JP5511552B2 - Vibration measuring device - Google Patents

Description

  The present invention relates to a vibration type measurement apparatus, and more particularly to a vibration type measurement apparatus configured to increase measurement accuracy.

  As a measuring device that measures a physical quantity (mass, density, etc.) of a measured fluid by vibrating a sensor tube having a flow path through which the measured fluid flows, a vibration measuring device called a Coriolis mass flow meter or a vibrating density meter is used. is there. Hereinafter, a Coriolis mass flow meter that measures the mass flow rate of the fluid to be measured will be described.

  In this vibration type measuring apparatus, for example, when measuring the mass flow rate of the fluid to be measured, the sensor tube through which the fluid to be measured flows is vibrated in the radial direction by the vibrator at the natural frequency (resonance frequency) of the sensor tube. The displacement of the sensor tube due to the Coriolis force proportional to the mass flow rate is detected by a pickup by increasing the amplitude of the sensor tube with a small driving force (see, for example, Patent Document 1).

  In the vibration type measuring apparatus, the difference between the inflow side displacement and the outflow side displacement of the sensor tube is obtained, and the flow rate of the fluid to be measured flowing through the sensor tube is calculated based on the displacement difference. Therefore, in order to increase the measurement accuracy, it is necessary to match the amplitudes of the detection signal on the inflow side and the detection signal on the outflow side.

JP 2008-64544 A

  In the conventional vibration type measuring apparatus, as means for eliminating the discrepancy in amplitude between the detection signal on the inflow side and the detection signal on the outflow side, for example, the amplitude of the detection signal on the inflow side and the outflow side by AGC control (automatic gain control). A method of matching the amplitudes of the detection signals is used.

  However, in the vibration type measuring apparatus, for example, when the sensor tube is processed into a predetermined shape, or when the pickup is attached to a predetermined position of the sensor tube, the displacement of the shape of the sensor tube or the position of the pickup mounting position is not detected. May occur. In that case, since the DC voltage of the detection signal for detecting the displacement of the sensor tube is shifted and a DC offset occurs, even if the amplitudes of the two detection signals are matched, the midpoint of the amplitude is shifted from the zero cross position, and the measurement accuracy There was a problem that decreased.

  Therefore, in view of the above circumstances, an object of the present invention is to provide a vibration type measuring apparatus that solves the above problems.

In order to solve the above problems, the present invention has the following means.
The present invention includes a sensor tube through which a fluid to be measured flows,
A vibrator for vibrating the sensor tube by inputting a vibration signal;
Excitation control means for controlling the excitation force by the vibrator;
An inflow side detector for detecting displacement on the inflow side of the sensor tube;
An outflow side detector for detecting displacement on the outflow side of the sensor tube;
A calculating means for calculating a difference between the inflow side displacement detected by the inflow side detector and the outflow side displacement detected by the outflow side detector;
In a vibration type measuring apparatus equipped with
Correction means for correcting the DC offset so that the duty ratio of the detection signal obtained from the inflow side detector matches the duty ratio of the detection signal obtained from the outflow side detector;
The calculation means calculates a difference between the inflow side displacement and the outflow side displacement using the signal whose duty ratio is corrected by the correction means ,
Before SL correction means, the inflow-side detector and the duty ratio of the signal obtained from the outflow side detector, the inflow side so as to coincide with the duty ratio of the excitation signal input to the shaker at zero crossing The level of the signal obtained from the detector and the outflow side detector is changed.

According to the present invention, the DC offset is corrected so that the duty ratio of the detection signal obtained from the inflow side detector matches the duty ratio of the detection signal obtained from the outflow side detector, and the corrected signal is used. The difference between the inflow-side displacement and the outflow-side displacement is calculated , and the duty ratio of the signal obtained from the inflow-side detector and the outflow-side detector by the correction means is calculated based on the excitation signal input to the vibration exciter at zero crossing. Since the level of the signal obtained from the inflow side detector and outflow side detector is changed so as to match the duty ratio, the amplitude deviation of the signal may occur due to, for example, sensor tube shape deviation or detector position deviation. Even if a DC offset occurs, the difference between the inflow side displacement and the outflow side displacement can be accurately measured, and the measurement accuracy can be further improved.

