Programmable Logic Controllers (PLC)
PLC Presentation Contents • • • • • • • •
Introduction What is a PLC PLC Types Choosing PLC Hardware PLC Applications Programming PLC’s Advantages of PLCs Questions
What is a PLC?
Nema Definition circa 1978 . The PLC, also known as programmable controller is defined by the National Electrical Manufacturers Association (NEMA) in 1978 as: "a digitally operating electronic apparatus which uses a programmable memory for the internal storage of instructions for implementing specific functions, such as logic, sequencing, timing, counting and arithmetic, to control through digital or analog input/output, various types of machines or process".
Traditional PLC Concept
• • • •
PLC performs relay equivalent functions PLC performs ON/OFF control Ladder diagram programming Designed for industrial environment
Relay Logic vs. PLC & Ladder Logic PB1
LS1
PB2
LS1
SOL2
Outputs
Inputs
Programmable Logic Controller
CR3
C R
LS3 I/4
I/6
||
CR3 |/|
LS4
M1
||
O/0
()
I/7
I/5
B/0
||
||
()
I/8
||
B/0
|/|
I/9
||
O/1
()
Input Wiring: PLC input is the load in the circuit, sensing if voltage is present Isolation Barrier
Terminal Block
Input Devices
1 2 3
L1 L1
4 5 6 7 8 9
L2
10 COM
P L C
Input Devices • Pushbuttons
• 120/230 VAC
• Selector Switches
• 24 VDC
• Limit Switches
– Sourcing
• Level Switches
– Sinking
• Photoelectric Sensors • Proximity Sensors • Motor Starter Contacts • Relay Contacts • Thumbwheel Switches
Output Wiring: PLC output is the switch, controlling current flow to load Isolation Barrier
CR
Terminal Block
OUT 1 OUT 1
Output Devices L1 L2
OUT 2
P L C
OUT 2 OUT 3 OUT 3 OUT 4 OUT 4 OUT 5 OUT 5 OUT 6 OUT 6
L1 L2
Output Devices • • • • • • • •
Valves Motor Starters Solenoids Control Relays Alarms Lights Fans Horns
• Relays – 120 VAC/VDC – 240 VAC – 24 VAC/VDC
• Triac – 120/230 VAC
• Transistor MOSFET – 24 VDC
Inside a PLC Communications
I n p u t
High Voltage Isolation Barrier
C i r c u i t s
Central Processor
MEMORY data
program Low Voltage AC Power Supply 85-264 VAC, 50/60Hz
or
External DC Power Supply
O u t p u t
C i r c u i t s Isolation Barrier
CR
High Voltage
PLC Operating Cycle START
Housekeeping Internal checks on memory, speed and operation. Service any communication requests, etc.
Output Scan The Output Image data is transferred to the external output circuits, turning the output devices ON or OFF.
Input Scan The status of external inputs (terminal block voltage) is written to the Input image (“Input file”).
Program Scan Each ladder rung is scanned using the data in the Input file. The resulting status (Logic being solved) is written to the Output file (“Output Image”).
PLC Hardware Types
Most Basic of PLC Systems In the most basic of PLC systems, a self contained (shoe box) PLC has 2 terminal blocks, one for Inputs and one for Outputs Today, most PLC’s in this category are know as Micros. Typically they provide front panel LED status indication of I/O and Processor states Outputs
Inputs
Programmable Controller C R
Modular Chassis Based PLC’s The vast majority of PLC’s installed today are modular chassis based systems consisting of: 2. Processor Module (CPU) 3. Input & Output Modules 4. Chassis 5. Power Supply
Modular Chassis-less PLC Systems Also available from many vendors are “Chassis less” but still Modular PLC systems. These systems still require a Processor, I/O Modules, and Power Supply, but in place of a chassis these components mount directly onto a panel, din rail, and many use a tongue and grove system to allow easy insertion and removal
Choosing PLC Hardware
PLC Application Considerations • Inputs/Outputs – Type, • AC, DC, sourcing, sinking, etc.
