JP6285981B2 - Abnormality diagnosis method for liquid level gauge - Google Patents

Description

  The present invention relates to a liquid level gauge abnormality diagnosis method applied to a servo balance type liquid level gauge.

  A servo balance type liquid level gauge using a displacer is described in Patent Document 1, for example.

  The abnormality diagnosis function in industrial instruments is an important matter, and it is no exception in liquid level gauges. As an abnormality alarm means of a conventional liquid level gauge, an abnormality is determined and an alarm is issued when the measured liquid level or the torque value of the length measuring wire exceeds a specified value.

Japanese Utility Model Publication No. 64-34521

  In the servo balance type liquid level gauge, there is a problem that an accurate measurement value cannot be obtained because the responsiveness of the liquid level measurement is deteriorated due to deterioration of the motor due to deterioration over time or increase in friction of the friction drive system.

  Permanent magnets are generally used as the magnetic field of servo motors used in servo balance type liquid level gauges, but the same deterioration phenomenon occurs when the magnetic effect decreases with time. . In the liquid level gauge, the other main occurrence of deterioration is the mechanical drive system, which is caused by mechanical wear that occurs over time. This mechanical wear with time mainly occurs in the drum shaft and the bearing portion that holds the drum.

  FIG. 10 shows the relationship between the T-ω curve of the torque speed of the AC servo motor built in the level gauge and the load line. When a control voltage e1 is applied to the servo motor, the servo motor rotates at an angular speed ω1 at the intersection P1 of the load line T = K1ω (K1 proportional constant) corresponding to the load and the torque speed curve, and this rotational speed determines the response speed of the servo system. . When the friction on the load side increases due to changes over time, the load line changes to T = K2ω, the intersection with the T-ω curve decreases to P2, and the rotation speed decreases to ω2. In order to maintain the same speed as normal, it is necessary to increase the control voltage from e1 to e2.

  In general, a permanent magnet is used for the servo motor magnetic field. However, when the effect of the servo motor decreases with time, the T-ω curve is equivalently changed from e2 to e1 in FIG. It can be considered the same as having changed.

  For example, if such a deterioration phenomenon occurs in a servo motor and this deterioration phenomenon appears as an abnormality in the measured value, an alarm can be issued based on this deterioration, but the wear of the friction drive system has been reduced due to long-term use. Thus, it is impossible to predict the progress of the abnormality due to the time-dependent change of the parameter due to the deterioration of the above, or how the abnormality will progress in the future.

  An object of the present invention is to solve the above-described problems and provide an abnormality diagnosis method for a liquid level gauge that measures parameters caused by deterioration of components and diagnoses the progress of abnormality.

  In order to achieve the above object, a method for diagnosing abnormality of a liquid level gauge according to the present invention lowers the displacer of a servo balance type liquid level gauge and measures parameters of a mechanical drive system including a motor at every predetermined diagnostic cycle τ. Approximate the change over time in the numerical value of the parameter recorded for each predetermined diagnostic period τ up to the previous time with an approximate line, and the numerical value of the parameter obtained in the current diagnosis exceeds a predetermined degradation specified value In addition, the abnormal condition is diagnosed when the parameter obtained in the current measurement is on an extension line of the approximate line.

  In addition, the liquid level gauge abnormality diagnosis method according to the present invention lowers the displacer of the servo balance type liquid level gauge every predetermined diagnostic cycle τ, measures and records the parameters of the mechanical drive system including the motor, Approximating the change over time of the numerical values of the parameters recorded at the predetermined diagnosis cycle τ until the current diagnosis with an approximate line, and the time when the extended line of the approximate line reaches a predetermined deterioration regulation value It is characterized by making a diagnosis.

  Furthermore, the liquid level gauge abnormality diagnosis method according to the present invention lowers the servo balance type liquid level gauge displacer at every predetermined diagnostic cycle τ, measures and records the parameters of the mechanical drive system including the motor, Approximating the change over time of the numerical value of the parameter recorded at each predetermined diagnostic cycle τ until the current diagnosis with an approximate line, the approximate line has a tendency to deteriorate, and the numerical value of the parameter obtained this time is a predetermined value When approaching the specified deterioration value and exceeding a predetermined deterioration warning value, it is diagnosed that the interval of the subsequent predetermined diagnosis cycle should be shortened.

