Intro to Applied Process Control Introduction to process control

Tom Potts UARK Chem. Eng 1

Process Control on the Chemical Plant Floor

• Data acquisition – Gathering data from sensors• Process Control – Using the results of data acquisition to adjust process parameters

• Controlled Variables – Process conditions desired• Manipulated Variable – Condition adjusted to achieve desired value of controlled variables

What Variables can be Controlled?




Temperature Pressure Flowrate Liquid level



Temperature Pressure Flowrate Liquid level pH Concentrations SpeedMixer ConveyorMill




Electrical Contactor Pumps Valves Igniter Lights Sirens & Horns




Electrical Contactor (On/Off) Pumps Valves Igniter Lights Sirens & Horns

Position Linear (1, 2, 3 dimension) Rotary



Just about anything that can be measured!

Point Control System, a.k.a. Single Loop Controller


Typically one input (e.g. Temperature sensor), one output (e.g. Opening in control valve)

Comprises the vast majority of control applications

spiraxsarco.com

Central Control System, a.k.a. Direct Digital Control System


http://accessscience.com/content/Distributed-systems-%28control-systems%29/201460

Block Diagram

Honeywell Series 16 Direct Digital Control System, 1969

Computer & Multiplexer

Actuators (I/P typical)

Distributed Control System


asiaautomation.comwww.slideshare.net/.../distributed-control-system-basics

Data bus ordata highway



lamspeople.epfl.ch/kirrmann/Slides/AI_150_Architecture.pp

Proprietary data bus




Token Ring bus




Ethernet bus is becoming more common

Rockwell/AB proprietary bus

A lower level data bus developed by a consortium of

hardware vendors




Developed by Rosemont for communicating with smart devices




Supposed to be an industry standard,

but many incompatible versions

exist



instrumentation.co.za

Yokogawa Distributed Control System

Supervisory Control and Data Acquisition (SCADA)


Adds data acquisition to process controlExtends control and data acquisition to remote sitesShares data with other parts of the business entity

Inventory controlSafetyPlant and equipment maintenanceSales & marketingProduction managementQuality AssurancePlant level managementCorporate managementProcess engineeringDesign engineering

Provides data for decision making Statistical process control & Six Sigma Trending Real time cost of production

Low Level Process ControlComputer Control


Based on interface hardware added to a computer Reads and conditions signals from the “real world” Sends supervisory signals from the computer to the “real world”

Often adds data acquisition (DA) capabilities Not common in production settings Often found in academia & R&D facilities Requires software to implement control and DA algorithms

User generated software (C, C++, Fortran, etc) Commercial software (LabView)

Low Level Process ControlEmbedded Controller


Single chip or single board microcomputer designed for limited control applicationsCommon uses

Cell phones Appliances Military hardware

Low Level Process ControlPLC Control


A small, specialized computer designed for process control First unit developed by Bedford Associates

MODICON1968General Motors

US Rockwell/Allen Bradley (80%) Europe Rockwell/Allen Bradley (60%), Siemens (30%) Asia Rockwell/Allen Bradley (40%), Koyo (40%), Siemens (10%) Each vendor has own proprietary software for programming

Automation Direct (Koyo distributer for the US)


Specifications


DL05 CPU, 8 DC in / 6 Relay out, 110/220 VAC power supply. 6k words total (2048 words ladder - flash, 4096 words V-memory), RLL/RLLPLUS programming, built-in RS-232C programming port and additional RS-232C communications port. Inputs: 8 DC inputs, 12-24 VDC current sinking/sourcing, 2 isolated commons. First 3 inputs are configurable in one of several high-speed I/O features such as 5kHz counter input, pulse catch input, or interrupt input. Outputs: 6 relay outputs, 6-27 VDC, 6-240 VAC, 2A/point max., 2 isolated commons. One option slot available for I/O or communication module.

$119

DL05-DRDL06 CPU (requires 12-24 VDC power), 20 DC in / 16 Relay out, 12/24 VDC power supply. 14.8k words total (7679 words ladder - flash, 7488 words V-memory), RLL/RLLPLUS programming (DirectSOFT32 Version 4.0 or higher), two built-in RS-232C communication ports. Secondary communications port supports RS-232C/RS-422/RS-485, DirectNET Master/Slave, MODBUS RTU, Master/Slave, and ASCII In/Out. Inputs: 20 DC inputs, 12-24 VDC current sinking/sourcing, 5 isolated commons (4 inputs per common). First 4 inputs are configurable in one of several high-speed I/O features such as 7kHz counter input, pulse catch input, or interrupt input. Outputs: 16 Relay outputs, 6-27 VDC, 6-240 VAC, 2A/point max., 4 isolated commons (4 points per common). Four option slots available for I/O or communication modules.

DL06-DR-D

$239

Software, DirectSoft5 and DirectSoft100


DirectSOFT 100, same features as the full version of DirectSOFT5 but allows only 100 words of ladder code to be downloaded to the PLC. Programs DL05/06/105/205/305/405 systems, only available for download online. (Order programming cable separately.) 32-bit application, Windows 2000 or Windows XP (Pro or Home) or Windows Vista (Home, Basic, Premium, 32-bit) recommended.

http://www.automationdirect.com/adc/Shopping/Catalog/Software_Products/Directsoft_PLC_Programming_Software/Directsoft_Software/PC-DS100

Digital In/OutKoyo modules available


Analog In/Out


Analog In/Out


Commonly Used Sensors


Temperature• Thermocouple• RTD – Resistance Temperature Detectors• IC Temperature Sensors• Thermistors (not with PLCs)




