I would like to ask for advice on shielding the following setup.
I have a measurement target sitting inside a Faraday cage, connected through a shielded cable to a measurement circuit. The cable shield would be connected to the Faraday cage. The circuit mainly includes a microcontroller, AD converters and a single op-amp inverting transimpedance amplifier. The circuit sits inside a metallic box connected to the cable shield.
As the instrumentation needs to be battery powered (3.3V), the transimpedance amplifier is referred to the mid-level potential of 1.65V (wrt battery negative terminal) to allow measurement of current flow in both directions. This in turn means that at zero current flow, the measurement sample is at 1.65V wrt the negative terminal of the battery powering the measurement circuit. The analog signal bandwidth to be recorded is on the order of 10Hz-500Hz.
The device would occasionally have to be connected to a desktop computer through a USB interface. Then, the USB ground has to be connected to the negative terminal of the battery, 0V for the microcontroller and ADCs, -1.65V regarding zero transimpedance output.
I have received conflicting advice on how best to shield this circuit, one idea being to connect the shield to 1.65V, coupling the shield to the zero level of the transimpedance amplifier or alternatively, connecting the shield to the battery negative terminal, zero for the digital components.
In either case, a further question is whether the USB cable shield can or should be connected to the metal enclosure of the measurement circuit.
I have read a number of other posts on shielding, mainly as this, this and this, however I have not been able to piece these together for my case. Any help pointing me in the right direction would be much appreciated.