op amp formal lab report

[stealthelectric]

Hi:
I have a formal lab report to write up about op ams.
I chose this subject as this is the topic I have least understanding about and am finding it very hard. It also needs to be handed in on 15th march in the morning. So I'm starting to panic now.
I have written up everything but the discussion of the results but am not sure if it is very good or to the point.
Would somebody be kind enough to look and comment for me please?
I have a word file but can't upload it. I can send to you though. Use this email or send me a notification.
stealthelectric@TempEMail.net
thank you

 

[stealthelectric]

i just realised i can upload a zip
please see attachment

 

[Hero999]

Why not post it here?

No one's going to email you, it defeats the object of a forum which is that everyone can join in and help. Posting your email address online is also a bad idea.

 

[stealthelectric]

yeah I used a temporary email account that only lasts for a 14 days before it deletes itself. I didn't realize I could upload zip files so it's attached to the second post, which I guess you didn't see before you answered my first. Sorry about that.

 

[Hero999]

Sorry, you have posted it, we posted at the same time.


Not everyone has Word or the latest version (I don't) so I opened it in Word viewer and printed it to a PDF using PDF Creator.

I'd say it needs more detail.

What op-amp IC did you use?

You did an experiment with a diode but didn't give the schematic: where did you put the diode in the circuit?

What frequency did you test the circuit at?

There's no time scale on either of the plots.

Show the power supply on the schematic and measure it, the actual voltage may differ from the setting.

Compare the voltages at clipping with the saturation positive and negative satiation voltages on the data sheet.

What was the tolerance of the resistors?

If you know what it is then maybe you can figure out whether the error is down to the resistors or poorly calibrated rest equipment.

Look at the percentage error rather than the absolute error. Hint the results for non-inverting amplifier with a gain of 2 are worse than the inverting amplifier with a gain of 10.

EDIT:
You do realise you can draw a sinewave in spreadsheet program Excel?

It will look better than any sinewave you can draw.

What about taking pictures of the 'scope display? Or do you not have a digital camera at school?

 

[stealthelectric]

HI Hero999

What op-amp IC did you use?
What does the term IC refer to? Is it input current?

Compare the voltages at clipping with the saturation positive and negative satiation voltages on the data sheet.
What is clipping? How do I do this?

What was the tolerance of the resistors?
Nobody has mentioned this during the project. Why is this important and how do I do that?

Look at the percentage error rather than the absolute error. Hint the results for non-inverting amplifier with a gain of 2 are worse than the inverting amplifier with a gain of 10.
Are my errors the difference between theoretical and measured values. I then find percentage error from them?

You do realise you can draw a sinewave in spreadsheet program Excel?
No I didn't. If there is time after I have succeeded in completing the content correctly, I will take a look at that. Thanks.


Unfortunately I didn't draw graphs for the first inverting scope graph when looking at the gain, and so am now guessing the time scale based on the next graph. What do you think? I can't get back into the lab before the report is due either.

added:
-Diagrams of circuits connections for inverting and non-inverting amps and diode connection.
-Set up of circuit connection. The power supply was set to 15V. The signal generator was set to give 2.0V peak-to-peak at a frequency of 1.0kHz, for both types of amp.
- input time scale and voltage to graphs
- created .pdf file

 

[Hero999]

HI Hero999

What op-amp IC did you use?
What does the term IC refer to? Is it input current?

Google it.

Compare the voltages at clipping with the saturation positive and negative satiation voltages on the data sheet.
What is clipping?

See the drawing at the top of page 7 of your assignment.

How do I do this?

I think you said somewhere that the op-amp's output voltage reaches the supply voltage but it doesn't, it never reaches the supply voltage.

You've already partly done it. When the output voltage tries to exceed the supply voltage minus the op-amp's saturation voltage , it stops rising and gets stuck. All you need to do is compare the measured saturation voltage with what's listed on the datasheet.

What was the tolerance of the resistors?
Nobody has mentioned this during the project. Why is this important and how do I do that?

Well you've been asked to explain why the the values you've measured differ from the calculated values?

As I think you've said there's a variance in the component values, this is known as the tolerance. If the results differ more than the tolerance of the component values used in the circuit then, there must be another source of error.

Look at the percentage error rather than the absolute error. Hint the results for non-inverting amplifier with a gain of 2 are worse than the inverting amplifier with a gain of 10.
Are my errors the difference between theoretical and measured values. I then find percentage error from them?

