This invention relates to electric motors and more particularly it relates to electronic detection and monitoring equipment displaying the operation parameters of electric motors.
Various types of motor parameter monitors such as load and speed indicators are known in the art. In general, these are of limited use since electric motors have many different characteristics that require special consideration. Thus, motors of the same ratings from different manufacturers usually have different operating characteristics. This means that it is very difficult to have universal monitors that accurately display the motor parameters.
Also, the matter of retrofitting motors in the field with monitors and detectors is difficult, and amounts to an economically insurmountable problem because of space limitations, access difficulties and the need for most electronic monitors to have wires connected thereto and for some to be incorporated into existing motor wiring for response to current flow, etc.
Furthermore, operating parameters vary with not only individual motor characteristics but also with applied temperatures and voltages so that it is difficult to provide precision measurements that hold over a wide range of motor operating characteristics. For example, the iron temperature and ambient temperature of a motor are different and can affect slip, current, torque, speed and other parameters. The same for changes of voltage to the motor. There is no known prior art device that has successfully overcome all these problems, and thus limited use of motor parameter monitors has resulted.
It is therefore a general object of the invention to provide electric motor monitors overcoming some of these prior art deficiencies.
A further object of the invention is to provide electric motor monitors matched to the characteristics of individual motors which are inexpensive and universally useable under various conditions and in different installations.
Another object of the invention is to improve the accuracy of electric motor parameter monitoring systems.
A more specific object of the invention is to provide improved electronic load monitoring systems for electric induction motors.
Therefore in accordance with this invention, an individually tailored parameter detector may be installed inexpensively in an electric motor at the factory that fully corresponds to the dynamic performance of that motor, and this detector may be coupled conveniently to corresponding monitoring equipment in the field. To resolve problems of access and location of intercouplings between the built-in detector and external signal processing equipment, the monitored signal is coupled to the electric motor powerlines in carrier current mode by a r-f carrier so that the monitoring equipment can be installed at any convenient location to pick up the dynamic motor parameter signal without wiring or access to internal space compartments of the motor, or distortion of any kind in the signal characteristics. Because of factory installation the detector can be engineered for compatible operation with the particular motor characteristics, and can be located in a non-interfering place within the motor housing, where changes in motor temperature and motor operating voltage, for example, are present, so that exact parameter conditions are monitored for better accuracy. The signal is then conveyed to an external circuit further processing displaying and conveying the monitored and processed motor parameter signals for appropriate use.
In a preferred embodiment, the load characteristic of an induction motor is monitored by detecting pulses from the motor shaft revolution and processing them by slip analysis to relate to the loading on the motor. The detector portion is mounted on an electronic chip within the motor housing to modulate a carrier current r-f transmitter which induces the desired signal into the electric power line to the motor for external detection. The external detector-demodulator located somewhere along the power line then can process the signal for alarm or display purposes, and yet can monitor exact temperatures, voltages, currents, etc., within the motor as it operates dynamically under different conditions.