Evening all.
Clarifier bridge, rotating, so no cable to it. 1734-AENTR with six modules out on the bridge, a pair of industrial wireless bridges back to the plant switch, CompactLogix 5069-L320ER in the building. RPI on the AENTR is 20 ms, left at default.
A few times an hour the rack drops with 16#0204 connection timed out, back within a second or two, and the scraper drive stops because its run permissive comes through that rack. Signal on the bridge's page sits at -55 to -60 dBm, which the radio vendor says is good.
We moved the antenna higher and then swapped to a bigger directional one, no change at all. What happens when a wifi link retries, does it drop everything for a moment? Do I need a different radio? Or is 20 ms just asking too much of a radio link?
What's the connection timeout on that rack. Not the RPI. The timeout.
OG
Didn't know there was one separate from the RPI, maybe I've never looked properly. I can't see it on the Connection tab, just RPI 20 ms and the inhibit box.
It isn't on the tab. Timeout is RPI times a multiplier, 4 by default, so 80 ms. On a bridge here the access point's own log showed retries and roams of 100 to 200 ms every time the bridge swung past a section of steel handrail. Every one of those is longer than 80 ms, so the connection gets declared dead before the radio has finished retrying. Signal strength looks fine because it is fine, most of the time.
Two things, both in the AENTR's module properties. Raise the RPI to what the process actually needs, a clarifier bridge doesn't need 20 ms, 100 ms is plenty, and that alone takes the timeout out to 400 ms with the default multiplier, longer than any retry pete has seen. Some modules let you change the multiplier as well, the AENTR I don't think does from Logix, so RPI is your lever.
And the scraper permissive. If it can't wait 400 ms it shouldn't be on a radio at all, put it on a hardwired pair through the slip ring. Anything time critical stays on copper. There's a writeup on wireless I/O here: https://plctr.com/integrating-wireless-communication-with-plc-systems/
OG
RPI to 100 ms yesterday afternoon. Zero drops overnight, first clean night in a month. The scraper permissive is moving to a hardwired pair through the slip ring, it should never have been on the radio in the first place.
So it was the 80 ms timeout at 20 ms RPI, shorter than the radio's own retries. RPI 100 ms fixed it and the permissive comes off wifi. The antenna money was wasted.
Still not sure what makes the bridge retry in the same spots each turn, the handrail idea sounds right. Thanks billr, petek.
Steel handrail is my bet. Walk it round with the laptop and watch the RSSI.