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What Is a Programmable Logic Controller (PLC)

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The document provides information on programmable logic controllers (PLCs), including common brands of PLCs, the basic components and functions of a PLC, why PLCs are used, advantages over electromechanical relays, differences from PCs, digital and analog I/O devices, programming languages, applications, safety considerations, and key terms. It discusses inputs, logic processing, outputs, and the PLC scan cycle in detail.

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Brands of PLC’c A lle n B r a d le y S ie m e n s M it s u b is h i T a t a H o n e y w e ll A B B A L S T O M F E S T O F u j i E le c t r ic R e lia n c e B & R T o s h ib a C u t le r H a m m e r A n s h u m a n S c h n e id e r K o y o S ig m a t e k M e s s u n g O m r o n F a n u c M o d ic o n
P.L.C. Programmable Logic Controller • CPU - Decision Making Unit • Inputs-Digital/Analog/High Speed • Outputs - Digital / Analog • Power Supply - 24 VDC / 110VAC / 220VAC / +/- 12V • Timers / Counters / Flags / Registers / Memory • Communication - Serial - RS232C / Equivalent • Programming - Through PC /
Why to use PLC’s ? • COST :- PLC can scan Digital & Analog Inputs through relevant S . It can execute the Logic w.r.t. the Scanned Inputs, take necessary decision and send it to Digital / Analog Outputs. It can also perform PID control Functions. The cost of all this is much less than a conventional DATA Logger !! • Versatility :- The ability to combine discrete (Digital) & Analog logic is a powerful tool for the Control Engineers. Control of critical start-up parameters, such as temperature and pressure, can be precisely pre-programmed for each start-up step.
Why to use PLC’s ? • Expandability :- As a process matures, it is inevitable that enhancements will be needed. These usually require more outputs. For hard-wire Relays system this usually necessitates extensive panel changes, which generally are problematic. A PLC easily accommodates the additional I/O’s without requiring changes in the existing wiring. If a PID loop is to be added, no panel rework is necessary; only the wiring of new points and some re- programming to incorporate them is required.
Why to use PLC’s ? • Flexibility :- As a process goes ONLINE and Refined, the Control Equipment should be easily reconfigured to accommodate such modifications. Bottling Plant Control, Traffic Light Control, Process Control of Temp., Pressure, Level, Flow etc., Car Parking Control etc. are all within the Capabilities of PLC’s. • As one common device (PLC) performs multiple functions in a Plant, fewer spare parts are needed . • The Digital nature and self- Diagnostic capabilities are strong
Advantages of PLC over Electro-mechanical Relays • Ability to interface / communicate with Computers • Simple Programming • Field Programming possible (HHT) • High Reliability (Better MTBF) • Easy Maintenance • Rugged Construction - Can operate in Extremely harsh field conditions • Smaller Size • Easy Expandability (Due to Modular Design)
Differences between - PLC & PC / Computers • Real Time Operation - PLC’s are designed to operate in a REAL-TIME control Environment. Most PLC’s have internal clocks and built-in “Watch-Dog Timers”.
PLC’s Vs PC’s • Environmental Conditions PLC’s are designed to operate near the equipment they are meant to control. This means that they function in hot, humid, dirty, noisy and dusty industrial environments. PLC’s can operate in 60 Deg C as well as 0 Deg C, with tolerable relative Humidities ranging from 0% to 95% non-condensing.
PLC Vs PC • Programming Languages & Techniques - • PLC - Ladder Diagram format is read & understood world- wide by maintenance technicians as well as by engineers. • Unlike Computer Programming, PLC Programming does not require extensive special training. • Programme operation are performed by the PLC in the order they were programmed . This allows easy programming of Shift Registers
PLC Vs PC • Maintenance & Trouble-shooting • As PLC is a Plant Floor Controller it has to be maintained / serviced by plant electrician or the Instrument Technician. • It would be highly impractical to require computer type maintenance service. • Most PLC Components are modular and simple to isolate, remove-and-place (system
Digital I/O Devices • Digital Input Field Devices • Pushbuttons, • Thumbwheel Swiches • Limit Switches • Selector Switches • Proximity Sensors • Photoelectric Sensors • Digital Output Field Devices • Discrete Outputs - Relays, Solenoids, Contactors, Motors starters, Annunciator Windows, Pilot Lights etc. • Register Outputs - Displays,
Various Types of Transmitters T r a n s m itte r s T e m p e ra tu re T ra n s m itte rs P re s s u re T ra n s m itte rs F lo w T ra n s m itte rs L e v e l T ra n s m itte rs
Analog I/O Devices • Analog Outputs – 4 to 20mA / 0 to 5V DC – Can drive signals to variable speed drives etc., Control Temperature, Pressure, Level, Flow, pH, Conductivity etc. • Analog I/P - • 4 to 20 mA / 0 to 5V DC • 12 Bit or better ADC • 32 Bit Storage (For SCADA) • Thermocouples T/C / RTD’s • Flow Transmitters • Temperature Transmitters • Level Transmitters • Pressure Transmitters • Strain Guage
Digital / Analog I/O’s • Digital Inputs - 1-4096 / more • (Useful for sensing of entry of CAR) • (To Sense COIN in vending machine) • (To sense if Door Bell is pressed) • Digital Outputs – 1-4096 / more • (To indicate Traffic Light Signals) • (To display Alarm indication) • (To display CAR is exiting parking) • Analog Inputs - 1-4096 or more • (To continuously Scan the Temp.) • (To continuously Scan Level / Flow) • Analog Outputs - 1-4096 / more
Digital I/O Voltages • DC Input Modules - 24 V DC 48 V DC 10-60 V DC 120 V DC 230 V DC 5-50 V DC Sink /Source 5 V DC TTL Level 5/12 V DC TTL Level • AC Input Modules – 24 V AC 48 V AC 120 V AC / Isolated 240 V AC / Isolated 24 V AC / DC
Analog I/O Voltages Voltage Range Decimal Equivalent -10 V to + 10V - 32768 to + 32767 0 to + 10V 0 to + 32767 0 to +5V 0 to + 16384 1V to + 5V 3277 to + 16384 Current Range Decimal Equivalent -20mA to +20mA -16384 to +16384 0 to +20mA 0 to +16384 4 to +20mA 3277 to +16384
PLC Programming Languages • Ladder Diagram Programming • Function Block Diagram • Sequential Function Chart • Statement / Instruction List • Structured Text
PLC Programming [1] Edit / Write a Ladder Programme [2] Simulate Programme using Simulator [3] Change the Programme if necessary [4] Download the Programme PC to PLC [5] Execute the Programme in PLC [6] Change Inputs to see effects on Outputs [7] Modify the Programme for different field conditions & repeat steps 4,5,6.
PLC Applications using Static Application Panels • CAR PARKING • TRAFFIC LIGHT CONTROL • SOFT DRINK DISPENSER • WASHING MACHINE • REACTION VESSEL • PROCESS CONTROL • TANK LEVEL CONTROL • DOOR BELL DIGITAL LOCK • MICROWAVE OVEN • BOTTLING PLANT • SEQUENTIAL CONTROL MOTORS • SWITCHING OF LIGHTS • MIXING OF 2 CHEMICALS • STARER CONTROL • STAR-DELTA STARTER
Other Applications of PLC’s [1] Control of SPM’s (Special Purpose Machines - Like Drilling M/c or Grinding M/c or Lathes etc. [2] Packing Machines Like - Capsule Packing Machines Tablet Packing Machines; Milk Pouches Packing M/c.
