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2
Programmable Controller
Inputs Outputs
CR
So what is a Programmable Logic Controller?
• A solid state device that controls output devices based on input signals and a user developed program.
• Originally developed to directly replace relays used for discrete control.
3
What are typical Input devices for PLC’s?
Type of Device• Pushbuttons
• Selector Switches
• Limit Switches
• Level Switches
• Photoelectric Sensors
• Proximity Sensors
• Motor Starter Contacts
• Relay Contacts
• Thumbwheel Switches
• Temperature Sensors
Device Ratings
• 120/240 VAC
• 24 VDC – Sourcing
– Sinking
• 24 VAC
• 4-20mA
• 0-10VDC
4
What are typical output devices for PLC’s?
Type of Device• Valves• Motor Starters• Solenoids• Control Relays• Alarms• Lights• Fans• Horns• Heaters
Device Ratings• Relays
– 240 VAC– 85-120 VAC/VDC– 24 VAC/VDC
• Triac– 120/230 VAC
• Transistor MOSFET– 24 VDC
• 4-20mA• 0-10VDC
5
General PLC Concept
• PLC performs relay equivalent functions
• PLC performs ON/OFF control• Ladder diagram program
representation• Designed for industrial
environment• Designed for ease of use and
maintenance
• Easy to program• Easy to maintain• Quick to install• Adaptable to change
Great low cost alternative to
multiple individual relays, timers
and counters as well as dedicated
single board controllers.
6
CR
IsolationBarrier
IsolationBarrier
MEMORY
program data
HighVoltage
HighVoltage
Low Voltage
AC Power Supply85-264 VAC,
50/60Hz
Output
Circuits
ExternalDC Power Supplyor
RS-232
Communications
Input
Circuits
CentralProcessor
(CPU)
What's really inside a PLC?
7
PLC’s Come in a Variety of Sizes...• Pico
– Typically less than 20 I/O
• Micro– Typically less than 32 I/O
• Small– Typically less than 128 I/O
• Medium– Typically less than 1024 I/O
• Large– Typically greater than 1024 I/O
8
Today's Applications require high Level Control Capability
• Arithmetic (Addition, Subtraction, Multiplication, Division, etc)
• Data Comparison (Equal, Greater Than or Equal, Less Than or Equal)
• Word Manipulation (Copy, Move, etc)
• Sequencing• Data Manipulation• Proportional, Integral, Derivative (PID) Control
9
So where could you use a PLC?
• Conveyor control• Printed circuit board handling equipment• SCADA(Supervisory Control And Data Acquisition)
– remote pump/lift station (water/wastewater)– Flow monitoring for leak detection (oil&gas)
• Strapping machinery / trash compactors• Palletizers• Compressor control• Replace hard-wired relay panels or SBCs• Many, many more
10
What to consider when applying a PLC• Inputs/Outputs
– Type, • AC, DC, Analog, Thermocouple
sourcing, sinking, etc.
– Number of Inputs/Outputs including embedded, local expansion, and networked I/O
• 10, 16, 20, 32, 138, 156, >256
• Memory– Size
• 1k, 6k, 8k 12k, 14k,
• Functions required– PID– PTO/PWM (Pulse Train Output/Pulse Width Modulated)– Data Logging– Messaging between PLC’s– Math Calculations
• Communications Networks• DeviceNet, Ethernet• DF1 Full Duplex, DF1 Half Duplex, DF1
Radio Modem, DH485, ModBus Master / Slave
12
Memory Organization
MicroLogixMEMORY
PROGRAMFILES 0
12
34
56 - 15
System
ReservedM
ain P
rog
ramE
rror F
ileH
SC
File
ST
I File
Su
bro
utin
eF
iles
DATAFILES 0
12
34
56
7
Ou
tpu
t File
Inp
ut F
ileS
tatus F
ileB
it File
Tim
er File
Co
un
ter File
Co
ntro
l File
Integ
er Files
13
PROGRAM FILES
PROGRAMFILES
0
1
2
34
5
6 - 15
Sys
temR
eservedM
ain P
rog
ramE
rror F
ileH
SC
File
ST
I File
Su
bro
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iles
MicroLogixMEMORY
There are several different program files inside of a PLC.
Lets talk about the main one we will use today.
14
File #2 = Main Program
Dedicated & Open file• Main Ladder Program
– Most important file– Typically is where the “main” user program resides– Must have some program logic– Where jump to subroutines originate
16
Data definitions and data types
PLC Data Types• Bit
– B3 file of PLC
• Integer (signed) -32768 to 32767– N7 file of PLC
• Floating Point– F8 file of PLC
• ASCII– String data “My Text String”
Remember :
Bits 1 or 0
Words(16 bits) 2 bytes
18
O0:0/0
File Type
File Number
Output NumberWhere the Output
Was connected to the PLC0
Outputs
11 0
0 0 0 0 0 0 0 0 0 0 0 0Word 0
15 0
Word 0
I1:0/0File Type
File Number
Input NumberWhere the Input
Was connected to the PLC
1Inputs
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
File #0
File #1
Addressing Inputs and Outputs
19
B/16
OR
B3:1/0
0000 0000 0000 000015 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Word 0:
Word 1: 0000 0000 0000 000015 14 13 12 11 10 9 8 7 6 5 4 3 2 1 031 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
File #3 = Bit File
Bits in a PLC can be used to turn on a real device, or bits can be used as “storage”. They may just indicate when a condition exists within your program that you want to use in another part of your logic.
