JP2011064494A - Coriolis flowmeter and frequency measuring method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a coriolis flowmeter and a frequency measuring method having small errors and variations of measurement frequency even when noise is superimposed on a detection signal or a signal obtained by digitally processing the same. <P>SOLUTION: In the coriolis flowmeter 100 in which a measuring tube through which a measurement fluid flows is vibrated and which includes an in-phase digital filter means 21A detecting a vibration including coriolis force generated in the measurement fluid by the vibration and for output of a digital signal having a phase the same as the detection signal and an out-of-phase digital filter means 21B for output of a digital signal having a phase different from the detection signal by 90 degrees, the coriolis flowmeter includes a frequency calculation means 110 for calculating a frequency of the detection signal on the basis of the in-phase digital signal DA4 and the digital signal DA5 having the phase that is different by 90 degrees when a value based on the in-phase digital signal DA4 and the digital signal DA5 having the phase that is different by 90 degrees is outside a prescribed range. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a Coriolis flow meter, and more particularly to frequency measurement of a detection signal.

  In flow control performed in a chemical plant or the like, a Coriolis flow meter is used for measuring a flow rate of a fluid to be measured. As an example, Patent Document 1 discloses a configuration of a Coriolis flow meter. Such a Coriolis flow meter will be described with reference to FIGS.

  4A is a configuration diagram of the detection unit SNS of the Coriolis flow meter, FIG. 4B is an operation explanatory diagram illustrating the operation of the detection unit SNS, and FIG. 5 is a configuration diagram of the Coriolis flow meter 10.

  First, FIG. 4 will be described. In FIG. 4A, the measurement tube may be another method such as a U-shaped tube method, but for simplicity, a measurement tube will be described.

  Reference numeral 1 denotes a measurement tube for flowing a fluid to be measured, and the fluid to be measured flows from left to right. Both ends of the measurement tube 1 are fixed to the support members 2 and 3. In the vicinity of the center portion of the measuring tube 1, a vibrator 4 is installed for mechanically vibrating the measuring tube 1 up and down.

  An upstream sensor 5 </ b> A and a downstream sensor 5 </ b> B for detecting vibration of the measurement tube 1 are fixed in the vicinity of the measurement tube 1 fixed to the support members 2 and 3. A temperature sensor 6 used for temperature compensation is provided in the vicinity of the support member 3. The sensor unit SNS is configured as described above.

  In FIG. 4B, when a fluid to be measured flows through the measurement tube 1 in a state where vibration is applied from the vibrator 4 to the measurement tube 1 in the shape of the primary mode as indicated by M1 and M2, Coriolis force is generated in the measurement fluid, and the measurement tube 1 vibrates in a secondary mode shape as indicated by M3 and M4.

  Actually, the measuring tube 1 vibrates in a form in which these two types of vibration patterns are superimposed. Based on the displacement signals (detection signals) SA and SB detected by the upstream sensor 5A and the downstream sensor 5B, the Coriolis flowmeter measures the mass flow rate of the fluid to be measured.

  Next, FIG. 5 will be described. The clock signal oscillator 17 generates a timing signal TC having a predetermined sampling period regardless of the vibration of the measuring tube 1.

On the other hand, the displacement signal SA is output to the sample and hold (T & H) circuit 18 in the form of A × SIN (ω × t ₀ ), for example, and is sequentially sampled / held by the timing signal TC that determines the sampling time. . Here, A is the amplitude (V), ω is the angular velocity (rad / s), and t ₀ is an arbitrary time point.

  The held displacement signal SA is output to an analog / digital converter (A / D) 19 where it is sequentially converted into a digital signal DA2 and output to a low-pass filter (LPF) 20 processed in digital form.

  The low-pass filter (LPF) 20 removes a frequency component higher than the vicinity of the vibration frequency of the measuring tube 1 and outputs it as a digital signal DA3 to an FIR filter 21A which is a kind of digital filter. “FIR” is an abbreviation for “Finite Impulse Response”.

The FIR filter 21A is an in-phase digital filter that converts an output signal having the same phase as the input signal, and basically outputs a digital signal DA4 in the form of A × SIN (ω × t ₀ ) at its output end. That is, the output signal DA4 of the FIR filter 21A and the displacement signal SA have the same phase.

