An in-situ sensor system and method which measures the density of a liquid accurately with pressure sensors by measuring pressure in the liquid at two separate positions defined by a fixed distance. Initially data is received on a frequency channel at a CMTS, specifically an upstream receiver, and by a narrow bandwidth detector, connected to a processor also used by components in the CMTS. A plurality of valves are disposed in valve openings in the housing. Due to the high impedance control circuit, an exclusive terminal for high impedance control is not necessary. The arithmetic unit includes a multiply adder and a non-restoring divider.