While Chosing PLC for an Application, following points should be taken into consideration • Maintenance • Spare Parts • Operation • Modifications • Losses (Production, Equipment, Personnel) • Information Technology • Space & Weight • Flexibility • Expandability • Operability • Cost of Control & Instrumentation
Aspects of Control & Instrumentation • Standardisation • Speed of Response • Hardware Variety • Software Portability • User Interface • Memory • Compactness • Power Requirement • System Integrity (Reliability, Availability, Security) • Control & Logic Algorithms
A Control Unit Should have following capabilities as Standard • Continuous Control • Batch Control • Logic • Advanced Control • Simulation • Neural Network & Knowledge based Systems • A PC-Oriented Programming Language • Dual or Triple Redundancy • High Scan rates (1 to 10 mS) • High Resolution Time Stamping (1 mS) • A Communication Processor that can handle popular protocols
Safety Considerations • The most important safety feature, which is often neglected is PLC system design. This feature must be included whenever a hardwired device is used in order to ensure operator protection against the unwanted application of power. • Emergency STOP function should be completely hardwired. Software functions should not be relied upon to shut-off the process or the machine.
NOISE • Electro-Magnetic Interference / NOISE / Unwanted Electrical Signals can generate problems for all solid state circuits, particularly Micro- processors. Each PLC manufacturer suggests methods for designing a noise-immune system. • I/O system are isolated from the field, but voltage spikes can still appear within the low-voltage environment of the PLC if Proper Grounding practices are not followed. Often it is necessary to keep AC and DC wiring bundles apart, particularly when high-voltage AC is used at the same time that low-level analog signals are present.
Temperature Considerations • Installing any solid state device requires paying attention to – • Ambient Temperature • Radiant Heat Bombardment • And the Heat generated by the Device itself. • PLC’s are typically designed for operation over a broad range of Temperatures, usually from 0 to 60 Deg.C • For Cooling, blowing filtered air through the enclosure can resolve minor difficulties.
Enclosures • Enclosure of PLC protects PLC’s from moisture, Oil, Dust Particles and unwanted tampering. • Most Manufaturers recommend NEMA 12 Enclosure for the Standard Industrial Environment. • PLC’s are designed to be located close to the machine or the process under control. This keeps the wiring runs short and aids in the trouble- shooting procedure. • It is not advisable to place a PLC near a Virating Machine, Electrical NOISE Interference or Excessive Heat Environment conditions.
KEY-WORDS of PLC • PLC - Programmable Logic Controller • PID – Proportional + Integral + Derivative Control Function. • DCS – Distributed Control System • SCADA – Supervisory Control & Data Acquisition System • RTOS- Real Time Operating System
KEY-WORDS of PLC • RTC - Real Time Clock • RTU – Remote Terminal Unit • Timers – On-Delay Off-Delay Monoshot / Monostable Pulse Flasher Astable Bistable • Counters – Up / Down
KEY-WORDS of PLC • Flags / Registers / Latches / Memory Set-Reset / Retentive – Non-Retentive • HHT – Hand Held Terminal • HHP – Hand Held Programmmer It is used for PLC Programming at the Installation site. • MMI – Man-Machine Interface • HMI – Human Machine Interface Useful for ease of operation of PLC by operator/s.
H.H.T./ H.H.P.- Advantages • Easy transfer of PLC Program to HHT / HHP for editing or troubleshooting. • Easy transport of a program to the field to update a current machines program. • Rugged and industrially hardened for the factory environment. • Low cost, cheaper than a notebook computer. • Easy to use & easy to learn, no software required. • Compact Size (pocket size) • Easy storage of Program • Monitor resident PLC Program for trouble shooting.
H.H.T./ H.H.P.– Disadvantages • Not supported by some PLC’s. • An HHP can hold only one program at a time – whereas a Laptop / PC can hold many programs on its HDD. • HHP’s usually require more keystrokes to enter and get the same information as compared to a laptop / PC. • Limited capability to display ladder rungs due to screen size • Documentation not displayed • Different HHPs are needed for different PLC manufacturers if more than 1 PLC’s are in field. • If the Battery of the HHP discharges, a program stored
KEY-WORDS of PLC • Memory Cartridge / Module Consists of either – RAM ---- Random Access Memory. (Volatile) EPROM -- Erasable Programmable Read Only Memory. EEPROM -- Electrically Erasable Programmable Read Only Memory. FLASH --- Non-Volatile
Softwired Vs Harwired components of PLC • Soft-wired Components – Timers Counters Logic Circuits Latches • Hard-wired Components - 24 V DC Lamps Relays Contactors Solenoid Valves
Scan-Time / Scan-Cycle • Scan Time of PLC – It is the time between an Input being sensed & the corresponding output. • Single Scan Cycle – Single Scan Cycle function enables the circuit diagram to run for one processing cycle and then stop. This is useful in analyzing the circuit diagram and observing how it works.
PLC Scan • Input Scan – PLC scans all Inputs • Logic / Process Scan PLC goes through the ladder program / logic • Output Scan – PLC sends Outputs as per various Inputs and the corresponding
Input Scan • During the Input Scan the CPU scans each Input module for the ON / OFF states of each of the associated input points. • The ON / OFF input states are stored in the input status file.
Program Scan • After the inputs are read and stored in the input status file, the processor will use this information to solve the user ladder program. • The processor scans the user program starting at rung zero at the left power rail, working left to right and evaluating one instruction at a time until the output instruction is reached. • The Output status is the logical resultant of the solved input logic for that rung. The logical one or zero output status is placed in the output status file. • After completing rung zero, the processor goes on to rung 1,2,3… and so on, sequentially, to the last rung except in case of Master Control Relay (MCR) • At the end of the program, an END- Rung is automatically inserted which alerts the CPU the it has reached the
PLC – Concepts • Forcing Inputs / Outputs • RS232C / RS422 Ports • Source-Sink Concept in PLC • How to select a PLC for a particular project ? • PLC Types –
PLC – Concepts • Online (Run) / Offline Mode of operation. • Uploading/ Downloading of Programmes from - PLC to PC & PC to PLC • Display – LEDs / LCDs / VFD – Vacuum Florescent Display.
PLC – Concepts •MCR – Master Control Relay Function • File Handling / Addressing System •PLC Simulator Software
Key-Words of PLC • WDT - Watch-Dog-Timer – In case of PLC control loss due to EMI / NOISE, WDT brings back control of CPU to a Known State. This Timer Circuit usually resides on the CPU card itself. It works like a MONOSHOT PULSE GENERATOR of width greater than MAXIMUM SCAN TIME.
WDT - Watch-Dog-Timer • In order to insure system predictability a WDT is used to insure that the processor completes each scan in a timely manner. • WDT is a hardware timer incorporated into the CPU’s circuitry that monitors the cyclical process / scan of the CPU. • WDT is a safeguard that verifies the processor does not become stuck while scanning the user program or for some other reason, become unable to complete the current scan.
WDT - Watch-Dog-Timer • The WDT is reset at the end os each Scan Cycle by the CPU when the scan time is less than WDT’s preset time. • In case of one or more sub- routines, program scan time can exceed WDT time value. In some cases increasing the WDT’s preset value can solve the problem. • Some PLC’s have WDT with fixed time intervals, while others are adjustable within specific limits. • A typical default time of 100 / 200 mS is standard for many PLC’s with either fixed or
SLC-500 - Processor operating modes • Program Mode • Run Mode • Remote Run Mode • Remote Program Mode • Test Mode • Single-Step Test Mode • Single – Scan Test Mode • Continuous Scan Test Mode • Test Mode – Test Program execution before allowing the PLC to operate the actual Hardware.
