Measuring and testing – Volume or rate of flow – Mass flow by imparting angular or transverse momentum to the...
Reexamination Certificate
1999-06-28
2001-11-20
Noori, Max (Department: 2855)
Measuring and testing
Volume or rate of flow
Mass flow by imparting angular or transverse momentum to the...
Reexamination Certificate
active
06318186
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to electronic components for controlling a drive signal in an apparatus that measures properties of material flowing through at least one vibrating conduit in the apparatus. More particularly, this invention relates to a system that determines parameters for generating a drive signal from the frequency of oscillation of a vibrating conduit.
PROBLEM
It is known to use Coriolis effect mass flowmeters to measure mass flow and other information for materials flowing through a conduit in the flowmeter. Exemplary Coriolis flowmeters are disclosed in U.S. Pat. Nos. 4,109,524 of Aug. 29, 1978, 4,491,025 of Jan. 1, 1985, and Re. 31,450 of Feb. 11, 1982, all to J. E. Smith et al. These flowmeters have one or more conduits of straight or curved configuration. Each conduit configuration in a Coriolis mass flowmeter has a set of natural vibration modes, which may be of a simple bending, torsional or coupled type. Each conduit is driven to oscillate at resonance in one of these natural modes. Material flows into the flowmeter from a connected pipeline on the inlet side of the flowmeter, is directed through the conduit or conduits, and exits the flowmeter through the outlet side of the flowmeter. The natural vibration modes of the vibrating, material filled system are defined in part by the combined mass of the conduits and the material flowing within the conduits.
When there is no flow through the flowmeter, all points along the conduit oscillate due to an applied driver force with identical phase or small initial fixed phase offset which can be corrected. As material begins to flow, Coriolis forces cause each point along the conduit to have a different phase. The phase on the inlet side of the conduit lags the driver, while the phase on the outlet side of the conduit leads the driver. Pick-off sensors on the conduit(s) produce sinusoidal signals representative of the motion of the conduit(s). Signals output from the pick-off sensors are processed to determine the phase difference between the pick-off sensors. The phase difference between two pick-off sensor signals is proportional to the mass flow rate of material through the conduit(s).
It is a problem that sometimes a flow is sporadic and contains entrained air. This entrained air causes the vibrations of the tubes to change amplitude. This can cause errors in the measured properties of the flowing material, such as mass flow. This is especially true in a straight flow tube configuration because straight flow tubes must be driven to vibrate at a much high frequency than flow tubes of a curved configuration and any disruption of the vibration of the straight flow tubes can more adversely affect calculations of the properties.
A transmitter generates a drive signal to operate the driver and determines a mass flow rate and other properties of a material from signals received from the pick-off sensors. A conventional transmitter is made of analog circuitry which is designed to generate the drive signal and detect the signals from the pick-off sensors. Analog transmitters have been optimized over the years and have become relatively cheap to manufacture. It is therefore desirable to design Coriolis flowmeters that can use conventional transmitters.
It is a problem that conventional transmitters must work with signals in a narrow range of operating frequencies. This range of operating frequencies is typically between 20 Hz and 200 Hz. This limits the designers to generating a narrow range of drive signals that will resonate the flow tubes at these frequencies. Therefore, it is impossible to use a conventional transmitter to generate the drive signals for some flowmeters, such as a straight tube flowmeter, which operate in a higher frequency range of 300 Hz-800 Hz. Therefore, a conventional transmitter cannot be used to generate the drive signal for straight tube flowmeters.
Those skilled in the Coriolis flowmeter art desire to design a transmitter that can be used with several different types of flowmeters. This would allow the manufacturers to take advantage of economies of scale to produce less expensive transmitters for flowmeters. A digital signal processor is desirable because the higher demand in measurement resolution and accuracy put on analog electronic components by flowmeters operating at higher frequencies, such as straight tube designs, are avoided by the digitalization of signals from the pick-offs as the signals are received by the transmitter. Furthermore, the instructions for signaling processes used a digital processor may be modified to operate at several different frequencies for both determining the properties of a material and generating the drive signals.
SOLUTION
The above and other problems are solved and an advance in the art is made by the provision of a system that initializes the parameters of a drive signal in a transmitter of a Coriolis flow meter. The system of this invention is comprised of processes that are stored in a memory and executed by a processor in order to generate drive signals for a driver of a vibrating conduit. Alternatively, the processes of this invention could also be performed by analog circuits. The processes of this invention allow a transmitter to determine the type of flow tube configuration that is attached to the transmitter and then set the parameters needed to generate the drive signals. This invention also uses a third parameter of integral drive gain to allow for better control of the drive signal in order to gain more robust control of the vibration of the flow tubes.
In a preferred embodiment of this invention, the system is provided by a digital signal processor such as the Texas Instruments TM3205xx, Analog Devices ADSP21xx, or Motorola 5306x. The processes of this invention are stored as instructions in a memory connected to the digital signal processor. The digital signal processor reads and executes the instructions to perform the processes of this invention.
The process begins by the flow tube being vibrated by an initial drive signal. The frequency of vibration of the flow tube is then determined. From the frequency of vibration, the type of flow tube is determined. A pre-stored set of parameters is then set as the parameters used to generate the drive signal.
The parameters include an integral drive gain component. The integral gain component controls the error between a set point and an actual target. This allows for a more robust control of the drive signal which allows the amplitude of the vibration to be more precise. This allows optimal power to be supplied to the sensor even under adverse flow conditions.
REFERENCES:
patent: 4817488 (1989-04-01), Hargarten et al.
patent: 4823614 (1989-04-01), Dahlin
patent: 4934196 (1990-06-01), Romano
patent: 5321991 (1994-06-01), Kalotay
patent: 5555190 (1996-09-01), Derby et al.
patent: 5734112 (1998-03-01), Bose et al.
patent: 3738018 A1 (1989-05-01), None
patent: 0 866 319 A1 (1998-09-01), None
Smith Brian T.
Smith Richard L.
Chrisman Bynum & Johnson, P.C.
Micro Motion Inc.
Noori Max
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