Instrumentation & Control: An Overview

Introduction to Instrumentation & Control

• Instrumentation involves the design, equipping, and use of measuring instruments
• These instruments determine real-life conditions in a plant's process.
• It provides timely data for decisions and performance analysis, which is useful for industrial automation.
• Accuracy is important for the safety of people and instruments, product quality, and business profitability.
• Industrial automation enhances operational efficiency and product quality.
• It enhances workplace safety by automating hazardous tasks.

Instrumentation & Control (I&C)

• I&C studies measurement and control of process variables like pressure, temperature, humidity, flow, pH, force, and speed.
• Instrumentation Engineering and Control Engineering are the 2 branches of engineering within I&C.
• I&C plays a significant role in gathering information from a system and changing its parameters, making them key parts of control loops.

Instrumentation Engineering

• Instrumentation engineering focuses on the design, development, and maintenance of instruments and devices used for measuring, monitoring, and controlling.
• It integrates principles from various disciplines to ensure precise and reliable operation.
• Instrumentation uses devices like sensors and transducers to ensure accurate data collection.

Control Engineering

• Control Engineering, also known as "control systems engineering," applies control theory to design systems with desired behaviors.
• It applies gathered data within feedback systems to regulate and automate processes.

Control Methods

• Control methods employ sensors to measure the output variable of a device and provide feedback.
• Automatic control manages a device without the need for human inputs for correction.

Purpose of Instrumentation & Control

• Consists of quality control and conservation of energy and raw materials.
• Quality control helps maintain consistent standards and minimizes variation in production.
• Conserving energy and raw materials by optimizing resource utilization.
• Promotes sustainable production, lowers costs, and lessens environmental impact.
• Safety measures include protecting workers, equipment, and the environment.
• Ensures timely responses to potential risks, minimizing accidents.
• Savings in installation simplify setup processes, reduce installation time, and minimize costs.
• Provides better performance with fewer components and less complexity.
• Material balance and product accounting ensures accurate tracking of materials entering and leaving a system.
• These practices also enhance transparency and efficiency in process management.
• Coordination of process variables synchronizes multiple process variables for optimal system performance.
• Supports smooth operation and reduces fluctuations.
• Research & development enables precise measurements and control for experiments and innovation.
• Allows researchers to simulate, test, and refine processes, leading to advancements.
• Enterprise management integrates I&C into broad organizational strategies.
• Results in better resource allocation, process optimization, and overall business efficiency.

Instruments

• Instruments are used for direct or indirect measurement, monitoring, and/or control of a variable.
• Instruments measure or manipulate physical variables.

Classification of Instruments

• Critical instruments, if not conforming to specifications, could compromise product or process quality with pressure gauges representing an example.
• Non-critical instruments are not critical to product or process quality.
• Reference only instruments have a function with operational significance, such as operating logs.
• Reference only instruments are not critical to product quality and equipment operation, routine calibration and verification being examples.

Instrumentation Systems

• Instrumentation systems provide information about the physical value of some variable.
• They state a condition of a process fluid that can change the manufacturing process.

Elements of Instrumentation Systems

• Sensor (primary sensor) is the first element in any measuring system.
• It is effectively in contact with the process and gives an output.
• Examples include liquid in glass thermometers, thermocouples, and strain gauges.
• Mercury in glass thermometers are a complete measurement system.
• Other sensor types are only part of a measurement system.
• Variable Conversion is needed when the output variable of a primary transducer is in an inconvenient form and needs to be converted.
• Displacement-measuring strain gauges may require conversion of varying resistance into change in voltage with a bridge circuit.
• A transducer is a primary sensor combined with a variable conversion element.
• A Signal Processing Element improves the quality of the output of a measurement system.
• An electronic amplifier amplifies the output to improve sensitivity and resolution.
• It is particularly important when the primary transducer has low output.
• Other types of signal processing elements filter out induced noise and remove mean levels.
• A transmitter includes signal processing and a transducer.
• Signal Transmission Element is needed when the observation or application point of output is some distance from the site of the primary transducer.
• More often follows from physical inaccessibility or unsuitable environmental factors.
• Signal transmission traditionally consisted of single or multi-cored cable.
• Fibre-optic cables offer low transmission loss and imperviousness to effects of electrical and magnetic fields.
• A Signal Presentation/Recording is the final optional element of signal utilization.
• the final element is omitted when the transmitted signal is fed directly into the control system.
• In other cases it takes the form of either a signal presentation or recording unit.

Control

• Control involves regulating, commanding, or directing various aspects of a process to ensure it operates within desired parameters.
• It has the goal to maintain optimal performance, minimize waste, and ensure safety.

