Lecture 1: Intro to Process Control PDF

Lecture 1: Intro to Process Control Control Systems – ENGI 24495 Outline of Presentation Administration Process and Motion control Open- and closed-loop control Feedback and Feedforward control Instrumentation Piping and Instrumentation Diagram (P&ID) Hosn...

Lecture 1: Intro to Process Control Control Systems – ENGI 24495 Outline of Presentation Administration Process and Motion control Open- and closed-loop control Feedback and Feedforward control Instrumentation Piping and Instrumentation Diagram (P&ID) [email protected] Lecture1 – Intro to Process Control Page 1 of 27 Administration q Lecturer: Ahmed Hosny, Ph.D Email: Slate or Outlook: [email protected] q Textbook: Terry Bartelt, Industrial Automated Systems: Instrumentation and Motion Control, Cengage Learning, 2011. q Assignments: Labs (8 @5 % each) 40% Quizzes (2 @ 5% each) 10% Midterm Exam 25% Final Exam 25% q Passing grade: A student must receive a final grade of at least 50%. A failure to meet this criterion will result in an “F” grade. [email protected] Lecture1 – Intro to Process Control Page 2 of 27 q Late Assignment – results in a 10% deduction per day. A zero grade is earned after 3 days. q Missed Evaluation – results in a zero grade. In case of illness or injury, please report to [email protected] and copy me. q Academic Integrity – Lab – Submitted work must be the student’s own work. If you are assigned to work with a partner, only one report is to be submitted per group. Breach of academic integrity will be treated seriously. Please read and understand the full text of the policy at: http://www.sheridancollege.ca/life- at-sheridan/student-services/student-rights.aspx [email protected] Lecture1 – Intro to Process Control Page 3 of 27 Detailed Course Content Table 1: Timelines approximate Week Content Lab/Assignment 1 Intro to process control – control loops, modes, Lab 0 2 Piping and Instrumentation Diagram (P&ID) Lab 1 3 Pressure and Temperature control Lab 2 4 Level and Flow control Lab 3 5 Transducers (I/P, P/I), final control element, controllers Lab 4 / Quiz 1 6 PID tuning methods – trial-and-error, Zeigler-Nichols 7 Midterm Exam BREAK Reading Week 8 Intro to PLC – relay ladder logics, PLC components Lab 5 9 Intro to PLC – memory map, I/O modules, addressing format Lab 6 10 PLC programming – Ladder Diagram, logic instructions Lab 7 11 Programming Timers – on delay, off delay, retentive on delay Lab 8 / Quiz 2 12 Programming counters – up and down counters 13 Data manipulation and math instructions 14 Final Exam [email protected] Lecture1 – Intro to Process Control Page 4 of 27 Course Schedule Lectures – 2 Sections Section 1: Mon 8-10AM; Section 2: Tue 8-10AM Lab hours – 2 Sections Section 1: Wed 8–10AM; Section 2: Thu 5–7PM M T W R F Lecture Lecture Sec 1 Lab 8 –10 AM 8 –10 AM 83905 (C138) (H250) (C331) 8 – 10 AM Sec 2 Lab 83909 (C142) 5 –7 PM [email protected] Lecture1 – Intro to Process Control Page 5 of 27 Industrial Control Systems Industrial control systems are often classified by what they control (or controlled variable): either motion or process. Motion Control System: controls the motion or position of an object Controlled variable (CV): position, speed, acceleration, or deceleration. Designed to make CV precisely tracking the set point (SP) Examples: robot arm performs Response time is a fraction of second welding and assembly Also known as servo or servomechanism procedures; CNC machine tool; Office copiers; PCB assembly machine [email protected] Lecture1 – Intro to Process Control Page 6 of 27 Process Control System Controlled variable (CV): Temperature, pressure, level, flow, pH, or humidity. Response time is from several seconds to several minutes; comparatively slow. Also known as instrumentation and classified into: 1. Batch process: Products are made one batch at a time; a sequence of timed operations is performed on the product; also known as sequence (or sequential) process; Examples: mixing/blending, chemical reaction, separation 2. Continuous process: Raw materials continuously passed through manufacturing equipment; Examples: oil refining, wastewater treatment, etc. [email protected] Lecture1 – Intro to Process Control Page 7 of 27 Closed-Loop System Industrial control systems are also classified by how they control variables, either manually in an open-loop