It is a front view of one Example of the vibration type measuring apparatus by this invention. It is a side view of a vibration type measuring apparatus. It is a block diagram which shows a flow measurement control circuit. It is a wave form diagram of the normal displacement detection signal detected by the inflow side vibration pickup and the outflow side vibration pickup. It is a wave form diagram of the displacement detection signal by which DC offset was detected by the inflow side vibration pickup and the outflow side vibration pickup. It is a flowchart for demonstrating the process sequence of the flow measurement process 1 which a flow measurement control circuit performs. It is a flowchart for demonstrating the process sequence of the flow measurement process 2 which a flow measurement control circuit performs.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.

  FIG. 1 is a front view of an embodiment of a vibration type measuring apparatus according to the present invention. FIG. 2 is a side view of the vibration type measuring apparatus. In addition, since a vibration type measuring apparatus can obtain | require a mass flow rate using the density and density of a fluid to be measured, it is used as a vibration type density meter and a Coriolis type mass flow meter. Since the vibration type density meter and the Coriolis type mass flow meter have the same configuration, this embodiment will be described in detail when used as a mass flow meter.

  As shown in FIGS. 1 and 2, the vibration measurement apparatus 10 includes a manifold 11, inverted U-shaped sensor tubes 12 and 13 connected to the upper surface of the manifold 11 and formed in parallel, and the sensor tube 12. , 13 of the arc-shaped intermediate portions 12c, 13c, an inflow-side vibration pickup (inflow-side detector) 15 for detecting relative displacement on the inflow side of the sensor tubes 12 and 13, An outflow side vibration pickup (outflow side detector) 16 for detecting the relative displacement of the sensor tubes 12 and 13 on the outflow side is provided.

  The manifold 11 is made of, for example, a rectangular parallelepiped metal block, and has an inflow port 11a at one end and an outflow port 11b at the other end. The inflow side ends 12a and 13a of the sensor tubes 12 and 13 are communicated with the inflow port 11a, and the outflow side ends 12b and 13b of the sensor tubes 12 and 13 are communicated with the outflow port 11b. Therefore, the fluid that has flowed into the inflow port 11a passes through the sensor tubes 12 and 13 and flows out from the outflow port 11b.

  The vibrator 14 includes an excitation coil 14 a attached to the tip of the sensor tube 12 and a magnet 14 b attached to the tip of the sensor tube 13. The outflow side vibration pickup 16 shown in FIG. 2 includes a sensor coil 16 a attached to the sensor tube 12 and a magnet 16 b attached to the sensor tube 13. The inflow side vibration pickup 15 does not overlap with the outflow side vibration pickup 16 in FIG. 2, but, like the outflow side vibration pickup 16, the sensor coil 15 a attached to the vibrating sensor tube 12 and the sensor tube 13 and a magnet 15b attached to 13.

  Further, in this embodiment, as shown in FIG. 1, a temperature sensor 17 that measures the temperature on the inflow side of the sensor tubes 12 and 13 or in the vicinity of the inlet 11 a of the manifold 11 is provided.

  As shown in FIG. 1, the vibrator 14, the inflow-side vibration pickup 15, and the outflow-side vibration pickup 16 are symmetrical with respect to a vertical line crossing the intermediate position of the sensor tubes 12 and 13 as viewed from the front, and The inflow side vibration pickup 15 and the outflow side vibration pickup 16 are provided symmetrically with respect to the center. The vibrator 14 is driven and controlled by the flow rate measurement control circuit 20, and the detection signals detected by the inflow side vibration pickup 15 and the outflow side vibration pickup 16 are input to the flow rate measurement control circuit 20.

  The exciter 14 is configured so that the magnet 14b attracts or repels a magnetic field generated when a positive and negative alternating voltage (AC signal) is applied to the excitation coil 14a, thereby moving the middle portion of the sensor tube 12 in the horizontal direction (Y direction). , See FIG. 2). Naturally, the same force acts on the sensor tube 13 as its reaction force, and the sensor tube 13 vibrates in the opposite direction.

  Since the inflow side vibration pickup 15 is composed of a sensor coil 15a and a magnet 15b, the sensor coil 15a and the magnet 15b come close to and away from the sensor tube 12 and the sensor tube 13 on the inflow side. A detection signal corresponding to the displacement amount (displacement speed) of the sensor coil 15a and the magnet 15b on the inflow side is output.

  Further, since the outflow side vibration pickup 16 is composed of the sensor coil 16a and the magnet 16b, the sensor coil 16a and the magnet 16b come close to and away from the outflow side sensor tubes 12 and 13, and therefore the sensor coil 16a. From, the detection signal according to the displacement amount (displacement speed) of the sensor coil 16a and the magnet 16b in the outflow side is output.

