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FA-92291 / PLC ladder logic scan cycles / Open access

Stack light ignores alarms already active on the first scan · case 01

An alarm present when the panel starts never flashes or sounds the horn.

Verified by executionVariant 1 · 8 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

New activations are only computed once a previous scan exists.

THE FAILURE

New activations are only computed once a previous scan exists.

Unsuccessful approach: Treating every active-but-acknowledged alarm as new re-announces alarms immediately after ack.

Case contract

Stack light and horn logic. alarms is a list of [name, high|low]; each scan gives the active alarm names plus optional ack and silence buttons. An alarm becomes unacknowledged on its inactive-to-active transition and stops being unacknowledged when it clears or ack is pressed. Any new activation cancels silence; silence (pressed after that) mutes the horn. The lamp is red if any high alarm is active, else amber if any alarm is active, else off; it flashes if an unacknowledged alarm of the displayed level exists. The horn sounds while any unacknowledged alarm exists and not silenced. Return [color, flashing, horn] per scan.

Why this case matters

Ladder programs are executed as repeated scans; each defect here changes what a rung, timer, counter or data-table instruction reports on a particular scan, which is how commissioning and field faults are actually observed.

1 / The failure

Exit 1
"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(alarms, scans):
    level = dict(alarms)
    prev = set()
    unacked = set()
    silenced = False
    out = []
    for s in scans:
        active = set(s.get('active', []))
        new = active - prev if prev else set()
        if new:
            silenced = False
        unacked = (unacked | new) & active
        if s.get('ack'):
            unacked = set()
        if s.get('silence'):
            silenced = True
        if any(level[a] == 'high' for a in active):
            shown = 'high'
        elif active:
            shown = 'low'
        else:
            shown = None
        color = {'high': 'red', 'low': 'amber', None: 'off'}[shown]
        flashing = any(level[a] == shown for a in unacked)
        horn = bool(unacked) and not silenced
        prev = active
        out.append([color, flashing, horn])
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['regression: escalation sequence',
   [[['A', 'high'], ['B', 'low']],
    [{'active': ['B']},
     {'active': ['B'], 'silence': True},
     {'active': ['A', 'B']},
     {'active': ['A', 'B'], 'ack': True},
     {'active': ['B']},
     {}]],
   [['amber', True, True],
    ['amber', True, False],
    ['red', True, True],
    ['red', False, False],
    ['amber', False, False],
    ['off', False, False]]],
  ['regression: low alarm while high acked',
   [[['A', 'high'], ['B', 'low']],
    [{'active': ['A'], 'ack': True},
     {'active': ['A', 'B']},
     {'active': ['A', 'B'], 'silence': True},
     {'active': ['A', 'B']}]],
   [['red', False, False], ['red', False, True], ['red', False, False], ['red', False, False]]],
  ['regression: alarm clears unacknowledged',
   [[['A', 'high'], ['B', 'low']], [{'active': ['A']}, {}, {'active': ['B']}]],
   [['red', True, True], ['off', False, False], ['amber', True, True]]],
  ['regression: alarm present at first scan',
   [[['A', 'high'], ['B', 'low']], [{'active': ['A']}, {'active': ['A']}]],
   [['red', True, True], ['red', True, True]]],
  ['regression: silence then new low alarm',
   [[['A', 'high'], ['B', 'low']],
    [{'active': ['A']}, {'active': ['A'], 'silence': True}, {'active': ['A', 'B']}]],
   [['red', True, True], ['red', True, False], ['red', True, True]]],
  ['regression: scenario 1',
   [[['PT101', 'high'], ['LT200', 'low'], ['TT300', 'low'], ['ZS400', 'high']],
    [{'active': ['TT300'], 'ack': True},
     {'active': ['TT300']},
     {'active': ['ZS400'], 'ack': True, 'silence': True},
     {'active': []},
     {'active': ['ZS400'], 'silence': True},
     {'active': ['TT300', 'ZS400']},
     {'active': ['LT200', 'TT300', 'ZS400']},
     {'active': ['LT200', 'TT300', 'ZS400']},
     {'active': ['LT200', 'ZS400'], 'ack': True}]],
   [['amber', False, False],
    ['amber', False, False],
    ['red', False, False],
    ['off', False, False],
    ['red', True, False],
    ['red', True, True],
    ['red', True, True],
    ['red', True, True],
    ['red', False, False]]],
  ['regression: scenario 2',
   [[['PT101', 'high'], ['LT200', 'low'], ['TT300', 'low'], ['ZS400', 'high']],
    [{'active': ['TT300'], 'silence': True},
     {'active': ['ZS400']},
     {'active': ['LT200', 'TT300']},
     {'active': ['LT200', 'PT101', 'TT300', 'ZS400']},
     {'active': ['LT200', 'PT101', 'TT300'], 'silence': True},
     {'active': ['LT200', 'PT101', 'TT300'], 'silence': True}]],
   [['amber', True, False],
    ['red', True, True],
    ['amber', True, True],
    ['red', True, True],
    ['red', True, False],
    ['red', True, False]]],
  ['regression: scenario 3',
   [[['PT101', 'high'], ['LT200', 'low'], ['TT300', 'low'], ['ZS400', 'high']],
    [{'active': [], 'ack': True},
     {'active': []},
     {'active': ['ZS400']},
     {'active': ['ZS400']},
     {'active': ['LT200', 'PT101', 'ZS400'], 'silence': True},
