JP4251595B2 - Vibrating tube density sensor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a vibrating tube density sensor, and more particularly to a density sensor of a type that measures the density of a fluid to be measured by measuring the natural frequency of the vibrating tube.
[0002]
[Prior art]
The simulated moving bed type chromatographic separation apparatus is widely used for the purpose of extracting one or more components from a raw material fluid obtained by a natural or chemical reaction in a variety of manufacturing industries such as sugar industry and pharmaceutical industry. Yes. In the simulated moving bed type chromatographic separation apparatus, a vibrating tube density sensor is used for the purpose of detecting the state (phase) of the internal fluid.
[0003]
The vibration tube type density sensor measures the natural frequency of the vibration system and converts it into density. The natural frequency is determined by the mechanical size, elasticity, and weight of the vibration system. During density measurement, the size and elasticity of the vibration system hardly change and can be regarded as a constant. Therefore, the natural frequency of the vibration system can be treated as a function of its weight. Actually, since the cross section of the vibration tube is hollow and is filled with the fluid to be measured, the natural frequency of the vibration system is the sum of the weight of the vibration tube itself and the weight of the filled fluid to be measured. Determined.
[0004]
A conventional vibration tube type (vibration type) density sensor is described in, for example, Japanese Patent Application Laid-Open No. 6-94592. The density sensor described in the publication has two permanent magnets fixed to a vibration tube for vibration tube excitation and vibration frequency detection of the vibration tube, and a drive coil at a position facing both permanent magnets. And the detection coil is fixedly arranged. The vibration tube is vibrated by a set of a drive coil and one permanent magnet, and the frequency of the vibration tube is detected by a set of the other permanent magnet and a detection coil.
[0005]
In the density sensor described in the above publication, in order to obtain continuous vibration of the vibration tube, it is necessary to apply excitation from the drive coil as a positive feedback signal to vibration of the vibration tube detected by the detection coil. There is. For this reason, the phase of the detection signal from the detection coil is advanced by 90 degrees by a phase shift circuit, which is amplified and used as a drive signal for the drive coil.
[0006]
[Problems to be solved by the invention]
In the conventional vibration tube type density sensor, two permanent magnets are attached to the vibration tube itself for the purpose of driving (vibration) and vibration detection. For this reason, the weight of the permanent magnet and the weight of the vibration tube are added to the weight of the fluid to be measured, thereby constituting the total weight of the vibration system. Here, the detection sensitivity as the density meter decreases as the weight of the vibration tube and the permanent magnet in the vibration system is larger than the weight of the fluid to be measured. That is, even when a sufficiently thin and short vibrating tube is used, there is a problem that the weight of the permanent magnet cannot be ignored in order to obtain sufficient sensitivity for detecting the density of the fluid to be measured.
[0007]
Further, in the conventional vibration tube type density sensor, as described above, two coils are used for vibration detection and excitation. Here, it is known that when two coils for detection and excitation are brought close to each other, magnetic coupling occurs between the two coils and oscillation occurs at a frequency different from the natural frequency of the vibration system. . In order to prevent such oscillation, it is necessary to maintain a separation distance that does not cause magnetic coupling between the two coils. Therefore, both permanent magnets that form a pair with these coils have the same separation distance. Is required. As a result, the vibration system of the vibration tube type density sensor has a limit on downsizing.
[0008]
Furthermore, in the vibration tube type density sensor, in order to maintain continuous vibration of the vibration system, the phase of vibration obtained from the vibration detecting means is advanced 90 degrees using a phase shift circuit, and this is amplified and added. The vibration coil is driven. In this case, since the phase shift circuit also has frequency characteristics, it is difficult to advance the phase angle accurately by 90 degrees. As a result, the vibration tube density sensor continues to vibrate at a frequency with the highest efficiency in a state where the vibration system and the phase shift circuit are combined. This vibration has a frequency slightly different from the natural frequency of the vibration system, and causes a decrease in sensitivity as a density meter.
[0009]
SUMMARY OF THE INVENTION In view of the above, an object of the present invention is to provide a vibrating tube density meter that improves the detection sensitivity by reducing the number of members attached to the vibrating tube, and enables the miniaturization thereof.
