JP2011033439A - Coriolis mass flowmeter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a Coriolis mass flowmeter reducing a load of a CPU, while keeping accuracy of a phase difference. <P>SOLUTION: In this Coriolis mass flowmeter, each frequency detection signal from an upstream side sensor and a downstream side sensor arranged at a prescribed distance in a measuring conduit is inputted into a signal processing part through an amplifying circuit and an AD converter, and a temperature detection signal is inputted into the signal processing part through the AD converter, and a phase difference signal, a frequency signal and a temperature signal of the frequency detection signal are calculated. The flowmeter is equipped with: a phase difference error correction table means for acquiring and updating a phase difference error signal operated when a frequency detection signal of either of the upstream side sensor and the downstream side sensor is connected to the other amplifying circuit at a prescribed updation timing, the frequency signal and the temperature signal; and a phase difference correction means for correcting the calculated phase difference signal, based on the phase difference error signal read from the phase difference error correction table means. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention inputs a frequency detection signal of each of an upstream sensor and a downstream sensor arranged at a predetermined distance in a measurement pipe line to a signal processing unit via an amplifier circuit and an AD converter, and a temperature detection signal Is input to a signal processing unit via an AD converter, and relates to a Coriolis mass flowmeter that calculates a phase difference signal, a frequency signal, and a temperature signal of the frequency detection signal.

  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. 4 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 Q to be measured flows are fixed to the support members 2 and 3. In the vicinity of the central portion of the measurement pipe 1, a vibration exciter 4 is installed to mechanically vibrate the measurement pipe 1 up and down.

  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. 5 is a schematic diagram for explaining the primary mode and the secondary mode vibration. When the fluid Q to be measured flows through the measurement pipe 1 in the state where the vibration is applied from the vibrator 4 to the measurement pipe 1 in the shape of the primary mode as shown by M1 and M2, 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 by the frequency detection signal VS1 and the frequency detection signal VS2.

  FIG. 6 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 amplification circuits 7 and 8, respectively, and then passed through the low-pass filters 9 and 10 for noise suppression to the AD converter. 11 is converted into a digital signal and input to a signal processing unit 12 constituted by CPU means.

  A temperature detection signal from the temperature sensor 13 of the fluid Q provided in the measurement pipe 1 is digitally converted by the AD converter 14 and input to the signal processing unit 12. The signal processing unit 12 acquires digital signals from the AD converter 11 and the AD converter 14 and calculates and outputs a phase difference signal Δθ by a Hilbert transform process or the like, a frequency signal F by a frequency detection algorithm, and a temperature signal T. Although not shown, the mass flow rate of the fluid Q is calculated based on these output signals. The details of this signal processing are disclosed in Patent Document 1.

  The first input circuit composed of the amplification circuit 7 and the low-pass filter 9 on the upstream sensor 5 side and the second input circuit composed of the amplification circuit 8 and the low-pass filter 10 on the downstream sensor 6 side are the upstream sensor 5 and the downstream sensor 6. The phase difference calculated by the signal processing unit 12 is affected and a phase difference error is generated due to the change in the frequency characteristic and the temperature characteristic change due to temperature fluctuation.

  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%). For this reason, since the phase difference error becomes a cause of high accuracy, it is necessary to provide a mechanism for error correction.

  A switching circuit 15 and a corrector 16 are provided for phase difference error correction. In accordance with a periodic correction command C from the CPU of the signal processing unit 12, the switching circuit 15 is switched for a certain time.

  The switching circuit 15 connects the input of the amplifier circuit 8 to the downstream sensor 6 via the contact a in a steady state, but the input of the amplifier circuit 8 is connected via the contact b by the switching operation according to the correction command C. Connect to upstream sensor 5.

  In this connection state, since the input signals of the amplifier circuits 7 and 8 are the same signal Vs1, the phase difference is ideally zero. Therefore, the phase difference signal calculated and output by the signal processing unit 12 is the phase difference error signal Err caused by an input circuit error or the like.

  The corrector 16 acquires and holds the phase difference error signal Err, and the phase difference signal Δθ obtained by correcting the phase difference signal Δθ calculated with the contact of the switching circuit 15 returned to the steady connection by the phase difference error signal Err. ´ is output. Thereby, a phase difference error due to an input circuit error can be corrected.

Japanese Patent Laid-Open No. 7-181069

The conventional apparatus has the following problems.
(1) In the calculation period of the phase difference error signal in which the switching circuit 15 is switched, the frequency detection signal VS2 of the downstream sensor 6 is disconnected, and there is a period in which continuous measurement cannot be performed periodically.

