Abstrict A method and apparatus for utilizing a controller to monitor a
flow volume in a fluid transportation system. The controller being
operably connected to a module. The module being operably connected
to a flow meter. The module senses a series of pulses that represent
a known fluid volume in a proving loop. The module also measures
the fluid density of the fluid in the proving loop. The controller
utilizes a dynamic density of the fluid and the sensed pulses to
determine a correction factor to more accurately calculate the flow
volume through the measuring flow meter. The controller ensures
the accuracy of the flow meter by utilizing the partial pulses sensed
during a meter-proving period by using an interpolation method.
Claims I claim:
1. For a fluid transportation system having a controller for monitoring
fluid flow and controlling transportation of the fluid, a method
of proving a flow meter, the flow meter being operably connected
to a controller and a proving loop having a known flow volume, wherein
the controller monitors the fluid flow within the proving loop and
executes a proving process, the method comprising the steps of:
starting a meter-proving period; sensing a pulse signal responsive
to a flow meter being operably connected in the path of the fluid,
the flow meter generating the fluid flow, wherein the sensed pulse
signal may include fractional pulse signals; ending the meter-proving
period; calculating the amount of sensed pulse signals occurring
during the meter-proving period, wherein the amount of sensed pulse
signals may include fractional pulse signals; sensing a density
of the fluid; utilizing the sensed density and the calculated amount
of sensed pulse signal to calculate a flow volume of the proving
loop; and, comparing the known flow volume of the proving loop to
the calculated flow volume of the proving loop, wherein any difference
between the known flow volume and the calculated flow volume can
be utilized to improve the accuracy of the flow.
2. The method of proving a flow meter of claim 1 wherein the known
flow volume of the proving loop is substantially equivalent to 10000
pulse signals.
3. The method of proving a flow meter of claim 1 further including:
adjusting the flow meter in response to the comparison of the known
flow volume of the proving loop to the calculated flow volume of
the proving loop.
4. The method of proving a flow meter of claim 1 further including:
adjusting a module operably connected to the controller in response
to the comparison of the known flow volume of the proving loop to
the calculated flow volume of the proving loop, wherein the module
more accurately calculates the fluid flow.
5. The method of claim 1 wherein calculating the amount of sensed
pulse signals occurring during the meter proving period comprises
interpolating a partial pulse signal of the sensed flow meter signal
occurring after sensing has begun and before a first full pulse
signal, and interpolating a partial pulse signal of the sensed flow
meter signal occurring after the last full pulse signal of the flow
meter signal and before sensing has stopped.
6. The method of claim 5 wherein the calculation of the sensed
flow meter pulse signal utilizes a double chronometry method of
interpolation.
7. The method of claim 1 wherein the flow meter is a turbine.
8. For a fluid transportation system having a controller for monitoring
fluid flow and controlling transportation of the fluid, a method
of measuring a flow volume of the fluid within a conduit, wherein
a controller having a module and being operably connected to a flow
meter and the conduit determines the flow volume of the fluid within
the conduit, the method comprising the steps of: sensing a number
of pulse signals, wherein at least one of the pulse signals comprises
a partial pulse signal and wherein at least one of the pulse signals
comprises an integral pulse signal; interpolating the partial pulse
signals; calculating the total number of pulses by adding the integral
pulse signals and the interpolated partial pulse signals; sensing
a density of the fluid; storing the sensed density value as a dynamic
variable in the controller; and, calculating a correction factor,
M, by utilizing the sensed dynamic density of the fluid.
9. The method of claim 8 wherein the flow meter is a turbine.
10. A controller for monitoring and controlling a fluid transportation
system, the system comprising a flow meter operably connected to
a conduit, the controller monitors a fluid within the system and
calculates a flow volume of the fluid flowing through the conduit,
the controller comprising: a module being operably connected to
the controller, the module for sensing a pulse signal generated
by the flow meter, wherein the pulse signal comprises integral pulse
signals and at least one partial pulse signal; an input channel
being operably connected to the module and adaptable to a range
of input voltages; a densitometer being operably connected to the
input channel, the densitometer senses the real time density of
the fluid and stores the sensed value as a dynamic variable in the
controller; and, a calculator for determining a correction factor
for the volumetric flow of the fluid by utilizing the sensed dynamic
density value and the sensed pulse signals.