  According to the abnormality diagnosis method for a liquid level meter according to the present invention, numerical values of parameters in a predetermined diagnosis cycle are stored, and it is possible to predict an abnormality of a component part and at which point an abnormality occurs from the change over time.

It is explanatory drawing of the measurement state by a servo balance type liquid level meter. It is a block diagram of the detection part of a servo balance type liquid level gauge. It is an operation | movement flowchart figure at the time of a liquid level measurement. It is explanatory drawing of the control pattern at the time of lowering of a displacer. It is a flowchart figure of the abnormality diagnosis of Example 1. It is a graph of the relationship between a diagnosis time and the constant speed of a displacer. It is explanatory drawing in the case of estimating the future deterioration time. It is explanatory drawing in the case of shortening a diagnostic period. FIG. 10 is a flowchart of Example 4. It is explanatory drawing of deterioration of a servomotor.

  The present invention will be described in detail based on the embodiment shown in FIGS.

  As shown in FIG. 1, the servo balance type liquid level gauge is used for measuring the liquid level in the tank 1 having a depth of, for example, 30 m. A displacer 2 floating on the liquid surface is suspended in the tank 1 by a length measuring wire 3.

  Above the tank 1, a detection unit of a liquid level gauge as shown in FIG. A drum 5 is rotatably held by a drum shaft 4 supported by a base directly or by a magnetic coupling 6, and a driving force is transmitted to the drum 5 by the drum shaft 4. A measuring wire 3 is wound around the drum 5, and a displacer 2 fixed to the lower end of the measuring wire 3 is suspended in the tank 1.

  A servo motor 7 is fixed to the other side of the base, and the rotation of the rotation shaft of the servo motor 7 is transmitted to the worm gear 10 via the pulley 8 and the belt 9. The worm gear 10 meshes with the gear of the worm wheel 11 that rotates concentrically with the drum 5.

  The end portions of the coil springs 12a and 12b are fixed to the upper and lower portions sandwiching the center of the side surface of the worm wheel 11. The other ends of the coil springs 12a and 12b are respectively attached to arms 13a and 13b protruding from both sides of the balance arm 13 fixed to the drum shaft 4, and these coil springs 12a and 12b are connected to the left and right arms 13a and 13b, respectively. They are arranged almost perpendicular to each other. That is, the upper end of the coil spring 12a is fixed to the upper arm 13a protruding rightward, and the lower end of the coil spring 12b is fixed to the lower arm 13b of the left direction.

  A fixed arm 15 having a magnet 14 attached to the tip is fixed to the balance arm 13. A magnetic sensor 16 is attached to the surface of the worm wheel 11 in the vicinity of the magnet 14 to detect the rotational displacement of the balance arm 13, that is, the fluctuation of the tension of the length measuring wire 3, in response to the magnetic flux of the magnet 14. The detection output from the magnetic sensor 16 is input to an arithmetic control circuit 17 equipped with an MPU that supplies a drive signal to the servo motor 7.

  The calculation control circuit 17 is connected to the power supply and the output of the magnetic sensor 16, the output of the calculation control circuit 17 is connected to the servo motor 7, and a liquid level measurement signal is output from the calculation control circuit 17 to the display 18. Has been.

  When measuring the liquid level of the liquid in the tank 1, the buoyancy of the displacer 2 is detected as the tension T of the length measuring wire 3, and this tension T passes through the drum 5, the drum shaft 4, the balance arm 13, and the coil spring 12 a. , 12b, transmitted to the worm wheel 11.

  The rotational driving force of the servo motor 7 is transmitted to the worm wheel 11 through the worm gear 10, and further transmitted to the drum shaft 4 through the coil springs 12a and 12b and the balance arm 13, so that the drum 5 rotates and the length measuring wire is transmitted. 3 is taken up and fed out.

  By detecting the number of rotations of the drum 5, the feed amount and the winding amount of the length measuring wire 3 are detected by a rotation sensor (not shown) as the rotation of the drum 5, and the liquid level according to the position of the displacer 2 is measured.

Considering the balance at the time of measuring the liquid level, the following two equations are established.
T + (V / 2) · ρ = W (1)
T ・ R = 2 ・ x ・ k ・ r (2)

  Where T: tension of the measuring wire 3 at the time of liquid level measurement, V: volume of the displacer 2, ρ: specific gravity of the liquid, R: radius of the drum 5, k: spring constant of the coil springs 12a and 12b, r : Mounting radius of the coil springs 12a and 12b, x: Elongation of the coil springs 12a and 12b at the time of measuring the liquid level, W: Weight of the displacer 2

  From the elongations x of the coil springs 12a and 12b obtained from the equations (1) and (2), the balance stop position (balance midpoint) of the balance arm 13 during the liquid level measurement is determined. The measured value for the detection output of the magnetic sensor 16 at this time is stored in the arithmetic control circuit 17 as the set value of the tension T of the length measuring wire 3 at the balance stop position.

