Podcast
Questions and Answers
A transducer translates a mechanical signal into a thermal signal.
A transducer translates a mechanical signal into a thermal signal.
False
A sensor is responsible for adjusting the process conditions in a control system.
A sensor is responsible for adjusting the process conditions in a control system.
False
Transmitters convert a signal from a sensor into a standard signal to be sent to a controller.
Transmitters convert a signal from a sensor into a standard signal to be sent to a controller.
True
Final control elements can include valves that open or close based on controller commands.
Final control elements can include valves that open or close based on controller commands.
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An indicator is used to measure and monitor different variables in a process system.
An indicator is used to measure and monitor different variables in a process system.
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Calculating the size of a control valve is not a relevant aspect of process dynamics and control.
Calculating the size of a control valve is not a relevant aspect of process dynamics and control.
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A converter is a device that performs a mathematical function using received input.
A converter is a device that performs a mathematical function using received input.
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The transmission line is a crucial component that directly measures process variables.
The transmission line is a crucial component that directly measures process variables.
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A standard temperature transmitter typically outputs a signal of 0–20 mA.
A standard temperature transmitter typically outputs a signal of 0–20 mA.
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The input range of a sensor must be compatible with the output signal from the transmitter.
The input range of a sensor must be compatible with the output signal from the transmitter.
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Gain Km of a transmitter increases when the span is changed.
Gain Km of a transmitter increases when the span is changed.
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Transmitters are generally designed to be non-direct acting, where the output signal decreases as the measured variable increases.
Transmitters are generally designed to be non-direct acting, where the output signal decreases as the measured variable increases.
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A liquid column pressure gauge is an example of a temperature transmitter.
A liquid column pressure gauge is an example of a temperature transmitter.
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Most commercial transmitters can have their input range adjusted.
Most commercial transmitters can have their input range adjusted.
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The relation between temperature transmitter input and output remains unchanged regardless of zero adjustments.
The relation between temperature transmitter input and output remains unchanged regardless of zero adjustments.
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Pressure transmitters convert pressure into capacitance variation.
Pressure transmitters convert pressure into capacitance variation.
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The measurement time constant, represented as m, describes how quickly a measuring element can fully sense changes in a system.
The measurement time constant, represented as m, describes how quickly a measuring element can fully sense changes in a system.
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The final control element is responsible for manipulating the process variable, like flow rate.
The final control element is responsible for manipulating the process variable, like flow rate.
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A control valve is less commonly used than a variable speed pump for handling abrasive liquids.
A control valve is less commonly used than a variable speed pump for handling abrasive liquids.
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The valve body of a control valve is designed to contain a fixed orifice that does not change.
The valve body of a control valve is designed to contain a fixed orifice that does not change.
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The valve seat of a control valve is always made of soft polymer to ensure tight shutoff.
The valve seat of a control valve is always made of soft polymer to ensure tight shutoff.
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Actuators used in control valves can be powered by pneumatic, electric, or hydraulic means.
Actuators used in control valves can be powered by pneumatic, electric, or hydraulic means.
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The position of the valve stem in a control valve does not affect the flow rate.
The position of the valve stem in a control valve does not affect the flow rate.
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The actuator spring in a control valve provides the force necessary for closing but not for opening the valve.
The actuator spring in a control valve provides the force necessary for closing but not for opening the valve.
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The dynamic behavior of a control valve can be approximated by a second-order transfer function.
The dynamic behavior of a control valve can be approximated by a second-order transfer function.
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The valve time constant, $ au_v$, is typically larger than the largest process time constant, $ au_p$.
The valve time constant, $ au_v$, is typically larger than the largest process time constant, $ au_p$.
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Control valves are always fail-close by default.
Control valves are always fail-close by default.
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A larger size control valve can exhibit slower dynamics compared to smaller valves.
A larger size control valve can exhibit slower dynamics compared to smaller valves.
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The valve positioner adjusts the pneumatic control signal based on the comparison of actual and desired stem positions.
The valve positioner adjusts the pneumatic control signal based on the comparison of actual and desired stem positions.
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The volumetric flow rate $q$ is not part of the valve sizing equation.
The volumetric flow rate $q$ is not part of the valve sizing equation.
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The specific gravity of the liquid, $gs$, influences the control valve's sizing and operation.
The specific gravity of the liquid, $gs$, influences the control valve's sizing and operation.
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In a control valve system, 0 ≤ valve stem position ≤ 1 represents the full range of possible stem positions.
In a control valve system, 0 ≤ valve stem position ≤ 1 represents the full range of possible stem positions.