[0010]
Another object of the present invention is to provide a vibrating tube density meter capable of further improving the detection sensitivity because the natural frequency of the vibration meter can be obtained accurately because no phase shifter is used. .
[0011]
[Means for Solving the Problems]
In order to achieve the above object, a vibrating tube densimeter according to a first aspect of the present invention includes a vibrating tube that contains a fluid to be measured and that is supported so that a predetermined portion can vibrate, and a vibration waveform of the vibrating tube. Vibration detecting means for detecting the current, and energizing means for passing a current to the predetermined portion of either or both of the vibration tube and the fluid in the vibration tube at a predetermined timing of the vibration waveform detected by the vibration detection means, Magnetic field applying means for applying a magnetic field in a direction orthogonal to the current to the predetermined portion, wherein the current and the magnetic field generate an electromagnetic force that becomes a positive feedback signal with respect to vibration of the vibrating tube. To do.
[0012]
In the vibrating tube density sensor according to the first aspect of the present invention, the current flowing through the predetermined portion and the magnetic field applied by the magnetic field applying means generate an electromagnetic force that provides positive feedback due to vibration of the vibrating tube. The vibration of the vibrating tube oscillates. Therefore, it is not necessary to attach a member that increases the weight of the vibration tube to a predetermined portion of the vibration tube for vibration, so that the density detection accuracy is not lowered and a separation distance is necessary. Since it is not necessary to attach a member, the vibration system can be easily downsized.
[0013]
The vibration tube density sensor according to the second aspect of the present invention includes a vibration tube that contains a fluid to be measured and is supported so that a predetermined portion can vibrate, and vibration detection means that detects a vibration waveform of the vibration tube. And a vibrating tube density sensor that includes a vibrating unit that applies a vibrating force as a positive feedback signal to the vibration of the vibrating tube at a predetermined timing of the vibration waveform detected by the vibration detecting unit.
The vibration detecting means includes a set of a light source and a light receiving element whose amount of passing light beam is changed by vibration of the vibrating tube.
[0014]
In the vibration tube density sensor according to the second aspect of the present invention, it is not necessary to attach the vibration detecting means to the vibration tube, and therefore, the vibration tube does not need to be attached with members that need to be separated from each other. Miniaturization is easy. It is preferable that the vibrating means is constituted by a combination of members that generate electromagnetic force between a predetermined portion of the vibrating tube and a fixed portion facing the predetermined portion.
[0015]
In a preferable aspect of the vibration tube type density sensor of the second viewpoint, the excitation means includes a magnetic material disposed in a predetermined portion of the vibration tube, and a coil fixed to a position facing the predetermined portion; An energization unit that passes current through the coil at a predetermined timing of the vibration waveform detected by the vibration detection unit, and the current generates an attractive force that becomes a positive feedback signal with respect to the vibration of the vibration tube. Occurs in wood. In this case, the structure of the vibration means is simpler. As the magnetic material, it is preferable to form a thin film made of a magnetic material on a predetermined portion of the vibration tube. In this case, the density sensor can be configured by a vibration means having a particularly simple configuration.
[0016]
In the vibration tube type density sensor according to the first aspect of the present invention and the density sensor according to the preferred aspect according to the second aspect of the present invention, the energization means detects a predetermined timing from the vibration waveform, and It is preferable to include pulse generation means for generating a current pulse in synchronization with a predetermined timing. In this case, a current pulse having a desired phase can be obtained without using a phase circuit.
