The compact device solution for non-contact flow measurement in tunnels The VM400 flow velocity measuring device is a compact and space-saving device solution for continuous point-to-point measurement of the air velocity in road and railway tunnels or comparable traffic infrastructure constructions. The VM400 can be assembled easily at nearly any point on tunnel walls. The measured values and status information are transmitted to a monitoring system via the integrated analog or digital interface, as wells as via an Ethernet interface in the VM400E variant.