HOW TO FORCE A MODBUS SCREEN TO REFRESH OR UPDATE THE CONTENT; LIKE FORCING THE CONTROLLER TO READ ALL DIGITAL INPUTS IN THIS PARTICULAR RTU ?

[RAUL]

IN A SCADA SYSTEM, USING A MODBUS DRIVER, THE POLL RATE IS DEFINED TO BE 3 MINUTES POLL FOR EVERY RTU.
QUESTION IS HOW TO FORCE AN INMEDIATELY UPDATE OR FORCE THE CONTROLLER TO REQUEST A SPECIAL POLL TO A PARTICULAR RTU, INSTEAD OF WAIT FOR THE NEXT POLL INTERVAL ? WE HAVE 10 RTUS IN THE POLLING SEQUENCE.
THANK YOU FOR THE ASSISTANCE.

[tommy_scharmann]

In the Modbus driver (I am assuming you are using Lookout 4) you have two "yellow" fields: PollRate and Poll. Obviously you have 3 minutes entered in the PollRate field as "00:03:00" or as a fraction of a day: ".00208333". You can use the Poll field to initiate an immediate poll. Since this field is yellow it can accept complex expressions. In this case you want your expression to evaluate as either true or false. True=Poll Now.

If I understand your question, you want the controller to cause an RTU to immediately poll the controller, probably in response to an event that requires immediate data collection. Correct?


Here is the problem. The RTU's window into the controller is the Modbus Driver set at 3 minutes. How does Lookout know you need an immediate poll if its only window into the controller opens every 3 minutes?
What came first the chicken or the egg? 🙂


I use TIWAY drivers over Ethernet to communicate with TI-505 PLCs. The way I would accomplish this is as follows: I would have two drivers for every PLC. One driver is set at a relatively slow poll rate that does the bulk of data collection. Another driver is set at a very fast poll rate (say 1 second or a fraction of a second). This second driver only looks at one bit in the PLC. This way the "fast" driver is not putting too much traffic on my network. This bit turns on in the PLC in response to logic that indicates immediate data collection is needed. In Lookout I would include this bit of the fast driver in the Poll expression of the slow driver.


The problem you may run in to:
1.)Does the Lookout Modbus driver allow two Modbus objects to "look" at the same address? In Lookout 3.8 the TIWAY drivers I use did not. In Lookout 4.0 they do.
2.)If Lookout is only "using" one bit of the fast Modbus driver will the driver only poll that bit or will it poll all addresses. The TIWAY driver uses an algorithim that ensures minimization of data collection based on what is used in the Lookout. Maybe the Modbus driver does too.


Hope you got some ideas.


Regards,
Tommy Scharmann

[Khalid]

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Hi,

There's nothing more one can add to Tommy's response.. great job! I will only summarize it here so you don't think it's too difficult..

Create a new Panel and place 10 pushbuttons on it. Connect these to the Poll datamember for each of the RTU. Now, whenever you want to force an immediate poll for a particular RTU, you just hit the pushButton for that RTU. The regular polling will continue otherwise.

Rgds,

Khalid 🙂


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