     {'active': ['LT200', 'PT101'], 'ack': True}]],
   [['off', False, False],
    ['off', False, False],
    ['red', True, True],
    ['red', True, True],
    ['red', True, False],
    ['red', False, False]]]],
 [['regression: alarm clears unacknowledged',
   [[['A', 'high'], ['B', 'low']], [{'active': ['A']}, {}, {'active': ['B']}]],
   [['red', True, True], ['off', False, False], ['amber', True, True]]],
  ['regression: low alarm while high acked',
   [[['A', 'high'], ['B', 'low']],
    [{'active': ['A'], 'ack': True},
     {'active': ['A', 'B']},
     {'active': ['A', 'B'], 'silence': True},
     {'active': ['A', 'B']}]],
   [['red', False, False], ['red', False, True], ['red', False, False], ['red', False, False]]],
  ['regression: escalation sequence',
   [[['A', 'high'], ['B', 'low']],
    [{'active': ['B']},
     {'active': ['B'], 'silence': True},
     {'active': ['A', 'B']},
     {'active': ['A', 'B'], 'ack': True},
     {'active': ['B']},
     {}]],
   [['amber', True, True],
    ['amber', True, False],
    ['red', True, True],
    ['red', False, False],
    ['amber', False, False],
    ['off', False, False]]],
  ['regression: alarm present at first scan',
   [[['A', 'high'], ['B', 'low']], [{'active': ['A']}, {'active': ['A']}]],
   [['red', True, True], ['red', True, True]]],
  ['regression: silence then new low alarm',
   [[['A', 'high'], ['B', 'low']],
    [{'active': ['A']}, {'active': ['A'], 'silence': True}, {'active': ['A', 'B']}]],
   [['red', True, True], ['red', True, False], ['red', True, True]]],
  ['regression: scenario 1',
   [[['PT101', 'high'], ['LT200', 'low'], ['TT300', 'low'], ['ZS400', 'high']],
    [{'active': ['ZS400'], 'silence': True},
     {'active': ['LT200', 'ZS400']},
     {'active': ['LT200', 'ZS400']},
     {'active': ['LT200', 'ZS400']},
     {'active': ['LT200', 'ZS400']},
     {'active': ['LT200']}]],
   [['red', True, False],
    ['red', True, True],
    ['red', True, True],
    ['red', True, True],
    ['red', True, True],
    ['amber', True, True]]],
  ['regression: scenario 2',
   [[['PT101', 'high'], ['LT200', 'low'], ['TT300', 'low'], ['ZS400', 'high']],
    [{'active': ['PT101']},
     {'active': ['ZS400'], 'ack': True},
     {'active': ['TT300']},
     {'active': ['TT300']},
     {'active': ['PT101', 'TT300']},
     {'active': ['PT101']},
     {'active': ['LT200', 'ZS400']},
     {'active': ['LT200', 'PT101', 'TT300', 'ZS400']},
     {'active': ['LT200', 'TT300', 'ZS400']},
     {'active': ['LT200', 'PT101', 'TT300', 'ZS400']},
     {'active': ['LT200', 'TT300'], 'ack': True},
     {'active': ['LT200', 'TT300']}]],
   [['red', True, True],
    ['red', False, False],
    ['amber', True, True],
    ['amber', True, True],
    ['red', True, True],
    ['red', True, True],
    ['red', True, True],
    ['red', True, True],
    ['red', True, True],
    ['red', True, True],
    ['amber', False, False],
    ['amber', False, False]]],
  ['regression: scenario 3',
   [[['PT101', 'high'], ['LT200', 'low'], ['TT300', 'low'], ['ZS400', 'high']],
    [{'active': ['LT200', 'PT101', 'ZS400']},
     {'active': ['LT200', 'PT101', 'TT300', 'ZS400']},
     {'active': ['LT200', 'PT101', 'TT300', 'ZS400']},
     {'active': ['LT200', 'PT101', 'ZS400'], 'ack': True},
     {'active': ['LT200', 'PT101']},
     {'active': ['LT200', 'PT101', 'TT300', 'ZS400']},
     {'active': ['ZS400']},
     {'active': ['PT101', 'ZS400']},
     {'active': ['PT101', 'ZS400'], 'ack': True},
     {'active': ['PT101', 'ZS400']}]],
   [['red', True, True],
    ['red', True, True],
    ['red', True, True],
    ['red', False, False],
    ['red', False, False],
    ['red', True, True],
    ['red', True, True],
    ['red', True, True],
    ['red', False, False],
    ['red', False, False]]]],
 [['regression: alarm present at first scan',
   [[['A', 'high'], ['B', 'low']], [{'active': ['A']}, {'active': ['A']}]],
   [['red', True, True], ['red', True, True]]],
  ['regression: scenario 5',
   [[['PT101', 'high'], ['LT200', 'low'], ['TT300', 'low'], ['ZS400', 'high']],
    [{'active': ['LT200', 'PT101', 'TT300']},
     {'active': ['PT101', 'TT300']},
     {'active': ['PT101', 'TT300', 'ZS400'], 'ack': True},
     {'active': ['ZS400'], 'silence': True},
     {'active': ['ZS400']},
     {'active': [], 'ack': True}]],
   [['red', True, True],
    ['red', True, True],
    ['red', False, False],
    ['red', False, False],
    ['red', False, False],
    ['off', False, False]]],
  ['regression: escalation sequence',
   [[['A', 'high'], ['B', 'low']],
    [{'active': ['B']},
     {'active': ['B'], 'silence': True},
     {'active': ['A', 'B']},
     {'active': ['A', 'B'], 'ack': True},
     {'active': ['B']},
     {}]],
   [['amber', True, True],
    ['amber', True, False],
    ['red', True, True],
    ['red', False, False],
    ['amber', False, False],
    ['off', False, False]]],
  ['regression: alarm clears unacknowledged',
   [[['A', 'high'], ['B', 'low']], [{'active': ['A']}, {}, {'active': ['B']}]],
   [['red', True, True], ['off', False, False], ['amber', True, True]]],
  ['regression: low alarm while high acked',
   [[['A', 'high'], ['B', 'low']],
    [{'active': ['A'], 'ack': True},
     {'active': ['A', 'B']},
     {'active': ['A', 'B'], 'silence': True},
     {'active': ['A', 'B']}]],
