design is not symmetric in the areas of application of the initial load on a photoelastic element, and therefore, has a different stiffness in mutually perpendicular directions, which cannot ensure the isotropy of compression photoelastic element when the temperature changes, and therefore, may not provide sufficient temperature compensation strain gauge pre is brazaletes.

Disclosure of inventions

The objective of the invention is to create such a design strain-gauge transducer, in which, first, the consolidation of the photoelastic element in the initially loaded condition is more simple in comparison with Morse taper, by the way, and secondly, the temperature compensation was provided a more reliable method.

The technical result - the simplification of the structure, increasing its reliability and accuracy deformation measurements.

The problem is solved due to the fact that in the known device, comprising a load element mounted on a controlled object, piezooptical Converter that converts into an electrical signal the magnitude of stresses on the photoelastic element, which is fixed in an obviously loaded condition, and the unit signal processing, according to the invention, the load element is a plate with a cylindrical hole in the center, in which the photoelastic element of cylindrical shape adjustable clamped in the direction of action of the measured strains using two rods made of a material with a coefficient of thermal expansion greater than the corresponding coefficient of the plate, the length of rods designed in such a way that preserves the value of initial compression changed from what I temperature.

The material of the rods and their length are selected so that with the change of temperature change of the total length of the rods Lcmand the width of the photoelastic element of LFewas equal with sufficient accuracy the change of the distance between the places of attachment of the rods in the load element (plate) LPL. In other words, the elongation of the plate is equal to the relative lengthening of the structure of the rod-photoelastic element is a rod. If the plate is made of a material with a coefficient of linear expansion αPLthe rods have a coefficient of linear expansion αarticleand the coefficient of linear expansion photoelastic element αFethen the above condition can be written as follows:

ΔLpl(T)=ΔLcm(T)+ΔLfe(T),(1)

αplLplΔT=αcmLcmΔ T+αfeLfeΔT.(2)

Given that LPL=Lcm+LFereceived total length of the rod:

Lcm=αpl-αfeαcm-αplLfe.(3)

Thus, under the conditions according to equation (3), when the temperature of the transducer on a photoelastic element will not experience additional stress and, thus, the effect of the independence of the readings of the transducer from the temperature.

For example, consider a plate, made of steel SHKH15 with a coefficient of linear thermal expansion αPL=11.9×10-6K-1; photoelastic element diameter LFe=6 mm, made of fused silica with αFe=0.395×10-6K-1; rods made of stainless steel with αcm=16.6×10-6K-1. Tog is a, substituting values in the formula (3), we get the total length of the rods Lcm=At 14.68 mm If the rods are the same length, the length of one rod is Lcm/2=7.34 mm

The initial load on the photoelastic element is provided, for example, screws, Cruciferae in the plate, and clamping rods, between which is located a photoelastic element. The screws are made of a material plate.

As a photoelastic material element can be used, for example, fused silica, having a high damage threshold in compression, which provides a high dynamic range measurements of deformations and reliability of the Converter. In addition, the processing technology of fused silica is well developed, which reduces the design strain of the Converter.

A load element (plate) with piezooptical Converter is attached to the test object so that the axis of the rod coincides with the direction of the measured deformation of the test object. The deformation of the test object is transmitted to the plate, then to the rods and the photoelastic element piezooptical Converter, the optical axis of which lies in a plane perpendicular to the direction of the measured strain.

The load element is provided with a mounting hole the threads for attachment to a controlled object. To improve the reliability of fastening of a load element on its surface in contact with the controlled object may be fulfilled by the teeth lying in the same plane.

To increase the sensitivity of the strain gauge transducer to deformation, the plate can be made grooves that do not violate its integrity, which reduce the stiffness of the plate in the direction of the measured deformations and without introducing distortion in the transmission of deformation in a photoelastic element.

To ensure reliable contact of the rods with a photoelastic element, on the surface of the cylinder can be performed symmetrically located flat platforms (flats), which rest against the bars.