  For example, when the maintenance and inspection work is completed and the measurement of the liquid level is resumed, the measurement is started by lowering the displacer 2 that has been raised to the liquid level and balancing it. For example, when the liquid level rises during measurement, the buoyancy of the displacer 2 increases and the tension T of the length measuring wire 3 decreases, so that the elongation x of the coil springs 12a and 12b decreases. As a result, the balance arm 13 rotates, the relative position of the magnet 14 and the magnetic sensor 16 changes, and the increased amount of change is output from the magnetic sensor 16 to the arithmetic control circuit 17.

  The arithmetic control circuit 17 that receives the output of the magnetic sensor 16 compares the output of the magnetic sensor 16 with a set value, and the servo motor 7 moves in the winding direction of the measuring wire 3 until the comparison value becomes zero. A signal is supplied to the servo motor 7 so as to rotate. As a result, the worm wheel 11 rotates via the worm gear 10, and the relative position between the magnetic sensor 16 of the worm wheel 11 and the magnet 14 attached to the balance arm 13 returns to the state before the change, that is, the balance stop position. . At this time, the drum 5 is rotated by the drum shaft 4 and the length measuring wire 3 is wound, and the measured value of the liquid level is determined from the winding length of the length measuring wire 3, that is, the pulse integrated value corresponding to the rotational speed of the drum 5. Is required.

  Further, when the liquid level is lowered, the buoyancy of the displacer 2 is reduced and the tension T is increased, the coil springs 12a and 12b are extended, and the relative position of the magnet 14 and the magnetic sensor 16 is changed in the direction in which the output of the magnetic sensor 16 is reduced. To do. As a result, the servo motor 7 reverses to the balance stop position by the reverse operation described above, so that the drum 5 rotates in the feeding direction of the length measuring wire 3. And the measured value of a liquid level is calculated | required from the pulse integration value corresponding to the rotation speed of the drum 5 at this time.

  FIG. 3 is a flowchart of the control operation by the program of the arithmetic control circuit 17 when the rebalance control is performed by lowering the displacer 2 that has been raised in the servo balance type liquid level gauge.

  FIG. 4 is an explanatory diagram of a control pattern when the displacer 2 is lowered. The horizontal axis represents the integrated value Σn of pulses n transmitted from the arithmetic control circuit 17 to the servo motor 7, and the vertical axis represents the lowering speed of the displacer 2.

  The displacer 2 starts to descend from above, and a feed pulse (n) is transmitted from the arithmetic control circuit 17 to the servo motor 7. Accordingly, the servo motor 7 and the drum 5 rotate and the measuring wire 3 is wound down, so that the displacer 2 accelerates at the initial speed V (step S1), and the integrated value Σn from the start of the pulse n becomes N1. (Step S2).

  When the integrated value Σn of the pulse n reaches N1, the displacer 2 descends at a constant speed V2 (step S3), and descends as it is until the integrated pulse value reaches N2 (step S4).

  When the integrated value Σn of the pulse n reaches N2, the displacer 2 descends while decelerating at a constant acceleration (step S5). When the integrated value Σn of the pulse n reaches N3 (step S6), the lowering of the displacer 2 is stopped (step S7). Thereafter, balance control is performed so that the deviation of the force balance becomes zero, and the liquid level measurement is stabilized (step S8).

  The set number of pulses in the set state is N4, the conversion coefficient is k, and k · N4 is the output of the level gauge.

  In the abnormality diagnosis according to the present embodiment, the liquid level measurement is interrupted, and the descending speed of the displacer 2 is measured while the raised displacer 2 is lowered as the numerical value of the deterioration diagnosis parameter at every predetermined diagnosis period τ. carry out. The predetermined diagnostic cycle τ is selected as the minimum unit of the proof test interval defined by the maintenance cycle of the level gauge and the functional safety (commonly known as SIL), for example, based on the elapsed time of a half year, one year, or several years cycle. Perform in conjunction with maintenance inspection.