Types of Control

• Requires human operators who are directly responsible.
• Requires the direct observation of measurements from instruments, with the manual manipulation of devices to achieve desired conditions.
• Advantages of manual control are flexible, allows human judgment for unexpected situations.
• Disadvantages of manual control is it is prone to human error, slower response time, less precise adjustments.
• Automatic Control uses instruments and systems to monitor process variables, Programmable Logic Controllers (PLC) and Distributed Control Systems (DCS).
• It makes adjustments automatically without human intervention.
• Advantages of automatic control is precise, consistent, faster response.
• Disadvantages of automatic control is higher initial cost and requires maintenance.

Process

• A process is a series of methods or steps used to transform raw materials into finished products.
• Processes focus on efficiency, quality, and cost-effectiveness.

Process Control

• Process control involves regulating or manipulating key variables in a process and aiming to maintain variables within acceptable limits to prevent equipment damage and ensure safety.

System

• A system is a collection or arrangement of physical components that work together to achieve a specific purpose.

Control System

• Control systems regulate or direct the behavior of another system or itself.
• They are composed of interconnected physical components.

Types of Control Loop

• In open control loop, there is no feedback to compare the process variable to a set point.
• Actions are taken from a pre-determined schedule.
• It cannot account for disturbances or variations in the process.
• Advantages of open systems are simple, inexpensive, and easy to implement.
• Disadvantages of open systems are prone to inefficiencies and errors.
• Closed Control Loop uses feedback to maintain process variable at desired set point.
• Continuously measures a variable and makes adjustments to correct variations.
• Advantages of open systems are accurate, self-correcting, responsive to change.
• Disadvantages of open systems are more complex components, slower in responding to rapid changes.

Instrumentation & Control Loop

• Instrument loop combines two or more interconnected instruments or control functions to manage and regulate a process variable.

Instrumentation & Control Loop - Elements

• Process: the operation where raw materials are transformed into desired products.
• Measuring Element: a device that senses and measures a process variable, converting it into a signal.
• Receiving Element: a controller or indicator that interprets the signal from the measuring element and determines the necessary action.
• Final Control Element: a valve or motor that directly manipulates the process based on signals to maintain desired conditions.

Instrumentation & Control Loop - Foundational Concepts

• Process Variable: the property of a process that is measured and controlled.
• Set Point (SP): the target value or desired level defined by an operator or system.
• Controller Output: the signal sent by the controller to the final control element in response to deviations.
• Manipulated Variable: the variable directly adjusted by the controller output to bring the measured variable closer to the set point.

Process Technology

• Process technology is made up of techniques, tools, equipment, and methods used to transform raw materials into desired outputs.
• Process technology includes design, development, and operation of systems and equipment in industries.

Process Diagrams

• They are simplified representations of a process showing the main process units and their interconnections.

Block Flow Diagram

• It provides a high-level overview without detailed equipment or process information.
• It is the simplest type of diagram.
• Only feed and product streams are identified.
• Input-output diagrams are useful in early stages of a process.
• Flow of raw materials and products may be included.
• Processes are broken down into basic functional elements.
• It identifies recycle streams and additional unit operations to achieve desired conditions.

Process Flow Diagram

• A more detailed representation of a process.
• It includes major equipment, process flowlines, but avoids showing piping details or minor instruments.
• Flow rate, composition, operating conditions, heat addition or removal, utility flows, major equipment symbols, names, identification, and other specific info.

Piping & Instrumentation Diagram

• It is a highly detailed schematic showing all piping, equipment, valves, and instrumentation.
• It includes tag numbers, process control loops, and interconnections, serving as a blueprint.
• An overall design document and demonstrates interconnection of process equipment.

Instrumentation Symbols

• Sets of symbols used to depict mechanical equipment, piping, valves, etc.

Types of Instrumentation Symbols

• Instrument Symbols: Circles, lines, letters, and numbers that provide information about the process.
• They may represent devices or indicate how devices are connected to each other, with shapes signifying function.
• Lines indicate location or mounting.
• Line Symbols: Represent connections between instruments, equipment, and processes.
• They visually convey the type of connection or signal being transmitted.

Types of Lines Symbols

• Show how process materials flow through the system and how instruments connect to the process.
• Thick solid lines designate main process piping that transports materials between major equipment.
• Thin solid lines designate instrument connection to the process, such as tubing.
• Signal Line Symbols represent the type of signal used to connect instruments, controllers, and the final control element.
  • Solid represents electrical or mechanical signals.
  • Dotted represent pneumatic signal, signals transmitted via compressed air systems commonly found in older industries.
  • Dashed represents hydraulic signal, transmitted via fluid systems.
  • Wavy represents software or digital signal, used for data communication.

