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.
Waste weirs were often located near feeders that might carry flood waters into the canal, and they often emptied into existing streams. This waste weir was located in the town of Sweden, near Brockport. Similar to a dam, the central section of this waste weir is a three-part spillway with a towpath running above it.