GE – 90-70 CPU - Processor operating modes • Run with Outputs Enabled • Run with Outputs disabled • Stop Mode • Stop & I/O Scan Mode • Run Mode Store Function.
Key-Words of PLC • CCU - Central Control Unit - It consists of a CPU + PALS- GALS + RTOS + EPROM / RAM / EEPROM • Process / Ladder Logic Memory It could be integrated with CPU or in a separate DATA / MEMORY CARTRIDGE / MODULE. Usually it is a replaceable Cartridge. • Optoisolation - Analog I/O’s should be isolated otherwise induction / pickup can lead to malfunctioning of PLC
Digital Electronics • Boolean Algebra • Binary / Hexadecimal nos. • Logic Gates & Truth Tables • AND • OR • NAND • NOR • Ex-OR • Ex-NOR • NOT
L o g ic F u n c t io n s A N D O R N A N D N O R N O T E x - O R E x - N O R T I M E R C A S C A D E T I M E R S R F L I P - F lo p C O U N T E R
PLC Programming AND Timers APPLICATIONS Astable OR Monostable Traffic Light Control Process Control Bistable NOT Tank Level Control Bottling Plant NAND Counters Digital Lock NOR Flags Microwave Oven Retentive Ex-OR Non-Reten Washing Machine Door Bell & Alarm Ex-NOR Registers Sequential Control Retentive Silo Control
Functioning of Timers / Counters / Flags / Registers PLC T IM E R S CO UNTERS FLAG S R E G IS T E R S 0 t o 2 5 6 in A n s h u m a n 0 t o 2 5 6 n o s in A n s h u m a n 0 t o 2 5 6 n o s in A n s h u m a n 0 t o 2 5 6 n o s in A n s h u m a n M o n o s t a b le U p C o u n te r R e t e n t iv e R e t e n t iv e A s t a b le D o w n C o u n te r N o n - R e t e n t iv e N o n - R e t e n t iv e
DCS / SCADA •D.C.S. :- Distributed Control Systems •S.C.A.D.A.:- Supervisory Control And Data Acquisition System. (Through Network Data Acquisition, Data Display, Data Processing, Data Storage, Data Analysis etc.)
DCS Vs SCADA • Generally supplied by • Normally supplied by a single Vendor with Multiple / Competing dedicated H/W & Vendors S/W. • Competitive cost due to Multi-Vendor products. • Costly due to • Can be applied to redundent design very low cost applications • Application Areas - • Comm’n - Can cover Large Mfg. Facilities larger geographical area by use of modems and T/p lines • Comm’n - Confined to factory premises (LAN for H/W) • Small to medium Analog I/O’s with / without PID. • Analog Processing - Large Analog I/O’s • Programming - PLC by using PID’s relay Ladder Diagram or STL and SCADA using built-in graphics • Programming - by editor and drivers. creating drawing like charts called as configuration diagram • Suppliers - PLC’s - Siemens, Allen Bradley, Omron etc. • Suppliers - Honeywell, SCADA - Intellution, NI-Lookout / Labview
Following Displays are available in most Control Systems • Overview • Area • Group • Details • Trends • Configuration • Diagnostics • Alarm Summary • System Status (LAN) • Scratch Pad
Solid State O/P Switching • Advantages – [1] Fast Switching Speeds [2] High Reliability & almost infinite life [3] Low Power required to energize [4] No Contact Arcing [5] Little / nil Switching noise [6] +ve switching, no contact bounce [7] Can be hermetically sealed – good for hostile environments. • Disadvantages – [1] May be destroyed by overload [2] Tend to fail in ON state [3] Heat dissipation [4] Expensive to purchase [5] Possibility of false trips from electrical noise.
Relay O/P Switching • Advantages – [1] Contacts forgiving to a temporary overload [2] Immune to false trips from elec noise [3] Little voltage drop across contacts [4] No restrictions when connecting in series or parallel configurations [5] Difinite ON / OFF state, with contacts physically open. [6] No Leakage [7] Contacts generate little heat [8] Inexpensive to purchase • Disadvantages – [1] Mechanical switching is slow [2] Mechnical life is limited by demands of the load and the contacts. [3] Require 50mA or more to energize [4] Subject to contact arcing or welding [5] Subject to contact bounce
PLC – Reference Books • Programmable Logic Controllers. – By – John Web • Programmable Controllers – By – Richard Cox. • Introduction to Programmable Logic Controllers – By – Gary Dunning
Other Terms related to Control Systems • UCP - Unified Control Panel • UCS - Unified Control System • UCN - Universal Control Network • UOC - Unit Operation Controller • TDC - Totally Distributed • Control System • SOE - Sequence Of Events • SP --- Set-Point • SFC - Sequential Function Chart • SAT - Site Acceptance Test • SAS - Safety & Automation Systems
Other Terms Used in Control Systems RTU - Remote Terminal Unit ROC - Rate of Change PV --- Process Variable PS --- Process Station PSD - Process Shut-Down PIU - Plant Interface Unit PIN - Plant Interface Network PCS - Process Control System PFD - Process Flow Diagram PCN - Process Control Network
Other Terms Used in Control Systems OBT - Optical Bus Terminal OLE - Object Linking & Embedding OLM - Optical Link Module NIU - Network Interface Unit MC---- Multifunction Controller MTU - Master Terminal Unit MCS - Master Control Station MAS - Manufacturing Automation System MAP - Manufacturing Automation Proto’l MTBF - Mean Time Between Failure MTTR - Mean Time To Repair
Other Terms Used in Control Systems • LLPIU - Low-Level Process Control Station • LCN --- Local Control Network • LCR --- Local Control Room • LAN --- Local Area Network • ISA - Instrument Society of America • ISO - International Standards Organization • HSE ---- High Speed Ethernet • HIPPS -- High Level Process Protection System • HAZOP - Hazard & Operability Study
Other Terms Used in Control Systems • FAT- Factory Acceptance Test • EUC - Equipment Under Control • ESD - Emergency Shut-Down System • EC --- Extended Controller • DPS - Dynamic Positioning System • AC --- Adaptive Control • CFC - Continuous Function Chart • C & I - Control & Instrumentation • CCR -- Central Control Room
• Other Terms Used in Control Systems • BCL -- Batch Control Language • BC --- Basic Controller • AEC - Advanced Extended Controller • AMC - Advanced Multifunc’n Controller • CAD - Computer Aided Design • CADAS - Computer Aided Design Analysis & Application
FF-Bus -Foundation Field Bus • FF-Bus is a Digital Comm’n System • A Summary of improvements, which FF-Bus will offer as it becomes more widely applied are – * Higher Communication Speed - 10 to 100 M Baud * Higher nos. of modes per branch to reduce cabaling & termination effort • More efficient Communication • Better diagnostics & predictive maintenance in field
FF-Bus • More reliable Control System because of better maintenance & Higher distribution control. • Faster Control System Response. • Saving in Hardware (Cabling, I/O cards, Cabinets) • Higher Accuracy because Process Parameters are Sampled Locally & Transmitted Digitally to local / remote Control Units. • Major Improvements in System
FF-Bus • Reduction in Documentation (No. of Loop Diagrams, Termination Schedules etc.) • Possibilities od using Multifunction Instruments - Where one Transmitter measures multiple variables (e.g. A Corolis meter can measure - flow, Density & Temperature ) • A High Degree of Inter- operability among system Computers & Instruments from different Vendors.