11. The controller of claim 10 comprising a display for displaying
a system error, the error is identified with the input channel.
12. The controller of claim 10 wherein the range of input voltages
is 25 mV-30V DC.
13. The controller of claim 10 wherein the flow meter is a turbine.
14. A controller for meter proving a fluid transportation system,
the fluid transportation system comprising a conduit being operably
connected to a flow meter, and a proving loop attached to the conduit,
the proving loop having a known flow volume measured in pulse signals
generated by the flow meter during a meter-proving period, the controller
comprising: a module being operably connected to the controller;
a plurality of input channels being operably connected to the module;
a pulse monitor having a 5 MHz resolution clock, the pulse monitor
being operably connected to the flow meter wherein a pulse signal
generated by the flow meter during the meter-proving period is capable
of being sensed by the pulse monitor; an interpolator being operably
connected to the pulse monitor wherein the interpolator is capable
of determining a fractional pulse signal amount of the sensed partial
pulse signal; an accumulator being operably connected to the interpolator
and capable of summing all the pulse signals sensed during the meter
proving period, the sensed pulse signals include the full and interpolated
partial pulse signals, a calculator utilizing the accumulated pulse
signals during the meter-proving process to calculate the flow volume
of the proving loop, the calculated flow volume being measured in
pulse signals; and, a comparator for comparing the known number
of pulses of the proving loop and the accumulated pulse signals
sensed during the meter proving period, wherein any difference between
the known flow volume and the calculated flow volume can be utilized
to improve the accuracy of the flow meter.
15. The controller of claim 14 wherein the meter proving period
for sensing the pulse signal generated by the flow meter is approximately
10000 pulse signals.
16. The controller of claim 14 wherein the interpolator utilizes
a double chronometry pulse interpolation.
17. The controller of claim 14 wherein the plurality of input channels
are each adaptable for receiving an input signal having a voltage
range of 25 mV-30V DC.
18. The controller of claim 14 wherein the flow meter is a turbine.
Description The present invention is generally related to monitoring and controlling
a fluid transportation system. More specifically, the present invention
is directed to a controller having a flow meter module for monitoring
and controlling a fluid flow volume in a fluid transportation system.
BACKGROUND OF THE INVENTION
The production, transportation and sale of energy products has
always required some form of measurement to determine the quantity
produced, bought or sold. The accuracy and reliability of a system
that measures an energy product, i.e., gas and liquid, is extremely
important to the buyers and sellers involved. A seemingly insignificant
error within the measuring system can result in extensive monetary
losses.
Technological advances in the areas of fluid flow metering and
computation has led to improved accuracy and reliability. Some of
these advances have been made in the area of metering, or measuring,
transported energy products. These advances have also focused on
factors such as safety, reliability and standardization.
Today's metering and transfer system involves more than simply
measuring fluid flow; it can also involve extensive electronics,
software, communications interfaces, analysis and control. Measuring
fluid flow includes multiple turbine meters with energy flow computers,
densitometers, gas chromatography, meter-proving systems and RTU
or SCADA interfaces. Measurement and control of energy sources is
a valuable process for companies producing and transporting energy
sources. Many governments, organizations and industries have enacted
standards and regulations related to the recovering, refining, distributing
and selling of oil and oil by-products, i.e., gasoline, kerosene,
butane, ethanol, etc. The energy resource industry has various standards
and regulations to ensure the accuracy and safety of transporting
and metering these energy sources.
The process of transporting fluid, typically oil, through a pipeline
is monitored and controlled with the assistance of a combination
of sensors and process computers. Generally, a computer processor
monitors the several aspects of the oil transportation, such as
fluid flow volume. The control of the equipment facilitating the
transportation of oil is generally performed by environmentally
robust devices such as a controller. The controller regulates valves,
tanks and scales without requiring an individual to constantly interact
with the system.
A very important aspect of a fluid transportation system involves
the fluid flow meters utilized to monitor the amount of oil delivered
to a customer. Because of the vast amounts of fluid delivered, the
accuracy of the fluid flow meter must be ensured at regular intervals.
An inaccurate fluid flow meter can result in overcharging or undercharging
a customer for the delivered product.
