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A method for measurement of mean wind direction with the use of standard potentiometric transducers
Armosphrnc
Envrronment
Vol. IO, p. 415. Pergamon
Press
1976. Printed
in Great
Britain.
TECHNICAL NOTE A METHOD FOR MEASUREMENT OF MEAN WIND DIRECTION WITH THE USE OF STANDARD POTENTIOMETRIC TRANSDUCERS (First received 21 April 1975 and in jinalform
17 September 1975)
Abstract-A brief description of a method used in measuring the mean wind direction with standard potentiometric transducers is given. The principle is based on a numerical extension of the compass card, by summing 1000 three-digit numbers where the first figure is an index of periodicity and the ones following represent the wind direction. The index is increased or decreased by one unit at each passage through the gap of the potentiometer. Therefore. after summing 1000 numbers, the second and third digit represent the required mean direction. The problem of obtaining the mean wind direction with potentiometric transducers originates from the discontinuity that occurs when the sliding contact moves across the gap of the potentiometer, so that the transfer function is fluctuating between its maximum and minimum values. In order to circumvent this drawback some special feature potentiometers with switching arrangements (Smith, 1959; Kronengold, Loewenstein and Berman, 1965; Slade, 1968; Moses and Kulhanek, 1962; Longhetto and Persano, 1968; Jones, 1970; Civitano and Longhetto, 1973) or without discontinuity (Camuffo, 1974) have been used. We propose here a method for measuring the mean wind direction with standard instruments, where the vane is coupled to a potentiometer with a gap and only one sliding contact. The principle of operation is illustrated. If the compass card is divided into 100 parts, each one can be represented by a two-digit number lying between 00 and 99. Thus, if we sum loo0 of these numbers, we obtain a five-digit number, and the first two figures represent the mean value. Again, if we consider three-digit numbers and we regard the first figure as an index of periodicity, then the two figures following the first one in the sum of loo0 numbers, represent the mean value related to the compass card. The index of periodicity disappears if we neglect the first figure, even if it has been used in computing the sum. In our example we can use an index of periodicity lying between 0 and 9, which is sufficient to allow 10 complete rotations of the wind vane during the averaging period. Of course 10 rotations are excessive and their average has no physical interest, The real aim is to add or subtract only one unit to the index, depending if the wind vane is oscillating clockwise or counterclockwise about the discontinuity, so that at the beginning the index can be put equal to 1 and become 0 or 2 during the addition. Therefore, when the wind is shifting, e.g. from the direction labelled 99900, the corresponding numbers are 199 and 200 without discontinuity. Actually we obtain the mean direction by converting an analog voltage into frequency and counting the pulses during the sampling period. In this case, before conversion, the voltage applied to the terminals of the potentiometer must be added to the signal measured at the brush if this has shifted to the lower value across the gap, or subtracted for the opposite rotation. It is also possible to supply the potentiometer with a fixed voltage and convert the varying signal at the brush into digital numbers. The latter, with its proper index, can be summed to obtain the mean value as explained.
415
CONCLUDING
REMARKS
In practice, the continuity of the output is extended to 3 x 360”. The idea of a range extension with switching arrangements is not new and in particular an anemometer which changes the sign of an output voltage as the brush traverses the gap of a step potentiometer was designed at Porton Down (Jones, 1970). The present work suggests a method of averaging the wind direction, where the analog output of a windvane is converted into pulses of specific frequency range or into digital numbers. The method is proposed because it can be used inexpensively with standard potentiometric transducers. C.N.R. Laboratorio per lo Studio della Dinamica delle Grandi Masse, Venice, Italy
DARIO CAMUFFO ANGELO DENEGRI
REFERENCES
Cam&o D. (1974) A multi-purpose integrating Anemometer. p. 199-207. In European Symposium on Ofihore Data Acquisition Systems, pp. 199-207. Organized by Society for Underwater Technology, Southampton. Civitano L. and Longhetto A. (1973) A liquid-suspension, high sensitivity Anemograph. Atmospheric Environment 7, 12851288.
Kronengold M., Loewenstein J. M. and Berman G. A. (1965) Sensors for the observation of wave height and wind direction. In Proceedings of the 3rd National Marine Science Symposium, (Edited by Knopf W. C. and Cook H. A.), pp. 2733388. Miami, FL. Jones J. I. P. (1970) A new recording wind vane. J. Phys. E: Scient. Instrum. 3, 9-14.
Longhetto A. and Persano A. (1968) A “running-average” anemograph. Atmospheric Environment 2, 77-82. Moses H. and Kulhanek F. C. (1962) Argonne automatic meteorological data processing system. J. appl. Met. 1, 69-80.
Slade D. H. (1968) Meteorology and atomic energy 1968. U.S. Atomic Energy Commission, TID 24190, 445 pp. Smith M. E. (1959) A potentiometer system for the continuous indication or recording of wind direction. J. Meteorol. 16, 335-337.