• DPS - Dynamic Positioning System • Availability = MTBF / (MTBF + MTTR) • Categories of Consequences Definitions • Catastrophic ---- Multiple Loss of Life • Critical -------- Loss of a Single Life • Marginal ------- Major injuries to one or more persons. • Negligible ------ Minor injuries at worst
Catagories of Likelihood Categories Definition Failures of Likelihood (in System Life) Per Year Frequent Many Times > 10-3 -4 Probable 10 to Several Times -3 10 -5 Occasional One Time 10 to -4 10 -6 Remote Unlikely 10 to -5 10 -7 Impossible Very 10 to -6 Unlikely 10 Incredible Cannot believe < 10-7 it could happen
* Analog Input :- DC models of Pico are provided with two analog inputs I7 and I8. The permissible input voltages are between 0 V and 10 V. The measured data is evaluated by an integrated Analog Value Comparator relay. * Circuit Connection: Each line in the circuit diagram display is a circuit connection.
Circuit Diagram Elements: The circuit diagram is made up of circuit diagram elements from conventional wiring practice. These include input, output and auxiliary relays as well as function relays and P buttons. Contact/Coil Monitor: The Contact/Coil Monitor is a dialog for displaying and forcing the logic states of selected relays (contacts / coils).
Device Test :- The device test shows in plain text the results of comparison between the selected Pico device and the circuit diagram. All contact/coil elements that are not available on the device used will be listed, and the number of circuit connections used will be checked. If the Pico device cannot properly process the circuit diagram, a device will be suggested on which the circuit diagram can be used successfully.
Function Relay :- Function relays are used for complex switching tasks. Pico devices are provided with the following function relays: Timing relays (T), Time switches (H), Counters (C), Analog value comparators (A), Text relays (D). Impulse Relay :- An impulse relay is one that changes and then retains this state if a voltage is momentarily applied to it.
Input :- External contacts are connected to the inputs of the device. Inputs are evaluated in the circuit diagram via the switching contacts I1 to I12 and R1 to R12. The 24 V DC Pico models can also receive additional analog data via inputs I7 and I8. Input Debounce :- Input signals can be evaluated by the device with a delay in order to compensate for the contact bounce of switches and pushbuttons.
Interface :- The device interface allows circuit diagrams to be exchanged and stored on a memory card or PC. A memory card saves both the circuit diagram and device settings. PicoSoft PC software allows you to control the device from the PC. The PC is connected to Pico via the "1760-CBL-PM02" cable.
I/Q Window :- The I/Q window contains the input simulator and the display for Q and S coils. The input simulator or I window is used as a central tool in circuit diagram simulation. It enables you to create dynamic input signal states for the simulated circuit diagram. For this you can also assign different functions to the I and R buttons.
I/R Function :- The I/R Function determines the switching function of the elements I1 to I16 and R1 to R16. These can be latching make contacts, latching break contacts, momentary make contacts or momentary break contacts.
Operator Buttons :- The device features 8 operator buttons by which you can select the menu functions and also enter the circuit diagram directly via the Pico display. The centrally arranged cursor buttons are used to move the cursor in the Pico display. DEL, ALT, ESC and OK are also provided with additional functions.
Output :- The outputs are used to switch loads such as contactors, lamps or motors. The outputs are controlled in the circuit diagram via the output relay coils Q1 to Q8 and S1 to S8. Parameters :- Function relays are assigned particular parameters by the user. Set values may include, for example, switching times or counter setpoints. These are set in the Contact/Coil
P Buttons :- The P buttons allow you four additional inputs that are switched via the cursor buttons on Pico instead of external contacts. The switching contacts of the P buttons are wired in the circuit diagram.
Retention :- This function allows data to be retained in the device even after its power supply has been switched off. Retentive data consists of: Device circuit diagram, parameters, setpoints, text, system settings, password, actual values of auxiliary relays (markers), timing relays, counters.
Signal Diagram :- The Signal Diagram allows you to display the behavior up to eight selected relays along a time axis. The diagram produced can also be printed out for documentation purposes. Single Cycle :- The Single Cycle function enables your circuit diagram to run for one processing cycle and then stop. This helps you in analysing the circuit diagram and observing how it works. This function is only available during Simulation.
Startup Behavior :- The startup behavior is an important help during commissioning. The circuit diagram may not be completely wired when it is transferred to Pico, or the system/machine to be controlled is in a state in which it cannot be controlled by Pico. If Pico is then switched on, it may therefore be desirable for the outputs to remain inactive. For this set the startup behavior to STOP. If the startup behavior is set to RUN, Pico will start processing the circuit diagram as soon as it is switched on.
Stop Point :- In order to analyse your circuit diagram effectively, you need a tool to interrupt processing selectively, evaluate the state of selected contacts or coils and continue processing. The Stop Point function makes this possible. It is only available during Simulation.
Wiring via the Keyboard PicoSoft also enables you to wire up your circuit diagram via keyboard commands. Selecting Make/Break Contact Behavior :- Entering letters in lower case selects make contacts, and entering letters in upper case selects break contacts.
Adding / Deleting Contacts :- Position the cursor on the contact field required and enter the contact via the keyboard. Use the following shortcuts for contacts & f’n relays: i, I Controller Inputs p, P Soft Inputs - Keypad q, Q Controller Outputs m, MInternal Marker Bits c, C Counters t, T Timers h, H Time Switch Relay a, A Analog Setpoint Compare d, D Text Display r, R Expansion Inputs s, S Expansion Outputs or Internal Marker Bits To delete the contact, press the Del key
Adding / Deleting Coils Position the cursor on the coil field required and enter the coil via the keyboard. Use the following shortcuts for coils and coil functions: q Controller Outputs m Internal Marker Bits t Timer "Trigger" coil c Counter "Trigger" coil d Text Display "contactor" function s Internal Marker "contactor" function
To select the coil function required, press the Shift key and select the appropriate coil function letter below: Shift + E Impulse relay Shift + S Latching (Set) Shift + R Unlatching (Reset) Shift + D Direction coil for counter The default setting is for the contactor function. To revert to the simple contactor function of the coil, press the letter for the coil concerned.
To delete the coil, press the Del key. Connecting Inputs and Outputs Use Shift+Cursor key to make the connection between the individual contacts and coils. Adding Empty Lines Position the cursor on the circuit connection in front of which you wish to add the empty circuit connection. Press Ctrl+I to add the empty circuit connection.
Deleting Circuit Connections Position the cursor on the circuit connection you wish to delete. Press Ctrl+D to delete the entire circuit connection. Deleting Connections Position the cursor on the connection you wish to delete. To delete the connection, press the Del key. If the circuit connection contains branches, the selected connection will only be deleted up to the next node.

