JP2011033385A - Coriolis mass flowmeter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a Coriolis mass flowmeter capable of increasing the S/N ratio to enhance accuracy and increase noise resistance, by introducing a simple addition means. <P>SOLUTION: The Coriolis mass flowmeter inputs respective frequency detection signals of an upstream-side sensor and a downstream-side sensor arranged being separated at a predetermined distance in a measuring pipeline, to a signal processing part through an amplifying circuit, a low-pass filter, and an AD converter, calculates a mass flow rate on the basis of the phase difference between the frequency detection signals, and updates calculation results at a predetermined period. The flowmeter includes a signal clamping means for clamping parts not lower than negative and positive predetermined levels of the frequency detection signals, or their predetermined periods excluding the vicinities of zero-crosses while holding phase information on the frequency detection signals. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  In the present invention, the frequency detection signals of the upstream sensor and the downstream sensor arranged at a predetermined distance in the measurement pipeline are input to the signal processing unit via an amplifier circuit, a low-pass filter, and an AD converter, The present invention relates to a Coriolis mass flowmeter that calculates a mass flow rate based on a phase difference of a frequency detection signal and updates a calculation result at a predetermined cycle.

  Patent Document 1 discloses a detailed technical disclosure regarding the configuration of the sensor unit of the Coriolis mass flow meter and the signal processing for mass flow calculation. The configuration of the sensor unit and the primary mode and secondary mode vibration will be briefly described.

  FIG. 7 is a basic configuration diagram of the sensor unit of the Coriolis mass flow meter. Both ends of the measurement pipe line 1 through which the fluid F to be measured flows are fixed to the support members 2 and 3. In the vicinity of the central portion of the measurement pipeline 1, a vibration exciter 4 for mechanically vibrating the measurement pipeline 1 up and down is installed.

  An upstream sensor 5 and a downstream sensor 6 that detect vibrations of the measurement pipe 1 are fixed in the vicinity of the measurement pipe 1 fixed to the support members 2 and 3.

  FIG. 8 is a schematic diagram for explaining the primary mode and the secondary mode vibration. When the fluid to be measured F flows through the measurement pipe 1 in the state where the vibration is applied in the shape of the primary mode as shown by M1 and M2 from the vibrator 4 to the measurement pipe 1, the current flows to M3 and M4. The measurement pipe line 1 vibrates in the shape of the secondary mode as shown.

  Actually, the measurement pipe line 1 vibrates in a form in which these two kinds of vibration patterns are superimposed. This vibration deformation of the measurement pipe line 1 is detected by the upstream sensor 5 and the downstream sensor 6 using the frequency detection signal VS1 and the frequency detection signal VS2.

  FIG. 9 is a functional block diagram showing a configuration example of a conventional Coriolis mass flow meter. The frequency detection signal VS1 of the upstream sensor 5 and the frequency detection signal VS2 of the downstream sensor 6 are amplified to predetermined levels by the amplifier circuits 7 and 8, respectively, and input to the AD converters 11 and 12 via the low-pass filters 9 and 10, respectively. Converted into a digital signal. The low-pass filters 9 and 10 are added to prevent aliasing noise of the AD converters 11 and 12 and to suppress external noise.

  The digital signals of the AD converters 11 and 12 are input to the signal processing unit 20, the mass flow rate is calculated at a predetermined calculation cycle, and the mass flow rate holding value of the holding unit 31 of the output unit 30 is updated by the calculation output Fm.

  The signal processing unit 20 includes Hilbert transform means 21 and 22 for inputting digital signals from the AD converters 11 and 12, and phase detection means 23 and 24 for detecting the phases θ1 and θ2 of the frequency detection signals VS1 and VS2 from the processing results. Prepare. The Hilbert transforming unit can also be realized by an FFT processing unit or the like.

  The phase signals θ1 and θ2 are input to the phase difference detection means 25, and the phase difference Δθ is calculated. The mass flow rate calculation means 26 that inputs this phase difference Δθ calculates the mass flow rate Fm at a predetermined calculation cycle and passes it to the output unit 30. Details of the signal processing unit 20 are disclosed in Patent Document 1.

  FIG. 10 is a waveform diagram for explaining the noise superimposed on the frequency detection signal as the subject of the present invention.

Japanese Patent Laid-Open No. 7-181069

The conventional Coriolis mass flowmeter has the following problems.
The phase difference signal Δθ proportional to the mass flow rate is several tens of milliradians at the maximum measurable flow rate, and measurement accuracy of several microradians is required to achieve high accuracy (for example, ± 0.1%). Since a very weak signal (S) is handled in this way, it is easily affected by the noise component (N) generated in each part and appears as output fluctuation.