Similarly, the digital signal DA3 is output to an FIR filter 21B, which is a kind of digital filter. The FIR filter 21B is a different-phase digital filter that converts an input signal into an output signal that is 90 degrees different from the input signal, and basically outputs a digital signal DA5 in the form of A × COS (ω × t ₀ ). That is, the output signal DA5 of the FIR filter 21B and the displacement signal SA are 90 degrees out of phase. The FIR filter 21A and the FIR filter 21B constitute the Hilbert conversion means 21.

The phase calculating means 23 calculates a ratio KA (= A × SIN (ω × t ₀ ) / A × COS (ω × t ₀ )) between the digital signal DA4 and the digital signal DA5. Since this value is equal to tan (ω × t ₀ ), the tan ⁻¹ (inverse tangent) is further calculated to calculate the phase θA2 (= ω × t ₀ ) (rad) of the displacement signal SA.

The displacement signal SB is output to the sample and hold (T & H) circuit 24 in the form of B × SIN (ω × t ₀ + ΔΦ), for example, and is sequentially sampled / held by the timing signal TC that determines the sampling time. The Here, B is the amplitude (V), ω is the angular velocity (rad / s), t ₀ is an arbitrary time point, and ΔΦ is a phase difference (rad) with respect to the displacement signal SA at the time point t ₀ .

  The held displacement signal SB is output to an analog / digital converter (A / D) 25, where it is sequentially converted into a digital signal DB2 and output to a low-pass filter (LPF) 26 that is processed in digital form. The low-pass filter (LPF) 26 has the same configuration as the low-pass filter (LPF) 20, and gain characteristics, group delay characteristics, and the like are selected in common.

  Similarly to the low-pass filter (LPF) 20, the low-pass filter (LPF) 26 removes a frequency component higher than the vicinity of the vibration frequency of the measuring tube 1 and supplies the digital signal DB3 to the FIR filter 27A which is a kind of digital filter. Output as.

Similar to the FIR filter 21A, the FIR filter 27A is an in-phase digital filter that converts it into an output signal having the same phase as the input signal, and basically has a digital output of B × SIN (ω × t ₀ + ΔΦ) at its output end. The signal DB4 is output. That is, the output signal DB4 of the FIR filter 27A and the displacement signal SB have the same phase.

The digital signal DB3 is output to an FIR filter 27B, which is a kind of digital filter. This FIR filter 27B is a different-phase digital filter that converts it into an output signal having a phase different by 90 degrees from the input signal, and basically outputs a digital signal DB5 in the form of B × COS (ω × t ₀ + ΔΦ). That is, the output signal DB5 of the FIR filter 27B and the displacement signal SB are 90 degrees out of phase. The FIR filter 27A and the FIR filter 27B constitute a Hilbert conversion means 27.

The phase calculating means 29 calculates the ratio KB (= B × SIN (ω × t ₀ + ΔΦ) / B × COS (ω × t ₀ + ΔΦ)) between the digital signal DB4 and the digital signal DB5. Since this value is equal to tan (ω × t ₀ + ΔΦ), the tan ⁻¹ (inverse tangent) is further calculated to calculate the phase θB2 (= ω × t ₀ + ΔΦ) (rad) of the displacement signal SB. .

  The phase difference calculating unit 30 calculates a difference (= ΔΦ) between the phase θA2 sequentially output from the phase calculating unit 23 and the phase θB2 sequentially output from the phase calculating unit 29, and the average unit 31 Output sequentially as phase difference θd2. This phase difference θd2 is proportional to the mass flow rate QM of the fluid to be measured.

Time delay means 32, FIR filter 21A, the phase [Theta] a2 obtained in the previous timing t _-1 of the output process timing t ₀ of _{21B (= ω × t -1)} , and held as the phase θA2 '(rad) ing. Note that t _-1 indicates a timing point one time before t ₀ . The output processing period of the FIR filters 21A and 21B is T.

The frequency calculation means 33 receives the phase θA2 (= ω × t ₀ ) from the phase calculation means 23 and the phase θA2 ′ (= ω × t ₋₁ ) from the time delay means 32, and the difference between these phases θA2 and θA2 ′. Is divided by 2πT to calculate the frequency fc (= (ω × t ₀ −ω × t ₋₁ ) / 2πT) of the displacement signal SA at time t ₀ .

