Abstract: A single jet liquid meter includes a measurement chamber connected to an injector and an ejector and equipped with a turbine having a plurality of blades, two consecutive blades being disposed at an angle .beta., the measurement chamber having two end walls opposite to each other and perpendicular to the axis of the chamber, one of the two end walls being constituted by a plate equipped with an even number of ribs, n, greater than four, projecting in the chamber and equally distributed in two sets, two consecutive ribs of the same set being disposed at an angle .alpha. which is determined by the following conditions: .alpha.=(I+2/n).beta./(n/2-1) and (n/2-1).alpha.<90.degree., where I is an integer value greater or equal to zero.

Abstract: An apparatus for monitoring the state of operation of lamp (2) in a public lighting network is provided comprising a sensing unit (6) associated with each lamp (2) for measuring the voltage of and luminous flux emitted by each lamp (2). Each sensing unit (6) also calculates the efficiency of lamp using an efficiency index given by the gradient of the line which, in a Cartesian diagram in which the voltage of the lamp is the x-coordinate and the flux the y-coordinate, represents the instantaneous relationship between the parameters.