An optical flow meter comprising a source of light, an optical
fiber, a connector, a detector, and output electronics. The optical
fiber is connected to the source of light so as to transmit light
therethrough. The connector is arranged for attaching the optical
fiber in a position generally adjacent to a rotating body. The detector
is a photodetector that is arranged to receive light from the optical
fiber after the light is reflected by the rotating body. The source
of light is a light-emitting diode. The optical fiber is a single
optical path. A lens is disposed generally about one end of the
optical fiber for directing and focusing light relative to the rotating
body. The end of the optical fiber is sealed so as to isolate the
end of the fiber from the environment of the rotating body. A beamsplitter
is included as an optical coupler between the light-emitting diode,
the optical fiber, and the photodetector.
1. An optical device for measuring the flow rate of a fluid through
a pipe comprising:
a source of light;
fiberoptic means for transmitting light from said source of light
to a location distal from said source of light, said fiberoptic
means comprising a single optical path;
connection means for attaching said fiberoptic means to said pipe
such that one end of said fiberoptic means faces the interior of
a flow-responsive turbine having a plurality of blades extending
radially outwardly, said blades being angularly offset relative
to the axis of fluid flow through said pipe, said fiberoptic means
for directing light toward the edge of said blades, each of said
blades having a light-reflective surface;
a collimating lens positioned at the end of said fiberoptic means
opposite said source of light, said collimating lens for directing
light to and receiving light from said rotating body;
detector means connected to the end of said fiberoptic means opposite
said pipe and arranged so as to receive light from said fiberoptic
means, said detector means being responsive to said light from said
fiberoptic means as reflected by the blades of said turbine; and
output means electrically connected to said detector means for
producing a signal relative to said light as received by said detector
means, said signal corresponding to the flow rate of said fluid
passing through said pipe.
2. The device of claim 1 said source of light being a light-emitting
3. The device of claim 2 said source of light being electrically
connected to a constant DC current source.
4. The device of claim 1 further comprising:
beamsplitter means disposed adjacent said source of light, said
fiberoptic means, and said detector means, said beamsplitter means
for passing light from said source of light to said fiberoptic means
and passing said light from said fiberoptic means to said detector
5. The device of claim 1 said lens being sealed about the end
of said fiberoptic means so as to maintain said fiberoptic means
in an environment isolated from said rotating body.
6. The device of claim 1 said detector means further comprising:
amplifier means electrically connected to said photodetector; and
pulse shaping means electrically connected to said amplifier means
for converting the signal from said amplifier means into a digital
7. The device of claim 6 said detector means further comprising:
a transconductance amplifier electrically connected to said photodetector
for converting the current from said photodetector into a voltage
a Schmitt trigger electrically connected to said amplifier means
for converting the wave form of said voltage signal into a square
8. The device of claim 7 said output means comprising a pulse
forming means electrically connected to said Schmitt trigger for
providing a constant pulse width from the leading edge of said signal
from said Schmitt trigger.
FIELD OF THE INVENTION
The present invention relates to optical devices for measuring
the rotation of a rotating body. More particularly, the present
invention relates to fiberoptic systems for measuring fluid flow
by the speed of rotation of a turbine that is interactive with the
Fiberoptics is the branch of physics concerned with the propagation
of light that enters a thread or rod of transparent material at
one end and is totally reflected back inward from the wall, thereby
being transmitted within the fiber from one end to the other. Fiberoptics
is widely applied in medical practice to observe the human body
internally. Fiberoptic fibers have also been used to transmit light
signals carrying information from both electronic and optical sensors.
In the chemical industry, flow rate measurement is essential in
controlling all phases of processing and in determining the material
balance for processing units. Once manufactured, the transmission
of materials through pipelines between distant places calls for
an accurate measurement of flow rate. A multiplicity of techniques
is used in this measurement. Flow rate may be determined by measuring
the change in pressure caused by either a constriction in a pipe
or the insertion of a disk within an orifice into the flow stream.
Measuring the impact pressure upon a probe inserted into the process
stream will yield the flow rate, as would measuring change in pressure
resulting from a change in the direction of this stream. It is also
possible to derive the flow rate by measuring the change in the
velocity of sound as it passes through the material.
