Pulsar Ultrasonics boost confidence
11 August 2005, News release from Pulsar Process Measurement Ltd
Derby Sewage Treatment works is the major works for the city, with a capacity of 500,000 population equivalent. Raw sewage comes into a transfer pumping station, from where it is distributed to the process.
The large pumps in the 10m deep sump have a combined capacity of around 6000 litres per second. The control system incorporates a number of float switches that have been prone to severe "ragging-up". Even in normal circumstances the task of cleaning the float switches is difficult and unpleasant, with a proposal made to introduce davits to allow the floats to be winched out of the way for maintenance.
There is no consented emergency overflow near the works resulting in flooding of land with raw sewage were the pumping station to fail. Severn Trent Water's commitment to protect the environment and serve the community dictates that the pumping station and the components used must be robust and reliable.
Having originally tried a different manufacturers ultrasonic system, the results were disappointing and left the company with no confidence in the units ability to cope with the conditions. After a trial of the alternatives, Severn Trent installed a Pulsar non-contacting ultrasonic level measurement system, teaming the company's "Advanced 120" control unit with their dB15 transducer. The only available position for the transducer requires a reliable signal to be obtained from a position between two of the pump heads.
The tight beam angle and high power of the dB15 made sure that strong echoes were achieved from the area, while Pulsar's DATEM echo processing handled the analysis of the echo profile, zeroing in on the true level while ignoring competing signals from pump heads, girders and the like. An extra complication on this site is that the surface of the sewage can be very foamy.
The Pulsar system has proved so successful that confidence in the ultrasonic measurement system has been restored to the point that the site is in the process of removing the majority of the float switches altogether, the intention to make this a maintenance-free system. Staff time can be devoted to more productive tasks.
For further information please email Pulsar Process Measurement Ltd