Patent Application
20210033450
This invention relates to the field of equipment vibration monitoring and analysis. More particularly, this invention relates to removing the DC disturbance component from vibration waveform data.
Vibration waveforms have what could be classified as two components. The first component is what is often called the direct current or DC component, which often reflects the electrical bias of the output amplifier that is boosting the vibration signal. The second component is what is often called the alternating current or AC component, which reflects the vibration signal that is produced by the accelerometer or other vibration sensing device. The AC component tends to oscillate around the level of the DC component, whatever that level might be. In many applications, the DC component is of lesser interest when analyzing the vibration of monitored equipment, while the AC component is of primary interest.
Unfortunately, if the DC component changes, it is difficult to determine what exactly has changed. For example, if the DC component suddenly increases, it is difficult to know if the increase is a result of the electrical amplifier bias or a major change in the condition of the AC vibration component. This problem is especially pronounced if the DC component is changing frequently and erratically.
Such a dramatic shift in the DC component can occur during one or more of several common events. For example, the mere placement of a vibration sensor against the equipment to be monitored can cause such a shift. Similarly, a hard, physical jolt to the monitored equipment can also produce such a shift. In a different manner, starting or stopping electrical equipment that is not adequately isolated from the vibration sensor can create such a shift. Thus, these troublesome shifts in the waveform data can be created by many different events and at various times.
When a Fast Fourier Transform is performed on the disturbed waveform, the resulting frequency spectrum can contain a significant amount of spurious low frequency components as a result of the DC disturbance. These spurious signals can be misinterpreted by the technician as problems with the monitored equipment.
What is needed, therefor, is a system that tends to address issues such as those described above, at least in part.
The above and other needs are met by a method for removing DC disturbance in a vibration waveform, by receiving the vibration waveform and detecting and removing a DC disturbance component of the vibration waveform, leaving substantially only an AC component of the vibration waveform, which is stored on a non-transitory computer-readable medium.
In various embodiments according to this aspect of the invention, the step of detecting the DC disturbance component of the vibration waveform comprises computing a running average of the vibration waveform and using the running average as the DC component of the vibration waveform. In some embodiments, the step of removing the DC component of the vibration waveform includes subtracting the running average of the vibration waveform from the vibration waveform. In some embodiments, the step of receiving the vibration waveform includes receiving the vibration waveform directly from a vibration sensor. In some embodiments, the step of receiving the vibration waveform includes receiving the vibration waveform as stored data from a memory.
In some embodiments, the step of storing the AC component of the vibration waveform includes storing the AC component of the vibration waveform in a memory that located locally where the detecting and removing of the DC component of the vibration waveform is performed. In some embodiments, the step of storing the AC component of the vibration waveform includes storing the AC component of the vibration waveform in a memory that is located remotely from where the detecting and removing of the DC component of the vibration waveform is performed. In some embodiments, an FFT is performed on the AC component of the vibration waveform to produce a vibration spectrum.
According to another aspect of the invention there is described a non-transitory, computer-readable storage medium having stored thereon a computer program with a set of instructions for causing a computer to remove the DC disturbance component in a vibration waveform. The vibration waveform is received, and a DC component of the vibration waveform is detected and removed, leaving substantially only an AC component of the vibration waveform. The AC component of the vibration waveform is then stored on a non-transitory computer-readable medium.
In various embodiments according to this aspect of the invention, the step of detecting the DC component of the vibration waveform includes computing a running average of the vibration waveform and using the running average as the DC component of the vibration waveform. In some embodiments, the step of removing the DC component of the vibration waveform includes subtracting the running average of the vibration waveform from the vibration waveform. In some embodiments, the step of receiving the vibration waveform includes receiving the vibration waveform directly from a vibration sensor. In some embodiments, the step of receiving the vibration waveform includes receiving the vibration waveform as stored data from a memory.
In some embodiments, the step of storing the AC component of the vibration waveform includes storing the AC component of the vibration waveform in a memory that is located locally to where the detecting and removing of the DC component of the vibration waveform is performed. In some embodiments, the step of storing the AC component of the vibration waveform includes storing the AC component of the vibration waveform in a memory that is located remotely from where the detecting and removing of the DC component of the vibration waveform is performed. In some embodiments, an FFT is performed on the AC component of the vibration waveform to produce a vibration spectrum.
According to yet another aspect of the invention, there is described an apparatus for removal of the DC disturbance component in a vibration waveform. The apparatus has an input to receive the vibration waveform, and a processor that detects and removes the DC disturbance component of the vibration waveform, leaving substantially only an AC component of the vibration waveform remaining. A non-transitory storage medium stores the AC component of the vibration waveform.
In various embodiments according to this aspect of the invention, the input includes a vibration sensor that produces a live vibration waveform. In some embodiments, the input includes a memory that provides a stored vibration waveform. In some embodiments, an interface is adapted to receive instruction from and present information to an operator.
Further advantages of the invention are apparent by reference to the detailed description when considered in conjunction with the figures, which are not to scale so as to more clearly show the details, wherein like reference numbers indicate like elements throughout the several views, and wherein:
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The method 600 can be performed either as pre-processing on a live waveform data stream as it is produced, or on waveform data that has been saved to a storage device. Regardless of the immediate source of the waveform data, M samples of waveform data are placed in a random access memory, as given in block 608, and the sample number n is set to 1, as given in block 610. The average of M waveform samples is calculated as given in block 612, and the average so calculated is subtracted from sample n of the waveform data, as given in block 614. The sample n is then saved, as given in block 616, and the value of n is incremented by 1, as given in block 618.
If n is less than N, then the next waveform sample is read from the memory as given in block 624, and is added to the buffer for averaging, where only M samples are held in the buffer at a time, and the newly input sample pushes out an earlier-acquired sample according to a first-in-first-out methodology. The method 600 then falls back to block 612, where a new average of the M sample is calculated. This process repeats until n is equal to N, as given in block 620, at which point the DC component 202 is removed from the buffered waveform, as given in block 622, and is either passed along for further processing or saved to a non-transitory computer-readable storage device.
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The number of waveform samples to average is set, in one embodiment, to an integral number of the equipment turning speed, and includes two full rotational cycles of the equipment. This helps to capture bearing faults that might appear at about one-half of the turning speed. The number of samples to average can be a user-configurable number, or can be set to a default value, depending on the type of faults the equipment may exhibit.
With reference now to
The embodiment of apparatus 800 as depicted in
In one embodiment, the apparatus 800 receives stored waveform data through the input/output 808. In other embodiments, the apparatus 800 receives waveform data from the vibration sensor 814. In either embodiment, the apparatus 800 removes the DC disturbance component in the waveform data as described herein, and then sends the adjusted waveform data out through the input/output 808 for remote storage or further processing, or directly to the storage module 804. In some embodiments the steps of the method as described herein are embodied in a computer language on a non-transitory medium that is readable by the apparatus 800 of
The foregoing description of embodiments for this invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Obvious modifications or variations are possible in light of the above teachings. The embodiments are chosen and described in an effort to provide illustrations of the principles of the invention and its practical application, and to thereby enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.
