Abstract: Blood component processing systems and methods are adapted to be coupled to a blood component processing device. The systems and methods employ a fluid circuit comprising at least one fluid pressure actuated pump station, at least one fluid flow path communicating with the pump station, and at least one valve in the fluid flow path. A control module sized and configured to interact with the fluid circuit includes an actuator to selectively apply fluid pressure to the pump station in concert with operation of the valve to pump fluid through the fluid flow path in response to a control program. A circuit board assembly is associated with the actuator in electrical conductive interaction with fluid in the pump station. The circuit board assembly comprises a part of a capacitive sensing circuit. The circuit board assembly can comprise, e.g., a printed circuit board assembly, or a flexible circuit, or a molded circuit. The circuit board assembly can, e.g.