THE IMPACT OF LOW-FREQUENCY PULSATIONS ON A DUAL- BEAM ULTRASONIC FLOWMETER |
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| E. van Bokhorst, M. C. A. M. Peters |
- Abstract:
- The impact of flow and pressure pulsations on flowmeters of various measuring principles, like turbine, vortex or DP-based flowmeters is well known and published at several occasions. To the author’s knowledge, there have been no publications on investigations regarding the impact of low frequency pulsations on commercially available ultrasonic flowmeters. The influence of high frequency acoustic noise, as caused by control valves, is part of several investigations and reported in recent publications. This paper describes the impact of low frequency, almost sinusoidal pulsations in the range from 25 to 100 Hz, which are imposed on a 4-inch, dual-beam, commercially available ultrasonic flowmeter.
The results of our experiments show a strong impact as a result of the aliasing effect for pulsation frequencies coinciding with the sample frequency or multiples thereof. Moreover considerable errors also occur if pulsation frequencies are below the sampling frequency. Errors in reading are over 5 % at a pulsation frequency of 25 Hz with a flow pulsation amplitude of 8 % rms.
It is obvious that ultrasonic flowmeters, as well as turbine, vortex or DP-based flowmeters, will not operate properly close to compressor stations as flow pulsation levels over 50 % rms occur even up to partial flow reversal in case of acoustical resonance. However also flow induced pulsations (FIPS) in metering stations, due to vortex shedding at T-joints, can be considerable in case of acoustical resonance and can result in misreading of the ultrasonic flowmeter. Typical frequencies of FIPS, determined by gas properties, operating conditions and piping geometry, are found in practice to be in the same range as the sample frequencies of the ultrasonic flowmeter.
It is not likely that the phenomenon observed is restricted to the meter under investigation.
The TNO Institute of Applied Physics is therefor working on a program in which the impact of pulsations on commercially available ultrasonic flowmeters for gas is investigated systematically.
This paper presents the first results of this investigation. In addition appropriate methods in signal processing will be investigated, so that measures can be taken to minimise the uncertainty in the flowmeter reading.
The aim of the future investigations is to improve the ultrasonic flowmeter by using appropriate signal processing, so that it can operate properly and without misreading caused by flow pulsations. - Keywords:
- pulsations, installation effects, aliasing error, ultrasonic flowmeters
- Download:
- IMEKO-TC9-2000-082.pdf
- DOI:
- -
- Event details
- IMEKO TC:
- TC9
- Event name:
- FLOMEKO 2000
- Title:
- 10th Conference on Flow Measurement
- Place:
- Salvador, Bahia, BRAZIL
- Time:
- 04 June 2000 - 08 June 2000