Noises, troubleshooting

Because of its small size and portabiHty, the hot-wire anemometer is ideally suited to measure gas velocities either continuously or on a troubleshooting basis in systems where excess pressure drop cannot be tolerated. Furnaces, smokestacks, electrostatic precipitators, and air ducts are typical areas of appHcation. Its fast response to velocity or temperature fluctuations in the surrounding gas makes it particularly useful in studying the turbulence characteristics and rapidity of mixing in gas streams. The constant current mode of operation has a wide frequency response and relatively lower noise level, provided a sufficiently small wire can be used. Where a more mgged wire is required, the constant temperature mode is employed because of its insensitivity to sensor heat capacity. In Hquids, hot-film sensors are employed instead of wires. The sensor consists of a thin metallic film mounted on the surface of a thermally and electrically insulated probe. 

In modern chemical plants, thousands of measurements are recorded at frequencies that can exceed 1 Hz. Aside from plant operating conditions including pressures, temperatures, flow rates, and stream composition, other recorded variables include product purity, contamination levels (air, water, soil), and even safety compliance. All this information is stored in enormous databases. This historical record may be interrogated to monitor process performance, and control, for troubleshooting, to demonstrate environmental compliance and modeling. Often smoothing techniques are required to help identify trends in the data that may be masked by low signal-to-noise ratios. 

Many process equipment failures are preceded by unusual noises and vibrations. An alert operator can prevent damage to a vital refinery component by identifying such sounds. The troubleshooter may be asked to explain the cause of the noise and how to stop it. The origin of some of these problems are ... 

The ability to locate a leaking block valve audibly is a skill that the troubleshooter will want to acquire. Hold your ear near the bottom of the valve and the sound of the rushing liquid will be quite distinct. Chances are, if you cannot hear any noise, the valve is not leaking through more than a few gpm. 

A frequency counter measures the frequency of electrical signals. The frequency counter is often used during troubleshooting and assembly procedures for computers and other electronic devices as well as any device using oscillators. A frequency counter with a lowpass filter eliminates incorrect signals due to high-frequency noise. 

Giampaolo, T. 2009. The Gas Turbine Handbook, 4th ed., Lilbum, GA Fairmont Press. This work examines the various types of gas turbines, including microturbines, and their applications, operation, and troubleshooting. Turbine theory, control systems, inlets and exhaust, accessories, acoustics, and noise control and prevention are also addressed. Four case studies offer real world examples of various issues related to gas turbines. 

A common technique for measuring noise is frequency domain analysis, such as plotting the acceleration power spectral density (PSD) of the seismic data over some time period. While tmies are readily distinguishable from broadband noise, nonstationary events such as pops have a broadband spectral characteristic (typically proportional to j) that can nuslead the troubleshooter. However, small pops may not be readily identified by examining the time-domain time-series data as they may have amplitudes too small to be distinguished from the background seismic activity. 

In summary, the Galperin geometry has proven to offer significant benefits to seismometer users and manufacturers and through use and experience has proven to have significant additional benefits in terms of remotely troubleshooting station noise. 

Returning to the output baseline displayed on the oscilloscope, if it is not smeared at all by noise, then the PA is saturated somewhere. Again, in this case, a complete troubleshooting procedure has to be carried out starting from dc analys is. 

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