PLC - PLC Programming & Automation

PLC vs DCS Programming: Where the Two Part Ways

Timing chart of an analog HI alarm: the process value crosses the limit, a three second on-delay expires, the alarm goes active and stays unacknowledged until the operator acknowledges it, then clears when the value returns below the limit

PLC vs DCS programming compared by an engineer who works on both: tags and rungs against loops and blocks, redundancy, alarms, batch and real cost.

Rockwell PLC Software: Which Tool for Which Controller

by PLC

Ladder rung drawn in Studio 5000 notation: XIC Start sealed in by an XIC Motor branch, XIO Stop in series, OTE Motor as the output

A working map of Rockwell PLC software: Studio 5000 editions, RSLogix 500, RSLinx Classic against FactoryTalk Linx, View ME and SE, Emulate and firmware.

Paper Machine Draw Control, Consistency and Winder Tension

by PLC

Timing chart of a sectional drive ramp: master run starts, wire, press and dryer sections reach reference in turn, and draw trim is only enabled once the whole line is at reference

Sectional drive draws on a paper machine, the ratio calculation in ST, consistency and basis weight loops, and winder taper tension that holds.

HVAC Point Names, BACnet Objects and Overrides That Expire

by PLC

Ladder rung for stage 2 cooling: cooling demand in series with stage 1 running, the interstage delay timer done bit, and a normally closed contact on the minimum off timer, driving the stage 2 command

PLC building automation that a stranger can maintain: naming, sequences of operation in the code, staging, BACnet mapping, trends, alarms and overrides.

PLC Data Logging and Remote Monitoring: Practical Rules

by PLC

Timing chart comparing periodic and change based logging: a one second sample tick, a deadband window where the process value is moving, and the six rows actually written to the database

PLC data logging that stays useful: sampling rates, retention math, a ring buffer in the controller, FactoryTalk datalog, SQL logging, safe remote access.

Predicting the Demand Peak and Shedding Load from the PLC

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 Industry 4.0: OPC UA, MQTT and Real Data Models

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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.

PLC Batch Control with ISA-88 Phases in Studio 5000

by PLC

Timing chart of a heat phase: Phase_Running drops when Hold_Request arrives, Phase_Held rises, the steam valve closes, then the phase restarts and the valve reopens

Build PLC batch control the ISA-88 way: procedure and phase breakdown, the phase state model, recipe parameters in a UDT, hold and restart logic.

PLC Motion Control: Kinetix 5700 and Logix MAM Moves

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Timing chart of one MAM move: the execute pulse, the accelerating, at-speed and decelerating phases, then the process complete bit

PLC motion control step by step: motion group setup, coarse update period, axis scaling, MSO and MAM moves, homing, gearing and position error faults.

Redundant PLC Systems: ControlLogix Pairs and S7-1500R/H

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Timing chart of a redundancy switchover: chassis A stops being primary, chassis B takes over, the remote I/O connections drop for a few RPIs and come back, and the pair stays unsynchronised until the repaired chassis requalifies

What a 1756-RM2 pair buys you, the design restrictions nobody mentions until commissioning, real switchover times, and when redundancy is the wrong answer.

Remote PLC Monitoring and Control Without Open Ports

by PLC

Ladder rung for a remote write permissive: XIC on Remote_Session in series with XIO on the Local_Only key switch and XIO on WDog_Fault, driving the Remote_Write_OK coil

Remote access to a PLC that security will sign off: outbound VPN routers, read-only web HMI, an access rights table, a permissive rung and an audit trail.

SunSpec Inverter Curtailment and Wind Pitch Rate Limits

by PLC

Timing chart of a battery state of charge window: grid charge command stops when state of charge passes 90 percent, charge inhibit latches, and discharge inhibit latches below 15 percent

SunSpec Modbus inverter limits, tracker stow, wind turbine pitch and yaw, a battery SoC window with BMS handshake, and curtailment setpoints over DNP3.