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What Is a Programmable Logic Controller (PLC)

  • 1. Brands of PLC’c A lle n B r a d le y S ie m e n s M it s u b is h i T a t a H o n e y w e ll A B B A L S T O M F E S T O F u j i E le c t r ic R e lia n c e B & R T o s h ib a C u t le r H a m m e r A n s h u m a n S c h n e id e r K o y o S ig m a t e k M e s s u n g O m r o n F a n u c M o d ic o n
  • 2. P.L.C. Programmable Logic Controller • CPU - Decision Making Unit • Inputs-Digital/Analog/High Speed • Outputs - Digital / Analog • Power Supply - 24 VDC / 110VAC / 220VAC / +/- 12V • Timers / Counters / Flags / Registers / Memory • Communication - Serial - RS232C / Equivalent • Programming - Through PC /
  • 3. Why to use PLC’s ? • COST :- PLC can scan Digital & Analog Inputs through relevant S . It can execute the Logic w.r.t. the Scanned Inputs, take necessary decision and send it to Digital / Analog Outputs. It can also perform PID control Functions. The cost of all this is much less than a conventional DATA Logger !! • Versatility :- The ability to combine discrete (Digital) & Analog logic is a powerful tool for the Control Engineers. Control of critical start-up parameters, such as temperature and pressure, can be precisely pre-programmed for each start-up step.
  • 4. Why to use PLC’s ? • Expandability :- As a process matures, it is inevitable that enhancements will be needed. These usually require more outputs. For hard-wire Relays system this usually necessitates extensive panel changes, which generally are problematic. A PLC easily accommodates the additional I/O’s without requiring changes in the existing wiring. If a PID loop is to be added, no panel rework is necessary; only the wiring of new points and some re- programming to incorporate them is required.
  • 5. Why to use PLC’s ? • Flexibility :- As a process goes ONLINE and Refined, the Control Equipment should be easily reconfigured to accommodate such modifications. Bottling Plant Control, Traffic Light Control, Process Control of Temp., Pressure, Level, Flow etc., Car Parking Control etc. are all within the Capabilities of PLC’s. • As one common device (PLC) performs multiple functions in a Plant, fewer spare parts are needed . • The Digital nature and self- Diagnostic capabilities are strong
  • 6. Advantages of PLC over Electro-mechanical Relays • Ability to interface / communicate with Computers • Simple Programming • Field Programming possible (HHT) • High Reliability (Better MTBF) • Easy Maintenance • Rugged Construction - Can operate in Extremely harsh field conditions • Smaller Size • Easy Expandability (Due to Modular Design)
  • 7. Differences between - PLC & PC / Computers • Real Time Operation - PLC’s are designed to operate in a REAL-TIME control Environment. Most PLC’s have internal clocks and built-in “Watch-Dog Timers”.
  • 8. PLC’s Vs PC’s • Environmental Conditions PLC’s are designed to operate near the equipment they are meant to control. This means that they function in hot, humid, dirty, noisy and dusty industrial environments. PLC’s can operate in 60 Deg C as well as 0 Deg C, with tolerable relative Humidities ranging from 0% to 95% non-condensing.
  • 9. PLC Vs PC • Programming Languages & Techniques - • PLC - Ladder Diagram format is read & understood world- wide by maintenance technicians as well as by engineers. • Unlike Computer Programming, PLC Programming does not require extensive special training. • Programme operation are performed by the PLC in the order they were programmed . This allows easy programming of Shift Registers
  • 10. PLC Vs PC • Maintenance & Trouble-shooting • As PLC is a Plant Floor Controller it has to be maintained / serviced by plant electrician or the Instrument Technician. • It would be highly impractical to require computer type maintenance service. • Most PLC Components are modular and simple to isolate, remove-and-place (system
  • 11. Digital I/O Devices • Digital Input Field Devices • Pushbuttons, • Thumbwheel Swiches • Limit Switches • Selector Switches • Proximity Sensors • Photoelectric Sensors • Digital Output Field Devices • Discrete Outputs - Relays, Solenoids, Contactors, Motors starters, Annunciator Windows, Pilot Lights etc. • Register Outputs - Displays,
  • 12. Various Types of Transmitters T r a n s m itte r s T e m p e ra tu re T ra n s m itte rs P re s s u re T ra n s m itte rs F lo w T ra n s m itte rs L e v e l T ra n s m itte rs
  • 13. Analog I/O Devices • Analog Outputs – 4 to 20mA / 0 to 5V DC – Can drive signals to variable speed drives etc., Control Temperature, Pressure, Level, Flow, pH, Conductivity etc. • Analog I/P - • 4 to 20 mA / 0 to 5V DC • 12 Bit or better ADC • 32 Bit Storage (For SCADA) • Thermocouples T/C / RTD’s • Flow Transmitters • Temperature Transmitters • Level Transmitters • Pressure Transmitters • Strain Guage
  • 14. Digital / Analog I/O’s • Digital Inputs - 1-4096 / more • (Useful for sensing of entry of CAR) • (To Sense COIN in vending machine) • (To sense if Door Bell is pressed) • Digital Outputs – 1-4096 / more • (To indicate Traffic Light Signals) • (To display Alarm indication) • (To display CAR is exiting parking) • Analog Inputs - 1-4096 or more • (To continuously Scan the Temp.) • (To continuously Scan Level / Flow) • Analog Outputs - 1-4096 / more
  • 15. Digital I/O Voltages • DC Input Modules - 24 V DC 48 V DC 10-60 V DC 120 V DC 230 V DC 5-50 V DC Sink /Source 5 V DC TTL Level 5/12 V DC TTL Level • AC Input Modules – 24 V AC 48 V AC 120 V AC / Isolated 240 V AC / Isolated 24 V AC / DC
  • 16. Analog I/O Voltages Voltage Range Decimal Equivalent -10 V to + 10V - 32768 to + 32767 0 to + 10V 0 to + 32767 0 to +5V 0 to + 16384 1V to + 5V 3277 to + 16384 Current Range Decimal Equivalent -20mA to +20mA -16384 to +16384 0 to +20mA 0 to +16384 4 to +20mA 3277 to +16384
  • 17. PLC Programming Languages • Ladder Diagram Programming • Function Block Diagram • Sequential Function Chart • Statement / Instruction List • Structured Text
  • 18. PLC Programming [1] Edit / Write a Ladder Programme [2] Simulate Programme using Simulator [3] Change the Programme if necessary [4] Download the Programme PC to PLC [5] Execute the Programme in PLC [6] Change Inputs to see effects on Outputs [7] Modify the Programme for different field conditions & repeat steps 4,5,6.
  • 19. PLC Applications using Static Application Panels • CAR PARKING • TRAFFIC LIGHT CONTROL • SOFT DRINK DISPENSER • WASHING MACHINE • REACTION VESSEL • PROCESS CONTROL • TANK LEVEL CONTROL • DOOR BELL DIGITAL LOCK • MICROWAVE OVEN • BOTTLING PLANT • SEQUENTIAL CONTROL MOTORS • SWITCHING OF LIGHTS • MIXING OF 2 CHEMICALS • STARER CONTROL • STAR-DELTA STARTER
  • 20. Other Applications of PLC’s [1] Control of SPM’s (Special Purpose Machines - Like Drilling M/c or Grinding M/c or Lathes etc. [2] Packing Machines Like - Capsule Packing Machines Tablet Packing Machines; Milk Pouches Packing M/c.
