Environmental regulations now require strict reporting of all discharges, with accompanying fines or penalties. However, when plant managers take steps to reduce pollution and discharges, they need an effective way to measure their progress.
At one time, the only option was to use magmeters, which are expensive and not always practical for many open channel installations. Accurate measurement of open channel flow is now not only achievable but simple and cost-effective with the MCERTS approved Siemens OCM III.
When combined with an ultrasonic transducer, it monitors flow and provides data you can use for rainfall / stormwater studies, inflow / infiltration studies and sewer system evaluations.
An extensive data log memory permits logging from 31 days of one-minute entries up to 24 months with daily entries.
Advanced functions include variable data logging. Under normal flow conditions, the OCM samples flow at a pre-determined rate – every 15 minutes, for instance – but it can be programmed to automatically sample at a higher frequency during rapid flow rate changes.
This provides a highly detailed profile of a sudden inflow of effluent into the system or storm water flood conditions. Under steady conditions, the OCM automatically logs less frequently to conserve data log space. It accommodates AC and DC operation, automatically switching to battery operation for uninterrupted power.
With so many variations of weirs and flumes, flow calculations can be complex, but the OCM makes it easy.
It is fully programmed with calculations for all standard primary devices, including Parshall, Palmer-Bowlus and other flumes, various weir configurations, and BS 3680 European standard.
For non-standard weirs or flumes, the programmable head-versus-flow curve (up to 16 points) accurately defines flow rate.
Information can be programmed and downloaded locally by calibrator or PC, or remotely via telemetry. The OCM has two-way communications via RS-232 with a modem for remote or a direct cable for local connection. Data logs can be downloaded with Flow Reporter PC software for viewing logged data, or conversion to spreadsheet format.
After installation and calibration, logged data can be downloaded from several locations without ever leaving the office. It saves time and money while providing important data.
Accurate, verifiable records of flow volumes help users to comply with environmental reporting requirements, track their pollution reduction efforts, and ensure that they are never overcharged for discharge.
David Hewitt is product
manager for level at Siemens Automation and Drives.
T: 0161 446 6400
Tips for effective open channel flow measurement
- Ensure the primary device (weir or flume) is the right type and size for the expected flow rate, and be sure it is installed properly. Discrepancies from the standard design, dimensions, or set-up will adversely affect the accuracy of flow measurement devices. Ensure that it is properly cleaned and maintained. Any build-up of sediment or vegetation can influence flow and flow measurement
- Check upstream conditions that may create waves or surging. Hydraulic jumps, flow pipes or drops in approach pipes located close to the flume can interfere with measurement
- When installing flow measurement devices, follow the installation guidelines in the instruction manual to ensure correct set-up and to be aware of any limitations
- Field calibration of the primary element will tell you if the actual head corresponds to the head-to-flow calibration information supplied by the manufacturer. If not, a new curve can be determined through field testing. This is essential on special applications or non-standard weirs and flumes
- Install the head measuring device in a relatively calm, stable portion of the channel. It should not be positioned in a channel approach that has high velocity of water, turbulence, gates, valves, pumps or a sudden change in section
· Make sure the measurement device has been properly zeroed in reference to the primary device