Local display and local heat output can be optional. Instead of the docile, smoothly changing sine waveforms we usually take for granted, nonlinear and fast-changing electrical loads cause distorted waveforms on your power line. When you power your instrumentation from such supplies, you may encounter process upsets caused by corruption of the internal digital circuitry. Some instrument manufacturers severely torture-test their products as part of the design process and ensure they are virtually immune to bad power quality and electromagnetic interference. If you are experiencing process interruptions, you may suspect your power quality or see a distorted and spiky waveform on your oscilloscope.
Devices can range from effective to useless, so be sure to read specifications and ask questions.
These problems lead distributed control equipment manufacturers to use a stable and clean low voltage DC supply to power the equipment. Much of my incoming e-mail has been lost in transit. Arthur Holland runs Holland Technical Skills, Oakville, ON, a consulting firm specializing in tempeature and power control technology, training and technical writing. Copyright 2001 by Business News Publishing Co.