(2) If the period during which continuous measurement cannot be performed is shortened, the calculation accuracy of the phase difference error deteriorates. Also, the phase difference error calculation process increases the CPU load of the signal processing unit 12 and leads to an increase in power consumption.

  An object of the present invention is to realize a Coriolis mass flow meter that can reduce the load on the CPU while maintaining the accuracy of the phase difference.

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 the signal processing unit via the amplifier circuit and AD converter, and the temperature detection signal is In a Coriolis mass flow meter that inputs a signal processing unit via an AD converter and calculates a phase difference signal, a frequency signal, and a temperature signal of the frequency detection signal,
Obtaining a phase difference error signal calculated when one frequency detection signal of the upstream sensor or the downstream sensor is connected to the other amplifier circuit at a predetermined update timing, the frequency signal, and the temperature signal; Updated phase difference error correction table means;
Phase difference correction means for correcting the calculated phase difference signal based on the phase difference error signal read from the phase difference error correction table means;
A Coriolis mass flow meter comprising:

(2) The Coriolis mass according to (1), wherein the phase difference correction means reads the phase difference error signal from the phase difference error correction table means by a search using the frequency signal and the temperature signal as keys. Flowmeter.

(3) The Coriolis mass flowmeter according to (1) or (2), wherein the phase difference error correction table means is written with a default value acquired by learning a test environment at the time of factory shipment.

(4) The Coriolis mass flowmeter according to (3), further comprising a fine adjustment phase difference error correction table means for updating the default value in a short period during operation.

(5) When the phase difference error signal calculated by the signal processing unit at the predetermined update timing is compared with the phase difference error signal read from the phase difference error correction table means, and the difference exceeds a predetermined threshold value The Coriolis mass flowmeter according to any one of (1) to (4), further comprising diagnostic means for outputting an alarm signal.

(6) The Coriolis mass flow rate according to any one of (1) to (5), wherein the phase difference error signal is an input circuit error between the upstream and downstream sensors and the AD converter. Total.

According to the present invention, the following effects can be expected.
(1) Since the signal switching by the switching circuit 15 is not required except for the update period of the phase difference error correction table means executed in a relatively long cycle, the mass flow rate can be continuously measured.

(2) Since the correction is executed with the phase difference error signal read from the phase difference error correction table means, it is not necessary to calculate the input circuit error amount in a short period, and the load on the CPU is reduced.

(3) Since real-time correction can be performed, measurement accuracy can be improved.

It is a functional block diagram which shows one Example of the Coriolis mass flowmeter to which this invention is applied. It is an example of a structure of the phase difference error correction table employ | adopted by this invention. It is a flowchart which shows the procedure of a phase difference error correction table update. 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.

  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.

  A structural feature of the present invention compared to the conventional configuration is that a phase difference error correction table means 100, a phase difference correction means 200, and a switch 300 are provided. The phase difference correction means 200 has the same function as the corrector 16 described with reference to FIG. 6, and outputs a phase difference signal Δθ ′ obtained by correcting the phase difference signal Δθ with the phase difference error signal Err.

  In response to an update command D output from the CPU of the signal processing unit 12 at a predetermined update cycle, the switching circuit 15 is operated for a certain time, and the frequency detection signal VS1 of the upstream sensor 5 is amplified by the downstream sensor 6 during the update period. Switch to circuit 8 for connection.

  During this update period, the phase difference error signal Err calculated by the signal processing unit 12, the frequency signal F and the temperature signal T at this time are acquired, and the data of the phase difference error correction table means 100 is updated.

  During the update period of the table means, the phase difference correction means 200 is corrected by the phase difference error signal Err calculated by the signal processing unit 12 by the switch 300 operated from the CPU, as in the conventional configuration. ´ is output.

  The phase difference correction unit 200 acquires and corrects the phase difference error signal Err read from the phase difference error correction table unit 100 during a period other than the update period of the table unit by switching the switch 300 operated by the CPU. A phase difference signal Δθ ′ is output.

  During the correction period by the phase difference error signal Err read from the phase difference error correction table means 100, the CPU load can be greatly reduced by stopping the calculation process of the phase difference error signal Err by the signal processing unit 12. .

  In the present invention, the period of the update command D output from the CPU of the signal processing unit 12 can be set sufficiently longer than the period of the correction command C in the conventional configuration by introducing the phase difference error correction table means 100. Therefore, continuous measurement of mass flow rate is possible.