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A control valve is considered fully open when its characteristic value is 1.
A control valve is considered fully open when its characteristic value is 1.
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The valve coefficient, Cv, determines the process fluid type in the system.
The valve coefficient, Cv, determines the process fluid type in the system.
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Rangeability in control valves refers to the ability to adjust the flow rate over a broad range of values.
Rangeability in control valves refers to the ability to adjust the flow rate over a broad range of values.
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Equal percentage trim design provides a constant flow change for each incremental movement of the valve stem.
Equal percentage trim design provides a constant flow change for each incremental movement of the valve stem.
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A non-flushing liquid is used in a system solely for cleaning purposes.
A non-flushing liquid is used in a system solely for cleaning purposes.
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To size a control valve, the pressure drop across the valve must be fixed.
To size a control valve, the pressure drop across the valve must be fixed.
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The difference between the pump characteristic curve and the valve pressure drop curve is represented as ΔPm.
The difference between the pump characteristic curve and the valve pressure drop curve is represented as ΔPm.
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The units conversion factor in valve sizing is denoted by the letter N.
The units conversion factor in valve sizing is denoted by the letter N.
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Study Notes
Control System Instrumentation
- Key components include transducers, transmitters, final control elements, sensors, transmission lines, and calculation of control valve sizing.
Process Control: Key Concepts Revisited
- Diagrams of a process control system are shown depicting various components including thermocouples, heaters, and valves.
Process Control: Key Concepts Revisited (Figure 10-1)
- A stirred-tank chemical reactor is illustrated.
- The diagram shows flow inputs and outputs, heating coil, a controller, and measuring components.
Instrumentation in Process Control
- Various devices and instruments are used to measure, monitor, and control process variables.
- Sensors/Transducers translate mechanical signals to electrical signals.
- Converters change one signal type to another.
- Transmitters convert sensor readings to standard signals and transmit to controllers.
- Final Control Elements adjust process conditions (e.g., valves).
- Indicators/Displays visually represent process conditions.
- Controllers receive inputs, process data, and output control signals.
Sensor, Transmitter & Transducer
- Measurement ranges (span) are defined for different variables (e.g., temperature, flow, pressure, level, composition).
- Performance and cost, reliability, and materials of construction are factors of instrumentation considerations (e.g., thermocouples, flow meters).
- Methods for measuring variables include thermocouples, resistance temperature detectors (RTDs), filled-system thermometers, and pressure gauges, among others.
Examples of Instrumentation
- Thermocouples and float-activated level sensors are examples of actual instrumentation components.
- Pressure Gauge Liquid Columns are also shown as an example of instrumentation.
- Orifice plates are also shown for flow measurement.
Sensor transmitter / Transmitter
- Standard transmitters and their output signal ranges are discussed (eg., 4-20 mA).
- The functionality of a standard temperature transmitter is explained in terms of input and output signals.
- Specific calculations relating to output signal ranges and variables (eg., temperature) are given.
Sensor transmitter / Transmitter (continued)
- A diagram shows a linear instrument calibration, including zero and span points.
- Transfer functions are shown for various transmitters.
- Time constants for measuring components (e.g., control valves) are described.
Final Control Element
- The final control element manipulates the process variable (eg., flow rate).
- Control valves and variable speed pumps are prominent examples
- Actuators, such as air-to-open (A-O) and air-to-close (A-C) pneumatic actuators are important for control valve function
Control Valve: Valve Positioners
- Valve positioners are mechanical or digital feedback controllers.
- Valve positioners adjust pneumatic signals to control valve position.
Control Valve: Dynamic Behaviour
- Control valve dynamic behavior is approximated by a first-order transfer function.
- Time constants (
τ_v) for control valves are typically smaller than process time constants (τ_p). - Model parameters depend on step signal size for control valves.
Control Valve: Sizing
- Equations for control valve sizing (eg., volumetric flow rate (q), pressure drop(ΔP), specific gravity(gs), and valve coefficient (Cv)) are presented.
- Rangeability (R*) for control valves is also defined.
Control Valve Characteristics (Trim)
- Different control valve trim types and their characteristics are described (e.g., linear, quick opening, equal percentage).
Selection of an Equal Percentage Trim
- Steps to select an equal percentage trim system are shown (and calculations related to the steps are provided).
- Diagrams of specific components (e.g., pump characteristics) are shown in the context of trim calculations.
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Description
This quiz covers essential components of process control systems, including transducers, sensors, transmitters, and indicators. It explores how these elements interact with each other and their role in maintaining process conditions. Additionally, you'll gain insights into the characteristics of measurement and control devices.
