1. Programmable Logic Controllers PLC’s
An Overview, Use in HVAC and Web Technologies
By Sleepy Wombat

2. Overview What is a PLC ? History Overview of Technology
PLC Configuration and Selection
Programming PLC’s
PLC’s in HVAC
Web Technologies

3. What is a PLC ? PLC (Programmable Logic Controller)
A PLC works by looking at its inputs and depending on their state, and the user entered program, turns on/off outputs.
A PLC can be thought of as:
Industrial Computers with specially designed architecture in both their central units (the PLC itself) and their interfacing circuitry to field devices (input / output connections to the real world).

4. History 1/4
Early control systems consisted of huge control boards consisting of hundreds to thousands of electromechanical relays.
An Engineer would design the system logic.
Electricians would receive a schematic outline of logic then implement the logic with relays.
The schematic was commonly called “Ladder Schematic”
The Ladder displayed all switches, sensors, motors, valves, relays etc in the system.
Problems: Long commissioning time, Mechanical Reliance, Any system logic design change required the power to the control board to be isolated stopping production.

5. History 2/4
General Motors was among the first to recognise a need to replace the systems “wired control board”
Hydramatic Division of GM specified the design criteria for the programmable controller in 1968.
Goal – Eliminate the high cost associated with inflexible, relay controlled systems.

6. History 3/4 New Controller Specifications: Solid State System
Computer Flexibility
Operate in Industrial Environment (vibrations, heat, dust etc.)
Capability of being reprogrammed
Easily programmed and maintained by electricians and technicians.

7. History 4/4 In 1969 Gould Modicon developed the first PLC.
Strength – Programmed with Ladder Logic
Initially called Programmable Controllers PC’s
Now - PLC’s, Programmable Logic Controllers
PLC’s have evolved from simple on/off control to being able to communicate with other control systems, provide production reports, schedule production, diagnose machine and process faults.

8. Overview of Technology

9. Basic PLC Schema CPU Power Supply Memory Input Blocks Output Blocks
Communications
Expansion Connections

10. CPU Module
The Central Processing Unit (CPU) Module is the brain of the PLC.
Primary role to read inputs, execute the control program, update outputs.
The CPU consists of the arithmetic logic unit (ALU), timing/control circuitry, accumulator, scratch pad memory, program counter, address stack and instruction register.
A PLC works by continually scanning a program
PLC Program
SCAN 1

11. Memory
The memory includes pre-programmed ROM memory containing the PLC’s operating system, driver programs and application programs and the RAM memory.
PLC manufacturer offer various types of retentive memory to save user-programs and data while power is removed, so that the PLC can resume execution of the user-written control program as soon as power is restored. 1

12. Memory cont’d
Many PLCs also offer removable memory modules, which are plugged into the CPU module.
Memory can be classified into two basic categories: volatile and non-volatile.
- Volatile memory is that which loses state (the stored information) when power is removed.
- Nonvolatile memory, on the other hand, maintains the information in memory even if the power is interrupted.

13. Memory cont’d Some types of memory used in a PLC include:
ROM (Read-Only Memory)
RAM (Random Access Memory)
PROM (Programmable Read-Only Memory)
EPROM (Erasable Programmable Read-Only Memory)
EEPROM (Electronically Erasable Programmable Read-Only Memory)
FLASH Memory
Compact Flash – Can store complete program information, read & write text files

14. I/O Modules
Input and output (I/O) modules connect the PLC to sensors and actuators.
Provide isolation for the low-voltage, low-current signals that the PLC uses internally from the higher-power electrical circuits required by most sensors and actuators.
Wide range of I/O modules available including: digital (logical) I/O modules and analog (continuous) I/O modules. 1

15. Inputs Modules
Inputs come from sensors that translate physical or chemical phenomena into electrical signals.
The simplest form of inputs are digital/discrete in AC/DC.
In smaller PLCs the inputs are normally built in and are specified when purchasing the PLC.
For larger PLCs the inputs are purchased as modules, or cards, with 8,16, 32, 64, 96 inputs of the same type on each card. 1

16. Inputs Modules The list below shows typical ranges for input voltages.
5 Vdc
12 Vdc
24 Vdc
48 Vdc
12 Vac
24 Vac
120 Vac
240 Vac 1

17. Example of Input Card 1

18. Outputs Modules
Output modules rarely supply any power, but instead act as switches.
External power supplies are connected to the output card and the card will switch the power on or off for each output.
A common choice when purchasing output cards is relays, transistors or triacs.
Relay are the most flexible output devices. They are capable of switching both AC and DC outputs. But, they are slower, cost more, and they will wear out after millions of cycles. 1

19. Relays
The most important consideration when selecting relays, or relay outputs on a PLC, is the rated current and voltage.
For transistor outputs or higher density output cards relay terminal blocks are available.
Advantage of individual standard replaceable relays 1

