PLC - PLC Programming & Automation

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

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.

Generator Start Permissives, Sync Handover and Load Shed

by PLC

Ladder rung for a generator start permissive: start push button sealed in, lube oil pressure healthy, generator breaker open, lockout relay reset, driving the start sequence coil

Where the PLC stops and the relay starts, a generator start permissive rung, the synchronising handshake, load shed stages and switchgear interlocks.

Sequential Function Chart PLC Programming, Step by Step

by PLC

Timing chart of SFC step activity in a batch sequence, showing Step_Fill, Step_Mix, Step_Drain and the mixer output over sixty seconds

Build a working SFC in Studio 5000: steps, transitions, action qualifiers, the SFC Execution settings that decide what happens on a restart, and S7-GRAPH.

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

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.

PLC Troubleshooting: A Method That Finds Real Faults

by PLC

Ladder rung that latches the first I/O connection fault so it survives the recovery, with a reset pushbutton

A repeatable PLC troubleshooting order: module LEDs, controller major faults, I/O connection status, forces, cross-reference, trends and Ethernet checks.

Fuzzy Logic PLC Control: Rule Tables, Inference in ST and a Dryer Example

by PLC

Ladder rung with Dryer_Run examined on, Burner_Fault examined off and HMI_Fuzzy_Sel examined on in series, driving the Fuzzy_Active output coil

Where fuzzy control beats PID, how to hand-code memberships, a 3×3 rule table and weighted-average defuzzification in Logix ST, with a dryer example.

SCADA PLC Integration: Connect Ignition to ControlLogix

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.

IIoT PLC Data with MQTT, Sparkplug B and an Edge Gateway

by PLC

Timing chart comparing a fixed one second poll against report by exception, where the gateway publishes only when the tag moves past its deadband

A working IIoT setup for a plant floor PLC: edge gateway choice, MQTT and Sparkplug B topics, a decoded payload, store and forward, deadbands and security.

PLC Scan Time and Cycle Time: Measure It, Then Cut It

by PLC

Timing chart of two 10 ms periodic task cycles showing input image update, program scan, output image update and comms overhead in sequence

Read real scan times with GSV on a ControlLogix and the cycle time view on an S7-1500, then find what is eating them before the watchdog does.

Studio 5000 Watch Window: Monitor Tags While Online

by PLC

Timing chart: a 40 ms bit pulse in the controller against a 500 ms Watch window read, showing that three of four pulses are never sampled

Build watch lists in the Studio 5000 Watch window, monitor and write tag values online, and know when the sample rate hides what you are chasing.