  The averaging means 34 calculates the average of the frequencies fc obtained at a number of timings and outputs the average as the average frequency fc '.

  In addition, the displacement signal SA is input to the excitation circuit 35, and an excitation voltage corresponding to the displacement signal SA is output to the vibration exciter 4 to drive the vibration exciter 4 in a sine wave shape, for example.

  On the other hand, a temperature signal ST1 is output from the temperature sensor 6 to a sample and hold (T & H) circuit 37, and a number of temperature signals held by a timing signal TC that determines a sampling time point are converted into analog / digital converters (A / A). D) It is converted into a digital signal at 38 and outputted to the averaging circuit 39, where it is averaged and outputted as an average temperature signal ST2.

The density calculating means 40 receives the average frequency fc ′ and the average temperature signal ST2, and calculates the density D of the fluid to be measured based on the following equations (1) and (2). At the reference temperature, when the resonance frequency when the fluid to be measured is filled in the measurement tube 1 is fv, the resonance frequency when the measurement tube 1 is empty is f0, and K1 and K2 are constants,
fv = fc ′ + K1 × ST2 (1)
D = K2 × (f0 ² −fv ² ) / fv ² (2)
As a result, a density signal D is obtained.

The mass flow rate calculation means 41 receives the density signal D, the average frequency fc ′, the phase difference θd2 (= ΔΦ) and the average temperature signal ST2, and the mass flow rate QM of the fluid to be measured is based on the following formula (3). Is calculated.
QM = f (ST2) × f (D) × tan (θd2) / fc ′ (3)
Note that f (ST2) is a temperature correction term, and f (D) is a density correction term.

Japanese Patent Laid-Open No. 7-181069

The frequency fc is calculated from the difference between the phases θA2 and θA2 ′. The phases θA2 and θA2 ′ are obtained by calculating tan ⁻¹ of the ratio KA between the digital signal DA4 and the digital signal DA5.

  If no noise component is superimposed on the digital signal DA4 and the digital signal DA5, the ratio KA, the phases θA2, θA2 ', and the frequency fc can be accurately obtained.

  When the noise component (N) is superimposed on the digital signal DA4 and the digital signal DA5, if the absolute value (signal component S) of the digital signal DA4 and the digital signal DA5 is large, the S / N ratio becomes large, and the influence of the noise component is small. For this reason, the error (deviation from the true value) of the ratio KA, the phases θA2, θA2 ′, and the frequency fc is small.

  However, if the absolute value of the digital signal DA4 or the digital signal DA5 is small in the range of Z1 near zero, the S / N ratio is small and the influence of the noise component is large. For this reason, there is a problem that errors and variations in the ratio KA, the phases θA2, θA2 ′, and the frequency fc are increased.

  An object of the present invention is to provide a Coriolis flowmeter and a frequency measurement method in which a measurement frequency error and variation are small even when noise is superimposed on a detection signal or a signal obtained by digitally processing the detection signal.

