I am building a 3 phase power logger with the ability to measure 3-phase AC and 2 DC inputs as well for a final year project. A typical application would be measuring a small inverter for a solar application on both the AC and DC sides. I am using CT's and a burden resistor for AC currents, a hall effect sensor for DC currents, and simple voltage dividers to bring down the AC and DC voltage to within the range of the ADC. I am using a 12 channel single ended ADC with simultaneous sampling. Sampling the voltage and currents for each phase simultaneously and sending it via I2C to a raspberry Pi where all the calculations etc. is done.
My problem is that the ADC only takes voltages from 0 - 2.5 V as analog inputs. All my signals are voltage signals that ranges from -V to +V. So my signals need to be scaled down and lifted with a DC offset. I have found a couple of ways in doing it but would like some advice. Another thing is that I've read that a Low Pass filter needs to be added before the analog input to eliminate aliasing effects etc. So I need to shrink voltage, add a DC offset and a low pass filter.
I would want to capture at least 30 harmonics for a 50 Hz AC signal so the filter needs to let those through. I simulated a simple 3 resistor voltage divider network that lifts and shrinks the voltage to the correct level but will it work on all the frequencies and is it reliable? and where do I need to place the filter, cause the moment I add a filter the wave-forms change, do I need to add Op-amp buffer between the divider network and the filter? Is it best to use a op amp for the low pass filter?
I've added a picture of my suggested circuit.
Any advice would be highly appreciated. Thank you