  Next, the above-described flow rate measurement control circuit 20 will be described with reference to FIG.

  FIG. 3 is a block diagram showing a flow rate measurement control circuit. As shown in FIG. 3, the flow measurement control circuit 20 is configured to include an intrinsically safe explosion-proof barrier circuit 30 (hereinafter abbreviated as a barrier circuit 30), a signal processing circuit 40, and an arithmetic circuit 50. Yes.

  The signal processing circuit 40 is composed of a microcomputer, and is configured to include amplitude detection / excitation detection means 41, excitation means 42, temperature measurement means 43, and duty ratio correction means 44.

  The arithmetic circuit 50 includes a microcomputer, and is configured to include a time difference calculation means 51, a correction calculation means 52, a flow rate calculation means 53, an analog output means 54, and a pulse output means 55.

  Further, the flow rate measurement control circuit 20 includes a power supply circuit 70 that supplies power from the external power supply 60 to the entire circuit.

  The barrier circuit 30 intrinsically explosion-proofs the signals for the sensor coils 15a and 16a of the sensor unit, the excitation coil 14 of the vibrator 14 and the temperature sensor 17 in the present embodiment. The barrier circuit 30 is composed of, for example, a voltage / current limiting element (for example, a Zener diode or a resistor).

  In the signal processing circuit 40, the amplitude detection / excitation detection means 41 outputs each displacement detection signal obtained from the sensor coils 15a, 16a to the duty ratio correction means 44 described later, and from each displacement detection signal, the sensor tube 12, 13 is detected to detect whether or not the sensor tubes 12 and 13 are amplified to the amplitude of the resonance state, and an excitation signal for controlling the amplitude of the resonance state according to the amplitude detection result or the like is detected.

  Further, the amplitude detection / excitation detection means 41 outputs the detected excitation signal to the excitation means 42. Further, the amplitude detection / excitation detection means 41 generates a control signal for controlling the voltage / current limit in the barrier circuit 30 and the power supply from the power supply circuit 70 from the detected result, and outputs information corresponding to each control signal. Specifically, the amplitude detection / excitation detection means 41 monitors the vibration of the sensor tubes 12 and 13 to determine whether or not the amplitude has been amplified to the resonance state, and as a result, a sufficient amplitude is obtained. In this case, high (High) is output to the power supply circuit 70 when a sufficient amplitude is not obtained.

  The excitation means 42 generates an excitation signal for applying a positive / negative alternating voltage to the excitation coil 14 a of the above-described vibrator 14 and outputs the excitation signal to the excitation coil 14 a via the barrier circuit 30. Further, the temperature measuring means 43 measures the temperature from the temperature signal detected by the temperature sensor 17 and outputs the measured temperature data to the correction calculating means 52 of the calculating circuit 50.

  The duty ratio correction means 44 measures the duty ratio of a displacement detection signal (sensor signal) indicating the displacement of the sensor coils 15a, 16a obtained via the amplitude detection / excitation detection means 41, and the duty ratio of each displacement detection signal is The duty ratio is corrected by shifting the DC offset of each displacement detection signal so as to match.

  As a method of matching the duty ratio of each displacement detection signal, the duty ratio of one displacement detection signal is adjusted by adjusting the shift amount corresponding to the DC offset of one displacement detection signal. You may make it match. Also, the shift amount of each displacement detection signal may be adjusted so that the duty ratio of each displacement detection signal becomes a predetermined duty ratio (for example, 50% (1: 1)).

  Here, the duty ratio in the present embodiment will be described. When the sensor tubes 12 and 13 vibrate, the sensor coil 15a (16a) and the magnet 15b (16a) are relatively displaced, and an induced electromotive force is generated in the sensor coil 15a (16a). By detecting this change in induced electromotive force (displacement detection signal), the displacement of the sensor tubes 12 and 13 can be measured.

  Since the sensor tubes 12 and 13 vibrate (that is, repeat reciprocating motion), the displacement detection signal is described in a graph with the induced electromotive force on the vertical axis and the time axis on the horizontal axis. It turns out that it becomes the signal of. In one cycle of this sinusoidal signal, the time when the positive induced electromotive force is generated when the value of a predetermined induced electromotive force (for example, 0 mV) is zero, and the negative induced electromotive force is generated. The ratio with the time is called “duty ratio”.

