JP4715491B2 - Coriolis mass flow meter - Google Patents

Description

  The present invention relates to a zero correction technique for a Coriolis mass flow meter.

  The Coriolis mass flowmeter is configured to detect at least a pair of pickups (vibration detectors) changes in the vibration tube caused by Coriolis force generated in proportion to the mass flow rate.

  A Coriolis mass flow meter constructed in this way should ideally have a measured value of zero in the absence of fluid flow, but in practice it is an electronic component that processes signals from tubes and pickups. Due to variations in characteristics, environmental conditions such as temperature, and aging of structures such as tubes, a slight flow rate output Qzero is generated, its value fluctuates, and so-called zero point fluctuation occurs.

In order to solve such a problem, for example, Patent Document 1 has a zero point correction switch / timer and averages the time difference between two pickup signals under a specific condition to improve the usability of zero point correction. However, it is necessary to operate the zero point switch, and it cannot be said to be fully automatic. Further, although the unit of time difference is used for the zero point value and the determination criterion, it is easier to improve the accuracy by using the flow rate signal <kg / h> subjected to various corrections such as temperature. Furthermore, since analog signal processing is premised, signal processing such as averaging processing is complicated and lacks flexibility, and in addition, various circuits such as timers and latch means are required.

Further, Patent Document 2 describes that a state in which no flow occurs is detected based on a signal from a switch or a sensor that detects the movement of the operating means, and the flow rate at this time is corrected as an offset amount. However, there is a problem that a signal transmission means to the flow meter is required, resulting in an increase in cost.
JP-A-5-26708 Japanese Patent Laid-Open No. 8-100893

  The present invention has been made in view of such a problem, and the purpose thereof is to determine that the flow rate is zero and to determine the flow rate component in a state where no flow is generated as an offset amount. It is to provide a Coriolis flowmeter that automatically and continuously executes the operation of outputting the mass flow rate by subtracting the offset amount when calculating the flow rate.

In order to achieve such an object, the invention of claim 1 includes a vibration measuring means for detecting vibration of a tube whose vibration form changes according to a flow, and a temperature detecting means for detecting the temperature of the environment, and the vibration measurement. An average flow value is obtained based on the instantaneous flow rate detected by the means and the temperature detection means, and if the average flow value is within a preset average flow rate threshold, it is determined that there is no flow, and correcting the zero point of the average flow rate value as an offset amount of zero, the calculation of the average flow, and with time running update of the identification and zeros the offset value of the zero flow is continuously performed automatically at all times, than the average flow threshold range A wide range of instantaneous flow rate threshold ranges are set in advance, the average flow rate value is within the average flow rate threshold range, and the instantaneous flow rate is calculated in the average flow rate value calculation period, or the period before and after the calculation period. Serial in the case of the range of the instantaneous flow rate threshold, it is determined that there is no flow to correct the zero point of the average flow rate value as an offset amount.

The invention of claim 2 separates the offset amount into two types of components, a default zero value that is uniquely determined for the device, and a zero fluctuation value that changes due to a change in the surrounding environment or a secular change, The difference from the default zero value is updated.

The invention according to claim 3 detects the average flow rate value in a state where no flow theoretically exists and sets it as the default zero value.

According to a fourth aspect of the present invention, the state in which there is no theoretical flow is detected based on a valve drive detection signal of valve means connected to the flow path.

According to the first aspect of the present invention, it is possible to improve the stability and accuracy by minimizing the influence of zero point change and drift. In other words, it is possible to detect the state where there is no flow without human intervention and continuously perform automatic zero adjustment, which not only saves labor but also prevents human error and errors such as judgment errors. it can.
In addition, the latest zero adjustment result is constantly reflected in the measurement value, and the flow rate can be measured with high accuracy and stability.
Furthermore, since there is no flow based on the measurement result of the flow meter, there is no need for a signal transmission means or input port from an external switch or sensor to the flow meter, and an automatic zero adjustment function with a simple structure Can be realized. Further, the present invention can be easily applied to an existing line in which an external switch or sensor cannot be used.
Without overlooking the presence of a flow in a short time, it is possible to accurately and reliably detect the absence of a flow and realize a highly accurate and stable flow rate measurement.

According to the invention of claim 2, the zero fluctuation with a small fluctuation range is managed by separately managing the offset quantity (default zero value) inherent in the measurement system and the offset quantity (zero fluctuation value) that fluctuates due to environmental change or secular change. By making the management focused on the value, the threshold value for determining whether or not there is a flow is set to an optimal narrow range, so that even a minute flow can be detected reliably and a zero correction error can be prevented.

