Adaptive filtering for a vortex flowmeter
First Claim
1. A method for processing vortex generated signal pulses representing the shedding frequency of alternating differential pressure vortices of a process flow, said method comprising:
- a) determining an operating range, the operating range representing a range of vortex shedding frequencies of the process flow, said operating range bounded by a first frequency limit and a second frequency limit;
b) receiving the vortex generated signal;
c) filtering the vortex generated signal relative to a bandwidth, the bandwidth representing a range of vortex shedding frequencies within the operating range which will be preserved, said filtering attenuating a range of vortex shedding frequencies outside of the bandwidth;
d) computing the vortex shedding frequency of the vortex generated signal and generating a vortex frequency signal representative thereof;
e) checking for a rapid change within the vortex frequency signal and altering said filtering step to widen the bandwidth to at least one of said first frequency limit and said second frequency limit if the rapid change is detected;
f) adjusting said filtering step to preserve the bandwidth about the vortex frequency signal; and
g) transmitting the vortex frequency signal to further signal processing circuitry for outputting the vortex frequency signal in a desired manner.
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Abstract
A method and apparatus for increasing the resolution and accuracy of flow measurements made by vortex flowmeters through the use of an adaptive filter. A vortex sensor signal is conditioned by a bandpass filter whose corner frequencies are dynamically altered as a function of the measured frequency of the vortex sensor signal. When the change in frequency is relatively small, the filters'"'"' corner frequencies are set to track the frequency signal in accordance with a specified bandwidth thereby improving the signal-to-noise ratio. For large frequency changes, a new frequency signal is searched for thereby avoiding tracking erroneous noise signals. Furthermore, compensation for additional or missed vortex pulses is made thereby generating a more accurate vortex frequency measurement.
59 Citations
13 Claims
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1. A method for processing vortex generated signal pulses representing the shedding frequency of alternating differential pressure vortices of a process flow, said method comprising:
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a) determining an operating range, the operating range representing a range of vortex shedding frequencies of the process flow, said operating range bounded by a first frequency limit and a second frequency limit; b) receiving the vortex generated signal; c) filtering the vortex generated signal relative to a bandwidth, the bandwidth representing a range of vortex shedding frequencies within the operating range which will be preserved, said filtering attenuating a range of vortex shedding frequencies outside of the bandwidth; d) computing the vortex shedding frequency of the vortex generated signal and generating a vortex frequency signal representative thereof; e) checking for a rapid change within the vortex frequency signal and altering said filtering step to widen the bandwidth to at least one of said first frequency limit and said second frequency limit if the rapid change is detected; f) adjusting said filtering step to preserve the bandwidth about the vortex frequency signal; and g) transmitting the vortex frequency signal to further signal processing circuitry for outputting the vortex frequency signal in a desired manner. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. A vortex flowmeter for determining the flow rate of a process flow comprising:
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a) means for generating a vortex signal representing a frequency of alternating differential pressure vortices of a process flow, said vortices generated by the vortex flowmeter; b) means for determining an operating range, the operating range representing a range of possible vortex frequencies of the process flow, said operating range bounded by a first frequency limit and a second frequency limit; c) means for filtering from the vortex signal a range of vortex frequencies outside of a variable bandwidth and preserving the range of vortex frequencies defined by the bandwidth; d) means for computing the frequency of the vortex signal in order to determine a process flow rate; e) means for detecting changes in the frequency of the vortex signal; f) means for altering said filtering means relative to said detection means in order to preserve variable bandwidth about the vortex frequency signal, thereby generating an improved vortex frequency signal and a more accurate measurement of the process flow rate; and g) means for checking for a rapid change within the vortex frequency signal and altering said means for filtering to widen the bandwidth to at least one of said first frequency limit and said second frequency limit of the operating range if the rapid change is detected.
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12. A method for processing vortex generated signal pulses representing the shedding frequency of alternating differential pressure vortices of a process flow, said method comprising:
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a) determining an operating range, the operating range representing a range of vortex shedding frequencies of the process flow; b) receiving the vortex generated signal; c) filtering the vortex generated signal relative to a bandwidth, the bandwidth representing a range of vortex shedding frequencies within the operating range which will be preserved, said filtering attenuating a range of vortex shedding frequencies outside of the bandwidth; d) computing the vortex shedding frequency of the vortex generated signal and generating a vortex frequency signal representative thereof, said computing including; i) sampling a portion of the vortex generated signal pulses over a sampling period; ii) determining a number of added vortex signal pulses and a number of dropped vortex signal pulses contained within the portion of said sampling; and iii) computing the vortex frequency as a function of the sampled portion and the number of added and dropped vortex signal pulses; e) adjusting said filtering step to preserve the bandwidth about the vortex frequency signal; and f) transmitting the vortex frequency signal to further signal processing circuitry for outputting the vortex frequency signal in a desired manner.
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13. A system for processing vortex generated signal pulses representing the shedding frequency of alternating differential pressure vortices of a process flow, said system comprising:
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a) means for determining an operating range, the operating range representing a range of vortex shedding frequencies of the process flow; b) means for receiving the vortex generated signal; c) means for filtering the vortex generated signal relative to a bandwidth, the bandwidth representing a range of vortex shedding frequencies within the operating range which will be preserved, said means for filtering attenuating a range of vortex shedding frequencies outside of the bandwidth; d) means for computing the vortex shedding frequency of the vortex generated signal and generating a vortex frequency signal representative thereof, said means for computing including; i) means for sampling a portion of the vortex generated signal pulses over a sampling period; ii) means for determining a number of added vortex signal pulses and a number of dropped vortex signal pulses contained within the portion of said sampling; and iii) means for computing the vortex frequency as a function of the sampled portion and the number of added and dropped vortex signal pulses; e) means for adjusting said filtering step to preserve the bandwidth about the vortex frequency signal; and f) means for transmitting the vortex frequency signal to further signal processing circuitry for outputting the vortex frequency signal in a desired manner.
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Specification