Here is a datasheet to an IA that I have used. Note the wierdness of the output and the reference.
https://www.electro-tech-online.com/custompdfs/2011/01/AD625.pdf Here is another IA
https://www.electro-tech-online.com/custompdfs/2011/01/AMP02.pdf
Here is a differrential amplifier IC.
https://www.electro-tech-online.com/custompdfs/2011/01/dn454fa.pdf
Note the big difference. The output of a differential amplifier is differential, the output of an IA is single ended.
This is similar to a couple of devices:
The BALUN transformer used for Coax to twinlead applications.
And balanced (XLR cnnectors) to unbalanced audio signals RCA. You can transmit audio signals a greater distance without noise using the balanced method. Any signal picked up from the environment will be cancelled.
For reference:
Twisted pair cable tends to resist inductive coupling.
and
Shielded cable tends to reduce RFI. For process signals the shield is grounded at the signal source only to avoid ground loops.
I added some extra stuff here and I hope I didn't confuse you.
I think we are confusing "difference amplifier" and "Differential amplifier" and IA's. I too am now seeing somewhat of a blur. Because of "differential probes for oscilloscopes", "Differential operation of a 2 channel scope (A-B mode)", and Instrumentation amplifiers. There is even somthing called pseudo differential amplifiers. The A-B operation of a scope is indeed pseudo differential because it contains a ground.
True differential amplifiers wound not require a ground. This can get complicated too because some require a bias return path.
I'm getting really confused.
If i have 5v and 5,1v into a DA what will it then gain?
would be either (5-5,1)*A or (5,1-5)*A where A is the gain of the amplifier.
Where common mode comes into play is say when a low level signal is transmitted where 50 or 60 Hz power is found. If the signal is transmitted differentially and received differentially, the 50 Hz noise nearly goes away. If it's received in a differential fashion, the noise of the 50 or 60 Hz is typically attenuated.
My head hurts.