I have built a signal amplification unit on a protoboard so that I can read the signal coming from each of 4 pressure transducers (see pic). The plan is to move everything to PCB boards as soon as possible. I am trying to understand how the COM port on my power supply functions, with the goal of eventually building my own separate 15V power supplies for each unit (to eliminate signal bleed between pressure transducers). Any insight is appreciated. Background: I initially had the system connected to a 2-port power supply (see pic), but the unit would not function correctly without grounding the OpAmps and pressure transducers. I also tried grounding everything to earth and that also did not work. Eventually, I switched to a 3-port power supply and grounded everything to the COM terminal, causing everything to work beautifully aside from a little signal bleed across the transducers. I'm still a little fuzzy on why the common terminal works for grounding my unit, but the ground terminal does not work. I have not yet been able to locate a clear schematic showing where the COM port attaches to inside the power supply. Thanks in advance for any comments or suggestions!