The viscometer comprises a vibratory transducer with at least one flow tube for conducting a fluid to be measured and for producing friction forces acting in the fluid. To vibrate the at least one flow tube, an excitation assembly is provided, which in operation is traversed by an excitation current. To generate the excitation current and a viscosity value representing the viscosity of the fluid, the viscometer includes meter electronics which are connected to, and supplied with electric power from, a two-wire process control loop. The meter electronics feed a viscosity signal corresponding to the measured viscosity value into the two-wire process control loop. The viscometer is suitable for measuring a fluid flowing in a pipe, particularly in potentially explosive atmospheres.