A common flow-rate measuring device is the orifice meter. A plate
with a circular orifice at the center is inserted into the process
stream, causing the fluid as it passes through the orifice to increase
in velocity and correspondingly decrease in pressure. A differential-pressure
measuring device measures the fluid pressure just before and just
beyond the orifice. Knowledge of this differential pressure allows
calculation of the flow rate. This type of flow meter is the most
widely used because it is simple and has been long established in
One of the most widely used methods is the turbine flow meter.
A turbine rotor is allowed to rotate freely in the moving fluid,
and its rotation causes a sudden distortion in the field of a small,
powerful magnet located in a sensor unit outside the pipe. This
distortion generates an alternating-current voltage that is transmitted
to a small computer. The computer analyzes this information and
calculates and displays the flow rate.
These devices measure the volume-flow rate. This knowledge is useful
in monitoring, for instance, the blending of two fluids the density
of which are known, such as gasoline and tetraethyllead. In other
cases, such as that in which a large quantity of raw material is
being transmitted by pipeline and sold by weight, determination
of the mass-flow rate is vital. This may be found by adding to a
volume flow meter a device that measures the density of the material
and calculates mass flow from these two measurements.
There are also flow meters that directly measure mass-flow rate.
One of these utilizes two turbines in the flow stream, the first
of which, driven at a constant speed, acts as an impeller and imparts
a certain velocity to the fluid, depending on the fluid's mass.
The second turbine located downstream is adjusted to slow the flow
to its original rate; in doing so it receives a torque, or turning
force, proportional to the force of the flow (angular momentum).
The turbine deflects a spring at an angle proportional to the torque
exerted upon it by the fluid. The result is a very accurate and
direct measure of the mass flow.
While many systems have been available for the measurement of fluid
flow, it is not believed that these systems have usefully incorporated
fiberoptics for the transmission of such information. Furthermore,
no systems herein before have utilized single optical pathways for
the transmission of information to and from the fluid flow being
measured. In addition, it is believed that none of the prior art
devices have utilized a single optical pathway for the measurement
of the rotation of a rotating body, such as a turbine, regardless
of the need to measure the fluid flow therein.
It is an object of the present invention to provide an optical
flow meter that is inherently safe even in the most hazardous of
It is another object of the present invention to provide a optical
flow meter that imparts no electrical disturbances on or about the
It is still another object of the present invention to provide
an optical flow meter that is more accurate and reliable than traditional
It is still a further object of the present invention to provide
an optical flow meter that is adaptable for the measurement of the
speed of rotation of a rotating body.
These and other objects and advantages of the present invention
will become apparent from a reading of the attached specification
and appended claims.
DISCLOSURE OF THE INVENTION
The present invention is an optical device for the measuring of
the rotation of a rotating body comprising: a source of light, an
optical fiber for transmitting light from the source of light to
a location distant from that light, a connector for attaching the
optical fiber in position generally adjacent the rotating body,
a detector arranged so as to receive light from the optical fiber
after the light has been reflected from the rotating body, and suitable
output electronics electrically connected to the detector for producing
a signal that is relative to the light as received by the detector.
In this invention, the source of light is a light-emitting diode
that is electrically connected to a constant direct current source.
The optical fiber comprises a single optical pathway. This optical
fiber includes a lens disposed generally about one end of the optical
fiber opposite the source of light. This lens is designed so as
to direct light to and receive light from the rotating body. Ideally,
this lens is collimating lens.
The detector of the present invention is a photodetector that is
positioned relative to the optical fiber so as to be electrically
responsive to light that is emitted by the optical fiber. The light
that is emitted by the optical fiber is the light that is reflected
by the rotating body. This detector further includes an amplifier
that is electrically connected to the photodetector and a pulse
shaping circuit that is electrically connected to the amplifier
for converting the signal from the amplifier into a digital pulse.
The output electronics of the present invention includes a pulse
forming circuit for providing a constant pulse width from the leading
edge of the signal from the pulse shaping circuit. In application,
this pulse forming circuit allows measurable and uniform pulses
to be generated relative to the rotation of the rotating body. The
present invention also includes a beamsplitter that is disposed
about the light source, the optical fiber, and the photodetector.
This beamsplitter passes light from the source of light to the optical
fiber and passes light from the optical fiber to the photodetector.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a cross-sectional view in side elevation of the optical
device in combination with the turbine in accordance with the present
FIG. 2 is a schematical representation of the electronics in operation
of the present invention.
