Going Wireless with N2, HELP ?
Greetings from South Africa
We have a project to link up 40 Power sub stations to our Johnson Controls
existing M3 site. Adding Energy monitoring over 4 university campus', each with its own N30.
We are using IME Nemo 96 meters (comes with N2bus / com's )
Some of the Sub Stations are not easily accessible and up to 1km
away and so we are using 2,4Ghz transceivers RS485 ( eg attached settings options) instead of hard wiring the N2 network to each Substation.
On one campus we are using these Radios with Point to multi point ( 1
Server talking to 7 slaves (substations) , 1) Do you see problems with this ? We can see readings from some Nemo meters but, M Explorer shows them offline most the time.
We would like to improve the coms, but we dont know enough about N2 and the radio
settings to get the best results.
I need to understand N2 protocol better to help me understand the settings required etc.
Think, End Char. is best option
In Recieve mode , Promiscious , Unicast/Broadcast or unicast only ? Client and server the same ?
Any advise would be appreciated , or if you know anyone who has done n2 / rs485 wireless bridges that could help ?
THANKS FOR YOUR TIME
you may talk to these guys:
They have dealt with N2 bus for a long time and can probably help you in any particular settings that are inherent in this protocol.
They may have even done wireless applications such as yours so might be able to quickly direct you to a fix.
Wow, what you got there is a RAW transceiver. This unit should work with N2, but without fully digesting the 50 some page manual I cant be of much help. Give me a day to review and Ill give you a hand setting it up.
I assume you have the necessary antennas, TTL to RS232 to RS485 converters, cables and power supplies. And of course, enough electrical knowlage to mash it all together.
I agree with amigo, that company out of Canada is extremely knowledgeable when it comes to N2. I have spoke with them before and they are very nice to deal with. Other then that, I wish you good luck!!!
I Bleed Johnson Blue
Settings I would try:
Serial Interface Mode 02 - Transparent End Character
All N2 messages begin with “>” – 3Eh
N2 messages end with carriage return - 0Dh
N2 standard baud settings are 9600, 8 data bits, 1 stop and start bits, no parity, half-duplex. The messages will have a varying length depending on what is going on. That’s why I would suggest end character mode.
Auto Destination mode sounds like the addressing scheme I would start with.
Broadcast mode enabled on the server transceiver, you may want to set the broadcast attempts to something small like 2-5. Turbo mode will probably not work to well with point to multi point setup you’re working on.
Receive mode, use Promiscuous to receive all messages from the server. If this where a wired link all devices would receive all messages on the buss, which is what you need to duplicate.
I assume that this unit expects RS232 serial data. You must have some sort of adapter to switch that over to RS485. Usually the 485 adapters have a pin to enable transmit. This radio looks to have an output to handle this. You will have to check your converter for the proper setup. Again the transceiver is TTL level so you may need yet another converter if you’re 485 converter is true RS232 @ +-13v. Max input voltage is 5.9V, much more could toast the input.
Once you get everything setup you may want to turn off the AT command feature. There could be a possibility that the N2 commands will contain characters that the transceiver may confuse for AT commands.
Keep in mind the 2.4Ghz cannot penetrate much. Any obstacles will cut the signal down a good deal. Extension cables also kill signal pretty quick with 2.4, keep them short as possible. Antenna alignment and a clear path are going to be fairly critical at the distances you’re talking about. Before you pull your hair out trying to make this work, I would verify that the signal is good and constant. Two outputs are provided on the radios to verify this. You could also use laptops at each side with windows hyperterminal to test or the included software. If you need a source for antennas, cables, etc check out FAB corp @ http://www.fab-corp.com/. Hopefully you got the 200mw radios as 10mw is pretty weak for long haul links.
Last edited by orion242; 02-24-2007 at 11:24 AM.
Thanks Orion for your help , it is working on End Char mode !! the Broadcast setting can only be done in API mode !