   [['red', False, False], ['red', False, True], ['red', False, False], ['red', False, False]]],
  ['regression: silence then new low alarm',
   [[['A', 'high'], ['B', 'low']],
    [{'active': ['A']}, {'active': ['A'], 'silence': True}, {'active': ['A', 'B']}]],
   [['red', True, True], ['red', True, False], ['red', True, True]]],
  ['regression: scenario 1',
   [[['PT101', 'high'], ['LT200', 'low'], ['TT300', 'low'], ['ZS400', 'high']],
    [{'active': ['PT101']},
     {'active': ['LT200', 'PT101']},
     {'active': ['LT200', 'PT101']},
     {'active': ['LT200', 'PT101'], 'silence': True},
     {'active': ['LT200', 'PT101']},
     {'active': []},
     {'active': []},
     {'active': []},
     {'active': [], 'ack': True},
     {'active': ['LT200']},
     {'active': ['LT200', 'TT300']}]],
   [['red', True, True],
    ['red', True, True],
    ['red', True, True],
    ['red', True, False],
    ['red', True, False],
    ['off', False, False],
    ['off', False, False],
    ['off', False, False],
    ['off', False, False],
    ['amber', True, True],
    ['amber', True, True]]],
  ['regression: scenario 2',
   [[['PT101', 'high'], ['LT200', 'low'], ['TT300', 'low'], ['ZS400', 'high']],
    [{'active': []},
     {'active': ['ZS400']},
     {'active': ['ZS400']},
     {'active': ['ZS400'], 'silence': True},
     {'active': ['ZS400']},
     {'active': []},
     {'active': ['LT200', 'ZS400']},
     {'active': ['LT200', 'PT101', 'ZS400']},
     {'active': ['PT101', 'TT300', 'ZS400']}]],
   [['off', False, False],
    ['red', True, True],
    ['red', True, True],
    ['red', True, False],
    ['red', True, False],
    ['off', False, False],
    ['red', True, True],
    ['red', True, True],
    ['red', True, True]]]],
 [['regression: silence then new low alarm',
   [[['A', 'high'], ['B', 'low']],
    [{'active': ['A']}, {'active': ['A'], 'silence': True}, {'active': ['A', 'B']}]],
   [['red', True, True], ['red', True, False], ['red', True, True]]],
  ['regression: scenario 2',
   [[['PT101', 'high'], ['LT200', 'low'], ['TT300', 'low'], ['ZS400', 'high']],
    [{'active': []},
     {'active': ['PT101', 'TT300']},
     {'active': ['PT101', 'TT300'], 'ack': True},
     {'active': ['PT101', 'ZS400'], 'silence': True},
     {'active': ['PT101']},
     {'active': ['PT101'], 'silence': True}]],
   [['off', False, False],
    ['red', True, True],
    ['red', False, False],
    ['red', True, False],
    ['red', False, False],
    ['red', False, False]]],
  ['regression: escalation sequence',
   [[['A', 'high'], ['B', 'low']],
    [{'active': ['B']},
     {'active': ['B'], 'silence': True},
     {'active': ['A', 'B']},
     {'active': ['A', 'B'], 'ack': True},
     {'active': ['B']},
     {}]],
   [['amber', True, True],
    ['amber', True, False],
    ['red', True, True],
    ['red', False, False],
    ['amber', False, False],
    ['off', False, False]]],
  ['regression: alarm clears unacknowledged',
   [[['A', 'high'], ['B', 'low']], [{'active': ['A']}, {}, {'active': ['B']}]],
   [['red', True, True], ['off', False, False], ['amber', True, True]]],
  ['regression: low alarm while high acked',
   [[['A', 'high'], ['B', 'low']],
    [{'active': ['A'], 'ack': True},
     {'active': ['A', 'B']},
     {'active': ['A', 'B'], 'silence': True},
     {'active': ['A', 'B']}]],
   [['red', False, False], ['red', False, True], ['red', False, False], ['red', False, False]]],
  ['regression: alarm present at first scan',
   [[['A', 'high'], ['B', 'low']], [{'active': ['A']}, {'active': ['A']}]],
   [['red', True, True], ['red', True, True]]],
  ['regression: scenario 1',
   [[['PT101', 'high'], ['LT200', 'low'], ['TT300', 'low'], ['ZS400', 'high']],
    [{'active': ['PT101'], 'ack': True},
     {'active': ['PT101']},
     {'active': ['PT101'], 'ack': True},
     {'active': ['PT101']},
     {'active': ['PT101']},
     {'active': ['LT200', 'PT101', 'TT300']},
     {'active': ['LT200', 'PT101', 'TT300'], 'ack': True},
     {'active': ['LT200', 'TT300']}]],
   [['red', False, False],
    ['red', False, False],
    ['red', False, False],
    ['red', False, False],
    ['red', False, False],
    ['red', False, True],
    ['red', False, False],
    ['amber', False, False]]],
  ['regression: scenario 3',
   [[['PT101', 'high'], ['LT200', 'low'], ['TT300', 'low'], ['ZS400', 'high']],
    [{'active': ['LT200', 'PT101', 'TT300']},
     {'active': ['LT200', 'PT101', 'TT300', 'ZS400']},
     {'active': ['LT200', 'PT101', 'TT300'], 'silence': True},
     {'active': ['LT200', 'PT101', 'TT300']},
     {'active': ['PT101', 'TT300']},
     {'active': ['TT300'], 'ack': True},
     {'active': ['ZS400']},
     {'active': ['TT300', 'ZS400']}]],
   [['red', True, True],
    ['red', True, True],
    ['red', True, False],
    ['red', True, False],
    ['red', True, False],
    ['amber', False, False],
    ['red', True, True],
    ['red', True, True]]]],
 [['regression: scenario 1',
   [[['PT101', 'high'], ['LT200', 'low'], ['TT300', 'low'], ['ZS400', 'high']],
    [{'active': [], 'silence': True},
     {'active': [], 'silence': True},
     {'active': [], 'silence': True},
     {'active': []},
     {'active': ['ZS400']},
     {'active': ['ZS400'], 'ack': True},
     {'active': ['TT300']},
     {'active': ['PT101', 'TT300'], 'ack': True},
     {'active': ['PT101', 'TT300']},
     {'active': ['PT101', 'TT300'], 'silence': True},
