Plc by Mohamed Al-Emam, Session3

Session 03
By Emamof
Presented in 12-02-2009

Review Session 1
 CONTROL SYS.
 Automatic Controller
 WHAT
 Origin of PLC
 History
 Sizes of PLC’s
 Cycle of Operation
 Which
 APPLICATIONS N REAL
 PLC H.W Components:
 INPUT TO PLC ,SENSING CONCEPTS

Review  Session 2
 PLC’s 4 u
 Actuators
 Example show
SensorcontrollerActuator
 Logic Gate Review
 Modeling
 Waterfall …kiss philosophy 
 Programming
 ISaGRAF

Target to 
 ISaGRAF Users
 Plz Do Not Think To 4 Get This
 Fatal And Non-Fatal Errors
 Retain Values
 LD prog. Notes
 project development cycle and V methodology
 EX: Car Safety Alarm
 EX: Three-way Light Control
 Actually Case Study Machine partial control by
video
 Actually Case Study Dam Hole analysis 4 model

Cycle of operate PLC’s
 input
scan

execute
programme

degonistic and
commenucation
scan

output scan

Diagnostics
Mr. PLC will performs many pre-defined
diagnostic routines with every CPU
scan. The diagnostics can detect various
errors or failures in the PLC. The two
primary error classes are fatal and non-
fatal.

It is common for micro

Fatal Error
Fatal errors are errors which may cause the system to
function improperly, perhaps introducing a safety
problem. The CPU will automatically switch to Program
Mode if it is in Run Mode. (Remember, in
Program Mode all outputs are turned off.) If the fatal
error is detected while the CPU is in Program
Mode, the CPU will not allow you to transition to Run
Mode until the error has been corrected.
Some examples of fatal errors are:
• Power supply failure
• Parity error or CPU malfunction
• Particular programming errors

Non-Fatal Error
Non-fatal errors are errors that need your
attention, but should not cause improper
operation. They do not cause or prevent
any mode transitions of the CPU. The
application program can use special
relay contacts to detect non-fatal
errors, and even take the system to an
orderly shutdown or switch the CPU to
Program Mode if desired.

special relay contacts to detect
non-fatal errors

Accumulator
CPU Status Status
Relays Relays

System Monitoring
Relays

Non-Fatal Error
Program Error Codes
As program syntax and runtime error codes. Error
detection occurs during a Program-to-Run mode
transition.
PLC Error Codes
These errors can be generated by the CPU or by the
Handheld Programmer, depending on
the actual error
The errors can be detected at various times.
However, most of them are detected at power-up,
on entry to Run Mode, or when a Handheld
Programmer key sequence results in an error or
an illegal request.

Under IEC 61131-3
standard
LD

IL SFC

PROGRAMMING

ST FBD

Mnemonics is also another name for IL ,we have FC 

Benefits and Challenges of
open standards as IEC 61131-
3
 Interoperability
 Portability
 Configurability
 Usability

www.plcopen.org

Retain Value in PLC

 retain value keep when power is off.
 Disadvantage  The retained value
will be lost when download a modified
project to the controller.

Properly formatted outputs
Output should appear only one time in all module

Properly formatted outputs
We can not put two outputs in series in the same rung

But we can put it in parallel

EX: Car safety alarm
• Design a car safety alarm considering four
inputs
– Door closed (D)
–Key in(K)
– Seat pressure (S)
– Seat belt closed (B)
• The alarm (A) should sound if
– The key is in and the door is not closed, or
– The door is closed and the key is in and
the driver is in the seat and
the seat belt is not closed

How to solve By Kiss ph 
 No we will use truth table
and get a Boolean exp.
implement Ms. Truth Table

A(D,K,S,B)=D’KS’
B’+D’KS’B+D’KSB
’+D’KSB+DKSB’

Implementation by logic
gates

Now let me go 2 write it in Ms. ISaGRAF 

Three-way light control

• Assume a room has three doors and a switch
by each door controls a single light in the
room.
– Let x, y, and z denote the state of the switches
– Assume the light is off if all switches are open
– Closing any switch turns the light on. Closing
another switch will have to turn the light off.
– Light is on if any one switch is closed and off if
two (or no) switches are closed.
– Light is on if all three switches are closed

Design 
 By using the
( Kiss philosophy)’
we can write the truth
table as :

The Boolean exp will
 f(x,y,z)=x’y’z+x’yz’+xy’z’+xyz
Then we can draw the logic gates as

Now let me go 2 write it in Ms. ISaGRAF 

New Check goal is to maintain
upstream water level

Goal is to maintain water level. In order to change the water level, we
need to adjust the flow through the gate.

How much should you adjust the flow?
How often?
How long will it take the canal to respond?
What happens if something else causes the flow to change?

Algorithm
 For a given water level or flow error in
the canal, how much should you adjust
the gate opening?
 Flow Control
 Downstream Control
 Upstream Control

Algorithm1 Flow Control
 Calculate the required gate move based
upon the desired change in flow.
Commonly called flow control.
The challenge with this method is anticipating
the desired/required flow change.

Anticipating=do the other desired before that say

Algorithm2 Downstream
Control.
 Observe a water level at some location
downstream from the gate, if the water
level gets too low, open the gate, if it
gets too high, close the gate.
 This method requires a way to adjust the
flow going into the system. This method
is commonly called downstream
control.
 The challenge is determining how much
should the gate be opened or closed
and adjusting the flow into the canal.

Algorithm3 Upstream
Control.
 Observe the upstream water level and if
it is too high, open the gate. If it is too
low close the gate. Commonly called
upstream control. This approach
passes errors downstream.

PCs vs. PLCs
PCs PLC
 Linux  Perhaps 100s of
 Windows different platforms.
 Mac

PCs vs. PLCs
PCs PLC
 C, C++,C#4snap  Each manufacturer
 Java has their own
 Ruby programming
language.
 Sometimes the
same manufacturer
may have different
languages for
different PLCs.

PCs vs. PLCs
Portability!
PCs PLC
 If you have a fairly  You’ve got to be
current operating kidding!
system, you can run  Maybe within a
most windows manufacturer.
applications on any  Almost non-existent
PC made by any otherwise
manufacturer.
 Kind of the same for
Macs and Linux
based PCs

PLCs

Siemens S7 series

Part of Upstream Control Flow Chart

KEY TERMS 
 Plz write your terms 4 yourself

Plc by Mohamed Al-Emam, Session3

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