Control loop cookbook pdf

Control Systems study material includes control systems notes, control systems book, courses, case study, syllabus, question paper, MCQ, questions and answers and available in control systems pdf form.

Control Systems Notes can be downloaded in control systems pdf from the below article. A detailed control systems syllabus as prescribed by various Universities and colleges in India are as under. You can download the syllabus in control systems pdf form. PID controllers: Effects of proportional derivative, proportional integral systems on steady state error.

Root Locus Technique: Concept of root locus — Construction of root locus. A control system is a system, which provides the desired response by controlling the output.

The following figure shows the simple block diagram of a control system. Some of the control systems questions and answers are mentioned below. You can download the QnA in control systems pdf form. It will help you to understand question paper pattern and type of control systems question and answer asked in bba, bcom, mba control systems exam.

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The common industry standard pneumatic signal range is 3—15 psig. Pneumatic signalling is still common. However, since the advent of electronic instruments in the s, the lower costs involved in running electrical signal wire through a plant as opposed to running pressurized air tubes has made pneumatic signal technology less attractive. Analog Signals The most common standard electrical signal is the 4—20 mA current signal.

With this signal, a transmitter sends a small current through a set of wires. The current signal is a kind of gauge in which 4 mA represents the lowest possible measurement, or zero, and 20 mA represents the highest possible measurement.

This signal can be converted to a temperature reading or an input to a control device, such as a burner fuel valve. Other common standard electrical signals include the 1—5 V volts signal and the pulse output. Digital signals are discrete levels or values that are 6.

The methodology displays information about the used to combine the digital signals is referred to as protocol. Manufacturers may use either an open or a proprietary digital protocol. Open protocols are those that anyone who is developing a control device can use. Proprietary protocols are owned by specific companies and may be used only with their permission. See Module 8: Communication Technologies for more information on digital communication protocols. Which of the following are examples measurement point.

An indictor makes this reading possible. An of a digital signal? Indicators may be as simple as a pressure or temperature gauge or more complex, such as a digital read-out device. Some 1 Profibus indicators simply display the measured variable, while others have 2 4 - 20 mA control buttons that enable operators to change settings in the field.

A recorder is a device that records devices. In addition, manufacturers often use recorders to gather data for trend analyses. By recording the readings of critical measurement points and comparing those readings over time with the results of the process, the process can be improved. Different recorders display the data they collect differently. Some recorders list a set of readings and the times the readings were taken; others create a chart or graph of the readings.

Recorders that create charts or graphs are called chart recorders. Local controllers are usually one of the three types: pneumatic, electronic or programmable. Contollers also commonly reside in a digital control system. Controllers always have 9. Which of the following have the an ability to receive input, to perform a mathematical function with ability to receive input, to perform the input, and to produce an output signal.

Common examples of a mathematical function with the controllers include: input, and produce an output signal? The computers are programmed to respond to inputs by sending 1 Actuators outputs to maintain all processes at setpoint. Which of the following is the most Setpoint common final control element in process control industries?

In most cases, the final control element is a valve used to restrict or cut off fluid flow, but pump motors, louvers typically used to regulate air flow , solenoids, and other devices can also be final control elements. Final control elements are typically used to increase or decrease fluid flow. For example, a final control element may regulate the flow of fuel to a burner to control temperature, the flow of a catalyst into a reactor to control a chemical reaction, or the flow of air into a boiler to control boiler combustion.

In any control loop, the speed with which a final control element reacts to correct a variable that is out of setpoint is very important. Many of the technological improvements in final control elements are related to improving their response time.

The most common example of an actuator is a valve actuator, which opens or closes a valve in response to control signals from a controller. Actuators are often powered pneumatically, hydraulically, or electrically. Diaphragms, bellows, springs, gears, hydraulic pilot valves, pistons, or electric motors are often parts of an actuator system. The ISA Activities has developed a set of symbols for use in engineering drawings and You should be familiar with ISA symbology so that you can demonstrate possible process control loop solutions on paper to your customer.

Figure 7. Which of the following is a symbol of such as transmitters, sensors, and detectors Figure 7. A double line indicates that the 3 function is in an auxiliary location e. The absence of a line indicates that the function is field mounted, and a dotted line indicates that the function or instrument is inaccessible e.

Many modern transmitters are equipped with microprocessors that perform control calculations and send control output signals to final control elements. Which of the following is a symbol of a controller located behind a panel? Activities PLC Types The symbol displayed below denotes a PLC in a primary location.

An actuator is always drawn above the valve Figure 7. Pneumatic valve Manual valve Electric valve Which of the following is a symbol of a pneumatic valve? Valves 1 Pumps 2 Directional arrows showing the flow direction represent a pump Figure 7. The symbols displayed below represent a data link and a process connection.

The initial letter on an ISA symbol transmitter indicate: indicates the measured variable. The initial letter indicates the measured variable. The second letter indicates a modifier, readout, or device function. The third letter usually indicates either a device function or a modifier. What does the third letter on an ISA symbol indicate? Often 1 Device function or a modifier these numbers are associated with a particular control loop e. See Figure 7. In Figure 7.

The examples of control loops used thus far have been very basic. In practice, control loops can be fairly complex. The strategies used to hold a process at setpoint are not always simple, and the interaction of numerous setpoints in an overall process control plan can be subtle and complex.

In this section, you will be introduced to some of the strategies and methods used in complex process control loops.

Each type of contoller has advantages and disadvantages and will meet the needs of different 1. Which one of the following is an applications. Grouped by control mechanism function, the three everyday example of a discrete types of controllers are: controller? A common example of a discrete controller is a home hot water heater. When the temperature of the water in the tank falls below setpoint, the burner turns on. When the water in the tank reaches setpoint, the burner turns off.

Because the water starts cooling again when the burner turns off, it is only a matter of time before the cycle begins again. A controller with three or more possible position in addition to on and off. Multistep controllers set positions is called a continuous operate similarly to discrete controllers, but as setpoint is approached, controller. Is this statement true or the multistep controller takes intermediate steps. Therefore, the false? Process variable action Control action Figure 7.

If there is an error, the controller adjusts its output according to the parameters that have been set in the controller. The tuning parameters essentially determine: How much correction should be made? The magnitude of the correction change in controller output is determined by the proportional mode of the controller.

How long should the correction be applied? The duration of the adjustment to the controller output is determined by the integral mode of the controller How fast should the correction be applied? The speed at which a correction is made is determined by the derivative mode of the controller.

It determines: How much? Proportional Mode How long? Integral Mode How fast? Controllers are tuned in an effort to match the characteristics of the Activities control equipment to the process so that two goals are achieved: 3. GAIN Controller tuning is performed to adjust the manner in which a control valve or other final control element responds to a change in error. In particular, we are interested in adjusting the gain of the controller such that a change in controller input will result in a change in controller output that will, in turn, cause sufficient change in valve position to eliminate error, but not so great a change as to cause instability or cycling.

Gain is defined simply as the change in output divided by the change in input. The next three sections in this module discuss electricity, circuits, transmitters, and signals in greater detail so you can understand the importance of electricity in process control.

Gain Plot - The Figure below is simply another graphical way of Activities representing the concept of gain. Identify the major disadvantage controller. The setting for the proportional mode may be expressed of proportional action.

Proportional Gain 2. Proportional Gain Kc answers the question: 4 Can cause cycling in fast process "What is the percentage change of the controller output relative to the by amplifying noisy signals percentage change in controller input?

If proportional gain is 0. This is the frequency at which cycling may exist. This critical frequency is determined by all of the loop components. If the loop gain is too high at this frequency, the PV will cycle around the SP; i.

Low Gain Example - In the example below, the proportional band is high gain is low. The loop is very stable, but an error remains between SP and PV. Notice that the process variable is still not on set point. What will be the result if the 7 proportional gain is set too high?

SP 6 Select all options that apply. Proportional gain is expressed as the percentage change in output divided by the percentage change in input.

Proportional Mode Responds only to a change in error 2. Proportional mode alone will not return the PV to SP. The controller output from the integral or reset mode is a function of the duration of the error. This is accomplished by repeating the action of the proportional mode as long as an error exists. With the exception of some electronic controllers, the integral or reset mode is always used with the proportional mode.

Setting - Integral, or reset action, may be expressed in terms of: Repeats Per Minute - How many times the proportional action is repeated each minute. Minutes Per Repeat - How many minutes are required for 1 repeat to occur.

Which of the following are integral gain component to the loop. The faster the reset action, the greater or reset actions expressed in the gain.

Slow Reset Example - In this example the loop is stable because Select all options that apply. Identify the major disadvantages output is driven from a desired output level because of a large of integral action. The purpose of an anti-reset option is to allow Activities the output to reach its desired value quicker, therefore minimizing the overshoot. The units are in terms of repeats per minute or minutes per repeat.

Fast Return To Setpoint 3. Possible Cycling Slow Reset 1. Slow Return To Setpoint 3. For example, algorithm that is tied to the rate of a large liquid level process or a large thermal change in the error. To improve response, a large initial change in controller output may be applied. This action is the role of the derivative mode. The derivative action is initiated whenever there is a change in the rate of change of the error the slope of the PV.