Pressure• Strain gauge (piezoresistive)• Strain gauge (piezoelectric)• Capacitive• Electromagnetic• Optical• Potentiometric• Resonance• Thermal• Ionization





Mass/Weight• Physical deformation• Load cell (piezoresistive)• Load cell (piezoelectric)






Liquid Level• Pressure differential• Acoustic• Optical• Capacitive• Floats• Radar•Many others (see Google)






Liquid Level• Pressure differential• Acoustic• Optical• Capacitive• Floats• Radar•Many others (see Google)

Flow rate• Turbine• Paddlewheel• Thermal conductivity• Force plates• Venturi• Coriolis• Orifice plates• Ultrasonic flowmeters• Many others (see Google)

Using the PLC


Develop a PFD and a controls flow diagram: example Project 1


Develop a point contract diagram


Wiring the connectors


Connecting the Computer to the PLC


PLCProgramming

CableUSB to RS232

Adapter Computer

Making the Connections Work


1. Connect the USB/RS232 adapter to the computer2. (1st time) – Install the adapter driver3. Set the communications port & protocol in devices and printers4. Connect the programming cable to the adapter5. Connect the programming cable to the PLC6. Turn on the PLC7. Start the DirectSoft software using DSLaunch8. Set the comm link (right click, the add link)

1. Use your port number from above2. Use KSeq protocol3. 9600 baud4. Odd parity5. 8 data bits6. 1 stop bit7. no flow control

Start DirectSoft


Use the dialog box


Give your project a name

Select the proper PLC

Select the Comm Link you created earlier


Select PLC, then Connect, then select the appropriate link

Write your program


Load your program to the PLC


Use the Write icon


User Memory• Binary – C0-C777• BCD or Octal – V1200-V7377

Important memory information

Introduction to Relay Ladder Logic (RLL)


Allen-Bradley

Normally Open Contact


Automation Direct

Y0 will be closed as long as X0 is closed

Normally Closed Contact


Automation Direct

Y0 will be closed as long as X0 is open

Boolean And


Automation Direct

Y0 will be closed as long as X0 and X1 are closed

Boolean Or


Automation Direct

Y0 will be closed as long as X0 or X1 are closed

Boolean Complexities


Automation Direct

Boolean Comparisons


Automation Direct


Set and Reset

Y2, Y3, Y4, Y5 will turn on when X1 is closed, then they will stay on regardless of the state of X1

until they are turned off with a Reset

Timer


Timer function is a 0.1 second timer, 999.9 seconds is the maximum time that can be used

Note that timer number is expressed in octal

Counter


Note that counter numbers and V-memory locations are expressed in octal

Analog Input and Output


To be completed

PID Control


Homework – Download this file from Automation DirectVolume 2 chapter 8

http://www.automationdirect.com/static/manuals/d006userm/d006userm.html

Read chapter 8

Problematic Control Issues


• Process non-linearities, especially batch processing• Excessive dead time (lag)• Improperly nested cascade control• Interaction between controlled variables

Smith, Cecil, “Process Engineers Take Control”, Chemical Engineering Progress, August 2000, 19-29

http://people.clarkson.edu/~wwilcox/Design/proccont.pdf

Safety


• Use low voltage DC for as much circuitry as possible –European standard• Primary safety device cannot be controlled by the electronic controller.• The controller can be used for secondary safety device

Example:Over-pressure control in a reactor rated at 1000 psig and operated at 650 psig.

Secondary safety device could be a pressure transducer to read the tank pressure and a relief valve controlled by the PLC and vented safely. The PLC is programmed to open the relief valve when the tank pressure is greater than 750 psig

The primary safety device could be a rupture disk or blow-out plug vented safely and rated 850 psig.

Safe Failure Conditions


• Try to build your control system so that failure results in safe condition

• Safety sensors should be wired so that system good is indicated by a high signal, system alarm is low signal• Analog signals should be 4-20 mA whenever possible• Level/over flow signals should be such that broken wire or failed float gives alarm condition

• Use redundancy whenever possible• Check for logical consistancy• Provide error traps in your programming with appropriate alarms

Safety – MCR and SCR


Automation Direct DL05 User Manual

Project 1


Applied Process ControlProject 1: Tank Level Control

This project was taken from a real-world requirement some years back at a northeast Oklahoma production facility where chemicals in support of nuclear power applications were produced.

A liquid reactant is held in a holding or buffer tank. From time to time (no set schedule), liquid reactant is fed to a reactor in the plant. About 20% of the tank is used for each reaction. The holding tank is fed by a pump in a process line connecting the tank to a railroad tank car sitting next to the plant. The production managers want the tank to be maintained at a level between 1/3 and 2/3 full. Overfilling the tank will lead to spill of the expensive and hazardous reactant. An under filled tank can lead to a starved reaction in the plant (insufficient reaction), the starved reaction can lead to a run-away temperature in the reactor, which can lead to a damaged reactor or in extreme cases, explosion and loss of life.

This project is to construct a scale model of the above described system. You will be provided with the PLC, a tank (plastic bucket), three float sensors, and a relay driven pump. Your mission is to build an operating scale model, write a ladder logic (RLL) program, and submit your RLL program for testing on the actual system. Your project should include the following:A block flow schematic of the process.A Process Flow Diagram of the process.A P&ID flow diagram of the process.Bullet point discussion of the construction and assembly of the scale model. This should have enough information for a skilled technician (such as Potts or Fordyce) to put the scale model together.A point contact diagram for the I/O points of the PLC.The RLL program for the control strategy

Memory assignmentsThe ladder logicComments for the ladder logic

The project should conform to the safety guidelines given in the PowerPoint presentation.

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Intro to Applied Process Control Introduction to process control

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