     {'active': ['LT200', 'PT101', 'TT300'], 'silence': True},
     {'active': ['LT200', 'PT101', 'TT300']}]],
   [['off', False, False],
    ['off', False, False],
    ['off', False, False],
    ['off', False, False],
    ['red', True, True],
    ['red', False, False],
    ['amber', True, True],
    ['red', False, False],
    ['red', False, False],
    ['red', False, False],
    ['red', False, False],
    ['red', False, False]]],
  ['regression: scenario 4',
   [[['PT101', 'high'], ['LT200', 'low'], ['TT300', 'low'], ['ZS400', 'high']],
    [{'active': ['PT101', 'TT300']},
     {'active': ['PT101', 'TT300']},
     {'active': ['TT300'], 'ack': True},
     {'active': ['PT101', 'TT300']},
     {'active': ['TT300', 'ZS400']},
     {'active': ['ZS400'], 'silence': True},
     {'active': ['PT101', 'ZS400'], 'ack': True},
     {'active': ['LT200', 'PT101', 'ZS400'], 'ack': True, 'silence': True},
     {'active': ['LT200', 'PT101', 'TT300', 'ZS400']}]],
   [['red', True, True],
    ['red', True, True],
    ['amber', False, False],
    ['red', True, True],
    ['red', True, True],
    ['red', True, False],
    ['red', False, False],
    ['red', False, False],
    ['red', False, True]]],
  ['regression: escalation sequence',
   [[['A', 'high'], ['B', 'low']],
    [{'active': ['B']},
     {'active': ['B'], 'silence': True},
     {'active': ['A', 'B']},
     {'active': ['A', 'B'], 'ack': True},
     {'active': ['B']},
     {}]],
   [['amber', True, True],
    ['amber', True, False],
    ['red', True, True],
    ['red', False, False],
    ['amber', False, False],
    ['off', False, False]]],
  ['regression: alarm clears unacknowledged',
   [[['A', 'high'], ['B', 'low']], [{'active': ['A']}, {}, {'active': ['B']}]],
   [['red', True, True], ['off', False, False], ['amber', True, True]]],
  ['regression: low alarm while high acked',
   [[['A', 'high'], ['B', 'low']],
    [{'active': ['A'], 'ack': True},
     {'active': ['A', 'B']},
     {'active': ['A', 'B'], 'silence': True},
     {'active': ['A', 'B']}]],
   [['red', False, False], ['red', False, True], ['red', False, False], ['red', False, False]]],
  ['regression: alarm present at first scan',
   [[['A', 'high'], ['B', 'low']], [{'active': ['A']}, {'active': ['A']}]],
   [['red', True, True], ['red', True, True]]],
  ['regression: silence then new low alarm',
   [[['A', 'high'], ['B', 'low']],
    [{'active': ['A']}, {'active': ['A'], 'silence': True}, {'active': ['A', 'B']}]],
   [['red', True, True], ['red', True, False], ['red', True, True]]],
  ['regression: scenario 2',
   [[['PT101', 'high'], ['LT200', 'low'], ['TT300', 'low'], ['ZS400', 'high']],
    [{'active': ['LT200']},
     {'active': ['LT200'], 'ack': True},
     {'active': []},
     {'active': ['PT101'], 'ack': True},
     {'active': ['PT101'], 'ack': True},
     {'active': ['PT101']},
     {'active': ['LT200', 'PT101', 'TT300']}]],
   [['amber', True, True],
    ['amber', False, False],
    ['off', False, False],
    ['red', False, False],
    ['red', False, False],
    ['red', False, False],
    ['red', False, True]]]]]
for label, args, expected in fixtures[N-1]:
    check(label, solve(*args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
Boundary fixtureActualExpectedOutcome
regression: escalation sequence[['amber', False, False], ['amber', False, False], ['red', True, True], ['red', False, False], ['amber', False, False], ['off', False, False]][['amber', True, True], ['amber', True, False], ['red', True, True], ['red', False, False], ['amber', False, False], ['off', False, False]]Failed
regression: low alarm while high acked[['red', False, False], ['red', False, True], ['red', False, False], ['red', False, False]][['red', False, False], ['red', False, True], ['red', False, False], ['red', False, False]]Passed
regression: alarm clears unacknowledged[['red', False, False], ['off', False, False], ['amber', False, False]][['red', True, True], ['off', False, False], ['amber', True, True]]Failed
regression: alarm present at first scan[['red', False, False], ['red', False, False]][['red', True, True], ['red', True, True]]Failed
regression: silence then new low alarm[['red', False, False], ['red', False, False], ['red', False, True]][['red', True, True], ['red', True, False], ['red', True, True]]Failed
regression: scenario 1[['amber', False, False], ['amber', False, False], ['red', False, False], ['off', False, False], ['red', False, False], ['red', False, True], ['red', False, True], ['red', False, True], ['red', False, False]][['amber', False, False], ['amber', False, False], ['red', False, False], ['off', False, False], ['red', True, False], ['red', True, True], ['red', True, True], ['red', True, True], ['red', False, False]]Failed
regression: scenario 2[['amber', False, False], ['red', True, True], ['amber', True, True], ['red', True, True], ['red', True, False], ['red', True, False]][['amber', True, False], ['red', True, True], ['amber', True, True], ['red', True, True], ['red', True, False], ['red', True, False]]Failed
regression: scenario 3[['off', False, False], ['off', False, False], ['red', False, False], ['red', False, False], ['red', True, False], ['red', False, False]][['off', False, False], ['off', False, False], ['red', True, True], ['red', True, True], ['red', True, False], ['red', False, False]]Failed

