Lab 9.1

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Mechanical Engineering

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Dec 6, 2023

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MECH 313 Data and Acquisitions Laboratory Lab 9 Construct an Alarm System Using Motion Sensor Prof. Yuetong Lin Nathan Hernandez 10-7-2023
Hernandez 1 Purpose This purpose of this week’s lab was to construct a strain gauge configuration using a Wheatstone bridge based on the provided example from LabView. In our lab we covered how a myDAQ can be used to read the measurements from a strain gauge, created the bridge, and verified our results with LabView. The lab results were recorded and can be found at https://youtu.be/OePvCCgAamg . Objectives As mentioned, our objective for this week’s lab was to construct a Wheatstone bridge configuration and use it to read the measurement of a strain gauge by connecting it to myDAQ and LabView. We were also asked to add the additional functionality of a low-pass filter for signal noise, and having the results recorded by using the Write To Spreadsheet express VI. Equipment and Supplies For this lab the equipment we used were three 1k Ohm resistors, a strain gauge, a breadboard, myDAQ, and assorted jumper wires. The voltage signals were processed and read by LabView. Theory Strain gauges output very small changes in voltage or resistance when a heavy load is applied to them which makes capturing the measurements changes difficult. This is why they are usually measured using a Wheatstone bridge. The Wheatstone bridge applies an excitation voltage across the bridge and based on the output voltage being returned the resistance change of the strain gauge can be read. Assuming we know the values of the resistors the following equation can be used to find the resistance of 𝑅 4 which in our case would be the resistance across the strain gauge: 𝑉 𝑂 = ( 𝑅 3 𝑅 3 + 𝑅 4 𝑅 2 𝑅 1 + 𝑅 2 )𝑉 𝐸𝑋 Because we choose 1k Ohm resistors for our Wheatstone bridge we can simplify the equation to the following: 𝑅 3 = 𝑉 𝑂 𝑉 𝐸𝑋
Hernandez 2 The following diagram will also be used for our setup as a guide on how to connect to myDAQ.
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Hernandez 3 Observations
Hernandez 4
Hernandez 5 Discussion In the first image we can see the physical set up of the bridge with the three resistors and gauge connected via a breadboard. Our bridge is then being powered by myDAQ and the resulting output voltage is also being read by the DAQ. In the next image we can see the VI that was created to read and process the signals being received. The signals are passed from the DAQ Assistant to a low-pass filter to filter out signal noise. They are then split and passed to the output indicators 𝑉 𝑂 and 𝑉 𝐸𝑋 , these signals are then divided by each other and used to provide the signal for output indicator 𝑉 𝑂 /𝑉 𝐸𝑋 which is the potential change from the strain gauge. Finally, all our signals are merged and passed to the Write to Spreadsheet VI where there are recorded to a predetermined file location. Finally, we can see the output indicators on the Front Panel of our VI which displays the signals from our bridge. The values being displayed are about what we expected to receive and based on the video provided we can verify that our lab was setup successfully. Conclusion In conclusion, we were able to read the measurements of a strain gauge by configuring a Wheatstone bridge and passing them through LabView. We verified that we received the expected values and were able to successfully record the results. I found this lab more challenging than the others because I had a hard time setting up the bridge, however, once I did figure it out I had great satisfaction in seeing everything work.
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Hernandez 6 References LabView. (2023, October 7). Wheatstone Bridge Based Measurements with myDAQ and LabVIEW . Retrieved from NI LabView Forums: https://forums.ni.com/t5/Example-Code/Wheatstone-Bridge-Based- Measurements-with-myDAQ-and-LabVIEW/ta-p/3996487 Lin, Y. (2023, October 7). Canvas ERAU . Retrieved from 9.1 Lab: Wheatstone Bridge Based Measurements With myDAQ and LabVIEW: https://erau.instructure.com/courses/161583/assignments/3206322