A turbine flow meter is an accurate and reliable flow meter for
both liquids and gas volumetric flow. Some applications utilizing
a turbine flow meter involve water, natural gas, oil, petrochemical,
beverage, aerospace, and medical. The turbine comprises a rotor
having a plurality of blades mounted across the flow direction of
the fluid. The diameter of the rotor is slightly less than the inner
diameter of the conduit, and its speed of rotation is proportional
to the volumetric flow volume. Turbine rotation can be detected
by solid-state devices or mechanical sensors.
In one application incorporating a variable reluctance coil pick-up,
a coil is a permanent magnet and the turbine blades are made of
a material attracted to a magnet. As each blade passes the coil,
a voltage pulse is generated in the coil. Each pulse represents
a discrete volume of liquid. The number of pulses per unit volume
is called the meter's K-factor.
In another application utilizing inductance pick-up, a permanent
magnet is embedded in the rotor. As each blade passes the coil,
a voltage pulse is generated. Alternatively, only one blade is magnetic
and the pulse represents a complete revolution of the rotor. Depending
upon the design, it may be preferable to amplify the output signal
prior to its transmission.
Proving the fluid flow meter is a process for ensuring the accuracy
of the flow meter. Typically, a section of the fluid system called
a proving loop is utilized during the meter proving. The dimensions
of the proving loop are known and the flow of fluid within the loop
can be monitored by sensors wherein a variety of fluid characteristics
can be sensed. The meter-proving process simultaneously monitors
a pulse signal generated by a turbine operably connected within
the fluid system. The flow volume of the fluid is determined by
utilizing the sensed values with industrial standard flow volume
equations, e.g., American Gas Association and American Petroleum
Institute standard equations. The calculated flow volume is then
compared to the known flow volume of the proving loop. By comparing
the calculated fluid flow volume to the known fluid flow volume
of the proving loop, the accuracy of the flow meter can be determined.
The duration of a meter-proving process is generally one-hundred-thousand
turbine pulses. This amount of time is believed to be adequate to
accurately determine the fluid flow volume. Generally, the turbine
pulse signal is not in synch with the flow meter proving process,
i.e., the meter proving process will generally not start at the
beginning of the turbine pulse signal. When the pulses are counted
at the end of the proving period, the partial pulses occurring at
the beginning and end of the proving period are omitted. Because
of the duration of the proving period, it is generally believed
that these partial pulses are negligible. However, utilizing the
partial pulses and other characteristics of the monitored fluid
can reduce the time required for the meter proving process, thus
reducing the length of the proving loop.
This invention is directed to solving these and other problems.
SUMMARY OF THE INVENTION
The present invention is directed to utilizing a controller to
monitor a flow volume in a fluid transportation system. The controller,
preferably a programmable logic controller, cooperates with a flow
meter to sense a fluid and determine a flow volume. The controller
also ensures the accuracy of the flow meter using an interpolation
method. As a result, a less expensive implementation of monitoring
a fluid transportation system with a controller can be realized.
An embodiment of the present invention is directed to a method
of proving a flow meter. The flow meter is connected to a controller
and a proving loop within a fluid transportation system. The proving
loop has a known flow volume. The controller monitors a fluid flow
within the proving loop. The method comprises the steps of starting
a meter-proving period and sensing a pulse signal responsive to
a flow meter. The flow meter generates a fluid flow through the
fluid transportation system. The meter-proving process is terminated
and the amount of sensed pulse signals occurring during the meter-proving
period is calculated. The fluid flow volume of the proving loop
is determined in response to the pulse signals occurring during
the meter-proving process and other sensed characteristics, preferably
density, of the fluid. The calculated flow volume of the proving
loop is compared against the known volume of the proving loop. The
meter-proving process is executed within the controller.
The calculation of the sensed pulse signals is the sum of the full
pulse signals and the partial pulse signals occurring during the
meter-proving process. The partial pulse signals are interpolated
to provide an accurate pulse signal measurement.
A further aspect of the above embodiment of the present invention
is directed to adjusting the flow meter and/or controller in response
to the comparison of the calculated flow volume of the proving loop
and its known flow volume, wherein the fluid flow meter and/or controller
more accurately calculate the flow volume.