  The abnormality diagnosis is performed in the process of lowering the displacer 2 at the constant speed V2 (between N1 and N2 in FIG. 4) in step S3 in FIG. That is, the displacer 2 measures the constant speed V2 that is descending at the speed at which the integrated value Σn of the pulse n reaches N1, and determines abnormality based on the change in the constant speed V2.

  When the output decreases due to aging deterioration of the motor or the like, the acceleration from the initial speed V1 decreases, and the constant speed V2 at which the pulse integration number reaches N1 to N2 also decreases. If the constant speed V2 is smaller than a predetermined specified value, it means that an abnormality due to deterioration has occurred in the mechanical drive system including the servo motor 7.

  FIG. 5 is a flowchart of this abnormality diagnosis. The constant speed V2 of the displacer 2 is measured based on the number of accumulated pulses per time by means similar to step S3 in the normal liquid level measurement of FIG. 4 (step S11).

  The obtained constant speed V2 is recorded together with the measurement date in a ROM storage medium provided in the liquid level gauge (step S12). In FIG. 6, the horizontal axis represents the elapsed time, and the vertical axis represents the magnitude of the constant speed V2 of the liquid level meter at the past diagnosis time τ, and is a graph of the history of the constant speed V2, that is, the change with time. In addition, (circle) mark and x mark have each shown constant velocity V2 of two liquid level gauges.

In the current diagnosis, the obtained constant speed V2 is compared with the specified degradation value Δv (step S13). This specified degradation value Δv is a threshold value that, based on past experience and the like, when the constant speed V2 is further reduced, a problem occurs in measurement accuracy and responsiveness.
If the constant speed V2 exceeds the specified degradation value Δv and becomes a low speed in the current diagnostic cycle 5τ, degradation may have occurred. If V2> Δv, it can be determined that there is no deterioration to the point of replacement or repair (step S14).

  If there is a possibility that the diagnosis period 5τ has deteriorated as indicated by a circle or a cross, the change over time of the constant speed V2 in the previous diagnosis period τ is approximated by an approximate line consisting of a straight line or a curve. (Step S15). Then, it is confirmed whether the constant velocity V2 obtained this time is on an extension line of the approximate line (step S16).

  As shown in FIG. 6, the constant speed V2 of the liquid level gauge marked with ◯ is mechanically driven because the constant speed V2 in the diagnosis period 5τ is smaller than the specified degradation value Δv and is on the extension of the approximate line marked with ◯. It is determined that an abnormality due to deterioration has occurred in the system (step S17).

  If it is determined in step S17 that deterioration has occurred, it can be determined that at least a part of the component parts should be replaced and repaired, assuming that the mechanical drive system including the servo motor 7 has deteriorated. Accordingly, it is possible to further inspect which parts have deteriorated and to provide unnecessary alarm information when performing necessary part replacement, repair, or the like.

  On the other hand, even if the constant speed V2 is smaller than the degradation specified value Δv in the diagnosis cycle 5τ as indicated by a cross mark shown in FIG. 6, it does not lie on the extension line of the cross mark indicated by the dotted line. If there is almost no deterioration tendency due to the change, the constant speed V2 obtained this time may be a measurement error. Therefore, it is preferable that the liquid level gauge at the constant speed V2 indicated by X is not immediately diagnosed as being deteriorated, but is diagnosed as being suspected of being deteriorated, and a diagnostic test of the constant speed V2 is performed again for confirmation ( Step S18).

  If it is determined by this re-diagnosis that the deterioration is certain, it is determined that the deterioration has progressed rapidly, the deteriorated part is identified, and the part is repaired or replaced.

  Further, in the measurement at the current diagnosis cycle 5τ, even when the specified degradation value Δv is not exceeded, there is a case where a tendency of deterioration is recognized by the approximate line due to the change over time as shown in FIG. In this case, it is possible to estimate the deterioration time between the diagnostic cycles 5τ and 6τ that are considered to be in an abnormal state exceeding the specified deterioration value Δv by the approximate line. Therefore, it is desirable to replace and repair the component parts between the diagnostic periods 5τ and 6τ by displaying the estimated deterioration time.

  In the first and second embodiments described above, the case where the diagnosis is performed at the equal period τ has been described. However, when the constant speed V2 approaches the deterioration regulation value Δv, the deterioration will be noticeable soon, and the subsequent diagnosis period It is preferable to shorten τ.

