A stainless steel weir box to measure industrial discharge.  Weir boxes have great flexibility when it comes to how flow comes into / leave the box.  Here the inlet piping if offset from the centerline of the weri box.  To help normalize the flow, a baffled off area is used - over which the ultrasonic sensor is mounted.

Stainless steel is a popular option for weir boxes measuring industrial flows, although fiberglass weir boxes are also used.