Portable vibration monitoring device

Details Portable vibration monitoring device Portable vibration monitoring device

1998-05-21

2001-07-10

Kwok, Helen (Department: 2856)

Measuring and testing

Vibration

Sensing apparatus

C073S602000

Reexamination Certificate

active

06257066

ABSTRACT:

TECHNICAL FIELD
The present invention relates generally to vibration analysis, and more particularly to a portable vibration monitoring device useful as part of a predictive maintenance program.
BACKGROUND OF THE INVENTION
Vibration analysis is known in the art as an effective tool in a predictive maintenance program for machinery. Conventional vibration based predictive maintenance programs rely on Fast Fourier Transform (FFT) generated vibration signatures, collected using a portable data collector, and an expert system to process the data and determine which machinery needs attention. Increasingly, permanently installed systems are being used, both to provide continuous monitoring of critical machinery, and to reduce labor costs of data collection.
Such conventional technology, while effective, has various drawbacks associated therewith which limit applications to facilities having large costly machines, or critical machines where unexpected shutdowns are unacceptable. For example, the portable data collectors are complex devices which are expensive to design and build. The analysis of the vibration data using either manual or automated techniques requires a significant amount of study to be effective, and skilled labor to analyze the data and interpret the results.
Furthermore, data acquisition is costly because of the labor involved. The software which drives the technology is complex and expensive. Moreover, there is much set up time involved with configuring the data analysis to a new machine.
Simpler devices, known as vibration meters, measure the vibration from a machine and compare a single broadband level to a threshold. Such approach can be effective for detecting the deterioration of a machine, but the approach is severely limited because the overall level is controlled by the highest peak in the measured vibration. The overall vibration level may not change at all even though serious deterioration in the machine may be occurring.
In view of the aforementioned shortcomings associated with the above-described conventional approaches, there is a strong need in the art for a vibration monitoring device which is cost-effective even in smaller facilities with perhaps only a few machines. There is a strong need for a device which employs relatively low cost hardware/software, and which may be utilized by low skill workers without requiring significant training. On the other hand, there is a strong need for a simpler device which is not limited to measuring overall vibration level so as to be susceptible to false positive diagnoses.
SUMMARY OF THE INVENTION
The present invention relates to a vibration monitoring device that is portable, low cost, and still provides useful information regarding machine condition. In the hands of a plant mechanic or equipment operator, the present invention provides a quick indication of machinery condition. In addition, the invention provides information to aid in determining the underlying mechanical faults causing unacceptable vibration levels.
The portable vibration monitoring device uses an accelerometer mounted on a machine to measure the vibration of the machine, and a display to display the results. The results are displayed, for example, on four bargraphs to indicate good/marginal/unacceptable vibration levels. Additionally, the bargraphs provide an indication of the type of problem resulting in high vibration levels. Examples of such problem types include, but are not limited to, machine imbalance, misalignment, and general fault conditions.
The portable vibration monitoring device of the present invention measures the overall vibration displacement, velocity and acceleration levels. Each of these measurements is displayed on a respective bargraph and emphasizes a different part of the vibration signature (frequency band) of the machine under test. Consequently, small changes which would not be seen with a single measurement have a better chance of being observed. Moreover, such taking of measurements that emphasize different frequency ranges also provides some indication as to the frequency of the vibration, to allow analysis of the cause of the increased vibration levels.
According to one particular aspect of the invention, a portable vibration monitoring device is provided. The portable vibration monitoring device includes a portable housing; an accelerometer which may be mounted to a machine under test, the accelerometer providing an output signal representative of the acceleration of the machine; at least one integrator within the housing for processing the output signal to produce three measurands corresponding respectively to measured acceleration, velocity and displacement of the machine; scaling circuitry within the housing for scaling the levels of the three measurands relative to each other according to a predetermined relationship; and a display exposed via the housing for displaying the scaled levels of the three measurands in a manner which is indicative of a particular frequency content of the output signal.
According to another aspect of the invention, a portable vibration monitoring device is provided which includes a portable housing; a transducer which may be mounted to a machine under test, the transducer providing an output signal related to movement of the machine; processing circuitry within the housing for deriving acceleration, velocity and displacement measurands based on the output signal; scaling circuitry within the housing for scaling the levels of the measurands relative to each other according to a predetermined relationship; and a display exposed via the housing for displaying the scaled levels of the three measurands in a manner which is indicative of a particular frequency content of the output signal.
To the accomplishment of the foregoing and related ends, the invention, then, comprises the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative embodiments of the invention. These embodiments are indicative, however, of but a few of the various ways in which the principles of the invention may be employed. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1
is a top view of an exemplary portable vibration monitoring device in accordance with the present invention;
FIG. 2
is a side view of the portable vibration monitoring device in accordance with the present invention;
FIG. 3
is a block diagram illustrating the various components making up the portable vibration monitoring device in accordance with the present invention;
FIG. 4
is a diagram illustrating the response characteristics of the device with respect to the displacement, velocity and acceleration measurements as a function of the machine operating speed in accordance with the present invention;
FIG. 5
is a look-up table illustrating the different gain values which are employed by the portable vibration monitoring device in order to scale the displacement, velocity, acceleration and crest factor measurements as a function of operating speed in accordance with the present invention;
FIG. 6
illustrates, for comparison, three different points A-C on a response diagram of the type shown in
FIG. 4
;
FIGS.
7
(
a
),
7
(
b
) and
7
(
c
) illustrate exemplary displays produced as a result of measurements at points A-C, respectively, in
FIG. 6
for a 1200 rpm machine;
FIGS.
8
(
a
),
8
(
b
) and
8
(
c
) illustrate exemplary displays produced as a result of measurements at points A-C, respectively, in
FIG. 6
for an 1800 rpm machine;
FIGS.
9
(
a
),
9
(
b
) and
9
(
c
) illustrate exemplary displays produced as a result of measurements at points A-C, respectively, in
FIG. 6
for a 3600 rpm machine; and
FIGS.
10
(
a
),
10
(
b
),
10
(
c
),
10
(
d
),
10
(
e
) and
10
(
f
) illustrate exemplary displays representing satisfactory machine co

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