According to the invention of claim 3 , the work of obtaining and setting the default zero at the time of calibration before shipment becomes unnecessary, and the number of man-hours can be reduced. In addition, it is possible to adopt a more accurate and realistic default zero value because it is closer to the use situation after that when the default zero is obtained in the state where it is installed on the site than when it is obtained from a line such as a shipping inspection factory. it can.

According to the fourth aspect of the present invention, it is possible to prevent the zero point from being erroneously executed when unnecessary by taking in the valve drive detection signal indicating that the flow may exist.
If a certain large flow rate is detected for more than a certain period of time when the signal from the filling switch or nozzle switch indicates that the flow rate has stopped, it may be a malfunction of the flow meter, a malfunction on the meter side, or a leak. It can be determined that it has occurred, and failure diagnosis and leakage diagnosis are possible.

FIG. 1 shows a first embodiment of the present invention. As is well known, the vibration measuring means 1 comprises two different vibration forms of the tube, that is, the vibration frequency and the two vibration positions. The phase difference is detected, and the temperature measurement means 2 for detecting the temperature of the tube or the environment is output together with the detection signal to the instantaneous flow rate calculation means 11 for calculating the instantaneous flow rate.
In this case, it is preferable that the instantaneous flow rate is calculated after the signals of the vibration measuring means 1 and the temperature measuring means 2 are converted into digital signals by an A-D converter (not shown) and subjected to digital processing.

  The instantaneous flow rate calculated by the instantaneous flow rate calculation means 11 is subjected to zero point correction by the flow rate correction means 12 and output as a flow rate signal.

  The determination unit 15 compares the average flow rate value for a predetermined period calculated based on the instantaneous flow rate by the average flow rate calculation unit 13 and the average flow rate threshold value stored in advance in the average flow rate threshold value storage unit 14 to determine whether correction is possible. Is configured to output.

  When the flow rate correction unit 12 receives a correctable signal from the determination unit 15, the average flow rate value in the state where the flow detected as the average flow rate value in the predetermined period does not exist is set as the zero point and the offset amount, and the instantaneous flow rate The difference from the instantaneous flow rate of the computing means 11 is calculated and output as a flow rate signal.

The operation of the apparatus configured as described above will be described with reference to the flowchart of FIG.
The instantaneous flow rate calculating means 11 takes in the phase difference and frequency of the tube detected by the vibration measuring means 1 at a predetermined timing and the temperature detected by the temperature measuring means 2 (step 1), and instantaneously based on these data. The flow rate is calculated (step 2). The average flow rate calculation means 13 calculates the average flow rate when the instantaneous flow rate is calculated n times (step 3) and outputs it to the first flow rate determination means 15.

  The first flow rate determination unit 15 compares the average flow rate threshold value stored in the threshold value storage unit 14 (referred to as “auto-zero threshold value 1” in FIG. 2) (step 4), and the average flow rate is equal to the average flow rate threshold value. If it is within the range, it is determined that there is no flow in the fluid in the tube, and this average flow rate value is output to the flow rate correction means 12 as a zero point offset amount (referred to as “auto-zero value” in FIG. 2) (step). 5).

  The flow rate correction unit 12 calculates the difference between the instantaneous flow rate output from the instantaneous flow rate calculation unit 11 and the zero point offset amount (step 6), and outputs it as a flow rate signal (step 7). As a result, the zero point can be automatically corrected using the average flow rate value in the absence of flow as an offset amount, and a flow rate signal in which the zero point variation is corrected can be obtained regardless of changes in the measurement environment or changes over time. it can.

  That is, the instantaneous flow rate (in the embodiment, a digital value calculated about every 0.1 sec) fluctuates even when there is no flow as shown in FIG. ) Of the discrete data (instantaneous flow rate value) (the dotted average flow rate value in FIG. 3, for example, 0.02% of Full Scale (hereinafter referred to as% FS)), and this value is the average flow rate threshold storage means 14. If it falls within the range of the average flow rate threshold set in (for example, ± 0.1% (% FS)), it is determined that the fluid is not flowing.

  The average flow rate value (± 0.02% (% FS) in the above example) is set as a new zero point, and the flow rate correction unit 12 outputs the difference between the instantaneous flow rate value from the instantaneous flow rate calculation unit 11 and the average flow rate value as a flow rate signal. (For example, when a value of 90.0% (% FS) is calculated by the instantaneous flow rate calculation means 12, the flow rate correction means 12 outputs 89.98% FS obtained by subtracting the zero point offset amount 0.02% FS as a flow rate signal. )

  On the other hand, if the average flow rate value exceeds the average flow rate threshold, it is determined that fluid is flowing through the tube, and the previous zero offset amount is maintained without performing the zero offset offset update operation. After correcting with, output the flow rate signal.

  According to this embodiment, when it is mounted as a flow rate measuring means in a system that performs batch processing, a gasoline meter or various fuel gas meters, there is always a time when the fluid stops, so zero adjustment The function can be activated automatically and periodically, which is a very effective means.

