Orifice meter or orifice plate is a device used for measuring the rate of flow of a fluid through a pipe. It works on the same principle as a venturimeter. It consists of a flat circular plate which has a circular sharp edged hole called orifice. It is an opening in the side or bottom of a vessel or a tank through which liquid will flow under the condition that the liquid surface is always above the top edge of the opening. The orifice diameter is 0.5 times the diameter of the pipe. A differential manometer is connected at section 1 which is at a distance of about 1.5 to 2 times the pipe diameter upstream from the orifice plate, and at section 2, which is at a distance of about half the diameter of the orifice on the downstream side from the orifice plate.