I have lately came across an requirement that showed up in several tenders and left me a bit baffled. It can be summed up something like this:
- basic setup, several PLCs on a network connected to the SCADA server (since I’d be building a system with Ignition, this is Ignition GW)
- for simplicity, suppose Ignition GW is a standalone version, with DB installed on the same machine
- in normal operation, data from the PLC is polled and using tag historian stored stored in DB
- BUT: in case that GW goes offline, PLC should log data locally (for up to 24 h) and when the GW starts again all the locally stored data in all of the PLCs should be synchronized into the database.
Let’s suppose PLC supports data logging and has enough memory for all the tags for 24 h. We usually work with Micrologix 1400 or Siemens S7-1200, although we don’t have experience with data logging function.
Does anyone have a suggestion how to approach this problem and get historical data from PLC into Ignition and ultimately to correctly fill historical DB?