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The SaundersRoe Technograph Foil Strain Gauge

The SaundersRoe Technograph Foil Strain Gauge TEST EQUIPMENT The Saunders-Roe Technograph Also planned are miniature versions of the linear gauge, down to 0·25 in. by 0·20 in., or Foil Strain Gauge possibly even to 0·125 in. square. It may be necessary in these cases to modify the production technique (which at present produces micro­ A New Type of Gauge which scopically jagged edges to the element) to one employing direct optical reduction on to the foil. May Solve Many Problems Application The adhesives recommended for securing the The Requirement gauge, and a cross sensitivity lower than in wire strain gauges to the structure being tested are the gauges. The thin element reduces the shear lag in HEN using strain gauges of the normal transmission of strain from the specimen. Perhaps wire type in the dynamic testing of heli­ the most important advantage, after the mechani­ Wcopter components, notably rotor blades, cal robustness of this type of gauge, is its capacity Messrs. Saunders-Roe found that such a high to carry much higher currents than the wire gauge, proportion of the gauges were failing that de­ thus providing greater sensitivity. The large sur­ velopment was considerably retarded. The Elec­ face area/cross-sectional area ratio gives much tronics Division was therefore asked to devise an greater heat dissipation, and currents of 0· 5 amp. improved gauge and, in collaboration with can be carried, as compared with 10·12 ma. for Messrs. Technograph Printed Circuits Ltd., pro­ wire gauges. This makes it possible in some duced the foil strain gauge. applications to dispense with amplifying equip­ 'Araldite' glues manufactured by Messrs. Aero ment, which in aircraft work gives considerable The Basic Conception Research Ltd., Duxford, Cambridge. These do saving in weight and complication, FIG. 2 shows not absorb moisture appreciably and provide This gauge replaces the thin wire (often of the a record, reproduced full-size, made directly from order of 0·001 in. diameter) by a grid of foil good electrical insulation and high strength of a group of four gauges attached to a vibrating which, among other advantages, permits of the bond. By choosing a suitable adhesive the gauge cantilever. The system was calibrated by weights may be used at temperatures up to 170 deg. C. ends of the gauge element being increased in size hung from the end of the specimen, giving the Higher temperatures (up to 400 deg. C.) may be t o enable the leads to be soldered on without static calibration in pounds. made possible by the use of a silicone lacquer for difficulty. This point of attachment of the leads the base. Gas turbine applications requiring is a notoriously weak point in the normal type of operation at still higher temperatures might be strain gauge. The grid is produced by controlled catered for by depositing a foil gauge on a etching of a sheet of foil. The foil is first sprayed with a synthetic resin lacquer (Araldite) to form ceramic coating, and covering it with another. an insulating base between 0·001 in. an d 0·002 in. thick. A large-scale drawing of the grid is pre­ Waterproofing pared and from this a printing block is produced One of the possibilities arising from the use of photo-mechanically, reduced to the size required. Araldite adhesives is that of waterproofing the With this is printed on the foil an impression in gauge. This can be done by applying a thin mat etch-resisting ink. The remainder of the foil is of glass fibre to retain the glue while it is liquid, then etched away in an acid bath, leaving the and covering it with the casting resin. The result­ grid. In this way a grid can be produced to any ing smooth and thin protruberance need not pattern which may be required. appreciably disturb flow over the surface. Tests have been carried out in which water pressures of The Linear Gauge 90 lb./sq. in. have not affected the properties of The type of gauge so far produced is illustrated the gauge. in FIG. 1. In it the element is 1·0 in. by 0·25 in. Other Patterns Each filament is 0·010 in. wide, the separation between adjacent filaments being 0·0125 in. Two Gauges for particular purposes, having different Conclusion foils are in use; a 50/50 copper-nickel alloy having configurations, are under development. FIG. 3 It would appear that the new method of pro­ a thickness of about 0·0005 in., and gold-silver shows two of these. The double spiral type is in­ ducing gauges opens up the possibility of using which is believed to be about 0·00003 in. thick, tended for mounting on diaphragms and could, them for applications where it has hitherto been giving resistance values of 40 ohms and 230 ohms for example, be adapted for use as a pressure difficult or impossible. respectively. The tolerances to which these re­ gauge. The herring-bone pattern is for the sistances are held are less fine than those normally measurement of torque on a shaft. The gauge specified for wire gauges, but the foil gauges are would be produced in 12 in. lengths and cut off supplied in accurately matched pairs to overcome to the length required. The alignment on the BOOKS RECEIVED this. The method of manufacture has enabled the shaft would be much simpler than for two linear filament width to be increased at the grid ends type gauges, which have to be accurately fixed All books received from Publishers are listed under which results in a rapid build-up of stress in the at 45 deg. to the axis. this heading. Extended reviews of a selection appear later. Inclusion in this list, therefore, neither precludes, nor implies, in any particular instance, further notice. Shawcross and Beaumont on Air Law. Supplement to Second Edition, Paper bound. 128 pp. [Butter- worth. 17s. 6d.] Proceedings of the Society for Experimental Stress Analysis. Vol. IX, No. 2. 207 pp., illustrated. [Society for Experimental Stress Analysis, Central Square Station, P.O. Box 168, Cambridge, 39, Mass., U.S.A. $6.0.] The Development of Engineering Metrology. F. H. Rolt. Paper bound, 56 pp., illustrated. [The Insti­ tution of Production Engineers, 36 Portman Square, W.l. 5s.] Development of the Guided Missile. K. W. Gatland. 133 pp., illustrated. [Flight. 10s. 6d.] Research and Development in British Industry. Paper bound. 19 pp. [Federation of British Industries, 21 Tothill Street, S.W.I. 1s. 3d.] Mechanical Properties of Metals at Low Tempera­ tures (National Bureau of Standards Circular 520), 206 pp., illustrated. [Superintendent of Documents, Government Printing Office, Washington, 25, D.C., U.S.A. $1.50.] 348 Aircraft Engineering http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Aircraft Engineering and Aerospace Technology Emerald Publishing

