Abstract:
A Coriolis mass flowmeter includes a vibrator configured to vibrate a measurement conduct line, an upstream sensor and a downstream sensor, which are placed at a certain distance in the measurement conduct line and are configured to detect the vibration of the measurement conduct line, a first effective value reception section configured to receive an effective value of the first signal, a second effective value reception section configured to receive an effective value of the second signal, a ratio computation section configured to receive the effective value of the first signal and the effective value of the second signal and to compute the ratio of both values, and an anomaly diagnosis section configured to make a comparison between the computed ratio and a certain value and to generate an alarm.

Description:
TECHNICAL FIELD 
       [0001]    The present disclosure relates to a Coriolis mass flowmeter for computing the mass flow rate of a fluid flowing through a measurement conduct line based on the phase difference between a first signal of an upstream sensor and a second signal of a downstream sensor placed at a certain distance in the measurement conduct line vibrating by a vibrator, and having an excitation circuit section for receiving the first signal or the second signal and controlling a drive signal of the vibrator so that the amplitude of the first signal or the second signal becomes a target value. 
       RELATED ART 
       [0002]    Patent Document 1 discloses the configuration of a sensor section of a Coriolis mass flowmeter and signal processing of mass flow rate computation. Patent Document 2 discloses an excitation circuit section for controlling a drive signal of a vibrator. 
         [0003]      FIG. 4  is a basic configuration drawing of the sensor section of the Coriolis mass flowmeter. In a sensor section  10 , both ends of a measurement conduct line  11  for allowing a measured fluid F to flow are fixed to support members  12  and  13 . A vibrator  14  for mechanically vibrating the measurement conduct line  11  up and down is installed in the proximity of the center the measurement conduct line  11  and is driven by a drive signal DV. 
         [0004]    An upstream sensor  15  and a downstream sensor  16  for detecting vibration of the measurement conduct line  11  are placed in the proximity fixed to the support members  12  and  13  of the measurement conduct line  11 . 
         [0005]      FIG. 5  is a schematic drawing to describe primary mode and secondary mode vibration. When the measured fluid F flows into the measurement conduct line  11  in a state in which vibration is given to from the vibrator  14  to the measurement conduct line  11  in the primary mode as shown in M 1  and M 2 , the measurement conduct line  11  vibrates in the secondary mode as shown in M 3  and M 4 . 
         [0006]    In fact, the measurement conduct line  11  vibrates in a superposition form of the two types of vibration patterns. The vibration deformation of the measurement conduct line  11  is detected by a frequency detection signal (hereinafter, first signal) SA of the upstream sensor  15  and a frequency detection signal (hereinafter, second signal) SB of the downstream sensor  16 . 
         [0007]      FIG. 6  is a function block diagram to show a general configuration example of the Coriolis mass flowmeter. The first signal SA of the upstream sensor  15  (or/and the second signal SB of the downstream sensor  16 ) is input to an excitation circuit section  20  including auto gain control (AG C) for maintaining the amplitude of the first signal SA or the second signal SB in a target value, is smoothed in a smoothing circuit  21 , and is converted into DC voltage proportional to the effective value. 
         [0008]    The DC voltage is compared with a target voltage given in a target value setting section  22  by a comparison section  23 , the deviation is passed to a variable amplifier  24 , and a drive signal DV of a drive output section  25  controlled by output CV of the variable amplifier  24  is given to the vibrator  14 . This feedback control system controls the amplitude of the first signal SA to the target value. The excitation circuit section  20  is disclosed in Patent Document 2. 
         [0009]    The first signal SA of the upstream sensor  15 , the second signal SB of the downstream sensor  16 , and a temperature detection signal SH for compensation for temperature are input to a signal computation processing section  30 , and the signals SA, SB, and SIX are sampled/held by track-and-holds  31 ,  32 , and  33  controlled at a sampling timing T generated from a clock. 
         [0010]    Hold signals of the track-and-holds  31 ,  32 , and  33  are converted into digital signals by analog/digital converters  34 ,  35 , and  36 . The digital values of the first signal SA and the second signal SB provided by the analog/digital converters  34  and  35  are input to a flow rate computation section  39  through low-pass filters  37  and  38 . The digital value of the temperature signal SH provided by the analog/digital converter  36  is directly input to the flow rate computation section  39 . 
         [0011]    The flow rate computation section  39  computes and outputs mass flow rate Q of the fluid F flowing through the measurement conduct line  11  based on the input signals. Signal processing of the flow rate computation section  39  for executing phase difference computation, etc., by Hilbert transform processing, etc., is disclosed in Patent Document 1 and therefore will not be discussed. 