[0017]
Furthermore, it is also a preferable aspect of the present invention to include an excitation unit that excites vibration of the vibrating tube. Here, the vibration tube type density meter according to the preferred embodiment of the present invention detects noise existing in the natural world, excites vibration by its positive feedback, and then shifts to perform oscillation according to the natural frequency of the vibration meter. To do. However, there are rare cases where such self-oscillation does not occur, particularly in an environment with low noise. In such a case, the excitation means is used for a short time to excite vibration. If even a slight vibration occurs, the vibration is continued by positive feedback thereafter, and the excitation means is stopped.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in more detail based on embodiments of the present invention with reference to the drawings. FIG. 1 shows a vibrating tube density sensor according to an embodiment of the present invention. The vibration tube type density sensor is a vibration tube 13 bent in a U-shape and supported by support blocks 11 and 12 with a pair of U-shaped legs, and a current flow through the vibration tube 13 in the direction of arrow 16 in the figure. A pair of electrodes 14 and 15 and a pair of U-shaped permanent magnets 17 and 18 that apply a magnetic field that applies electromagnetic force to the current flowing in the vicinity of the U-shaped curved portion that forms the free end of the vibrating tube 13; Have The support blocks 11 and 12 are fixed to the base 20 via the insulating plate 19, and the permanent magnets 17 and 18 are directly fixed to the base 20.
[0019]
The vibration tube 13 is made of, for example, titanium or stainless steel, and is fixed to the support blocks 11 and 12 by U-shaped bolts 21. The U-shaped bolt 21 and the support blocks 11 and 12 are electrically and magnetically insulated by an insulating washer 22. The vibrating tube 13 is introduced with a fluid from a pseudo moving bed type chromatographic separation apparatus that is a density measurement target.
[0020]
The vibration in the vicinity of the U-shaped curved portion of the vibration tube 13 is detected by a combination of the light emitting diode 23 and the phototransistor 24 and a shutter 25 that blocks light from the light emitting diode. That is, when a current in the direction of the arrow 16 flows through the vibrating tube 13 via the electrodes 14 and 15, the vibrating tube 13 is known as the left Fleming method law due to the magnetic field applied by the permanent magnets 17 and 18. An upward electromagnetic force is generated. When the vibrating tube 13 vibrates due to this electromagnetic force, a part of the light beam from the light emitting diode 23 is blocked by the shutter 25. The shutter 25 is used when the size of the vibration tube 13 is sufficiently large and the influence on the vibration frequency of the vibration tube 13 is small. When the vibrating tube 13 is thin and short, it is preferable that a portion of the light beam is directly blocked or passed by the vibrating tube 13 itself to change the amount of the passing light beam.
[0021]
FIG. 2 is a block diagram of a signal processing circuit for passing a current between the electrodes 14 and 15. In the figure, an example in which a part of the light beam is directly blocked by the vibrating tube 13 is shown. The signal processing circuit includes a vibration detection unit 30 that detects vibration of the vibration tube 13, a timing signal generation unit 40 that generates a predetermined timing signal based on the detection signal waveform of the vibration detection unit 30, and the vibration tube 13 based on the timing signal. The driving unit 50 energizes a current for excitation, and the excitation unit 60 that generates a pulse for exciting the vibration of the vibrating tube 13.
[0022]
The vibration detection unit 30 receives the output signal from the light emitting diode 23 connected to the power source VCC via the current limiting resistor R1, the phototransistor 24 that receives the light flux from the light emitting diode 23, and the collector resistance R2 of the phototransistor 24. The voltage follower 32 is taken out via an RC filter 31 for blocking DC components. The voltage follower 32 includes an operation amplifier.
[0023]
The timing signal generation unit 40 compares the input signal input from the voltage follower 32 with the ground level, and when the input signal becomes a positive signal, the output is “1”. An OR gate 42 that takes an OR with the output and a one-shot circuit 43 that generates a one-shot pulse with a predetermined pulse width when the output of the OR gate 42 becomes “1”. In the comparator 41, a predetermined reference level can be used instead of the ground level.
[0024]
The drive unit 50 includes a choke coil 51 connected between the power supply VCC and one electrode 14 of the vibrating tube 13, an electrolytic capacitor 52 connected between the electrode 14 and the ground, and between the other electrode 15 and the ground. The power transistor 53 is inserted and driven by the output of the one-shot circuit 43. The current supplied by the power transistor 53 flows from the power supply VCC to the ground via the choke coil 51, the electrode 14, the vibrating tube 13, and the electrode 15.
