PLC Deterministic Controls

Programmable logic controllers run the plant's slower deterministic sequencing and interlocks, complementing the FPGA fast loops with certified logic.

Where PLCs fit

Not every deterministic function needs microsecond timing. Vacuum sequencing, cryoplant states, cooling-water permissives, and the machine's overall operating-state interlocks run on programmable logic controllers with scan-cycle determinism in the millisecond range. PLCs give Kronos a certified, auditable layer for plant-protection logic that changes rarely and must be transparent to operators and reviewers.

Scan-cycle model

A PLC executes a fixed scan: read inputs, evaluate logic, write outputs, repeat. The scan time is bounded and stable, so a permissive computed this scan is acted on by the next with known latency. This is deterministic in the same spirit as the FPGA loops, just at a coarser timescale suited to fluidic and thermal plant that cannot move in microseconds anyway.

Division of labor with FPGA

• FPGA: plasma stability, DEC modulation, quench detection — microsecond loops.
• PLC: vacuum, cryo, cooling, gas delivery permissives — millisecond sequencing.
• Hardware failsafe: magnet quench dump — zero-latency analog, below both.

The PLC layer also owns the master operating-state machine: which subsystems must be proven safe before the plasma or plug is energized. It gates the FPGA controllers' authority — an FPGA loop is only allowed to command an actuator when the PLC permissives for that subsystem are satisfied.

Auditability

PLC logic is written in transparent, reviewable form (ladder / structured text) precisely because plant-protection interlocks must be inspectable by safety reviewers. Kronos keeps this logic separate from the AI stack; a reviewer can read the interlock that isolates the vacuum system without understanding any model. This separation is deliberate and mirrors the determinism-vs-learning boundary at the plant scale.