How to identify which communication protocol is being used

Thread Starter

Green-0424

Joined May 2, 2016
4
I am trying to identify which communication protocol is being used in our irrigation system. It has a base field unit which communicates with the RTU's via a 2 wire system. The wire length to the last RTU is around 6 kms and the signal strength seems to be fairly marginal at that end. So I would like to be able to find some sort of signal booster to fit in the line, but first I think I need to know what type of signal protocol it uses. Any help would be greatly appreciated.
Thanks
 

WBahn

Joined Mar 31, 2012
25,121
Your best bet is to look for documentation, contact the manufacturer, or contact someone that installs and services that brand.

Otherwise, you will need to basically track down enough detailed information on every conceivable protocol that they might be using and then compare that to measurements made on the system to rule them out one by one -- and hope that they aren't using a proprietary variant of a possibly proprietary protocol that isn't on your list of conceivable protocols.

Yeah, I wouldn't want to do down that path, either.

Another option is to map out what is transmitted for each possible command and effectively build up a look up table of control signals.

If the communication is strictly one way (and I exclude from that things like the transmitter sensing the presence of the unit on the other end by its influence on the signal level at the transmitter), then putting in an amplifier that simply restores the signal to the same level as at the transmitting end probably wouldn't be too difficult and you wouldn't need to know the protocol. If the communication is two way, over a two-wire interface, then that gets quite a bit more complicated.
 

MaxHeadRoom

Joined Jul 18, 2013
19,786
One of the most common industrial system of remote control is via Modbus.
Basically a system with a single master and multiple slaves, with 2 way, 2 wire communication.
Max.
 

dendad

Joined Feb 20, 2016
3,261
It is most probably running RS485 levels and as MaxHeadRoom says, look for Modbus.
You could wire an RS585 driver across the lines and see what comes out.
A MAX485 chip will do. Just wire it up for receive and look at the output.
Some scopes have protocol analyzers in them. Even some relatively cheap USB ones.
And of course it may be a non standard closed protocol.
 

Thread Starter

Green-0424

Joined May 2, 2016
4
Your best bet is to look for documentation, contact the manufacturer, or contact someone that installs and services that brand.

Otherwise, you will need to basically track down enough detailed information on every conceivable protocol that they might be using and then compare that to measurements made on the system to rule them out one by one -- and hope that they aren't using a proprietary variant of a possibly proprietary protocol that isn't on your list of conceivable protocols.

Yeah, I wouldn't want to do down that path, either.

Another option is to map out what is transmitted for each possible command and effectively build up a look up table of control signals.

If the communication is strictly one way (and I exclude from that things like the transmitter sensing the presence of the unit on the other end by its influence on the signal level at the transmitter), then putting in an amplifier that simply restores the signal to the same level as at the transmitting end probably wouldn't be too difficult and you wouldn't need to know the protocol. If the communication is two way, over a two-wire interface, then that gets quite a bit more complicated.
Thanks for your reply, I think I will have to find some documentation. It is a two wire two way system so I think the easiest way would be to get the info directly from the manufacturer.
 

Thread Starter

Green-0424

Joined May 2, 2016
4
One of the most common industrial system of remote control is via Modbus.
Basically a system with a single master and multiple slaves, with 2 way, 2 wire communication.
Max.
I think you might be right with the Modbus, as it does use the single master multiple slaves, 2 way 2wire system. Thanks for your help.
 

WBahn

Joined Mar 31, 2012
25,121
I think you might be right with the Modbus, as it does use the single master multiple slaves, 2 way 2wire system. Thanks for your help.
There are many protocols that have this property, but Modbus is certainly a good candidate to start with -- you might well get lucky on the first shot.
 
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