Valve & Actuator Symbols

• Represent function, operation, and fail-safe positions of valves and their actuators.
• They indicate action of actuation and valve position during fail mode.
• Valves are usually drawn a bow tie shape.

Instrumentation Tagging System

• A complete alphanumeric code assigned to an instrument.

Tag Number

• A combination of both Functional Identifier and Loop Identifier, uniquely identifying each instrument in a plant or system.

Functional Identifier

• Letter code that specifies the type and function of the instrument.

Loop Identifier

• The numeric portion indicates the specific control loop or system the instrument belongs to.

Examples of Process Diagrams

• Consist of: Block Flow Diagram of production of Ethane from Ethanol, Process Flow Diagram for Ammonia Recovery & Liquid Ammonia Production Process.

Process Measurement

• Process measurement involves determining the magnitude or quantity of a specific variable.
• Determination is done by comparing the variable to a standard unit, providing a numerical value.
• Examples include thermometers and flow meters.
• Detection focuses on recognizing the existence or presence of a variable without quantifying it (e.g., smoke detector).
• Analog Measuring Devices generate proportional analog signals (continuous) from process variables for monitoring, display, or control.

Basic Characteristics of a Measuring Element

• Accurate Representation of Input where input variable is detected and reproduced without distortion.
• Ensuring the output accurately reflects the input variable.
• Proportional Input/Output Relationship allows consistent measurement and performance.
• No Effect of External Factors ensures that external factors do not impact the reliability and accuracy of measurements.

Definitions in Process Measurement

• Range: The limit or extent of variation, defined by a lower (LRV) and upper range value (URV).
• Span: units between LRV and URV, with the equation to solve Span = URV – LRV

Standard Instrumentation Signal

• Analog Signal: Continuous signal that can take on values within a range smoothly over time.
• Digital Signal: Uses binary digits (0,1) and operate in discrete value for representing data/conditions..

Continuous Process Measurement

• A real-time monitoring and measurement of process variables where data is continuously recorded and updated.
• Crucial in systems that require constant oversight.

Methods of Measurement

• Direct Method ensures the process variable is directly measured using a straight forward process
• Inferential Method involves indirect measurement of a process variable utilizing another related variable

Types of Measuring Elements

• Sensor initially detects process variable value, subsequently a corresponding and intelligible state or output.
• A Transmitter senses a process variable using a sensor and generates an output whose value changes dependent on the function of the sensor; Uses milliamps (mA).
• A Transducer receives information in the form of physical quantities and modifies it, producing output.
• It also converts a mechanical signal into an electrical, output in volts (V)

Single Point Type Measurement

• Depends on a fixed value of process variable.
• Reading shown as high (1) or low (0).

Continuous Type Measurement

• Ongoing measurement of a process variable.
• Allows constant monitoring.

Discrete Process Measurement

• Indicated by distinct, binary outcomes- discrete sensor shows is process is above or below setpoint.

Process Switch

• Monitors/controls process with switch based on predetermined conditional based on state.

Normal Status of a Switch

• Condition of electrical contacts when no physical stimulus is applied.

Classifications of Switches

• Normally open status means that contacts remain open when no stimulus is applied
• allows current to flow when switch is pressed; Normally-close contact is connected to an electrical when no stimulus is there
• If its pressed the circuit stops causing "form B" process

Types of Switches

• Hand switches are activated by hand, and proximity.
• Limit switches detect physical motion of an object and/or pressure.

Receiving Elements

• Receive signals from measuring instruments and processes into usable information.

Indicators

• Receives process variable signal, displays said value in actual engineering units.
• It shows only visible present value - provides real time info to current status of process.
• Analogue has needle, less reading; Digital is exact. Bar graph indicator for variable changes

Importance of Recording

• Acts as guide to operation and help troubleshoot to possible sources which is vital for management.

Controllers

• Receiving process variable signla and value of the screening or recording method makes for better output; calculated output can be form of a correction action - set operation to ensure process under a range.

Types

• Local, internal: operator adjusts; Remote, external external signal is there - pre-recorded that follows changes

Final Control Element

• Adjust measured variable - implement corrective action - set operation; variable changes using signal

Actuator

• Converts a controller into physical - action is desired causing the movement

Control Valves

• Main air flow - used for electric - manipulate electricity - entering

Range and Input/Output

• Uses electric pneumatic or pressure calculation - linear interpolation provides inbetween.

Importance of Instrumentation And Contol

• The industry demands high grade equipment and control; needs to produce without resources to save time energy/

Key Applications

• Factory automation in product lines - plant safety + workers w/ compliance; product qualify and manufacturing + environment regulations.