DE3600306A1 - METHOD AND DEVICE FOR GENERATING ANGLE SPEED SIGNALS BY MAGNETIC RECORDING AND PLAYBACK - Google Patents

Description

Method and device for generating angular velocity signals by magnetic recording and

Reproduction.

The invention relates to the field of tachometry and, more particularly, to a method and an apparatus for recording discrete areas of magnetism a revolving body to generate a repetitive signal in a reproducing mode that represents the Indicating angular velocity of the body.

The knowledge of the rotational speed or angular speed of a rotating element is often important the application, investigation and diagnosis of work machines. Speedometers have been developed that use

based on different working principles, do the required angular velocity to be obtained. For example One known method is to paint axial stripes on a rotating shaft and an optical one Use pickup> to make a change in the to scan reflected light as the strips pass the transducer as the shaft rotates. at Another method is to attach a toothed wheel or similar object with tooth-like projections to a rotatable » Shaft attached, and a magnetic pickup scans the passing teeth, which are counted, to determine the mean wave speed.

There are countless other tachometric methods and devices have been developed, all of which indicate the widespread requirement that a fairly fundamental one Measurement to get.

Although there are innumerable tachometric methods available, they may be perfectly satisfactory under certain circumstances work, inextricably linked requirements preclude their use in other circumstances. For example the methods described above require some additional physical installation Element to a rotatable body. Even in those cases where such an installation is physically is possible, the effort required can be disadvantageous. An optical process also has the further disadvantage that the light path between the indicator (e.g. strip) and the detector is clear and free of obstacles have to be. This is not always possible, especially if a darkening of the light may occur due to from oil or other liquid mist or because of a possible build-up of dirt or soot on the Indicator and / or detector.

An area where tachometric signals are of particular importance and where common means prove to be unsatisfactory have proven is the monitoring of torsional vibrations that occur in large rotors can, for example, for rotors and shafts in turbine generator sets, that are used to generate electrical energy. Signals with a repetition rate proportional the speed of rotation of the rotor, serve as an important input variable for vibration monitors. , as described, for example, in U.S. Patents 3,885 and 4,148,222. If not timely Correction against unwanted torsional vibrations can be permanent damage to the rotor and / or other elements of the turbine generator set occur. For maximum operational safety of monitoring instruments a very reliable rotor speed display is required for torsional vibrations, the very small changes in the instantaneous angular velocity of the rotor can specify.

It is therefore an object of the invention, a method and a device for generating an electrical signal to provide, its frequency or repetition rate, an indication of the instantaneous angular velocity a circumferential body is without a special attachment or an additional marking on the circumferential body is required.

According to the invention, tachometric signals are generated by that several discrete magnetic areas in the surface of a rotating body along a circumferential path are caused in a plane which is essentially perpendicular to the axis of rotation of the rotating body thereby creating separate or discrete areas of permanent magnetism which are scanned can when the body rotates to the desired one

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To provide a response signal that is a measure of the instantaneous angular velocity of the body. In one Preferred embodiment forms a single probe that is placed in the vicinity of a rotating shaft and is connected to an induction excitation source, in a first mode of operation a device to magnetic Areas to induce, and in a second mode of operation of a device to move the magnetic areas to feel. A time-varying signal whose frequency is controlled to be a multiple of the Shaft rotation speed or angular speed can be used to power the induction excitation source synchronize such that the induced magnetic regions are uniformly and continuously spaced are around the rotatable shaft, and the number of areas that are induced along the entire circumferential path is independent of the speed of rotation of the shaft. Embodiments of the invention are particularly suitable for generating signals which are a measure of the angular velocity of the rotor and which also have a Enable measurement of torsional vibrations in rotors of large turbine generator sets.

The invention now comes with further features and advantages explained in more detail with reference to the description and drawing of exemplary embodiments.

Figure 1 - shows a preferred circuit arrangement for generating a signal that is a measure of the Shaft rotation speed according to the invention.

Figure 2 - illustrates a preferred embodiment of a record / playback probe suitable for a Use with the circuit arrangement according to Figure 1 is suitable.