  Therefore, if the value of the induced electromotive force at the zero point is shifted to the positive side, for example, the time that the induced electromotive force on the positive side is generated is shortened accordingly, and the induced electromotive force on the negative side is generated. And the duty ratio shifts accordingly. That is, the duty ratio of the displacement detection signal can be changed by changing the value of the induced electromotive force as the zero point. In the present embodiment, the value of the induced electromotive force when the zero point is shifted is referred to as “DC offset”.

  The duty ratio corrected by the duty ratio correction unit 44 is output to the time difference calculation unit 51. As a result, the displacement detection signals having the same duty ratio are input to the time difference calculation means 51 of the calculation circuit 50. In the time difference calculation means 51, when each displacement detection signal crosses the zero point (zero cross). The time difference will be obtained. Therefore, the time difference calculation means 51 can accurately measure the time difference between the inflow side and the outflow side without being affected by the DC offset.

  The correction calculation unit 52 corrects the time difference based on the Young's modulus obtained from the temperature measurement unit 43. Further, the correction calculation unit 52 outputs the obtained correction information and time difference information to the flow rate calculation unit 52.

  The flow rate calculation means 53 converts the time difference information and the correction information input from the correction calculation means 52 into a flow rate. Further, the flow rate calculation unit 53 outputs the obtained flow rate information to the analog output unit 54.

  The analog output unit 54 generates an analog signal 71 corresponding to the instantaneous flow rate input from the flow rate calculation unit 53. The analog output means 54 outputs the instantaneous flow rate to the pulse output means 55 and outputs the obtained analog signal as an analog signal 71 via the barrier circuit 30.

  The pulse output unit 55 generates a flow rate pulse corresponding to the integrated flow rate from the instantaneous flow rate input from the analog output unit 54. Further, the pulse output means 55 outputs the obtained flow rate pulse as a flow rate pulse signal 72 via the barrier circuit 30.

  The power supply circuit 70 controls the voltage obtained from the external power supply 60 and supplies the power supply voltage (Vcc) to the signal processing circuit 40 and the arithmetic circuit 50. Further, the power supply circuit 70 outputs a reset signal or a reset release signal to the arithmetic circuit 50 at a predetermined timing, thereby causing the arithmetic circuit 50 to perform a flow rate calculation process or the like at an appropriate timing.

  In the vibration type measuring apparatus 10 having the above-described configuration, the vibration exciter 14 is driven by the flow measurement control circuit 20 during flow measurement, and the sensor has a period and amplitude corresponding to the vibration characteristics (natural frequency) of the sensor tubes 12 and 13. The intermediate portions 12c and 13c of the tubes 12 and 13 are vibrated. Then, the sensor tubes 12 and 13 vibrate in the approaching and separating directions (Y direction, see FIG. 2) with the arc-shaped intermediate portions 12c and 13c using both ends fixed to the manifold 11 as fulcrums.

  At this time, when a fluid flows through the vibrating sensor tubes 12 and 13, a Coriolis force having a magnitude corresponding to the flow rate is generated. Therefore, an operation delay occurs between the inflow side and the outflow side of the sensor tube 12, and a time difference is generated between the displacement detection signal of the inflow side vibration pickup 15 and the displacement detection signal of the outflow side vibration pickup 16. Here, since the time difference between the inflow side displacement detection signal and the outflow side displacement detection signal is proportional to the flow rate, the flow rate measurement control circuit 20 calculates the flow rate based on the time difference with the above-described configuration.

  Therefore, when the displacement of the sensor tubes 12 and 13 is detected by the inflow-side vibration pickup 15 and the outflow-side vibration pickup 16, the time difference associated with the vibration of the sensor tubes 12 and 13 is obtained. Is converted into a mass flow rate.

  Here, a displacement detection signal (sensor signal) detected by the inflow side vibration pickup 15 and the outflow side vibration pickup 16 will be described.

  FIG. 4A is a waveform diagram of normal displacement detection signals detected by the inflow side vibration pickup 15 and the outflow side vibration pickup 16. As shown in FIG. 4A, since the sensor tubes 12 and 13 are vibrated so as to vibrate at a natural frequency, the sensor coils 15a and 15a of the inflow side vibration pickup 15 and the outflow side vibration pickup 16 are measured during flow rate measurement. The displacement detection signals (sensor signals A and B) detected by 16a are detected as substantially sinusoidal waveforms.

