GLOSSARY
Aeration: air gap between nappe and weir.
Beam angle: angle between the opposing one-half power
limits (–3 dB) of the sound beam
Blanking: zone in which received echoes are ignored.
Crest: the edge ( sharp-crested weir ) or surface
( broad crested weir ) over which the flow passes.
EEPROM: electrically erasable programmable read only memory.
EPROM: erasable programmable read only memory.
Flume: a 3 part hydraulic structure, consisting of converging,
throat and diverging sections, to constrict the flow
through the throat, thereby increasing the head in the
converging section. The change in head is
proportional to the change in flow.
Free flow: downstream liquid level is low enough or the
discharge flow is fast enough, so as not to
impede flow through the flume or weir.
Gauge well: same as stilling well.
Head: liquid level above zero ( static ) reference level.
LCD: liquid crystal display.
Max head: head at maximum flow rate.
Measurement: each time a transmit pulse or set number
of pulses is sent to the transducer.
Nappe: the jet of liquid leaving the weir crest.
OCM: open channel measurement
Primary measuring device: hydraulic structure of an open channel
for measuring liquid flow. e.g. weirs and flumes.
Ringing: the inherent nature of the transducer to continue
vibrating after the transmit pulse has ceased.
Secondary measuring device: any instrument for measuring the head or flow
related to the primary measuring device.
PL-443 10 – 2
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