Figure 3 is a side view of the recording / reproducing probe according to Figure 2, which can be arranged so that it the speed of a rotating Monitored shaft and / or induced magnetic areas on the rotating shaft.

ff Figure 1 shows schematically a circuit arrangement and a device for generating a signal with a repetition rate or frequency, which is a display or a measure for the instantaneous angular velocity or rotational speed of a rotating shaft 10. A recording / playback probe 12 is arranged very close to the shaft 10 and can operate in selectable modes - a first mode for recording, wherein a magnetic flux generated by the probe or the measuring head 12 is small, localized, permanent- magnetic circumferential areas induced in the surface of the shaft 10,

mode
and a second 'for feeling or reproducing, wherein a movement of previously induced magnetic areas is scanned and an electrical signal responsive to the movement is generated. Shaft 10 may be a large shaft or a rotor of the type found in electric turbine generator sets of power companies. The recording / reproducing probe 12 may be an electromagnetic device such as will be further explained below.

A switch 13 can be operated to either the to select the first or second operating mode of the probe 12, which is activated by the switch positions R (record or record) and P (playback). In the recording mode, a common port is C of the switch 13 to a terminal R of the switch 13 connected so that the probe 12 can be supplied with an excitation signal, so that a sufficiently intense electrical Signal to induce magnetic areas

fed to the probe 12 on the surface of the shaft 10 will. In the preferred embodiment shown in Figure 1, the magnetic regions induced while the shaft 10 rotates. A synchronization device 14 can be a shaft rotation sensor or have a variable reluctance pickup for sensing physical nonuniformity, such as for example a projection or a recess in the shaft 10. The synchronization device 14 generates a synchronization or shaft rotation signal indicative of a full revolution of the shaft 10 and over an amplifier 16 of an induction excitation source 15 is fed to a limiter 17, a phase-locked loop 18, a time base generator 20, an active Filter 25 with a suitable bandpass filter for signal frequencies which are determined by the frequency divider 20, and has an amplifier 26. It is also possible to work without the active filter 25, whereby the values of the Divisors of the frequency divider 20 can be changed without affecting the frequency properties of the active filter 25 need to be changed. The synchronization signal, which is available at the input of the limiter 17, causes that the induction excitation source 15 the excitation signal, supplied by the probe 12 is synchronized with the angular velocity of the shaft 10, whereby uniformly spaced areas of magnetization are generated on the surface of the shaft 10 and ensured becomes that the number of induced magnetic areas on the entire circumferential orbit on the surface of the shaft 10 is independent of the angular velocity of the shaft 10. This means that the excitation source 15 does not run freely at a constant frequency, but that it is an output or an excitation signal generated at a frequency that is a predetermined multiple of the angular frequency of the shaft 10 to ensure that the magnetic circumferential pattern that

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to be induced around the shaft 10, is induced coincidentally with each revolution of the shaft 10.

The synchronization signal applied to the input of amplifier 16 can be in any suitable manner to be developed. In a turbine generator set of a power company, it is best from the generated signal the electrical power with a nominal or network frequency obtained, which is 60 Hz in the United States of America, for example.

It should be noted, however, that the exact frequency of the synchronization signal is not critical, it should only be proportional to the angular velocity of the shaft. The synchronization signal is generated in the amplifier 16 amplified, and the output signal of the amplifier 16 is fed to the limiter circuit 17, which the amplitude of the synchronization signal limited, so that a signal with a substantially constant amplitude and the same Frequency as the synchronization signal at the output of the limiter 17 is available. The output size of the limiter 17 is fed to a first input of a phase-locked loop 18. The phase-locked loop 18 and the time base generator 20 cooperate to form a frequency synthesis circuit for generating an output signal from phase locked loop 18 at a frequency that is an integral multiple of Signal that is applied to the first input of the phase-locked loop 18.