  In addition, each of the detection signals on the inflow side and the outflow side shows a state in which there is no DC offset at a duty ratio of 50% (1: 1) because the midpoint of the amplitude intersects with zero voltage (zero crossing). . That is, each of the detection signals on the inflow side and the outflow side has a period of T1 = T2 and T3 = T4, and the amplitude of the induced electromotive force voltage is D1 = D2 and D3 = D4. Since the time difference Δt1 between the inflow side displacement and the outflow side displacement in FIG. 4A is proportional to the flow rate flowing through the sensor tubes 12 and 13, the flow rate measurement value is obtained based on the time difference Δt1.

  FIG. 4B is a waveform diagram of a displacement detection signal with DC offset detected by the inflow side vibration pickup 15 and the outflow side vibration pickup 16. As shown in FIG. 4B, the detection signal indicating the inflow side displacement (sensor signal A) has a duty ratio of 50% (1) because the midpoint of the amplitude crosses the zero voltage of the induced electromotive force (zero cross). : 1). That is, the detection signal indicating the inflow side displacement has a cycle of T1 = T2 and an amplitude corresponding to a DC voltage of D1 = D2.

  However, the waveform of the detection signal (sensor signal B) indicating the outflow side displacement changes so that the DC voltage is asymmetric at the zero cross, and a DC offset (D1-D3) occurs. The center of amplitude does not cross the voltage zero and is not zero crossing. That is, the detection signal on the outflow side has a cycle of T3 <T1 <T4 and an amplitude corresponding to a DC voltage of D3 <D1 <D4. In this case, the duty ratio is, for example, 30% (3: 7) to 40% (4: 6) according to the DC offset.

  In this case, the time difference when the outflow side displacement falls is Δt2, while the time difference when the outflow side displacement rises is Δt3 (Δt2 <Δt1 <Δt3). As described above, when the waveform of the displacement detection signal has a DC offset, the amplitude at the zero cross does not match between the inflow side and the outflow side, and therefore, the time difference at the fall of the outflow side displacement does not match the time difference at the rise. Therefore, the time difference at the time of flow rate measurement cannot be detected stably, and the time difference Δt2 or Δt3 is detected where the time difference Δt1 is originally detected, which may cause an error in the flow rate measurement.

  Here, a control method for eliminating a time difference detection error as shown in FIG. 4B will be described with reference to FIG.

  FIG. 5 is a flowchart for explaining the processing procedure of the flow measurement processing 1 executed by the flow measurement control circuit 20. As shown in FIG. 5, the flow measurement control circuit 20 receives the displacement detection signals (sensor signals A and B) detected by the sensor coils 15a and 16a of the inflow-side vibration pickup 15 and the outflow-side vibration pickup 16 in S11. Read. Subsequently, in S12, an arbitrary shift amount d1 or d2 set in advance is added to the lower voltage value of the displacement detection signals (sensor signals A and B) detected by the sensor coils 15a and 16a. Thereby, the amplitude with respect to the displacement detection signal in which the DC offset has occurred is shifted to the + side, and the midpoint of the amplitude is corrected to the voltage zero side.

  In next S13, it is checked whether or not the displacement detection signal (sensor signal A) on the inflow side has measured one wavelength. In S13, when one wavelength of the displacement detection signal (sensor signal A) on the inflow side is measured (in the case of YES), the process proceeds to S14, and the duty ratio xa of the displacement detection signal (sensor signal A) on the inflow side is set. measure. Subsequently, in S15, the shift amount d1 is calculated based on the duty ratio xa, and the shift amount d1 is stored in the memory.

  In S13, when the inflow side displacement detection signal (sensor signal A) is not measured for one wavelength (in the case of NO), the process proceeds to S16 without performing the processes of S14 and S15.

  In S16, it is checked whether or not the outflow side displacement detection signal (sensor signal B) has measured one wavelength. In S16, when one wavelength of the displacement detection signal (sensor signal B) on the outflow side is measured (in the case of YES), the process proceeds to S17, and the duty ratio of the displacement detection signal (sensor signal B) on the outflow side Measure xb. Subsequently, in S18, the shift amount d2 is calculated based on the duty ratio xb, and the shift amount d2 is stored in the memory.

  In S16, when one wavelength is not measured for the displacement detection signal (sensor signal B) on the outflow side (in the case of NO), the process proceeds to S19 without performing the processes of S17 and S18.

