Measuring and testing – Specimen stress or strain – or testing by stress or strain... – Specified electrical sensor or system
Patent
1992-04-23
1994-07-12
Raevis, Robert
Measuring and testing
Specimen stress or strain, or testing by stress or strain...
Specified electrical sensor or system
73774, G01L 100
Patent
active
053277864
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
The invention relates to an apparatus for measuring axial tensile or compressive stresses on a rod.
A possible application for such an apparatus is the measurement of operating stresses in the control rod of certain taps, cocks or valves. The known apparatuses make it possible to measure said stress directly by the elongation or contraction of the rod or by means of an operating torque at the output of the servomotor controlling the rod. Certain of these apparatuses are too fragile to be used under all the possible operating conditions, particularly under high temperature, irradiation or in the presence of shocks. Others make it necessary to dismantle certain parts of the valve, which is incompatible with a measurement during normal operation. There are other apparatuses which make it possible to measure the stresses via a parameter such as the displacement of flexible washers of a stress limiter. It is also possible to use resistant sensors requiring no dismantling of the parts, but the accuracy obtained with such an indirect procedure is inadequate.
The fundamental aim of the invention is to directly measure the axial stresses in the rod by means of a robust apparatus and which requires no dismantling of parts of the valve. It is also essential that said apparatus can easily be fitted and dismantled, which is not the case with the strain gauge systems used at present for such measurements in other technical fields.
In its most general form, the apparatus comprises two rings, each formed by two sectors assembled to one another in a dismantlable manner and fixed to the rod by an internal contact surface, at least one contact-free distance measuring sensor fixed to one of the rings and a measuring means making it possible to measure the distance between the sensor and the other ring. The distance measuring sensor is materially separate from the other ring, so that no stress is transmitted between the rings, which therefore remain in place on the rod constituting their sole connecting means.
Preference is given to using two diametrically opposite sensors on the rings in order to avoid the measuring errors produced by parasitic bending stresses on the rod. A greater facility of use is offered if the sensors fitted to a ring are fixed to the same ring sector, which implies that the sectors of the rings have unequal dimensions.
The envisaged construction uses magnetic sensors, which emit a field, which closes on a magnetic target. More specifically, a sensor comprises a ferrite block containing an excited coil, as well as another magnetic measuring coil and emits a field on a target constituted by a facing magnetic part.
The reliability of the measurements is also increased if the rings have an internal collar bearing on the rod, preferably on a part remote to the other ring, so as to obtain a better sensitivity.
Finally, the apparatus can have a fitting part which is provided, like a sector of each of the rings, with dismantlable, mutual connection means and mutual positioning means. This guarantees that the rings will be placed at a uniform distance from one another at the time of installation.
The invention is described in greater detail hereinafter relative to non-limitative embodiments and with reference to the attached drawings, wherein show:
FIG. 1 a view of the apparatus in the fitted state, in a diametral section of the rod.
FIG. 2 a view from below of the upper ring.
FIG. 3 the sensors used in detail.
FIG. 4 a radial view of the fitting part.
FIG. 5 a plan view of said part.
Measurement takes place of the axial stresses on a rod 1, which in the envisaged application belongs to a valve and which controls a blanking cap 2 fixed to one of its ends. The control is brought about by a servomotor 3 at the other end of the rod 1. It is a question of periodically checking that the servomotor 3 can subject the rod 1 to adequate axial stresses to be able to displace the blanking cap 2, particularly against friction and the pressure forces of the fluid, whose flow is modified by the blanking cap 2. I
REFERENCES:
patent: 2099662 (1937-11-01), Slonneger
patent: 2382351 (1945-08-01), Thorpe
patent: 3151399 (1964-10-01), MacGeorge
patent: 3402472 (1968-09-01), Riley
patent: 4251918 (1981-02-01), Duggan
patent: 4275599 (1981-06-01), Kohlenberger et al.
patent: 4823473 (1989-04-01), McMahon
patent: 4930228 (1990-06-01), Anderson et al.
patent: 4936150 (1990-06-01), Burke et al.
Charron Jean-Louis
Guillet Jacques
Electricite de France (Service National
Raevis Robert
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