Tag Archive: “function block”

Jul
29

Fuzzy Logic Control

Fuzzy Logic Control Response vs PID

Fuzzy logic is a relatively new control technology. In the mid-1970s Mamdani began to investigate fuzzy logic as an alternative to the PID controller and sparked the first practical applications of fuzzy logic in the process control industry. The controller followed rules that generated an output by evaluating the error and the change in error. …

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Jul
16

Mode Structure

Mode

The PID block mode parameter as originally defined by ISA50 determines the source of the block setpoint and the source of its output. This mode parameter is structure to contain four attributes: Target – The mode of operation requested by the operator Actual – The mode of operation that may be achieved based on the …

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Jul
09

Mode – Bumpless Transfer

Block Calculation Sequence

As an operator changes the mode of a function block, it is important that this change not cause a sudden change in plant operation. In the ISA50 mode implementation, the status in the backward path plays an important role in providing bumpless transfer. For example, the actual mode of an analog output block will not transfer …

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Jul
02

Mode – The Role of Status

Propagation of Status

As the ISA50 function block team considered how to improve plant operations through a more comprehensive implementation of mode in the control system, they realized it would be important that the control blocks, such as the PID, be designed to automatically take into account up-steam and downstream conditions that impact control operation. Thus, inputs and …

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Jun
25

Distributed Control Systems’ Implementation of Mode

PID-Faceplate-Detail

To ease operator transition from panel-based systems to monitor-based systems, the manner in which first generation Distributed Control Systems (DCS) displayed information often mimicked the way this information had earlier appeared on the control panel. Since the control interface provided by the control panel was familiar and had proven to be effective, a similar presentation …

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Sep
19

Commissioning Control Systems – Selection of Control Structure

Selecting PID Structure

Most control systems allow the user to pick the components, also known as the structure of the PID algorithm, that will be used in a control application. In some cases, this is done by providing different control blocks for P, PI, or PID. However, some systems such as DeltaV provide a single PID block and …

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Mar
28

Process Simulation – Part 3

This is the third posting on highlights of Chapter 15, Process Simulation, in Control Loop Foundation – Batch and Continous Processes. In my March 14 and 21st postings on process simulation I addressed some of the some basics associated with the integration of process simulation into a control system. In this posting we will start …

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Mar
07

Model Predictive Control

Charlie Cutler and Ramaker caused quite a stir in 1980 when they presented a paper that provided information on a new technique known as Dynamic Matrix Control. Shell Oil had developed and deployed this technique for the control of large interactive multiple input-multiple output (MIMO) processes such as refinery distillation columns. This work by Shell …

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Feb
28

Ratio Control

For many processes, such as blending and boiler combustion, a key objective is to maintain the flow rates of two process streams in some proportion to one another. In such cases, ratio control may be applied. When ratio control is applied, one process input, the dependent input, is proportioned to the other process input, known …

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Feb
14

Split-range Control

A wide variety of processes may be described as having one controlled parameter and two or more manipulated process inputs. The challenge from a control perspective is that there is no unique set of input values that are required to maintain the controlled parameter at setpoint. One of the most common ways of addressing multiple …

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