  • 21. While Chosing PLC for an Application, following points should be taken into consideration • Maintenance • Spare Parts • Operation • Modifications • Losses (Production, Equipment, Personnel) • Information Technology • Space & Weight • Flexibility • Expandability • Operability • Cost of Control & Instrumentation
  • 22. Aspects of Control & Instrumentation • Standardisation • Speed of Response • Hardware Variety • Software Portability • User Interface • Memory • Compactness • Power Requirement • System Integrity (Reliability, Availability, Security) • Control & Logic Algorithms
  • 23. A Control Unit Should have following capabilities as Standard • Continuous Control • Batch Control • Logic • Advanced Control • Simulation • Neural Network & Knowledge based Systems • A PC-Oriented Programming Language • Dual or Triple Redundancy • High Scan rates (1 to 10 mS) • High Resolution Time Stamping (1 mS) • A Communication Processor that can handle popular protocols
  • 24. Safety Considerations • The most important safety feature, which is often neglected is PLC system design. This feature must be included whenever a hardwired device is used in order to ensure operator protection against the unwanted application of power. • Emergency STOP function should be completely hardwired. Software functions should not be relied upon to shut-off the process or the machine.
  • 25. NOISE • Electro-Magnetic Interference / NOISE / Unwanted Electrical Signals can generate problems for all solid state circuits, particularly Micro- processors. Each PLC manufacturer suggests methods for designing a noise-immune system. • I/O system are isolated from the field, but voltage spikes can still appear within the low-voltage environment of the PLC if Proper Grounding practices are not followed. Often it is necessary to keep AC and DC wiring bundles apart, particularly when high-voltage AC is used at the same time that low-level analog signals are present.
  • 26. Temperature Considerations • Installing any solid state device requires paying attention to – • Ambient Temperature • Radiant Heat Bombardment • And the Heat generated by the Device itself. • PLC’s are typically designed for operation over a broad range of Temperatures, usually from 0 to 60 Deg.C • For Cooling, blowing filtered air through the enclosure can resolve minor difficulties.
  • 27. Enclosures • Enclosure of PLC protects PLC’s from moisture, Oil, Dust Particles and unwanted tampering. • Most Manufaturers recommend NEMA 12 Enclosure for the Standard Industrial Environment. • PLC’s are designed to be located close to the machine or the process under control. This keeps the wiring runs short and aids in the trouble- shooting procedure. • It is not advisable to place a PLC near a Virating Machine, Electrical NOISE Interference or Excessive Heat Environment conditions.
  • 28. KEY-WORDS of PLC • PLC - Programmable Logic Controller • PID – Proportional + Integral + Derivative Control Function. • DCS – Distributed Control System • SCADA – Supervisory Control & Data Acquisition System • RTOS- Real Time Operating System
  • 29. KEY-WORDS of PLC • RTC - Real Time Clock • RTU – Remote Terminal Unit • Timers – On-Delay Off-Delay Monoshot / Monostable Pulse Flasher Astable Bistable • Counters – Up / Down
  • 30. KEY-WORDS of PLC • Flags / Registers / Latches / Memory Set-Reset / Retentive – Non-Retentive • HHT – Hand Held Terminal • HHP – Hand Held Programmmer It is used for PLC Programming at the Installation site. • MMI – Man-Machine Interface • HMI – Human Machine Interface Useful for ease of operation of PLC by operator/s.
  • 31. H.H.T./ H.H.P.- Advantages • Easy transfer of PLC Program to HHT / HHP for editing or troubleshooting. • Easy transport of a program to the field to update a current machines program. • Rugged and industrially hardened for the factory environment. • Low cost, cheaper than a notebook computer. • Easy to use & easy to learn, no software required. • Compact Size (pocket size) • Easy storage of Program • Monitor resident PLC Program for trouble shooting.
  • 32. H.H.T./ H.H.P.– Disadvantages • Not supported by some PLC’s. • An HHP can hold only one program at a time – whereas a Laptop / PC can hold many programs on its HDD. • HHP’s usually require more keystrokes to enter and get the same information as compared to a laptop / PC. • Limited capability to display ladder rungs due to screen size • Documentation not displayed • Different HHPs are needed for different PLC manufacturers if more than 1 PLC’s are in field. • If the Battery of the HHP discharges, a program stored
  • 33. KEY-WORDS of PLC • Memory Cartridge / Module Consists of either – RAM ---- Random Access Memory. (Volatile) EPROM -- Erasable Programmable Read Only Memory. EEPROM -- Electrically Erasable Programmable Read Only Memory. FLASH --- Non-Volatile
  • 34. Softwired Vs Harwired components of PLC • Soft-wired Components – Timers Counters Logic Circuits Latches • Hard-wired Components - 24 V DC Lamps Relays Contactors Solenoid Valves
  • 35. Scan-Time / Scan-Cycle • Scan Time of PLC – It is the time between an Input being sensed & the corresponding output. • Single Scan Cycle – Single Scan Cycle function enables the circuit diagram to run for one processing cycle and then stop. This is useful in analyzing the circuit diagram and observing how it works.
  • 36. PLC Scan • Input Scan – PLC scans all Inputs • Logic / Process Scan PLC goes through the ladder program / logic • Output Scan – PLC sends Outputs as per various Inputs and the corresponding
  • 37. Input Scan • During the Input Scan the CPU scans each Input module for the ON / OFF states of each of the associated input points. • The ON / OFF input states are stored in the input status file.
  • 38. Program Scan • After the inputs are read and stored in the input status file, the processor will use this information to solve the user ladder program. • The processor scans the user program starting at rung zero at the left power rail, working left to right and evaluating one instruction at a time until the output instruction is reached. • The Output status is the logical resultant of the solved input logic for that rung. The logical one or zero output status is placed in the output status file. • After completing rung zero, the processor goes on to rung 1,2,3… and so on, sequentially, to the last rung except in case of Master Control Relay (MCR) • At the end of the program, an END- Rung is automatically inserted which alerts the CPU the it has reached the
  • 39. PLC – Concepts • Forcing Inputs / Outputs • RS232C / RS422 Ports • Source-Sink Concept in PLC • How to select a PLC for a particular project ? • PLC Types –
  • 40. PLC – Concepts • Online (Run) / Offline Mode of operation. • Uploading/ Downloading of Programmes from - PLC to PC & PC to PLC • Display – LEDs / LCDs / VFD – Vacuum Florescent Display.
  • 41. PLC – Concepts •MCR – Master Control Relay Function • File Handling / Addressing System •PLC Simulator Software
  • 42. Key-Words of PLC • WDT - Watch-Dog-Timer – In case of PLC control loss due to EMI / NOISE, WDT brings back control of CPU to a Known State. This Timer Circuit usually resides on the CPU card itself. It works like a MONOSHOT PULSE GENERATOR of width greater than MAXIMUM SCAN TIME.
  • 43. WDT - Watch-Dog-Timer • In order to insure system predictability a WDT is used to insure that the processor completes each scan in a timely manner. • WDT is a hardware timer incorporated into the CPU’s circuitry that monitors the cyclical process / scan of the CPU. • WDT is a safeguard that verifies the processor does not become stuck while scanning the user program or for some other reason, become unable to complete the current scan.
  • 44. WDT - Watch-Dog-Timer • The WDT is reset at the end os each Scan Cycle by the CPU when the scan time is less than WDT’s preset time. • In case of one or more sub- routines, program scan time can exceed WDT time value. In some cases increasing the WDT’s preset value can solve the problem. • Some PLC’s have WDT with fixed time intervals, while others are adjustable within specific limits. • A typical default time of 100 / 200 mS is standard for many PLC’s with either fixed or
  • 45. SLC-500 - Processor operating modes • Program Mode • Run Mode • Remote Run Mode • Remote Program Mode • Test Mode • Single-Step Test Mode • Single – Scan Test Mode • Continuous Scan Test Mode • Test Mode – Test Program execution before allowing the PLC to operate the actual Hardware.
  • 46. GE – 90-70 CPU - Processor operating modes • Run with Outputs Enabled • Run with Outputs disabled • Stop Mode • Stop & I/O Scan Mode • Run Mode Store Function.
  • 47. Key-Words of PLC • CCU - Central Control Unit - It consists of a CPU + PALS- GALS + RTOS + EPROM / RAM / EEPROM • Process / Ladder Logic Memory It could be integrated with CPU or in a separate DATA / MEMORY CARTRIDGE / MODULE. Usually it is a replaceable Cartridge. • Optoisolation - Analog I/O’s should be isolated otherwise induction / pickup can lead to malfunctioning of PLC
  • 48. Digital Electronics • Boolean Algebra • Binary / Hexadecimal nos. • Logic Gates & Truth Tables • AND • OR • NAND • NOR • Ex-OR • Ex-NOR • NOT
  • 49. L o g ic F u n c t io n s A N D O R N A N D N O R N O T E x - O R E x - N O R T I M E R C A S C A D E T I M E R S R F L I P - F lo p C O U N T E R
  • 50. PLC Programming AND Timers APPLICATIONS Astable OR Monostable Traffic Light Control Process Control Bistable NOT Tank Level Control Bottling Plant NAND Counters Digital Lock NOR Flags Microwave Oven Retentive Ex-OR Non-Reten Washing Machine Door Bell & Alarm Ex-NOR Registers Sequential Control Retentive Silo Control
  • 51. Functioning of Timers / Counters / Flags / Registers PLC T IM E R S CO UNTERS FLAG S R E G IS T E R S 0 t o 2 5 6 in A n s h u m a n 0 t o 2 5 6 n o s in A n s h u m a n 0 t o 2 5 6 n o s in A n s h u m a n 0 t o 2 5 6 n o s in A n s h u m a n M o n o s t a b le U p C o u n te r R e t e n t iv e R e t e n t iv e A s t a b le D o w n C o u n te r N o n - R e t e n t iv e N o n - R e t e n t iv e
  • 52. DCS / SCADA •D.C.S. :- Distributed Control Systems •S.C.A.D.A.:- Supervisory Control And Data Acquisition System. (Through Network Data Acquisition, Data Display, Data Processing, Data Storage, Data Analysis etc.)
  • 53. DCS Vs SCADA • Generally supplied by • Normally supplied by a single Vendor with Multiple / Competing dedicated H/W & Vendors S/W. • Competitive cost due to Multi-Vendor products. • Costly due to • Can be applied to redundent design very low cost applications • Application Areas - • Comm’n - Can cover Large Mfg. Facilities larger geographical area by use of modems and T/p lines • Comm’n - Confined to factory premises (LAN for H/W) • Small to medium Analog I/O’s with / without PID. • Analog Processing - Large Analog I/O’s • Programming - PLC by using PID’s relay Ladder Diagram or STL and SCADA using built-in graphics • Programming - by editor and drivers. creating drawing like charts called as configuration diagram • Suppliers - PLC’s - Siemens, Allen Bradley, Omron etc. • Suppliers - Honeywell, SCADA - Intellution, NI-Lookout / Labview
  • 54. Following Displays are available in most Control Systems • Overview • Area • Group • Details • Trends • Configuration • Diagnostics • Alarm Summary • System Status (LAN) • Scratch Pad
  • 55. Solid State O/P Switching • Advantages – [1] Fast Switching Speeds [2] High Reliability & almost infinite life [3] Low Power required to energize [4] No Contact Arcing [5] Little / nil Switching noise [6] +ve switching, no contact bounce [7] Can be hermetically sealed – good for hostile environments. • Disadvantages – [1] May be destroyed by overload [2] Tend to fail in ON state [3] Heat dissipation [4] Expensive to purchase [5] Possibility of false trips from electrical noise.
  • 56. Relay O/P Switching • Advantages – [1] Contacts forgiving to a temporary overload [2] Immune to false trips from elec noise [3] Little voltage drop across contacts [4] No restrictions when connecting in series or parallel configurations [5] Difinite ON / OFF state, with contacts physically open. [6] No Leakage [7] Contacts generate little heat [8] Inexpensive to purchase • Disadvantages – [1] Mechanical switching is slow [2] Mechnical life is limited by demands of the load and the contacts. [3] Require 50mA or more to energize [4] Subject to contact arcing or welding [5] Subject to contact bounce
  • 57. PLC – Reference Books • Programmable Logic Controllers. – By – John Web • Programmable Controllers – By – Richard Cox. • Introduction to Programmable Logic Controllers – By – Gary Dunning
  • 58. Other Terms related to Control Systems • UCP - Unified Control Panel • UCS - Unified Control System • UCN - Universal Control Network • UOC - Unit Operation Controller • TDC - Totally Distributed • Control System • SOE - Sequence Of Events • SP --- Set-Point • SFC - Sequential Function Chart • SAT - Site Acceptance Test • SAS - Safety & Automation Systems
  • 59. Other Terms Used in Control Systems RTU - Remote Terminal Unit ROC - Rate of Change PV --- Process Variable PS --- Process Station PSD - Process Shut-Down PIU - Plant Interface Unit PIN - Plant Interface Network PCS - Process Control System PFD - Process Flow Diagram PCN - Process Control Network
  • 60. Other Terms Used in Control Systems OBT - Optical Bus Terminal OLE - Object Linking & Embedding OLM - Optical Link Module NIU - Network Interface Unit MC---- Multifunction Controller MTU - Master Terminal Unit MCS - Master Control Station MAS - Manufacturing Automation System MAP - Manufacturing Automation Proto’l MTBF - Mean Time Between Failure MTTR - Mean Time To Repair
  • 61. Other Terms Used in Control Systems • LLPIU - Low-Level Process Control Station • LCN --- Local Control Network • LCR --- Local Control Room • LAN --- Local Area Network • ISA - Instrument Society of America • ISO - International Standards Organization • HSE ---- High Speed Ethernet • HIPPS -- High Level Process Protection System • HAZOP - Hazard & Operability Study
  • 62. Other Terms Used in Control Systems • FAT- Factory Acceptance Test • EUC - Equipment Under Control • ESD - Emergency Shut-Down System • EC --- Extended Controller • DPS - Dynamic Positioning System • AC --- Adaptive Control • CFC - Continuous Function Chart • C & I - Control & Instrumentation • CCR -- Central Control Room
  • 63. • Other Terms Used in Control Systems • BCL -- Batch Control Language • BC --- Basic Controller • AEC - Advanced Extended Controller • AMC - Advanced Multifunc’n Controller • CAD - Computer Aided Design • CADAS - Computer Aided Design Analysis & Application
  • 64. FF-Bus -Foundation Field Bus • FF-Bus is a Digital Comm’n System • A Summary of improvements, which FF-Bus will offer as it becomes more widely applied are – * Higher Communication Speed - 10 to 100 M Baud * Higher nos. of modes per branch to reduce cabaling & termination effort • More efficient Communication • Better diagnostics & predictive maintenance in field
  • 65. FF-Bus • More reliable Control System because of better maintenance & Higher distribution control. • Faster Control System Response. • Saving in Hardware (Cabling, I/O cards, Cabinets) • Higher Accuracy because Process Parameters are Sampled Locally & Transmitted Digitally to local / remote Control Units. • Major Improvements in System
  • 66. FF-Bus • Reduction in Documentation (No. of Loop Diagrams, Termination Schedules etc.) • Possibilities od using Multifunction Instruments - Where one Transmitter measures multiple variables (e.g. A Corolis meter can measure - flow, Density & Temperature ) • A High Degree of Inter- operability among system Computers & Instruments from different Vendors.
