Instrumentation in Industrial Applications

Introduction to Instrumentation and Control Engineering

• The objectives of this course include gaining understanding of basic concepts and principles in instrumentation and control engineering, explaining instrument classifications, and recognizing control loop elements.
• Measurement is the science of determining physical variable values. It involves comparing an unknown quantity to a predefined standard and expressing the result numerically.

Measurement

• Measurement (also called metrology) is the science of determining values of physical variables.
• It's a method of obtaining information about physical values of a variable.
• Measurement of a given quantity is fundamentally an act or result of comparison between the quantity (whose magnitude is unknown) and predefined standards. The result is expressed numerically.

Why do we measure?

• Students to think of answers to this question and prepare to share it with the class.

The Needs for Measurement

• Carat was initially the weight of carob beans, and today is standardized as 0.2 grams. This is used to measure precious stones like diamonds.

Metric System

• A table of prefixes, symbols, and multiplying factors for the metric system is provided.

SI Units: Systemes Internationales d'Unites

• A table defining the seven fundamental quantities of the International System of Units (SI) is present, detailing their names, symbols and SI units

Derived Quantities and their SI Units

• A second table shows common derived quantities, their symbols and SI units, with formulas for some.

Standards

• Various standards organizations are listed, including ISO, IEC, ANSI, SCC, BS, and TSE.

Standard Bodies

• International standards are defined by international agreements.
• Primary standards are maintained at institutions around the world, their primary function is to check the accuracy of secondary standards.

Instrumentation

• Instrumentation is used in almost every industrial process and generating system.
• Instrumentation provides the means of monitoring, recording, and controlling a process to maintain it at a desired state.
• A typical industrial plant, like an electric generating station, generates many process variables that must be measured and manipulated.

Process Variables

• Variables such as boiler level, temperature, pressure, turbine speed, and generator output require prudent control for a plant's safe and effective operation.
• Instrumentation provides automatic control of those processes, allowing for the indication of process conditions, enabling corrective action if necessary.

Instrumentation based on industrial application

• A collection of instruments, devices, and functions are used to measure, monitor, or control industrial processes and machines.

What is an instrument?

• A device for direct or indirect measurement, monitoring, and/or control of a variable.
• Includes indicators, controllers, and other devices like annunciators, buttons, and switches.

Measurement Instrument

• A device that detects various physical changes in a process and converts them into a usable form of information for the user.

Instrument Examples

• Images/diagrams of various instruments are provided.

Classification of Instruments

• Critical instruments are essential for product quality and safety, and a failure in specifications can compromise these.

• Non-critical instruments are vital for operational significance, but not directly related to product quality and safety.

• Reference-only instruments have functions that are not critical to the operation and are not involved in quality decisions.

Control Systems and Process Control

• Control in process industries refers to the regulation, command, and direction of all process aspects.
• Two primary types of control systems are manual control and automatic control.

System

• Arrangement of physical components linked/connected so they behave or act as an entire unit.
• A system refers to the methods of changing or refining raw materials to create final products.

Process Control

• Process Controls are essential for maintaining plant processes at their desired states.
• Process control range from simple manual actions to sophisticated computer logic controllers.

Control Systems

• A system whose output can be regulated by altering its input is a control system.
• Control systems are often built with multiple smaller control systems.

Block Diagram of Control System

• A diagram illustrating the input-processing-output sequence in a control system is provided.

Mathematical Equation of Control System

• A simple control system can be illustrated using a mathematical formula (X + 5 = Y), where X is the input, Y is the output, and 5 is acting as the control system.
• The system's output (Y) can be altered by changing the input parameter value (X).

Explain the shown example of a simple Control System

• A diagram of a water level control system (with components like pulleys, cords, a stopper, water container, a ball float, and stopcock) is provided.

Open Control Loop

• A process variable isn't compared against a setpoint.
• Actions are taken independently of the current status of the process.

Closed Control Loop

• A process variable is measured and compared to a set point.
• Actions are taken in response to deviations from the set point.

In Open Loop Control Systems

• Three components are present: Input, Controller, and Output signals
• The input signal is directly fed to the controller.
• The output signal from the controller has no effect on the input signal.

Example of an Open Loop Control Systems

• The operation of a clothes dryer, where the dryer stops after a set time, is an example, regardless of whether the clothes are completely dry.

