Keeping pollution within U.S. Environmental Protection Agency (EPA) guidelines remains of great concern, and the engineering team often takes lead responsibilities for preventing environment-fouling releases. Although it may be scrubbers or physical containment that are needed for meeting actual requirements, the systems' monitoring and documentation system usually holds the most interest for government regulators.

Control engineers are usually called upon to design and commission data acquisition systems required at these industrial sites. These systems, difficult to install and maintain in small and medium-sized sites, can be a real headache in large-campus facilities. Pollutants such as particulate, hazardous airborne substances, facility-runoff, effluent discharge, and "assorted" spills can occur at many locations within a large industrial site. Accurate documentation of these occurrences and excursions is an absolute necessity.

Often, full-scale supervisory control and data acquisition (SCADA) technology provides the required compliance documentation. Full SCADA systems can be expensive, and their capital cost can play a prominent role in the purchase decision.

According to Dave DeFusco, engineering manager for Phonetics Inc. (Aston, Pa.), remote-monitoring systems can provide SCADA at lower cost. Such systems can immediately alert responsible personnel when pollution controls stop working properly or fail. Many systems also include datalogging capabilities, which can be used to keep a permanent record of system performance. The collected data can be used to schedule maintenance, troubleshoot system problems, and/or satisfy EPA requirements.

For communications, control engineers may set up the remote monitoring system to contact their facilities via telephone-enabled systems or auto-dialers. Here's how they work: "If an alarm is sounded, the auto-dialer unit can contact predetermined personnel and deliver the alarm message using voice messages, fax, pager or Internet e-mail. The number of dial-out destinations varies as usually specified at installation. Dial-out destinations can usually be changed as required. Some units can be dialed into at will so users can access time-sensitive status reports or check on plant conditions," Mr. DeFusco continues.

"Even a bare-bones remote monitoring system should include both analog and digital inputs so it is compatible with all types of transducers. A system with control capability should include either mechanical relays or solid-state outputs. To maintain system reliability, appropriate signal conditioning and isolation devices are a must. Alarm notification functions should provide a variety of options, including voice messages and both numerical and alphanumeric paging. Auto-dial systems have leveraged technology advances. Highly integrated systems can now be used to predict and schedule maintenance as well as control and monitor plant operations," DeFusco adds.

Although remote monitoring is not universally applicable in supervisory control and data acquisition, it clearly has advantages, especially where telephone access is readily available. Given the proliferation of telephone communications in all but the most sparsely populated areas, it remains a viable option for most wide-area control systems.

For more information about Phonetics Inc., visit www.controleng.com/freeinfo.