  In S19, it is checked whether the duty ratio xa on the inflow side and the duty ratio xb on the outflow side match. In S19, if the inflow side duty ratio xa and the outflow side duty ratio xb do not match (in the case of NO), the process proceeds to S20, and a predetermined value is added to or subtracted from the current shift amount d1 (or d2). The shift amount d1 (or d2) is updated. And it returns to S12 and repeats the process of S12-S19 using the updated shift amount d1 (or d2).

  In S19, when the inflow-side duty ratio xa and the outflow-side duty ratio xb match (in the case of YES), the process proceeds to S21. In S21, the time difference between the zero crosses of the shifted displacement detection signal (sensor signal A) and the shifted displacement detection signal (sensor signal B) is measured.

  In this manner, an arbitrary shift amount d1 (or d2) is added to or subtracted from the displacement detection signals detected by the sensor coils 15a and 16a so that the inflow side duty ratio xa and the outflow side duty ratio xb coincide. In order to measure the time difference between the zero crosses of the displacement detection signal on the inflow side and the displacement detection signal on the outflow side in a state where the duty ratio xa on the inflow side and the duty ratio xb on the outflow side coincide with each other, The time difference between the inflow side and the outflow side can be accurately measured without being subjected to the error, and due to variations in the shape of the sensor tubes 12, 13, the displacement of the attachment positions of the inflow side vibration pickup 15 and the outflow side vibration pickup 16, etc. Measurement errors can be eliminated.

  In the above embodiment, as a method of matching the duty ratios of the respective displacement detection signals, any one of the displacement detection signals is arbitrarily set until the duty ratio of one displacement detection signal matches the duty ratio of the other displacement detection signal. By repeatedly adding or subtracting the shift amount d1 (or d2), the duty ratio of one displacement detection signal matches the duty ratio of another displacement detection signal. However, the method for matching the duty ratios of the displacement detection signals is not limited to this. For example, an arbitrary duty ratio is determined in advance, and the duty ratios of the displacement detection signals are determined in advance. By repeatedly adding or subtracting an arbitrary shift amount d1 (or d2) to each displacement detection signal until the value becomes, the duty ratio of each displacement detection signal is made to match a predetermined duty determined in advance. You may make it make the duty ratio of a displacement detection signal correspond to the duty ratio of another displacement detection signal. Furthermore, the target duty ratio must be set to a specific ratio such as 50% (1: 1), for example, set to an arbitrary ratio such as 20% (2: 8). Also good.

Here, a modified example of the flow rate measurement process will be described.
[Modification 1]
FIG. 6 is a flowchart for explaining the processing procedure of the flow rate measurement process 2 executed by the flow rate measurement control circuit 20. In FIG. 6, S21 to S25 are the same processes as S11 to S15 described above, and thus description thereof is omitted.

  In S26, it is checked whether or not the shift amount a calculated in S25 is equal to or less than a preset abnormal shift amount H1 (lower limit threshold). In S26, when the shift amount a is not equal to or less than the preset abnormal shift amount H1 (in the case of NO), the process proceeds to S27, and whether or not the shift amount a is equal to or less than the preset abnormal shift amount H2 (upper limit threshold). Check.

  In S27, when the shift amount a is equal to or less than the preset abnormal shift amount H2 (in the case of YES), the process proceeds to S28, and the displacement detection signal (sensor signal A) detected by the sensor coil 15a of the inflow-side vibration pickup 15 is reached. ) Is a minor abnormality, and the determination result is stored in the memory.

  In S27, if the shift amount a is equal to or larger than the preset abnormal shift amount H2 (in the case of NO), the process proceeds to S29, and a displacement detection signal (sensor) detected by the sensor coil 15a of the inflow vibration pickup 15 is detected. It is determined that the signal A) is a serious abnormality, and the determination result is stored in the memory. Thereafter, the process proceeds to S31.

  In S26, when the shift amount a is equal to or less than the preset abnormal shift amount H1 (in the case of YES), or after performing the processing of S28, the process proceeds to S30, and the shift amount d1 is changed to the shift amount a. Update. Note that the shift amount a = d1 + Δd, and Δd is an arbitrary numerical value. Thereby, the shift amount a is set, and the shift amount is optimized.

  In S23, when one wavelength is not measured for the displacement detection signal (sensor signal A) on the inflow side (in the case of NO), the process proceeds to S31 without performing the processes of S24 to S30.

