The frequency of the sensor is proportional to the velocity of the fluid and is amplified and converted to a 4-20mA output signal. A vortex technology meter has no moving parts to jam and its bright LED displays flow in either liters or gallons. It can measure flow in either direction and can be used with non-viscous, clean or dirty water-like liquids. Pricing starts at $402.Omega Engineering Inc.www.omega.com203.359.1660