GuardLogix - PLC Programming & Automation

Functional Safety PLC: Risk Assessment to PLd Architecture

Timing chart of a guard door safety function: the door opens, the safety function result drops shortly after, the contactors release inside the response time budget, and the output only returns after a manual reset pulse with the door closed

How functional safety works on a PLC job: the ISO 13849-1 risk graph, PLr, category 3 architecture, MTTFd, DC, CCF, a PFHd budget and SISTEMA.

Injection Molding Cycle, Barrel Zones and Guard Interlocks

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Timing chart of one 22.5 s molding cycle: clamp locked from 1.5 s to 18.2 s, injection from 2 s to 3.2 s, hold pressure from 3.2 s to 6.2 s, cooling timer from 6.2 s to 18.2 s with screw rotation from 6.2 s to 12.7 s, mold open position reached at 20.2 s, ejector forward from 20.4 s to 21.4 s, mold closing again at 22.5 s and locked at 24 s

Injection molding from the controls side: the cycle as a state machine, barrel zone PID and thermocouple checks, EUROMAP 67 and 77, guards, and rubber.

PLC Safety Interlock: Dual-Channel E-Stop on GuardLogix

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Timing chart of a dual channel E-stop: channel A opens, channel B follows shortly after inside the discrepancy time, the safety output drops at once, the E-stop is released, and the output only returns after the reset button is pressed and released

When a standard interlock is not enough, how to wire and configure a dual-channel E-stop on GuardLogix safety I/O, and the reset rule nobody may break.

BPCS, SIS and the Cause and Effect Matrix on a Reactor

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Timing chart of a reactor high temperature trip: two of three jacket thermocouples vote high, the SIS trip relay trips, the feed valve closes and the quench valve opens

How the BPCS, the SIS and the package PLC split the work on a batch reactor, with a cause and effect matrix, cascade temperature control and IS barriers.

Sequential Function Chart PLC Programming, Step by Step

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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.

Allen-Bradley Function Block: What Decides Execution Order

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A function block routine that verified fine last week now has a question mark on four blocks and will not download. Or worse, it downloads, runs, and one value on the HMI is always one scan behind the others. Nobody moved a block. Somebody added a wire. Execution order in FBD has nothing to do … Read more

PLC Programming Exercises for Beginners: Six Worth Doing

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The first program almost everybody writes is a motor start and stop with a seal-in. It works on the bench. Wired into a real panel, the same logic can leave a motor running with the stop button pressed and a broken wire nobody can see. That gap between working and correct is what these exercises … Read more

Safety Add-On Instructions

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Safety Add-On Instructions Like standard Add-On Instructions, safety Add-On Instructions let you encapsulate commonly-used safety logic into a single instruction, making it modular and easier to reuse. In addition to the instruction signature used for high-integrity Add-On Instructions, safety Add-On Instructions feature a safety instruction signature ID for use in safety-related functions. Refer to the … Read more

Connect a button to the OperShelve tag

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OperShelve The alarm instruction only processes the OperShelve tag on transition from cleared to set to prevent unwanted reshelving of the alarm. For example, if an operator presses a push button to shelve the alarm while the ProgUnshelve tag is set, the alarm is not shelved because the ProgUnshelve tag takes precedence. To shelve the … Read more