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  1. #1
    Join Date
    Feb 2007
    Location
    Sacramento, CA
    Posts
    64

    N2 to Ethernet convertion?

    I have a high school with an older Johnson system that has the N2 comm wire run underground to the various buildings. The problem is the underground conduit is always getting full of water & messing up the comm wire. I am thinking of using RS-485 to ethernet converters on the school network to bypass the underground wiring. Has anyone tried this already? Any help and/or advice would be appreciated,

  2. #2
    Join Date
    May 2006
    Posts
    385
    I have used these to run N2 over fiber and they worked well.

    http://www.sitech-bitdriver.com/prod...heets/2110.pdf

  3. #3
    Join Date
    Apr 2005
    Location
    2444 Washington Blvd, Suite 100 Ogden, UT
    Posts
    359
    You might also consider our S4 Open Appliances, the S4 Open: OPC-N2 Router or S4 Open: BACnet-N2 Router for this application. This approach puts the management of the N2 bus in the local building and then publishes to OPC or BACnet, respectively so you can add a current generation standards-based head end to the solution. My contact information is in my profile if you would like more information.

    When we tested support for a number of manufacturer's Ethernet to RS-485 Serial Servers we found that the N2 bus timing is so sensitive that using them back to back in pairs does not work in many situations. Bus loading, poll rates, types of N2 devices, etc. all come into play in each situation. So, realize that you will need to perform a lot of testing to make sure that things do work properly in your application. We did find out that when we had our appliance handling one end of the Ethernet connection and an RS-485 Ethernet Serial Server on the other end we could very effectively extend the N2 bus over Ethernet.

    You might also take a look at the S Squared Innovations offerings.
    Steve Jones
    Managing Partner
    The S4 Group, Inc.

  4. #4
    Join Date
    Feb 2005
    Location
    Edmonton, AB Canada
    Posts
    603
    Quote Originally Posted by Ex-Man View Post
    I have a high school with an older Johnson system that has the N2 comm wire run underground to the various buildings. The problem is the underground conduit is always getting full of water & messing up the comm wire. I am thinking of using RS-485 to ethernet converters on the school network to bypass the underground wiring. Has anyone tried this already? Any help and/or advice would be appreciated,
    Good day Ex-Man,

    If you do a search on here you will find some info on this. In brief, using simple RS485 to Ethernet convertors is rarely successful unless you have a very specific and limited Ethernet setup. Even under these circumstances there are issues. Why is this the case? Ethernet is a collision based protocol and so there is no guarantee of a successful Ethernet packet transmission or how fast the packet is ultimately received. The more Ethernet traffic on your system the greater chance of more packet collisions and also increased packet delays. It is these packet losses and latencies which cause issues with the overall system. You see simple RS485 to Ethernet convertors do not have a lot of intelligence in them and simply transfer RS485 data to Ethernet and vice versa. If packets are lost, delayed, or out of sequence you will get RS485 (N2 bus) packet inconsistencies and delays... which tend to cause grief for the Supervisory controllers (i.e. offlines, onlines, etc). If you would like a proven product specifically designed for this application you can look to our S2N2E device.

    Cheers,

    Sam

  5. #5
    Join Date
    May 2006
    Posts
    665
    We used around 15 of the S2N2E device over our network. Sam stands behind his product and worked with us.

    The only draw back is that you can't download the N2 devices over the S2N2E - unless he changed things?

  6. #6
    Join Date
    Feb 2005
    Location
    Edmonton, AB Canada
    Posts
    603
    Quote Originally Posted by integrator View Post
    We used around 15 of the S2N2E device over our network. Sam stands behind his product and worked with us.

    The only draw back is that you can't download the N2 devices over the S2N2E - unless he changed things?
    Good day Integrator,

    Thank you for the compliment!

    Indeed, HVACPro tunneling over Ethernet will not work with the S2N2E. Is it possible for it to work? Yes, but the inherent Ethernet latencies and HVACPro idiosyncrasies work against this type of connectivity. On a side note...we created another product specially to allow for remote connectivity of HVACPro. Overall the device worked well... but decided to shelf the product because supporting it would have been quite difficult (HVACPro's age and lack of direct new operating system support and also customer Ethernet Network variances, etc).

    Cheers,

    Sam

  7. #7
    Join Date
    Apr 2005
    Location
    2444 Washington Blvd, Suite 100 Ogden, UT
    Posts
    359
    There is work in process at S4 to offer a replacement for the Metasys Passthrough mode for HVAC Pro and the other Metasys utilities. It is indeed a challenge with the constraints of the N2 protocol itself. Everything that happens is controlled by very sensitive timing. There are no transaction numbers, sequence numbers, etc. So, there is no safety net. You have to get it right the first time and every time. Added to that as Sam already mentioned is the age of the utilities themselves and the technology used to implement them. The approach of installing one of our S4 Open: BACnet-N2 Routers in each building and converting to BACnet avoids all of the issues we have been discussing. Each N2 device is published as its own BACnet device under a virtual BACnet network. The BACnet communications can then be successfully and reliably transported over the local Ethernet. Since we follow the BACnet IP standard and current generation BACnet OWS can then be added. I don't remember if you mentioned the current supervisory controller but if it is a NAE you could then discover the remote devices as a BACnet IP integration.
    Steve Jones
    Managing Partner
    The S4 Group, Inc.

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