-------------------------Monitor------------------------ The Newsletter for PC-Based Data Acquisition and Control Issue 161 www.windmill.co.uk 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 CONTENTS ======== * 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 220.127.116.11 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. Subnets 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 255.255.255.0 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. Gateways 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 work. 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 Subnet. 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 https://www.windmillsoft.com/monitor.xml or follow us on Twitter at http://twitter.com/#!/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 https://www.theengineer.co.uk/ 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 http://tinyurl.com/ccrkjkq 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 http://www.arcweb.com/ 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 http://www.odva.org/ ________________________________________________________ ________________________________________________________ * Copyright Windmill Software Ltd * Reprinting permitted with this notice included * For more articles see https://www.windmill.co.uk We are happy for you to copy and distribute this newsletter, and use extracts from it on your own web site or publication, providing the above notice is included and a link back to our website is in place. An archive of previous issues is at https://www.windmill.co.uk/newsletter.html and an index of articles at https://www.windmill.co.uk/monitorindex.html 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] https://www.windmill.co.uk/ https://www.windmillsoft.com/
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