Vízügyi Közlemények, 1959 (41. évfolyam)
4. füzet - V. Kisebb közlemények-Ismertetések
(75) Owing to different degrees of turbulence in the main branch and in the by-pass, the multiplicator (n = Q/q) is generally far from constant. The relationship between the discharge and the measuring head can be expressed in the main branch by Eq. (9), whereas in the by-pass by Eq. (10). Therefore, the multiplicator depends upon discharge as indicated by Eq. (12). The exponents M and m involved therein vary within the range from 1,8 to 2,0, yet differ in general from each other. Owing to this fact the multiplicator is also variable. The extent of variation depends upon the ratios M/m and Q m^/Q mi a. An average value n of the multiplicator over a certain period can be determined in principle on basis of the approximating knowledge of the inverted function of flow duration Q (t) shown in Fig. 5. according to Eq. (7). In the case of a linear inverted flow duration function (Fig. 6), n can be obtained from the relationships expressed by Eq. (18). The relation between possible extreme values of n, the average value and various approximations of the latter indicated in Table I, as well as in Figs. 7 to 13 for conditions likely to beencountered in irrigation practice. As to be seen the determination of the value of n is essential, because under adverse circumstances n ma l and n ml n may differ by as much as 10 per cent from the average value. In any given case the multiplicator can be determined by the following method: 1. Relationships (9) and (10), or occasionally directly that expressed by Eq. (12), are determined experimentally, i. e. the so-called n(Q) relationship is established. If M — m, then n is constant and equal to its own mean value. If M = m, then the following additional steps are necessary: 2. The anticipated limits of normal flow are established, Ç ma x and Ç ml n and the character of the inverted fiow duration curve Q (t ) is assumed. 3. The value of n is computed. a) If Q is constant, then n is also constant and can be computed from Eq. (12). b) If Q(t) is linear or can be assumed as such, the first step is to compute now Q a on basis ot Eq. (24). Hereafter, from the graph given in Fig. 13 the percentage is determined by which Q a must be increased to obtain the value Q„ pertaining to the value of n. Having computed Q n, the value of n is determined either from Eq. (12), or from the original.y available function, respectively graph n(Q). c) If Q (t ) is known, but cannot be considered even approximatingly as linear, the value of n may be computed from the relation expressed by Eq. (7). Should this involve difficulties, further approximations can be resorted to. Ci) If Q (t ) is mostly above the linear inverted function of flow duration, the value of n should be assumed between those pertaining to n(Q m a.,) and to the linear Q (f). c-J If Q (() is mostly below the linear inverted function of flow duration, the value of n should be assumed between those pertaining to n(Ç mi n) and to the linear Q (0d) If the extreme values are the only information available on Q (t), the n k value defined by Eq. (22) should be used instead of n. The formula for the multiplicator given by Eq. (12) is naturally valid between certain discharges. Beyond these limits a deviation due to internal friction of the meter respectively to changes in the degree of turbulence can be observed (Fig. 14). However, Eq. (12) applies to practical cases. Potential uses of proportionate measurement in Hungary lie mainly in the field of irrigation. A prerequisite for its application is a reliable filter in the bv-pass designed in accordance with water quality. (Author's summary translated by '/.. Szilvússg struct, eng.).
