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Old April 13th, 2019, 05:19 PM   #1
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shanefaulkner is offline
Join Date: Oct 2009
Location: Buffalo, NY
Posts: 7
Bently 3500/92 Prosoft MVI56E-MNET comm woes

I have used this exact setup before (4 or 5 times) with no issues. Last successful implementation was a couple of years ago. Now, I have two separate installations that are exhibiting slowness.

Bently Nevada 3500/92 Modbus communications gateway is being polled by a Prosoft MVI56E-MNET in a ControlLogix rack with a 1756-L73 processor. At this point I have the Prosoft module issuing one client command, once per second, reading one 4xxxx register in the Bently via ethernet. I am reading the Bently's internal clock second register. At the previous installations I could see the live second's value update every second in the CLX tag.

Now, at the new installations sites this value freezes for anywhere from 2 to 50 seconds. The client read command in the MNET will error for a while and then eventually work.

Prosoft tech support thinks the socket is opening too slowly, closing too quickly, or something like that. They requested a Wireshark log which I sent and am awaiting a reply. They also suggested that an MNETC module would likely solve the problem, but we already purchased about 10 MNETs.

Bently support basically admitted that the ethernet modbus capability of the 3500/92 is junk and that I should use the module's RS485 port instead, with a Lantronix ethernet to RS485 converter in the middle. This seems ridiculous to me since this has worked flawlessly before.

I thought maybe my Stratix 5400 switch might be the issue so I connected the Prosoft and 3500/92 directly and nothing changed.

The firmware of both the MNET and 3500/92 match the working installations. Who knows what internal components might have changed though.

- Aggravated in Texas
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Old April 14th, 2019, 05:35 PM   #2
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shanefaulkner is offline
Join Date: Oct 2009
Location: Buffalo, NY
Posts: 7

Solved! In the MNET config I changed Client config: minimum command delay from 10 to 0. I also changed each client command's poll interval from 10 to 0. No more errors and data updates rapidly.

I assume these changes caused the socket to stay open which eliminated all problems.

- no longer aggravated in Texas
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Old April 15th, 2019, 02:51 PM   #3
Ken Roach
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Ken Roach is offline
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Location: Seattle, WA
Posts: 14,711
Thanks for the followup !

My reading of the client's command delay and poll interval being set to zero is that the MNET will poll as fast as possible.

Did you Wireshark the difference between the previous and current traffic ?

Most implementations don't time out a TCP connection for 75 seconds or so (the usual TCP Keepalive interval).

I'm frowning at a Fanuc 30i-A CNC interface that's occasionally generating new TCP connections for no discernible reason so it's on my mind.
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