New self-build ultrasonic flowmeter: unsurpassed measuring accuracy ­ fall in real installed price

Citation

(1998), "New self-build ultrasonic flowmeter: unsurpassed measuring accuracy ­ fall in real installed price", Industrial Lubrication and Tribology, Vol. 50 No. 6. https://doi.org/10.1108/ilt.1998.01850fad.010

New self-build ultrasonic flowmeter: unsurpassed measuring accuracy ­ fall in real installed price

New self-build ultrasonic flowmeter: unsurpassed measuring accuracy ­ fall in real installed price

Keywords: Flowmeter, Ultrasonic

Danfoss Limited has launched the SONOFLO ultrasonic flowmeter in a kit form, enabling users to retrofit the flowmeter themselves to any pipe up to 4m in diameter and still achieve accuracy of ±0.3 per cent.

The new SONOKIT contains everything needed to build a complete SONO4100 ultrasonic flowmeter, without any welding. It includes a SONO3000 signal converter and, as an added advantage, the flowmeter can be retrofitted under full line pressure.

SONOFLO has always been aimed at the retrofit market. What's new and different about the SONOKIT is that by simplifying the installation procedure the cost of fitting an ultrasonic flowmeter has been significantly reduced in real terms. As the flowmeter can now be fitted by its end user there is no need to hire specialist contractors ­ and this will represent a real saving on the total installed price.

Danfoss has two sensor lines, the SONO4100 and SONO3300, as well as the SONO3000 signal converter in its SONOFLO ultrasonic flowmeter range. The new units provide a real alternative to other flowmetering technologies, such as Coriolis mass, PD meters and turbines. SONOFLO flowmeters are based on the proven transit time principle, and measure the volume flow of non-conductive fluids independently of viscosity, density, pressure or temperature variations. In short, the new units can be used for measuring almost anything that can be pumped. SONO3000 is a multipath ultrasonic time-of-flight flowmeter. It calculates flow by measuring the transmission time differential of an ultrasonic signal transmitted up and down stream. While the majority of ultrasonic flowmeters are basically velocity meters which provide an output signal proportional to the volumetric flow, SONO3000 also measures the actual sound velocity and can calculate mass flow. The quality of transit time meters is dictated by its resolution of the time measurement, the ability to recognise acoustic signals, the number of sound paths on which it operates and the positioning of the sound paths in the sensor. SONO3000, SONO3300 and SONO4100 are specifically designed to provide a significant improvement in all of these areas. Time resolution on the SONO3000 is better than 100 pico seconds and digital signal processing (DSP) techniques have significantly improved the signal recognition. SONO3000 continuously adapts to meet its operating conditions and actually builds a digital "fingerprint" of the signal it is expecting. The "fingerprint" consists of a series of calculated correlation coefficients, each of which is based on 800 samples. This calculation produces an outline which the processor stores and matches against all received signals. As a result, signal recognition is no longer affected by minor, temporary changes in signal shape, size and frequency. The calculation is so accurate that SONO3000 can also recognise very weak signals which may be damped up to 1,000 times (or 60dB) by gas and solid particles in the pipe. This offers very real, practical benefits. In the past ultrasonic flowmeters have been largely restricted to measuring clean, light fluids such as potable water, de-salted water, petrol and light fuel oils. However, today's new generation of products can now also measure "difficult" liquids such as crude oil and other hydrocarbons. SONO3000's DSP unit stores 75ms of the transmission time of each up and down stream signal. As the received signals have a typical duration of less than 40ms, the 75ms time window around the expected arrival time of each individual signal is sufficient to ensure the signal is captured. The correct positioning of the time window depends on the bore size of the sensor, the flow velocity and the sound velocity in the liquid. The SONO3000 automatically determines this, and uses a 20MHz counter to establish the time elapsing from signal transmission to expected arrival. The acoustic signal that the unit measures is generated by a piezoelectric crystal in a metal diaphragm which, traditionally, is subjected to either an electric current or a mechanical impact.

SONO3000 applies a new method of generating the acoustic signal: the ultrasound emitting diaphragm is no longer "shocked" by an electrical pulse, but oscillated. The sound signal is generated by sending a sinusoidal 1MHz signal of eight periods. This ensures that the transducer transmits a signal with a very narrow frequency band around 1MHz ­ the optimum frequency for the receiving transducer.

For further information please contact: Jonathan Smith, Danfoss Limited. Tel: +44 (0)181 991 7000.