unfortunately i couldn't find the AD620 here in my city's shops.

I guess 3rd world countries do not have modern good electronic parts.

 

Hello,

@ Audioguru,
You do not have to be grumpy when the OP can not get the part.
We all live in the same world.
Some have more well assorted shops than others.

Bertus

 

Mangrio,

Post a screen shot of your original non-working simulation. The original schematic has no errors and while it is not up to contemporary standards, it does work.

Dear JoeJester

here is the my orignal schmatic IS.

and one thing more... i have considerd below link much for the circuit, plz also have look on this link too
http://www.ee.latrobe.edu.au/~gt/ele2emi/Labs/lab5-instr-amp-2007.pdf

 

I guess 3rd world countries do not have modern good electronic parts.

very right

 

Hello,

Is the current setup to measure the common mode rejection?
If the common mode rejection is good there will be no signal at the output.

Bertus

 

Bertus gave you a link in his first response. Did you review that link, especially the signal generator called CMR and V1?

Also, in your original diagram, you did not follow the directions in the Lab per the schematic. U3A's inputs are 180 out. Pay attention to Vdd and Vss. They are not + and - 5 volts.

Review the link bertus gave you in his first post of this thread.

 

An IA is a differential amplifier. An ideal IA will only amplify the difference between the inputs. In your test setup you have the same input hence zero voltage as output. I have modified your test setup.
Despite what other poster have mentioned. You can build it using LM324. It will lack performance, and accuracy compared to a real IA. But it would be OK in a school assignment to test the principals. Remember to mention the problems then building your own IA in the report. And do not use this approach in any real life project
http://www.intersil.com/data/an/an1298.pdf

 

Sorry for late reply... because my semester exam are going on....


thankx to , tnk, bertus, audioguru, to6afre, joejester and who have participated...


Dear all I have gone through your all suggestion like as,

*Different inputs
*low voltage
*and all


now I have changed the circuit diagram as you have suggested

according to Robert pynter in "Introductory Electronics Devices and Circuits": 4th Edition

IC U1A & U2A are non-inverting op-amp and U3A is differential Amp. [pg:712]


so I have applied different inputs on v1 and v2, so that the third IC get the different input (whereas third IC is differential amp; if same input, output will be zero)

here is function generator setting and output at oscilloscope.

one thing more that when I change Rg (resistor gain) it doesn't show any major difference in output :S

now what should I do ????
why clipping occurs in output??
if we suppose don't take the clipping still same result as input is given. why not amplification???

 

I don't know what you are doing, but here is my results.

 

Follow the B input on XSC1. It has shorted/connected together R4/R5 since you find a red dot at both interceptions. Also I think the B input should be grounded. The whole XSC1 setup looks strange

 

I tried your design

My output is ;

​

 

If you left the B input of the oscilloscope open, then that may be your problem. It needs to be connected to circuit ground.

 

Try this as I have done in the picture. Note the polaraty for the sine sources. I used 0.25 volt as amplitude

 

done it) but please explain that ... why input amplitude at U3A at inverting pin is higher than output and non-inverting is lower than output...

Is this because of differential amplifier ... ????

here it is ..........

 

If you left the B input of the oscilloscope open, then that may be your problem. It needs to be connected to circuit ground.

that circuit has also connection error too.. I have plced wire connection before resistors mistakenly....

 

Mangrio screams:
I tried your design

My output is ;

Looking at your oscilloscope, you are attempting to see a 110 mV peak signal on the 5 Volt scale. To make it confusing, you've added a negative 4 volt bias by having your offset at -0.8 (y position).

Your Oscilloscope displayed the proper output.

Had you set the scale to 50 mV/div and zero offset (y position), you would have been closer to what I displayed.

Your errors stemmed from your inexperience with using an oscilloscope or your failure to calculate the expected output for the circuit, or a combination of them both.

Screaming does not attract the attention you desired, in fact, it will be detrimental to your goals.

 

Dear joe my .. have a look on this and tell me that it is right or has some mistakes

oscilloscope setting

Timebase=1ms/Div
Channel A=100mV/Div
offset=0

 

Ok ....

Ask yourself what am I measuring. If your measuring the input signal that is a common mode voltage of 5 V peak and the actual signal of 10 mV peak, you will not see the 10 mV signal as the 5 volt signal dominates. You will see it if the 10 mV peak was about 500 mV peak, but, your lab doesn't require that level. Your oscilloscope vertical will be at least 2 V / cm for viewing a 5 V signal. The offset is used when you want to have two different "zero reference" lines, in which case, you could view two signals each with their own vertical scales.

Attached shows the Input (Vi) which is the 10 mV 10 kHz signal riding on the 5 V 1 kHz signal. Note you do not see the 10 mV signal. The zero reference is two cm above centerline and the scale is 5V/div.

The output signal (Vo) is the 10 kHz signal. The zero reference is two cm below the centerline and the vertical scale is 100 mV/cm. If you look closely, there is a slight bias as the signal does not appear equally above and below the zero reference, however, the signal is approximately 210 - 215 mV peak to peak or 107 mV peak. That agrees somewhat with the x11 gain you (10 mv * 11 = 110 mV), but remember the LM324 doesn't perform as well at higher frequencies.



You must adjust the scales according to what you are expecting. That is why you don't see some signals (straight up and down lines) as you are overdriving the o'scope's display. I've done measurements like that, but, I was looking for "slight" deviations in the nanosecond region.

If your going to add multiple scope readings from various points in your diagram, it would be best to remove the oscilloscope from your report and just title each display independently.

 

Thaknx dear, but I am not getting that ... because you are only taking input from V1 test point.

Dear couldn't understand that why I cant see the 10mv riding on 5v ?

plz explain ??

and please will you tell me that which simulation software are you using.... I aslo try this on that software.

 

I think your simulation software doesn't know that a lousy old LM324 opamp has pretty bad crossover distortion: