Category Archive: Final Control Elements

Mar
17

Flow Control – Positive Displacement Pump Part 2

When using a positive displacement pump in flow control, then the minimum flow which may be achieved using a variable speed drive is limited by the motor low speed limit. It is possible to achieve a wider range of flow control by regulating flow using a fixed speed motor and a throttling valve in combination …

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Mar
10

Flow Control – Positive Displacement Pump Part 1

Positive displacement pumps may be used when it is necessary address flow requirements of 2GPM or less. The pump design ( e.g. vane, gear, peristaltic) selected for a particular application should be based on properties of the liquid and the expected operating condition. One characteristic of a positive displacement pump is that when it is …

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Mar
03

Flow Control – Centrifugal Pump

Centrifugal pumps can be used to transfer large volumes of liquid between vessels in an industrial process. When a constant speed motor is used to drive the pump then the pump flow rate may be controlled by adjusting a throttling valve that is installed after the pump discharge, as illustrated below. The pump discharge pressure …

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Feb
03

WirelessHART – Monitoring and Control of On-Off Valves

A number of WirelessHART devices have been introduced over the last few years to monitor the status of on/off valves. For example, the TopWorx 4310 WirelessHART Valve Position Monitor can be used detect linear and rotary movement using non-contact technology with limit switch feedback. Such devices provide a low cost way to monitor the position …

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Oct
14

Control Using Wireless Measurements

During the initial development of WirelessHart we began researching how to address control applications that use a wireless measurement and/or wireless actuator. To extend battery life a wireless transmitter may be setup to communication the measurement value much slower than the update rate of a wired installation. Also, when the transmitter supports Window communications (as …

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Mar
25

Split Range Setup

One of the most common ways of addressing multiple process inputs is split range control. A splitter block, which appears as one valve to the PID block, can be used in the control strategy to define a fixed relationship between the controller output and each manipulated process input. In Advanced Control Foundation – Tools, Techniques, …

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Mar
18

Impact of Changing Process Gain

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
11

Evaluating Valve/Actuator Performance

When a control loop is placed in automatic control, it is easy to detect if a valve or actuator is not responding correctly to the control system. As discussed in Chapter 3 of Advanced Control Foundation – Tools, Techniques and Application, this can be done by observing the response of the controlled parameter to control …

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Dec
10

Foundation Book Promotional Kit

The single loop and multi-loop control techniques most often used in automating continuous and batch processes are addressed in the book Control Loop Foundation – Batch and Continuous Processes. Similarly, the advanced control techniques that are most often utilized in the process industry are addressed in the book Advanced Control Foundation – Tools, Techniques, and …

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Sep
17

Control Loop Foundation Class – Nov 5-9

I worked closely with Emerson’s education department to establish the class Control Loop Foundation (9025). This 4 ½ day class is intended primarily for people who are new to the process industry and process control. Approximately 30% of the class is dedicated to workshops in which the students get hands on experience working with the …

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