         [0012]    In the Coriolis mass flowmeter, when a sensor signal is affected by disturbance of fluid density, flow rate, temperature, vibration of the measurement conduct line, etc., whether the cause is disturbance or the effect produced by an anomaly of the sensor or the measurement conduct line is not determined and an erroneous diagnosis is conducted. Thus, a degradation diagnosis function of the measurement conduct line is required. 
         [0013]    A related-art degradation diagnosis technique disclosed in Patent Document 3 is an offline diagnosis wherein a sensor tube is once vibrated and the excitation is stopped in a state in which a fluid does not flow into the sensor tube, vibration attenuation after the stop of the excitation is measured, an anomaly is detected, and an alarm is issued. 
         [0014]    [Patent Document 1] Japanese Patent Laid-Open No. 181069/1995 
         [0015]    [Patent Document 2] Japanese Patent Laid-Open No. 2003-302272 
         [0016]    [Patent Document 3] Japanese Patent Laid-Open No. 52516/1992 
         [0017]    The related-art degradation diagnosis technique of the measurement conduct line involves the following problems: 
         [0000]    (1) In an online state in which the mass flow rate of a fluid flowing through the measurement conduct line is measured, a degradation diagnosis cannot be conducted.
 
(2) A special measuring device for a degradation diagnosis needs to be added and the cost of the device is increased.
 
       SUMMARY 
       [0018]    Exemplary embodiments of the present invention provide a Coriolis mass flowmeter for malting it possible to conduct a degradation diagnosis of a measurement conduct line based on a signal in an online state without adding a special measuring device for the degradation diagnosis. 
         [0019]    A Coriolis mass flowmeter, according to an exemplary embodiment, comprises: 
         [0020]    a vibrator configured to vibrate a measurement conduct line; 
         [0021]    an upstream sensor and a downstream sensor, which are placed at a certain distance in the measurement conduct line and are configured to detect vibration of the measurement conduct line; 
         [0022]    a signal computation processing section configured to compute a mass flow rate of a fluid flowing through the measurement conduct line vibrated by the vibrator based on a phase difference between a first signal of the upstream sensor and a second signal of the downstream sensor; 
         [0023]    an excitation circuit section configured to receive the first signal or the second signal and to control a drive signal of the vibrator so that the amplitude of the first signal or the second signal becomes a target value; 
         [0024]    a first effective value reception section configured to receive an effective value of the first signal; 
         [0025]    a second effective value reception section configured to receive an effective value of the second signal; 
         [0026]    a ratio computation section configured to receive the effective value of the first signal and the effective value of the second signal and to compute the ratio of both values; and 
         [0027]    an anomaly diagnosis section configured to make a comparison between the computed ratio and a certain value and to generate an alarm. 
         [0028]    The Coriolis mass flowmeter may further comprises: 
         [0029]    a sensor signal assignment section configured to periodically switch the first signal and the second signal, and to output the switched signal to the excitation circuit section, 
         [0030]    wherein the excitation circuit section is configured to receive the first signal or the second signal through the sensor signal assignment section, and to control the drive signal of the vibrator so that the amplitude of the received signal becomes the target value, and 
         [0031]    wherein the ratio computation section is configured to receive a hold voltage of the effective value of the first signal and a hold voltage of the effective value of the second signal in operative association with the switching, and to compute the ratio of both voltages. 
         [0032]    The Coriolis mass flowmeter may further comprises: 
         [0033]    an analog/digital converter configured to convert the first signal and the second signal into digital signals, 
         [0034]    wherein the effective value of the first signal and the effective value of the second signal are given based on digital values of the digital signals. 
         [0035]    The effective value of the first signal and the effective value of the second signal may be given based on detection values of the first signal and the second signal 
         [0036]    The anomaly diagnosis section may be configured to directly receive the hold voltages of the effective values of the first signal and the second signal, to compare one of the voltages with a threshold value, and to generate an alarm. 