SHA-256 / 5384da96452783e304d412fc455cb776438b6ffa02a54632347850739d271927

2 / The unsuccessful fix

Exit 1
"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(alarms, scans):
    level = dict(alarms)
    prev = set()
    unacked = set()
    silenced = False
    out = []
    for s in scans:
        active = set(s.get('active', []))
        new = active - (prev & unacked)
        if new:
            silenced = False
        unacked = (unacked | new) & active
        if s.get('ack'):
            unacked = set()
        if s.get('silence'):
            silenced = True
        if any(level[a] == 'high' for a in active):
            shown = 'high'
        elif active:
            shown = 'low'
        else:
            shown = None
        color = {'high': 'red', 'low': 'amber', None: 'off'}[shown]
        flashing = any(level[a] == shown for a in unacked)
        horn = bool(unacked) and not silenced
        prev = active
        out.append([color, flashing, horn])
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['regression: escalation sequence',
   [[['A', 'high'], ['B', 'low']],
    [{'active': ['B']},
     {'active': ['B'], 'silence': True},
     {'active': ['A', 'B']},
     {'active': ['A', 'B'], 'ack': True},
     {'active': ['B']},
     {}]],
   [['amber', True, True],
    ['amber', True, False],
    ['red', True, True],
    ['red', False, False],
    ['amber', False, False],
    ['off', False, False]]],
  ['regression: low alarm while high acked',
   [[['A', 'high'], ['B', 'low']],
    [{'active': ['A'], 'ack': True},
     {'active': ['A', 'B']},
     {'active': ['A', 'B'], 'silence': True},
     {'active': ['A', 'B']}]],
   [['red', False, False], ['red', False, True], ['red', False, False], ['red', False, False]]],
  ['regression: alarm clears unacknowledged',
   [[['A', 'high'], ['B', 'low']], [{'active': ['A']}, {}, {'active': ['B']}]],
   [['red', True, True], ['off', False, False], ['amber', True, True]]],
  ['regression: alarm present at first scan',
   [[['A', 'high'], ['B', 'low']], [{'active': ['A']}, {'active': ['A']}]],
   [['red', True, True], ['red', True, True]]],
  ['regression: silence then new low alarm',
   [[['A', 'high'], ['B', 'low']],
    [{'active': ['A']}, {'active': ['A'], 'silence': True}, {'active': ['A', 'B']}]],
   [['red', True, True], ['red', True, False], ['red', True, True]]],
  ['regression: scenario 1',
   [[['PT101', 'high'], ['LT200', 'low'], ['TT300', 'low'], ['ZS400', 'high']],
    [{'active': ['TT300'], 'ack': True},
     {'active': ['TT300']},
     {'active': ['ZS400'], 'ack': True, 'silence': True},
     {'active': []},
     {'active': ['ZS400'], 'silence': True},
     {'active': ['TT300', 'ZS400']},
     {'active': ['LT200', 'TT300', 'ZS400']},
     {'active': ['LT200', 'TT300', 'ZS400']},
     {'active': ['LT200', 'ZS400'], 'ack': True}]],
   [['amber', False, False],
    ['amber', False, False],
    ['red', False, False],
    ['off', False, False],
    ['red', True, False],
    ['red', True, True],
    ['red', True, True],
    ['red', True, True],
    ['red', False, False]]],
  ['regression: scenario 2',
   [[['PT101', 'high'], ['LT200', 'low'], ['TT300', 'low'], ['ZS400', 'high']],
    [{'active': ['TT300'], 'silence': True},
     {'active': ['ZS400']},
     {'active': ['LT200', 'TT300']},
     {'active': ['LT200', 'PT101', 'TT300', 'ZS400']},
     {'active': ['LT200', 'PT101', 'TT300'], 'silence': True},
     {'active': ['LT200', 'PT101', 'TT300'], 'silence': True}]],
   [['amber', True, False],
    ['red', True, True],
    ['amber', True, True],
    ['red', True, True],
    ['red', True, False],
    ['red', True, False]]],
  ['regression: scenario 3',
   [[['PT101', 'high'], ['LT200', 'low'], ['TT300', 'low'], ['ZS400', 'high']],
    [{'active': [], 'ack': True},
     {'active': []},
     {'active': ['ZS400']},
     {'active': ['ZS400']},
     {'active': ['LT200', 'PT101', 'ZS400'], 'silence': True},
     {'active': ['LT200', 'PT101'], 'ack': True}]],
   [['off', False, False],
    ['off', False, False],
    ['red', True, True],
    ['red', True, True],
    ['red', True, False],
    ['red', False, False]]]],
 [['regression: alarm clears unacknowledged',
   [[['A', 'high'], ['B', 'low']], [{'active': ['A']}, {}, {'active': ['B']}]],
   [['red', True, True], ['off', False, False], ['amber', True, True]]],
  ['regression: low alarm while high acked',
   [[['A', 'high'], ['B', 'low']],
    [{'active': ['A'], 'ack': True},
     {'active': ['A', 'B']},
     {'active': ['A', 'B'], 'silence': True},
     {'active': ['A', 'B']}]],
   [['red', False, False], ['red', False, True], ['red', False, False], ['red', False, False]]],
  ['regression: escalation sequence',
   [[['A', 'high'], ['B', 'low']],
    [{'active': ['B']},
     {'active': ['B'], 'silence': True},
     {'active': ['A', 'B']},
     {'active': ['A', 'B'], 'ack': True},
     {'active': ['B']},
     {}]],
   [['amber', True, True],
    ['amber', True, False],
    ['red', True, True],
    ['red', False, False],
    ['amber', False, False],
    ['off', False, False]]],
  ['regression: alarm present at first scan',
   [[['A', 'high'], ['B', 'low']], [{'active': ['A']}, {'active': ['A']}]],
   [['red', True, True], ['red', True, True]]],
  ['regression: silence then new low alarm',
