Monday, February 6, 2017

Blog sheet week 5
1.       Functional check: Oscilloscope manual page 5. Perform the functional check (photo).



figure 1.1: Shows the functional check of oscilloscope probe



We verified that the oscilloscope probe was functioning correctly here above.

2.       Perform manual probe compensation (Oscilloscope manual page 8) (Photo of overcompensation and proper compensation).



figure 2.1: Photo of proper compensation



figure 2.2: Photo of overcompensation


When manually compensating the oscilloscope probe we were able to properly compensate the probe and also show what it looks like when we overcompensate.

3.       What does probe attenuation (1x vs 10x) do (Oscilloscope manual page 9)?

     The probe attenuation affects the vertical scale of the signal. 1x limits the bandwidth of the oscilloscope to 7Mhz while the 10x setting allows the full bandwidth of the oscilloscope to be used.

4.       How do vertical and horizontal controls work? Why would you need it (Oscilloscope manual pages 34-35)?

The horizontal and vertical controls allows adjustments of the scale of time and voltage. There is a vertical knob for each channel and one knob to adjust the position horizontally. There is also a horizontal scale knob to adjust the time frame of the signal. If a signal had a very short period you may need to shorten the time frame horizontally to view the signal. 

5.       Generate a 1 kHz, 0.5 Vpp around a DC 1 V from the function generator (use the output connector). DO NOT USE oscilloscope probes for the function generator. There is a separate BNC cable for the function generator.
a.       Connect this to the oscilloscope and verify the input signal using the horizontal and vertical readings (photo).



figure 5.1:horizontal and vertical readings on oscilloscope


We can view the horizontal and vertical readings on the oscilloscope and make adjustments on the scaling as well.

b.       Figure out how to measure the signal properties using menu buttons on the scope.

We pushed the autoset button to track the signal. Then adjusted the vertical and horizontal settings to get a good view the of the signal. Also note that we adjusted our function generator to .4V pp.

6.       Connect function generator and oscilloscope probes switched (red to black, black to red). What happens? Why?

When hooking the probes backwards the voltage signal is very low because the signal connected to ground and the ground is connected the signal measuring connector.

7.       After calibrating the second probe, implement the voltage divider circuit below (UPDATE! V2 should be 0.5Vac and 2Vdc). Measure the following voltages using the Oscilloscope and comment on your results:

a.   Va and Vb at the same time (Photo)


figure 7.1: Measuring ac voltage with oscilloscope at Va and Vb at the same time

Note that our amplitude was 1Vac with 2Vdc offset in our measurements.
b.   Voltage across R4.

The voltage across R4 was about 73.6 mVac peak to peak with an rms value of 25.0 mVac. Note that our function generator was set to 1Vac with 2Vdc offset in our measurements. 

8.       For the same circuit above, measure Va and Vb using the handheld DMM both in AC and DC mode. What are your findings? Explain.

Measuring with the multimeter we achieved .480Vac and .2.71Vdc on Vb. On Va there was .480Vac and 2.71Vdc. The multimeter gives the correct voltage reading because it is not grounded like the oscilloscope. There should be equal AC and DC at each point because the resistors have equal resistance and they are in series.


9.       For the circuit below
a.       Calculate R so given voltage values are satisfied. Explain your work (video)


Video 9.1 Shows how to calculate R7 using voltage divider

We had to convert the 2 Vac pp to rms value first, which is about .71 V rms. Then we knew that R7 consumed the other 4.29 V rms. Since R7 consumed about six times as much voltage as R6, we calculated R7 to be about 6K ohms.

b.       Construct the circuit and measure the values with the DMM and oscilloscope (video). Hint: 1kΩ cannot be probed directly by the scope. But R6 and R7 are in series and it does not matter which one is connected to the function generator.






Video 9.2: measuring R6 and R7 values with the DMM and oscilloscope.

We are just verifying our calculations from the problem above using the DMM and oscilloscope.

10. Operational amplifier basics: Construct the following circuits using the pin diagram of the opamp. The half circle on top of the pin diagram corresponds to the notch on the integrated circuit (IC). Explanations of the pin numbers are below:
1: DO NOT USE
8: DO NOT USE
2: Negative input
7: +10V
3: Positive input
6: output
4: -10 V
5: DO NOT USE

a.       Inverting amplifier: Rin = 1kΩ, Rf = 5kΩ (do not forget -10 V and +10 V). Apply 1 Vpp @ 1kHz. Observe input and output at the same time. What happens if you slowly increase the input voltage up to 5 V? Explain your findings. (Video)



Video 10.1 Shows our connections of an inverting amplifier

When we slowly increased the voltage on the function generator, the V out of the amplifier was changed from a sine wave to a digital signal (dc voltage).

b.       Non-inverting amplifier: R1 = 1kΩ, R2 = 5kΩ (do not forget -10 V and +10 V). Apply 1 Vpp @ 1kHz. Observe input and output at the same time. What happens if you slowly increase the input voltage up to 5 V? Explain your findings. (Video)

Video 10.2 Shows the connections on non-inverting amplifier

When we increased the input voltage on the non-inverting amplifier, we did not get a change  from a sine wave to a digital signal on the output this time. We believe there was an error in the connections because our output had a digital signal regardless of increasing or decreasing the input voltage.

11 comments:

  1. I really like your blog. It is easy to read, and I like how you added a figure number along with a description under your photos instead of just a description. I also like how you explained how you found R7 in 9a it was easy to follow. My group got the same answer, and the rest of our data matches with yours as well.

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    1. Thank you we are glad you like our blog.

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  2. For Question 6, we did not even get a reading for when we switched the black to red and red to black for the Oscilloscope. It might be because we had a realitivly low voltage from the function generator, not sure how your voltage compared so cant make that conclusion with assurance.

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    1. I guess so. That is why we said that the voltage was very low because the signal connected to ground and the ground is connected the signal measuring connector.

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  3. For number 6, why does connecting to the ground make the reading zero; you could expand on this more. Also, why do you think you obtained the measurements you did for Va and Vb in number 7, and how do these values relate to the value of the voltage drop across R4?

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    1. As I said toLima Mitchell, we just tried to keep the answer clear without expanding and make it confusing. Anyway, you could be right and we will take note for next time especially in questions like #7 to make it more clear.

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  4. Expand more on your answers, explaining your observations helps us as well as yourselves understand what is happening. For #7a the formatting is a little funky. Good job on #10, next time just show your oscilloscope's display, we might be able to help in the comments. Either way you explained their functions pretty well, I'd have to say this lab was pretty difficult.

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    1. I agree the lab was pretty difficult. We just tried to keep the answer clear without expanding and make it confusing, but you are right it might help.
      Thank you.

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  5. For number 3 I read that there is 1Mohm of resistance in the oscilloscope and 9Mohm in the probe. Switching the probe on and off just switches it from 1M to 10M and that is how it works. I’m not sure if that is 100% accurate, but was curious if you read that anywhere? For number 4 I said that these adjustments allow you to compare multiple graphs to each other by lining them up. For number 6 did you experience a crazy static graph? Ours was not just a flat 0V line. Our graphs for number 7 seemed to be the same. I would suggest making your photos larger so it is easier to see the details when viewing the blog. It would also reduce white space.

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    1. We are not really sure as well about question #3, but that what we got. As I see there are many differences between one group to another in graphs. If you click twice on the photos it will make it bigger then you can see better.
      Thanks.

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