Permissive Chain Not Satisfied

Walt — Simple Man Takeaway

A permissive chain is a room full of people saying yes. One no keeps the door shut.

Plain-English Summary

Use this flow when the final run, enable, start, ready, or permissive output is false and the machine is waiting for one or more conditions to become true.

R.E.A.L. firstRead-only firstCapture before changingReverse-trace failed conditionsTrap intermittent ghosts

First-Check Flow

1. Find the final run or enable result

Start at the output/result that represents the machine being allowed to run.

2. Look only at false conditions

Do not waste time on satisfied permissives. Identify the no vote in the chain.

3. Classify the false condition

Separate safety, mode, machine-ready, product-ready, downstream-ready, operator command, and environmental conditions.

4. Reverse-trace the false permissive

Use Find All to locate what drives the failed permissive and make that OTE/result the new target.

5. Respect legitimate protection

A permissive may be doing its job. Do not bypass safety, guarding, pressure, overload, or interlocks without proper procedure.

6. Trap flickering permissives

If the permissive chain drops briefly or only under load/timing, use Ghost Busting™ to capture the context window.

Field Checks

Final permissive/run/enable output identified
False condition isolated
Mode and recipe confirmed
Safety status confirmed through approved methods
Upstream/downstream ready signals checked
Drive/air/hydraulic/power ready conditions checked
False condition reverse-traced to its source

Watch Out For

Bypassing legitimate protection to make production move
Multiple permissives with one real cause upstream
A true-looking HMI status using stale or wrong tag data
Brief permissive flicker that drops a sequence
Mode mismatch between HMI and PLC
A condition false because another machine never answered

Reverse-Trace or Ghost Busting™?

Use Reverse-Trace Logic Solving™
when the failure is stable and visible live. Open the PLC program, monitor in RUN mode, chase only failed conditions, find the driving OTE, and repeat failure-to-failure.

Use Ghost Busting™
when the failure is intermittent, self-clearing, timing-based, or disappears before maintenance sees it. Select the suspect routine from the HMI and let the comparator trap expected-vs-actual mismatch every scan.

Find the failed result. Identify the blocking condition. Reverse-trace only what is failing. If the truth disappears, trap the ghost.

Related Calculators / SWAT Screens

Industrial Controller™ Backup / Restore Readiness Volta™ 24VDC Power Supply Load Check

Walt says STOP! - Safety First

Make these checks prior to proceeding.

Do not bypass safety, force outputs, defeat guards, or work live beyond your qualification and site procedure. If motion, stored energy, live electrical exposure, lockout/tagout requirements, or personnel inside guarded areas are involved, stop and follow the required safety process.