A spiral wound assembly including a pressure vessel including an inner chamber, feed inlet, concentrate outlet and permeate outlet and a spiral wound membrane module located within the inner chamber of the pressure vessel; wherein the assembly is characterized by including: i) a flow restrictor comprising: a first and second plate in sealing contact with one another; and a fluid channel located between the first and second plate and including a first end in fluid communication with at least one of the concentrate outlet and the permeate outlet, and a second end adapted for discharging fluid from the spiral wound assembly; and ii) a sensor sheet comprising at least one sensor element located between the first and second plates and in contact with the fluid channel, wherein the sensor sheet is adapted for measuring a property of fluid passing through the fluid channel.