I'm trying to measure a low frequency (0.1 - 100 Hz) signal with an ADC module. After powering the sensor up the signal can have common mode voltage from -15 V to +15 V and is tuned manually (the mechanical part of the sensor). The problem is that the ADC inputs can withstand only +/-10 V in unpowered state.
I want to add some buffer op-amp with +/-10 V supply to protect the ADC, besides this particular ADC module has no internal anti-aliasing filter, so op amp will work as 2-order LPF. The op amp itself will be protected with a pair of BAS85 diodes to rails and a current limiting resistor on the filter's circuit input.
The situation that I'm most concerned about is when the signal source is powered first and op amp is unpowered. As far as I understand the sensor will be charging op amp's supply's output capacitors via current limiting resistor and one of two diodes, depending on the common mode voltage polarity and can theoretically charge them to more then +/-10 V.
The solution that I came up with is to add a small reed relay between the signal source and the filter circuit. After powering the op amp up relay closes with a small delay provided by simple circuit.
So my question is: are those precautions really necessary and will the solution I described above work properly?