   [[['A', 'high'], ['B', 'low']],
    [{'active': ['A']}, {'active': ['A'], 'silence': True}, {'active': ['A', 'B']}]],
   [['red', True, True], ['red', True, False], ['red', True, True]]],
  ['regression: scenario 1',
   [[['PT101', 'high'], ['LT200', 'low'], ['TT300', 'low'], ['ZS400', 'high']],
    [{'active': ['ZS400'], 'silence': True},
     {'active': ['LT200', 'ZS400']},
     {'active': ['LT200', 'ZS400']},
     {'active': ['LT200', 'ZS400']},
     {'active': ['LT200', 'ZS400']},
     {'active': ['LT200']}]],
   [['red', True, False],
    ['red', True, True],
    ['red', True, True],
    ['red', True, True],
    ['red', True, True],
    ['amber', True, True]]],
  ['regression: scenario 2',
   [[['PT101', 'high'], ['LT200', 'low'], ['TT300', 'low'], ['ZS400', 'high']],
    [{'active': ['PT101']},
     {'active': ['ZS400'], 'ack': True},
     {'active': ['TT300']},
     {'active': ['TT300']},
     {'active': ['PT101', 'TT300']},
     {'active': ['PT101']},
     {'active': ['LT200', 'ZS400']},
     {'active': ['LT200', 'PT101', 'TT300', 'ZS400']},
     {'active': ['LT200', 'TT300', 'ZS400']},
     {'active': ['LT200', 'PT101', 'TT300', 'ZS400']},
     {'active': ['LT200', 'TT300'], 'ack': True},
     {'active': ['LT200', 'TT300']}]],
   [['red', True, True],
    ['red', False, False],
    ['amber', True, True],
    ['amber', True, True],
    ['red', True, True],
    ['red', True, True],
    ['red', True, True],
    ['red', True, True],
    ['red', True, True],
    ['red', True, True],
    ['amber', False, False],
    ['amber', False, False]]],
  ['regression: scenario 3',
   [[['PT101', 'high'], ['LT200', 'low'], ['TT300', 'low'], ['ZS400', 'high']],
    [{'active': ['LT200', 'PT101', 'ZS400']},
     {'active': ['LT200', 'PT101', 'TT300', 'ZS400']},
     {'active': ['LT200', 'PT101', 'TT300', 'ZS400']},
     {'active': ['LT200', 'PT101', 'ZS400'], 'ack': True},
     {'active': ['LT200', 'PT101']},
     {'active': ['LT200', 'PT101', 'TT300', 'ZS400']},
     {'active': ['ZS400']},
     {'active': ['PT101', 'ZS400']},
     {'active': ['PT101', 'ZS400'], 'ack': True},
     {'active': ['PT101', 'ZS400']}]],
   [['red', True, True],
    ['red', True, True],
    ['red', True, True],
    ['red', False, False],
    ['red', False, False],
    ['red', True, True],
    ['red', True, True],
    ['red', True, True],
    ['red', False, False],
    ['red', False, False]]]],
 [['regression: alarm present at first scan',
   [[['A', 'high'], ['B', 'low']], [{'active': ['A']}, {'active': ['A']}]],
   [['red', True, True], ['red', True, True]]],
  ['regression: scenario 5',
   [[['PT101', 'high'], ['LT200', 'low'], ['TT300', 'low'], ['ZS400', 'high']],
    [{'active': ['LT200', 'PT101', 'TT300']},
     {'active': ['PT101', 'TT300']},
     {'active': ['PT101', 'TT300', 'ZS400'], 'ack': True},
     {'active': ['ZS400'], 'silence': True},
     {'active': ['ZS400']},
     {'active': [], 'ack': True}]],
   [['red', True, True],
    ['red', True, True],
    ['red', False, False],
    ['red', False, False],
    ['red', False, False],
    ['off', False, False]]],
  ['regression: escalation sequence',
   [[['A', 'high'], ['B', 'low']],
    [{'active': ['B']},
     {'active': ['B'], 'silence': True},
     {'active': ['A', 'B']},
     {'active': ['A', 'B'], 'ack': True},
     {'active': ['B']},
     {}]],
   [['amber', True, True],
    ['amber', True, False],
    ['red', True, True],
    ['red', False, False],
    ['amber', False, False],
    ['off', False, False]]],
  ['regression: alarm clears unacknowledged',
   [[['A', 'high'], ['B', 'low']], [{'active': ['A']}, {}, {'active': ['B']}]],
   [['red', True, True], ['off', False, False], ['amber', True, True]]],
  ['regression: low alarm while high acked',
   [[['A', 'high'], ['B', 'low']],
    [{'active': ['A'], 'ack': True},
     {'active': ['A', 'B']},
     {'active': ['A', 'B'], 'silence': True},
     {'active': ['A', 'B']}]],
   [['red', False, False], ['red', False, True], ['red', False, False], ['red', False, False]]],
  ['regression: silence then new low alarm',
   [[['A', 'high'], ['B', 'low']],
    [{'active': ['A']}, {'active': ['A'], 'silence': True}, {'active': ['A', 'B']}]],
   [['red', True, True], ['red', True, False], ['red', True, True]]],
  ['regression: scenario 1',
   [[['PT101', 'high'], ['LT200', 'low'], ['TT300', 'low'], ['ZS400', 'high']],
    [{'active': ['PT101']},
     {'active': ['LT200', 'PT101']},
     {'active': ['LT200', 'PT101']},
     {'active': ['LT200', 'PT101'], 'silence': True},
     {'active': ['LT200', 'PT101']},
     {'active': []},
     {'active': []},
     {'active': []},
     {'active': [], 'ack': True},
     {'active': ['LT200']},
     {'active': ['LT200', 'TT300']}]],
   [['red', True, True],
    ['red', True, True],
    ['red', True, True],
    ['red', True, False],
    ['red', True, False],
    ['off', False, False],
    ['off', False, False],
    ['off', False, False],
    ['off', False, False],
    ['amber', True, True],
    ['amber', True, True]]],
  ['regression: scenario 2',
   [[['PT101', 'high'], ['LT200', 'low'], ['TT300', 'low'], ['ZS400', 'high']],
    [{'active': []},
     {'active': ['ZS400']},
     {'active': ['ZS400']},
     {'active': ['ZS400'], 'silence': True},
     {'active': ['ZS400']},
     {'active': []},
     {'active': ['LT200', 'ZS400']},