In order to achieve such an object, the invention of claim 1
In-phase digital filter means for vibrating a measurement tube through which the fluid to be measured flows, detecting vibration including Coriolis force generated in the fluid to be measured by the vibration, and outputting a digital signal having the same phase as the detection signal; and the detection signal And a Coriolis flow meter having a different-phase digital filter means for outputting a digital signal having a phase different by 90 degrees,
When a value based on the digital signal having the same phase and the digital signal having a phase different by 90 degrees is out of a predetermined range, the frequency of the detection signal is set based on the digital signal having the same phase and the digital signal having a phase different by 90 degrees. Frequency calculating means for calculating,
It is provided with.
The invention of claim 2 is the invention of claim 1,
The frequency calculating means uses near zero as the predetermined range, and calculates the frequency when values of the digital signal having the same phase and the digital signal having a phase different by 90 degrees are outside the predetermined range. .
The invention of claim 3 is the invention of claim 1,
The frequency calculation means uses near zero, a first predetermined value or more and a second predetermined value or less as the predetermined range, and a ratio between the digital signal having the same phase and the digital signal having a phase different by 90 degrees is out of the predetermined range. In this case, the frequency is calculated.
The invention of claim 4 is the invention of claim 1,
The frequency calculating means uses a vicinity of zero, a third predetermined value or more and a fourth predetermined value or less as the predetermined range, and a phase obtained from a ratio between the digital signal having the same phase and the digital signal having a phase different by 90 degrees is obtained. When the frequency is outside the predetermined range, the frequency is calculated.
The invention according to claim 5 is the invention according to any one of claims 1 to 4,
A counting means for counting at the processing timing of the in-phase digital filter means or the out-of-phase digital filter means,
The frequency calculating means obtains a frequency calculation time based on the count value of the counting means, and calculates a frequency at a starting point of the frequency calculation time from a ratio between the digital signal having the same phase and the digital signal having a phase different by 90 degrees. Obtaining one phase and a second phase at an end point of the frequency calculation time, and calculating the frequency by dividing a difference between the first phase and the second phase by the frequency calculation time;
It is characterized by that.
The invention of claim 6 is the invention according to any one of claims 1 to 5,
The predetermined range can be changed.
The invention of claim 7
In-phase digital filter means for vibrating a measurement tube through which the fluid to be measured flows, detecting vibration including Coriolis force generated in the fluid to be measured by the vibration, and outputting a digital signal having the same phase as the detection signal; and the detection signal And a Coriolis flow meter frequency measurement method having a different-phase digital filter means for outputting a digital signal having a phase different by 90 degrees from
A determination step of determining whether a value based on the digital signal of the same phase and the digital signal of the phase different by 90 degrees is out of a predetermined range;
A frequency calculating step of calculating a frequency of the detection signal based on the digital signal of the same phase and the digital signal of a phase different by 90 degrees when it is determined by the determination step that it is outside the predetermined range;
It is provided with.

  According to the present invention, when the value based on the digital signal having the same phase as the detection signal and the digital signal having the phase different by 90 degrees from the detection signal is out of the predetermined range, the frequency calculating means has the digital signal having the same phase and the phase different by 90 degrees. The frequency of the detection signal is calculated based on the digital signal. As a result, even if noise is superimposed on the detection signal or a signal obtained by digitally processing the detection signal, errors and variations in the measurement frequency can be reduced.

It is an example of the block diagram of the Coriolis flowmeter to which this invention is applied. It is an example of the flowchart figure of the frequency calculation process to which this invention is applied. It is an example of the wave form diagram for demonstrating the frequency calculation process to which this invention is applied. It is the example of operation | movement explanatory drawing (b) explaining the structure figure (a) of the detection part of a Coriolis flow meter shown in background art, and operation | movement of a detection part. It is an example of the block diagram of the Coriolis flow meter shown by background art.

  FIG. 1 is a configuration diagram of a Coriolis flow meter 100 to which the present embodiment is applied, and will be described using this. In FIG. 1, the same components as those in FIG. 5 are denoted by the same reference numerals and the description thereof will be omitted, and the description will focus on the frequency calculation means 110 that is a feature of this embodiment.

  First, the structure of the frequency calculation means 110 after the Hilbert transform means 21 will be described. The frequency calculation means 110 includes near-zero determination means 111A and 111B, a phase calculation means 112, a time delay means 113, a frequency calculation means 114, and an averaging means 115.

  The Coriolis flow meter 100 includes a counting unit 120 in addition to such a frequency calculation unit 110.

  The digital signal DA4 of the FIR filter 21A is input to the near zero determination unit 111A and the phase calculation unit 112. The digital signal DA5 of the FIR filter 21B is input to the near zero determination unit 111B and the phase calculation unit 112.

  Output signals representing the determination results of the near-zero determination units 111A and 111B are input to the phase calculation unit 112 and the count unit 120.

  The phase calculation means 112 outputs the phase θA2 of the displacement signal SA to the time delay means 113 and the frequency calculation means 114 based on the determination results of the near zero determination means 111A and 111B.

  The frequency calculation means 114 receives the phase θA2 from the phase calculation means 112, the phase θA2 'from the time delay means 113, and the count value N from the count means 120, and calculates the frequency fc of the displacement signal SA.

  The averaging means 115 calculates the average of the frequencies fc obtained at a number of timings and outputs the result as an average frequency fc ′.

  Next, the operation of the frequency calculation process will be described with reference to FIG. FIG. 2 is a flowchart of the frequency calculation process.

In step S10 of FIG. 2, the FIR filter 21A performs a Hilbert transform process on the input signal DA3 and outputs a digital signal DA4 of A × SIN (ω × t ₀ ).

