Monday, March 27, 2017

Blog 11 group 1

Part A: Strain Gauges:
Strain gauges are used to measure the strain or stress levels on the materials. Alternatively, pressure on the strain gauge causes a generated voltage and it can be used as an energy harvester. You will be given either the flapping or tapping type gauge. When you test the circle buzzer type gauge, you will lay it flat on the table and tap on it. If it is the long rectangle one, you will flap the piece to generate voltage.
1. Connect the oscilloscope probes to the strain gauge. Record the peak voltage values (positive and negative) by flipping/tapping the gauge with low and high pressure. Make sure to set the oscilloscope horizontal and vertical scales appropriately so you can read the values. DO NOT USE the measure tool of the oscilloscope. Adjust your oscilloscope so you can read the values from the screen. Fill out Table 1 and provide photos of the oscilloscope.

Table 1: Strain gauge characteristics

 Minimum voltage:-2V
Maximum voltage:3V

Minimum voltage:-40V
Maximum voltage:45V
Image 1: Shows the output of the strain gauge
Image 2: Shows the output of the strain gauge
2. Press the “Single” button below the Autoscale button on the oscilloscope. This mode will allow you to capture a single change at the output. Adjust your time and amplitude scales so you have the best resolution for your signal when you flip/tap your strain gauge. Provide a photo of the oscilloscope graph.
Image 3:  Shows the use of the "single" button

Part B: Half-Wave Rectifiers
1. Construct the following half-wave rectifier. Measure the input and the output using the oscilloscope and provide a snapshot of the outputs.
Image 4: shows the output of the halfway rectifier 

2. Calculate the effective voltage of the input and output and compare the values with the measured ones by completing the following table.
Effect (rms) Values       Calculated     Measured
                                           3.535                  Input 3.72
                                        2.5                     Output 2.15

3. Explain how you calculated the rms values. Do calculated and measured values match?
(Come back)

4. Construct the following circuit and record the output voltage using both DMM and the oscilloscope.

Column1 Oscilloscope DMM
Output Voltage (p-p) 2.4 1.848
Output Voltage (mean) 2.84 2.79
Table 1: Shows the output voltages using the different devices

5. Replace the 1 µF capacitor with 100 µF and repeat the previous step. What has changed?

Column1 Oscilloscope DMM
Output Voltage (p-p) 120 mV 62.2 mV
Output Voltage (mean) 3.27 3.22
Table 2: Shows the output voltages for thee 100uf capacitor

Part C: Energy Harvesters
1. Construct the half-wave rectifier circuit without the resistor but with the 1 µF capacitor. Instead of the function generator, use the strain gauge. Discharge the capacitor every time you start a new measurement. Flip/tap your strain gauge and observe the output voltage. Fill out the table below:

Tap frequency Duration Output Voltage
1 flip/second 10 seconds 617 mV
1 flip/second 20 seconds 1.37
1 flip/second 30 seconds 3.07
4 flip/second 10 seconds 3.29
4 flip/second 20 seconds  4.84
4 flip/second 30 seconds 8.8
Table 3: Shows the output for flips per second

2. Briefly explain your results.
As the flips increased in speed and in a longer duration, the voltage all increased from there, the faster you tap for the longer amount of time will give you higher outputs. 

3. If we do not use the diode in the circuit (i.e. using only strain gauge to charge the capacitor), what would you observe at the output? Why?
If we didn't use a diode, the circuit would not work because the capacitor would immediately discharge and there would be no built up charge.  

4. Write a MATLAB code to plot the date in table of Part C1.
hold on
legend('1 flip/second','4 flip/second')
xlabel('Duration (s)')
ylabel('Output Voltage (V)')
title('Half-wave recitifier')


  1. For the first part, we seemed to have gotten much different values. I think this is because our group used the wrong attenuation (1x instead of 10x). Assuming you guys used the correct setting, it is interesting to see what the real values are.

    1. That is one possibility or maybe it could have been caused by simply a difference in how the forces were applied!

  2. In all oscilloscope graphs you got more clear graphs than what we had I think that because you used range smalle than what we used. It is cool to learn that from you.
    For the values in think the difference come from the tapping and flipping power on strain gauges.
    Good job.

    1. Yes, I was quite surprised how clear of graphs we got! Thanks!

  3. For part B our graphs look the same. We also got different values for our calculated and measured effective rms value. Why do you think that is? I'm assuming a rounding error because the 2 values are fairly close to each other.

    1. Im not sure! I could show you our calculations that we used for our calculated value but since our measured values are differnce there must have been a difference in our pk values and im not sure why that is.

  4. It looks like we had VEEERRYYY different graphs and values for part A. Maybe we had a different strain gauge than you guys did? Or maybe we had a greater amount of random error than you. Overall I think you guys did a good job on your blog this week! I noticed that our part C is very similar, and did you have a problem with the tapping? I felt like sometimes my taps wouldn't really register on the oscilloscope so I did every trial a couple of times. I think the tapping would be easier if the circle that registers the taps was a little bigger... Also your MatLab code looks good and I like the graph you obtained with it. Great job this week!

    1. I personally had a hard time having the taps register but luckily Scout did not so he did the tapping for us.

  5. Everything looks good. Our measuring for the tapping and flipping were not nearly as high as yours, but luckily it was consistent through out the experiment and did not affect the outcome of the graphing.

  6. See, I am curious with your part A number 1 if you had used a single wave capture method for those, as we did not use that for ours. Regardless of our method, our waves individually are very different. Still, well done.