We connected Hyperterminal to the n2 bus at the N30 and the data is coming through fine , however the amount of data is less than without the radios ! So it is slowing things down a little ! However the radios values update nicely in M explorer
I noticed the AT commands also end in OD hex ( page 30 of AC5124 spec ) so im wandering if this will confuse the RAdio as to real N2 data and AT commands ??
Is this why you recommend turning it off ? , only then we cant make changes to the Radio !
S2 gave me this response , which is no help and unfortunatly we have to get this working so no throwing in the towel now !
"As for your wireless issue, I could not comment on the configuration of your wireless devices, as I have no experience with them. What I can say is that your network will probably not work consistently or reliably. I say this, as the N2 bus has very specific timing requirements that cannot be met with wireless/Ethernet networks directly/easily. The N2 bus specification is quite clear that N2 devices must respond within 10 ms from a request from a N2 bus supervisory controller (NCM, N30, NAE, etc). In practice, this latency can be somewhat longer than 10 ms, but varies with the supervisory controller (NAEs are much, much less tolerant of delays). Since your wireless controllers must:
1. Receive N2 data from supervisory controller
2. Convert it to a wireless packet,
3. Transmit the packet
4. Receive the wireless packet
5. Decode the packet to RS-485
6. Transmist the RS-485
7. Wait for a Response
8. Convert it to a wireless packet,
9. Transmit the packet
10. Receive the wireless packet
11. and then finally decode the packet to RS-485 to return it to the supervisory controller
All of the above steps must be done technically within 10 ms. In most cases, their are delays with the wireless transmissions (terrestrial issues, electrical noise, etc) and so this further adds to the delays (latencies) which causes grief with the supervisory controller. The bottom line is that the supervisory controller is not tolerant of excessive N2 bus packet delays. Interestingly, these are the same issues that one faces when once communicates with Ethernet and is why one cannot connect simple RS-485 to Ethernet devices in order to extend the N2 bus over Ethernet. In order to have consistent and reliable operation over these type of networks (wireless, Ethernet, etc) one must have a very sophisticated system that can compensate for these variable packet delays/latencies (hence the reason for our S2N2E product).
At any rate, I hope I shedded some light on some of the issues you face. "
>however the amount of data is less than without the radios ! So it is slowing things down a little
This is not a speed issue. You’re losing data for whatever reason. Those radios are rated for 115.2Kbps, 9600 is no sweat.
>Broadcast setting can only be done in API mode !
My bad, keep in mind you’re the one that bought the equipment and have it in hand.
>The N2 bus specification is quite clear that N2 devices must respond within 10 ms from a request from a N2 bus supervisory controller
10ms is a pretty quick window for a reply, yet still possible with today’s radios. Most of my experience with N2 supervisory controllers is with “relocation programs”. We relocate the NCM, N30, NAE, etc into the nearest dumpster and replace with ours. I have worked on software interfaces for N2 that talk with the unitary controllers. As such, I can tell you the end devices are more tolerant to delays then the 10ms quoted. Even using worst case figures, readily at hand, it would seem you could achieve this with solid signal.
>I noticed the AT commands also end in OD hex ( page 30 of AC5124 spec ) so im >wandering if this will confuse the RAdio as to real N2 data and AT commands ??
It would still need to begin with “AT” and some other valid characters. It’s a slim possibility, yet it could happen. Hence why I say setup the radios and turn it off.
Figure out why your losing data and this setup will probably work. My guess poor signal is causing retransmits, packet loss, and other issues. With 2.4Ghz line of site is exactly that. If you do not have a clear path to the other end, it’s not likely to be reliable regardless of what equipment is being used.
Personally I wouldn’t screw around with these radios, not worth the headache. If the customer has the money for this project, I would get parts I KNOW work. Not only will my life be much easier, and they will also be happier with a reliable system.
What does the manufacture of the radios say about your issue?? Let me guess, you didn’t buy 5000 units and not willing to help…..
Last edited by orion242; 03-07-2007 at 10:08 PM.