Controllers And Detectors

Front 1

is a system of integrated elements whose function is to maintain a process variable at a desired value or within a desired range of values.

Back 1

control system

Front 2

is the stimulus applied to a control system from an external source to produce a specified response from the control system.

Back 2

Control system input

Front 3

is the actual response obtained from a control system.

Back 3

Control system output

Front 4

Control systems are classified by the control action (the method for activating the control system to produce the output).
An _____ is one in which the control action is independent of the output.

Back 4

open-loop control system

Front 5

Control systems are classified by the control action (the method for activating the control system to produce the output).
A_____ is one in which control action is dependent on the output.

Back 5

closed-loop control system

Front 6

information in a closed-loop control system about the condition of a process variable.

Back 6

Feedback

Front 7

is the process variable that is maintained at a specified value or within a specified range.

Back 7

controlled variable

Front 8

is the process variable that is acted on by the control system to maintain the controlled variable at the specified value or within the specified range.

Back 8

manipulated variable

Front 9

In any automatic control system, the four basic functions that occur are:

Back 9

Measurement
Comparison
Computation
Correction

Front 10

The three functional elements needed to perform the functions of an automatic control system are:

Back 10

A measurement element
An error detection element
A final control element

Front 11

System or process through which a particular quantity or condition is controlled.

Back 11

Controlled System

Front 12

The ____ are components needed to generate the appropriate control signal applied to the plant.
These elements are also called the “controller”

Back 12

control elements

Front 13

The ___ are components needed to identify the functional relationship between the feedback signal and the controlled output.

Back 13

feedback elements

Front 14

The ___ is an external signal applied to the summing point of the control system to cause the plant to produce a specified action.

This signal represents the desired value of a controlled variable and is also called the "setpoint."

Back 14

reference point

Front 15

The ____ is the quantity or condition of the plant which is controlled.

This signal represents the controlled variable.

Back 15

controlled output

Front 16

The ____ is a function of the output signal.

It is sent to the summing point and algebraically added to the reference input signal to obtain the actuating signal

Back 16

feedback signal

Front 17

The ____ represents the control action of the control loop and is equal to the algebraic sum of the reference input signal and feedback signal.

This is also called the "error signal."

Back 17

actuating signal

Front 18

The ______ is the variable of the process acted upon to maintain the plant output (controlled variable) at the desired value.

Back 18

manipulated variable

Front 19

is an undesirable input signal that upsets the value of the controlled output of the plant.

Back 19

disturbance

Front 20

____ is the ability of a process to store energy.
The walls of the tubes in the lube oil cooler, the cooling water, and the lube oil can store heat energy.
This energy-storing property gives the ability to retard change.
It will take a period of time for more energy to be removed.

Back 20

Capacitance

Front 21

____ is that part of the process that opposes the transfer of energy between capacities.
The walls of the lube oil cooler oppose the transfer of heat from the lube oil inside the tubes to the cooling water outside the tubes.

Back 21

Resistance

Front 22

____ is time required to carry a change in a process variable from one point to another in the process.
If the temperature of the lube oil is lowered by increasing the cooling water flow rate, some time will elapse before the lube oil travels from the lube oil cooler to the temperature transmitter.

Back 22

Transportation time

Front 23

If the transmitter is moved farther from the lube oil cooler, the transportation time will increase.

not just a slowing down or retardation of a change; it is an actual time delay during which no change occurs.

Air signal vs. electric signal

Back 23

Transportation time

Front 24

A ___ is a device that has two operating conditions: completely on or completely off.

Back 24

two position controller

Front 25

This device provides an output determined by whether the error signal is above or below the setpoint.
The magnitude of the error signal is above or below the setpoint.
The magnitude of the error signal past that point is of no concern to the controller.

Back 25

Two Positron Controller

Front 26

Four modes of control commonly used for most applications are:

Back 26

Proportional
proportional plus reset (PI)
proportional plus rate (PD)
proportional plus reset plus rate (PID

Front 27

In the _______ mode, there is a continuous linear relation between value of the controlled variable and position of the final control element.

Controller output (i.e. amount of valve movement) is directly proportional to the amount of deviation.

Back 27

proportional (throttling)

Front 28

____ perform the function of a controller and provide additional controls and indicators to allow an operator to manually adjust the controller output to the final control element.

Back 28

Control stations

Front 29

An advantage of ____ actuators is their quick operation. Also, they are much easier to install than pneumatic or hydraulic actuators.
Disadvantages:
Two positions only: fully open and fully closed.
They don't produce much force, so they usually only operate relatively small valves

Back 29

solenoid

Front 30

Can be used to throttle valve position.
Motor reverses its rotation to either open or close the valve.
The clutch and clutch lever disconnect the electric motor from the gear assembly and allows the valve to be operated manually with the handwheel.
Most electric motor actuators are equipped with limit switches, torque limiters, or both.
Limit switches de-energize the electric motor when the valve has reached a specific position.
Torque limiters de-energize the electric motor when the amount of turning force has reached a specified value
The turning force normally is greatest when the valve reaches the fully open or fully closed position.
This feature can also prevent damage to the actuator or valve if the valve binds in an intermediate position.

Back 30

Electric Motor

Front 31

However, when a large amount of force is required to operate a valve (for example, the main steam isolation valves), _____ are normally used

Back 31

hydraulic actuators

Front 32

____ are used to control steam admission based on a controlling oil signal.

Back 32

Hydraulic actuators

Front 33

_____ are capable of placing the valve in any position but do not permit automatic operation.
Handwheels fixed to the stem, hammer handwheels, and handwheels connected to the stem through gears.
Hammer handwheel moves freely through a portion of its turn and then hits against a lug on a secondary wheel.
Secondary wheel is attached to the valve stem.
With this arrangement, the valve can be pounded shut for tight closure or pounded open if it is stuck shut

Back 33

Manual actuators

Front 34

CONTROL STATIONS:In many cases, controller output signals of the automatic mode and manual mode may not be the same.

If the controller were directly transferred from automatic to manual or manual to automatic, the controller output signal could suddenly change from one value to another.
The final control element would experience a sudden change in position or "bump”.
This can cause large swings in the value of the process variable and possible damage to the final control element

Bumpless transfer is the smooth transfer of a controller from one operating mode to another.
To ensure a bumpless transfer from manual to automatic, the manual output signal, indicated by the output meter, is adjusted to match the controlled variable value to setpoint.

_____ describes a control station in which the non-operating mode output signal follows (tracks) the operating mode output signal.

Back 34

Self-balancing