[0025]
The excitation unit 60 generates an excitation pulse oscillator 61 that generates a pulse train that serves as an excitation pulse for exciting the vibration of the vibration tube, and an AND gate 62 that performs an AND operation between the excitation permission signal 63 and the output from the excitation pulse oscillator 61. Consists of The output of the AND gate 62 is given to one input of the OR gate 42 as an output of the excitation unit 60 as described above.
[0026]
The vibration tube type density sensor of the above-described embodiment starts to vibrate by positive feedback in the presence of noise existing in nature, and shifts to oscillate at a natural frequency determined by the weight of the vibration tube 13 and the internal fluid. When the density sensor does not self-oscillate in an environment with extremely low noise, the excitation pulse oscillator 61 is turned on, the excitation permission signal 63 is input to the excitation unit 60, and excitation is performed via the AND gate 62. The pulse train is given to the timing signal generator 40. The excitation pulse train excites the vibration of the vibrating tube 13 by driving the power transistor 53 via the one-shot circuit 43. Instead of the configuration including the excitation unit 60, an excitation unit that mechanically vibrates the vibrating tube 13 by some means may be provided. Or you may vibrate by the hand of an operator.
[0027]
When the vibrating tube 13 starts to vibrate even slightly due to positive feedback or application of an excitation pulse train, the vibrating tube 13 blocks or passes a part of the light beam from the light emitting diode 23 toward the phototransistor 24. Due to the change in the luminous flux, only the AC component of the electrical signal generated in the phototransistor 24 is extracted by the DC component blocking filter 31 and input to the voltage follower 32.
[0028]
The output signal of the voltage follower 32 is compared with a reference potential that forms a ground potential by the comparator 41, and when the positive signal is higher than the reference potential, the one-shot circuit 43 is activated. This positive signal is generated while the luminous flux passing above the vibrating tube 13 is decreasing, that is, when the vibrating tube 13 moves upward and the vibrating tube 13 is at the center position of vibration.
[0029]
The one-shot circuit 43 drives the power transistor 53, and the power transistor 53 flows a short-time pulse current through the vibrating tube 13. The magnetic field applied by the permanent magnets 17 and 18 generates an electromagnetic force between the pulse current and gives an upward force to the vibrating tube 13. Thereby, the upward movement of the vibration tube 13 is accelerated. The amplitude of the vibration tube 13 gradually increases by this positive feedback, and continues to vibrate with a constant amplitude and its natural frequency after a predetermined time has elapsed from the start of operation.
[0030]
The density sensor of the present embodiment calculates the vibration frequency of the vibration tube 13 by measuring the period of the pulse train generated by the one-shot circuit 43 with a counter (not shown) or the like, and based on this, the fluid to be measured Calculate the density of. The vibration frequency is not limited to this, and can be obtained by measuring the period or frequency of any signal.
[0031]
The above embodiment example was applied to produce a vibrating tube density sensor having a vibrating tube having an inner diameter of 2 mm and a U-shaped longitudinal dimension of 47 mm. The vibration tube oscillated in about 30 seconds due to natural noise in a normal environment. In an environment with extremely small noise, vibration could be excited by applying an excitation permission signal for about 10 seconds.
[0032]
In the vibration tube type density sensor of the above embodiment, in principle, it is not necessary to attach a member that affects the natural vibration frequency of the vibration tube 13, so that a highly accurate density measurement value can be obtained. In addition, since no phase circuit is used, a density measurement value can be obtained with high accuracy. Further, since it is not necessary to attach two members that require a separation distance from each other, the size can be easily reduced.
[0033]
In the above embodiment, the vibration tube 13 is formed of a conductor and an electric current is passed through the vibration tube itself. However, this current forms the vibration tube with an insulator and covers the vibration tube. It may flow through a conductive film or the like. Alternatively, it may flow through the fluid to be measured, or may flow through both the fluid and the vibrating tube.
[0034]
In the above embodiment, the vibration tube 13 is formed in a U-shape. However, it is not essential to form the vibration tube in a U-shape. A vibrating tube of the shape can be adopted.
