PLC and PMS

[Manoj M]

Hello Experts,
I am trying to write a program in Step 7. The scenario is there is a platform management system (PMS) which communicates with S7-300 PLC in remote mode. PMS ask for deploy, deploy reset, recover, recover reset and so on. Every command consists of command request and command type. For example if PMS ask for Deploy, then command request will go high and then PLC look for what is the command type (integer value) 1 for deploy 2 for deploy reset. During this process PLC also needs to send back the boolean signal saying command request acknowledged or command request failed, which proves to PMS there is no communication failure.
Can somebody help me writing this logic.
Also if there is a communication problem then how can PLC send back the Command request failed bit.

Regards
Manoj

 

[xzen]

A lot of people in the forum could write this program for you. But then they would do your job.

 

[boneless]

What have you got so far?
How are you receiving these commands?
What are your outputs?

 

[Manoj M]

Hello Boneless,
I have already written the software for local control which is from HMI and also connected parallel connections for PMS in case if remote is selected. All of the send/receive signals to/ from PMS are stored in data blocks. I am not looking for how to deploy or retract. The only point where I have concerned is sending acknowledged or fail bit from PLC back to PMS. Should I be using a watchdog...
Please suggest...

Regards
Manoj

 

[boneless]

Yes, I think you should always use a watchdog.

My watchdog usually are just a bit that toggles at a certain frequency. If no change is detected in x amount of time, alarm is initiated. This should be done on both sides.

 

[Saffa]

This PMS system (sounds like a suitable acronym! ) should be able to signal a fault to the operator if it requests an operation and does not receive an acknowledgement within a suitable timetable. As for a watchdog, I prefer a rolling counter... If the value doesn't change from the last value read within a suitable timeframe, raise an alarm.

Whether the above is easily implemented in this PMS system is the next question. What is the name of the package? Is it your responsibility to configure it?

 

[Manoj M]

Hi Saffa,
The worst part is I don't have this PMS as a hardware sitting next to me. I have a sample program for this but for me it is of no use..I am not the one who is doing programming of PMS. So when boneless said implementation of Watchdog on both sides then for obvious reason I cant do it on the PMS side....PMS company have given me read/write data blocks where I should send/receive data to/from PMS and like I said my only worry is Acknowledge/fail bit sending back to PMS.

Regards
Manoj

 

[Saffa]

I would tell this PMS company that you are placing a free running counter into one of those registers. Then leave it up to them to worry about "what if" comms stops. It should be up to them to manage this fault state on their end. If your machine needs to go to some "safe state" if comms fails, then request a free running counter from their end and monitor it for changes.

This sort of thing takes cooperation and communication from both parties to make it work if there's no detailed spec on this mechanism!

 

[BobB]

Sounds like PMS suits them!