The operation of the phase locked loop 18, a known circuit arrangement, is designed so that the Frequency of the signal that is present at the output of the time base generator 20 and is fed to a second or feedback input of the phase-locked loop 18, is controlled so that the frequency of the second input

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output of the phase-locked loop 18 is precisely the same as the frequency of the signal that is fed to the first input of the phase-locked loop 18. The time base generator 20 has a frequency divider or counter whose signal output frequency is a preselected submultiple of the input frequency of the signal which is fed to the time base generator 20 from the output of the phase locked loop 18. Since the frequency of the Signal at the second input of the phase-locked loop 18 is conditioned so that it precisely equals the Frequnez of the signal at the first input of the phase-locked loop 18 is therefore the output signal of the phase-locked loop Loop 18 necessarily a multiple of the frequency of the signal at the first input of the phase-locked loop 18, the multiple being precisely equal to the divisor of the time base generator 20. For example, the time base generator 20 be constructed in such a way that the frequency of its input signal is divided by a factor of 60 will. The phase-locked loop 18, which has the function, the frequency of the signal delivered at the second input for example to keep one cycle per revolution so that it is equal to an assumed signal frequency of one cycle per revolution at the first input of the phase-locked loop 18, a signal must then have a Supply frequency of 60 cycles / revolution at the output of the phase-locked loop 18.

The active filter 25, the input of which is connected to the output of the phase-locked loop 18, has a narrow one Bandpass filter and a smoothing filter, the bandpass filter of which is centered around the desired excitation frequency. The smoothing effect of the filter 25 is designed so that the output signal of the phase-locked loop 18, which is substantially Can have the construction of a square wave, gets a sine wave quality before going to a power amplifier 26 is fed. The output signal from the line

power amplifier 26 is via a series resonance capacitor 27 and a switch 13 of the probe 12 is supplied. The capacitor 27 provides in connection with the inductance the probe 12 also for filtering so that the active filter 25 can be omitted if so desired is.

The probe or the sensor 12, which is shown in FIGS 3 is shown in more detail, contains a laminated iron core 51 with a narrow transverse gap 52 through one End and with two coils 53 and 54, which are wound around opposite legs of the core 51. The slot

52 is preferably long enough in the axial direction to accommodate axial movement of the shaft 10, for example due to thermal expansion or bearing wear, adequate magnetic flux communication can occur to maintain between the probe 12 and the magnetic areas that are on the surface of the shaft 10 are induced. A toroidal ferrite core can also be used for the core 51. The coils 53 and 54 For example, about 550 turns of wire with the US standard AWG No. 26 have. The spools

53 and 54 are preferably connected in parallel during the recording mode and in series during the playback operation; the desired connection configuration can be made selectable with a switch. In FIG. 1, the probe 12 is shown with only a single coil in order to explain the preferred circuit arrangement and to facilitate understanding.

In operation, the probe 12 becomes very close to the shaft 10 fixedly arranged so that the slot 52 is substantially parallel to the axis of rotation of the shaft 10, as shown in FIG Figure 3 is shown. The magnetic flux generated in the laminated core 51 by excitation current from the capacitor 27 (Figure 1) through the coils 53 and 54 of the probe

is generated is essentially enclosed in the core 51, except above slot 52. When energizing current is supplied to coils 53 and 54 of probe 12, Magnetic flux traverses the slot or gap 52 so that some of the flux from the gap 52 bounding it Exits edges of the core 51 and enters the rotating shaft 10, creating localized areas of magnetism be induced into the surface of the shaft 10. The magnetic pattern induced in this way agrees with the time-varying one Shape of the excitation current that the coils 53 and 54 from the amplifier 26 through the capacitor 27 "is supplied so that, with a sinusoidal excitation current, the magnetic pattern around the circumference of the shaft 10 has a substantially sinusoidal waveform. A sine wave is preferred as the excitation signal in order to generate inductive effects, such as ringing, with signals to avoid having a faster rate of change to have. The positioning of the probe 12 to induce magnetic areas on the surface of the shaft 10, ensures that the probe 12 is in magnetic flux communication with the induced magnetic areas during the playback mode.