A further embodiment of the present invention is directed to method
of measuring a flow volume of a fluid within a conduit. A controller
is connected to a flow meter and the conduit. The controller monitors
the fluid flow volume through a plurality of input channels operably
connected to the flow meter of a fluid transportation system. The
controller senses a pulse signal generated by the flow meter over
a period of time determined by the size of the meter-proving loop.
A densitometer being operably connected to the controller senses
the real time density of the fluid. The density of the fluid is
sensed and stored by the controller as a dynamic variable to be
utilized in the determination of the flow volume. The controller
utilizes the sensed dynamic density in cooperation with an industrial
standard, API 2540 which yields a correction factor, M, to be used
by another standard industrial equation, AGA-7 for calculating
a flow volume through the measuring flow meter.
Significant cost savings can be attained by implementing a less
expensive controller capable of performing the monitoring and control
functionality required for determining a flow volume. In addition,
more accurate flow volume calculations can be obtained by utilizing
additional characteristics, i.e., real time density values, in cooperation
with the industrial standard equations.
Other advantages and aspects of the present invention will become
apparent upon reading the following description of the drawings
and detailed description of the invention.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is diagram depicting one embodiment of a turbine flow meter;
FIG. 2 is a diagram depicting another embodiment of a turbine flow
meter;
FIG. 3 is a block diagram of one embodiment of the present invention;
FIG. 3A is a block diagram of an embodiment of a proving loop used
with the present invention;
FIG. 4 is a block diagram of another embodiment of the present
invention; and,
FIG. 5 is a timing diagram of the preferred interpolation method
of the present invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENT
While this invention is susceptible of embodiments in many different
forms, there is shown in the drawings and will herein be described
in detail a preferred embodiment of the invention with the understanding
that the present disclosure is to be considered as an exemplification
of the principles of the invention and is not intended to limit
the broad aspect of the invention to the embodiment illustrated.
A flow meter 10 preferably a turbine, comprises a rotor 12 having
a plurality of blades 14 mounted across the flow direction of the
fluid within a conduit 16. See FIGS. 1 and 2. The diameter of the
rotor 12 is slightly less than the inner diameter of the conduit
16 or pipe, and its speed of rotation is proportional to the volumetric
flow volume. Turbine rotation can be detected by solid-state devices
or mechanical sensors. As each blade 14 revolves, a voltage pulse
is generated. Each pulse represents a discrete volume of liquid.
Alternatively, only one blade 14 can generate a pulse, thus, each
pulse represents one complete revolution of the rotor 12. The number
of pulses per unit volume is called the meter's K-factor.
The volume of rotation and registration of each rotor blade 14
implies the passage of a fixed volume of fluid. Fluid flow in a
pipeline is the actual volume of fluid that passes a given point
during a specified time. Volumetric flow can be calculated by monitoring
various characteristics of the fluid, such as velocity, density,
temperature and pressure. These characteristics are monitored by
a controller 20 for use with industrial standard equations for fluid
flow calculation, preferably in accordance with AGA and API standards.
A controller 20 having a module 22 operably attached to the backplate
of the controller, is operably connected to the flow meter 10 via
a plurality of input channels. See FIG. 3. The pulse signal generated
by the turbine 10 is received by the module 22. The input channels
of the module 22 are adapted to receive input signals in the range
of 25 mV-30V DC. Thus, the module 22 can be directly connected to
the flow meter 10. The module 22 receives the flow meter frequency
signal and can be programmed with K and M factors for converting
the frequency input to a specified volumetric flow volume measurement
unit. Typical units of volumetric flow include gallons (or liters)
per minute and cubic feet (or meters) per minute.
A more accurate flow volume can be obtained by utilizing an additional
characteristic, i.e., real time fluid density, of the monitored
fluid in cooperation with the industrial standard equations. See
FIG. 4. A densitometer 24 is operably connected to an input channel
of the controller 20. The densitometer 24 senses the density of
the fluid within the pipeline. The real-time sensed density value
is utilized with the API 2540 standard to calculate a correction
factor, M, for the AGA-7 flow equation that measures the fluid flow
through a flow meter. Preferably, the real-time sensed density values
are stored as a dynamic variable within the module 22. Utilizing
dynamic density values with an API 2540 dual chronometry pulse interpolation
standard equation takes into account the effects that changing pressure
and temperature of the fluid (and the material of the conduit 16
itself) will have on the calculated flow volume. The use of the
dynamic density values provides for a more accurate flow volume
than a flow volume calculated with a static density variable for
the fluid having an assumed temperature and pressure value.