Yes that's it.

Always calculate the percentage error, for example 100mV of error isn't much when the voltage is 20V, but when it's 1V, 100mV is a significant error.

You do realise you can draw a sinewave in spreadsheet program Excel?
No I didn't. If there is time after I have succeeded in completing the content correctly, I will take a look at that. Thanks.

See attached.

Note that I don't have Excel, I saved the file from OpenOffice which is 99% MS Office compatible but that means that some documents saved with it might not open brilliantly with MS Office. I checked the file with MS Excel viewer and it seems all right but just letting you know that if it's slightly scrambled it's not my fault.

Unfortunately I didn't draw graphs for the first inverting scope graph when looking at the gain, and so am now guessing the time scale based on the next graph. What do you think? I can't get back into the lab before the report is due either.

You know the frequency so you should be able to calculate the time scale.

added:
-Diagrams of circuits connections for inverting and non-inverting amps and diode connection.
-Set up of circuit connection. The power supply was set to 15V. The signal generator was set to give 2.0V peak-to-peak at a frequency of 1.0kHz, for both types of amp.
- input time scale and voltage to graphs
- created .pdf file[/QUOTE]

 

[stealthelectric]

The op-amp IC was a tutor kit. I don't have the name of it.
There was no tolerance values of resistors given.
I did some reading last night and update the assignment.

Is this correct for the percentage error for the op-amps?
For the inverting op-amp the error is 0.7V.
Percentage error = 18.6/2 =9.3
0.7/18.6x100=3.8%
0.7/2x100=35%
3.8%+35%=38.8%
0.338x9.3=3.1V

For the non-inverting op-amp the error is 0.1V.
Percentage error = 3.80/2 =1.9
0.1/3.8x100=0.03%
0.1/2x100=0.05%
0.03%+0.05%=0.08%
0.0008x1.9=0.0015V

I may have screwed that up some - not sure.

The power supply voltage on the data sheet was +-15V.
Clipping has occurred at 14.0V on the inverting op-amp, before the connection of diode.
Clipping has occurred at 15.0V after the diode connection. I'm not sure why this is.

Maybe - As the diode starts to draw the current the voltage across RF drops. When the diode is 0.7V, it is now opened and drawing all the current and voltage. So after the diode has been connected the signal clips at max voltage of 15.0V because all the current is being drawn by the diode.
The feedback voltage is drawn to the reverse bias of the diode which blocks it and so the negative voltage now clips at -1.0V

The op-amps saturation voltage is 1.0V. Does this mean that the amplifier is operating somewhere within its linear range and is not saturated until it gets to 1.0V from the input current. So it clips 1.0V from the input voltage?

thanks

 

[Hero999]

The percentage error calculation looks wrong.

%error = 100×error/gain

So if the amplifier's gain is 0.7 less than it should be and the amplfier has a gain of 10:

%error = 100×-0.7/10 = -7%

If the error was positive, the sign would be positive.

As I said before, you'll find that the non-inverting amplifier actually has the greatest %error which is what's important.

The diode should remove all the negative part of the signal below 0.6V

 

[stealthelectric]

thanks hero
but my non-inverting percentage error is lower than inverting.
inverting - %error = 100×-0.7/10 = -7%
non-inverting - %error = 100×0.1/2 =5%

As I said before, you'll find that the non-inverting amplifier actually has the greatest %error which is what's important.
Why is that important?

 

[Hero999]

thanks hero
but my non-inverting percentage error is lower than inverting.
inverting - %error = 100×-0.7/10 = -7%
non-inverting - %error = 100×0.1/2 =5%

Sorry you're right, the inverting amplifier error is greater.

As I said before, you'll find that the non-inverting amplifier actually has the greatest %error which is what's important.
Why is that important?

I hinted on this before.

The problem with electronics and maths, is that sometimes it's often to apply the principles to real life situations. I'll give you a cookery example, then it should become obvious:

I'm making a curry, but I make a mistake when measuring out two of the ingredients:

1) Rather than using 10g of chilly powder I put 20g in.

2) Rather than using 100g of rice I put 110g in.

Which mistake is going to mess up the recipe more? #1 or #2

To put this into perspective both are the same absolute error, in both cases I've added 10g more than I should have, but #1 is a 10% error and #2 is a 50% error.

 

[stealthelectric]

yes. I do like a spicy curry. Thank you Hero