  • 67. • DPS - Dynamic Positioning System • Availability = MTBF / (MTBF + MTTR) • Categories of Consequences Definitions • Catastrophic ---- Multiple Loss of Life • Critical -------- Loss of a Single Life • Marginal ------- Major injuries to one or more persons. • Negligible ------ Minor injuries at worst
  • 68. Catagories of Likelihood Categories Definition Failures of Likelihood (in System Life) Per Year Frequent Many Times > 10-3 -4 Probable 10 to Several Times -3 10 -5 Occasional One Time 10 to -4 10 -6 Remote Unlikely 10 to -5 10 -7 Impossible Very 10 to -6 Unlikely 10 Incredible Cannot believe < 10-7 it could happen
  • 69. * Analog Input :- DC models of Pico are provided with two analog inputs I7 and I8. The permissible input voltages are between 0 V and 10 V. The measured data is evaluated by an integrated Analog Value Comparator relay. * Circuit Connection: Each line in the circuit diagram display is a circuit connection.
  • 70. Circuit Diagram Elements: The circuit diagram is made up of circuit diagram elements from conventional wiring practice. These include input, output and auxiliary relays as well as function relays and P buttons. Contact/Coil Monitor: The Contact/Coil Monitor is a dialog for displaying and forcing the logic states of selected relays (contacts / coils).
  • 71. Device Test :- The device test shows in plain text the results of comparison between the selected Pico device and the circuit diagram. All contact/coil elements that are not available on the device used will be listed, and the number of circuit connections used will be checked. If the Pico device cannot properly process the circuit diagram, a device will be suggested on which the circuit diagram can be used successfully.
  • 72. Function Relay :- Function relays are used for complex switching tasks. Pico devices are provided with the following function relays: Timing relays (T), Time switches (H), Counters (C), Analog value comparators (A), Text relays (D). Impulse Relay :- An impulse relay is one that changes and then retains this state if a voltage is momentarily applied to it.
  • 73. Input :- External contacts are connected to the inputs of the device. Inputs are evaluated in the circuit diagram via the switching contacts I1 to I12 and R1 to R12. The 24 V DC Pico models can also receive additional analog data via inputs I7 and I8. Input Debounce :- Input signals can be evaluated by the device with a delay in order to compensate for the contact bounce of switches and pushbuttons.
  • 74. Interface :- The device interface allows circuit diagrams to be exchanged and stored on a memory card or PC. A memory card saves both the circuit diagram and device settings. PicoSoft PC software allows you to control the device from the PC. The PC is connected to Pico via the "1760-CBL-PM02" cable.
  • 75. I/Q Window :- The I/Q window contains the input simulator and the display for Q and S coils. The input simulator or I window is used as a central tool in circuit diagram simulation. It enables you to create dynamic input signal states for the simulated circuit diagram. For this you can also assign different functions to the I and R buttons.
  • 76. I/R Function :- The I/R Function determines the switching function of the elements I1 to I16 and R1 to R16. These can be latching make contacts, latching break contacts, momentary make contacts or momentary break contacts.
  • 77. Operator Buttons :- The device features 8 operator buttons by which you can select the menu functions and also enter the circuit diagram directly via the Pico display. The centrally arranged cursor buttons are used to move the cursor in the Pico display. DEL, ALT, ESC and OK are also provided with additional functions.
  • 78. Output :- The outputs are used to switch loads such as contactors, lamps or motors. The outputs are controlled in the circuit diagram via the output relay coils Q1 to Q8 and S1 to S8. Parameters :- Function relays are assigned particular parameters by the user. Set values may include, for example, switching times or counter setpoints. These are set in the Contact/Coil
  • 79. P Buttons :- The P buttons allow you four additional inputs that are switched via the cursor buttons on Pico instead of external contacts. The switching contacts of the P buttons are wired in the circuit diagram.
  • 80. Retention :- This function allows data to be retained in the device even after its power supply has been switched off. Retentive data consists of: Device circuit diagram, parameters, setpoints, text, system settings, password, actual values of auxiliary relays (markers), timing relays, counters.
  • 81. Signal Diagram :- The Signal Diagram allows you to display the behavior up to eight selected relays along a time axis. The diagram produced can also be printed out for documentation purposes. Single Cycle :- The Single Cycle function enables your circuit diagram to run for one processing cycle and then stop. This helps you in analysing the circuit diagram and observing how it works. This function is only available during Simulation.
  • 82. Startup Behavior :- The startup behavior is an important help during commissioning. The circuit diagram may not be completely wired when it is transferred to Pico, or the system/machine to be controlled is in a state in which it cannot be controlled by Pico. If Pico is then switched on, it may therefore be desirable for the outputs to remain inactive. For this set the startup behavior to STOP. If the startup behavior is set to RUN, Pico will start processing the circuit diagram as soon as it is switched on.
  • 83. Stop Point :- In order to analyse your circuit diagram effectively, you need a tool to interrupt processing selectively, evaluate the state of selected contacts or coils and continue processing. The Stop Point function makes this possible. It is only available during Simulation.
  • 84. Wiring via the Keyboard PicoSoft also enables you to wire up your circuit diagram via keyboard commands. Selecting Make/Break Contact Behavior :- Entering letters in lower case selects make contacts, and entering letters in upper case selects break contacts.
  • 85. Adding / Deleting Contacts :- Position the cursor on the contact field required and enter the contact via the keyboard. Use the following shortcuts for contacts & f’n relays: i, I Controller Inputs p, P Soft Inputs - Keypad q, Q Controller Outputs m, MInternal Marker Bits c, C Counters t, T Timers h, H Time Switch Relay a, A Analog Setpoint Compare d, D Text Display r, R Expansion Inputs s, S Expansion Outputs or Internal Marker Bits To delete the contact, press the Del key
  • 86. Adding / Deleting Coils Position the cursor on the coil field required and enter the coil via the keyboard. Use the following shortcuts for coils and coil functions: q Controller Outputs m Internal Marker Bits t Timer "Trigger" coil c Counter "Trigger" coil d Text Display "contactor" function s Internal Marker "contactor" function
  • 87. To select the coil function required, press the Shift key and select the appropriate coil function letter below: Shift + E Impulse relay Shift + S Latching (Set) Shift + R Unlatching (Reset) Shift + D Direction coil for counter The default setting is for the contactor function. To revert to the simple contactor function of the coil, press the letter for the coil concerned.
  • 88. To delete the coil, press the Del key. Connecting Inputs and Outputs Use Shift+Cursor key to make the connection between the individual contacts and coils. Adding Empty Lines Position the cursor on the circuit connection in front of which you wish to add the empty circuit connection. Press Ctrl+I to add the empty circuit connection.
  • 89. Deleting Circuit Connections Position the cursor on the circuit connection you wish to delete. Press Ctrl+D to delete the entire circuit connection. Deleting Connections Position the cursor on the connection you wish to delete. To delete the connection, press the Del key. If the circuit connection contains branches, the selected connection will only be deleted up to the next node.