What is a 'quiet ground' / 'Ground plane'
I'm not sure I understand how you set up your ground noise measurement. To me it sounds like you have this:







simulate this circuit &ndash; Schematic created using CircuitLab

If this is what you're doing, you are not measuring the noise on the ground node of the in-amp circuit; more likely you're measuring emi pick-up from the two leads connecting the circuit under test to the DAQ.

What you probably want to do (although it won't distinguish ground noise from other noise in your system) is connect the negative input of the DAQ to the in-amp circuit's ground, and the positive input to either the input or output of the in-amp circuit. This will give you an idea what kind of noise is present in the circuit. But be aware that if the input bandwidth of the DAQ system is not the same as the bandwidth of the in-amp circuit, you still won't be seeing exactly the same noise as will be present in the final system you're designing.


  Is this a Quiet ground?


A "quiet ground" basically means there shouldn't be any large currents flowing through the ground, particularly between the amplifier and whatever sensor/device it is amplifying. For example, switching currents from switching power regulators (and probably you should prefer a linear regulator for the in-amp's supply), or ground currents of any microcontroller or large digital circuits shouldn't be routed near the in-amp circuit.