Connecting devices

Before you start

For each site, have:

• how the device is reached — serial settings, or IP address and port
• the point list: register addresses and function codes for Modbus, object and index for DNP3, or node identifiers for OPC UA
• data types, word order and scaling for anything that is not a plain integer
• the engineering units each point is in
• which well, facility or tank each point belongs to

The last two are the ones most often missing, and they are the two that decide whether the data is usable once it arrives.

Direct connections

For Modbus, DNP3 and OPC UA, the platform connects to the device and maps each point onto the asset model. See protocols for the differences between them and how to choose.

Configuration records, per point: the source device, the original device tag or address, the data type and scaling, the resulting engineering units, and the model point it resolves to. That mapping stays inspectable — when a number looks wrong you can follow it back to the register it came from.

Edge gateway connections

Where the link is metered or intermittent, put an edge gateway at the site.

The gateway holds the local protocol conversation with the devices and publishes to a broker over MQTT with Sparkplug B. Only changes cross the expensive link.

The gateway also makes device state explicit: Sparkplug B birth certificates declare what a device will report, and death certificates make a disconnection an event rather than an absence. The platform records that state rather than inferring it from silence.

Verifying a connection

Three checks, in order:

1. Does a value arrive at all? If not, the platform reports the connection failure with what failed — it does not show an empty chart that looks like a quiet well.
2. Is the value right? Compare against the device’s own display. A value out by a large factor or oscillating implausibly is almost always word order or scaling.
3. Are the units right? A correct number in the wrong units is the hardest error to catch later, because nothing about it looks wrong until it is compared against something else.

Commissioning control

Control is not enabled by connecting a device. Control authority is a separate grant, scoped per device group, and can be left off entirely while telemetry runs.

Turn it on deliberately, on a defined set of equipment, once the telemetry from that equipment has been verified. See control.