The noise component (N) is generated and mixed from the detection coils of the sensors 5 and 6 to the outputs of the AD converters 11 and 12, and mainly includes the following.
(A) Noise of the OP amplifier used in the amplifier circuits 7 and 8 (b) External noise (the cable connecting the detection coil and the amplifier circuit may be extended, and noise is likely to be mixed)
(C) Quantization error of AD converters 11 and 12

  For (a), a low-noise OP amplifier may be used, but this increases the cost. For (b), the extension cable may be a shielded cable, but this also causes an increase in cost. As for (c), although it depends on the resolution of the AD converter, there are not many options, and it is difficult to improve the parts selection.

  Thus, in the prior art, both high accuracy and high noise immunity measures by improving the S / N ratio cause cost increases.

  An object of the present invention is to realize a Coriolis mass flowmeter that can improve the S / N ratio and achieve high accuracy and high noise resistance by introducing simple additional means.

In order to achieve such a subject, the present invention has the following configuration.
(1) The frequency detection signals of the upstream sensor and the downstream sensor arranged at a predetermined distance in the measurement pipeline are input to a signal processing unit via an amplifier circuit, a low-pass filter, and an AD converter, and the frequency In the Coriolis mass flowmeter that calculates the mass flow rate based on the phase difference of the detection signal and updates the calculation result at a predetermined cycle,
A Coriolis mass flowmeter comprising signal clamping means for clamping a predetermined period excluding a predetermined level of positive or negative of the frequency detection signal or a vicinity of a zero cross while maintaining phase information of the frequency detection signal.

(2) The Coriolis mass flowmeter according to (1), wherein the signal clamping means is provided between the amplifier circuit and the low-pass filter or between the low-pass filter and the AD converter.

(3) The Coriolis mass flowmeter according to (1), wherein the signal clamping means is provided on the output side of the AD converter.

(4) The Coriolis mass flowmeter according to any one of (1) to (3), further including gain variable means for increasing the gain of the amplifier circuit outside the clamp range of the frequency detection signal.

(5) The apparatus according to any one of (1) to (4), further comprising a noise processing unit that detects noise generated on an output side of the signal clamping unit and stops updating the calculation result. Coriolis mass flow meter.

(6) The Coriolis mass according to any one of (1) to (5), further comprising a processing stop unit that stops processing of the AD converter and the signal processing unit during a clamping period of the signal clamping unit. Flowmeter.

According to the present invention, the following effects can be expected.
(1) Since white noise generated from a circuit element such as an OP amplifier does not exist in the clamped portion of the frequency detection signal, the entire amount of noise can be reduced.

  By making the sine wave signal into a clamp waveform, an increase in the amount of noise due to the inclusion of harmonic components can be considered, but filtering during signal processing such as Hilbert transform or FFT performed by the signal processing unit 20 The effect can be removed.

(2) Disturbance noise cannot be completely removed depending on its magnitude, but the influence can be reduced. That is, it is possible to improve the S / N ratio and achieve high accuracy without using an expensive low noise OP amplifier.

(3) Further, since the use range of the shielded cable can be limited to an environment with a lot of external noise, high noise resistance can be realized at low cost.

It is a functional block diagram which shows one Example of the Coriolis mass flowmeter to which this invention is applied. It is a wave form diagram explaining the clamp with respect to a frequency detection signal. It is a functional block diagram which shows the other Example of the Coriolis mass flowmeter to which this invention is applied. It is a functional block diagram which shows other Example of the Coriolis mass flowmeter to which this invention is applied. It is a functional block diagram which shows other Example of the Coriolis mass flowmeter to which this invention is applied. It is a functional block diagram which shows other Example of the Coriolis mass flowmeter to which this invention is applied. It is a basic block diagram of the sensor part of a Coriolis mass flowmeter. It is a schematic diagram explaining primary mode and secondary mode vibration. It is a functional block diagram which shows the structural example of the conventional Coriolis mass flowmeter. It is a wave form diagram explaining the noise superimposed on a frequency detection signal.

  Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a functional block diagram showing an embodiment of a Coriolis mass flow meter to which the present invention is applied. The same elements as those of the conventional configuration described with reference to FIG.

  The characteristic part of the present invention added to the conventional configuration is that signal clamping means 101 and 102 are provided between the amplifying circuit 7 and the low-pass filter 9 for the frequency detection signal VS1 and between the amplifying circuit 8 and the low-pass filter 10 for the frequency detection signal VS2. It is the structure which made it insert.

  These signal clamping means 101 and 102 limit the analog signal at a predetermined level, and the insertion position may be between the low-pass filter 9 and the AD converter 11 and between the low-pass filter 10 and the AD converter 12.

  FIG. 2 is a waveform diagram for explaining clamping with respect to the frequency detection signals VS1 and VS2. A waveform obtained by removing voltage information in a high voltage region and a low voltage region is input to the AD converters 11 and 12. In the clamping process for the frequency detection signal, the phase information is not changed, so that there is no influence on the mass flow rate calculation.

