Specifying PLCs for a new line: what to ask the machine builder for OEE/SCADA?

[HMIDesign]

We're ordering a new filling line from a machine builder and the technical specification is being written now. Last time we bought a machine, it came with a closed PLC and connecting it to anything later was expensive and slow.
This time I want to write the right requirements into the contract so we can connect the line to OEE and SCADA later without surprises. Which protocol should we ask for, and what else should be in the specification? The builder offers OPC UA, Modbus TCP, or "whatever you want".

[Technical Support]

Writing this into the specification is the right moment; it's much cheaper than adding it later. Here's what we recommend.
1. Protocol
Ask for Modbus TCP server (slave) access on the PLC as a minimum. It's supported by Proveris OEE and Omnivex SCADA and by almost every PLC brand. Proveris OEE also supports Modbus RTU, Modbus RTU Over TCP, MQTT and BACnet, and Omnivex SCADA supports Modbus TCP/RTU variants and MQTT.
If the builder also provides OPC UA, there's no harm in having it, but please contact us before relying on OPC UA for our products, so we can confirm support for your version.
2. A documented register map
This is more important than the protocol. Require a list with address, data type, unit, scaling and description for every signal, delivered with the machine and updated with every software change.
3. The signals OEE needs
At minimum:
- Machine running / stopped
- Good part counter and, if possible, reject counter
- Fault state, and ideally a fault code
- Optionally, product/recipe number
Ask for counters as continuously increasing values rather than ones that reset every shift.
4. Group the addresses
Ask for SCADA/OEE signals in continuous address blocks. That allows efficient reading with a few large requests.
5. Network
A separate Ethernet port or a defined IP for monitoring, so you don't need access to the builder's internal machine network.
6. Acceptance test
Include a test where your team reads the signals with your own tools before acceptance.
Background reading:
- https://greensoft.ai/blog/modbus-tcp...communication/
- https://greensoft.ai/blog/what-is-op...protocol-work/
- https://greensoft.ai/documentation/p...ion-protocols/