Data processing: measuring – calibrating – or testing – Calibration or correction system – Fluid or fluid flow measurement
Reexamination Certificate
2001-03-13
2003-01-07
Shah, Kamini (Department: 2863)
Data processing: measuring, calibrating, or testing
Calibration or correction system
Fluid or fluid flow measurement
C702S054000, C073S861354, C073S861355, C073S861356
Reexamination Certificate
active
06505135
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 an algorithm used to initialize and maintain a drive signal that oscillates the conduit at a desired frequency.
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. No. 4,109,524 of Aug. 29, 1978, U.S. Pat. No. 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).
Meter electronics 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. Conventional meter electronics are made of analog circuitry which is designed to generate the drive signal and detect the signals from the pick-off sensors. Analog meter electronics 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 meter electronics.
It is a problem that conventional meter electronics 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 ineffective to use conventional meterelectronics 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. Straight tube flowmeters operate at 300 Hz-800 Hz because straight tubes tend to exhibit smaller sensitivity to Coriolis effects used to measure mass flow rate. Therefore, conventional meter electronics cannot effectively be used to generate the drive signal for straight tube flowmeters.
Those skilled in the Coriolis flowmeter art desire to design meter electronics 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 meter electronics 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 meter electronics. Furthermore, the instructions for signaling processes used by 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.
One problem in designing meter electronics, that is to be used with several different types of flowmeters, is the start up or initialization of the flowmeter. Straight tube flowmeters are highly damped when compared to a dual curved tube counterpart. Typically, a straight tube flowmeter has zeta values on the order of 10
−4
which causes the straight tube flowmeters to be an order of magnitude more damped. This makes starting the straight tube flowmeters problematic.
One particular problem in starting a straight tube flowmeter is when the material flowing through the meter includes entrained air. The entrained air causes problems on start up as it is difficult to get a reliable reading of the proper drive frequency. At the same time, one must ensure not to overstress the sensor due to excess drive excitation on start up. Therefore, most current start operations stall or in other words never reach the desired drive frequency. Thus, a more reliable start up algorithm is needed in order to provide meter electronics that can be used with any type of flowmeter.
SOLUTION
The above and other problems are solved and an advance in the art is made by a drive algorithm for a Coriolis flowmeter in accordance with this invention. A first advantage of this invention is that a reliable start up for many types of Coriolis flowmeters under many types of material flow is ensured. A second advantage is that normal flow operation is maintained under varying flow conditions including flow conditions that cause existing Coriolis flowmeters to stall.
A drive algorithm in accordance with this invention is performed by meter electronics used to control operation of a Coriolis flowmeter. In a preferred embodiment, the meter electronics include a processor that executes instructions for the drive algorithm that are stored in a memory associated with the processor. Alternatively, this algorithm may also be performed by firmware or other types of circuitry.
A drive algorithm in accordance with this invention is performed in the following manner to assure proper start up of a Coriolis flowmeter. The algorithm begins by applying signals to a driver at a predetermined gain to initiate vibrating of a flow tube. The vibration of the flow tube is measured by pick-off signals received from pick-off sensors associated with the flow tube. The voltage of signals applied to the driver are then controlled to maintain a velocity of pick-off signals received from the pick-off sensors. The pick-off signals are then used to converge a notch filter to a drive frequency of the flow tube. After the notch filter is converged upon the drive frequency, voltage of the signals applied to the driver is controlled to maintain a displacement of the flow tubes.
The drive algorithm may also determine a frequency of oscillation of said flow tube from the pick-off signals. The frequency of oscillation may then be compared to a threshold frequency to determine whether the flow tube is a straight tube or a dual curved flow tube. If the frequency of oscillation is greater than the threshold frequency, the flow tube is a straight flow tube. If the frequency of oscillation is less than the threshold frequency, the flow tube is a dual curved flow tube.
The application of signals to the driver to initiate vibrating of the flow tube may include setting at least one variable for use in generating said drive signals. The variables may include a pick-off amplitude, a flow tube period, and a desired drive target. During application of the signals to the driver to initiate vibration, a kick gain signal is set to off and a programable gain amplifier is set to unity gain. At this time, a timer and a notch filte
Faegre & Benson LLP
Micro Motion Inc.
Shah Kamini
LandOfFree
Initialization algorithm for drive control in a coriolis... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Initialization algorithm for drive control in a coriolis..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Initialization algorithm for drive control in a coriolis... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3000715