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Change DCS from Single Loop Control of a Process Variable

The post Change DCS from Single Loop Control of a Process Variable first appeared on the ISA Interchange blog site.

AutoQuiz is edited by Joel Don, ISA’s community manager.

Today’s automation industry quiz question comes from the ISA Certified Control Systems Technician (CCST) program. Certified Control System Technicians calibrate, document, troubleshoot, and repair/replace instrumentation for systems that measure and control level, temperature, pressure, flow, and other process variables. Click this link for information about the CCST program. This question is from the Level III study guide, Domain 2, Loop checking. Level III represents a professional who has a 13-year total of education, training, and/or experience.


With a DCS it is possible to change from single loop control of a process variable to cascade, ratio, feedforward, adaptive, or multi-variable control, by ___________ if all of the peripheral hardware is installed in the field and connected to the DCS terminal board.

a) relocating the transmitters and FCE
b) reconfiguring the loop
c) installing a UPS and inverter
d) installing another CPU
e) none of the above


<span class="collapseomatic " id="id3624" tabindex="0" title="Click Here to Reveal the Answer” >Click Here to Reveal the Answer

In that all the peripherals and hardware are present and in order, the task of changing control strategies and algorithms and how the gathered data from the process undergoes manipulation by the distributed control system.

In ratio control, the DCS maintains a predetermined ratio between two variables. In cascade control, one controller output is the input for another controller. Feedforward input comes from some possible disturbance that then converts to corrective action to the process. Feedforward takes place outside the feedback loop. Adaptive and multivariable control strategies also leverage numbers per their own dispositions.

These control strategies use process data, process numbers, and manipulate those inputs mathematically. How that data parses depends on the configuration of the loop. The DCS doesn’t care; it can do the arithmetic for all these control strategies.

The best answer is B.

Source: ISA News