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Pulsar Process Measurement Ltd design, manufacture and market level, volume, open channel flow, pipe flow and pump control instrumentation. Our company specialises in non-intrusive measurement, and our technology is used in a wide variety of industries and applications worldwide. By concentrating on the development of ultrasonic level measurement, we believe that Pulsar can be fairly described as the world technology leader in this field. The product range has been designed to provide a full range of alternatives, from single point of measurement installations right through to complex multi-point applications with digital communications. The ultrasonic range has been augmented with other products, so for the water industry, interface monitors for tricky sludge level measurement application have been added together with units that can be used to warn of pump failure. In more general level applications, single point measurement devices are available where continuous level measurement is inappropriate.


Mr Alistair MacKinnon
Cardinal Building, Enigma Commercial Centre
Sandy's Road
WR14 1JJ

Pulsar's DUET brings First Class measurement to Manchester Airpor

Pulsar Process Measurement have supplied a non-contacting ultrasonic open channel flow measurement system featuring their DUET transducer array to give excellent measurement accuracy in the airport's critical API hydrocarbon separation unit. Pulsar's FlowCERT system featuring the DUET transducer has achieved Class 1 MCERTs certification.

Surface water runoff in an area as large as a major airport is considerable, and in certain areas may be mixed with aviation fuel, oil and other contaminants, so it has to be treated in the same way as any other industrial effluent before it can be discharged. That means separation, treatment and measurement of the final effluent flow, which is where Pulsar comes in.

Pulsar supplied a v-notch weir plate along with a DUET transducer array and FlowCERT control unit to measure effluent flow through an open channel. As can be seen in the picture, the channel was in an exposed position, where solar radiation can be a significant factor affecting the accuracy of the measurement. The v-notch weir plate was sized for a maximum flow rate of 25 litres per second, although the actual flow can be very small indeed in dry periods of the year.

It is vital that the measurement remains reliable and accurate. The measurement of this type of application is particularly difficult; the ultrasonic technique is based on the measurement of the time taken for an echo to return to the face of a transducer, which is in turn dependent on the speed of sound.

The speed of sound in air varies with air density, which is affected by air temperature. If the measurement device does not compensate quickly and accurately, errors are introduced into the result. In this case, because the head varies by around 200mm between high flow and zero, it is crucial that the measurement is accurate and repeatable right down to the very lowest flows, and records a genuine zero when there is no flow at all.

DUET is perfect for this type of application, consisting as it does of an array of two transducers that fire ultrasonic pulses simultaneously, which are then received at the lower transducer only. The FlowCERT controller then compares the two returning echoes. The two transducers are mounted on a heavy frame and the separation of the two transducers is a fixed distance, so any changes in the measured distance when comparing the two ultrasonic pulses must be down to variations in the speed of sound.

This strategy allows the FlowCERT controller to compensate dynamically and accurately for these variances, applying that compensation to the flow measurement. Under MCERTs tests, this unique system has allowed FlowCERT and DUET to achieve industry-leading total error levels of only 0.037%, even under the new, stringent, solar radiation test.

As Mark Stewart, the Airport's Water Services Engineer in charge of the project, put it: 'We were very pleased with the way that Pulsar responded to the project brief, and have been delighted with the performance of the DUET. We're confident about the measurement, so we know we are submitting exactly the right figures to the EA. We're now in the process of standardising on Pulsar equipment for all our flow and level measurement applications'.

For further information please email Pulsar Process Measurement Ltd

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