Block Diagram of a Cloth Dryer Control System (Example)

• A block diagram of a clothes dryer system showing the input (Desired Time), controller (Timer), output (Heating Elements), and process (Clothes Drying) is shown.

Example of Open Loop Traffic Light Control System

• The operation of a traffic light system is a further example of open loop system.

Closed Loop Control System

• An advanced automated system that generates desired outputs using inputs, controllers, and feedback elements.

• Output is fed back to the controller, allowing for comparison against input signal to determine errors.

Example of an Closed Loop Air Conditioner System

• The operation of air conditioners adjusting room temperature by sensing and responding to variations is an illustration of closed loop control, using feedback loop to maintain desired temperature.

Four Basic Elements of a Control Loop:

• Primary Element/Sensor
• Secondary Element/Signal-Generating Element
• Controlling Element/Controller
• Final Control Element

Primary Elements/Sensors

• Measure process parameters and variables based on unique physical, chemical, thermo-electrical phenomena.
• They generate an output signal indicative of the process variable.
• Process Variables sensed are not transmittable unless converted to an electric (or pneumatic) signal by a secondary element

Primary Element Examples

• Sensors
• Detectors (detect presence of something like flammable gases or discrete parts)..

Secondary Elements/Signal-Generating Element

• Primarily transduce to convert different physical quantities into electrical/electronic signals
• They convert readings from sensors into standard signals for monitoring and control applications.

Transmitter Examples

• Converters
• Transmitters

Types of Signal

• Analog Signals (no discrete positions or states, value changes) :
• Pneumatic (3-15 psi)
• Electrical (4-20 mA (Current) or 1-5 VDC (Voltage))
• Digital Signals (binary digit signals to represent continuous values or discrete states)

Controlling Element/Controller

• The brain of the control system.
• Receives data from the measurement instrument, compares it to setpoints, and signals control elements for action, if necessary.

Common examples of controller

• Programmable Logic Controller (PLC)
• Distributed Control System (DCS)

Final Control Element

• The component of a control system that physically alters the manipulated variable (such as increasing/decreasing fluid flow)
• Actuators and Control Valves are common examples

Common Final Control Elements

• Actuators: Component in a final control device which causes a physical change.
• Control Valves: Manipulates the flow rate of fluid/gases; Control switches manipulate the electric energy entering the system

Instrument applications

• Factory automation instruments
• Plant safety instruments
• Product quality instruments
• Environmental condition instruments
• Process variable measurement and control instruments

Piping & Instrumentation Diagram Fundamentals

• A P&ID is a design document showing equipment interconnected with control instrumentation.
• P&IDs use standardized symbols for elements like mechanical equipment, valves, and instrumentation
• Tag numbers associate specific devices and their functions

Objectives: Understanding a P&ID Layout

• Symbology, Piping (that connects equipment), Lines and instruments (to monitor and control processes).
• Tag numbers and functional identifiers are essential for recognizing specific components..

Piping and Instrumentation Diagram

• An overall process plant design document.
• Shows how process equipment and instrumentation are interconnected.
• Utilizes symbols to depict mechanical equipment like piping components, valves, and instrumentation.

P&IDs

• Piping and instrumentation drawings, or P&IDs, are the schematics used within instrumentation and control systems

Process Flow Diagram

• A fundamental representation of how raw materials transform into finished products.
• Shows material and utility flows, with pressure and temperature ratings for each piece of equipment.

Instrument List

• An alphanumeric list of instrumentation in a facility and its related functional details.
• References other documents for installation details.

Logic Diagrams

• Illustrate on-off/sequential functions of a process plant.

Instrument Loop Diagrams

• Schematic representations of control loops, including their hydraulic, electric, magnetic, and pneumatic components.

Installation Details

• Outline how instrumentation/control system components are connected to the process.
• Details the requirements for correct instrumentation/control component installation

Location Plans

• Provide orthographic views of the plant at scale, showing instrument and control system component placement.
• Display other critical plant elements including instrument racks, control panels, power panels etc.

Different Engineering Documents

• Process Flow Diagram, Piping & Instrumentation Diagram (P&ID), Instrument List, Logic Diagrams, Instrument Loop Diagram, Installation Details, and Location Plans summarize all information needed for the process.

Instrument Ranges/Spans

• Instrument range refers to an instrument’s capacity to measure variables.
• Calibration range identifies the output and measures variables within the range.
• Instrument span is the difference (or distance) between the upper and lower range limit values.