20. Outputs Typical output voltages are listed below, 5 Vdc 12 Vdc 24 Vdc
24 Vac
120 Vac
240 Vac
WARNING: Always check rated voltages and currents for PLCs and never exceed. 1

21. Example of Output Card 1

22. Analogue Cards Typical Analogue Input signals are:
Flow sensors
Humidity sensors
Load Cells
Potentiometers
Pressure sensors
Temperature sensors
Vibration
Analogue Output signals control:
Analogue Valves
Actuators
Chart Resorders
Variable Speed Drives
Analogue Meters
Typical Analogue Signal Levels
4-20mA
1-5 Vdc
0-10 Vdc
-10 – 10Vdc 1

23. Analogue Inputs/Outputs
Analogue input cards convert continuous signals via a A/D converter into discrete values for the PLC
Analogue output cards convert digital values in then PLC to continuous signals via a D/A converter.
Resolution can be important in choosing an applicable card
Example, for a temperature input of 0 to 100 degrees C
For 8 bit resolution the value in the PLC is 0 to 255
For 12 bit resolution the value in the PLC is 0 to 4095
For 12.5 bit resolution the value in the PLC is 0 to 6000
For 13 bit resolution the value in the PLC is 0 to 8192
For 16 bit resolution the value in the PLC is 0 to 32768

24. Special Modules RF ID Voice Gas Flow Calculation Weigh Cell
Hydraulic Servo
ASCII
Fuzzy Logic
Temperature Sensor
Temperature Control
Heat/Cool Control
Field Bus Cards
DeviceNet, Profibus etc
Lonworks, BACNet
Fast Response (Interrupt)
PID
Loop Controller
BASIC Cards
RS232 Comm’s
Modbus ASCII/RTU
Ethernet Comm’s
High Speed Counters
Position Control Cards
Per to Per Comm’s
Controller Link
DH+
Modbus Plus

25. Available Instructions
Sequence
Input
Output
Control
Logic
Timer and Counters
Comparison
Range Comparison
Data Movement
Data Shift
Step / Step Next
Serial Communications
Text String Processing
File Manipulation
Increment/Decrement
Conversion
ASCII
Number Systems
Math
Floating Point Math
Statistics
Scaling
PID
PID with Auto tune
Clock / Date
Block Processing
IF,THEN,ELSE,LOOP
Table Processing
LIFO, FIFO

26. Networks
ASI
Devicenet
Interbus-S
Profibus
Interbus
Fieldbus
Ethernet I/P
Smart Distributed System (SDS)
Seriplex
CANopen
Lonworks
BACNet
Gateways enable communications between different network topologies

27. PLC Configuration
MINI
RACK
SHOE BOX
MICRO

28. The Configuration of PLC
The configuration of PLC refers to the packaging of the components.
Typical configurations are listed below from largest to smallest.
Rack Type : A rack can often be as large as 18” by 30” by 10”
Mini: These are similar in function to PLC racks, but about the half size. Dedicated Backplanes can be used to support the cards OR DIN rail mountable with incorporated I/O bus in module.
Shoebox: A compact, all-in-one unit that has limited expansion capabilities. Lower cost and compactness make these ideal for small applications. DIN rail mountable.
Micro: These units can be as small as a deck of cards. They tend to have fixed quantities of I/O and limited abilities, but costs will be lowest. DIN rail mountable. 1

29. Sizing of PLC Micro PLCs: I/O up to 32 points
Small PLC: I/O up to 128 points
Medium PLC: I/O up to 1024 points
Large PLC: I/O up to 4096 points
Very Large: I/O up to 8192 points 1

30. Selecting a PLC Criteria Number of logical inputs and outputs Memory
Number of special I/O modules
Expansion Capabilities
Scan Time
Communication
Software
Support
Dollars 1

31. Selecting a PLC 1

32. Example of PLC Specifications1

33. Example of PLC Specifications1

34. Manufactures Major Brands OMRON Allen Bradley
Schneider (Modicon, Telemecanique, Square D)
GE Fanuc
Siemens
Automation Direct (Koyo)
Toshiba
Mitsubishi
Hitachi
Keyence
Festo
Eberle
Texas Instruments
April

35. Programming PLC’s

36. Programming PLC’s
Ladder Logic remains the most common technique for programming PLC’s

38. PLC Standardization Open Controller
IEC 61131
Based on IEC 1131 (1992) standard, developed to be a common and open framework for PLC architecture.
IEC Overview
IEC Requirements & Test Procedures
IEC Data Types & Programming
IEC User Guidelines
IEC Communications
IEC Fuzzy Control
IEC Guidelines for the application and implementation of programming languages

39. IEC 61131-3 IL (Instruction List) – mnemonic programming
LD (Ladder Diagram) – Relay logic
ST (Structured Text) – A BASIC like programming language
FDB (Functional Block Diagram) – Graphical dataflow programming language
SFC (Sequential Flow Chart) – Graphical method for structured programs