Envrronment
Vol. IO, p. 415. Pergamon
Press
1976. Printed
in Great
Britain.
TECHNICAL NOTE A METHOD FOR MEASUREMENT OF MEAN WIND DIRECTION WITH THE USE OF STANDARD POTENTIOMETRIC TRANSDUCERS (First received 21 April 1975 and in jinalform
17 September 1975)
Abstract-A brief description of a method used in measuring the mean wind direction with standard potentiometric transducers is given. The principle is based on a numerical extension of the compass card, by summing 1000 three-digit numbers where the first figure is an index of periodicity and the ones following represent the wind direction. The index is increased or decreased by one unit at each passage through the gap of the potentiometer. Therefore. after summing 1000 numbers, the second and third digit represent the required mean direction. The problem of obtaining the mean wind direction with potentiometric transducers originates from the discontinuity that occurs when the sliding contact moves across the gap of the potentiometer, so that the transfer function is fluctuating between its maximum and minimum values. In order to circumvent this drawback some special feature potentiometers with switching arrangements (Smith, 1959; Kronengold, Loewenstein and Berman, 1965; Slade, 1968; Moses and Kulhanek, 1962; Longhetto and Persano, 1968; Jones, 1970; Civitano and Longhetto, 1973) or without discontinuity (Camuffo, 1974) have been used. We propose here a method for measuring the mean wind direction with standard instruments, where the vane is coupled to a potentiometer with a gap and only one sliding contact. The principle of operation is illustrated. If the compass card is divided into 100 parts, each one can be represented by a two-digit number lying between 00 and 99. Thus, if we sum loo0 of these numbers, we obtain a five-digit number, and the first two figures represent the mean value. Again, if we consider three-digit numbers and we regard the first figure as an index of periodicity, then the two figures following the first one in the sum of loo0 numbers, represent the mean value related to the compass card. The index of periodicity disappears if we neglect the first figure, even if it has been used in computing the sum. In our example we can use an index of periodicity lying between 0 and 9, which is sufficient to allow 10 complete rotations of the wind vane during the averaging period. Of course 10 rotations are excessive and their average has no physical interest, The real aim is to add or subtract only one unit to the index, depending if the wind vane is oscillating clockwise or counterclockwise about the discontinuity, so that at the beginning the index can be put equal to 1 and become 0 or 2 during the addition. Therefore, when the wind is shifting, e.g. from the direction labelled 99900, the corresponding numbers are 199 and 200 without discontinuity. Actually we obtain the mean direction by converting an analog voltage into frequency and counting the pulses during the sampling period. In this case, before conversion, the voltage applied to the terminals of the potentiometer must be added to the signal measured at the brush if this has shifted to the lower value across the gap, or subtracted for the opposite rotation. It is also possible to supply the potentiometer with a fixed voltage and convert the varying signal at the brush into digital numbers. The latter, with its proper index, can be summed to obtain the mean value as explained.
415
CONCLUDING
REMARKS
In practice, the continuity of the output is extended to 3 x 360”. The idea of a range extension with switching arrangements is not new and in particular an anemometer which changes the sign of an output voltage as the brush traverses the gap of a step potentiometer was designed at Porton Down (Jones, 1970). The present work suggests a method of averaging the wind direction, where the analog output of a windvane is converted into pulses of specific frequency range or into digital numbers. The method is proposed because it can be used inexpensively with standard potentiometric transducers. C.N.R. Laboratorio per lo Studio della Dinamica delle Grandi Masse, Venice, Italy
DARIO CAMUFFO ANGELO DENEGRI
REFERENCES
Cam&o D. (1974) A multi-purpose integrating Anemometer. p. 199-207. In European Symposium on Ofihore Data Acquisition Systems, pp. 199-207. Organized by Society for Underwater Technology, Southampton. Civitano L. and Longhetto A. (1973) A liquid-suspension, high sensitivity Anemograph. Atmospheric Environment 7, 12851288.
Kronengold M., Loewenstein J. M. and Berman G. A. (1965) Sensors for the observation of wave height and wind direction. In Proceedings of the 3rd National Marine Science Symposium, (Edited by Knopf W. C. and Cook H. A.), pp. 2733388. Miami, FL. Jones J. I. P. (1970) A new recording wind vane. J. Phys. E: Scient. Instrum. 3, 9-14.
Longhetto A. and Persano A. (1968) A “running-average” anemograph. Atmospheric Environment 2, 77-82. Moses H. and Kulhanek F. C. (1962) Argonne automatic meteorological data processing system. J. appl. Met. 1, 69-80.
Slade D. H. (1968) Meteorology and atomic energy 1968. U.S. Atomic Energy Commission, TID 24190, 445 pp. Smith M. E. (1959) A potentiometer system for the continuous indication or recording of wind direction. J. Meteorol. 16, 335-337.