The present invention relates to a sampling apparatus for fluids. More particularly, it relates to a sampling apparatus capable of obtaining a sample, the quantity of which is proportional to the total flow of the fluid.
When a fluid is flowing in an open channel or aqueduct and the flow is obstructed by a notched dam or weir, the height of the head above the edge of the weir is determined by the rate of flow of the fluid. Thus, the flow rat may be calculated as a function of the head in accordance with the general equation: EQU F = f(h) (1)
where F represents the volume rate of flow of the fluid and h represents the height of the head. In a well-known dam or weir type flowmeter, the function f(h) will be expressed by the simple relationship with regard to h, as follows: EQU F = f(h) = Kh.sup.n ( 2)
where
K -- a coefficient for flow quantity; PA1 n -- an index number defined in accordance with the cross-sectional shape of the weir or notch in the dam (n = 5/2 when the cross-section is triangular while n = 3/2 when it is rectangular).
Assume, now, that the following relation is achieved between Q and k, where Q is the volume of a fluid sample and k is a constant: EQU Q = k .sup.. f(h) (3)
Accordingly, from equations (1) and (3), we obtain: EQU Q = k .sup.. F (4)
this equation shows that the volume of a sampled quantity can be proportional to the flow rate of the fluid in the open channel or aqueduct.