         [0037]    A Coriolis mass flowmeter, according to an exemplary embodiment, comprises: 
         [0038]    a vibrator configured to vibrate a measurement conduct line; 
         [0039]    an upstream sensor and a downstream sensor, which are placed at a certain distance in the measurement conduct line and are configured to detect vibration of the measurement conduct line; 
         [0040]    a signal computation processing section configured to compute a mass flow rate of a fluid flowing through the measurement conduct line vibrated by the vibrator based on a phase difference between a first signal of the upstream sensor and a second signal of the downstream sensor; 
         [0041]    a sensor signal assignment section configured to periodically switch the first signal and the second signal; 
         [0042]    an excitation circuit section configured to receive the first signal or the second signal through the sensor signal assignment section, and to control a drive signal of the vibrator so that the amplitude of the received signal becomes a target value; 
         [0043]    a ratio computation section configured to receive a hold voltage of an effective value of the drive signal of the vibrator or a hold voltage of an effective value of a signal proportional to the drive signal in operative association with the switching, and to compute the ratio of the hold voltage received at the switching to the first signal and the hold voltage received at the switching to the second signal; and 
         [0044]    an anomaly diagnosis section configured to make a comparison between the computed ratio and a threshold value, and to generate an alarm. 
         [0045]    The anomaly diagnosis section may be configured to directly receive the hold voltage of the effective value of the drive signal of the vibrator or the hold voltage of the effective value of the signal proportional to the drive signal in operative association with the switching, to compare the voltage with a threshold value, and to generate an alarm. 
         [0046]    According to the exemplary embodiments, the following advantages can be expected: 
         [0000]    (1) A degradation diagnosis in the online state in which the mass flow rate of a fluid flowing through the measurement conduct line is measured can be conducted.
 
(2) A special measuring device for a degradation diagnosis need not be added, a degradation diagnosis of the measurement conduct line can be conducted based on a signal in the online state, and the cost of the device can be reduced.
 
         [0047]    Other features and advantages may be apparent from the following detailed description, the accompanying drawings and the claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0048]      FIG. 1  is a function block diagram to show one embodiment of a Coriolis mass flowmeter according to the invention; 
           [0049]      FIG. 2  is a function block diagram to show another embodiment of a Coriolis mass flowmeter according to the invention; 
           [0050]      FIG. 3  is a function block diagram to show still another embodiment of a Coriolis mass flowmeter according to the invention; 
           [0051]      FIG. 4  is a basic configuration drawing of the sensor section of the Coriolis mass flowmeter; 
           [0052]      FIG. 5  is a schematic drawing to describe primary mode and secondary mode vibration; and 
           [0053]      FIG. 6  is a function block diagram to show a general configuration example of the Coriolis mass flowmeter. 
       
    
    
     DETAILED DESCRIPTION 
       [0054]    Exemplary embodiments will be discussed below in detail with the accompanying drawings:  FIG. 1  is a function block diagram to show one embodiment of a Coriolis mass flowmeter according to the invention. Components identical with those previously described with reference to  FIG. 6  are denoted by the same reference numeral in  FIG. 1  and will not be discussed again. 
         [0055]    A section added to the general configuration described in  FIG. 6  is a diagnosis section  100 . The diagnosis section  100  includes a first effective value reception section  101 , a second effective value reception section  102 , a ratio computation section  103 , and an anomaly diagnosis section  104 . 
         [0056]    The first effective value reception section  101  receives the effective value of a sine wave output by a low-pass filter  37 , provided by converting a first signal SA into a digital value, and outputs MA. The second effective value reception section  102  receives the effective value of a sine wave output by a low-pass filter  38 , provided by converting a second signal SB into a digital value, and outputs MB. 
         [0057]    The ratio computation section  103  receives the signals MA and MB, computes a ratio R of the two signals as R=MB/MA, and passes the result to the anomaly diagnosis section  104 . The anomaly diagnosis section  104  makes a comparison between the ratio R and a threshold value and determines whether or not the state is abnormal. If the state is abnormal, the anomaly diagnosis section  104  outputs an alarm AL to the outside. The alarm based on monitoring the ratio R is effective for an anomaly diagnosis of partial corrosion, wear, clogging, etc., in a measurement conduct line. 
         [0058]    An operation example of the anomaly diagnosis section  104  will be discussed. For example, at the normal time, it is assumed that the first signal SA and the second signal SB deviate about 5%. However, the deviation varies because of disturbance. If a threshold value is set for detecting the effect of partial corrosion only when the deviation changes by ±15% of its initial deviation or more, if the ratio R is 0.8075 (R=0.95×0.85=0.8075) or less and 1.0925 (R=0.95×1.15=1.0925) or more, the state is determined to be abnormal. 
         [0059]    That is, at the normal time, if the normalized effective MA value of the first signal SA whose amplitude is controlled constant by AGC of an excitation circuit section  20  is 1.00 and the effective value MB of the second signal is 0.95, the ratio R is R=MB/MA=0.95/1.00=0.95. 
         [0060]    At the abnormal time, the ratio R is R=0.95×(1-0.15)=0.8075 or less or R=0.95×(1+0.15)=1.0925 or more. 
