In a Siemens-powered plant, that data lives deep inside the PLC. The goal of a connected factory is simple: full Siemens PLC data access – every operationally relevant value the controller holds reaching the systems that act on it. While OPC UA is the standard starting point, the densest controllers often hold more than their built-in servers can expose. When you hit that ceiling, you need a second path: Siemens’ S7plus (S7+) protocol, native and high-performance, reaching past the built-in server’s limits.
Expert article by
Dr. Diwaker Jha
Industrial Connectivity Expert, Cybus
For full Siemens PLC data access, every tag has to be reachable – yet the densest controllers hold more than the built-in server is sized to expose. Take a case we ran into in the field: a Siemens S7-1200 holding over 18,000 tags. The customer connected via OPC UA and the first couple of thousand tags flowed – then the count stopped just under 2,000. That is the server’s node cap, the number of tags it can expose. Live updates are a separate budget: about 1,000 monitored items at 1,000 ms sampling, dropping to roughly 100 when you need 100 to 500 ms. The remaining 16,000 tags were healthy and present, but they sat just past what the built-in server is sized to expose. For complex datatypes, it falls further still – to a few variables. Not enough for modern, data-rich production environments.
For a decision-maker, those locked tags aren’t just a technical hurdle; they are a blind spot. Your historian, MES and analytics dashboards can only optimize what they can see. In complex batch plants, the variables out of reach are often the ones that matter most: yield, energy efficiency and quality metrics. The breakthrough? The customer didn’t have to touch the controller. They simply opened the second path: native S7plus.
| Feature | OPC UA (Built-in) | S7plus (via Connectware) |
|---|---|---|
| Visibility Ceiling | ~2,000 Nodes (S7-1200) | No node cap (All 18,000+ Tags) |
| Read Speed | Bounded by node + sampling caps | ~40 ms single / ~100 ms complex (tested on S7-1200) |
| Native Symbol Support | Yes (within budget) | Yes (Symbolic Addressing) |
The traditional way past these limits is painful: “split” the controller. This involves adding new CPUs, spreading the logic across them and then performing a complete rewiring and revalidation. It is a capital-intensive project that demands significant downtime.
A Factory Data Hub approach changes the math. By using S7plus – Siemens’ own native, high-speed protocol – you gain full visibility into the existing hardware. You keep the same CPU and the same program. You simply choose the right path for the volume of data required. Connectware speaks both, allowing you to lead with OPC UA and transition to S7plus as your data needs scale.
Many platforms stop at the built-in server’s limit. Connectware speaks both OPC UA and native S7plus – two paths to your Siemens data.
The alternative to a second data path is re-engineering the controller: adding CPUs, rewiring and revalidating, with the line down throughout. Production stoppages are expensive – Siemens’ own True Cost of Downtime 2024 puts unplanned downtime at 11% of annual revenue for the world’s largest manufacturers. S7plus avoids that work entirely: same controller, same program, every tag.
As the single reliable source of truth between OT and IT, Connectware ensures your infrastructure never becomes your bottleneck. Whether you need the open standard of OPC UA or the full depth of S7plus, you have the road already paved. Don’t let a built-in server limit your factory’s intelligence.
Every tag your built-in server hides is a blind spot in your historian, MES and analytics. Connectware gets all of them into MQTT – OPC UA first, native S7plus when you need every tag, no re-engineering.
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