Acoustic Signals Measurement: A non-intrusive measurement principle that uses sound waves to determine velocity.

Alarms: Indication of faults within the channel, such as high flow, low flow and high differential.

Automatic Gain Control: Monitor the receive signal and perform an adjustment based on the signal quality.

Automatic Gate Control: Primarily used for water treatment works, a 4-20 mA output drives the gate to control the flow into the channel.

Flowmeter: An instrument used to monitor, measure and/or record the flow rate of a fluid.

Flow Comparison: Determination of differential flow from two flowmeters in the same channel.

Flume: A flow measurement device formed by a constriction in the channel.

Master & Slave Flow Measurements: In this configuration, two flowmeters (a master and a slave) are used to measure differential flow; additional analog outputs and alarm relays are used to enable preventive action if flow exceeds thresholds between the two meters.

Multi-Drop Transducers: Daisy-chainable devices that enable connection of four ultrasonic transducers to a single cable.

Multi-path System: A flowmeter using up to eight pairs of transducers that provide eight parallel acoustic paths; known to increase the accuracy of the measurement.

Penstock Protection: A valve that operates to shut the system down or stop the incoming flow.

Profile: The shape of the channel.

Shaft Encoder: An incremental device that measures level using a float.

Smart Transducer: A microprocessor-based device that provides a better signal to noise ratio.

System Protection: To alleviate a pipe burst, the flow is stopped at the inlet of the channel; also used to monitor high flow rates that could damage instrumentation such as turbines.

Transit Time: The time of flight difference between an ultrasonic pulse sent in the flow direction and an ultrasound pulse sent opposite the flow direction; measures the average velocity of the fluid along the path of the ultrasound beam.

Velocity x Area Measurement: Velocity times the cross-sectional area yields a flow rate that can be integrated into volumetric flow.

Velocity of Sound: The speed of sound in water.

This glossary of terms and definitions was contributed by Andy Kenworthy, a regional manager at Thermo Fisher Scientific (www.thermo.com). Thermo Fisher manufactures a range of flowmeters, including open channel, ultrasonic, turbine and positive displacement.