system or automatically in a closed-loop system. Energy Process Comparator variable (PV) (error detector) SP E=SP-FB CO Actuator MV CV + Controller Process - (FCE) FB Measurement device Measured value Sensor Setpoint (set value) = SP Error = E Closed-loop control automatically regulates output Controlled Variable = CV based on the measured values of CV. Controller output = CO Measured value compared to setpoint and used to Manipulated Variable = MV Feedback signal = FB maintain desired value when disturbances occur Final control element = FCE Closed-loop control uses feedback of output to input. [email protected] Lecture1 – Intro to Process Control Page 8 of 27 Open-Loop System Energy SP CO MV CV Controller Actuator Process Open-loop control modifies output based on predetermined control values. There is no actual measurement of controlled variable. No feedback signal, comparator and measurement device Example: automatic washing machine, clothes drier, electric hand drier, etc. [email protected] Lecture1 – Intro to Process Control Page 9 of 27 Example 1: Heating System in a House Feedback system aims to make CV = SP Error must exist before corrective action is made. Causses of error: – Setpoint is changed – Disturbance occurs – Load demand varies Desired Room temperature temperature Furnace House Thermostat (SP) (FCE) (process/plant) (CV) [email protected] Lecture1 – Intro to Process Control Page 10 of 27 Example 2: Heat Exchanger Elements of Feedback Control Process – maintain water temp. at desired value Measurement – sensor Controller – generate corrections Final Control Element – modify process Desired Temp. Heat Water Temp. ∑ Controller Steam valve (SP) + exchanger (CV) - Sensor [email protected] Lecture1 – Intro to Process Control Page 11 of 27  Example 3: Auto Cruise Control Disturbances Mechanical Fuel flow Power FCE Actual Set Speed E Speed Fuel ∑ Controller Engine Auto + Injectors - Speed Sensor Disturbances: Up hill/ down hill Head wind/ tail wind [email protected] Lecture1 – Intro to Process Control Page 12 of 27 Dynamic Response of Closed-Loop System Underdamped Overdamped SP Process CV ∑ Controller Actuator + (Plant) - Sensor Feedback control takes some time delay to correct controlled variable. This is known as dynamic response or response time. Factors contribute to response delay are: 1. Response time of instruments in control loop. 2. Time duration as signal passes from one instrument to another. 3. Static inertia of controlled variable (CV) or Pure lag (CV resists to change when energy is applied). This depends on the capacity of process. 4. Dead time: elapsed time between the instant a deviation of controlled variable occurs and corrective action begins. [email protected] Lecture1 – Intro to Process Control Page 13 of 27 Feed-Forward Control Disturbances FF Controller Energy SP + E + CV ∑ Controller + ∑ Actuator Process - FB Sensor Feed-forward is open-loop scheme used to minimize the dynamic response of closed-loop control. It is not used alone, used with feedback control. FF control prevents or minimizes error, but feedback control works on error. Feedforward makes corrections for measurable disturbances while feedback makes corrections for unmeasurable disturbances. [email protected] Lecture1 – Intro to Process Control Page 14 of 27 Instrumentation Block Diagram Energy SP + E CO MV CV ∑ Controller Actuator Process - FB Closed-loop Sensor/ Transmitter Indicator Monitoring Closed-loop performs control, instruments Alarm measurement, manipulation functions recorder Monitoring instruments are not part of the closed-loop, but they provide information to operator about the loop status. [email protected] Lecture1 – Intro to Process Control Page 15 of 27 Sensor Characteristics Sensors do not respond to input changes immediately. Response time is the amount of time the sensor takes to respond to a change in the measured variable. Flow and pressure sensors respond faster than temperature sensor. [email protected] Lecture1 – Intro to Process Control Page 16 of 27 Static Characteristics of Sensor Sensitivity: Change in output for change in input. Equals the slope of I/O curve in linear device. Hysteresis: Output different for increasing or decreasing input. Resolution: Smallest measurement a sensor can make. Linearity: How close is the I/O relationship to a straight line. 