IIoT, SCADA & Edge Connectivity worked example

PLC Data Availability at 110% opc scanner uptime: a worked example

What does the result look like when opc scanner uptime reaches 110%? The full calculation is worked below with real intermediate numbers. Use it when a controls engineer is sizing the PLC scanner load on Kepware, FactoryTalk Linx, or a vendor OPC UA server before adding more tags or another machine to the line.

The inputs for this scenario

  • Tags polled per scan cycle: 500 tags / cycle (unchanged)
  • Planned scan cycles in the period: 60 cycles (unchanged)
  • OPC scanner uptime: 110 % (raised for this scenario; the documented default is 99)
  • Clean-poll rate without retry: 99 % (unchanged)

Working through the calculation

  • Applying the documented formula (Gross PLC poll capacity = tags per scan cycle × planned cycles) to the inputs above produces each figure below.
  • At this operating point the engine returns 32,670 tags for good plc tag polls per period, the number this scenario is built around.
  • At this operating point the engine returns 30,000 tags for gross plc tag polls per period.
  • At this operating point the engine returns -3,000 tags for scanner downtime loss.
  • At this operating point the engine returns 330 tags for retry loss.

How this compares with the baseline

  • Against the tool's baseline example, where opc scanner uptime sits at 99% and the headline result is 29,403 tags, this scenario comes in 11.11% above the baseline at 32,670 tags.
  • A figure at this level is achievable when opc scanner uptime is genuinely sustained, not just peaked for a shift. It assumes uptime and clean-poll losses are independent and uniform; bursty network faults or a single offline PLC can concentrate losses in ways this average hides.

Results at a glance

  • Good PLC tag polls per period: 32,670 tags (headline result)
  • Gross PLC tag polls per period: 30,000 tags
  • Scanner downtime loss: -3,000 tags
  • Retry loss: 330 tags

Run it with your numbers

  • Every input above is editable in the live PLC Data Availability calculator, which recalculates instantly and can be shared with the inputs intact.

Last reviewed 2026-05-12.