[0035]
As another embodiment of the present invention, instead of the configuration in which current is passed through the vibrating tube in the previous embodiment, a thin film made of a magnetic material is formed on the predetermined portion of the vibrating tube by plating, and the thin film is opposed to the thin film. The coil is fixedly arranged at the position to be. The signal processing circuit adopts the same configuration as the previous embodiment. For example, when the vibrating tube moves upward, the coil is energized by the energizing means to bias the vibrating tube upward. That is, a suction force that generates positive feedback with respect to the vibration of the vibration tube is generated between the fixed coil and the thin film of the vibration tube. Compared with the conventional configuration in which two magnets are arranged in a predetermined portion of the vibration tube, it is possible to measure the density with high accuracy and to reduce the size of the vibration system.
[0036]
Although the present invention has been described based on the preferred embodiment thereof, the vibrating tube density sensor of the present invention is not limited to the configuration of the above embodiment example. Various modifications and changes are also included in the scope of the present invention.
[0037]
【The invention's effect】
As described above, the vibration tube type density sensor according to the first aspect of the present invention does not require the attachment of a member for excitation to the vibration system, so that vibration with high accuracy can be measured. There is a remarkable effect of providing a tubular density sensor.
[0038]
In the vibration tube type density sensor according to the second aspect of the present invention, the vibration detection means for detecting the vibration of the vibration tube can be installed away from the vibration tube, so that the vibration tube is provided with a member that requires a separation distance. There is no need for mounting, and the vibration system can be downsized.
[Brief description of the drawings]
FIG. 1 is a perspective view of a vibrating tube density sensor according to an embodiment of the present invention.
2 is a circuit block diagram of the vibrating tube density sensor of FIG. 1;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 11, 12: Support block 13: Vibrating tube 14, 15: Electrode 16: Current direction 17, 18: Permanent magnet 19: Insulating plate 20: Base 21: U-shaped bolt 22: Insulating washer 23: Light emitting diode 24: Phototransistor 30: Vibration detection unit 31: RC filter 32: Voltage follower 40: Timing signal generation unit 41: Comparator 42: OR gate 43: One-shot circuit 50: Drive unit 51: Choke coil 52: Electrolytic capacitor 53: Power transistor 60: Excitation Unit 61: Excitation pulse oscillator 62: AND gate 63: Excitation permission signal

Claims (2)

A vibrating tube that contains a fluid to be measured and is supported so that a predetermined portion can vibrate;
A vibration detection unit that detects a vibration waveform of the vibration tube, and a current at a predetermined timing of the vibration waveform detected by the vibration detection unit in one or both of the vibration tube and the fluid in the vibration tube. Energizing means that pass through,
Magnetic field applying means for applying a magnetic field perpendicular to the current to the predetermined portion ;
An excitation means for exciting the vibration of the vibration tube ,
The current and magnetic field, generates an electromagnetic force which is a positive feedback signal to the vibration of the vibrating tube,
The vibration detection means includes a set of a light source and a light receiving element in which a passing light flux amount is changed by vibration of the vibration tube,
The vibration tube density sensor , wherein the energizing means includes a timing detection unit that detects the predetermined timing from the vibration waveform, and a pulse generation unit that generates a current pulse in synchronization with the predetermined timing. . A vibrating tube that contains a fluid to be measured and is supported so that a predetermined portion can vibrate;
Vibration detecting means for detecting a vibration waveform of the vibration tube, and an excitation for applying an excitation force as a positive feedback signal to the vibration of the vibration tube at a predetermined timing of the vibration waveform detected by the vibration detection means. Means ,
A vibrating tube densitometer sensor comprising an excitation means for exciting a vibration of the vibrating tube,
The vibration detection means includes a set of a light source and a light receiving element in which a passing light flux amount is changed by vibration of the vibration tube ,
The excitation means includes a magnetic material disposed in a predetermined portion of the vibration tube, a coil fixed at a position facing the predetermined portion, and a predetermined timing of a vibration waveform detected by the vibration detection means. An energization means for passing current through the coil;
The vibration tube density sensor , wherein the energizing means includes a timing detection unit that detects the predetermined timing from the vibration waveform, and a pulse generation unit that generates a current pulse in synchronization with the predetermined timing. .

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