Modbus to Lonworks

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Thread Starter

Darren Haun

What the deal is is we have some VFDs on some HVAC equipment that talk MODBUS. I need to convert that to LONWORKS to talk to the DDC controls system. Any help would be appreciated.
 
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James Freeman

The North Compass product could help you. This can provide interoperability between different building automation systems, such as Modbus, LONworks, BACnet, EIB, etc.

Visit the solutions pages at http://www.northbt.com for more information.
 
Be careful here. LonWorks doesn't have polling architecture as do most industrial protocols. LonWorks devices produce and consume data autonomously. You can obtain LonWorks data explicitly, but its not the way the network was designed to operate and can be exceptionally slow relative to industrial protocol standards, even compared with Modbus. Additionally, you could be undermining the function of the existing network. Even with bound nodes, trying to apply a polling scheme to a LonWorks network is like putting a square peg in a round hole.

I've consulted on a few data links into LonWorks networks and in more than one case had to recommend abandoning the effort as impossible. Even for those that worked, it was by no means ideal.


On July 25, 2003, Darren Haun wrote:
> What the deal is is we have some VFDs on some HVAC equipment that talk MODBUS. I need to convert that to LONWORKS to talk to the DDC controls system. Any help would be appreciated. <

( Complete thread: http://www.control.com/1026178001/index_html )
 
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Peter Whalley

Hi All,

Lonworks does support polling but the implementation in the Neuron chip is very poor. Basically it sends out a poll for a variable and then waits for the response to come back before sending out the poll for the next variable. At 78kbps at best you get about 40 polls per second.

You can get a HMI type application to poll much faster (few thousand per second) using Echelon's VNI (virtual network interface) driver or you can bind points to a cache and then poll the cache.

LonWorks to MODBUS gateways are a fairly common requirement in larger HVAC automation projects. Do a Google search or talk to the major Lon suppliers such as Echelon, TAC, Siebe, Honewell, etc.

Regards

Peter Whalley
Magenta Communications Pty Ltd
Melbourne, VIC, Australia
e-mail: peter*no-spam*@magentacomm.com.au
delete *no-spam* before sending
 
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