MVP 2021 Ausman Posted June 1, 2017 MVP 2021 Report Share Posted June 1, 2017 Hi all, Something interesting and useful. Would like some suggestions on an observation. I have a V130 talking with a 120 via Unican, and over time with program improvements I have been adding more and more communicating of parameters both ways between the two via Unican sends. I posted about this some time back and the answer was pretty much just send blocks concurrently as things will work. This has all been working fine with my having a trigger for the operation in both units based on SB13 and 202. I have always been a little frustrated by the lag in response of the 120 when accessing remotely through the 130 via the LAN. Recently I was onsite which is imperative for an "iffy" change in such a crucial system, so I decided to change the trigger to SB15 (instead of 13) in both units. There was a definite improvement in remote access timing, and all the information needed was still being transferred correctly. Left 3 hours later all still working OK. Next day logging in remotely I couldn't get into the 120 at all, not even to do an initialise and reset. I ended up having to firstly change the 130 back to SB13 and then that let me get back into the 120 to also change it back, but with some timeout hiccouphs along the way. A bit of nail biting as this was all being done remotely as the site is two hours away! So....I obviously had some sort of buffer issue that gradually built up over time to eventually make the bandwidth needed for access via Unican unworkable, but there was still enough for the Send/Receive components to still be working fine. I don't know whether the inter-unit accessing "linkage" is also controlled by the Unican parameters I have set for the send blocks.....someone know? I have always thought my SB13 timer a clumsy method of control as the two PLCs might drift around to hitting it concurrently, but I have also been under the impression that although Unican didn't really mind this it still needed some sort of buffering. My experience shows that some sort of buffer allowance is definitely needed, so I can't just use SB202 as the trigger. It would seem that even if 202 says things are ok, there might be another few scans needed to really clear things. So what is the best solution here? Is it to setup a count based system where the two units "ping-pong" off each other? ie 130 does it's sends, and in doing that it sends one bit that is read and reset by the 120 which waits a few scans and then does the same thing back to the 130 ad nauseum etc etc? The ideal number of scans would have to be ascertained by trial and error. The problem I see with this is if something goes astray, because it relies on the link working perfectly each and every time, the entire link will fall over. But I could cover this with a master "timeout" of say 10 seconds in each plc monitoring the bit changes. Or use some of the SIs to better control things? There is not a lot of help info about Unican capabilities, perhaps a bit more involved detail would be good. cheers, Aus Quote Link to comment Share on other sites More sharing options...
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