  FIG. 4 shows a second embodiment of the present invention. In this embodiment, in addition to the average flow rate value being smaller than the average flow rate threshold value, the individual instantaneous flow rates are always smaller than the instantaneous flow rate threshold value. Only in such a case, the automatic zero adjustment function is configured to work.

  The apparatus of the second embodiment includes an instantaneous flow rate threshold value storage means 16 storing instantaneous flow rate threshold value data for determining that there is no further flow in the apparatus of the first embodiment, and an instantaneous flow rate calculation means 11. The second flow rate determining means 17 for comparing the instantaneous flow rate from the flow rate and the instantaneous flow rate threshold value to determine the presence or absence of flow is added, and both the first flow rate determining means 15 and the second flow rate determining means 17 are combined. When it is determined that the state is suitable for correction (a state in which no flow exists), the flow rate correction unit 12 is configured to execute correction via the gate 18.

  The instantaneous flow rate threshold value set in the instantaneous flow rate threshold value storage unit 16 is set to a value wider than the average flow rate threshold value range set in the average flow rate threshold value storage unit 14 as shown in FIG.

The operation of the apparatus configured as described above will be described based on the flowchart of FIG.
The operation of step (4 ′) is executed between steps (1) to (4) and steps (5) to (7) of the apparatus of the first embodiment.

  That is, the operation of step (4 ′) is an operation executed by the second flow rate determination unit 17 after the first flow rate determination unit 15 determines that the average flow rate is within the average threshold range. The individual instantaneous flow rate during the sampling period for calculating the flow rate value is compared with the instantaneous flow rate threshold value, and if no flow exceeding the instantaneous flow rate threshold range occurs, it is determined that there is no flow and a signal is output. When signals are output from the two determination means 15 and 17, a correction command is output from the gate 18 to the flow rate correction means 12.

  The flow rate correction means 12 is an average flow rate (zero offset amount) calculated by the average flow rate calculation means 13 from the instantaneous flow rate calculated by the instantaneous flow rate calculation means 11 as in step (5) in the first embodiment. Is output as a flow rate signal.

  In the first embodiment, the weight of each instantaneous value is reduced by the averaging operation, and there remains a possibility that it is determined that no flow occurs. However, in the second embodiment, the average flow rate remains. When the instantaneous value of the instantaneous flow rate calculation means 11 exceeds 0.2% FS in order to perform an operation for comparison with a value larger than the threshold value, for example, the instantaneous flow rate threshold value set to about ± 0.2% FS (indicated by an arrow in FIG. 6). In addition, even if the average flow rate value itself is smaller than the average flow rate threshold value, this state is not erroneously determined that no flow has occurred.

  That is, as shown in FIG. 6, it is possible to prevent a mistake in judging that there is no flow when the fluid starts flowing from the end of the average flow rate calculation section to the end of the average flow rate calculation section. It is possible to detect and correct the zero point offset amount with high accuracy.

  In the above-described embodiment, when the instantaneous flow rate value exceeds the instantaneous flow rate threshold value even once in the instantaneous value observation range, it is determined that a flow exists. It may be determined that there is a flow when exceeding. According to this, it is possible to prevent the zero point correction operation from being stopped unnecessarily for a long period of time by reliably detecting the presence of the flow.

  By the way, the offset value of the zero point is often determined by the combination of the detector and the converter of the flow meter, and generally the fluctuation due to the environmental change is small. As for the former offset amount, the zero point at a reference temperature, for example, 20 ° C. is called a default zero value, and the individual difference for each device is large and shows a different value in a range of about ± 2% FS. The latter fluctuation is called zero fluctuation and fluctuates within about ± 0.2% FS.

  Therefore, the auto zero value is divided into two types of elements, the default zero value and the zero fluctuation value, and the threshold value for determining the zero flow rate (average flow threshold value) is set to a value slightly larger than the zero fluctuation value. By doing so, the state where there is no flow can be performed more accurately.

  For example, taking a CNG gas flowmeter for CNG gas with a full-scale of 1500 kg / h, the typical zero value at 20 ° C, ie, the default zero value, is +16.5 kg / h (= 1. 1% FS) When the environmental temperature changes in the range of 0 ° C to 40 ° C, the zero fluctuation value is about ± 1.5 kg / h (= 0.1% FS). That is, it has been experimentally confirmed that the total zero offset amount varies within a range of + 16.5 ± 1.5 kg / h (15.0 to 18.0 kg / h).