The value of the capacitor 27 shown in Figure 1 is selected so that when the switch 13 is in the receiving position R is, the probe 12 and the capacitor 27 form a tuned series resonant circuit based on the frequency of the excitation signal oscillates in resonance. As is characteristic of tuned series resonant circuits, lift the reactance of the probe 12 (mainly inductive) and the capacitor 27, with the result that the current, that flows through the probe 12 during the acquisition is a lot is greater than it is generally achievable without a tuned series resonant circuit, whereby the magnetic Recording is improved. The value of the capacitor is chosen so that in the playback position P the switching

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ter 13 connects the probe 12 in parallel with the capacitor 28 in order to form a tuned parallel resonant circuit, which resonates at the frequency of the excitation signal which is used to record the magnetic areas in the surface of the shaft 10. In those Cases where the shaft of a turbine generator is monitored, the resonance frequency can for example 3600 Hz. The tuned parallel resonant circuit delivers a much larger amplitude in the playback mode of the induced signal than an untuned circuit would, at and near the resonance frequency. This in The signal induced in the parallel resonant circuit is fed to the input of an amplifier 30. The playback signal, in which a frequency is encoded proportional to the instantaneous speed of the shaft 10 is given by the Amplifier 30 amplified, and the amplified signal that is present at the output of amplifier 30, for example can be used as the input variable to a torsional vibration monitoring instrument, for example for electric turbine generators from energy supply companies. Of course it is not necessary that the circuits having the capacitor 27 and the capacitor 28 exactly to their corresponding predetermined ones Resonance frequencies are matched. It should be noted, however, that for circuits that do not have the appropriate predetermined resonance frequency are tuned, the voltages and the current are smaller than they in one Resonant circuit are achievable, and it may be possible that values for the capacitor 27 and the capacitor 28 are provided that the corresponding circles are so badly detuned that the voltages and currents in the corresponding Circuits are insufficient to produce the desired effects according to the present invention.

For monitoring the current angular speed of shaft 10 is the mode of operation of the circuit arrangement

according to Figure 1 as follows. The switch 13 is initially brought into the position R for the recording mode in order to avoid magnetization of small, circumferentially arranged, localized areas on the surface of the shaft 10 through the probe 12 to enable acting as a Electromagnet works to induce a magnetic pattern in an excitation signal current, which is preferably is sinusoidal and is supplied from the amplifier 26 via the capacitor 27. The induced magnetic areas are preferably arranged along a circumferential path in a shaft section that is substantially is perpendicular to the axis of rotation. The inductance of the probe 12 forms together with the predetermined capacitance of the capacitor 27 is preferably a series resonant circuit which is tuned to the desired frequency of the excitation signal is. The excitation signal supplied to the probe 12 becomes with the rotation of the shaft 10 by the synchronization signal synchronized, for example one signal per revolution, as described above, which is supplied by the shaft rotation sensor 14. the Frequency of the synchronization signal is multiplied by the phase-locked loop 18 and the time base generator 20, and a signal with a frequency that is an integral multiple of the synchronization signal, is fed to the power amplifier 26 via the active filter 25. The permanence of the magnetic pattern that recorded on the shaft 10 depends on the permeability of the material of the shaft 10 and on the physical Treatment of the shaft 10, for example exposure to stray magnetic fields. For usual However, shafts that have magnetic material such as iron, especially when these shafts are in ainer Operating environment, the pattern is relatively permanent, so that when the magnetized Areas once induced on the surface of the shaft 10, the switch 13 is brought to the playback position P.

can be used to monitor the rotational speed or the playback signal induced in the probe 12 by the magnetized areas as the shaft 10 rotates. The playback signal is developed in a parallel resonant circuit which contains the predetermined capacitance of the capacitor 28 and the inductance of the probe 12 / and the parallel resonant circuit preferably vibrates at the frequency of the excitation signal used to induce the magnetic regions on the surface of the shaft 10. A frequency is encoded in the playback signal which is proportional to the instantaneous angular velocity of the shaft 10, so that very small changes in the shaft velocity can be determined, e
announce.

on the order of 2x10 radians per se-

Compared to the preferred embodiment described above however, other exemplary embodiments are also possible. For example, there was an electromagnetic Probe 12 described with two modes of operation for recording and playback, but two separate modes can also be used Probes 12 and 40 can be used, with probe 12 is used for recording and the probe 40 is used for playback, as shown in the circuit arrangement according to FIG is. In this case, the switch 13 permanently selects the R position, or the probe 12 is directly connected to the capacitor 27 connected without a switch 13. This arrangement allows continuous recording and continuous Playback when shaft 10 rotates. The probe 40, which is fixedly arranged with respect to the shaft 10 and is displaced in the circumferential direction relative to the probe 12, is in magnetic flux communication with the magnetic pattern induced by the probe 12 on the surface of the shaft 10.

