Abstract: This lap report will represent the Experiment
6 which its title is Measurement of Young’s Modulus using Strain
Gauges. This Experiment will go through two goals. First goal is
Assemble a Wheatstone bridge circuit to measure a signal from two strain gauges affixed to a cantilevered beam. Second goal is
Collect enough strain and loading data to perform a linear regression to estimate Young’s modulus, E, of the cantilevered beam. Compare the experimental value with published values.
I.
Introduction:
The primary objective for this lab was to become familiar with Simulink, and with a basic experimental set up.
However, in this experiment we used some equipment that helped us concluding the experiment. The equipment were:
1) Cantilevered beam with mounted strain gauges.
2) AD622 Instrumentation Amp.
3) Powered Breadboard.
4) Unpowered Breadboard.
5) Table-top Digital Multi-Meter.
6) Wire & Resistor Kits.
7) Screw Driver, Pliers, Wire Stripper.
8) Precision Matched Resistors.
9) Calipers.
10) Measuring Tape.
11) Weight Set.
In part one, we created a Simulink program to acquire and display the output voltage from the bridge circuit. We measured the length between the center of the strain gauge and point of loading, L f
, the width of the beam, w, and the thickness, t, and record all associated uncertainties.
Also, we built a half arm Wheatstone bridge circuit, and we used the two strain gauges mounted to the cantilevered beam as resisters R#1 and
R#2. We connected the output of the instrumentation amplifier to the table top multi-meter. Then, we used the power supply and provide the amplifier and the bridge with a 10V excitation voltage. Finally, we used Simulink and the table top DMM to measure the amplified output voltage, V*G, from the instrumentation amplifier to check that our measurement system is working properly.
In part two, first we make a voltage measurement of the beam unloaded. Then, we loaded the beam and recorded the change in voltage and the amount loaded. Lastly, we unload the beam and record the voltage again. That gave us the change from unloaded to load and the change from loaded to unload.
Also, this experiment can be done by going through two parts.
First part is about building and testing a Half Arm Wheatstone
Bridge Circuit. Second part is about Taking Load and Strain
Data for the Cantilevered Beam.
II.
Methods:
In this part we will go through the steps of how we did the two parts that mentioned above in the introduction.
III.
Results:
The data displayed below is the comparison between the voltage reading on the DMM and the Simulink scope. The data from the DMM only has two significant figures beyond the decimal point, Simulink gives four significant figures regardless of where the decimal point is located.
Mass(kg) (Volts)
Stress
(Pa)
Young’s
Modulus
0.1 0.0000408 1331037 0.000374
0.2 0.000078 2662074 0.000374
0.3 0.0001138 3993111 0.000374
0.4 0.0001544 5324148 0.000374
0.5 0.0001982 6655185 0.000374
0.7 0.0002766 9317259 0.000374
0.8 0.0002868 10648296 0.000374
0.9 0.0003453 11979333 0.000374
1 0.0003791 13310371 0.000374
Strain
3558922460
7117844920
10676767380
14235689840
17794612299
24912457219
28471379679
32030302139
35589227273

The results above form the table is showing the measurement of young’s Modulus using Strain Gauges .the experiment values are very close to the published values. Nine different points were taken. To calculate the standard error of the fit equation is
(1)-S_xy=(normal^2/N-(m+1))^0.5
IV.
Discussion And Conclusions
The goal of this lab was to become familiar with a basic lab setup along with how the amplifier can be used to adjust resistors. The two strain gauges are used to connect to the input voltage and ground voltage to the two resistors as well. And connected that to the half AS622 instrumentation amplifier.it was easier to use simply by connecting the power supply to pin
4 and pin 7, resistors to pines 1 and 8, reference ground to pin
5, sensor low voltage and high voltage to pins 2 and 3, and output is pin 6.
The values were showing from the scope a litter bit different actually, we haven’t got that part right however, in the end we got some results and they were closed the actual values of the published values.
Some problems with the Wheatstone bridge and the instrumentation amplifier are wires and connection. Both of them need to be set up very careful and right.
When getting out of the elastic region of the beam the results will not be valid anymore