modbus tcp - 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 Energy Management: Metering, Demand and Shedding

September 13, 2026January 21, 2024 by PLC

Ladder rung for load shedding: predicted demand high in parallel with the shed seal-in bit, in series with the shed permit and the chiller alarm contact, driving the shed output for chiller 2

Wire a power meter into Logix or S7, totalize kWh in Structured Text, hold the demand peak with priority load shedding, and check if a VFD retrofit pays.

PLC Water Treatment: Levels, Lead/Lag Pumps and Dosing

September 12, 2026January 18, 2024 by PLC

Timing chart of lead and lag pump alternation: the lead call starts pump 1, the lag call brings in pump 2 at high level, and on the next cycle pump 2 takes the lead

Wet well level control, pump alternation that shares the wear, chlorine dosing with long dead time, and remote sites over cellular Modbus that go quiet.

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.