  FIG. 2 is a configuration example of a phase difference error correction table employed in the present invention. The frequency signals F1, F2,..., The temperature signals T1, T2,..., The phase difference error signals Err1, Err2 acquired at each update cycle after the time when the frequency and temperature of the stable frequency detection signals VS1, VS2 can be detected. , ... are registered.

  The phase difference correction means 200 reads out and corrects the phase difference error signal Err having the optimum value from the phase difference error correction table means 100 for each correction cycle by a search using the frequency signal F and the temperature signal T as keys. Execute.

  The reading accuracy of the phase difference error correction table means 100 can be learned by continuing to update, but at the time of shipment from the factory, a default value acquired by learning the test environment can be written as initial data.

  FIG. 3 is a flowchart showing a procedure for updating the phase difference error correction table. When the update process starts in step S1, a phase difference error is obtained in step S2, and a difference from the phase difference error one sample before is obtained in step S3.

  In step S4, it is checked whether or not the difference is equal to or less than a threshold value. If it is determined that the difference is equal to or less than the threshold value, the phase difference error signal is considered to converge, and a timer for registering the table after a predetermined time is started.

  If it is determined in step S5 that the timer has been activated, it is confirmed in step S6 that the timer has expired. In step S7, the phase difference error signal obtained together with the frequency and temperature is registered in the table, and the process ends in step S8.

  If it is determined in step S6 that the timer has not expired, the process proceeds to step S8 and ends without being registered in the table.

  If the timer is not activated in the timer activation check in step 5, the phase difference error signal is temporarily stored in step S9, and then the timer is activated in step S10. Then, the process proceeds to step S8 and ends without being registered in the table. To do.

  If it is determined in step S4 that the difference is not less than or equal to the threshold value, the phase difference error signal is temporarily stored in step S11. Then, in step S12, if the timer is running, it is stopped and the process proceeds to step S8. Finish without registering in the table.

  As an embodiment of the present invention, a phase difference error correction table means for fine adjustment for updating the default value registered in the table at the time of shipment from the factory during operation in a short period is added, and the offset value from the correction table means is set as the default value. In addition, a learning function for correcting the default value may be provided.

  Furthermore, as an embodiment of the present invention, the phase difference error signal Err calculated by the signal processing unit 12 at a predetermined timing is compared with the phase difference error signal Err read from the phase difference error correction table means 100, and the difference is determined as predetermined. A diagnostic means for outputting an alarm signal indicating an abnormality of the system when the threshold value is exceeded may be provided.

DESCRIPTION OF SYMBOLS 1 Measurement pipe line 5 Upstream sensor 6 Downstream sensor 7, 8 Amplification circuit 9, 10 Low-pass filter 11, 14 AD converter 12 Signal processing part (CPU)
13 Temperature sensor 100 Phase difference error correction table means 200 Phase difference correction means 300 Switch

Claims (6)

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 the amplifier circuit and the AD converter, and the temperature detection signal is input to the AD converter. In the Coriolis mass flowmeter that inputs to the signal processing unit and calculates the phase difference signal, frequency signal, and temperature signal of the frequency detection signal,
Obtaining a phase difference error signal calculated when one frequency detection signal of the upstream sensor or the downstream sensor is connected to the other amplifier circuit at a predetermined update timing, the frequency signal, and the temperature signal; Updated phase difference error correction table means;
Phase difference correction means for correcting the calculated phase difference signal based on the phase difference error signal read from the phase difference error correction table means;
A Coriolis mass flow meter comprising:   2. The Coriolis mass flowmeter according to claim 1, wherein the phase difference correction means reads the phase difference error signal from the phase difference error correction table means by a search using the frequency signal and the temperature signal as keys.   The Coriolis mass flowmeter according to claim 1 or 2, wherein the phase difference error correction table means is written with a default value acquired by learning a test environment at the time of factory shipment.   The Coriolis mass flowmeter according to claim 3, further comprising a fine adjustment phase difference error correction table means for updating the default value in a short period during operation.   The phase difference error signal calculated by the signal processing unit at the predetermined update timing is compared with the phase difference error signal read from the phase difference error correction table means, and an alarm signal when the difference exceeds a predetermined threshold The Coriolis mass flowmeter according to claim 1, further comprising: a diagnostic unit that outputs   The Coriolis mass flowmeter according to any one of claims 1 to 5, wherein the phase difference error signal is an input circuit error between the upstream sensor and the downstream sensor and the AD converter.

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