FIG. 3 is a close-up view of the optical fiber and lens as used
in position relative to the spinning turbine.
BEST MODE FOR CARRYING OUT THE INVENTION
Referring to FIG. 2 there is shown at 10 the optical flow meter
in accordance with the present invention. As seen in FIG. 2 optical
flow meter 10 includes light source 12 fiberoptic means 14 connector
means 16 detector means 18 and output means 20.
Light source 12 includes a light-emitting diode 22. Light-emitting
diode 22 is a semiconductor device that produces a visible or invisible
luminescence when a voltage is applied to it. The power for light-emitting
diode 22 is provided by LED driver 24. LED driver 24 provides a
stabilized output current to the light-emitting diode 22. It is
powered by a precision constant direct current source.
Light-emitting diode 22 is connected and coupled to beamsplitter
26. Beamsplitter 26 includes a housing that contains the beamsplitter
and receives the light-emitting diode 22 the optical fiber 28
and the detector components of the present invention. Specifically,
beamsplitter 26 is an optical arrangement that reflects part of
the beam of light and transmits part of that beam of light. The
fiberoptics 14 are arranged such that the optical fiber 28 receives
the light as transmitted by light-emitting diode 22. In the preferred
embodiment of the present invention, these components are arranged
such that light will be transmissive therebetween. In other words,
light from light-emitting diode 22 should pass through the beamsplitter
and be received by optical fiber 28 within casing 30. The light
returning through fiberoptics 14 from the flow turbine 32 is reflected
off beamsplitter 26 and is received by photodetector 34.
Fiberoptics 14 is a single optical path extending from beamsplitter
26 to connector 16 of flow turbine 32. Optical fiber 28 is a type
of transmission media that allows light to be transmitted long distances
and around corners with little loss and without interference from
other light sources. Optical fiber 28 is a very thin tube of quartz,
glass, or plastic which is designed to transmit a beam of light
from one end to the other by essentially reflecting it from side
to side as it travels down the fiber. In accordance with the present
invention, fiberoptics 14 comprises a single optical fiber pathway.
One end of fiberoptics 14 is coupled to the beamsplitter 26 and
arranged so as to receive light from light-emitting diode 22. The
light from light-emitting diode 22 will travel along optical fiber
28 to its other end within connector 16. Many individual optical
fibers 28 may be joined, in end-to-end relationship, to form the
single optical pathway. As a result, optical fiber 28 may have a
length as long as several kilometers. This maximizes the distance
between the electrical circuitry of the present invention and the
potentially hazardous environment of flow turbine 32.
Fiberoptics 14 is interconnected with flow turbine 32 by connector
16 as is illustrated in FIG. 1. In FIG. 1 connector 16 is comprised
of a housing 40. Housing 40 is a generally cylindrical member having
an internal cavity extending thereto for the receipt of fiberoptics
14. Housing 40 includes a threaded section 42 that is received by
a correspondingly threaded section within pipeline 44. The opening
within pipeline 44 that receives connector 16 is arranged so as
to receive connector 16 and allow the end 46 of connector 16 to
enter the interior 48 of pipeline 44. A hexagonal nut 50 generally
surrounds the outer diameter of body 40. Nut 50 allows connector
16 to be fastened into the opening within pipeline 44.
A housing that contains lens 50 occurs about end 46 of connector
16. An elastomeric O-ring 52 is disposed in a groove between housing
40 and the housing that contains the lens 50. O-ring 52 is included
to isolate the interior 48 of pipeline 44 from the exterior environment.
Lens 50 is sealed within body 40 of connector 16 to 10000 p.s.i.
This pressurized sealing should be of sufficient strength to adequately
protect optical fiber 28 from the rigors of the fluid passing through
and the environmental conditions within pipeline 44.
Within the interior of pipeline 44 is a turbine 60. Turbine 60
has blades 62 extending thereacross. Blades 62 are somewhat elevated
from the surface 64 of rotor 60. Turbine 60 is mounted onto axle
66. Axle 66 is received by and extends generally about flow straightening
vanes 68. Depending on the embodiment desired of the present invention,
turbine 60 can either be a freely-moving turbine that is rotated
purely by the flow of fluid therethrough, or, it may be a rotor
that is powered by some external force. The optical flow meter 10
of the present invention is adaptable to a wide variety of configurations.