     {'active': ['LT200', 'PT101', 'ZS400']},
     {'active': ['PT101', 'TT300', 'ZS400']}]],
   [['off', False, False],
    ['red', True, True],
    ['red', True, True],
    ['red', True, False],
    ['red', True, False],
    ['off', False, False],
    ['red', True, True],
    ['red', True, True],
    ['red', True, True]]]],
 [['regression: silence then new low alarm',
   [[['A', 'high'], ['B', 'low']],
    [{'active': ['A']}, {'active': ['A'], 'silence': True}, {'active': ['A', 'B']}]],
   [['red', True, True], ['red', True, False], ['red', True, True]]],
  ['regression: scenario 2',
   [[['PT101', 'high'], ['LT200', 'low'], ['TT300', 'low'], ['ZS400', 'high']],
    [{'active': []},
     {'active': ['PT101', 'TT300']},
     {'active': ['PT101', 'TT300'], 'ack': True},
     {'active': ['PT101', 'ZS400'], 'silence': True},
     {'active': ['PT101']},
     {'active': ['PT101'], 'silence': True}]],
   [['off', False, False],
    ['red', True, True],
    ['red', False, False],
    ['red', True, False],
    ['red', False, False],
    ['red', False, False]]],
  ['regression: escalation sequence',
   [[['A', 'high'], ['B', 'low']],
    [{'active': ['B']},
     {'active': ['B'], 'silence': True},
     {'active': ['A', 'B']},
     {'active': ['A', 'B'], 'ack': True},
     {'active': ['B']},
     {}]],
   [['amber', True, True],
    ['amber', True, False],
    ['red', True, True],
    ['red', False, False],
    ['amber', False, False],
    ['off', False, False]]],
  ['regression: alarm clears unacknowledged',
   [[['A', 'high'], ['B', 'low']], [{'active': ['A']}, {}, {'active': ['B']}]],
   [['red', True, True], ['off', False, False], ['amber', True, True]]],
  ['regression: low alarm while high acked',
   [[['A', 'high'], ['B', 'low']],
    [{'active': ['A'], 'ack': True},
     {'active': ['A', 'B']},
     {'active': ['A', 'B'], 'silence': True},
     {'active': ['A', 'B']}]],
   [['red', False, False], ['red', False, True], ['red', False, False], ['red', False, False]]],
  ['regression: alarm present at first scan',
   [[['A', 'high'], ['B', 'low']], [{'active': ['A']}, {'active': ['A']}]],
   [['red', True, True], ['red', True, True]]],
  ['regression: scenario 1',
   [[['PT101', 'high'], ['LT200', 'low'], ['TT300', 'low'], ['ZS400', 'high']],
    [{'active': ['PT101'], 'ack': True},
     {'active': ['PT101']},
     {'active': ['PT101'], 'ack': True},
     {'active': ['PT101']},
     {'active': ['PT101']},
     {'active': ['LT200', 'PT101', 'TT300']},
     {'active': ['LT200', 'PT101', 'TT300'], 'ack': True},
     {'active': ['LT200', 'TT300']}]],
   [['red', False, False],
    ['red', False, False],
    ['red', False, False],
    ['red', False, False],
    ['red', False, False],
    ['red', False, True],
    ['red', False, False],
    ['amber', False, False]]],
  ['regression: scenario 3',
   [[['PT101', 'high'], ['LT200', 'low'], ['TT300', 'low'], ['ZS400', 'high']],
    [{'active': ['LT200', 'PT101', 'TT300']},
     {'active': ['LT200', 'PT101', 'TT300', 'ZS400']},
     {'active': ['LT200', 'PT101', 'TT300'], 'silence': True},
     {'active': ['LT200', 'PT101', 'TT300']},
     {'active': ['PT101', 'TT300']},
     {'active': ['TT300'], 'ack': True},
     {'active': ['ZS400']},
     {'active': ['TT300', 'ZS400']}]],
   [['red', True, True],
    ['red', True, True],
    ['red', True, False],
    ['red', True, False],
    ['red', True, False],
    ['amber', False, False],
    ['red', True, True],
    ['red', True, True]]]],
 [['regression: scenario 1',
   [[['PT101', 'high'], ['LT200', 'low'], ['TT300', 'low'], ['ZS400', 'high']],
    [{'active': [], 'silence': True},
     {'active': [], 'silence': True},
     {'active': [], 'silence': True},
     {'active': []},
     {'active': ['ZS400']},
     {'active': ['ZS400'], 'ack': True},
     {'active': ['TT300']},
     {'active': ['PT101', 'TT300'], 'ack': True},
     {'active': ['PT101', 'TT300']},
     {'active': ['PT101', 'TT300'], 'silence': True},
     {'active': ['LT200', 'PT101', 'TT300'], 'silence': True},
     {'active': ['LT200', 'PT101', 'TT300']}]],
   [['off', False, False],
    ['off', False, False],
    ['off', False, False],
    ['off', False, False],
    ['red', True, True],
    ['red', False, False],
    ['amber', True, True],
    ['red', False, False],
    ['red', False, False],
    ['red', False, False],
    ['red', False, False],
    ['red', False, False]]],
  ['regression: scenario 4',
   [[['PT101', 'high'], ['LT200', 'low'], ['TT300', 'low'], ['ZS400', 'high']],
    [{'active': ['PT101', 'TT300']},
     {'active': ['PT101', 'TT300']},
     {'active': ['TT300'], 'ack': True},
     {'active': ['PT101', 'TT300']},
     {'active': ['TT300', 'ZS400']},
     {'active': ['ZS400'], 'silence': True},
     {'active': ['PT101', 'ZS400'], 'ack': True},
     {'active': ['LT200', 'PT101', 'ZS400'], 'ack': True, 'silence': True},
     {'active': ['LT200', 'PT101', 'TT300', 'ZS400']}]],
   [['red', True, True],
    ['red', True, True],
    ['amber', False, False],
    ['red', True, True],
    ['red', True, True],
    ['red', True, False],
    ['red', False, False],
    ['red', False, False],
    ['red', False, True]]],
  ['regression: escalation sequence',
   [[['A', 'high'], ['B', 'low']],
    [{'active': ['B']},
     {'active': ['B'], 'silence': True},
