25s interval time between plc tag value refresh

I have a site siemens 400 plc. it is.connected to a wonderware scada at the moment.

I set up an ignition local gateway taking only 10000 tags, but the refresh time is 25+ seconds.

if i remove the tags to only 500, the refresh time is 2 seconds as per designed in tag group.

what is the possible solutions I should try to improve the comms speed? most of the tags are configured to 5s scan time.
It is a local ignition gateway with lan cable to the 400 plc.

there are 7349 tags in the gateway.
at 3584ms

at 5020ms

at 7421ms

at 8401ms

Is it because simply the plc cannot handle the comms with two scada systems?
never have such issue with 1500 or compactlogix or m340.

That 's certainly what it looks like. Not surprising with such an old processor, I would think.


I'm not a Siemens guy, but the S7-400 supports a 480 byte PDU, while Ignition's default size is 240. That would help a bit.


Thank you for the hint.

I changed the value to 480 in the driver advance setting, the overloads are back to normal

Sampling time is around 4sec, which is acceptable to this project.