         [0061]    The anomaly diagnosis section  104  directly receives hold voltages MA and MB of the effective values of the first signal and the second signal, compares the side where the amplitude is not controlled constant, namely, in the embodiment, the second signal MB with a threshold value, and can give an alarm of an anomaly of the second sensor (downward sensor)  16  detecting the signal. 
         [0062]      FIG. 2  is a function block diagram to show another embodiment of a Coriolis mass flowmeter according to the invention. The difference from the embodiment in  FIG. 1  will be discussed. A first signal SA and a second signal SB are switched periodically by a sensor signal assignment section  40  and the switched signal is input to a smoothing section  21  of an excitation circuit section  20  having an AGC function. 
         [0063]    The sensor signal assignment section  40  is subjected to toggle operation by a switch control signal SW from a switch control section  50 . The switch control signal SW is given to a first selection section  105  and a second selection section  106  of a diagnosis section  100 . 
         [0064]    The first selection section  105  and the second selection section  106  select an effective value MA of the first signal SA and an effective value MB of the second signal SB, pass the values to a first voltage hold section  107  and a second voltage hold section  108 , and cause them to hold the values. 
         [0065]    A ratio computation section  103  receives a hold voltage VA of the first voltage hold section  107  and a hold voltage VB of the second voltage hold section  108 , computes a ratio R, and passes the ratio R to an anomaly diagnosis section  104 . The operation of the anomaly diagnosis section  104  is similar to that of the embodiment in  FIG. 1 . 
         [0066]    If a signal input to the excitation circuit section  20  by the sensor signal assignment section  40  is the first signal SA, the first selection section  105  does not output the effective value MA to the first voltage hold section  107 . On the other hand, if the signal input to the excitation circuit section  20  is the second signal SB, the first selection section  105  outputs the effective value MA to the first voltage hold section  107 . 
         [0067]    If a signal input to the excitation circuit section  20  by the sensor signal assignment section  40  is the second signal SB, the second selection section  106  does not output the effective value MB to the second voltage hold section  108 . On the other hand, if the signal input to the excitation circuit section  20  is the first signal SA, the second selection section  106  outputs the effective value MB to the second voltage hold section  108 . 
         [0068]    The advantage in the embodiment is to make good the detection sensitivity of anomaly diagnosis. In the embodiment, a sensor signal used as a criterion of AGC of the excitation circuit section  20  is switched and attention is focused on a sensor signal which is not a criterion. AGC always works so as to keep the voltage of the sensor signal constant. At the normal time, when the first signal SA and the second signal SB are switched, both signals are controlled to a constant value and no change is observed. 
         [0069]    For example, it is assumed that the voltage of the first signal SA is smaller than the voltage of the second signal SB because of an anomaly of a measurement conduct line. At this time, when the first signal SA is criterion of AGC, the voltage of the second signal SB becomes larger than the criterion. 
         [0070]    Next, when the criterion of AGC is switched and the second signal SB is the reference of AGC, the voltage of the first signal SA becomes smaller than the criterion. In the embodiment, sensor voltage which is not the criterion of AGC is compared. 
         [0071]    That is, when the criterion of AGC is not switched (the criterion is the first signal SA) as in the embodiment in  FIG. 1 , the voltage of SA becomes the criterion and the hold voltage VB of the second signal SB becomes larger than the criterion. 
         [0072]    On the other hand, in the technique of switching the reference of AGC as in the embodiment in  FIG. 2 , the hold voltage VA of the first signal SA becomes smaller than the reference and the hold voltage VB of the second signal SB becomes larger than the reference. That is, when reference input of AGC is switched, the difference between VA and VB is enlarged and the ratio of both largely changes, so that the sensitivity of the anomaly diagnosis can be improved. 
         [0073]    An operation example of the anomaly diagnosis section  104  will be discussed. For example, at the normal time, it is assumed that the first signal SA and the second signal SB deviate about 5%. However, the deviation varies because of disturbance. If a threshold value is set for detecting the effect of partial corrosion only when they deviate ±15 or more, if the ratio R is 0.7691 or less and 1.0405 or more, the state is determined to be abnormal. 
         [0074]    That is, at the normal time, if the normalized effective MA value of the first signal SA whose amplitude is controlled constant by AGC of an excitation circuit section  20  is 1.00 and the effective value MB of the second signal is 0.95, the value is one of ratio computation. 