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A capacitor 44 and the probe 4O form a parallel resonant circuit, and the value of the capacitance of the capacitor 44 is chosen so that the parallel resonant circuit is preferred resonates at the predetermined frequency of the excitation signal. The playback signal present at the output the parallel resonant circuit, which consists of the probe 40 and the capacitor 44, becomes an amplifier 42, the output of which is used as the input to a torsional vibration monitoring instrument can be used, for example, for electric turbine generators from utility companies, such as it has been described above.

Furthermore, it is not necessary that the shaft 10 have magnetic regions that are induced during it is located in its desired operating environment. The magnetic areas can be on the surface of the shaft 10 may be induced at some point away from their final place of use, in part due to permanence of the induced magnetic areas, and the reproducing circuit as described here can be used for this are to scan the previously induced magnetic areas at the final place of use of the shaft 10. the Knowing the frequency of the excitation signal used to induce the magnetic areas allows the value of the capacitor 28 or 44 is chosen to form a parallel resonant circuit.

Thus, a method and a device have been described for generating an electrical signal, its frequency or repetition rate is a measure of the instantaneous angular velocity of a rotating body, without the need for a special fastening or additional markings on the rotating body.

Claims (19)

Claims 1. Speed measuring instrument for measuring angular speed a rotatable shaft characterized by: an electromagnetic probe (12) related to on the shaft (10) is arranged in a fixed position near the shaft surface and the in a first mode of operation for inducing a magnetic circumferential pattern on the shaft surface and can operate in a second mode of operation to generate an output signal upon movement of the magnetic pattern as the wave rotates, the output signal being a frequency has, which is a measure of the instantaneous angular velocity of the shaft, a switching device connected to the probe (12) (13) to switch between the first and second operating modes and an excitation device (15), the output of which in the first operating mode via the switching device (13) is connected to the probe (12) and the one Provides excitation signal which is supplied to the probe (12) during the first mode of operation, the thereby induces the magnetic pattern, the excitation device (15) synchronizing comprises means for synchronizing the frequency of the excitation signal with the speed of rotation of the shaft in such a way that the magnetic pattern is independent of the rotational speed of the shaft is. 2. Measuring instrument according to claim 1, characterized in that a first capacitor (27) between the Output of the excitation device (15) and the switching device (13) is connected to the formation ^{w of} a series resonant circuit with the probe in the first mode, and a second * capacitor (28) connected to the probe to form a parallel resonant circuit with the probe in the second operating mode. 3. Measuring instrument according to claim 2, characterized in that that the series resonant circuit and the parallel resonant circuit each at the frequency of the excitation signal vibrate in resonance. 4. Speed meter for measuring angular speed a rotating shaft, characterized by: a first electromagnetic probe (12) which is in a fixed position with respect to the shaft (10) is arranged close to the shaft surface and the one extending in the circumferential direction magnetic Pattern induced on the wave surface, a second electromagnetic probe (40) which is in a fixed position with respect to the shaft (10) and disposed in magnetic flux communication with the magnetic pattern and having an output signal upon movement of the magnetic pattern generated when the wave rotates, the output signal having a frequency that is a measure of is the instantaneous angular velocity of the shaft, and an excitation device (15) connected to the first probe (12) for generating an excitation signal is connected, whereby the first probe (12) induces the magnetic pattern, and the excitation device has synchronization means for Synchronizing the frequency of the excitation signal with the speed of rotation of the shaft such that the magnetic pattern is independent of the speed of rotation of the shaft. 5. Measuring instrument according to claim 4, characterized in that a first capacitor (28) between the first Probe (12) and the excitation device (15) ge λ is switched to form a series resonant circuit with the first probe, and that a second capacitor (44) is connected to the second probe (40) to form a parallel resonant circuit with the second probe. 