PI&D Exam (1)

Padding

Refers to the process of making a product of higher-quality than it needs to be to meet specifications.

Process Variable

A condition of the process fluid (a liquid or gas) that can change the manufacturing process in some way.

Error

Is the difference between the measured variable and the setpoint and can be either positive or negative.

Integral Mode

The continuously cause the controller to adjusts its output until the offset return to zero.

Time

The derivative mode adjustment is called.

Close control

It exists where a process variable is measured compared to a setpoint and action is taken to correct any deviation from setpoint.

Measured

The condition of the controlled variable at a specific point in time.,

Proportional Control

Percentage change of the controller input span will cause a 100% change in controller output.

PDI, Pressure Differential Indicator

Which means that the instrument displays differential pressure

Proportional Integral

Control is used where no offset can be tolerated where noise may be present and where excessive dead time is not a problem.

Dead zone

This type of control doesn’t actually hold the variable at setpoint but keeps the variable within proximity of setpoint in what is known as ________.

Cascade Control

A control system in which a secondary loop is set up to control a variable that is a major source of load disturbance for another control loop.

On-Off

A method in which the output signal at the controller is continually switch fully on and fully off.

Batch process

A system which only involve getting the correct proportions of ingredients hence it is not practical to have a continuous running process.

Magnitude

Error it is simply the deviation between the values of the setpoint and the process variable.

Offset

Sustained deviation of the process variable from the setpoint.

Fuzzy Control

A form of adaptive control in which controller use computer logic to make decisions about adjusting the process.

Converter

A device that converts one type of signal into another type.

4-20 mA

The most common standard electrical signal in a current signal.

Pneumatic signals

Signals produced by changing the air pressure in a signal pipe in proportion measured in a process variable.

Indicators

A human readable device that displays information about the process.

PLCs

Are usually computer connected to a set of input/output device.

DCSs

Controllers that in addition to performing control functions, provide readings of the status of the process maintain database and advanced man-machine interface.

Final control element

The part of the control system that acts to physically change the manipulated variable.

Transmitter

A device that converts reading from a sensor into a standard signal and transmits into a controller.

Actuators

Part of the final control device that cause a physical change in the final control when signaled to do so.

Controllers

Automatically compare the value of the PV to the SP to determine if an error exists.

Multistep controllers

Controllers that have at least one other possible position in addition to on and off.

Discrete Controllers

Controllers that have only on and off positions

A boiler operating in an on-off mode is an example of…

Feedback loop

Measures a process variable and sends the measurement to a controller for comparison to setpoint.

Flow control loop

Regarded as fast loops that respond to changes quickly.

Feedforward

A control system that anticipates load disturbances and control them before they can impact the process variable.

Feedforward plus feedback

A controller with a summing function totals the input from both the feedforward loop and the feedback loop and sends a unified signals to the final control element.

PID

For sudden set point or quick load changes in a slow response system..

Selective

Refers to control system in which the more important of two variables will be maintained.

PDAH

Indicates that the instrument is a differential pressure alarm that pressure is activated when the pressure is too low.

Proportional

The magnitude of the correction (change in controller output) is determined by the ___________ I mode of the controller.

Tuning

Reduce PB (increase gain) until the process cycles following a disturbance, then double PB (reduce gain by 50%).

Shutdown

Reset windup is common on ________ because the process variable may go to zero, but the set point has not changed therefore large error will drive the output to one extreme.

Compress the setpoint to the feedback signals.

Detector