40. IEC 61131-3 Examples Ladder Instruction List Structured Text
Function Block
Sequential Flow Chart

41. PLC’s in HVAC control

42. PLC’s in HVAC control
Despite the versatility of today’s PLC’s, many controls professionals are skeptical of applying PLC’s to new applications such as HVAC control.
Reasons included :
Lack of knowledge of these systems
Requirement for programming
Lack of initial capability of technology
Premium first up cost

43. Advantages
PLC’s remain a predominate piece of equipment on the factory floor and will probably remain so for some time to come.
The advantages they offer are:
Cost effective for controlling complex systems
Flexible and can be reapplied to control other systems quickly and easily
Computational abilities allow more sophisticated control
Trouble shooting aids make programming easier and reduce downtime
Reliable components (high MTBF) ensure operation for years

44. Advantages continued….
Variety of I/O interfaces
Small size
Growing with technology, faster scan times, capability etc
Quick I/O disconnects that aids in field servicing
Modularity in hardware architecture
Modularity in software design (programmer dependant)
Software Timers/Counter, Relays
Clean failure mode
On-line programming
Self inspecting for operation code during execution
Availability of programmers/trouble shooters/integrators
Availability of replacement parts

45. Benefits
The benefits achieved with programmable controllers will grow with the individual using them:
“The more you learn about PLC’s, the more you will be able to solve other control problems.”

46. Examples Southgate – Melbourne Millennium Dome – London
Woolworths – Britain
ST Microelectronics – France
Einstein III Building - Munich

47. Web Technologies

48. Web Enabled Automation...?
Is it just more Internet hype or is there some benefit behind the idea.
Is it possible to connect all of these systems by their PLC’s to the Internet ?
Is it practical ?
Is it profitable ?

49. Short Answers……
Internet access can provide compelling competitive advantages linking customers, suppliers, subcontractors, front line management.
Improve fault reporting and response time
Enhance flexibility
Optimise process control
Proven affordable technologies are readily available to connect any PLC, Process Controller or I/O to the Internet and Intranet.
Process to Internet access has the potential to become a standard utility.

50. What is Web Enabling
Web enabling gives real time access to data and control, virtually anytime, anywhere.
It uses communication with any manufactures PLC or I/O to send information via the Internet to anywhere in the world.
Web enabled automation drives real-time accessibility “Vertically Down” to the control device level.

51. What can we do with it ?
Check real time process data without waiting for end of shift reports
Track equipment run time and initiate maintenance requests
Automatically notify a technician via or GSM phone etc of faults and allow rectification
Collect process data on a server PC and analyse with statistics and control (SPC)
Use HTML help files including graphics
Monitor and control remote operations reducing field staffing and unnecessary travel

52. What pieces and parts are required ?
Interface
Web Server
Data Service
Browser

53. Interface
An interface to the equipment to be monitored and controlled via the web (network) connection
Ethernet Line
Modem / Phone line
ISDN
Wireless Modem (eg b Ethernet)
Type of connection is typically determined by the thin server and the existing network infrastructure – or lack thereof

54. Web Server
Web Server (or “thin server” data service) to enable the remote browser to view the desired displays and web pages.
Typical installation requires a connection to an existing PLC or proprietary controller.
Most PLC’s support at least a serial connection using the vendor supplied protocol to communicate.
Use an Open network controller (interface)
Some PLC’s have Web Servers built into their Ethernet Units.

55. Data Service
A data service or interface to handle exchanging data between the local equipment/ process (server) and the remote system (client)
A common “language”, protocol is required..
XML (Extended Markup Language)
Benefit of XML is its independence from senders and receivers hardware, OS, and application.

56. Browser Interface
Use the thin servers assigned IP address to access the remote system.
Simple browsing requires standard browser interface found on a desktop computer, PDA, WAP, or “Thin Client”
For application information sharing (SPC, Enterprise Software), if the thin server and remote application software support a common interface such as OPC, setting up the data exchange can be accomplished in a couple of minutes

57. New term … OPC OLE for Process Control Object Linking and Embedding
One of industries most popular standards
Maintained by OPC foundation
OPC standard is non proprietary technical specification based on Microsoft's OLE/DCOM technology.

61. Web Servers Computer Based Displays
SCADA – Supervisory Control and Data Acquisition
Citect, Wonderware, Fix, Iconics, Genius
Ethernet, Serial, OPC (OLE for Process Control), Dedicated Computer Boards for Propriety Buses
Dedicated Packages for BMS
Citect SCADA Facilities
Embedded Web Servers
Open Network Controller Interface – Gateway
Embedded Web Servers in PLC’s Ethernet cards
New Dedicated HMI Screens – some have embedded Web Servers
Example of Web Technology visit

64. Thank you….
Questions ?