International Journal of Scientific & Engineering Research, Volume 6, Issue 4, April-2015 1825 ISSN 2229-5518 IJSER © 2015 http://www.ijser.org Design, construction and Testing of a strain gauge Instrument Oluwole O.O, Olanipekun A.T, Ajide O.O Abstract— The research work is on the design, construction and testing of a quarter bridge strain gauge based measuring instrument. This was achieved by dividing the whole measurement system to power section which consist of batteries, voltage regulators and operational amplifier, arithmetic, logic section consist the microcontrollers that arithmetically compute the strain, and finally input and output section for user dialog. The governing equation for the design revolves around Hooke’s law and ohm’s law. In the design we considered the instrumentation of the measuring strain gauge system which includes the Wheatstone bridge set up, microcontroller, IC programming followed by simulation using proteus design software. After the construction we carried out a uniaxial stress analysis testing with the designed strain gauge measurement instrument on a clamped wooden beam that has a modulus of elasticity 10700 N/ 2 , length of 250mm and cross-sectional area of h = 4.5 mm , b = 25mm applying load in an incremental succession, the strain and stress at different load interval is then determined. Theoretical strain calculation is then used to validate experimental analysis. For applied load 0.9806N we have the experimental strain value to be 250.14×10 −6 while the theoretical strain value is 271.54 ×10 −6 and for applied load 1.4709 the experimental strain value is 362.12×10 −6 , while theoretical strain value is 407.31×10 −6 . Experimental strain and theoretical calculated strain value obtained agreed to some extent. Index Terms— Strain gauge, stress, strain, load ——————————  —————————— 1 INTRODUCTION Any device that is used to measure surface deformation can be classified as a strain gauge (Perry, 1984). A strain gauge, in mechanical term, is a device for measuring mechanical strain. However, in instrumental term, it is generally taken to mean the electrical resistance strain gauge, and as the name implies, the strain gauge is an electrical conductor whose resistance varies in proportion to the amount of strain in the device. It is thus transducer, whereby strain is converted into change of electrical resistance (Hilal M & Mohamed.S. 2011). Strain gauges are popular means to measure mechanical movements in micro components. They are employed, e.g., in acceleration sensors, vibration sensors, acoustic sensors and especially pressure sensors (Middelhoek S and Audet S, 1994). Since their invention in 1938 by Arthur Ruge and Edward Simmons, strain gauges are all around us. The measurement of the small displacements that occur in a material or object under mechanical load can be accomplished by methods as simple as observing the change in the distance between two scribe marks on the surface of a load-carrying member, or as advanced as optical holography. In any case, the ideal sensor for the measurement of strain would have good spatial resolution, implying that the sensor would measure strain at a point, be unaffected by changes in ambient conditions; and have a high-frequency response for dynamic (time-resolved) strain measurements. A sensor that closely meets these characteristics is the bonded resistance strain gauge (Richard & Donald 2011). During the course of his seismic insulation research, Ruge discovered that he needed to measure the stress on the water tanks that was caused by the earthquakes, and so he set about devising a means for attaining this measurement. According to Ruge, he had a Eureka moment on April 3, 1938 when “the invention just popped into my mind, whole. I could see it clearly and knew that it would work.” His solution was to glue a piece of cigarette paper on the tank and glue a small wire with end connections to the paper. Ruge and his assistants quickly developed this rudimentary device into the more advanced version that would later be patented (MIT, 2011). According to Karl (1989:1), “The usual way of assessing structural parts of machines, buildings, vehicles, aircraft, etc. is based on strength of material calculations. This method is satisfactory provided the component loads are known both qualitatively and quantitively. Problems arise particularly where the loads are unknown or where they can only be roughly approximated. Formerly the risk of overloading was countered by using safety margins, i.e. through over dimensioning. However, modern design strategies demand savings in material, partly for reasons of cost and partly to save weight; this is clearly illustrated, for example in aeronautics. In order to satisfy the safety requirements and to provide an adequate component service life, the material stresses must be known. Therefore measurements under ———————————————— • Dr Oluwole is lecturing in the Department of Mechanical Engineering, University of Ibadan, Nigeria.PH:+2348033899701. E-mail: oluwoleo2@asme.org • Olanipekun Ayorinde has a Masters in Mechanical Engineering from the University of Ibadan. He is presently working with Prototype Engineering Development Institute Ilesa, (National Agency for science and Engineering infrastructure, Nigeria). PH: +2347061541108. E-mail :olanipekunayo2010@yahoo.com • Ajide is lecturing at the Mechanical Engineering Department of the University of Ibadan. He is into Materials Development, characterization and treatment.PH:+2348062687126. E-mail: getjidefem2@yahoo.co.uk IJSER