– Number of • 10, 16, 20, 32, 156
• Memory – Type • Flash or Battery backed
– Size • 1k, 6k, 12k, 16k, 64k
• Functions required – Instruction set • Messaging • PID • PTO, PWM
– Arithmetic – Communications • DeviceNet, Ethernet • Remote I/O, DH+
– Report generation
SOURCING vs. SINKING
SOURCING Pushbutton (PNP)
SINKING Pushbutton (NPN) +VDC
+
+ DC Power Suppl y
-
DC Power Suppl y
-
DC COM
SOURCING vs. SINKING DC Inputs
SINKING (NPN)
SOURCING (PNP) Field Device
+ DC Power Suppl y
-
+VDC IN1
DC
Input DC COM
Modul e
+ DC Power Suppl y
-
DC Input Field Device
Modul e
IN1
Rules
RULES • Field devices on the positive side (+VDC) of the field power supply are sourcing field devices. • Field devices on the negative side (DC COM) of the field power supply are sinking field devices. • Sourcing field devices must be connected to sinking I/O cards and vice versa. • Sinking field devices must be connected to sourcing I/O cards and vice versa.
PLC Applications
Installed and Running Systems in RI -
Conveyors Curtain rods Deodorants Donuts Duplex Receptacles Fibers Filters Forged Parts Glass Goggles Grinding and Polishing Heat Treating Metal Products Jails Lenses Nails Natural Gas Paper
-
Pharmaceuticals Plastics Plating Plating Machines Power Generation Power Supplies Product Assembly Machines Rubber products Seafood Processing Soda Staples Warehouse Automation Waste Water Systems Drinking Water Systems Water Heaters Web Handling (paper/plastic) Wire / Cable
Typical PLC Application
Solenoid 1
Motor
Solenoid 2
Ingredient A
Ingredient B
Sensor 1
Sensor 2
Solenoid 3
Operation of Mixer (Sequence of Control) • Solenoid 1 – On = Sol 3 is off, and Motor is off, and Sensor 2 is off, and Auto Switch is on – Off = Sol 3 is on, or Motor is on, or Sensor 2 is on
• Solenoid 2 – On = Sol 3 is off, and Motor is off, and Sensor 2 is on – Off = Sol 3 is on, or Motor is on, or Sensor 1 is on
• Motor – On = Sensor 1 is on, and Solenoid 2 is off, and Solenoid 1 is off – Off = Solenoid 3 on
• Solenoid 3 – On = Sol 1 is off, and Sol 2 is off, and Motor has run for 30 sec. – Off = Solenoid 3 has been on for 60 sec. Solenoid 1
Solenoid 2
Motor
Ingredient A
Ingredient B
Sensor 1
Sensor 2
Solenoid 3
PLC Applications: Packaging De-Palletizing, Washing, Filler, Capper, Case Packaging, Wrapping, Cartoning, Labeling, & Bagging Machines
PLC Application: SCADA & RTU Supervisory Control and Data Acquisition (SCADA)/Remote Terminal Unit (RTU) •
puts the remote site report data at your fingertips, but also provides affordable remote communications and control, minimizing the likelihood of remote site issues.
PLC Applications: Material Handling • Control of rollerbed conveyors or towveyors, and mobile equipment including transfer vehicles, elevated transfer vehicles, lifts and hoists, and stacker cranes.
PLC Applications: Distribution Start and stop conveyors, control traffic at merge points, redirect packages at divert points, and control a wide assortment of OEM machines such as palletizers and accumulators.
