Windmill Software Ltd
Data Acquisition Intelligence

December 2011

The Newsletter for PC-Based Data Acquisition and Control
Issue 161       December 2011
--------------------ISSN 1472-0221----------------------

Welcome to the last newsletter of 2011: our compliments 
of the season to you.

Today we have an article on understanding the complex 
working of TCP/IP, with particular relevance to 
connecting measurement devices to your PC. 

Look out for our next issue to see how we've improved 
the free comDebug software we offer all our subscribers 
to log data from devices connected over TCP/IP 
(eg Internet and Ethernet), RS232, RS422, RS485 
and Modbus. 

I hope you find the newsletter useful, but should you 
wish to remove yourself from our mailing please go to 
Monitor Newsletter

* Windmill News: Coming soon, free logging software for 
  devices connected over TCP/IP
* Understanding TCP/IP: connecting over 
  Ethernet and Internet
* DAQ News Round-up

Windmill News: Coming soon, free logging software for 
devices connected over TCP/IP

In the New Year we are pleased to be launching a new 
version of our comDebug fault-finding and data 
acquisition software. As well as collecting data from 
devices connected over RS232, RS422, RS485 and Modbus, 
we have added TCP/IP capabilities.  This means that 
you will be able to log data over Ethernet or Internet.

Monitor subscribers will be able to download the new 
comDebug for free.  If you need to log data from more 
than one instrument, you can add the Windmill software 
suite for just 50 pounds.  This logs and charts data 
from up to 10 instruments. Data can also be passed to 
other software like Excel or Matlab.

Further Reading:

Understanding TCP/IP

Download TCP/IP Data Logging Software

Understanding TCP/IP: connecting over Ethernet 
and Internet

TCP/IP is a standard method for sending messages across 
a network. It is used on many networks including the 
Internet. You do not need to be a network expert to use 
it but some key facts will make it more understandable. 

IP Address
  Each computer on the network has an IP Address. This is 
  actually a 32 bit binary number. Since such numbers 
  are not user friendly they are usually presented in 
  Dotted Decimal Notation. This splits the 32 bits into 
  four 8-bit chunks. Each chunk is then converted to a 
  decimal number in the range 0 to 255. For example 
  01011001 00011101 11001100 00011000 becomes

  You can think of this address as being roughly like a 
  postal address arranged as Country / City / Street / 
  House Number. 

Static IP Addresses
  An instrument may have a fixed IP Address which is 
  allocated to it by a Network Administrator. The 
  allocated address will be unique for the network.  
  Your instrument will have a utility supplied by the 
  manufacturer which will allow you to set the address.

Dynamic IP Addressees
  Alternatively an instrument may be allocated its 
  IP Address  when it powers up.  This uses a process 
  called Dynamic Host Configuration Protocol (DHCP).  
  In this system the unit is identified by a name eg 
  "My Instrument".  When it powers up it asks a 
  DHCP server to allocate an IP Address to "My 
  Instrument".  As the user, you need only decide to 
  address the instrument by its IP Address or by its 
  Name: the rest is done for you by the operating system.

Port Number
  TCP/IP messages are sent not just to an IP Address but 
  also to a Port Number within that address. This allows 
  the message to be directed to one of potentially many 
  applications running on the computer or instrument. 
  Some port numbers are allocated to functions which all 
  devices will support whilst others are for more general 
  use. Your Instrument documentation must tell you which 
  port to contact.

  Large networks are physically divided into subnets. Two 
  devices which are on the same subnet can send messages 
  directly to each other without the messages being seen 
  by the rest of the network. This reduces traffic in the 
  wider network. 
  The subnet is defined by the Subnet Mask.  You can view 
  this via Control Panel and the TCP/IP properties of your 
  computer. This is another dotted decimal arrangement.  For 
  2 units to be on the same subnet the parts of their 
  IP Addresses which are covered by a binary 1 in the Mask 
  must be the same. So if the Mask is 
  then the first 3 elements of both IP Addresses must be 
  the same to be on the same subnet.  (255 is the decimal
  equivalent to binary 11111111.)

  If a unit whose IP Address puts it onto one subnet is 
  physically plugged into another subnet then you will not 
  be able to talk to it as your messages will be sent 
  to the wrong subnet.

  When your computer wishes to send a message to a device 
  on another subnet it sends the message via a Gateway. 
  This is another computer which relays the message to the 
  destination address. Your computer needs to know the 
  IP Address of the Gateway. You can view this in the 
  TCP/IP properties of your computer.