𝐶! = 𝑚. 𝐶 + 𝐶" Where, C = control variable, m = slope, C0 = offset (y intercept), Cm = sensor output. [email protected] Lecture1 – Intro to Process Control Page 17 of 27 Cont. Accuracy: How closely a sensor measures the actual value of the controlled variable. It is considered accurate if the measurement are within a tolerance value. Precision: How consistently a sensor responds to the same input value. It is also known as “repeatability.” [email protected] Lecture1 – Intro to Process Control Page 18 of 27 Transducers and Transmitters Controlled Feedback variable signal Sensor Transmitter Transducer Transmitter – (1) Amplifies sensor output signal, (2) Converts sensor signal to a standard signal. Standard instrumentation signals: Pneumatic: 3 – 15 psi Electronic: 0 – 10VDC, 0 - 20 mA DC, 4 – 20 mA DC; current signal is preferred over voltage signal as it is independent of wire resistance. [email protected] Lecture1 – Intro to Process Control Page 19 of 27 Controller Accepts error signal (E=SP-CV) and generates corrections to maintain the controlled variable at the desired value. Control law could be on/off or PID Controller output: – Dimensional: absolute value e.g., 0-10V, 0-20mA, 3-15psi – Nondimensional: percentage value (0-100%) makes more sense to the operator and tracks a wide range of the signal. Controller types: – Pneumatic: produces pneumatic output signal applied to control valve – Panel-mounted: microprocessor-based small device performs on/off and PID – Programmable Logic Controller (PLC) – Personal Computer (PC) [email protected] Lecture1 – Intro to Process Control Page 20 of 27 Final Control Element (Actuator) In process-control systems, the final control element is the device that directly influences the process variable. Types of final control element: Solenoid Valve – electromagnetic device converts on/off electrical signal to on/off flow control DC and AC Motor – converts electrical energy into mechanical energy Control Valve – sliding-stem valve and rotary-motion valve [email protected] Lecture1 – Intro to Process Control Page 21 of 27 Monitoring Instruments Monitoring instruments are used to provide information about the control loop to the operator. They do not perform any of the loop functions. Monitoring instruments are: Indicator – Displays data for the operator use such as SP, CV, CO, etc. Modern example is human machine interface (HMI) Alarm – warns the operator or initiate an action if undesirable condition occurs e.g., limit alarm is initiated if CV exceeded or dropped below a predefined value. Recorder – acquire data for future use (called data acquisition) [email protected] Lecture1 – Intro to Process Control Page 22 of 27 Control System Drawings Industrial system standard ANSI/ISA-S5.1-198 uniform designation for instruments, instrument systems and control. It is called Piping and Instrumentation Diagram (P&ID) Instrument Line Symbols Functional Identifier Piping Process Loop connection Identifier Electric General Instrument signal Symbol Pneumatic First ID Letter Following ID Letter signal A = Analysis C = Controller Software or L = Level I = Indicator Data link T = Temperature R = Recorder Capillary P = Pressure T = Transmitter tube F = Flow V = Valve Hydraulic Y = Relay/Converter signal [email protected] Lecture1 – Intro to Process Control Page 23 of 27 General Instrument Symbols Primary location Auxiliary location normally accessible Field- normally accessible to operator mounted to operator Discrete instrument Shared display, shared control Computer function Programmable logic controller (PLC) [email protected] Lecture1 – Intro to Process Control Page 24 of 27 More Symbols Programmable Discrete logic Computer instrument controller function Normally inaccessible or behind-the-panel devices or functions may be depicted by using a dashed horizontal line. [email protected] Lecture1 – Intro to Process Control Page 25 of 27 Control System Drawings 401 = Temperature loop Electrical signal Temperature Indicator/Controller Temperature Transmitter I/P Transducer Pneumatically actuated valve Capillary tube [email protected] Lecture1 – Intro to Process Control Page 26 of 27 Control System Drawings Flow orifice Flow valve Flow computer Data link Level computer Level transmitter PLC Indicator/Controller [email protected] Lecture1 – Intro to Process Control Page 27 of 27