30 Questions
What are the three tasks that are always present in control loops?
Measurement, Comparison, Adjustment
Define Process Variable.
The condition of a variable being observed in a process that can change the manufacturing process.
Give examples of common process variables.
Pressure, Flow, Level, Temperature, Density, pH, Liquid interface Mass, Conductivity
What is a Set-point?
A value for a process variable that is desired to be maintained.
Explain Measured Variable.
The condition of a process that must be kept at the designated set-point.
Provide an example where the measured variable is different from the process variable.
Measuring flow into and out of a storage tank to determine tank level.
What is the manipulated variable in a control system?
The variable that is changed to keep the measured variable at setpoint.
Define 'controller' in the context of process control.
The element that decides and commands actions to reduce the error.
Explain what 'controller output (CO)' represents.
The signal from the controller to the final control element.
What is meant by a 'loop' in process control?
The signal flow from measurements to error detector, controller, and final control element.
Define 'instrument' as used in process control.
Any device used for indicating or measuring physical quantities or conditions.
What are 'sensors' in the context of process control?
Devices that detect physical variables and provide measurable outputs.
What is the Process variable in the context of a pressure sensor measuring the level of liquid?
Level of liquid
Identify the Measured variable when a pressure sensor is used to measure the liquid level.
Pressure of liquid
What is the Manipulated variable when controlling the liquid flow based on the pressure measured by a sensor?
Liquid flow
What device is used to change the value of the Manipulated variable in a control system?
Final control element
What is the variable that is changed to maintain the Measured variable at a specific setpoint in a control system?
Manipulated variable
In the context of controlling a loop in a process, what is the proper sequence of Adjustment, Comparison, and Measurement?
Measurement, Comparison and Adjustment
What is the purpose of an Error Detector in a control system?
Detects the difference between actual (measured) values and the corresponding set points (desired values).
In a process control system, what is the role of the Manipulated Variable?
To control the process by adjusting a factor such as steam flow or fluid flow.
What is the feedback path in a control system and how does it contribute to the control process?
The feedback path includes the measured variable, which provides information to the controller for adjustments.
Define the Process Variable in the context of process control.
The process variable is the parameter being controlled, like fluid temperature or flow rate.
What is the final control element in a control system and how does it impact the process?
The final control element, like a valve or pump, directly affects the process variable based on controller inputs.
Explain the role of a Sensor in a process control system.
The sensor, like a temperature sensor, measures the process variable and provides feedback to the controller.
What is the range of a sensor or measurement?
The lowest and highest values it can measure within its specification.
Define the span of a sensor.
The high end of the Range minus the low end of the Range.
How is accuracy of an instrument determined?
By comparing an indicated reading to that of a known standard.
How is accuracy typically specified?
As a plus-or-minus deviation from true, normally specified as a percentage of reading, span, or full-scale reading or deflection (% FSD).
What is the range of a pressure sensor that has a range of 25 to 150 psi?
25 to 150 psi
Why should instruments be selected with a range that includes expected disturbances and possible failures?
To ensure that the sensor can measure all values a process will normally encounter.
Test your knowledge of control systems by identifying and labeling process variables, measured variables, and manipulated variables in a given diagram. Additionally, determine the correct sequence of controlling a loop based on the options provided.
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