Tag Archive: response

Aug
12

Fuzzy Logic Control – Commissioning

Tuner Interface for Fuzzy Logic Control

To allow consistent implementation of control applications, fuzzy logic control may be implemented as a function block. The fuzzy rules and membership functions can be predefined except for the scaling of the membership functions for error, change in error, and change in output.  As addressed in Chapter 6 of Advanced Control Foundation – Tools, Techniques, …

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Jun
03

Robustness-Based Tuning

Robustness Map

Before tuning calculations are applied in a control loop, it is good to consider how much the process gain and deadtime can change before the loop becomes unstable. In the DeltaV control system, this information is provided using a robustness plot that shows gain margin and phase margin as illustrated below. Information on this type …

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Apr
29

Selecting Control Response

After the process characteristics are identified, the information is then used to calculate the recommended loop tuning. The tuning rules used to derive controller parameters from process characteristics can be chosen as appropriate for the specific process and the desired speed of response. As addressed in Chapter 4 of Advanced Control Foundtion – Tools, Techniques, …

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Apr
15

On-Demand Tuning

Self Regulating Response

During the commissioning of feedback control based on the PID algorithm, the PID tuning parameters (that is, the proportional, integral, and derivative gain) must be set to specific values to achieve the best controller response to setpoint and disturbance input changes. To minimize process variations and the response time to setpoint and disturbance input changes …

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Mar
18

Impact of Changing Process Gain

non-linear valve characteristics

From a control perspective, it is highly desirable that the process gain is constant. If the process gain is constant, then the same proportional gain can be used over the entire operating range of the control loop. Using a control valve as an example, if the valve characteristic was not properly selected based on the …

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Mar
04

Addressing Incorrect Tuning

DCS tuning Support

A Loop tuning has a significant impact on control loop utilization and performance. Controller tuning parameters can be easily changed over a wide range to adjust loop operation for various process requirements. However, some expertise in tuning is required even when advanced control tools are used, and there is a chance that the behavior of …

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Nov
14

Recovery from a Process Saturation Condition

Recovery from a Process Saturation Condition

At Emerson Exchange, 2011, I had the pleasure of working with Daniel Coyne, Manager, Automation, BP America Inc., to host a workshop on Recovery from a Process Saturation Condition. The workshop addresses the improved recovery from a process saturation condition that is provided by the PIDPlus option of the PID function block in the DeltaV …

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Sep
26

Commissioning Control Systems – Setting Controller Action

Setting Controller Action

The process gain may be negative or positive depending on the process design. To provide the correct response a feedback control block must take into account the process gain direction—whether to increase or decrease the manipulated input to correct for a control error. For example, the inlet flow to a tank may be manipulated to …

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Aug
22

Commissioning Control Systems – Control Response

Adaptive Control Using DeltaV Insight

In many processes, it is desirable to have an overdamped response. To achieve that response, the proportional gain used in the PID is typically much less than that required for an underdamped or unstable response. When selecting the PID gain, it is important to consider that the process gain may change with the operating conditions. …

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Dec
27

Process Characterization – Inverse Process Response

Process characterization is the identification of the dynamic responses of a process to changes in its inputs. As part of the chapter on process characterization in Chapter 9 of Control Loop Foundation, we address inverse process response. A few processes exhibit a behavior where for a step change in input, the output initially changes in …

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