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Airlink Celluar Modems
- Thread starter QuadDude
- Start date
EddieWillers
Electrical
I helped an unfortunate municipal customer use the Airlink Raven.
The problem was that he was using Allen-Bradley DF1 full duplex protocol between a Kepware data server and a ControlLogix controller in the field.
DF1 Full Duplex sends an "DLE ACK" acknowledgement after it receives every packet, so the modem had to 'key up' (I know that's an inaccurate term' to send that little 2-byte acknowledgement for every packet that came in. Connecting to the GPRS system takes about 1 second, so every single 'read' operation took 4 connections and over 4 seconds.
Airlink says that if you're going from the Internet to these modems there is no such delay, or if you're sending large packets the delay doesn't matter.
But they stink for small packet polling, just because of the way they work.
It probably would have been less difficult using the DF1 Radio Modem protocol, but the Logix controllers (and the Kepware driver) don't support that yet.
The problem was that he was using Allen-Bradley DF1 full duplex protocol between a Kepware data server and a ControlLogix controller in the field.
DF1 Full Duplex sends an "DLE ACK" acknowledgement after it receives every packet, so the modem had to 'key up' (I know that's an inaccurate term' to send that little 2-byte acknowledgement for every packet that came in. Connecting to the GPRS system takes about 1 second, so every single 'read' operation took 4 connections and over 4 seconds.
Airlink says that if you're going from the Internet to these modems there is no such delay, or if you're sending large packets the delay doesn't matter.
But they stink for small packet polling, just because of the way they work.
It probably would have been less difficult using the DF1 Radio Modem protocol, but the Logix controllers (and the Kepware driver) don't support that yet.
robertjo24
Industrial
We utilize their product polling Modbus, and it works fine.
You can poll from one unit as master, in a point to multi-point configuration. The master will have a lookup table and communicate with the appropriate remote based on RTU number.
You can also poll directly from a control system that will poll TCP, connecting a socket directly to the modem. We created a secure VPN tunnel to our carrier, and have a block of static IP's isolated from the internet. This provides secure links to the field devices.
We have done it both ways, both ways work.
I would contact one of their regional sales engineers to discuss system configurations.
Check with your local carrier to determine wireless coverage in the area you wish to deploy the units.
If the possible implementation includes a large number of units, the local carrier may loan you a couple modems to test for compatability.
Best O' luck
You can poll from one unit as master, in a point to multi-point configuration. The master will have a lookup table and communicate with the appropriate remote based on RTU number.
You can also poll directly from a control system that will poll TCP, connecting a socket directly to the modem. We created a secure VPN tunnel to our carrier, and have a block of static IP's isolated from the internet. This provides secure links to the field devices.
We have done it both ways, both ways work.
I would contact one of their regional sales engineers to discuss system configurations.
Check with your local carrier to determine wireless coverage in the area you wish to deploy the units.
If the possible implementation includes a large number of units, the local carrier may loan you a couple modems to test for compatability.
Best O' luck
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