Name Servers
  When your computer wishes to send a message to a named 
  destination then it asks a Name Server to resolve the 
  name to an IP Address. Your computer needs to know the 
  IP Address of the Name Server. You can view this in the 
  TCP/IP properties of the computer.

Ping Utility
  This is a test utility which sends a message to a defined 
  port within your instrument. The instrument replies with 
  a short data message. Virtually every unit on TCP/IP will 
  support this action. If you cannot Ping your instrument 
  you will not be able to talk to it. 

Direct Connection Instrument to Computer
  It is a good idea when first connecting instruments to 
  keep things as simple as possible. A direct connection 
  between Instrument and computer with no wider network 
  connection seems sensible but it has some pitfalls. 

  1. To connect your computer Ethernet port directly to the 
     Instrument requires a special twisted cable. The cable 
     used to connect your computer to a network hub will not 
  2. If your computer uses a Dynamic IP Address then it cannot 
     get an IP Address unless connected to a DHCP server.  So 
     in this arrangement it will not work. 
  3. If the instrument uses a Dynamic IP Address it will not work 
     unless your computer is configured as a DHCP server. 
     Your computer will also need to perform the Name Server 
     function to deal with such an instrument. 

  4. Both computer and instrument will need to be on the same 
  A direct connection is only easy if both computer and 
  instrument use fixed IP Addresses on the same subnet and 
  you have the correct cable. 

Connection via Wider Network
  Using the wider network provides the servers needed for 
  DHCP and Names. Once a Dynamic IP Address instrument is 
  plugged into the network then it should be possible to find 
  it via its Name and the Ping utility. If it is a fixed 
  IP Address and it is plugged into the correct subnet it 
  should again be possible to Ping it.

Trouble Shooting
  - I can Ping my Instrument but I can't Connect to it : - 
    If you are sure that you are Pinging your instrument and 
    not some other unit then it is likely to be because the 
    port number is incorrect. You cannot connect to a 
    port number which your instrument does not support. 

  - I cannot Ping my Fixed IP Address instrument : - 
    Obviously you must enter the correct IP Address. 
    The Instrument must be physically plugged into the 
    correct subnet to match its IP Address. 

  - I cannot resolve the Name of my Instrument to an 
    IP Address. Ping the IP Address of the Name Server 
    to check that it is on line. Ask your Network 
    Administrator to check that your instrument is 
    being registered with the name server. 
I hope this has clarified some terms and connection 
issues for you. If you need any more information please 
get in touch.

Further Reading:
Understanding TCP/IP
Download TCP/IP Data Logger Software

DAQ News Round-up

Welcome to our round-up of the data acquisition and 
control news.  If you would like to receive more 
timely DAQ news updates then either grab our RSS 
newsfeed at 
follow us on Twitter at!/DataAcquisition

LEDs could provide better data transmission under water
  Researchers are working on a device that will gather 
  measurements on swimmers' movements such as stroke 
  count and then send it wirelessly in real time to a 
  heads-up goggle display.  Underwater wireless 
  communication is a particularly challenging area, with 
  potential applications in tsunami and earthquake 
  monitoring, marine archaeology, and search and rescue.
  Source: The Engineer

ISA100 Wireless Standard Approved as American National Standard
  The American National Standards Institute (ANSI) has 
  announced the approval of ISA-100.11a-2011, "Wireless 
  Systems for Industrial Automation: Process Control and 
  Related Applications," as an American National Standard.
  Source: International Society for Automation

Global Automation Markets on Track to Return to Pre-Recession Levels in 2011
  According the ARC Advisory Group, there has been a 
  return to growth for many automation products and 
  suppliers.  The timing of the recovery, however, was 
  not felt evenly across the various suppliers and 
  product segments.  Orders increased almost 
  unilaterally for all of the major automation suppliers 
  but the ability to turn these increased orders into 
  recognized revenues varied significantly across the 
  major suppliers.
  Source: ARC Advisory Group

ODVA Release Cyber-security guidelines for industrial Ethernet | Windmill Software
  Manufacturers are increasing connectivity between 
  plant floor and enterprise systems to boost productivity 
  and reduce time to market, but interconnectivity can 
  also bring undesirable security risks.
  Source: ODVA

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Windmill Software Ltd, PO Box 58, North District Office,
Manchester, M8 8QR, UK
Telephone: +44 (0)161 833 2782
Facsimile: +44 (0)161 833 2190
E-mail: [email protected]


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