PLC to dashboard, without touching the control program
The design we would propose for the most common request we get: 'the PLC knows, but nobody upstream can see it.' Published in full so it can be judged technically.
Disclosure. This is a reference architecture, not a delivered customer project. It describes the design we would propose for the situation above. No client, installation or result is represented.
Context
Why this exists
A plant with existing, working control systems wants visibility without risking the thing that currently runs the factory. The engineering question is not how to read a register — it is how to guarantee that reading it cannot affect production, and how to keep the resulting system maintainable.
The constraints
- 01
The control system must not be modified, and must not be at risk from the monitoring layer
- 02
The OT network cannot be exposed to the business network
- 03
Values needed for reporting are not all exposed as tags today
- 04
The plant has one short maintenance window per week
- 05
The result must be maintainable by the plant's own team afterwards
The approach
- 01
Read-only, rate-limited, on a separate interface
The gateway sits dual-homed: one NIC on the OT network reading the PLC, one on a separate network publishing upward, with no routing between them. Poll rates are set per tag and bounded so controller load stays negligible and measurable.
- 02
Identify the gap honestly
Some values — reject counts, changeover state — often exist only as internal variables. These are identified during the survey, and where a small, scoped PLC addition is genuinely required, it is quoted and scheduled before commitment rather than discovered afterwards.
- 03
Design the tag model first
A naming and unit standard defined before configuration, so machine 7 and machine 12 are described the same way and adding machine 13 is instantiation rather than redesign.
- 04
Edge state machine
Run, idle, stop, changeover and fault derived at the edge from PLC signals, with debounce and minimum durations so that micro-stops are captured without generating noise.
- 05
One window, reversible
Physical installation is a gateway, a switch and a cable run — one maintenance window, with nothing that cannot be undone by unplugging it.
Want this walked through on a call?
We will screen-share the rig, show the data path end to end, and answer the awkward questions about where the limits are.