Radio communications

[Buzzen]

Hello everyone,
I need to pick your brains and get your opinions. I will be starting a new project that will be on our local scada. The Scada that we have I inherited, and it doesn't always communicate as well as I think that it should. Right now we are using a Message-Based polling scheme, that was written by a sub-contractor. What are the advantages and disadvantages of going to a Standard Polling mode. All equipment is Allen Bradley except for the radio which is a SRM6000 BY DATA-LINC.
Thanks in advance.

 

[diat150]

Ive worked on those types of systems and they seem to be nothing but trouble for the most part. Id move to a standard scheme and get rid of the headache.

the data-linc is a good little radio.

 

[Buzzen]

Thanks for input! I feel the same way. its always faulting somewhere.

 

[Ken Roach]

Most radio networks can be improved by careful analysis of the radio performance and the message logic.

But I wouldn't say "Message-based is bad, standard polling is good".

Can you characterize what you mean by "not as good as it could be", and "always faulting somewhere" ?

For systems that are principally collecting data from the field and sending setpoints and commands only occasionally, I find Standard Polling to be simpler, requiring less logic in the master controller.

If you need programmable prioritization, or you need to frequently enable and disable traffic to stations that are offline, then Message-Based is necessary.

What type of A-B controllers are you using; SLC, MicroLogix, PLC, ControlLogix, etc ?

 

[Buzzen]

For on-site we are using SLC 5/03and5/04 and Micrologix 1000. Out in the field we are using Industrial control links,Etherlogic advanta. Right now the on-site radios were used to turn pumps on/off. Off-site with the advanta controllers we use to open some actuators, and get flow and levels in streams. Could the problems be with the programming. U said careful analysis. Well I am pretty new at this, reading books and such but, where would I even start.

 

[Ken Roach]

I'll try to be more precise with my questions.

1. What are the "Master" controllers ? My guess is that they are SLC-5/03 or 5/04 controllers.

2. When you describe "on-site" and "in field", are we discussing separate systems with different master devices, or a single large radio network ?

3. How many slave controllers are on the radio network ?

4. Are there slave controllers that are frequently taken offline ? I'm asking because the SLC-5/0x DF1 Master has a fixed Polling List that can't be modified at runtime, and you're going to slow down your "Standard Polling" if devices are frequently offline.


I am not familiar with Etherlogic Advanta, unfortunately. Do these use the A-B DF1 Half Duplex protocol, or Modbus RTU, or their own serial protocol ?

The first thing to do is describe in detail what you mean by "faulting out". Does a CPU actually go to Fault mode ? Does a specific MSG instruction return an Error code ? Does the sequential MSG logic stop incrementing in sequence ?

The second thing to do is to start examining what diagnostic items are available to you. The first place to start, in my opinion, is the Channel 0 serial diagnostics table for the DF1 Master controller. If there hasn't been one defined, then schedule some downtime to load a program that includes one.

RA has a "SCADA Application Guide" that includes a lot of good information on the SLC controllers and DF1 Half Duplex protocol: http://literature.rockwellautomation.com/idc/groups/literature/documents/um/ag-um008_-en-p.pdf

In my opinion, serial telemetry can only be well-diagnosed using protocol analyzers in tandem with the tools the radio and controller devices give you. It takes time, it takes money, and it takes expertise. You can substitute generous amounts of one for the other, but you're always going to need at least two of the three factors.

 

[Buzzen]

master=slc 5/03 and 5/04

There are two master controllers. One for the Telemetry. One for the ON-site.

There are 14 slaves for the Telemetry

There are 5 slaves On-site

We are running DF-1 half duplex with messaging polling

The devices go offline if batteries in the field fail, radio transmission faults out due to error, no more retries

Each station on telemery will be green on computer when the slave is functioning. will go red when there is a fault. Which usually has to be reset in the field. The CPU does not fault out.

 

[Ken Roach]

Well, I'm sure there's nothing you can program around when the batteries in the field fail. Do these RTU devices allow you to monitor the battery voltage ?

If I was repairing this system, I would focus on what you describe as "radio transmission faults out due to error, no more retries".

Figuring out exactly what this means might involve careful examination of the SLC-5/0x master serial port and protocol settings, as well as the logic driving the MSG instructions and the status values for the serial port.

Do you experience errors on both the On-Site and Telemetry systems ?

Are the Data-Linc SRM radios used for both the On-Site and Telemetry systems ?