Monitoring Strains And Stresses With Strain Gauges, Wheatstone Bridge, Arduino, And NI LabVIEW

Importance of Strain Gauges

Due to the increasing complication of systems in modern environment, there is a greater demand for monitoring and analysis of strains and stresses created in parts, as well as the ability to control from a distant location. For these kind of measures, several industry areas . The importance of strain gauges cannot be overstated. Devices with accurate measurements can determine the amount of strain generated in a variety of constructions, ranging from structural to biomechanical technology. Strain assessment can be used to determine the lifespan and threat of a specific structure. Strain is the deformation that occurs as a result of stress, (Cabaleiro, Riveiro, Arias and Caamaño, 2015). Connected electronic strain gauges are the most common and dependable means of monitoring strain. The strain gauge's electrical resistance varies when the conducting grid deforms. The Wheatstone Bridges are used to translate changes in resistance into electrical impulses, i.e., in accordance with the defined voltage, as the strain gauge provides measurements in terms of resistance. However, because the voltage difference is so small, it must be amplified to a particular level in order for the controller to perceive it. A full bridge circuit is created by attaching a strain gauge to one of the Wheatstone bridge circuit's four legs, which improves the micro strain values from each strain gauge as well as gives responsiveness that is two to four times higher than the Half Bridge as well as Quarter Bridge setups, respectively. The differential voltage between two output terminals is the output value as a result. Stress measurements & analyses on a Simply Supported beam were performed in this research; a setup was built and fabricated for the test, and samples were recorded; the acquired experimental data were verified with theoretical data as well as the NI-DAQ modules, (Tebedge, Alpsten and Tall, 2018).  

Developing a circuit to measure the output voltage of a quarter bridge configuration with a strain gauge using a schematic depiction.

The resistance levels selected for the Wheatstone bridge's remaining 3 arms.

The rheostat arm of the bridge (R2 in the diagram) is normally set to the strain gauge resistance when no force is applied. The two ratio arms (R1 and R3) of the bridge are set to the same value. If no force is given to the strain gauge, the bridge will be symmetrically balanced and the voltmeter will show 0 volts, reflecting zero force on the strain gauge, (POPLE, 2016).

What should be considered before connecting the circuit to a Daq device?

We'll use an Arduino to monitor strain and stress from a Wheatstone bridge, as well as the output voltage from a signal conditioning circuit. Arduino is an open-source tool for creating online technology and interacting items that can detect as well as function both manually as well as electrically or programmatically utilizing single-board embedded systems and microprocessor kits. A 16 MHz clock drives it. Additional circuits & devices like as sensors, switches, as well as displays are connected to the boards using a range of digital and analog input/output (I/O) pins. Serial communications interfaces, such as the Universal Serial Bus (USB), are also supported on the boards, which are used to load programs from computers, (?RSEL, 2021).

Using Wheatstone Bridges to Monitor Strains

LabVIEW is a visual programming language that facilitates in the analysis of all aspects of the application. LabVIEW works as an interface and makes it simple to connect hardware. The stress was estimated using a theoretical approach. NI LabVIEW software was used to create the equation for computing theoretical pressure, (WHITLEY and BLACKWELL, 2016). Equations are created using the LabVIEW software's Boolean & logic operations. The theoretical stress is determined directly using the loading & length inputs on the front panel.

The DAQ assistance input is used to calculate the actual strain values. The stress value is determined by multiplying the measured strain number by the modulus of elasticity, as well as the change in length on the cantilever beam and the strain gauge sensitivity. On the front panel, the quantities are shown. A graphic indication is used to verify and represent the analytical and empirical estimates of stresses, (Mereen Hassan Fahmi, 2017). 

A single op-amp IC 741 (IC3) enhances the outputs from a series of three resistors (R1 through R3) as well as a strain gauge SG1 in this circuit. Because the strain gauge specified for this circuit has a nominal resistance of 120 ohms, every one of the resistors R1 through R3 should be 120 ohms as well. The resistors should also have a tolerance of better than 0.1 percent, so that any temperature variations don't affect the meter's reading, (Ohashi, Kishii and Tateno, 2016).

Acquire data from your circuit's output using the analogue inputs pin on the NI breadboard.

The closest power rail to the IC control input will be used. In this instance, you can see that we've connected our -15V energy to the positive voltage rail on the left side of our IC setup. Using a jumper wire, connect the -15V bank to the + strip on the right side.

A basic potentiometer is the simplest simple approach for implementing the offsets null, however frequently, digitized feedback is employed, and the performance is calculated at a specified automatically by the system, (Arab et al., 2017). The circuits below illustrates this. 

This number indicates that the metals has a Poisson's ratio of 0.5 in the maximum bound. Poisson's ratio is only between 0 & 0.5. It is between 0.42 and 0.44 for gold, 0.33 for copper, and 0.27 & 0.30 for steel.

The length difference can be attributed to two factors. Force 2F is the primary cause of the length variation. Because the beam's cross section area is AS, the stress is?=2F / AS. The length change is?x1, and the beam deformation is?1=?x1/x.

Conclusion

Using the DAQ module & NI LabVIEW, as well as Arduino, an exploratory study for a simple supported beams were developed and implemented. Because the theoretically and experimentally values were so similar, stress measurements were carried out. During the test, the margin of error was maintained below 10%. Because of the assumptions made, there was a disparity between the theoretical and experimental results. DAQ module & Arduino were used to compute the experimental results. 

References

Arab, M., Zegaoui, A., Petit, P., Djahbar, A. and Aillerie, M., 2017. Output-voltage feedback control topology for inverters dedicated to renewable energy systems. International Journal of Circuit Theory and Applications, 45(12), pp.2270-2280.

Cabaleiro, M., Riveiro, B., Arias, P. and Caamaño, J., 2015. Algorithm for the analysis of deformations and stresses due to torsion in a metal beam from LIDAR data. Structural Control and Health Monitoring, 23(7), pp.1032-1046.

?RSEL, G., 2021. Research on electrical strain gages and experimental stress analysis: Case study for a full wheatstone bridge. DÜMF Mühendislik Dergisi, pp.783-792.

Mereen Hassan Fahmi, D., 2017. Effect of Stress – Strain Relationship on the Elasticity Modulus and Moment Capacity. AL-Rafdain Engineering Journal (AREJ), 13(2), pp.13-32.

Ohashi, M., Kishii, N. and Tateno, S., 2016. New bridge-circuit-type detector to measure precise resistance change of strain gauge at low temperature and magnetic field. Japanese Journal of Applied Physics, 55(4), p.046601.

POPLE, J., 2016. Increasing the voltage output of a Wheatstone bridge having one or two active strain gauge arms. Strain, 12(1), pp.31-36.

Tebedge, N., Alpsten, G. and Tall, L., 2018. Residual-stress measurement by the sectioning method. Experimental Mechanics, 13(2), pp.88-96.

WHITLEY, K. and BLACKWELL, A., 2016. Visual Programming in the Wild: A Survey of LabVIEW Programmers. Journal of Visual Languages & Computing, 12(4), pp.435-472.