The rationale put signs

As a photoelastic element is clamped by means of cores having a flat end face, there is no need to make a Morse taper, which is associated with serious technological difficulties. As a photoelastic element is initially compressed, the strain gauge transducer with the same sensitivity works both in compression and in tension. The length of the rods is chosen in such a way as to satisfy the condition of formula (3), while resizing elements load element associated with changes in temperature do not cause additional stress on the photoelastic element, t what is the effect of temperature compensation.

By mounting a photoelastic element using rods calculated length is achieved by simplifying the design and provide more reliable compensation of the stresses associated with the temperature change of strain of the Converter.

Thus, the proposed set of characteristics that defines the design of the strain gauge Converter, allows to achieve the stated technical result: simplify the construction, increase its reliability and precision of measurement of the deformations of the test object.

Description strain gauge transducer

The description of the device illustrated by figures 1, 2 and 3, where:

figure 1 shows the design of the strain gauge transducer with a photoelastic element made in the form of a cylinder with two symmetrically arranged attened;

figure 2 shows the load element (plate) top (view A-a in figure 1);

figure 3 shows a General view of the load element (plate).

On the figures the figures showing: 1 - load element (plate), 2 - mounting holes, 3 - photoelastic element, 4 - flats. In the plate made two holes 5, which are inserted rods 6, which are clamped by screws 7. To improve the reliability of fastening of a load element 1 to the controlled object on the surface of the plate facing the load El is the COP, made the teeth 8. To reduce the stiffness of the load element in the direction of the measured deformations in the plate made the grooves 9. The optical axis of piezooptical Converter is shown by a line 10.

Description of the device

Strain the Converter operates as follows.

A load element 1 is fixed on the object surface by means of mounting holes 2 and the teeth 8 so that the axis of the plate coincides with the axis of loading X. Deformation of tension or compression that occurs in a controlled object in the X-direction is transferred to the plate 1 through the attachment 2. The deformation of the plate is transferred to a photoelastic element 3 through the rods 6, which leads to additional compression (+Δ) or stretching (-Δ) photoelastic element. As a result, in piezooptical Converter, an additional phase difference of ±Δ between mutually perpendicular polarization components of the beam passed through a photoelastic element, which leads to the change of the electric signal at the output of the photodetector piezooptical Converter, which is detected and processed by the processing unit of the signal.

Used sources of information

1. Slesinger I.I. Piezooptical transducers. Measurement technology, 1985, No. 11, p.45-48.

3. RF patent №222786 dated 23.04.2010.

1. Strain gage transducer comprising a load element mounted on a controlled object, piezooptical Converter that converts into an electrical signal the magnitude of stresses on the photoelastic element, which is fixed in an obviously loaded condition, and the processing unit of the signal, wherein the load element is a plate with a cylindrical hole in which a photoelastic element of cylindrical shape adjustable clamped in the direction of action of the measured strains using two rods made of a material with a coefficient of thermal expansion greater than the corresponding coefficient of the plate, the length of the rods is designed in such a way that preserves the value of initial compression from temperature changes.

2. The Converter according to claim 1, characterized in that to increase the efficiency of the transfer of the measured strain on the photoelastic element plate is purified in a place of fastening of a photoelastic element.

3. The Converter according to claim 1, characterized in that on a photoelastic element made in the form of a cylinder made two symmetrically located the flats facing the clamping bars.

4. The Converter according to claim 1, characterized in that the plate is made of a threaded screw holes rests on the rods, clamping photoelastic element, and the screws are made from a single plate material.

5. The Converter according to claim 1, characterized in that the plate is made grooves, reducing the rigidity of the plate in the direction of the measured strain.

6. The Converter according to claim 1, characterized in that on the surface of the plate in contact with the controlled object, performed the teeth lying in the same plane.

7. The Converter according to claim 6, characterized in that to ensure contact between the plate and the controlled object along the plane of the plate facing toward the object, the shape and size of teeth are selected in such a way that when the mounting plate on the object, the teeth are completely submerged in the body of the test object.



 

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