Hi,

I used INA111 instrumentation amplifier with gain 100 , and the Vin+ and Vin- has 2.6 degree phase shift , the difference (Vin+ - Vin-) shown by oscilloscope is 120 Vpp.The output of the INA111 is 4 Vpp after gain of 100, meaning the difference Vin+ - Vin- is 4/100 = 40mVpp .

The INA111 gain works good when the Vin+ is any AC voltage and Vin- is grounded(no phase change).

Could anyone say what is correct at difference in input (scope-120mVpp or INA_Gain-40mVpp) ?
I have attached the scope image.Thank you.

 

Is oscilloscope shows wrong value or the calculated one?
Which is correct and why?

 

V2pk-pk = 860 mV
V1pk-pk = 840 mV

V2pk-pk = 120 mV

Your scope should be on infinite persistence because you have significant
noise as evidenced by the V1pk-pk - V2pk-pk

Or BW limit V1 & V2 in order to get meaningful data.

Does the scope have individual samplers on each channel, or is it
shared, that compounds error in noisy environment.

Regards, Dana.

 

Thankyou, so noise is the culprit here.

Means then 4Vpp / 100 = 40mVpp should be the I/p voltage difference,right ?