In step S20, the FIR filter 21B performs Hilbert transform processing on the input signal DA3, and outputs a digital signal DA5 of A × COS (ω × t ₀ ).

In step S30, the phase calculating means 112 calculates a ratio KA (= A × SIN (ω × t ₀ ) / A × COS (ω × t ₀ )) obtained by dividing the digital signal DA4 by the digital signal DA5.

In step S40, the phase calculating means 112 calculates tan ⁻¹ (inverse tangent) of the ratio KA to obtain the phase θA2 (= ω × t ₀ ) of the displacement signal SA.

  In step S50, the near zero determination unit 111A determines whether or not the value of the digital signal DA4 is out of the range (predetermined range) near zero Z1. Further, the near zero determination unit 111B determines whether or not the value of the digital signal DA5 is outside the range (predetermined range) of the near zero Z1 (determination step).

  If it is determined that at least one of the digital signal DA4 and the digital signal DA5 is within the range of Z1 near zero ("Yes" in step S50), the process proceeds to step S60, and the counting means 120 counts Increment the value. After execution of step S60, the frequency calculation process ends, and the steps after step S10 are repeated at the output processing timing of the next FIR filters 21A and 21B.

  That is, the counting unit 120 determines that at least one of the digital signal DA4 and the digital signal DA5 is within the range of Z1 near zero at the output processing timing (steps S10 and S20) of the FIR filters 21A and 21B. If so ("Yes" in step S50), it is incremented (step S60).

  On the other hand, if it is determined in step S50 that both the digital signal DA4 and the digital signal DA5 are outside the range of Z1 near zero (“NO” in step S50), the process proceeds to step S70.

  In step S70, the frequency calculation unit 114 calculates the frequency calculation time FT (= N × T) by multiplying the count value N by the output processing period T of the FIR filters 21A and 21B.

In step S80, the frequency calculation means 114 divides the value obtained by subtracting the phase θA2 ′ (= ω × t _−N ) from the phase θA2 (= ω × t ₀ ) by the value obtained by multiplying the frequency calculation time FT by 2π. Then, the frequency fc (= (ω × t ₀ −ω × t _−N ) / 2πNT) is calculated (frequency calculation step). Note that π is the circumference ratio.

Note that t _−N indicates a timing point before the frequency calculation time FT from t ₀ . That is, the phase [Theta] a2 'were made to the frequency calculation time FT before t _0, the computed phase [Theta] a2, time delay means 113 is the phase [Theta] a2 in step S40' is a value which has been held as.

t _−N is the start point of the frequency calculation time FT, and the phase θA2 ′ calculated and held at that time is called a first phase. Further, t ₀ is the end point of the frequency calculation time FT, and the phase θA2 calculated at that time is called a second phase.

  In step S90, the time delay means 113 holds the phase θA2 as the phase θA2 ′. This is a preparation for the next frequency calculation, and the current phase θA2 is used as the starting phase θA2 ′ (first phase) in the next frequency calculation.

  The frequency calculation process from step S70 to step S90 will be described in detail with reference to FIG.

  In step S100, the counting means 120 sets an initial value 1 to the count value. After the execution of step S100, the frequency calculation process ends, and the steps after step S10 are repeated at the output processing timing of the next FIR filters 21A and 21B.

  Next, the processing of steps S50 to S100 in FIG. 2 will be specifically described with reference to FIG.

  First, the outline of FIG. 3 will be described. In FIG. 3, the values of the digital signal DA4 and the digital signal DA5 are plotted with black circles with respect to the time axis, and the black circles are connected with a curve. Here, the curve of the digital signal DA4 represents A × SIN (ω × t), and the curve of the digital signal DA5 represents A × COS (ω × t).

  A dotted line is drawn vertically (positive and negative) with respect to zero, and the range of the dotted line is set to a range of Z1 near zero (predetermined range).

  Times t1, t1a, t2,..., T11 are output processing timings of the FIR filters 21A and 21B, and the values of the digital signal DA4 and the digital signal DA5 at this timing are plotted with black circles. Therefore, each time interval (for example, the interval between t1 and t1a) is the output processing cycle T of the FIR filters 21A and 21B.

  .Theta.A2 shown in the lower part of time t1, t2... T11 indicates the phase .theta.A2 calculated in step S40 in FIG. 2 as .theta.1, .theta.2,.

