IIoT, SCADA & Edge Connectivity worked example

PLC Data Availability at 71% opc scanner uptime: a worked example

This worked example runs the plc data availability numbers for a tougher week than the baseline: 71% opc scanner uptime instead of the typical 99%. Estimate how many PLC tags can be polled cleanly per period from tags polled per scan cycle, planned scan cycles in the period, scanner uptime, and the share of polls that return fresh data without retry.

The inputs for this scenario

  • Tags polled per scan cycle: 500 tags / cycle (held at the documented default)
  • Planned scan cycles in the period: 60 cycles (held at the documented default)
  • OPC scanner uptime: 71 % (the input this scenario stresses; the baseline uses 99)
  • Clean-poll rate without retry: 99 % (held at the documented default)

Working through the calculation

  • The calculation starts from the formula this tool documents: Gross PLC poll capacity = tags per scan cycle × planned cycles.
  • Good PLC tag polls per period works out to 21,087 tags at these inputs, and this is the headline figure for the scenario.
  • Gross PLC tag polls per period works out to 30,000 tags at these inputs.
  • Scanner downtime loss works out to 8,700 tags at these inputs.
  • Retry loss works out to 213 tags at these inputs.

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 28.28% below the baseline at 21,087 tags.
  • Use it when scoping an OPC/edge gateway, a historian ingest rate, or a data-quality SLA and you need expected delivered tag volume, not theoretical. A result at this level usually justifies acting on the stressed input before touching anything else, because every other figure in the table is downstream of it.

Results at a glance

  • Good PLC tag polls per period: 21,087 tags (headline result)
  • Gross PLC tag polls per period: 30,000 tags
  • Scanner downtime loss: 8,700 tags
  • Retry loss: 213 tags

Run it with your numbers

  • To rerun this with your own numbers, open the live PLC Data Availability calculator, set opc scanner uptime to your actual value, and adjust the remaining inputs to match your operation.

Last reviewed 2026-05-12.