Method and system for fast probe failure determination

Details Method and system for fast probe failure determination Method and system for fast probe failure determination

1998-04-06

2001-03-13

Raevis, Robert (Department: 2856)

Measuring and testing

Instrument proving or calibrating

Apparatus for measuring by use of vibration or apparatus for...

Reexamination Certificate

active

06199422

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to monitoring probes. More particularly, the invention relates to determining a status condition of vibration monitoring probes.
2. Description of the Related Technology
Machinery used in manufacturing facilities and power generating stations, for instance, employ vibration monitoring equipment to detect variations in their vibration characteristics. By careful monitoring, a company may determine appropriate intervals for machine maintenance and obtain indications of imminent machine failures. Naturally, the proper scheduling of maintenance improves the operating efficiency of a facility.
Furthermore, by measuring specific parameters associated with a machine, a company may assess its operating conditions to predict the failure of components before it occurs.
By providing a warning of imminent machine failure, a company can avoid catastrophic machine damage as well as danger to facility personnel. Additionally, by monitoring the efficiency and operation of machinery used in manufacturing and process plants, for example, a company may achieve a competitive advantage by reducing unscheduled machine downtime, reducing repair times and optimizing machinery performance.
With many current monitoring systems, the concept is to measure and monitor operational parameters, such as vibration levels, of a given machine, and shut the machine down via a relay actuation if the measured parameters exceed user-determined set points. Each industry recognizes the need for this type of protection, and many have developed standards which establish electromechanical requirements for the systems and equipment used to monitor machinery. Such requirements include maximum times to detect a machine fault condition, optimal levels and tolerances for power supply inputs and outputs, system inputs and outputs, and so forth.
One of the most stringent of the electromechanical standards for vibration monitoring equipment is the American Petroleum Institute (API) Standard 670, Third Edition. And more specifically, one area within this standard where the current technology is inadequate is in meeting fault condition detection timing requirements. API 670, 3
rd
Edition, Paragraph 3.5.1.1.p states “The time required to detect and initiate an alarm (alert) or a shutdown (danger) shall not exceed 100 milliseconds.” By this standard, therefore, an almost immediate alarm and/or shutdown is required if vibrational data indicates faulty machine operation.
The prescribed time limits must be met not only for alarm and shutdown but also to validate the data so as to verify its accuracy and reliability. One process of validating the data involves determining if a probe is in proper working condition. If it is not, data received from the probe may be inaccurate, leading to an incorrect evaluation of a machine being tested. In such a case, the machine may be unnecessarily shut down, or alternatively, the machine which is on the brink of breakdown may be allowed to continue operating, ultimately leading to a fatal failure of the machine. Validating the test data avoids false alarms and unnecessary machine shutdowns and/or catastrophic breakdowns.
Current technology typically determines whether the probe is functioning properly by processing data received from the normal data acquisition path used for evaluating the status of the machine being tested. One inadequacy of this method is that the data flow paths for normal data acquisition and probe failure detection are the same, i.e., the analog input signals are first conditioned, multiplexed, converted to a digital equivalent value, and finally received by the digital circuitry, prior to any determination of whether the probe is in a proper working state. Thus, any delays introduced to the normal data acquisition time are introduced to the probe failure detection time as well. Additionally, the delay introduced by a given system is not always the same, and thus the probe failure detection time can vary from one event to the next, making compliance with real-time detection needs extremely difficult.
Therefore, a method and system is desired to provide an early detection of whether the monitoring probe is in proper working condition and providing an early warning, e.g., a probe failure signal, if it is determined that the monitoring system has a faulty probe. Furthermore, a method and system is needed to determine the operational status of the probe prior to completion of the processing of test data received by the probe. In this way, any alarm or shutdown which may be initiated by test data received by the probe is not further delayed by an amount of time required to determine the operational status of the probe. Furthermore, by detecting a faulty probe prior to the completion of the conditioning and processing of vibration data, false alarms and/or unnecessary machine shutdowns are avoided.
SUMMARY OF THE INVENTION
The present invention addresses the above and other needs by providing a probe failure detection circuit that is separate and independent of the circuit used to detect a machine fault condition. The invention eliminates or substantially reduces delays associated with prior art probe failure detection. The determination of the operational status of the probe is generally completed prior to the completion of the processing of the test data.
In one embodiment of the invention, a system for monitoring the operational condition of a machine, includes: a test probe, capable of connecting to the machine, outputting a test signal representative of an operational parameter of the machine; a fault condition detection circuit receiving and processing the test signal so as to detect a fault condition of the machine; and a probe failure detection circuit receiving the test signal and detecting a failure condition of the test probe if the test signal is not within defined limits, wherein the probe failure detection circuit provides a data path that is separate from the fault condition detection circuit.
In another embodiment, a circuit for detecting a failure condition of a probe used for measuring operational parameters of a machine, includes: a first comparator comparing a test signal received from the probe to an upper limit voltage received from an upper limit voltage source; a second comparator comparing the test signal to a low reference voltage received from a low reference voltage source, wherein the first and second comparators are configured to cooperatively output a redundancy signal if the test signal is greater than the upper limit voltage or less than the low reference voltage; and a third comparator, having a first input coupled to respective outputs of the first and second comparators and a second input coupled to a third reference voltage source, comparing the redundancy signal to a third reference signal provided by the third reference voltage source, and outputting an interrupt signal if the redundancy signal is at a defined level with respect to the third reference signal, wherein if the redundancy signal and the interrupt signal are both at defined voltage levels, a probe failure condition is detected.
In a further embodiment, a system for monitoring the operational condition of a machine, includes: probe means, configured to be coupled to the machine, for measuring an operational parameter of the machine and for outputting a test signal representative of the measured operational parameter; machine fault detection means, coupled to the probe means, for receiving and processing the test signal so as to detect a fault condition of the machine; probe failure detection means, coupled to the probe means, for receiving the test signal and detecting a failure condition of the probe means if the test signal is not within defined limits, wherein the probe failure detection means operates independently of the machine fault detection means; and processor means, coupled to the machine fault detection means and the probe failure detection means, for initiating a defined action in response to sig

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