  Moreover, since the process of S31-S33 is the same as the process of S16-S18 mentioned above, the description is abbreviate | omitted.

  In S34, it is checked whether or not the shift amount b calculated in S33 is equal to or less than a preset abnormal shift amount H1 (lower limit threshold). In S33, when the shift amount b is not equal to or less than the preset abnormal shift amount H1 (in the case of NO), the process proceeds to S35, and whether or not the shift amount a is equal to or less than the preset abnormal shift amount H2 (upper limit threshold). Check.

  In S35, when the shift amount b is equal to or less than the preset abnormal shift amount H2 (in the case of YES), the process proceeds to S36, and the displacement detection signal (sensor signal B) detected by the sensor coil 16a of the outflow side vibration pickup 16 is reached. ) Is a minor abnormality, and the determination result is stored in the memory.

  In S35, when the shift amount b is equal to or larger than the preset abnormal shift amount H2 (in the case of NO), the process proceeds to S37, and the displacement detection signal (sensor) detected by the sensor coil 16a of the outflow side vibration pickup 16 is detected. It is determined that the signal B) is a serious abnormality, and the determination result is stored in the memory. Thereafter, the process proceeds to S39.

  In S34, when the shift amount a is equal to or less than the preset abnormal shift amount H1 (in the case of YES), or after performing the process of S36, the process proceeds to S38, and the shift amount d2 is changed to the shift amount b. Update. Note that the shift amount b = d2 + Δd, and Δd is an arbitrary numerical value. Thereby, the shift amount b is set and the shift amount is optimized.

  In S31, when one wavelength is not measured for the displacement detection signal (sensor signal B) on the inflow side (in the case of NO), the process proceeds to S39 without performing the processes of S32 to S38.

  In S39, it is checked whether the inflow side vibration pickup 15 and the outflow side vibration pickup 16 are normal. In S39, for example, if the displacement detection signals (sensor signals) detected by the sensor coils 15a and 16a of the inflow side vibration pickup 15 and the outflow side vibration pickup 16 are normal, it is determined to be normal (in the case of YES), Proceed to S40.

  In S40, it is checked whether the duty ratio xa on the inflow side and the duty ratio xb on the outflow side match. In S40, when the inflow side duty ratio xa and the outflow side duty ratio xb do not match (in the case of NO), the process proceeds to S41, and a predetermined value is added to or subtracted from the current shift amount d1 (or d2). The shift amount d1 (or d2) is updated. And it returns to S22 and repeats the process of S22-S40 using the updated shift amount d1 (or d2).

  In S40, if the inflow side duty ratio xa and the outflow side duty ratio xb match (in the case of YES), the process proceeds to S42. In S42, the time difference between the zero crosses of the shifted inflow side displacement detection signal (sensor signal A) and the shifted outflow side displacement detection signal (sensor signal B) is measured.

  In S39, if it is determined that the displacement detection signals (sensor signals) detected by the sensor coils 15a and 16a are minor abnormality or severe abnormality, the process proceeds to S43, and an alarm signal is output to cause an abnormality. Inform that there is.

  Subsequently, in S44, it is checked whether or not the displacement detection signal (sensor signal) detected by the sensor coils 15a and 16a is a slight abnormality. In S44, when the displacement detection signal (sensor signal) is a slight abnormality (in the case of YES), the process proceeds to S42, where the shifted inflow side displacement detection signal (sensor signal A) and the shifted outflow side displacement are processed. The time difference between the zero cross and the detection signal (sensor signal B) is measured.

  In S44, when the displacement detection signal (sensor signal) is severely abnormal (in the case of YES), the current process is terminated without performing the process of S42.

In this way, an arbitrary shift amount d1 (or d2) is added to or subtracted from the displacement detection signals detected by the sensor coils 15a and 16a so that the inflow side duty ratio xa and the outflow side duty ratio xb coincide. In order to measure the time difference between the zero crosses of the displacement detection signal on the inflow side and the displacement detection signal on the outflow side in a state where the duty ratio xa on the inflow side and the duty ratio xb on the outflow side coincide with each other, The time difference between the inflow side and the outflow side can be accurately measured without being subjected to the error, and due to variations in the shape of the sensor tubes 12, 13, the displacement of the attachment positions of the inflow side vibration pickup 15 and the outflow side vibration pickup 16, etc. Measurement errors can be eliminated.
[Modification 2]
In the second modification, the duty ratio of the displacement detection signal detected by each of the sensor coils 15 a and 16 a of the inflow side vibration pickup 15 and the outflow side vibration pickup 16 in the flow rate measurement control circuit 20 is input to the vibrator 14. You may use the duty ratio correction | amendment means which adjusts the shift amount of each displacement detection signal so that the duty ratio of an excitation signal may correspond.

