Noise Reduction and Isolation
Noise Reduction and Isolation CONTROLLING NOISE Control Panel Grounding Controlling noise in measurement systems is vital because it can become a serious problem Utility Circuit breaker Control even in the best instruments and data acquisi- distribution box panel transformer tion hardware. Most laboratories and industrial Hot phase A environments contain abundant electrical-noise sources, including AC power lines, heavy Hot phase B machinery, radio and TV stations, and a variety of electronic equipment. Radio stations generate Neutral high-frequency noise, while computers and Ground other electronic equipment generate noise in all frequency ranges. Building a completely noise- Earth Earth Enclosure free environment just for running tests and ground ground ground measurements is seldom a practical solution. Fortunately, simple devices and techniques such Fig. 10.01. Utility power transformers are typically as using proper grounding methods, shielded grounded to earth ground near the transformer, and and twisted wires, signal averaging methods, again at the input to the electrical junction box or filters, and differential input voltage amplifiers first switching panel. The switching panel, in turn, can control the noise in most measurements. may be connected to a rod driven into the earth to ensure that it too is at true ground potential. Some techniques preventFigure noise 10.01 from entering the system, while others remove extraneous noise from the signal. panel in the wired path to the eventual load. (See Figure 10.01.) The ground is a point within the THE GROUNDING CONFLICT panel connected to a nearby earth ground rod. A non-technical dictionary defines the term Typically, a large or significant structure (building ground as a place in contact with the earth, a frame) or metallic system (plumbing) is also common return in an electrical circuit, and an connected to the same point.
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