A parameter of a machine such as vibration may be measured and analyzed to monitor machine health. A parameter is used herein to refer to a physical property or other thing that is typically measurable such as vibration, pressure, voltage, current, temperature and the like. Vibration sensing instruments have been used to determine faults in machine function by detecting abnormalities in vibration, which correlates to different types of machine faults.
Typically, vibration measurement devices require significant power supplies, memories, and bulk data transfer capabilities. The power supply is used to power vibration sensors, other sensors such as temperature or pressure sensors, power regulators, a processor, a memory, and a communicator. As vibration waveforms generated by vibration sensors enter the devices, the waveforms must be stored in a memory. Such bulk vibration waveforms typically require large memory capacities for storage. Then, the waveforms are often transmitted in entirety or without significant compression to an outside system for machine health analysis. Also, network connections must accommodate bulk quantities of data such as vibration waveforms. Such vibration monitoring systems are not well suited for operation in a control protocol network.
In accordance with one embodiment disclosed herein, a measurement instrument has a sensor circuit for sensing a parameter of a machine and producing a dynamic signal based on the sensed parameter. An analog to digital converter is connected to receive the dynamic signal and convert the dynamic signal to a digital format, producing a digital signal having a plurality of data points. A processor is connected to receive the digital signal and determines a characteristic or characteristics of the dynamic signal. Characteristic is used herein to refer to values representing information about the dynamic signal such as root-mean-square value, peak value, frequency value, peak in frequency range, and the like. The processor also determines data corresponding to the characteristic or characteristics such as a level corresponding to the absolute peak of the digital signal over a predetermined range of data points of the digital signal. A power supply is connected to power the processor and is controlled by the processor to manage efficiently power consumption. The power supply may be a long-life, non-rechargeable battery or may be a rechargeable battery with a solar power supply for charging the battery. Alternatively, the power supply may be a power circuit connected to an outside source of power.
In some embodiments, the processor produces a PeakVue waveform as discussed in U.S. Pat. No. 5,895,857 to Robinson et al. (the '857 patent), which is incorporated in its entirety herein by reference. The PeakVue waveform is made up of many levels corresponding to the absolute peaks of different sequential sections of the digital signal and a single absolute peak level is determined over a time interval sufficient to include eleven or more shaft revolutions.
In other embodiments, the processor determines a true root-mean-square value representing the overall vibration level in velocity units which is an indicator of the condition of the machine.
In other embodiments, the measurement instrument has a communication module and a communication processor controls the communication module. A communication power supply is connected to the communication processor and powers the communication processor, and an antenna is connected to the communication processor for wirelessly communicating the peak level and the overall RMS level to a control protocol network, such as a HART or a Fieldbus protocol network. Some embodiments of the instrument have multiple sensors for measuring vibration or relatively steady-state measurements such as temperature and pressure.