The main purpose of the optical flow meter is to measure the rotational
speed of the turbine. Since it measures the rotational speed of
the turbine, regardless of the type of force acting on the turbine,
it is suitable for measuring both flow turbines, turbines that are
powered by external force, or any other type of bladed arrangements.
The example shown in FIG. 1 is merely one example of the many embodiments
of the present invention to which the optical flow meter is adaptable.
As can be seen in the close-up view of FIG. 3 lens 50 is a collimating
lens. In other words, the lens is designed to receive the light
from optical fiber 28 and collimate it so as to produce parallel
rays of light passing from end 46. These parallel rays of light
70 are directed toward the surface 72 of turbine 60. The surface
72 of turbine 60 also includes blades 74. As will be described hereinafter,
in operation, these parallel rays of light 70 are reflected from
either surface 72 or blades 74 back toward collimating lens 50.
These reflected rays of light are received by the collimating lens
and focused back into optical fiber 28. Since the amount of light
reflected back into optical fiber 28 is a function of the distance
of the reflective surface from the end 46 of lens 50 more light
will be reflected back into the optical fiber when the edge of blade
74 is adjacent end 46 than will be when surface 72 is adjacent end
46. In this manner, accurate measurements of the speed of rotation
of turbine 60 are accomplished.
Referring back to FIG. 2 the detection and output circuitry of
the present invention are described hereinafter. Detector 18 is
comprised of photodetector 34 transconductance amplifier 80 voltage
amplifier 82 rectifier 84 adaptive reference circuit 86 and Schmitt
trigger 88. Photodetector 34 receives the light transmitted from
flow turbine 32 by fiberoptics 14. Photodetector 34 converts this
light input into an electrical output. In this arrangement, photodetector
34 transmits an AC signal to transconductance amplifier 80. Tranconductance
amplifier 80 is electrically connected to photodetector 34 and converts
the current from photodetector 34 into a voltage. This voltage is
a function of the power of the light hitting photodetector 34. In
this manner, as more light is reflected by portions of the turbine
60 into optical fiber 28 the greater amount of voltage will be
transmitted by transconductance amplifier 80. Voltage amplifier
82 is electrically connected to transconductance amplifier 80. Voltage
amplifier 82 elevates the voltage produced by transconductance amplifier
80 into a level that is suitable for working with. Rectifier 84
converts the AC input into a DC output. Schmitt trigger 88 is electrically
connected to rectifier 84 and to reference circuit 86. This trigger
circuit 88 produces an output of fixed amplitude and duration. This
circuitry acts as a filter in eliminating many of the problems caused
by minor variations in voltage. The reference circuit 86 is also
electrically connected to both the rectifier 84 and the trigger
circuit 88. This reference circuit 86 follows the DC level produced
by the rectifier and assists in the usage of small voltage signals.
Together, rectifier 84 reference circuit 86 and trigger circuit
88 converts the wave form produced by the interaction of the photodetector
and the fiberoptics into a DC digital pulse. In essence, this produces
a square pulse train. These devices also solve many of the problems
associated with interference, misshapen pulses, and variations in
fluid viscosity passing through flow turbine 32.
The output circuitry 20 of the present invention includes pulse
forming circuit 90. Pulse former 90 is a circuit that is electrically
connected to the detector circuitry 18 of the present invention.
The design of such a pulse former is well-known in the art of electronics.
This pulse forming circuit 90 is adapted to produce a constant pulse
width that starts with the leading edge of the square wave form
from the Schmitt trigger 88. This pulse forming circuit gives a
precision wave form for use by a computer or a D.C. meter. In use,
this device produces electrical "blips" that correspond
to the occurrence of a turbine blade 74 adjacent to the end of the
fiberoptics 14. The number of turbine blade passes can be counted
in this manner. This figure could be passed as output from this
pulse forming circuit 90 and can be used to calculate the rate of
rotation of the turbine blade, the fluid flow rate through the turbine
blade, or any other calculation that requires knowledge of the rate
of turbine rotation. Also, this standard digital pulse output can
be electrically connected to a computer so as to produce a flow
rate that corresponds to the average electrical output.
