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AssigneeDanfoss A/S
InventorsHenning Max Hansen, Frands Wulff Voss, Niels Per Mondrup, Karsten Westermann, Hans Jørgen Moos, James D. Collier, Roger F. Sewell, Richard-Jan E. Jansen
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In a circuit arrangement for deriving the measured variable from the signals (S1 to S2) of at least two sensors (23, 24) of a flow meter, which flow meter comprises one or several parallel fluid lines (20, 21) and means (22) for exciting oscillations of a predetermined fundamental frequency (ω) in the fluid line(s), the sensors (23, 24) detect the oscillations and the sensor signals (S1 to S2) are supplied by way of a respective A-D converter (36; 37) to a digital processing unit (P) having a computation circuit (46), in which their phase difference (Φ) is determined as a measure of the flow. In order to be largely independent of unwanted changes in the fundamental frequency (ω) of the sensor signals (S1, S2), and to measure the flow with little effort and with as few errors as possible, provision is made for the processing unit (P) between the A-D converter (36; 37) of each sensor signal (S1, S2) and the computation circuit (46) to comprise a digital multiplier circuit (M) and a digital filter arrangement (F) downstream thereof, for the digital sensor signals (S1, S2) to be multiplied in the multiplier circuit (M) with respective digital signals (I, R) phase-displaced by 90° with respect to one another that represent sinusoidal oscillations of identical maximum amplitude (x) and of a frequency (ω+Δω) that varies by a slight difference frequency (Δω) from the fundamental frequency (ω), and for the pass band of the filter arrangement (F) to be matched to the difference frequency (Δω).
Circuit arrangement for deriving a measured variable from signals of at least two sensors of a flow meter, which flow meter comprises at least one fluid line and means for exciting oscillations of a predetermined fundamental frequency in the fluid line, the sensors detecting the oscillations and the sensor signals being supplied in parallel by way of a respective A-D converter for each signal to a digital processing unit having a computation circuit in which a phase difference of the sensor signals is determined as a measure of the flow, the digital processing unit comprising a digital multiplier circuit and a digital filter arrangement downstream thereof, the digital multiplier circuit having means to multiply a digital sensor signal from each A-D converter with each one of at least two digital signals, the two digital signals being phase-displaced by 90° with respect to each other and representing sinusoidal oscillations of identical amplitude and of a frequency that varies by a difference frequency from the fundamental frequency, and the digital filter arrangement having a pass band that is matched to the difference frequency.
Circuit arrangement for deriving a measured variable from signals of at least two sensors of a flow meter, which flow meter comprises at least one fluid line and means for exciting oscillations of a predetermined fundamental frequency in the fluid line, the sensors detecting the oscillations and the sensor signals being supplied in parallel by way of a respective A-D converter for each signal to a digital processing unit having a computation circuit in which a phase difference of the sensor signals is determined as a measure of the flow, the digital processing unit comprising a digital multiplier circuit and a digital filter arrangement downstream thereof, the digital multiplier circuit having means to multiply a digital sensor signal from each A-D converter with each one of at least two digital signals, the two digital signals being phase-displaced by 90° with respect to each other and representing sinusoidal oscillations of identical amplitude and of a frequency that varies by a difference frequency from the fundamental frequency, the digital filter arrangement having a pass band that is matched to the difference frequency, each A-D converter comprising a sigma-to-delta converter and a decimator connected downstream thereof, the decimator comprising a Hogenauer circuit having a first matrix of digital integrators followed by a corresponding second matrix of digital differentiating elements.
Circuit arrangement for deriving a measured variable from signals of at least two sensors of a flow meter, which flow meter comprises at least one fluid line and means for exciting oscillations of a predetermined fundamental frequency in the fluid line, the sensors detecting the oscillations and the sensor signals being supplied in parallel by way of a respective A-D converter for each signal to a digital processing unit having a computation circuit in which a phase difference of the sensor signals is determined as a measure of the flow, the digital processing unit comprising a digital multiplier circuit and a digital filter arrangement downstream thereof, the digital multiplier circuit having means to multiply a digital sensor signal from each A-D converter with each one of at least two digital signals, the two digital signals being phase-displaced by 90° with respect to each other and representing sinusoidal oscillations of identical amplitude and of a frequency that varies by a difference frequency from the fundamental frequency, the digital filter arrangement having a pass band that is matched to the difference frequency, and in which the computation circuit determines the phase difference of the sensor signals according to the relation ϕ = arc tan bc - ad a c + bd
Circuit arrangement for deriving a measured variable from signals of at least two sensors of a flow meter, which flow meter comprises at least one fluid line and means for exciting oscillations of a predetermined fundamental frequency in the fluid lines the sensors detecting the oscillations and the sensor signals being supplied in parallel by way of a respective A-D converter for each signal to a digital processing unit having a computation circuit in which a phase difference of the sensor signals is determined as a measure of the flow, the respective A-D converters sampling the sensor signals at a clock rate which is fixed and unsynchronized with the sensor frequency, the digital processing unit comprising a digital multiplier circuit and a digital filter arrangement downstream thereof, the digital multiplier circuit having means to multiply a digital sensor signal from each A-D converter with each one of at least two digital signals, the two digital signals being phase-displaced by 90° with respect to each other and representing sinusoidal oscillations of identical amplitude and of a frequency that may vary by a difference frequency from the sensor frequency, and the digital filter arrangement having a pass band that is matched to the difference frequency.
Dependencies are inferred from the claim text.