  The frequency calculation time FT shown in the lower part of θA2 indicates the frequency calculation time (T or 2T) used when calculating each frequency.

  Next, details of FIG. 3 will be described. If at least one of the digital signal DA4 and the digital signal DA5 is within the range of Z1 near zero, the frequency fc is not calculated. If both are outside the range of near zero Z1, the frequency fc is calculated.

  That is, the frequency fc is not calculated at times t1a, t2a, t3a, t4a, and t10a, and the frequency fc is calculated at other times.

  Processing for calculating the frequency fc at time t2 will be described. In order to explain this, the explanation starts from the processing at time t1.

  At time t1, since the values of the digital signals DA4 and DA5 are outside the range of Z1 near zero (“No” in step S50 in FIG. 2), the process proceeds to step S70 in FIG.

  Here, the description of steps S70 and S80 in FIG. 2 is omitted, and in step S90, the time delay means 113 holds θ1, which is the phase θA2, as the phase θA2 ′. This is a preparation for calculating the frequency at time t2. In step S100, the counting means 120 sets an initial value 1 to the count value.

  At time t1a in FIG. 3, since the value of the digital signal DA4 is within the range of Z1 near zero (“Yes” in step S50 in FIG. 2), the process proceeds to step S60 in FIG. In step S60, the counting means 120 increments the count value, and the count value N becomes 2.

  At time t2 in FIG. 3, since the values of the digital signal DA4 and the digital signal DA5 are outside the range of Z1 near zero (“No” in step S50 in FIG. 2), the process proceeds to step S70 in FIG.

  In step S70 of FIG. 2, the frequency calculation means 114 calculates the frequency calculation time FT. Here, since the frequency of the waveform of the displacement signal SA from time t1 to t2 is calculated, the frequency calculation time FT is the time from time t1 to t2.

  Specifically, the frequency calculation time FT is a value 2T obtained by multiplying the count value N (= 2) by the output processing period T of the FIR filters 21A and 21B.

  The phase at the start point (time t1) of the frequency calculation time FT is θ1 (phase θA2 ′ (first phase)), and the phase at the end point (time t2) of the frequency calculation time FT is θ2 (phase θA (second phase)). It becomes.

  Accordingly, in step S80, the frequency calculation means 114 divides the value obtained by subtracting the phase θ1 (first phase) from the phase θ2 (second phase) by the value obtained by multiplying 2T (frequency calculation time) by 2π, The frequency fc (= (θ2−θ1) / 4πT) is calculated. Thus, the frequency fc can be calculated at time t2.

  Then, in preparation for frequency calculation at time t3, θ2, which is phase θA2, is held as phase θA2 '(step S90), and initial value 1 is set as the count value (step S100).

  By the same processing, (θ3-θ2) / 4πT), (θ4-θ3) / 4πT), and (θ5-θ4) / 4πT) are calculated as frequencies fc at times t3, t4, and t5 in FIG. .

  After calculating the frequency at time t5, at time t6, the values of the digital signal DA4 and the digital signal DA5 are outside the range of Z1 near zero (“No” in step S50 in FIG. 2), so the process proceeds to step S70 in FIG. Frequency calculation is performed.

  Since the count value N is 1, the frequency calculation time FT is T (step S70). Accordingly, the frequency fc is (θ6-θ5) / 2πT (step S80).

  By similar processing, at the times t7, t8, t9, t10, and t11 in FIG. 3, the frequencies fc are (θ7−θ6) / 2πT), (θ8−θ7) / 2πT), and (θ9−θ8) / 2πT, respectively. ), (Θ10−θ9) / 2πT), (θ11−θ10) / 4πT).

  Note that the range of near zero Z1 is preferably a range according to the magnitude of noise (for example, an amplitude value). Specifically, the range of noise is several times to several tens of times. Specifically, when the noise amplitude is 1 mV, the range of Z1 near zero is, for example, −5 mV to +5 mV, or −50 mV to +50 mV.

  The value near zero range Z1 compared with the digital signal DA4 may be different from the value near zero range Z1 compared with the digital signal DA5.

  Thus, the frequency calculation means 110 does not calculate the frequency fc when at least one of the digital signal DA4 and the digital signal DA5 is within the range of near zero Z1. Further, when both the digital signal DA4 and the digital signal DA5 are outside the range of near zero Z1, the frequency fc is calculated.