     {'active': ['A', 'B']},
     {'active': ['A', 'B'], 'ack': True},
     {'active': ['B']},
     {}]],
   [['amber', True, True],
    ['amber', True, False],
    ['red', True, True],
    ['red', False, False],
    ['amber', False, False],
    ['off', False, False]]],
  ['regression: alarm clears unacknowledged',
   [[['A', 'high'], ['B', 'low']], [{'active': ['A']}, {}, {'active': ['B']}]],
   [['red', True, True], ['off', False, False], ['amber', True, True]]],
  ['regression: low alarm while high acked',
   [[['A', 'high'], ['B', 'low']],
    [{'active': ['A'], 'ack': True},
     {'active': ['A', 'B']},
     {'active': ['A', 'B'], 'silence': True},
     {'active': ['A', 'B']}]],
   [['red', False, False], ['red', False, True], ['red', False, False], ['red', False, False]]],
  ['regression: alarm present at first scan',
   [[['A', 'high'], ['B', 'low']], [{'active': ['A']}, {'active': ['A']}]],
   [['red', True, True], ['red', True, True]]],
  ['regression: silence then new low alarm',
   [[['A', 'high'], ['B', 'low']],
    [{'active': ['A']}, {'active': ['A'], 'silence': True}, {'active': ['A', 'B']}]],
   [['red', True, True], ['red', True, False], ['red', True, True]]],
  ['regression: scenario 2',
   [[['PT101', 'high'], ['LT200', 'low'], ['TT300', 'low'], ['ZS400', 'high']],
    [{'active': ['LT200']},
     {'active': ['LT200'], 'ack': True},
     {'active': []},
     {'active': ['PT101'], 'ack': True},
     {'active': ['PT101'], 'ack': True},
     {'active': ['PT101']},
     {'active': ['LT200', 'PT101', 'TT300']}]],
   [['amber', True, True],
    ['amber', False, False],
    ['off', False, False],
    ['red', False, False],
    ['red', False, False],
    ['red', False, False],
    ['red', False, True]]]]]
for label, args, expected in fixtures[N-1]:
    check(label, solve(*args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
Boundary fixtureActualExpectedOutcome
regression: escalation sequence[['amber', True, True], ['amber', True, False], ['red', True, True], ['red', False, False], ['amber', True, True], ['off', False, False]][['amber', True, True], ['amber', True, False], ['red', True, True], ['red', False, False], ['amber', False, False], ['off', False, False]]Failed
regression: low alarm while high acked[['red', False, False], ['red', True, True], ['red', True, False], ['red', True, False]][['red', False, False], ['red', False, True], ['red', False, False], ['red', False, False]]Failed
regression: alarm clears unacknowledged[['red', True, True], ['off', False, False], ['amber', True, True]][['red', True, True], ['off', False, False], ['amber', True, True]]Passed
regression: alarm present at first scan[['red', True, True], ['red', True, True]][['red', True, True], ['red', True, True]]Passed
regression: silence then new low alarm[['red', True, True], ['red', True, False], ['red', True, True]][['red', True, True], ['red', True, False], ['red', True, True]]Passed
regression: scenario 1[['amber', False, False], ['amber', True, True], ['red', False, False], ['off', False, False], ['red', True, False], ['red', True, True], ['red', True, True], ['red', True, True], ['red', False, False]][['amber', False, False], ['amber', False, False], ['red', False, False], ['off', False, False], ['red', True, False], ['red', True, True], ['red', True, True], ['red', True, True], ['red', False, False]]Failed
regression: scenario 2[['amber', True, False], ['red', True, True], ['amber', True, True], ['red', True, True], ['red', True, False], ['red', True, False]][['amber', True, False], ['red', True, True], ['amber', True, True], ['red', True, True], ['red', True, False], ['red', True, False]]Passed
regression: scenario 3[['off', False, False], ['off', False, False], ['red', True, True], ['red', True, True], ['red', True, False], ['red', False, False]][['off', False, False], ['off', False, False], ['red', True, True], ['red', True, True], ['red', True, False], ['red', False, False]]Passed

SHA-256 / 2991ebfc2a91c5cc370f983b71d5fe343da40164af7d611fba68174ddd7ec17c

HELD IN THE MEMBER ARCHIVE

The verified repair and its recorded checks are member-only.

This mechanism has 8 recorded checks per implementation. The open-access tier publishes the failure and the unsuccessful fix; the repaired source that passes every check, and the observations that prove it, are available to members.

Every case sharing this mechanism uses the same contract and the same repair, so this one record is held back for all of them.

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Verification & scope

A deterministic bounded teaching model of one PLC instruction or rung pattern evaluated scan by scan. The stated contract is a stipulated toy convention, not a claim of conformance to any vendor controller or IEC 61131-3 runtime. This reproducer isolates one failure mechanism. Results cover the supplied fixtures. Variants within a family share a test contract and should remain grouped when constructing evaluation splits. Related mechanisms with a shared evaluation_group must also remain together; these controlled models are not independent production incidents.

Observations recorded using Python 3.12.14 at 2026-09-29T14:51:44.338625+00:00.

Case digest / a161b8908bbc9cc2b9f4ffdc2631a9f2a6e02ea63d6d7653cd6f7c733bbce185