What are the differences between venturi and orifice plate flow measurement?

Venturi meters have a gradual converging inlet and diverging outlet, causing lower permanent pressure loss (10-15% vs 50-80% for orifice) and are better for high flow rates and dirty/slurry flows. Orifice plates are simpler, cheaper, and easier to replace but cause higher pressure loss and are susceptible to wear and deposits. Both use differential pressure principle; venturi has higher initial cost but lower operating cost for continuous high-volume applications.