Measurement of waste water subject to treatment with manhole flume

Task
In accordance with plant and legal regulations concerning water pollution control, see “Wasserhaushaltsgesetz” (WHG), waste water subject to treatment must be measured and recorded.

The following measurements have to be applied:

• Direct and indirect discharges into water or in waste water treatment plants for determining pollutants and water delivery (WHG).
• Operational requirements serve for an optimization and analysis of processes, also see self-monitoring ordinance for a self-monitoring requiring records on released waste water.

Solution
A manufacturer specific and geometrically defined flume with a level transmitter serve for a measuring device.

The physical measurand is the water level „h“ within flume’s feed. The measured values are the flow „Q“ and the batch „V“ calculated based on a clear „Q/h“-proportion.

Metrological requirements
Gravity flume requires a “shooting“ or “flowing“ feed in order to obtain a defined condition of flow, i.e. a change in flow in measurement cross-section. In order to keep it free from any influences, free drainage is required in the outlet.
Only under these conditions a reliable measurement is feasible and the Q/h-proportion between measurand “h“ and flow Q = c.hn becomes applicable. The two constants c and n are defined by the manufacturer.