The SaundersRoe Technograph Foil Strain Gauge

Aircraft Engineering and Aerospace Technology , Volume 24 (11): 1 – Nov 1, 1952

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Publisher
Emerald Publishing
Copyright
Copyright © Emerald Group Publishing Limited
ISSN
0002-2667
DOI
10.1108/eb032229
Publisher site
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Abstract

TEST EQUIPMENT The Saunders-Roe Technograph Also planned are miniature versions of the linear gauge, down to 0·25 in. by 0·20 in., or Foil Strain Gauge possibly even to 0·125 in. square. It may be necessary in these cases to modify the production technique (which at present produces micro­ A New Type of Gauge which scopically jagged edges to the element) to one employing direct optical reduction on to the foil. May Solve Many Problems Application The adhesives recommended for securing the The Requirement gauge, and a cross sensitivity lower than in wire strain gauges to the structure being tested are the gauges. The thin element reduces the shear lag in HEN using strain gauges of the normal transmission of strain from the specimen. Perhaps wire type in the dynamic testing of heli­ the most important advantage, after the mechani­ Wcopter components, notably rotor blades, cal robustness of this type of gauge, is its capacity Messrs. Saunders-Roe found that such a high to carry much higher currents than the wire gauge, proportion of the gauges were failing that de­ thus providing greater sensitivity. The large sur­ velopment was considerably retarded. The Elec­ face area/cross-sectional area ratio gives much tronics Division was therefore asked to devise an greater heat dissipation, and currents of 0· 5 amp. improved gauge and, in collaboration with can be carried, as compared with 10·12 ma. for Messrs. Technograph Printed Circuits Ltd., pro­ wire gauges. This makes it possible in some duced the foil strain gauge. applications to dispense with amplifying equip­ 'Araldite' glues manufactured by Messrs. Aero ment, which in aircraft work gives considerable The Basic Conception Research Ltd., Duxford, Cambridge. These do saving in weight and complication, FIG. 2 shows not absorb moisture appreciably and provide This gauge replaces the thin wire (often of the a record, reproduced full-size, made directly from order of 0·001 in. diameter) by a grid of foil good electrical insulation and high strength of a group of four gauges attached to a vibrating which, among other advantages, permits of the bond. By choosing a suitable adhesive the gauge cantilever. The system was calibrated by weights may be used at temperatures up to 170 deg. C. ends of the gauge element being increased in size hung from the end of the specimen, giving the Higher temperatures (up to 400 deg. C.) may be t o enable the leads to be soldered on without static calibration in pounds. made possible by the use of a silicone lacquer for difficulty. This point of attachment of the leads the base. Gas turbine applications requiring is a notoriously weak point in the normal type of operation at still higher temperatures might be strain gauge. The grid is produced by controlled catered for by depositing a foil gauge on a etching of a sheet of foil. The foil is first sprayed with a synthetic resin lacquer (Araldite) to form ceramic coating, and covering it with another. an insulating base between 0·001 in. an d 0·002 in. thick. A large-scale drawing of the grid is pre­ Waterproofing pared and from this a printing block is produced One of the possibilities