PLC Programming
Programming PLC’s The purpose of a PLC Program is to control the state of PLC outputs based on the current condition of PLC Inputs Different PLC’s support different languages, but the most popular PLC language is know as “Ladder Logic”. PLC Ladder Logic purposely resembles Relay Logic
Ladder Logic Concepts Read / Conditional Instructions Start (Rung #1)
||
()
|| ||
Write / Control Instructions
||
||
|/|
()
|/|
()
|/|
()
|/|
()
|| End (Rung #5)
||
Ladder Logic Concepts
Read / Conditional Instructions
Write / Control Instructions
|/|
||
()
T
F
F
No Logical Continuity
|/|
|/|
()
T
T
T
Logical Continuity
Logical AND Construction
IF input 4 AND input 5 have power THEN energize output 0 I/4
I/5
O/0
T
T
T
||
||
Logical Continuity
()
On
Logical OR Construction
IF input 4 OR input 5 have power THEN energize output 0 I/4
T
O/0
||
F
()
Logical Continuity
I/5
||
I/4
F
O/0
||
T
On
I/5
||
()
Logical Continuity
On
Complex Construction
I/4
I/0 I/1
||
|/|
||
I/5
I/1
I/7
I/2
I/3
||
|/|
||
|/|
I/9
||
I/8
|/|
||
I/11
|/|
I/1
||
I/10 O/0
|| ()
Read Instructions
Supply Voltage LS 1
Unused
Unused
COM
I/0
I/1
I/2
I/3
I/4
COM
I/5
I/6
I/7
The instruction is: If the input device is
The input bit is
Examine ON
Examine OFF
-| |-
-|/|-
XIC
XIO
Open (0)
Logic 0
False
True
Closed (1)
Logic 1
True
False
I/8
I/9
Write Instruction ||
|/|
()
T
T
T
OTE Output Energize
Rung State
Output Bit
Output Terminal
TRUE
ON
ENERGIZED
FALSE
OFF
De-energized
-( )-
L1
L2/N
GND
VAC VDC
Supply Voltage
O/0
VAC VDC
O/1
VAC VDC
O/2
VAC VDC
O/3
VAC VDC
O/4
O/5
Putting it Together
PB1
Supply Voltage
Unused
L1
Unused
COM
L2/N
GND
I/0
I/1
I/2
I/3
I/4
VAC
O/0
VAC
O/1
VAC
VDC
VDC
VDC
COM
O/2
I/5
I/6
I/7
I/8
I/9
VAC
O/3
VAC
O/4
O/5
VDC
Supply Voltage
I/8
||
O/0
()
VDC
Addressing Example
L1
L2 SOL6
PB1 LS1 PS2
I/5
||
DEVICE PB1
ADDRESS HHP Logix I/5 I:0/5
LS1
I/6
I:0/6
PS2
I/7
I:0/7
SOL6
O/0
O:0/0
I/6
I/7
O/0
||
||
()
Relay Logic to Ladder Logic PB1
LS1
LS1
SOL2
PB2
CR3
I/4
I/6
||
||
()
I/7
I/5
B/0
||
||
()
I/8
LS3
||
B/0 CR3 |/|
O/0
LS4
M1
|/|
INPUT Address Assignment: PB1- I/4 PB2- I/5 LS1- I/6 LS2- I/7 LS3- I/8 LS4- I/9 OUTPUT Address Assignment: SOL2- O/0 M1- O/1
I/9
||
O/1
()
Advanced Instructions
• SEQUENCERS • SHIFT REGISTERS • DATA HANDLING • HIGH SPEED COUNTER • SUBROUTINES
Advantages of a PLC
Basic PLC Advantages
• • • • •
Ease of programming Ease of maintenance Designed for industrial environment Quick installation Adaptable to change
Source: A-B’s Micro Solutions Presentation
Advantages over Relays • All the capabilities of the earlier systems • Dramatic performance increase over the relay logic systems • Greater reliability • Little maintenance due to no moving parts • No special programming skills required by maintenance personnel • Physical size of the PLC system is much smaller than the conventional relay based logic • And most importantly much lower cost Source:
[email protected]
Advantages over SBC’s (single board computers) • SBC’s have high design costs – Contract or Staff with overhead and maintenance issues associated with each
• SBC’s are Repair / Service nightmare for customers – Depending on markets served supplier must develop/support services
• SBC’s requires high level of technical expertise by technicians – Specialized circuit boards require specialized equipment and technical staff
• SBC’s not stocked through local distributors – Suppliers sell the controller imbedded, replacement parts are not readily available even in emergency situations
• SBC’s typically do not meet worldwide standards – Certifications cost money, typically a single controller does not warrant the investment. Volumes are not high enough and re-certification on each revision is unrealistic
• SBC’s typically a “Domestic” product – Because of these issues many manufacturers limit themselves to a single market. Source: A-B’s Micro Solutions Presentation
Advantages over Computer based Software • Maintenance personnel already experienced in PLC troubleshooting and servicing relay latter logic programming, not PC software • Better power failure response • Cost advantages for simple machine control • Higher reliability that minimizes the expense of shutdown, troubleshooting, repair, & startup • Industrially hardened packaging • Long availability and support for product models without the rapid obsolescence of PCs.