Abstract: An electrical conductor forming a grid only partially circumferentially surrounds the path of the outer portion of a rotatable member. The member has a magnet coupled thereto for influencing the grid to produce a signal indicative of vibration of the member whenever the magnet is within a predetermined distance of the grid. During the interval that the magnet does not influence the grid, a synthesis signal, indicative of vibration of the member during the previous influence portion of the revolution, is generated. The influence signal and the synthesis signal may be provided to processing apparatus for obtaining vibration information. Providing both an influence signal and a synthesis signal substantially simplifies processing apparatus that would otherwise be needed should only an essentially null signal be available during the interval in which the magnet does not influence the grid.

Abstract: A method and apparatus for continuously monitoring torque in a rotating shaft. The invention includes a pair of electromagnetic probes in fixed proximity to the shaft and spaced-apart in the direction of the shaft's longitudinal axis. The probes are operable in two modes. In the first, each probe is excited to cause a fixed magnetic pattern to be induced onto the surface of the shaft along a circumferential line adjacent to the probe. In the second mode, movement of the magnetic pattern due to the shaft rotation induces a signal into each probe. Each signal is indicative of the instantaneous angular velocity of the shaft at the corresponding shaft location. The two induced signals are conveyed to phase detection circuitry which produces a signal indicative of the phase relationship between the two input signals. The electrical phase relationship is a direct measure of the twist in the shaft, proportional to torque.

Abstract: Apparatus is disclosed for continuously monitoring the air gap torque acting on the rotor of a 3-phase electrical generator by sensing certain of the output voltages and currents produced by the generator as it supplies power to a connected load. In a preferred form of the invention, signals representing the three generator output voltages and two of the three line currents are conditioned and combined in electrical circuitry to produce a single output signal which is indicative of the air gap torque. The torque signal so produced is in a form easily handled by conventional means such as computers and recorders, and is appropriate for use by operating personnel in making decisions regarding generator operation.

Abstract: A calibration signal source for instruments to measure power and negative sequence current of a multi-phase electric power generator. Separate signals are provided to represent load current for each phase of the generator ultimately to be tested, and to represent the instantaneous differences in voltage between each phase and a reference phase. The calibration signals are derived from a single sine wave by providing a plurality of phase shift and voltage difference networks. Means are provided for amplitude control and elimination of harmonic distortion of the single sine wave, and therefore the output calibration signals share these characteristics.

Abstract: An improvement in torsional vibration monitors wherein a frequency shift is applied to the torsional vibration signal to achieve improved stability and increased confidence in the measurement. The torsional vibration signal is applied to parallel frequency shifters to produce a lower frequency measuring signal and a lower frequency reference signal. The two lower frequency signals are applied to parallel connected filters to obtain spectral content of the signals. Once the spectral content is obtained, each lower frequency measuring signal and each lower frequency reference signal is shifted back to the original frequency range to produce filtered reference signals and filtered measuring signals. These signals are then correspondingly summed to provide a set of torsional vibration signals segregated with respect to the frequency spectrum and meaningful with respect to a time base.

Abstract: Apparatus and method for monitoring torsional vibration in the rotor of a dynamoelectric machine by detecting electrical quantities available at the output terminals of the machine. For at least one phase of the machine, output voltage and current are detected and a composite signal is formed therefrom in signal processing circuitry. The composite signal is in synchronous phase with the mechanical angle of the rotor and may be demodulated to obtain the torsional vibration information.

Abstract: A method and apparatus are disclosed for accurately determining negative sequence current in a three-phase turbine-driven generator, the currents indicative of power oscillations and of torques harmful to turbine buckets. A signal conditioner and phase-shifter network are described which provide precise amplitude and phase angle adjustments and null balancing features which permit accurate determination of the magnitude of negative sequence current even though this current is a very small quantity determined as the difference between two large signals.

Abstract: A method and apparatus are provided for measuring torsional vibrations of a rotating member by sensing passage of a plurality of circumferentially spaced elements adapted for movement with the member and for producing an electrical signal including true components representing the torsional vibrations and from which selected false components representing inhomogeneities in the elements have been eliminated.

Abstract: Apparatus is described for monitoring phase currents and torsional vibrations of a turbine-generator which are indicative of the dynamic response of the machine during operation under load. The monitoring system disclosed includes probes which are operable to sense rotation of the main shaft of the turbine-generator and to feed the resulting signals to a vibration network. The vibration network eliminates from the signals any false components present at frequencies equal to multiples of the rate of rotation of the shaft and produces a composite vibration signal containing only true components of shaft torsional vibration. The composite vibration signal and a set of three phase current signals determined by stepping down, filtering, and amplifying the generator line currents are monitored continuously but recorded only when at least one of two signals derived from selected components of the composite vibration signal and phase current signals exceeds reference levels in an alarm system included in the monitor.

Abstract: An alarm system is disclosed for generating alarms when torsional oscillations of a rotating shaft exceed predetermined limits and fail to subside at a predetermined rate. The alarm system receives a torsional oscillation input signal developed by measuring the deviation of instantaneous shaft angle from a uniformly increasing value. The input signal is converted to a direct current torsional oscillation signal representative of the magnitude of oscillation. The torsional oscillation signal is compared against a first adjustable reference voltage representative of a first maximum magnitude of oscillation. A low level alarm signal is generated when the oscillation signal exceeds the first reference voltage for a predetermined length of time. The oscillation signal is also compared against a second reference voltage representative of a second maximum magnitude of oscillation. An output signal is generated when the oscillation signal exceeds the second reference voltage.

Abstract: Method and apparatus for applying controlled electromagnetic force to a test specimen such as a turbine bucket to induce vibration in the specimen. The force is applied by means of an electromagnetic field produced by an electromagnet. A controlled power source supplies current to the electromagnet to maintain the applied force at a predetermined magnitude over a predetermined range of frequencies. A comparator controls the power source in response to a sensor signal representative of the frequency and magnitude of the face actually applied so as to maintain at a minimum the difference between this signal and a reference signal representative of a desired frequency and magnitude. Tuning means are provided to nullify capacitive reactance of the electromagnet which would otherwise tend to limit the current supplied by the power source as frequency is increased.

Abstract: A monitor system is described which is capable of providing an output which indicates the oscillatory torque in each section of a multi-section shaft of a rotating system having plural masses. The system described is an electronic model of a mathematical analog of the rotating system and is based upon the assumption that the system may be represented as N inertias or masses interconnected by N-1 shafts -- represented as springs. For such a system there are n-1 primary frequency oscillatory torques. If the inertias are large, the frequencies of these torques are low. Electrical signals representing the torques are sensed at one or more shaft sections and are filtered, amplified, passed through a plurality of weighting network and recombined to provide an indication of the total oscillatory torque in each of the N-1 shaft sections. Such torque, or an electrical output signal from a generator, in the instance of a turbine-generator set may be used to actuate an operative means or actuate a system alarm.