Blog sheet Week 11: Strain Gauges
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 1.1:
Strain gauge characteristics
Flipping
strength

Minimum
Voltage

Maximum
Voltage

Low_{}

 1.36 V

3.52V

High_{}

1.44 V

5.92 V

Photo 1.1 Low Flipping strength graph.
Photo 1.2 High Flipping strength graph.
Table 1.2:
Strain gauge characteristics
Tapping strength

Minimum
Voltage

Maximum
Voltage

Low_{}

4 V

29.6 V

High_{}

12.2 V

56.8 V

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.
Table 2.1: Strain gauge characteristics
Flipping strength

Minimum Voltage

Maximum Voltage

Low_{}

 1.28 V

10.4 V

High_{}

1.4 V

16.4 V

Table 2.2: Strain gauge characteristics
Tapping strength

Minimum Voltage

Maximum Voltage

Low_{}

2.8 V

1.8 V

High_{}

12 V

8 V

Photo 2.3 Low Tapping strength graph.
Photo 2.4 High Tapping strength graph.
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.
Photo 1.1 Outputs Reading.
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) values

Calculated

Measured

Input

3.54 V

3.689 V

Output

2.5 V

2.6 V 
3.
Explain how you calculated the rms values. Do
calculated and measured values match?
(Peak to Peak Voltage)/(2*sqrt(2))
4. Construct
the following circuit and record the output voltage using both DMM and the
oscilloscope.
Oscilloscope

DMM


Output Voltage (pp)

2.16 V

1.78 V

Output Voltage (mean)

3.01 V

0.63 V

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

DMM


Output Voltage (pp)

.08 V

.028 V

Output Voltage (mean)

3.38 V

.011 V

Part C: Energy Harvesters
1.
Construct the halfwave rectifier circuit
without the resistor but with the 1 ÂµF 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

.65 V

1 flip/second

20 seconds

1.44 V

1 flip /second

30 seconds

3.46 V

4 flips/second

10 seconds

5.4 V

4 flips/second

20 seconds

6.5 V

4 flips/second

30 seconds

8.6 V

2. Briefly
explain your results.
As we tapped at 1time/sec the voltage would climb very slowly, but as we tapped 4times/sec the voltage would climb very rapidly and partially though the 30 second cycle it started to drop and then climbed rapidly through the rest of the cycle up to a much higher voltage than the 1 tap/second.
As we tapped at 1time/sec the voltage would climb very slowly, but as we tapped 4times/sec the voltage would climb very rapidly and partially though the 30 second cycle it started to drop and then climbed rapidly through the rest of the cycle up to a much higher voltage than the 1 tap/second.
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 leave the diode out of the circuit the output of the circuit would look more like a sine wave because you would see the negative and positive values from the capacitor. So the voltage would oscillate between negative and positive.
If we leave the diode out of the circuit the output of the circuit would look more like a sine wave because you would see the negative and positive values from the capacitor. So the voltage would oscillate between negative and positive.
4. Write
a MATLAB code to plot the date in table of Part C1.
close all;
x = [10 10 20 20 30 30];
y1 = [.65 5.4 1.44 6.4 3.46 8.6];
plot (x, y1)
grid on
xlabel('Time (s)')
ylabel('Vout (v)')
Graph 4.1 Voltage output of tapping strain gauge
For Question 1 A, we first had a very similar reading for our high output for the flipping gauge, but then we retested it and got very different values even though we tried to keep it as the same strength as the first one, did you happen to retest one of them as well and have the same outcome of an exceptionally larger value?
ReplyDeleteNo, we haven't retest any of them. I think if you retest anything you are not going to get the same results because I guess it is really sensitive.
DeleteThanks.
nice blog i think guys you made a very good job this week in part b #1 i thought we made a wrong thing in the circuit and the graph that we came up with is wrong but when i see yours i realize that we get the same thing with you.
ReplyDeleteI am glad that we got the same thing. I hope it is right.
DeleteThanks..
For part B 3, does this formula work for the input rms and the output rms or just one? Like my group, there was a small difference between your calculated and measured values for this part. What do you suspect the reason for this difference is?
ReplyDeleteI would suggest adjusting the vertical scale on your oscilloscope to make it easier for you to view your data and also to make it easier for us to see your graphs on the blog. On your half have graph, it is helpful to show the input voltage for comparison. Check out our blog to see what I am talking about. I do not think it is a requirement, however. Your matlab graph is confusing to me and I am unsure if you had the right axis or data. However, I have not done that part yet so I am not sure if I am right about this.
ReplyDeleteI recommend you explain the equation in B3 a little more, there are two different equations: 1 being for a halfwave rectifier and the other for full wave. Also for the last MATLAB plot, you should have two lines to plot the data rather than 1 (x being duration, y1 & y2 being the tap frequency.)
ReplyDelete