The magnitude of the derivative action is determined by the setting of the derivative. The Derivative setting is expressed in terms of minutes. In oper ation, the the controller first compares the current PV with the last value of the PV.

If there is a change in the slope of the PV, the controller etermines what its output would be at a future point in time Which of the following are derivative or the future point in time is determined by the value of the derivative rate actions expressed in terms of?

The derivative mode immediately increases the output by that amount. IN this example, the time scale has been The addition of derivative or rate alone lengthened to help illustrate controller actions in a slow process.

There is no reset at process variable to match the set point. Because temperature is a slow process the setting time after a change in error is quite long. And, in this example, the PV never becomes equal to the SP because there is no reset.

Rate Effect - To illustrate the effect of rate action, we will add the are mode with a setting of 1 minute. Notice the very large controller output at time 0. The output spike is the result of rate action. Recall that the change in output due to rate action is a function of the speed rate of change of error, which in a step is nearly infinite.

The addition of rate alone will not cause the process variable to match the set point. Activities The controller gain is now much higher. The point here is that increasing the rate setting will not cause the PV to settle at the SP.

Applications - Because this component of the controller output is dependent on the speed of change of the input or error, the output will be very erratic if rate is used on fast process or one with noisy signals. The controller output, as a result of rate, will have the greatest change when the input changes rapidly. This feature eliminates a major upset upset that would occur following a change in the setpoint. The units are minutes.

The action is to apply an immediate response that is equal to the proportional plus reset action that would have occurred some number of minutes I the future. Disadvantage - Dramatically amplifies noisy signals; can cause cycling in fast processes. Settings Large Minutes 1. High Gain 2. Large Output Change 3. Possible Cycling Small Minutes 1. Low Gain 2. Small Output Change 3. Stable Loop Trial-and-Error Tuning Increase the rate setting until the process cycles following a disturbance, then reduce the rate setting to one-third of the initial value.

If a small offset 1 P only has no impact on the process, then proportional control alone may be 2 PD sufficient. In processes where no offset can be tolerated, no noise is present, and where dead time is an issue, customers can use full PID control. Table 7. Because in some processes many variables must be controlled, and each variable can have an impact on the entire system, control systems must be designed to respond to disturbances at any point in the system and to mitigate the effect of those disturbances throughout the system.

A feedback loop measures a process variable and sends the measurement to a controller for comparison to setpoint. If the process variable is not at setpoint, control action is taken to return the 1 Discrete control loop process variable to setpoint. Controller Process fluid Steam valve Transmitter Feedback Loop An everyday example of a feedback loop is the cruise control system in an automobile.

A setpoint is established for speed. Feedback loops are commonly used in the process control industry. The advantage of a feedback loop is that it directly controls the desired process variable.

The disadvantage to feedback loops is that the process variable must leave setpoint for action to be taken. Pressure control loops vary in speed—that is, they can respond to changes in load or to control action slowly or quickly. The speed 1 Same rate required in a pressure control loop may be dictated by the volume of 2 Quicker the process fluid. High-volume systems e. Flow control loops are generally to changes quickly.

Therefore, flow control equipment must have fast considered to be slow responding sampling and response times. Because flow transmitters tend to be loops. To compensate for noise, many flow transmitters have a damping function that filters out noise. Sometimes, filters are added between the transmitter and the control system. Because the temperature of the process fluid affects its density, temperature measurements are often taken with flow measurements and compensation for temperature is accounted for in the flow calculation.

Typically, a flow sensor, a transmitter, a controller, and a valve or pump are used in flow control loops Figure 7. Redundant control systems are size and shape of the process vessel e. Manufacturers may use one of many different measurement often critically important. Is this technologies to determine level, including radar, ultrasonic, float statement true or false?

Because it is often critical to avoid tank overflow, redundant level control systems are sometimes employed. What type of control strategy is fluid, temperature loops tend to be relatively slow. Feedforward often used to increase the speed control strategies are often used to increase the speed of the of a temperature control loop? RTDs or thermocouples are typical temperature sensors. Temperature transmitters and controllers are used, although it is not uncommon to see temperature sensors wired directly to the input interface of a controller.

The final control element 1 Feedforward control for a temperature loop is usually the fuel valve to a burner or a valve 2 Feedback control to some kind of heat exchanger. Sometimes, cool process fluid is 3 Cascade control added to the mix to maintain temperature Figure 7.

A multivariable control loop controls one process variable by sending signals to a controller of a contains a primary and different loop that impacts the process variable of the primary loop. Is the fluid in a tank that is heated by a steam jacket a pressurized steam this statement true or false?

To control the primary variable temperature , the primary master controller signals the secondary slave controller that is controlling steam pressure.