  For example, in FIG. 8, the constant speed V2 does not exceed the specified deterioration value Δv in the period 5τ, but if the deterioration warning value a of a speed that is much larger than the specified deterioration value Δv is exceeded, the specified deterioration value Δv is soon reached. Therefore, in order to accurately grasp the deterioration, after the period 5τ, the conventional diagnosis period is shortened to, for example, 1/2, and diagnosis is performed at the diagnosis periods 5.5τ, 6τ, and 6.5τ. .

  In the diagnosis in the above-described first to third embodiments, just because the constant speed V2 exceeds the specified degradation value Δv, it does not immediately issue an alarm, but when there is an inquiry, it responds whether there is an abnormality. You may do it.

  FIG. 9 is a flowchart in the case of confirming the result of deterioration diagnosis at an arbitrary time.

  When there is an inquiry request signal regarding deterioration, data of the constant speed V2 obtained in step 12 of the flowchart of FIG. 5 is collected (step S21).

  Next, it is confirmed whether there is data of V2−Δv> 0 among the data of the constant speed V2 (step S22). If not, it is determined that there is no deterioration (step S23). The collected changes over time of the constant speed V2 are approximated to an approximate line (step S24). Then, it is confirmed whether the latest constant speed V2 is on an extension line of the approximate line (step S25).

  If the latest constant speed V2 is on the approximate line, it is diagnosed that there is deterioration (step S26). Even if the most recent constant speed V2 is not on the approximate line, since the most recent constant speed V2 is V2> Δv, it is diagnosed in step S27 that there is a suspicion of deterioration, and necessary measures are taken.

  In the first to third embodiments, the descending constant speed V2 of the displacer 2 is used as a parameter used as a diagnostic index. However, a voltage deviation voltage to be applied to the servomotor 7 for obtaining a predetermined speed, or application A diagnosis may be made by measuring this parameter using the control current corresponding to the voltage to be measured as a parameter.

  As the servo motor 7, a pulse motor can also be applied. In this case, the number of coggings unique to the pulse motor and the step-out can be avoided, and the frequency of the number of times of pressing back to the equilibrium position by the output of the encoder for each predetermined diagnostic cycle τ can be used as a parameter.

2 Displacer 3 Measuring wire 5 Drum 7 Servo motor

Claims (6)

  At every predetermined diagnostic cycle τ, the servo balance type liquid level gauge displacer is lowered, and the parameters of the mechanical drive system including the motor are measured and recorded, and the parameters recorded at the predetermined diagnostic cycle τ until the previous time are recorded. The numerical change over time is approximated by an approximate line, and the numerical value of the parameter obtained in the current diagnosis is within an abnormal range exceeding a predetermined deterioration regulation value, and the parameter obtained in the current measurement is the approximate line. An abnormality diagnosis method for a liquid level gauge, characterized by diagnosing an abnormal condition when it is on an extension line of   At every predetermined diagnosis period τ, the displacer of the servo balance type liquid level gauge is lowered, the parameters of the mechanical drive system including the motor are measured and recorded, and the previous diagnosis until the current diagnosis recorded at each predetermined diagnosis period τ An abnormality diagnosis method for a liquid level gauge, characterized by approximating a change in parameter values over time with an approximate line, and diagnosing a time when an extended line of the approximate line reaches a predetermined degradation specified value as a time when an abnormal state is reached.   At every predetermined diagnosis period τ, the displacer of the servo balance type liquid level gauge is lowered, the parameters of the mechanical drive system including the motor are measured and recorded, and the previous diagnosis until the current diagnosis recorded at each predetermined diagnosis period τ Approximate changes in parameter values over time with an approximate line, the approximate line has a tendency to deteriorate, and the numerical value of the parameter obtained this time approaches a predetermined deterioration regulation value and exceeds a predetermined deterioration warning value In this case, an abnormality diagnosis method for a liquid level gauge, characterized in that a diagnosis is made that the interval of the predetermined diagnosis period thereafter should be shortened.   The abnormality diagnosis method for a liquid level gauge according to any one of claims 1 to 3, wherein the diagnosis state is responded by a request signal from the outside.   The liquid level gauge abnormality diagnosis method according to any one of claims 1 to 3, wherein the parameter is a descending speed of the displacer.   The abnormality diagnosis method for a liquid level gauge according to any one of claims 1 to 3, wherein the predetermined diagnosis cycle τ is a proof test interval determined by a minimum maintenance cycle or functional safety.

Images