Capacitor coupling in high common mode noise enviroment

I’m designing an 8 channel analog data acquisition system that will operate in an industrial plant. The analog input signals will be jumper selectable for either ±10V or ±20ma. Typical input will be from various transducers (DC) and I anticipate common mode noise will be present. The analog input section will be isolated from the digital portion of the circuit with an isolated DC-DC converted and opto-isolators for the serial lines.

My question relates to the NG ground point for C1 and C2. NG will be common for all 8 channels. Am I better off connecting NG to chassis (earthed) ground or to the floating and isolated Analog ground?

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