Abstract: A filter assembly, in particular used as a portable service unit for hydraulic applications, has a motor-pump unit (8) with one outlet (14) connected to a filter element (18) in the main flow. Another other outlet (26) of the motor-pump unit is connected to a device for measuring particles in the fluid in a bypass flow having a particle sensor (36). As a component of the device for measuring particles, a fluid line (38) of predeterminable length as a stilling section is on the inflow side of the particle sensor (36) in such a way that gases carried along in the fluid re-dissolve in the fluid. The fluid line (38) of predeterminable length is accommodated in a housing part (52) of the assembly, combined to form at least one winding.