Loop Controllers: Lone Logic is More Connected
作者:Mark T. Hoske 发表时间:2005-12-05
is Schneider, product manager for Bulletin 900 Single Loop Temperature/Process Controllers at Rockwell Automation, was impressed with the increase in the use of single-loop and multi-loop controllers, 'especially in the use of single-loop controllers (7%) and a decrease in usage of all other controller types.'

The change makes sense, Schneider says, given functional enhancements and general improvements made in single-loop controller technology even before 2003. 'I believe that the control engi

neers are just now beginning to use the functions and also beginning to appreciate the flexibility and distributed control possibilities presented to them by this small, yet powerful and cost-effective device,' he adds.

In communications with field instruments, 4-20 mA is less dominant, respondents said. In 2005, the most common communications from stand-alone loop controllers to field instrumentation was 4-20 mA at 79%, down from 89% in 2003. Most common communications between controllers was Ethernet at 52%, about the same as 2003.

Have it both ways

Fabian Monino, product manager for controllers, Siemens Energy & Automation Inc., process instrumentation, says the most significant trend in loop controllers is communications. 'Traditional loop controller users still want the stand-alone controller, out on the floor and easily accessible to the operator. However, they also want to collect and record process data. There are a variety of reasons. Most often it is to satisfy the emissions reporting requirements for the EPA. In boiler control applications, energy use and steam generation data are used to monitor boiler and plant efficiencies. In heat treatment applications, the record of the heating cycle serves as part of the product documentation.'

In the next 12 months, 24% plan to increase purchases of stand-alone loop controllers compared to the past year, 52% remain the same, and 24% plan to purchase fewer.

About half of respondents said that stand-alone loop controllers