top ten programming mistakes by people new to siemens

Navigating the world of automation

2011 Automation Summit Orlando, FL

Navigating the world of automation

Navigating the world of automation Copyright © Siemens Industry, Inc. 2011. All rights reserved.

2011 Automation Summit

Title: Top Ten Programming Mistakes Made by People New to S7

Track:#56

Topic: Learn about some of the common problems experienced by people learning S7.

Presenter: Tim Jager

Company: DMC

Top Ten Programming Mistakes Made by People New to S7


Top Ten Programming Mistakes Made by People New to S7


30 Employees

Company Profile

Since 1996

Based In Chicago…

…but work Globally

DMC has the highest number of S7 certified engineers


Our customers


Manufacturing and Automation IntelligenceMicrosoft SharePoint Consulting ServicesTest and MeasurementCustom Software Engineering & Embedded Systems

Areas of Expertise


Dulles Airport Transit Tunnel Ventilation System WinCC Redundancy S7 400H Redundant PLC 4000 I/O Points

Relevant Siemens Projects


Batch Mixing Systems for Confectionary Company

S7-300 Standardized code base Deployment at multiple facilities Mixing/batching control Recipe management Web-based reporting system



Automotive Assembly Lines for Tier 1 Supplier

S7 400 PLC’s WinCC Flex HMI’s Standardized code base User Configurable JIT - Lean Manufacturing Deployment at multiple facilities



US Navy LCS-1

Littoral Combat Ship S7 400H Redundant PLC

Mission Critical Logic



Presenter Info

Tim Jager

Project Director at DMC

Mechanical Engineer (University of Illinois)

Licensed Professional Engineer in Illinois

With DMC since 1999


Top 10 S7 Mistakes

#1

Simple Hardware mistakes


Common Hardware Mistakes

My PLC Doesn’t Work???



It needs a memory card




It needs a memory card

It’s in STOP Mode




I wonder what’s on the MMC Card?



This is not an RS232 Serial Port!!!


Top 10 S7 Mistakes

#2

Using Absolute Address Priority instead of Symbolic


Set your Address Priority to Symbolic

You Just took the Red pill…. You are on your way down the rabbit hole that leads down the path of true object oriented PLC Programming.


A Typical Data Block

DB1 “dbGlobals”


A Typical Data Block

DB1 “dbGlobals”

Address:

DB1.DBX0.0

Symbol Name:

“dbGlobals”.bStart


A Typical Rung Of Ladder


A Typical Rung Of Ladder

Address Logic

Symbolic Logic


What happens if we change the Data Block?


Absolute vs. Symbolic Priority

In Symbolic Mode the intended logic is maintained

The address logic has changed from 0.1 to 0.2

The symbolic logic is maintained



But the Symbolic logic is totally wrong!

The Address logic is maintained

In Absolute Mode the intended logic is NOT maintained!



Absolute Address

2222N. Elston Ave

Chicago, IL 60614

Symbolic Address

[email protected]

VS.

You don’t have to know where the server lives or it’s IP address. You just need the symbolic name to send an email.

So start forgetting about addresses and start thinking about symbolic names.


Top 10 S7 Mistakes

#3

I/O Mapping


…I'M GONNA PROGRAM… LIKE IT'S 1999

Input / Output Mapping


Traditional Input / Output Mapping

1. At the beginning of the scan, Each physical input gets mapped to an internal variable…

Physical Input

Internal Variable




2. Now run all of the logic (which references only internal bits)…

Internal Variable

Internal Variable




2. Now run all of the logic (which references only internal bits)…

3. …At the end of the scan, internal “output” bits get mapped to physical outputs

Internal Variable

Physical Output


S7 I/O Mapping – Just use the Symbol Table

Make sure you are in Symbolic Priority Mode


Top 10 S7 Mistakes

#4

Improper Use of Bit Memory

AKA: Mbits


M0.0M0.1M0.2M0.3M0.4M0.5M0.6M0.7M1.0M1.1M1.2M1.3M1.4M1.5M1.6M1.7M2.0M2.1M2.2M2.3M2.4M2.5M2.6M2.7M3.0M3.1M3.2M3.3M3.4M3.5M3.6M3.7

