Method and apparatus for measuring the depth of a flowing liquid

In a method and apparatus for measuring the depth of a flowing fluid, and controlling the flow rate of the fluid based upon the depth measurement, the fluid is caused to flow through a conduit, where it is irradiated with a known intensity of light, and the fluid is caused to fall from a horizontally directed exit terminus into a reservoir having a reflective bottom. The fluid serves as a wave guide for the light it received within the conduit, and releases the light within the reservoir. The intensity of light reflected from the bottom of the reservoir and emergent from the fluid is directly proportional to the depth of the fluid in the reservoir, and is measured by a photodetector which transmits a control signal to a valve in the conduit.

BACKGROUND OF THE INVENTION 
This invention concerns the measurement of the depth of a flowing liquid, 
and control of the flow rate of said liquid based upon a depth 
measurement. 
Various methods and apparatus have been utilized to measure the depth of 
fluids under static and dynamic conditions. Such methods generally involve 
mechanical principles or the attenuation of a calibrated energy source 
such as electromagnetic waves, sound or radioactivity. When a calibrated 
energy source is employed, the energy is caused to pass through the liquid 
which absorbs the energy in an amount linearly proportional to the path 
length through the liquid. The intensity of the emergent energy is 
measured and compared to the intensity of the input energy, whereby the 
liquid path length is determined. In the case of the use of visible light 
directed through a liquid, the measurable interrelationships are governed 
by the classic Lambert's law equation: 
EQU log I/I.sub.e =kd 
where I is the intensity of the light transmitted at a given wavelength, Io 
is the intensity of the incident light, d is the thickness through which 
the light is transmitted, and k is the extinction coefficient for the 
particular liquid and wavelength. 
In most techniques which utilize transmission of a calibrated energy source 
through a fluid system, the transmission characteristics of the windows 
which permit entrance and exit of the energy with respect to the confined 
liquid are subject to uncertain variation due to sedimentation effects and 
other factors. 
Methods and apparatus for measuring liquid depth are generally not suitable 
for measuring or controlling the flow rate of the liquid. 
It is accordingly an object of the present invention to provide a method 
for measuring the depth of a flowing liquid by attenuation of a calibrated 
source of electromagnetic energy. 
It is another object of this invention to provide a method and implementing 
apparatus for measuring the depth of a flowing liquid with lessened 
dependence upon the transmission characteristics of windows. 
It is a further object of the present invention to provide a method and 
apparatus of the aforesaid nature for measuring the depth of a flowing 
liquid and controlling the flow rate of said liquid. 
It is still another object of this invention to provide an improved 
apparatus of the aforesaid nature of simple and rugged construction which 
may be economically manufactured. 
These objects and other objects and advantages of the invention will be 
apparent from the following description. 
SUMMARY OF THE INVENTION 
The above and other beneficial objects and advantages are accomplished in 
accordance with the present invention by a method comprising: 
(a) conducting a fluid through a conduit having a flow controlling device 
and downstream therefrom a window portion and further downstream a 
horizontally directed exit terminus, 
(b) directing a beam of light of known intensity onto said window portion, 
(c) permitting said fluid to fall by gravity from said exit terminus into a 
reservoir having a reflective flat bottom, 
(d) measuring the intensity of light reflected upwardly from said flat 
bottom, and converting said measured intensity into an electrical signal, 
and 
(e) causing said electrical signal to manipulate said flow controlling 
device. 
The apparatus of the present invention is comprised of: 
(f) a conduit having a flow controlling device and downstream therefrom a 
window portion, and further downstream a horizontally directed exit 
terminus, 
(g) means for directing a beam of light of controlled intensity onto said 
window portion, 
(h) a reservoir having a reflective flat bottom, said reservoir being 
positioned below said exit terminus, 
(i) means for measuring the intensity of light reflected upwardly from said 
flat bottom, 
(j) means for converting said measured intensity into an electrical signal, 
and 
(k) means for causing said electrical signal to manipulate said flow 
controlling device. 
An important aspect of the method and apparatus of the present invention is 
that the liquid, in falling from the exit terminus of the conduit into the 
reservoir, serves as its own wave guide for transporting light from the 
conduit to the reservoir. By virtue of said wave guide aspect of the 
liquid, the several monitoring and control components are not in actual 
contact with the liquid. In preferred embodiments of the invention, the 
conduit is of circular cylindrical configuration, and the exit terminus is 
located closely downstream from the window portion. 
The liquids which can be monitored by the present invention include aqueous 
and non-aqueous substances, pure liquids and solutions at various 
temperatures, and liquids carrying suspended particulate material.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIG. 1, apparatus useful in the practice of the present 
invention is shown comprised of horizontally disposed conduit 10 of 
circular tubular configuration having an in-line valve 11 and a 
transparent window portion 12 located downstream from said valve. An exit 
terminus 13 is located downstream from said window and closely adjacent 
thereto. A reservoir 14 is positioned below said exit terminus, said 
reservoir having a reflective flat bottom 15 and surrounding upright 
sidewalls 16. 
A source of light energy of controllable intensity and wave length, 
designated by numeral 17 is positioned adjacent window portion 12. The 
light energy source is preferably of conventional design as typically 
employed in spectrophotometers, and is adapted to direct a collimated beam 
perpendicularly onto said window portion. Although shown as being located 
outside the liquid, the light source may in certain embodiments be 
positioned within conduit 10. 
A photodetector device, designated by numeral 18, is positioned above said 
reservoir in a manner to sense light reflected upwardly from the flat 
bottom of the reservoir. The photodetector device is preferably of 
conventional design as typically employed in spectrophotometers. The 
photodetector generates an electrical potential which is fed into a 
feedback control unit designated by numeral 19. The feedback control unit 
amplifies the signal received from the photodetector, producing a a 
working electrical current. The working current is conducted to a 
synchronous motor 20 which turns valve 11 in a manner responsive to the 
magnitude of the working current. A calibration rheostat is associated 
with the feedback control unit in a manner such that, for a given 
electrical potential generated by the photodetector, the corresponding 
working current is of proper magnitude to correctly position valve 11. In 
alternative embodiments, the valve may be activated pneumatically in 
response to the working electrical current produced by the feedback 
control unit. 
The area of flat bottom 15 is preferably between 11/2 and 3 times the cross 
sectional area of exit terminus 13. Said flat bottom is preferably 
positioned between about 3 and 9 inches below the center axis of said exit 
terminus. The photodetector is preferably positioned so as to sense light 
reflected at an angle between 30.degree. and 85.degree. with respect to 
flat bottom 15. The window portion is preferably a glass or plastic tube 
matching the cross sectional configuration of the conduit. 
By virtue of the arrangement of the various components, a flowing liquid, 
designated by numeral 21, is irradiated by light as it passes the window 
portion. In its downwardly curved trajectory 22, the liquid stream 
functions as its own waveguide, retaining the light. Upon entering the 
reservoir, the light is given up to the confining surfaces of the 
reservoir, whereupon a fixed fraction is reflected upwardly by flat bottom 
15. 
While particular examples of the present invention have been shown and 
described, it is apparent that changes and modifications may be made 
therein without departing from the invention in its broadest aspects. The 
aim of the appended claims, therefore, is to cover all such changes and 
modifications as fall within the true spirit and scope of the invention.