For example, if the fact that a push button is pressed is important to the logic of your program, but additional conditions also need to be present for an real output to turn on, you may wish to store the state of the push button as a bit.
20
| |I:0.0
0
Timers
• Timer OperationThe timer times as long as its rung conditions are TRUE.
When the timer times up to a specified value, it alerts the rest of the program by setting a bit. When the rung becomes FALSE, the timer stops timing and resets itself to zero.
21
T4:0
File Type
File Number
Timer Number
4Timers
File #4 = Timers• File #4
– TON, TOF, and RTO• Timer On Delay (Turn On when the timer reaches preset value)• Timer Off Delay (Turn Off when the timer reaches preset value)• Retentive Timer On (Even after rung conditions are false this timer remembers where it left off.)
– .01 and 1 second time base
22
Preset T4:0.PRE How long the timer should time for.
Accumulated T4:0.ACC How long the timer has timed for already.
Done T4:0/DN Set to “1” when accumulated value > preset value.
Timer Timing T4:0/TT Set to “1” when accumulated value < preset value.
Enable T4:0/EN Set to “1” when the rung containing the timer is true.
T4:0
File Type
File Number
Timer Number
4Timers
Preset Value
Accumulated Value
15 14 13
EN TT DNWord 0
Word 1
Word 2
Addressing Timers
23
| |I:0.0
0
Counters
• Counter Operation– The counter counts (by one) every time its rung goes
from FALSE to TRUE. When a specified number of counts has been reached, the counter alerts the rest of the program by setting a bit. The program must reset the counter to start counting from zero again.
24
C5:0
File Type
File Number
Counter Number
5Counters
File #5 = Counters
• Up, Down, and Up/Down Counters
25
Preset C5:0.PRE How many the counter should count up to
Accumulated C5:0.ACC How many the counter has counted already.
Done C5:0/DN Set to “1” when accumulated value > preset value.
Count Up C5:0/CU Set to “1” when state of CTU rung are true.
Count Down C5:0/CD Set to “1” when state of CTD rung are true.
Over/Underflow C5:0/OV,UN Set to “1” when counter counts past 32,767 or -32,768.
C5:0
File Type
File Number
Counter Number
5Counters
Preset Value
Accumulated Value
15 14 13
CU CD DN OV UN
12 11
Word 0
Word 1
Word 2
Addressing Counters
Programmable Controller Basics
So what is ladder logic and how do I connect devices and write a
program?
27
• What is Relay Ladder Logic?– Is the primary programming language for PLCs– A graphical representation of the program designed to look
like relay logic– Called ladder logic because it resembles the rungs of a
step ladder you might have at home.
Relay Ladder Logic (RLL)
28
Conversion Example Relay Diagram to Ladder Logic
L1 L2
PB1 LS1 PS2 SOL6
DEVICE NAMEPB1
LS1
PS2
SOL6
| | ( )| | | |I/5 I/6 O/0I/7
PLC ADDRESSI:0/5
I:0/6
I:0/7
O:0/0
Relay Diagram Ladder Logic
29
Addressing Input Instructions
Unused I / 2I / 1I / 0COM I / 3 I / 6I / 5COMI / 4 I / 7 I / 9I / 8
Supply
Voltage
Unused
LS 1
False
True
Examine OFF
-|/|-XIO
False
The instruction is:The input
bit is
Logic 0
Logic 1 True
Examine ON
-| |-XIC
If the input
device is
Open (0)
Closed (1)
These are not normally open (N.O.) and normally closed (N.C.)
XIC = Examine When Closed, ON or when voltage is present
XIO = Examine When Open, OFF or when voltage is not present
30
GNDL 1 O / 0VACVDC
L 2 / N VACVDC
VACVDC
O / 2VACVDC
O / 1 O / 3 O / 5O / 4VACVDC
SupplyVoltage
Addressing Output Instructions
RungState
OutputBit
OutputTerminal
De-energized
TRUE
FALSE
ON
OFF
OTEOutput Energize
-( )-
| | |/| ( )
T T T
ENERGIZED
31
Ladder Logic Concepts
Read / Conditional Instructions
Write / Control Instructions
No Logical Continuity
|/| | |
T F F
( )
( )|/| | |
T T T
Logical Continuity
32
Logical AND example
IF input 4 AND input 5 have power THEN energize output 0
| |I/4
| |
I/5
( )O/0
Logical Continuity
T T T
On
33
Logical OR example
IF input 4 OR input 5 have power THEN energize output 0
| |I/4
| |I/5
( )O/0
Logical Continuity
F
T
On
T
| |I/4
| |I/5
( )O/0
Logical ContinuityF
On
34
TIMER ON DELAYTimer T4:0Time Base 1.0Preset 10Accum 0
TON
Stop Start Motor
]/[ ] [
] [
( )I:0/0I:0/1
M1O:0/3
O:0/3
] [
M1O:0/3
]/[T4:0/DN
(EN)
(DN)
Timer Done
Example Timer Program
• The Timer’s “done bit” turns the motor off after a 10 second time delay
35
Count UpCounter C5:0Preset 10Accum 0
CTU
Stop Motor
]/[
] [
( )
Start
] [I:0/0I:0/1
M1O:0/3
O:0/3
] [
M1O:0/3
]/[C5:0/DN
(CU)
(DN)
Counter Done
Reset
] [I:0/4
(RES)C5:0
Example Counter Program
• The Counters “done bit” stops the motor from running, after 10 operations.