  In the clamped period, noise superimposed on the frequency detection signals VS1 and VS2 is forcibly removed, so that noise superimposed on the frequency detection signals VS1 and VS2 can be greatly reduced.

  Clamping with respect to the frequency detection signals VS1 and VS2 is performed by monitoring a signal voltage level and clamping a period longer than or less than a set threshold, or by monitoring a signal frequency and excluding a predetermined time from the zero cross point. A technique of clamping the period can be employed.

  FIG. 3 is a functional block diagram showing another embodiment of the Coriolis mass flow meter to which the present invention is applied. In this embodiment, signal clamping means 201 and 202 realized by digital processing are inserted between the AD converter 11 and the Hilbert conversion means 21 and between the AD converter 12 and the Hilbert conversion means 22, respectively.

  The functions of these signal clamping means 201 and 202 are the same as the functions of the signal clamping means 101 and 102 in FIG. The signal clamping means may be inserted at any position as long as the condition for maintaining the phase information of the frequency detection signals VS1 and VS2 is satisfied.

  Another embodiment based on the signal clamp processing introduced in the present invention will be described with reference to FIGS. These embodiments show a configuration in which the signal clamping means 201 and 202 are inserted on the output side of the AD converters 11 and 12.

  FIG. 4 is characterized by comprising a gain variable means for increasing the gain of the amplifier circuit outside the clamp range of the frequency detection signal. The clamp range detecting means 301 and 302 monitor the outputs of the signal clamp means 201 and 202 to detect the clamp range, control the gain variable means 303 and 304 outside the detected range, and adjust the gains of the amplifier circuits 7 and 8. increase.

  By making the voltage range amplified by the increase in gain correspond to the input ranges of the AD converters 11 and 12, the gain of the amplifier circuit can be made larger than that of the prior art. This gain increase reduces the quantization error of the unclamped portion, and from this point, an improvement in the S / N ratio can be expected.

  FIG. 5 is characterized by a configuration including a noise processing unit that detects noise generated on the output side of the signal clamping unit and stops updating the calculation result. The noise processing means 400 monitors the outputs of the signal clamping means 201 and 202, determines the presence or absence of external noise, and when the noise is greater than a predetermined value, in order to ensure the reliability of the mass flow calculation, the output unit 30 The update stop command S is output to the holding means 31 and the output is held at the value at the previous update. It also alerts the user if necessary.

  FIG. 6 is characterized by comprising a processing stop unit that stops the processing of the AD converter and the signal processing unit during the clamping period of the signal clamping unit. The processing stop unit 500 monitors the outputs of the signal clamp units 201 and 202, and stops the functions of the AD converters 11 and 12 and the signal processing unit 20 while holding the output unit 30 during the clamp period.

  Power consumption can be reduced by stopping the AD converter in the clamp part of the frequency detection signal and the mass flow rate calculation function of the signal processing part. In addition, the memory capacity of the CPU of the signal processing unit can be reduced.

DESCRIPTION OF SYMBOLS 1 Measurement pipe line 5 Upstream sensor 6 Downstream sensor 7, 8 Amplifying circuit 9,10 Low pass filter 11,12 AD converter 20 Signal processing part 21,22 Hilbert conversion means 23,24 Phase detection means 25 Phase difference detection means 26 Mass Flow rate calculation means 30 Output section 31 Holding means 101, 102 Signal clamping means

Claims (6)

The frequency detection signals of the upstream side sensor and the downstream side sensor arranged at a predetermined distance in the measurement pipeline are input to the signal processing unit via an amplifier circuit, a low pass filter, and an AD converter, and the frequency detection signal In the Coriolis mass flowmeter that calculates the mass flow rate based on the phase difference and updates the calculation result in a predetermined cycle,
A Coriolis mass flowmeter comprising signal clamping means for clamping a predetermined period excluding a predetermined level of positive or negative of the frequency detection signal or a vicinity of a zero cross while maintaining phase information of the frequency detection signal.   2. The Coriolis mass flowmeter according to claim 1, wherein the signal clamping means is provided between the amplifier circuit and the low-pass filter or between the low-pass filter and the AD converter.   2. The Coriolis mass flow meter according to claim 1, wherein the signal clamping means is provided on the output side of the AD converter.   The Coriolis mass flowmeter according to any one of claims 1 to 3, further comprising gain variable means for increasing a gain of the amplifier circuit outside a clamp range of the frequency detection signal.   The Coriolis mass flowmeter according to any one of claims 1 to 4, further comprising a noise processing unit that detects noise generated on an output side of the signal clamping unit and stops updating the calculation result.   The Coriolis mass flowmeter according to claim 1, further comprising a processing stop unit that stops processing of the AD converter and the signal processing unit during a clamp period of the signal clamping unit.