  If a value of 16.5 kg / h is set as the default zero value, the fluctuation range of the zero fluctuation value, which is the remaining fluctuation, is suppressed to a very narrow range of ± 1.5 kg / h (= 0.1% FS). Means that

Under such a set value, when the average flow rate value in the absence of flow is measured as 17 kg / h by the automatic zero correction operation, the default zero value of the flow meter is 16.5 kg as described above. Because it is set to / h, the zero fluctuation value, which is the other fluctuation, is 0.5 kg / h (17 -16.5 = 0.5 kg / h).
When the instantaneous flow rate is calculated as 17.1 kg / h in the measurement mode, 0.1 kg / h, which is the difference from the auto-zero component {17.1-(16.5 + 0.5) = 0.1 kg / h}, is the correct instantaneous flow rate. Is output as

  By the way, since such default zero values are substantially determined for each device, they may be measured and set in advance at the time of shipment or the like, and there is no flow at the time of power activation as described later. Alternatively, the measurement operation may be performed in a state where the theoretical flow rate value is guaranteed to be zero, and the average flow rate value may be set as the default zero value.

  That is, the fluid is prohibited from flowing for a certain time after the power is turned on, and the average flow rate value of the flow rate component is calculated during this period. Then, the average flow value of the flow components in the state where the flow rate zero state is guaranteed is set as the default zero value, and the next power-off operation, the reset operation that is the same state as the power-off state, and the operation in the initial startup mode are performed. You may make it store in a memory | storage means until it says.

  In the above-described embodiment, it is configured to detect a state in which no flow exists based on the average flow rate calculated by the flow meter alone or a combination of the average flow rate and the instantaneous flow rate. When used as a flow rate measuring means for a weighing machine, there is a fluid ON / OFF switch or nozzle switch for the fluid supply device on the weighing machine side. In order to detect a signal from a means (for example, a nozzle switch) for detecting that it is removed from the latching portion and is in preparation for filling, or an operation signal for the valve means connected to the flow path, or a drive of the valve means If the signals from the above means (hereinafter collectively referred to as valve drive detection signals) are taken into the flowmeter and there is a possibility that liquid is being supplied, zero correction is not performed. It is possible to prevent the malfunction.

  Therefore, as shown in FIG. 7, for example, in the embodiment shown in FIG. 1, a gate operated by the above-described valve drive detection signal is connected between the first flow rate determination unit 15 and the flow rate correction unit 12, Only when the liquid is not supplied, the gate is opened and the signal from the first flow rate determining means is taken into the flow rate correcting means 12, so that a state where there is no flow is reliably detected and measured at this time. An automatic zero adjustment operation can be performed based on the average flow rate value.

According to this embodiment, when there is even a possibility that a flow exists, the zero point is not updated, and the occurrence of a flow measurement error due to a malfunction can be prevented.
Note that if the valve drive detection signal indicates that the liquid supply has been stopped, if a certain large flow rate is detected for a certain period of time, the flow meter may be in an abnormal state or a failure state. It can be determined that there is a malfunction or a fluid leak.

It is a block diagram which shows the 1st Example of this invention. It is a flowchart which shows operation | movement of a 1st Example. It is a figure which shows typically the time change of the instantaneous flow rate in the state where a flow does not exist. It is a block diagram which shows the 2nd Example of this invention. It is a flowchart which shows operation | movement of a 2nd Example. It is a figure which shows typically the time change of the instantaneous flow rate in the state where a flow does not exist. It is a block diagram which shows the other Example of this invention.

Claims (4)

A vibration measuring means for detecting the vibration of the tube whose vibration form changes according to the flow; and a temperature detecting means for detecting the temperature of the environment, and an average based on the instantaneous flow rate detected by the vibration measuring means and the temperature detecting means. A flow rate value is obtained, and if the average flow rate value is within the range of a preset average flow rate threshold value, it is determined that no flow exists, and the zero point is corrected using the average flow rate value as an offset amount of the zero point. the calculation, and during the operation to update the identification and zeros the offset value of zero flow along with continuously performed automatically at all times
An instantaneous flow rate threshold range that is wider than the average flow rate threshold range is set in advance, and the average flow rate is within the average flow rate threshold range, and the instantaneous flow rate during the calculation period of the average flow value, or the period before and after that, A Coriolis mass flowmeter that determines that there is no flow when within the range of the instantaneous flow rate threshold value and corrects the zero point using the average flow rate value as an offset amount . The offset amount is separated into two types of components, a default zero value that is uniquely determined by the device and a zero fluctuation value that changes due to changes in the surrounding environment or aging, and the difference between the offset amount and the default zero value The Coriolis mass flowmeter according to claim 1 , wherein the Coriolis mass flowmeter is updated. The Coriolis mass flowmeter according to claim 2 , wherein an average flow value in a state where no flow theoretically exists is detected and set as the default zero value. 4. The Coriolis mass flow meter according to claim 2, wherein the theoretically non-existing state is detected based on a valve drive detection signal of valve means connected to the flow path.

Images