arising from the use of photo-mechanically, reduced to the size required. Araldite adhesives is that of waterproofing the With this is printed on the foil an impression in gauge. This can be done by applying a thin mat etch-resisting ink. The remainder of the foil is of glass fibre to retain the glue while it is liquid, then etched away in an acid bath, leaving the and covering it with the casting resin. The result­ grid. In this way a grid can be produced to any ing smooth and thin protruberance need not pattern which may be required. appreciably disturb flow over the surface. Tests have been carried out in which water pressures of The Linear Gauge 90 lb./sq. in. have not affected the properties of The type of gauge so far produced is illustrated the gauge. in FIG. 1. In it the element is 1·0 in. by 0·25 in. Other Patterns Each filament is 0·010 in. wide, the separation between adjacent filaments being 0·0125 in. Two Gauges for particular purposes, having different Conclusion foils are in use; a 50/50 copper-nickel alloy having configurations, are under development. FIG. 3 It would appear that the new method of pro­ a thickness of about 0·0005 in., and gold-silver shows two of these. The double spiral type is in­ ducing gauges opens up the possibility of using which is believed to be about 0·00003 in. thick, tended for mounting on diaphragms and could, them for applications where it has hitherto been giving resistance values of 40 ohms and 230 ohms for example, be adapted for use as a pressure difficult or impossible. respectively. The tolerances to which these re­ gauge. The herring-bone pattern is for the sistances are held are less fine than those normally measurement of torque on a shaft. The gauge specified for wire gauges, but the foil gauges are would be produced in 12 in. lengths and cut off supplied in accurately matched pairs to overcome to the length required. The alignment on the BOOKS RECEIVED this. The method of manufacture has enabled the shaft would be much simpler than for two linear filament width to be increased at the grid ends type gauges, which have to be accurately fixed All books received from Publishers are listed under which results in a rapid build-up of stress in the at 45 deg. to the axis. this heading. Extended reviews of a selection appear later. Inclusion in this list, therefore, neither precludes, nor implies, in any particular instance, further notice. Shawcross and Beaumont on Air Law. Supplement to Second Edition, Paper bound. 128 pp. [Butter- worth. 17s. 6d.] Proceedings of the Society for Experimental Stress Analysis. Vol. IX, No. 2. 207 pp., illustrated. [Society for Experimental Stress Analysis, Central Square Station, P.O. Box 168, Cambridge, 39, Mass., U.S.A. $6.0.] The Development of Engineering Metrology. F. H. Rolt. Paper bound, 56 pp., illustrated. [The Insti­ tution of Production Engineers, 36 Portman Square, W.l. 5s.] Development of the Guided Missile. K. W. Gatland. 133 pp., illustrated. [Flight. 10s. 6d.] Research and Development in British Industry. Paper bound. 19 pp. [Federation of British Industries, 21 Tothill Street, S.W.I. 1s. 3d.] Mechanical Properties of Metals at Low Tempera­ tures (National Bureau of Standards Circular 520), 206 pp., illustrated. [Superintendent of Documents, Government Printing Office, Washington, 25, D.C., U.S.A. $1.50.] 348 Aircraft Engineering

Journal

Aircraft Engineering and Aerospace TechnologyEmerald Publishing

Published: Nov 1, 1952

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