Writing PLC Data to SQL: From the Gateway, Never From the Controller

A four-stage chain from controller through gateway and IDMZ broker to SQL Server, showing the controller setting DataReady, the gateway polling at one second into a SQLite queue, the broker carrying two sessions on TCP 8883, and a batched INSERT of 200 rows in 84 milliseconds, with three numbered break points on the arrows

A ControlLogix has no SQL client in it. What it has is a socket object on the Ethernet module, a WriteSocket service that carries 484 bytes at a time on a standard connection, and a MSG instruction whose default timeout is 30 seconds — which is 2500 scans of a 12 ms program. So a … Read more

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