6. Measuring instrument according to one of claims 1 to 5, characterized in that that the excitation device (15) has a phase-locked loop (18) for generating the excitation signal, and in that the synchronizing means comprises a shaft rotation sensor (14) for delivery a synchronization signal to the phase locked loop (18). 7. Measuring instrument according to claim 5, characterized in that the series resonant circuit and the parallel resonant • * · * ■■ * circle oscillate in resonance at the frequency of the excitation signal. 8. Device for measuring the angular velocity of a rotating shaft of a turbine generator set, characterized by: an electromagnetic probe that is in a fixed Position is arranged with respect to the shaft surface and in a first mode of operation induces a circumferential magnetic pattern on the shaft surface and in a second operating mode, an output signal is generated upon movement of the magnetic Pattern when the wave rotates, the output signal having a frequency that is a measure of is the instantaneous angular velocity of the shaft, a switching device connected to the probe (12) to selectively switch between the first and second operating modes, an excitation device, the output of which in the first operating mode via the switching device is connected to the probe and which supplies an excitation signal to the probe during the first operating mode, whereby the probe induces the magnetic pattern, a first capacitor (27) connected between the output of the excitation device and the switching device is switched to form a series resonant circuit with the probe in the first operating mode, and a second capacitor (28) connected to the switching device and in the second mode of operation forms a parallel resonant circuit with the probe. 3800306 9. Device according to claim 8,
characterized in that the series resonant circuit and the parallel resonant circuit each vibrate in resonance with the frequency of the excitation signal. 10. Device according to claim 8,
characterized in that the excitation means comprises a phase locked loop for generating the excitation signal upon a synchronization signal supplied to the phase locked loop by a shaft rotation sensor. 11. Device for measuring the angular velocity a rotating shaft of a turbine generator set, characterized by: a first electromagnetic probe (12) inserted in a fixed position near the shaft surface for inducing a circumferential direction running magnetic pattern on the shaft surface, a second electromagnetic probe (40) disposed in magnetic flux communication with the magnetic pattern is, an excitation device, the output of which is connected to the first probe, for supplying an excitation signal to the first probe, whereby the first probe induces the magnetic pattern, a first capacitor (28) connected between the Output of the excitation device and the first probe is connected to form a series Resonant circuit with the first probe, and a second capacitor (44) connected to the second Probe is connected to form a parallel Resonant circuit with the probe. 12. Device according to claim 11, characterized in that that the series resonant circuit and the parallel resonant circuit each at the frequency of the excitation signal vibrate in resonance. 13. Device according to claim 11, characterized in that the excitation device is phase-locked Loop for generating the excitation signal in the case of a synchronization signal which the phase locked loop is fed through a shaft rotation sensor. 14. Method for generating a repetitive signal whose repetition speed is proportional to the instantaneous angular velocity of a rotatable shaft, characterized in that that along a predetermined number of discrete magnetic areas in the surface of the shaft a circumferential path are induced and the movement of the magnetic areas on a stationary device is scanned for sensing magnetic fields while the The shaft rotates to produce the repetitive signal, with the sensing device in magnetic flux communication is arranged with the magnetic areas. 15. The method according to claim 14,
characterized in that the magnetic areas are induced, - 7 ""
while the wave rotates. 16. The method according to claim 15, characterized in that the magnetic areas are continuously in the Surface of the shaft are induced and the movement of the magnetic areas is continuous is scanned. 17. The method according to claim 15 or 16, characterized in that the predetermined number of discrete magnetic areas regardless of the speed of rotation the wave is. 18. The method according to claim 14, 15 or 16, characterized in that the magnetic areas are induced by an excitation signal from a series resonant circuit, which resonates at the frequency of the excitation signal. 19. The method according to claim 14, 15 or 16, characterized in that the magnetic areas are scanned by a current in a parallel resonant circuit which contains the sensing means and resonates at the frequency of the excitation signal swings.