Discrete Process Measurement

• Measurement of true-or-false conditions
• Discrete sensors use "switches" to indicate when a measured quantity exceeds or falls below a specified value.

"Normal" Status of a Switch

• The electrical status of a switch's contacts under minimal stimulus.
• Conditions are normally classified as "normally open" (NO) or "normally closed" (NC).

Hand Switches

• Electric switches operated manually via toggle, pushbutton, or rotary actions.

Limit Switches

• Detect physical object movement through direct contact.
• Status as "normal" when not in contact.

Proximity Switches

• Detect proximity to an object without physical contact.
• Use magnetic, electric, or optical methods for detection.

Pressure Switches

• Detect the presence of fluid pressure using diaphragms or bellows.

Level Switches

• Detect liquid or solid level in a vessel using floats as level sensing elements.

Temperature Switch

• Detect the temperature using bimetallic strips (two dissimilar metals).

Flow Switches

• Detect fluid flow through pipes using "paddles" as the flow sensing elements.

Discrete Control Elements

• On/Off Valves are the equivalent of an electrical switch.

On/Off Valves

• Regulate, direct, or control fluid flow by opening, closing, or partially obstructing passageways.

Process Valve Types

• Various valve types illustrated include ball, globe, butterfly, Saunders, angle, check, diaphragm, pressure relief, ball check valves.

Valve Actuator Types

• Devices that provide the motive force to operate the valve mechanism.
• Common types include pneumatic, hydraulic, electric motor, and hand (manual) actuators.

Control Valve Actuators

• Provide motive force to control valve mechanisms.

Hydraulic Actuators

• Use liquid pressure to move valve mechanisms.
• High pressure ratings are useful for overcoming friction in piston-type actuators.

Electric Actuators

-Use electric motors to actuate large valves. -Often used for on-off ("shut-off") and throttling valves. -Worm gear sets are typical to reduce high rotational speed for efficient valve movement.

Solenoid Actuators

• Utilized in small-sized valves (typically up to 1-inch).
• Employ the magnetic field of a solenoid.

Hand Actuators

• Use hand power for valve actuation.

Valve Failure Modes

• Ways in which a valve may not function as intended when power is lost or other issues arise.

Fail-Safe Concepts

• A mechanism that automatically mitigates harm to equipment or people should the primary system fail.

Fail-Open

• Indicates a valve will open if a system signal is lost/interrupted.

Fail-Closed Concept

• Indicates a valve will close if system signal is lost/interrupted.

Fail-Locked

• Indicates a valve will remain in its current position during a system failure.

Fail-Indeterminate

• Indicates that the valve's position cannot be determined during a failure.

FL/Drift Open and FL/Drift Closed

• Valves operate as in "Fail-last" for safety.
• They are locked in their last (open or shut) position during air or signal failure.

Applications of the Strain Gauges

• Measure strain (for analyzing internal forces on items) -Measure other related quantities from the change in resistance due to applied force like pressure, displacement, and acceleration.

Differential Capacitance Sensors

• Another type of pressure sensor based on the change of capacitance with applied pressure
• A capacitor is used as a component to store electrical charge.
• Two metal plates are separated by an insulator (forming a capacitor) in the sensor

Differential Pressure Transmitters

• Common method of measuring differential pressures in industry
• Outputs an electrical signal proportional to the pressure differential between two inputs.

Other Valve Types

• Check valves prevent backflow, opening when pressure moves forward and closing against backflow.
• Plug valves have a rotating plug inside the valve body. Valves are commonly used to control liquid or gas flow.

Indicators

• Materials specifically designed to change color with different pH values.
• Used to visually determine if a measured substance is more or less acidic or alkaline.

Colorimeter

• Device used for measuring pH using chemical reaction of a supplied reagent
• Involves adding the supplied reagent and then comparing color to a reference wheel/chart to determine pH value.

Potentiometric pH Measurement

• Based on electrochemical measurements. -Special pH-sensitive electrodes are used for measuring the voltage of the solution and this voltage is dependent on the pH value.

pH Measurement Methods

• Indicators, use of chemical reagents which change color based on pH of substance measured.
• Colorimetry, a device to measure color change of a test subject in correlation to a reference chart.
• Potentiometry, an electrochemical method using electrodes with standard potentials to measure pH value, according to Nernst equation