Loop Controllers: Lone Logic is More Connected
Mark T. Hoske

Stand-alone loop controllers, desired because of cost and simplicity, still need to collect and report data, even if they operate outside of a larger control system. External and peer-to-peer communications are the most important traits in such controllers, after ability to do PID (proportional-integral-derivative) control. Also, more users are checking daily to ensure controllers are operating closed-loop.

Those were among key

Responses to the 2005 survey from Control Engineering and Reed Research Group were based on 104 subscribers who buy or specify loop controllers. Of theseCONTROL ENGINEERING China版权所有, 62% were for in-plant requirements; 18% for OEM (resale) requirements; and 20% for both. Responses in 2003 numbered 127; 62% for in-plant requirements; 25% for OEM (resale requirements); and 10% for both.

In 2005www.cechina.cn, 52% of respondents listed continuous processing as the primary application; 28% both batch and continuous processing; 20% discrete manufacturing; 19% utilities services; 15% batch processing; and 2% other. In 2003CONTROL ENGINEERING China版权所有, the mix was 40% continuous processing, 12% both batch and continuous processing, 42% discrete manufacturing, 23% utilities services, and 10% batch processing.

More electronic, less pneumatic

More electronic single-loop controllers and fewer pneumatic loop controllers are being used for primary control. In 2005www.cechina.cn, type of loop controllers for primary controlCONTROL ENGINEERING China版权所有, in percentage of total responses, were (more than one answer allowed): 40% electronic single-loop controller; 25% PC-based controller; 21% electronic multiple-loop controller; 13% pneumatic loop controller; and 1% other. In 2003CONTROL ENGINEERING China版权所有, responses were 33% electronic single-loop controller; 26% PC-based controller; 22% electronic multiple-loop controller; 18% pneumatic loop controller; and 2% other.

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