Instrumentation and Control Fundamentals Exam Study Guide.
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Instrumentation and Control Fundamentals
Institution
Instrumentation And Control Fundamentals
Instrumentation and Control Fundamentals
Exam Study Guide.
Process - answerA series of actions or operations resulting in a change or a change of state
Process System - answerA system that changes the state of the fluid inside the system
Process Control System - answerMeasures the value of a pr...
Instrumentation and Control Fundamentals
Exam Study Guide.
Process - answer✔A series of actions or operations resulting in a change or a change of state
Process System - answer✔A system that changes the state of the fluid inside the system
Process Control System - answer✔Measures the value of a process system variable and causes an action
to occur that will maintain the controlled variable as desired
Variable - answer✔A quantity that is subject to variation or change
Measured Variable - answer✔The condition, property or quantity that is being measured
Controlled Variable - answer✔Any variable that we need to control for the proper operation of the
system (e.g. temperature, pressure, level or flow)
Detected Variable - answer✔The quantity that is measured by an indirect measurement instrument to
provide an indication of the desired measured variable
Manipulated Variable - answer✔The process system variable that is directly acted on by the control
action
Control System Input - answer✔Any information collected by the control system
Control System Output - answer✔A signal produced by the control system to adjust the controlled
variable
Setpoint - answer✔The desired value or setting for the controlled variable
Error Signal - answer✔The difference between the setpoint and the measured variable
Feedback - answer✔The system response monitored in a closed-loop control system
Direct Measurement - answer✔Instruments that measure and show process parameters without any
conversion (e.g. Gage glasses, dip sticks or manometers)
Indirect Measurement Instrument - answer✔Instruments that are measuring devices that sense or
detect a physical property of the system 9the detected variable0 and convert a change in that property
into an indication
Range - answer✔The limit is in which a quantity can be measured
Span - answer✔The algebraic difference between the highest and lowest values of the quantity that can
be measured
Accuracy - answer✔The ability of an instrument to measure the actual value of a parameter
Precision - answer✔The degree of agreement between repeated results
Drift - answer✔The slow change of a displayed indication, in either direction, without a change in the
measured variable
Sensitivity - answer✔How well an instrument can detect and indicate small changes in input
Digital Display - answer✔Usually a numeric display of the instantaneous value of the measured variable
Analog Display - answer✔A continuous display representative of the process, and has an apparent range
and span
Parallax - answer✔The apparent change in the position of an object resulting from a change in the
position or direction from which the object is viewed by the observer
How to avoid parallax - answer✔Operators should stand directly in front of the display while reading
meters and gauges
When recording a reading - answer✔Record the "as-found" reading off the meter or gauge. DO NOT
round-off the reading into specification. Record the actual reading indicated on the meter or gauge.
Live zero - answer✔An indicator that has an input signal greater than zero when it is indicating zero. The
advantage of using a live zero is that it gives the operator and indication that a particular instrument has
failed.
Basic Instrument Channel - answer✔Provides an output that accurately and precisely represents the
measured variable and makes that measurement available for protection, indication or control of the
measured variable.
Detector - answer✔Also called a sensor or measurement element. The device that senses the detected
variable and generates a signal proportional to the detected variable
Transducer - answer✔A device that takes an input signal (the controlled or measured variable) in one
form (electrical, mechanical, pneumatic or hydraulic) and converts it into a signal of a different form that
is proportional to the input signal
Amplifier - answer✔Increases or boosts the process signal to a useable magnitude
Transmitter - answer✔Also called a driver. Used to transmit data from one instrument component
(usually the transducer or amplifier) to another component (usually a controller or indicating device)
when they are physically separated
Indicator - answer✔Displays the measured process variable to the operator. Indicators include such
things as meters, gauges, recorders and computer screens. Indicators provide a means to monitor
parameters and to verify alarms.
Controller - answer✔The purpose of a controller is to regulate the controlled variable (pressure,
temperature, level etc.) at some desired value.
The controller performs the following functions:
1) Receives the measured variable signal from the detector via the transducer/transmitter
2) Receives the setpoint signal (desired value). This is usually set manually.
3) Compares the measured variable to the setpoint.
4) Computes an error signal.
5) Amplifies the error signal to produce an output signal. The output signal is sent to a final control
element.
Alarm - answer✔Also called an annunciator. A warning device that informs the operator that a
controlled parameter (e.g. Temperature, pressure, flow or level) exceeds the normal operating limits or
control band.
Final Control Element - answer✔Acts directly on the process system to regulate the controlled variable
Bistable control/protective device - answer✔Opens or closes electrical contacts that produce a control
action or an alarm when the measured variable reached a predetermined setpoint or limit. A bistable
device can only be ON or OFF.
Proportional Control/Protective Device - answer✔Produces an output that is proportional to the
difference between the measure variable and its setpoint
Redundant Instrument Channels - answer✔Used where process information is vital for the safe
operation of process equipment.
Dead band - answer✔The range through which the input signal can change with no change in the output
Ambient Temperature Variations - answer✔Will affect the accuracy and reliability of process
instrumentation. Variations in ambient temperature can directly affect the electrical resistance of
components in the instrumentation circuitry and therefore affect the calibration of electric/electronic
equipment.
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