         [0075]    By switching, if the effective MB value of the second signal SB controlled constant by AGC is 1.00 and the effective value MA of the first signal is 1.05, the value is the other of ratio computation. The ratio R at the normal time is R=MB/MA=0.95/1.05=0.9048. 
         [0076]    At the abnormal time, the ratio R is R=0.9048×(1−0.15)=0.7691 or less or R=0.9048×(1+0.15)=1.0405 or more. 
         [0077]    The anomaly diagnosis section  104  directly receives hold voltages VA and VB of the effective values of the first signal and the second signal, compares the voltage on the side which is not the criterion of AGC with a threshold value, and can give an alarm of an anomaly of each of the first sensor (upstream sensor)  15  and the second sensor (downstream sensor)  16  detecting the signals individually. Further, if the hold voltage VA and the hold voltage VB increase or decrease uniformly exceeding the threshold value, an alarm of uniform corrosion of the measurement conduct line can be given. 
         [0078]      FIG. 3  is a function block diagram to show still another embodiment of a Coriolis mass flowmeter according to the invention. The configuration in which a first signal SA and a second signal SB are periodically switched by a sensor signal assignment section  40  and the switched signal is input to a smoothing section  21  of an excitation circuit section  20  including the AGC function is the same as that of the embodiment in  FIG. 2 . 
         [0079]    The embodiment in  FIG. 3  is characterized by the fact that a diagnosis section  100  receives as a monitor target a drive signal DV output from the excitation circuit section  20  executing AGC to a vibrator  14  rather than the effective values of the first signal SA and the second signal SB as in the embodiments in  FIGS. 1 and 2 . 
         [0080]    The drive signal DV input to the diagnosis section  100  is converted into a digital signal by an analog/digital converter  110  through a track-and-hold  109  and the effective value is held in an effective value reception section  111 . 
         [0081]    If the criterion of AGC is selected as the first signal SA, an output destination switch section  112  outputs the hold voltage of the effective value reception section  111  to a first voltage hold section  113  and if the criterion of AGC is selected as the second signal SB, the output destination switch section  112  outputs the hold voltage of the effective value reception section  111  to a second voltage hold section  114  according to a switch control signal SW of a switch control section  50 . 
         [0082]    A ratio computation section  103  receives a hold voltage VA of the first voltage hold section  113  and a hold voltage VB of the second voltage hold section  114 , computes a ratio R, and passes the ratio R to an anomaly diagnosis section  104 . The operation of the anomaly diagnosis section  104  is similar to that of the embodiment in  FIG. 1 . 
         [0083]    An operation example of the anomaly diagnosis section  104  will be discussed. For example, at the normal time, it is assumed that the first signal SA and the second signal SB deviate about 5%. However, the deviation varies because of disturbance. If a threshold value is set for detecting the effect of partial corrosion only when they deviate ±15 or more, if the ratio R is 0.7691 or less and 1.0405 or more, the state is determined to be abnormal. 
         [0084]    That is, at the normal time, if the normalization value of a gain of the drive signal DV when a signal whose amplitude is controlled constant by AGC of the excitation circuit section  20  is the first signal SA is 1.00, the normalization value of a gain of the drive signal DV when a signal whose amplitude is controlled constant by AGC of the excitation circuit section  20  is the second signal SB is 0.95. The ratio R at the normal time is R=VB/VA=0.95/1.05=0.9048. 
         [0085]    At the abnormal time, the ratio R is R=0.9048×(1−0.15)=0.7691 or less or R=0.9048×(1+0.15)=1.0405 or more. 
         [0086]    The anomaly diagnosis section  1 C 4  directly receives the first hold voltage VA and the second hold voltage VB, compares the voltages with a threshold value and can give an alarm of an anomaly of each of the first sensor  15  and the second sensor  16  detecting the signals individually. Further, if the first hold voltage VA and the second hold voltage VB increase or decrease uniformly exceeding the threshold value, an alarm of uniform corrosion of the measurement conduct line can be given. 
         [0087]    In the embodiments in  FIGS. 1 and 2 , the effective values of the first signal SA and the second signal SB are input to the diagnosis section  100  as digital signals passed through the low-pass filters  37  and  38 , but the signals may be analog signals directly obtained from a sensor section  10 . In this case, the ratio computation section  103  executes ratio computation of the analog signals. 
         [0088]    In the embodiment in  FIG. 3 , the drive signal DV from the excitation circuit section  20  executing AGC to the vibrator  14  is input to the diagnosis section  100  as the monitor target, but output voltage CV of the variable amplifier  24  of the excitation circuit section  20  may be input to the diagnosis section  100 . 
         [0089]    While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.