opc ua - PLC Programming & Automation

PLC Communication Protocols for SCADA: What to Pick

September 12, 2026February 1, 2024 by PLC

Timing chart comparing polled Modbus TCP requests and responses at 25 ms against cyclic EtherNet/IP I/O packets at a 10 ms RPI

Modbus TCP, EtherNet/IP, PROFINET, OPC UA and MQTT compared by how they move data, with ports, poll rates and the mistakes that cost SCADA update time.

PLC Industry 4.0: OPC UA, MQTT and Real Data Models

September 13, 2026January 21, 2024 by PLC

Timing chart of an MQTT publish trigger: the broker connection drops and returns, a deadband exceeded pulse and a 30 second heartbeat each raise the publish trigger, and a store and forward flush follows the reconnection

What an Industry 4.0 project really changes on the PLC: the OPC UA server, a UDT to JSON data model, MQTT at the edge, retrofits and security.

Machine Learning PLC Integration: Where the Model Runs and What the Controller Owns

September 13, 2026January 20, 2024 by PLC

Ladder rung with ML_Valid examined on, ML_Stale examined off and Score_Hi examined on in series, driving the ML_Advisory output coil

The PLC does not run the model. What to publish, how the score returns as an advisory tag with a watchdog, and a pump anomaly detector on CompactLogix.

SCADA PLC Integration: Connect Ignition to ControlLogix

September 12, 2026January 19, 2024 by PLC

Timing chart of a one second SCADA tag group: the group tick, the CIP read request, the controller reply about 60 ms later, and the historian insert

Pick the protocol, prepare the controller tags, add the device in Ignition, set a sane tag group, then prove the link survives a network drop.

OPC UA PLC Integration: From PLC Tag to SCADA Client

September 12, 2026January 18, 2024 by PLC

Timing chart of an OPC UA subscription showing 250 ms sampling pulses, a PLC tag value change, and notifications leaving at the 1 second publishing interval

Connect a PLC to SCADA with OPC UA: KEPServerEX channels, the S7-1500 built-in server, certificate trust, subscription rates and why OPC DA kept breaking.

PLC vs DCS Integration: Getting a Skid onto the DCS

September 12, 2026January 17, 2024 by PLC

Timing chart of a DCS to PLC heartbeat: the DCS counter steps every second, the PLC echoes it, and the Comms OK bit drops three seconds after the counter freezes

How a packaged skid PLC gets tied into DeltaV, Experion or PCS 7: link protocol, Modbus register map, heartbeat, engineering units and alarm ownership.

PLC MES Integration: Tags, Handshakes and Work Orders

September 12, 2026January 17, 2024 by PLC

Timing chart of an MES to PLC work order handshake showing Request from the MES, Ack from the PLC, Done when the order is latched, and both bits clearing after Request drops

What MES really needs from the controller: OEE counters, downtime reason codes, a work order UDT, a request and acknowledge handshake, an OPC UA bridge.