  By such processing, when noise is superimposed on the displacement signal SA or the signals DA2 to DA5 obtained by digitally processing the displacement signal SA, the frequency fc is not calculated within the range of near zero Z1 where the influence of noise is large, and the influence of noise is exerted. By calculating the frequency fc outside the range of the small near zero Z1, errors and variations in the measurement frequency fc can be reduced.

  The frequency calculation time FT used for calculating the frequency fc is obtained from the count value N of the counting means 120. By counting (incrementing) the count value N at the output processing timing of the FIR filters 21A and 21B, the accurate frequency calculation time FT and frequency fc can be calculated.

  The count value may be incremented between steps S20 and S50 instead of the process at step S60 in FIG. 2, and the initial value 0 may be set at step S100.

  Further, instead of comparing / determining the digital signal DA4 and the digital signal DA5 with the range of near zero Z1, the ratio KA (calculated in step S30) between the digital signal DA4 and the digital signal DA5 is set to near zero Z2, the first predetermined value. The second predetermined value may be compared and determined. In this case, the phase calculation means 112 performs comparison / determination.

  When the digital signal DA4 is within the range of near zero Z1, the ratio KA obtained from KA = DA4 / DA5 is within the range of near zero Z2.

  On the other hand, when the digital signal DA5 is within the range of Z1 near zero and the digital signal DA4 is a positive value, the ratio KA is a very large positive value (first predetermined value), and the digital signal DA4 is a negative value. If so, the ratio KA is a very small negative value (second predetermined value).

  Therefore, the vicinity of zero Z2, the first predetermined value or more and the second predetermined value or less are set as the predetermined ranges, and if the ratio KA is within this predetermined range in step S50 of FIG. 2 (“Yes” in step S50), step The process proceeds to S60.

  That is, if the ratio KA is near zero Z2, greater than or equal to the first predetermined value or less than or equal to the second predetermined value, the process proceeds to step S60.

  On the other hand, if the ratio KA is outside this predetermined range (“No” in step S50), the process proceeds to step S70.

  That is, if the ratio KA is not near zero Z2, not less than the first predetermined value and not more than the second predetermined value, the process proceeds to step S70.

  Further, instead of comparing / determining the digital signal DA4 and the digital signal DA5 with the range of near zero Z1, the phase θA2 of the displacement signal SA (calculated in step S40) is set to near zero Z3, the third predetermined value, and the fourth predetermined value. You may compare and judge. In this case, the phase calculation means 112 performs comparison / determination.

When the digital signal DA4 is in the range of near zero Z1, the phase θA2 obtained from θA2 = tan ⁻¹ (DA4 / DA5) is in the range of near zero Z3.

  On the other hand, when the digital signal DA5 is in the range of Z1 near zero and the digital signal DA4 is a positive value, the phase θA2 becomes a very large positive value (third predetermined value), and the digital signal DA4 is a negative value. If so, the phase θA2 becomes a very small negative value (fourth predetermined value).

  Therefore, the vicinity of zero Z3, the third predetermined value or more and the fourth predetermined value or less are set as the predetermined ranges, and if the phase θA2 is within the predetermined range in step S50 of FIG. 2 (“Yes” in step S50), step The process proceeds to S60.

  That is, if the phase θA2 is near zero Z3, greater than or equal to the third predetermined value or less than or equal to the fourth predetermined value, the process proceeds to step S60.

  On the other hand, if the phase θA2 is outside this predetermined range (“No” in step S50), the process proceeds to step S70.

  That is, if phase θA2 is not near zero Z3, not less than the third predetermined value and not more than the fourth predetermined value, the process proceeds to step S70.

  As described above, in step S50 of FIG. 2, when the determination is performed using the digital signal DA4 and the digital signal DA5, there are two determination variables. On the other hand, when the ratio KA or phase θA2 is used, there is only one determination variable, and the determination processing load and time can be reduced.

  Further, in step S50 of FIG. 2, the determination may be performed by combining any one of the digital signals DA4 and DA5, the ratio KA, and the phase θA2. Since the determination is performed by combining a plurality of variables, it is determined whether or not the frequency fc is calculated more reliably, and the error and variation of the measurement frequency fc can be further reduced.