M0.0 – M0.7

M1.0 – M1.7

M2.0 – M2.7

M2.0 – M2.7

MBits



MB0M0.0 – M0.7

M1.0 – M1.7

M2.0 – M2.7

M2.0 – M2.7

MB1

MB2

MB3

MBits MBytes



MB0M0.0 – M0.7

M1.0 – M1.7

M2.0 – M2.7

M2.0 – M2.7

MB1

MB2

MB3

MBits MBytes

MW0

MWords

MW1



MB0M0.0 – M0.7

M1.0 – M1.7

M2.0 – M2.7

M2.0 – M2.7

MB1

MB2

MB3

MBits MBytes

MW0

MWords

MW1

MD0

MDoubleWords


When is it OK to use M Bits?

• Debugging• Quick prototyping / demonstrations• When you absolutely have to!



M-Bits

• Critical / Time-sensitive field fixes*

* As long as you promise to put in a permanent fix when the heat is off.



If you use MBits, make sure they are NOT IN USE already.



..and make sure to add symbol names in the symbol table.



Or suffer the consequences……



•Clock Byte


Top 10 S7 Mistakes

#5

Not using or Improperly using the Clock Byte


What is the Clock Byte?

Bit of the Clock Memory Byte 7 6 5 4 3 2 1 0Period Duration (s) 2.0 1.6 1.0 0.8 0.5 0.4 0.2 0.1Frequency (Hz) 0.5 0.625 1 1.25 2 2.5 5 10

Each bit of the clock memory byte is assigned a frequency.


Symbol Table Entry For Clock Byte

Reserve these so nobody uses Memory overlapping the Clock Byte


Clock Byte

The bits within the Clock byte can change at any time during the scan.


Clock Byte – Synchronous Global

UDT1 “udtClockByte”



DB1 “dbGlobals”



MB0 dbGlobals.ClockByte


M0.0

M0.1

M0.2

M0.3

M0.4

M0.5

M0.6

M0.7

“Always_False”

Mapped to M0.0

“Always_True”

Mapped to M0.1

What Happens If……


M0.0

M0.1

M0.2

M0.3

M0.4

M0.5

M0.6

M0.7

Clock Byte

Mapped to MB0

“Always_False”

Mapped to M0.0

“Always_True”

Mapped to M0.1

What Happens If……


Overlapping Mbits are BAD!


Top 10 S7 Mistakes

#6

Using Uninitialized Temp Memory


What is Temp Memory?


Improper Use of Temp Memory


Improper Use of Temp Memory

Don’t read from a TEMP unless you have written to it first!


Top 10 S7 Mistakes

#7

Not Using Timed Interrupts.


OB1 vs. OB30..38

OB1

Runs as fast as it can.

OB30…OB38

Run at specific time intervals.


Timed Interrupts OB30..OB38

PID Control Data Sampling


Top 10 S7 Mistakes

#8

Not using reusable function blocks


A Function Block is a piece of reusable code that consists of:

Code is encapsulated in a Highly reusable form

Increases Programming efficiency and reduces errors

What is a Function Block


One of the simplest and most commonly used function block is a

Timer.

TON

IN

T#200ms PT ET 178

Q

Timer


Creation of Function Block

Isolate Common/Duplicate Code

If the same code is used many times in your program, consider creating function blocks.


Step 1. locate common code.




Step 2. Replace duplicated code with function blocks.




Custom FB ExamplesMotor

FB

Pump

FB

Cylinder

FB

Barcode Scanner

FB

Label Printer

FB

Valve

FB

Machine Vision

FB

Robot Interface

FB


Top 10 S7 Mistakes

#9

Inconsistent Blocks


Check Block Consistency

Don’t forget to download the Data Block!!


Top 10 S7 Mistakes

And last but not least……..


Top 10 S7 Mistakes

#10

Going it Alone


Thank You!

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