top ten programming mistakes by people new to siemens

Navigating the world of automation

2011 Automation Summit Orlando, FL

Navigating the world of automation

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

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

#1Page 12

Simple Hardware mistakes

Common Hardware Mistakes

My PLC Doesn’t Work???

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

#2Page 21

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

Address Logic

Symbolic Logic

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

tim.jager@dmcinfo.com

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

#3Page 32

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

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

#4Page 38

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

MB0M0.0 – M0.7

M1.0 – M1.7

M2.0 – M2.7

MBits MBytes

MB0M0.0 – M0.7

M1.0 – M1.7

M2.0 – M2.7

MBits MBytes

MWords

MB0M0.0 – M0.7

M1.0 – M1.7

M2.0 – M2.7

MBits MBytes

MWords

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

#5Page 49

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

“Always_False”

Mapped to M0.0

“Always_True”

Mapped to M0.1

What Happens If……

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

#6Page 61

Using Uninitialized Temp Memory

What is Temp Memory?

Improper Use of Temp Memory

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

Top 10 S7 Mistakes

#7Page 65

Not Using Timed Interrupts.

OB1 vs. OB30..38

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

#8Page 68

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.

T#200ms PT ET 178

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

Cylinder

Barcode Scanner

Label Printer

Machine Vision

Robot Interface

Top 10 S7 Mistakes

#9Page 76

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

#10Page 79

Going it Alone

Thank You!

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