In operation, light source 12 and in particular light-emitting
diode 22 produces a constant light output toward one end of optical
fiber 28. This light is transmitted through the optical fiber 28
into the connector 16 within flow turbine 32. At its other end,
optical fiber 28 is connected to a collimating lens 50. Collimating
lens 50 causes parallel rays of light to be emitted from the end
of optical fiber 28 and directed toward the surface of turbine 60.
When a bladed portion 62 of turbine 60 passes adjacent to the end
46 of connector 16 a portion of the light emitted from optical
fiber 28 is reflected back toward lens 50. The lens 50 receives
this light and focuses this light into the end of optical fiber
28. The bladed portion 62 reflects a greater amount of light than
the non-bladed portion 64. Optical fiber 28 then passes this light
information back toward beamsplitter 26 and into photodetector 34.
Photodetector 34 receives the light transmitted by fiberoptics 14
and converts this light input into an electrical current output.
Transconductance amplifier 80 receives this current output and converts
this current output into a voltage output. This voltage is a function
of the power of the light hitting photodetector 34. Voltage amplifier
82 receives the output from transconductance amplifier 80 and converts
this into a voltage level that is suitable for working with. Rectifier
84 reference circuit 86 and Schmitt trigger 88 receive this voltage
from amplifier 82 filter it, and convert it into a digital pulse.
The digital pulse passes from Schmitt trigger 88 into pulse forming
circuit 90. Pulse forming circuit 90 receives this pulse and converts
it into a pulse of constant width that starts with the leading edge
of the square wave delivered by Schmitt trigger 88. This standard
digital pulse output from pulse forming circuit 90 can then be passed
to suitable electronics for use by a computer, by human observation,
or for other detection circuitry.
It should be noted here, that when the surface 64 of turbine 60
is adjacent the end 46 of connector 16 a lesser amount of light
is reflected back into he end 46 and into optical fiber 28. This
is because a greater amount of the light is deflected within pipeline
48 and away from the lens 50. As a result, a lesser amount of light
is transformed into a voltage acting on the Schmitt trigger. The
location of the turbine blade in this situation could be considered
as the lower part on a square wave form. In essence, the pulse produced
by the detection circuitry of the present invention would have a
high amplitude when the turbine blade 74 is adjacent the optical
fiber and would have a low amplitude when the surface 72 of turbine
60 would be adjacent the optical fiber. By counting the number of
high amplitudes, a calculation as to the rate of rotation of turbine
60 can be performed.
As an example, if turbine 60 would have five blades, then five
pulses would be created on each rotation of the turbine. The turbine
speed in rotations per second could be calculated by taking a count
on the number of pulses per second and dividing the total pulses
by the five turbine blades. Similarly, the rate of rotation of the
turbine blade can be analyzed so as to calculate and display the
flow rate of a fluid through the pipeline.
The present invention offers significant advantages over the traditional
magnetic pickups used to calculate the rotational rates of a turbine
within a fluid. The magnetic pickups have exhibited 7 to 9 percent
losses and inaccuracies when the turbine is moving with a slow rate
of rotation. At slow rates of rotations, the wave form generated
by the interaction of magnetic fields is relatively flat. This makes
it harder to analyze the blade movement, and as a result, more difficult
to calculate turbine rotation. In addition, traditional magnetic
pickups require the use of electricity in a potentially hazardous
environment. The present invention, through the use of fiberoptics
and light transmission, is inherently safe even in the most explosive
of environments. Since the electronics of the present invention
can be located at a distance remote from the fluid flow being measured,
the electricity can be effectively isolated from the hazardous environment.
Finally, by producing the pulse relative to the leading edge of
the blade, the present invention provides a standard digital pulse
output hat can be utilized by other systems and is very accurate
with regard to blade detection and turbine movement.
The present invention is also unique and advantageous through its
use of the single optical fiber transmission medium. The incorporation
of the single fiber with the beamsplitter arrangement eliminates
the need for fiberoptic bundles and the electronics associated with
each bundle. This produces a great cost savings, a significant improvement
in reliability, and a reduction in repair and maintenance.
The foregoing disclosure and description of the invention is illustrative
and explanatory thereof, and various changes in the size, shape,
and material, as well as in the details of the illustrated construction
and described method of operation, may be made within the scope
of the appended claims without departing from the spirit of the
invention. This invention should only be limited by the appended
claims and their equivalents.