  Further, the range of near zero Z1, Z2, and Z3, the first predetermined value, the second predetermined value, the third predetermined value, and the fourth predetermined value are set by the user or the like via input means or communication means (not shown). Can be changed.

  The magnitude of noise may change due to changes in the surrounding environment. The user or the like changes the noise range by changing the range of the vicinity of zero Z1, Z2, and Z3, the first predetermined value, the second predetermined value, the third predetermined value, and the fourth predetermined value to values corresponding to the magnitude of the noise. It is possible to reduce the error and variation of the measurement frequency fc in accordance with the size of.

  Note that the frequency of the displacement signal SB can be similarly calculated by using the displacement signal SB, the digital signal DB4, and the digital signal DB5 instead of the displacement signal SA, the digital signal DA4, and the digital signal DA5.

  The near zero determination means 111A and 111B, the phase calculation means 112, the time delay means 113, the frequency calculation means 114, the averaging means 115 and the count means 120 are executed by a processor according to a predetermined program or realized by a logic circuit. Also good.

  In addition, this invention is not limited to the above-mentioned Example, In the range which does not deviate from the essence, many change and deformation | transformation are included. Moreover, combinations other than the combination of each means mentioned above can be included.

21A, 21B, 27A, 27B FIR filter 100 Coriolis flow meter 110 Frequency calculation means 111A, 111B Near zero determination means 112 Phase calculation means 113 Time delay means 114 Frequency calculation means 115 Averaging means 120 Count means

Claims (7)

In-phase digital filter means for vibrating a measurement tube through which the fluid to be measured flows, detecting vibration including Coriolis force generated in the fluid to be measured by the vibration, and outputting a digital signal having the same phase as the detection signal; and the detection signal And a Coriolis flow meter having a different-phase digital filter means for outputting a digital signal having a phase different by 90 degrees,
When a value based on the digital signal having the same phase and the digital signal having a phase different by 90 degrees is out of a predetermined range, the frequency of the detection signal is set based on the digital signal having the same phase and the digital signal having a phase different by 90 degrees. Frequency calculating means for calculating,
Coriolis flowmeter characterized by comprising.   The frequency calculating means uses near zero as the predetermined range, and calculates the frequency when values of the digital signal having the same phase and the digital signal having a phase different by 90 degrees are outside the predetermined range. The Coriolis flow meter according to claim 1.   The frequency calculation means uses near zero, a first predetermined value or more and a second predetermined value or less as the predetermined range, and a ratio between the digital signal having the same phase and the digital signal having a phase different by 90 degrees is out of the predetermined range. The Coriolis flowmeter according to claim 1, wherein the frequency is calculated.   The frequency calculating means uses a vicinity of zero, a third predetermined value or more and a fourth predetermined value or less as the predetermined range, and a phase obtained from a ratio between the digital signal having the same phase and the digital signal having a phase different by 90 degrees is obtained. The Coriolis flowmeter according to claim 1, wherein the frequency is calculated when it is outside the predetermined range. A counting means for counting at the processing timing of the in-phase digital filter means or the out-of-phase digital filter means,
The frequency calculating means obtains a frequency calculation time based on the count value of the counting means, and calculates a frequency at a starting point of the frequency calculation time from a ratio between the digital signal having the same phase and the digital signal having a phase different by 90 degrees. Obtaining one phase and a second phase at an end point of the frequency calculation time, and calculating the frequency by dividing a difference between the first phase and the second phase by the frequency calculation time;
The Coriolis flowmeter according to any one of claims 1 to 4, wherein   The Coriolis flowmeter according to any one of claims 1 to 5, wherein the predetermined range can be changed. In-phase digital filter means for vibrating a measurement tube through which the fluid to be measured flows, detecting vibration including Coriolis force generated in the fluid to be measured by the vibration, and outputting a digital signal having the same phase as the detection signal; and the detection signal And a Coriolis flow meter frequency measurement method having a different-phase digital filter means for outputting a digital signal having a phase different by 90 degrees from
A determination step of determining whether a value based on the digital signal of the same phase and the digital signal of the phase different by 90 degrees is out of a predetermined range;
A frequency calculating step of calculating a frequency of the detection signal based on the digital signal of the same phase and the digital signal of a phase different by 90 degrees when it is determined by the determination step that it is outside the predetermined range;
A method for measuring the frequency of a Coriolis flowmeter, comprising:

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