Proving the fluid flow meter 10 is a process for ensuring the accuracy
of the flow meter. See FIGS. 3 and 3A. Typically, a section of the
pipeline 16 called a proving loop 26 is utilized during the meter
proving. The dimensions of the proving loop 26 are known and the
flow of fluid through the loop can be monitored by sensors wherein
a variety of fluid characteristics can be sensed. The flow volume
of the fluid is determined by utilizing the sensed characteristics
with industrial standard flow volume equations, e.g., AGA-7. A comparator
38 compares the calculated flow quantity to the known flow volume
of the proving loop 26.
During the meter-proving process, the controller 20 senses the
amount of pulse signals generated by a turbine 10 that occur. The
controller utilizes a calculator 30 to calculate the fluid volume
for the proving loop 26 in response to the sensed pulse signals
that occurred during the meter-proving process. By comparing the
calculated fluid flow volume to the known fluid flow volume of the
proving loop 26 one can determine the accuracy of the flow meter
10.
The proving loop 26 is a U-shaped conduit having a known fluid
volume. The proving loop 26 is operably attached to the fluid transportation
system. A pair of valves V1 V2 connect the ends of the proving
loop 26 to the system. At the start of the meter-proving process,
the valves are switched to allow fluid into the proving loop 26.
The fluid entering the proving loop 26 pushes a ball, also known
as a "pig," through the proving loop. Initially, the pig
passes and activates a first switch, S1. Upon activation of the
first switch, S1 the controller 20 senses the pulses generated
by the flow meter 10 until the meter-proving process is terminated
when the pig passes a second switch, S2. The time it takes the pig
to travel from the first switch, S1 to the second switch, S2 is
the duration of the meter-proving period.
During the meter-proving process, the module 22 senses the density
of the fluid flowing in the proving loop 26. The sensed density
values are linearized by the controller 20. The controller 20 utilizes
the linearized density value and the amount of pulses sensed during
the meter-proving process to calculate a correction factor, M, to
later be used by the controller, for determining the volume of fluid
flowing through the transportation fluid system. The correction
factor is utilized in equation AGA-7 to update the accuracy of the
flow meter 10 in the system. The accuracy of the flow meter 10 can
be improved by adjusting the flow meter or the factors (M or K),
used to determine the flow volume of the flow meter.
Generally, the turbine pulse signal is not in synch with the flow
meter 10 proving process, i.e., the meter-proving process will generally
not start at the beginning of the turbine pulse signal. See FIG.
5. Thus, partial pulses occur at the beginning and end of the proving
period. An interpolator 32 utilizes a pulse interpolation method
to improve the discrimination of the flow meter's output, thus requiring
a lesser amount of pulse signals to be collected during the meter-proving
process. Because fewer pulse signals are required, the proving loop
26 can be shortened, thus reducing the cost of the fluid transportation
system.
While various interpolation methods can be used, the preferable
interpolation method utilized by the controller 20 is double chronometry,
also found in the API 2540 standards. Double chronometry pulse interpolation
requires counting a total integral number of flow meter pulses,
Nm, generated during the proving process and measuring a set of
time intervals, T1 and T2. T1 is the time interval between the first
pulse before or after the first detection signal and the first pulse
before or after the last detection signal. T2 is the time interval
between the first and last detector pulses. See FIG. 5.
The pulse monitor 34 is started and stopped by a meter prover detector
28. The time intervals T1 and T2 correspond to Nm pulses and the
interpolated number of pulses, N1 respectively. The interpolated
pulse count, N1 is equal to Nm(T2/T1). An accumulator 36 sums and
stores the total number of pulse signals for use by the controller
10 in determining flow volume. The total number of pulses is the
sum of the integral pulses and the interpolated partial pulses.
At the beginning of another meter-proving process, the controller
20 resets the accumulator 36 calculator 30 and the pulse counter
21.
While the specific embodiment has been illustrated and described,
numerous modifications come to mind without significantly departing
from the spirit of the invention, and the scope of protection is
only limited by the scope of the accompanying claims. |