Â­TÂ­here are many different ways to create a motion sensor. For example: 1  It is common for stores to have a beam of light crossing the room near the door, and a photosensor on the other side of the Â­room. 2  When a customer breaks the beam, the photosensor detects the change in the amount of light and rings a bell.
Definition of weir. 1  1 : a fence or enclosure set in a waterway for taking fish. 2  2 : a dam in a stream or river to raise the water level or divert its flow.
A weir is a device for measuring flow in an open channel flow. Weirs are frequently used for flow measurement in open unpressurized channels such as wastewater systems and sewers.Weirs and flumes can be used to measure flow in open channels such as plant effluents or sewage flows.A weir is a device for measuring flow in an open channel flow.