  This duty ratio correction means converts the duty ratio of signals obtained from the sensor coils 15a and 16a of the inflow side vibration pickup 15 and the outflow side vibration pickup 16 to the duty of the vibration signal input to the vibration exciter 14 at the time of zero crossing. The levels of signals obtained from the sensor coils 15a and 16a of the inflow side vibration pickup 15 and the outflow side vibration pickup 16 are changed so as to coincide with the ratio.

  Therefore, in the second modification, the displacement detected by each of the sensor coils 15a and 16a so that the duty ratio xa on the inflow side or the duty ratio xb on the outflow side coincides with the excitation signal duty ratio to the vibrator 14. Arbitrary shift amounts d1 and d2 are added to the detection signal, and the zero cross between the inflow side displacement detection signal and the outflow side displacement detection signal in a state where the inflow side duty ratio xa and the outflow side duty ratio xb are matched. The time difference between the inflow side and the outflow side can be accurately measured without being affected by the DC offset, the variation in the shape of the sensor tubes 12, 13 and the inflow side vibration pickup 15 and Measurement errors due to a shift in the mounting position of the outflow side vibration pickup 16 can be eliminated.

  In the first and second modifications, the duty ratios xa and xb may be set to arbitrary duty ratios set in advance, or the other duty ratio is adjusted based on one of the duty ratios. You may use the correction method to do.

  In the above-described embodiment, the sensor tube is configured to be bent in an inverted U shape as an example. However, the configuration is not limited to this, and the sensor tube is configured to vibrate in another shape. Of course, the present invention can also be applied.

  In the above-described embodiment, the inflow side displacement and the outflow side displacement of the sensor tube have been described with respect to the configuration using a pickup that combines a coil and a magnet. Of course, a sensor may be used.

  In the above-described embodiment, the case where the time difference between the inflow side displacement detection signal and the outflow side displacement detection signal is obtained has been described as an example. However, the present invention is not limited to this. You may make it provide the phase difference calculating means which calculates the phase difference of a detection signal and an outflow side displacement detection signal.

DESCRIPTION OF SYMBOLS 10 Vibration type measuring apparatus 11 Manifold 12, 13 Sensor tube 14 Exciter 14a Excitation coil 14b Magnet 15 Inflow side vibration pickup 16 Outflow side vibration pickup 15a, 16a Sensor coil 15b, 16b Magnet 17 Temperature sensor 20 Flow measurement control circuit 30 Essential Safety explosion-proof barrier circuit 40 Signal processing circuit 41 Amplitude detection / excitation detection means 42 Excitation means 43 Temperature measurement means 44 Duty ratio correction means 50 Calculation circuit 51 Time difference calculation means 52 Correction calculation means 53 Flow rate calculation means 54 Analog output means 55 Pulse output means 60 External power supply 70 Power supply circuit 71 Analog signal 72 Flow rate pulse signal

Claims (1)

A sensor tube through which the fluid to be measured flows;
A vibrator for vibrating the sensor tube by inputting a vibration signal;
Excitation control means for controlling the excitation force by the vibrator;
An inflow side detector for detecting displacement on the inflow side of the sensor tube;
An outflow side detector for detecting displacement on the outflow side of the sensor tube;
A calculating means for calculating a difference between the inflow side displacement detected by the inflow side detector and the outflow side displacement detected by the outflow side detector;
In a vibration type measuring apparatus equipped with
Correction means for correcting the DC offset so that the duty ratio of the detection signal obtained from the inflow side detector matches the duty ratio of the detection signal obtained from the outflow side detector;
The calculation means calculates a difference between the inflow side displacement and the outflow side displacement using the signal whose duty ratio is corrected by the correction means ,
The correction means detects the inflow side so that the duty ratio of the signals obtained from the inflow side detector and the outflow side detector matches the duty ratio of the vibration signal input to the vibration exciter at the time of zero crossing. The vibration type measuring apparatus is characterized in that the level of the signal obtained from the detector and the outflow side detector is changed .

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