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.
Definition of backflow preventer. A backflow preventer is a check valve installed on potable water supply piping to prevent possible contamination of the water supply system by backflowing but contaminated water from the building into the outside public water supply mains.