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.
Flipping Strength

Min Voltage (V)

Max Voltage (V)

Low

2

4.4

High

27.2

14.4

Tapping Strenght

Min Voltage (V)

Max Voltage (V)

Low

1

1.8

4

24.8

Table 1: Strain gauge characteristics
Picture: Low tapping on the sensor
Picture: High tapping on the sensor
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.
Picture: Single Wave of Tapping Gauge
Picture: Single Wave of Flicking Gauge
Part B: HalfWave Rectifiers
1. Construct the following halfwave rectifier. Measure the input and the output using the oscilloscope and provide a snapshot of the outputs.
Picture: Oscilloscope reading of the halfwave rectifier
2. Calculate the effective voltage of the input and output and compare the values with the measured ones by completing the following table.
Effective Rms

Calculated

Measured

Input

7.07

7.25

Output

3.54

3.63

3. Explain how you calculated the rms values. Do calculated and measured values match?
The rms value of the input is calculated by by dividing the peak to peak input voltage by the square root of 2 as a simplification of the following integral for a sin wave:
Equation: RMS Equation as Found on Wikipedia
Because an integral describes the area under a curve, it is clear that the area of the output wave should be half of that of the input. So the simplified integral calculation for the output becomes the input peak to peak voltage divided by the quantity of 2 times the square root of 2.
With this calculation and the measurements at the output, there appears to be an apparent consistency within a reasonable margin of error.
4. Construct the following circuit and record the output voltage using both DMM and the oscilloscope.
Oscilloscope

DMM


Output Voltage (P2P) (V)

9.6

2.725

Out Put Voltage (Mean) (V)

.225

3.9

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

DMM


Output Voltage (P2P) (V)

.596

.125

Out Put Voltage (Mean) (V)

Jumps from 2 to4

6.44

With a higher capacitance, the range of the oscillations was significantly decreased, but the mean of the output voltage significantly increased presumably because the stronger capacitor stored more voltage. It also became difficult to get a consistent reading particularly for the output voltage mean. we hypothesize that this might be caused by the capacitor's function of storing and releasing voltage.
Part C: Energy Harvesters
1. Construct the halfwave 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:
Time (s)

Output (mV)


1 Flip per Second

10

26

1 Flip per Second

20

102

1 Flip per Second

30

61

4 Flip per Second

10

103

4 Flip per Second

20

346

4 Flip per Second

30

603

Time (s)

Output (mV)


1 Tap per Second

10

375

1 Tap per Second

20

430

1 Tap per Second

30

350

4 Tap per Second

10

2800

4 Tap per Second

20

2300

4 Tap per Second

30

3000

2. Briefly explain your results.
We noticed when doing the flips and taps per second, that if you hit it harder at first then not as hard the time after it started to decrease even though it was still being hit. After noticing this, it helped reason why some of our numbers ended up seeming off in perspective to the values before.
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?
There is little to no change in the graph, because the diode only allows the positive part of the wave to pass through and without it the wave ends up canceling itself out.This is because if only a positive input is allowed to effect the output, it can continue to increase the voltage, but if the negative portion of the wave passes through as well the output voltage would have a tendency to make a small increase followed by a small decrease and repeating this in a cyclical pattern resulting in no net gain in voltage.
4. Write a MATLAB code to plot the date in table of Part C1.
Flick Gauge MATLAB Code:
Flick plot:
x=[10 20 30];
y1=[26 102 61];
y2=[103 346 603];
y3=[375 430 350];
y4=[2800 2300 3000];
plot(x,y1,'o',x,y2,'s')
xlabel('Duration (s)')
ylabel('Output Voltage (mV)')
legend('1 Flick per second','4 Flicks per second')
Graph: Flick Gauge Voltages After Different Intervals of Consistent Flicking
Tap Guage MATLAB Code:
Tap plot:
plot(x,y3,'o',x,y4,'s')
xlabel('Duration (s)')
ylabel('Output Voltage (mV)')
legend('1 Tap per second','4 Taps per second')
Graph: Tap Gauge Voltages After Different Intervals of Consistent Tapping
Nice blog this week! I noticed a couple minor differences between our blogs so I figured I might as well point them out to you. For question 1 in part A our negative maximum value magnitude was less than our positive maximum value magnitude. However, the difference between magnitudes for us was much less than it was for you guys and I was curious as to why this was. It seems like that should be the case due to the wave resembling a dampening sinusoid however by that logic it would seems that they should be relatively similar. Also, I believe you put your diode in the opposite direction as us that is why your half wave rectifier is negative
ReplyDeleteFor question one we were having trouble getting a high maximum strength for our readings, which may have resulted in the difference you described. A possibility is that our tapping and flipping methods could have been different. I see what you mean about the diode; it does seem like ours was connected backwards.
DeleteGreat job. I found some slight differences between the two of our blogs. For part a, when using harder pressure we got a lot larger negative values for our minimum. Our max values were also slightly larger than what you guys obtained. Also, our oscilloscope photo for the half way rectifier were a lot different. We didn't obtain any negative values, but it is basically ours flipped around. Overall, great job.
ReplyDeleteFor the half wave rectifier, our diode was backwards, so it appeared to perform essentially the same function, except that it cut out the positive portion of the input voltage.
Deletei think guys you made a good job explaining everything in the blog for this week but i have one question about the first part for the low flipping strength values we got different but it is close to your values but the in the high flipping strength values our values is far away from yours.
ReplyDeleteWe had some trouble getting high values at first, so our method of flipping the gauge may have been inconsistent.
DeleteYou did a great job this week, all of the explanations were very well provided in each part. In part A your voltage values were much higher than ours, and in your oscilloscope picture your halfwave rectifier must have been backwards to only create the negative voltage values. Did you have any problems after that since the voltage values were backwards? Also in part C with the tapping did you have any trouble? We had a hard time getting consistent results with the taps so maybe my fingers were too big for the sensor or the sensor was too small. Great job this week though!
ReplyDeleteFor part A, I would suggest zooming in further on your oscilloscope so it is easier to read the graph not only for your own data, but also for us to compare when we view your blog. For part B, I noticed that your graph was pointed down instead of up. I believe ours was the opposite. You seem to be filtering out the positive wave instead of the negative. This may just be due to your probes being reversed on your readings (or our probes).
ReplyDeleteGood blog post, for our tables we considered flipping/tapping as a single action rather than separate. for part B3 there are two different types of ways to calculate values, depends weather the waves are full or half. Make sure to scale your amplitude and wavelength on the oscilloscopes for better visibility. Great job with your MATLAB plots, one of your flicking graph matched ours.
ReplyDelete