Programmable Controller Basics
Understanding the PLC operating cycle and examining a
real application.
37
Input Scan
Program ScanOutput Scan
Housekeeping
START
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”).
The status of external inputs (terminal block voltage) is written to the Input image (“Input file”).
The Output Image data is transferred to the external output circuits, turning the output devices ON or OFF.
Internal checks on memory, speed and operation. Service any communication requests, etc.
Understanding the PLC Operating Cycle
38
Motor
Ingredient ASolenoid Valve 1
Ingredient BSolenoid Valve 2
DrainSolenoid Valve 3
Sensor 2
Ingredient B
Typical PLC application
Start/ Stop Switch
Ingredient A
Sensor 1
39
Motor Solenoid Valve 1 Solenoid Valve 2
Solenoid Valve 3
Sensor 1
Sensor 2
Ingredient A
Ingredient B
Sequence of Operation of the MixerSolenoid Valve 1
On = Sol 3 is off, and Motor is off, and Sensor 2 is off, and Start
Switch is on
Off = Sol 3 is on, or Motor is on, or Sensor 2 is on
Solenoid Valve 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
Automatic / Manual Switch
Step One:
I need to add some ingredient A to the mixer, but I only want to do that when the mixer is empty, the drain is closed,
and the motor is not running. Stop when I fill to Sensor 2 level.
Step Two:
I then need to add some ingredient B to the mixer, but I only want to do that after I’ve added enough ingredient A, the drain is closed, and the motor is
not running. Stop when filled to Sensor 1 level.
40
Motor Solenoid Valve 1 Solenoid Valve 2
Solenoid Valve 3
Sensor 1
Sensor 2
Ingredient A
Ingredient B
Sequence of Operation of the MixerStep 3
Once I have added my ingredients, I need to mix them for 30 seconds, then I need to drain them from the
vessel. I can close the drain after a minute of draining.
Automatic / Manual Switch
Solenoid Valve 3On = 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, Sol 1 is on, Sol 2 is on, motor is running.
MotorOn = Sensor 1 is on, Sensor 2 is on and
Sol 1 is off, Sol 2 is off, Sol 3 is off
Off = Sol 3 on, Sol 1 is on, Sol 2 is on
42
• Customer: Tait Towers – World renowned stage design
• Concerts– Rolling Stones / U2– Brooks & Dunn / Reba McEntire
• Broadway– Phantom of the Opera– Miss Saigon
• Television– MTV Video Music Awards– VH-1 Fashion Awards
• Requirement: Solution to operate trendy “theater-in-the-round” set design with dramatic effects, flexibility of stage height, plus trouble-shooting capabilities so the show can go on!
• MicroSolution: 17 MicroLogix 1000s and 1 SLC 500 control and coordinate: (Other products include: limit switches, motors, operator interface, contactors)
– Motor driven raising/lowering of 2 band risers with variable height options– Rolling center deck to join both band pits– Fiery light show with 60 ft. tall “volcano” and drape
Boot Scootin’
43
Monster Truckin’• Customer: Dan Patrick
– Designer and driver of monster trucks• Sampson
• Requirement: Cost effective solution that provides accident-proofed muscle truck able to operate at max speed for most of race, and not require race-day repairs.
• MicroSolution: 1 MicroLogix 1000 and Hand-Held Programmer:
– Replaced relays– Controls shifting mechanism
• Race 5-6 seconds long• 1.5 seconds to shift from 1st to 4th gear with 100 shifts per night
– Keeps rpms steady by eliminating possibility of over-revving the motor– $300 control solution protects $55,000 investment in transmission and motor– Hand-Held Programmer trace key reduces troubleshooting time
44
“Operation MicroLogix”Customer: United States ArmyRequirement: Real-Time control of multiple targets on full scale 30
acre urban assault training site.
MicroSolution:
330+ MicroLogix 1500 controllers and 1761-NET-ENI’s. – Pop-Up targets and count successful hits.– Communicate using Ethernet and Fiber Optic cables to all
MicroLogix controllers.– Interface to advanced human interface software for control.