A measuring system for measuring at least one measurement variable, changeable as a function of time, of a fluid flowing along a flow path with a predetermined flow direction, the measuring system comprising:
- a tube arrangement comprising a lumen defining a first portion of the flow path, a second portion of the flow path disposed in a flow direction downstream of the first portion, and a third portion of the flow path disposed in the flow direction downstream of the second portion and a tube wall surrounding the lumen;
- a flow obstruction arranged within the tube arrangement in the second portion of the flow path, the flow obstruction configured to effect a disturbance in the flowing fluid, the disturbance dependent on the at least one measurement variable and/or serving as a measurable effect dependent on the at least one measurement variable;
- a first sensor arrangement configured to generate a first sensor signal having a first frequency spectrum influenced by the fluid flowing within the first portion;
- a second sensor arrangement configured to generate a second sensor signal having a second frequency spectrum influenced by the fluid flowing within the third portion, the second frequency spectrum deviating from the first frequency spectrum and/or including at least one wanted component, the at least one wanted component including a spectral signal component influenced by the at least one measurement variable as regards at least one signal parameter;
- and
- a transmitter electronics including a microprocessor and configured to:
- receive the first sensor signal and convert such into a first sensor signal sampling sequence approximating the first sensor signal, the first sensor signal sampling sequence including a first sequence of digital sampled values, defined by SD1[m]=SD1[tm·fs1], using a first sampling rate, defined by fs1=1/(tm+1-tm)=1/Ts1, from the first sensor signal at different sampling points in time, given by tn=n·Ts1;
- receive the second sensor signal and convert such into a second sensor signal sampling sequence approximating the second sensor signal, the second sensor signal sampling sequence including a second sequence of digital sampled values, defined by SD2[n]=SD2[tn·fs2] using a second sampling rate, defined by fs2=1/(tn+1-tn)=1/Ts2, from the second sensor signal at different sampling points in time, given by tn=n·Ts2, such that the second sensor signal sampling sequence approximates at least one wanted spectral signal component of the second sensor signal influenced by the at least one measurement variable;
- using a digital adaptive filter, ascertain from the first sensor signal sampling sequence a wanted signal filter coefficients set including a set of N filter coefficients;
- using the wanted signal filter coefficients set, generate a first z-transfer function of a wanted signal filter, defined as:
- G
- FIR
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-
- (
- z
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- =
- Z
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- (
- g
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- =
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- k
- =
- 0
- N
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- 1
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- k
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- z
- -
- k
- =
- ∑
- k
- =
- 0
- N
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-
- w
- k
- ·
- e
- -
- j
-
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- ω
-
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- T
- s
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- 2
- ,
- wherein wk are the filter coefficients, the wanted signal filter being a digital filter adapted to filter the second sensor signal sampling sequence such that the first z-transfer function of the wanted signal filter is determined by the wanted signal filter coefficients set;
- generate a wanted signal sequence, using the wanted signal filter and the second sensor signal sampling sequence, the wanted signal sequence being a sequence of digital function values defined by:
- S
- ^
- D
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- 2
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- n
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- =
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- ,
- to generate from the wanted signal sequence a measured values sequence, being a sequence of digital measured values representing the at least one measurement variable and following one after the other in time.