A lamp is on, but the team does not know who must respond, what condition must be corrected, or who may clear it. Commission the Andon system as an operating procedure first and a set of outputs second. Each color needs one documented meaning, an owner, an entry condition, a clearing condition, and a test that proves the complete response path.
Signal-State Charter
Before anything else, confirm the meaning of every installed color with production, quality, maintenance, and controls personnel. Color meanings are plant rules, not self-explanatory behavior. For the three-stage assembly-line scheme described here, use the following starting charter.
| Indication | Meaning | Required response | Clearing condition |
|---|---|---|---|
| Green | Line running normally | Continue production and monitor the process | A higher-priority condition becomes active or the line leaves its defined running state |
| Yellow | A problem is arising or a potential issue exists | Assign the designated responder and investigate before the issue stops the line | The triggering condition is corrected and the acknowledgement or reset rule is satisfied |
| Red | Line stopped | Identify the stop cause, make the equipment safe for the required work, and restore the permissives | The stop cause is removed and the approved restart sequence completes |
| Orange, blinking | An automated vision system diverted a part | Track and disposition the diverted part under the quality procedure | The event has been recorded or acknowledged according to the local rule |
| Orange, steady | Multiple parts have been diverted | Escalate the repeated diversion condition and inspect the process or vision decision path | The diversion condition is resolved and the affected parts are reconciled |
State whether orange is installed only on vision-equipped stations or across the whole line. Do not move on until an operator can read each indication and give the same meaning and required response recorded in the charter.
Priority and Display Rules
Define what the stack displays when conditions overlap. Without a priority rule, green can remain active while red reports a stop, or yellow can disappear when a more serious condition masks it. A practical priority for this scheme is red above yellow and green. Orange represents a quality or diversion state, so decide whether it operates independently or participates in the same priority chain.
- Remove green whenever the line no longer meets the documented running criteria. Do not drive green merely from control power or PLC run mode.
- Activate yellow when its process warning becomes true, even if production continues.
- Activate red from the line-stopped state defined by the machine sequence. Decide whether planned stops belong in that state or need a separate indication.
- Retain the underlying yellow condition while red has display priority. When red clears, yellow must reappear if its cause remains active.
- For vision stations, define whether a blinking orange event becomes steady after multiple diversions and whether steady orange remains latched until quality personnel acknowledge it.
A stack light communicates equipment status; it does not replace a designed safety function or authorize entry into hazardous areas. Prove the priority logic by forcing permitted simulated combinations and confirming that the displayed state matches the charter.
Initiation and Response Ownership
Assign responsibility by transition rather than by department name alone. The person who notices a problem, the person who diagnoses it, and the person authorized to restart the line may be different roles.
| Transition | Responsible role | Required action | Confirmation |
|---|---|---|---|
| Normal to yellow | Operator or automatic control | Report or generate the warning and continue only within the approved operating rule | The warning cause is visible at the station or operator interface |
| Yellow response | Assigned production, maintenance, or quality responder | Acknowledge ownership and diagnose the trigger | The response is recorded or otherwise visible to the operator |
| Any state to red | Automatic sequence or authorized operator action | Stop the line according to the machine control design | Motion and sequence status match the defined stopped state |
| Orange response | Quality or designated process owner | Reconcile diverted parts and investigate repeated diversions | Part disposition and process status are known |
| Return to green | Authorized restart role | Confirm corrected conditions and execute the normal restart sequence | The line resumes its defined running state |
Post the role assignments where the indication is used, including the escalation route when the primary responder is unavailable. Before commissioning the next function, stage a yellow event and have the assigned team demonstrate who takes ownership and what evidence releases the condition.
Acknowledgement, Reset, and Restart
Separate acknowledgement from correction. Acknowledgement means someone has accepted the response; reset means the control logic has verified that the trigger is no longer active and has cleared any permitted latch. Neither action should conceal an active fault or recreate green before the line is running.
- Trigger the condition and confirm the correct indication appears.
- Acknowledge it using the locally assigned control. Confirm that acknowledgement records ownership or silences an optional annunciation without removing the visual state while the cause remains.
- Correct the physical or process cause. Confirm the input, interlock, inspection result, or sequence state that generated the indication has returned to its acceptable state.
- Apply reset only where a latch is required. Confirm that an active cause prevents the latch from clearing.
- Execute the normal restart action after all run permissives are present. Confirm red turns off before green turns on and yellow remains visible if its warning still exists.
For orange indications, decide whether each diverted part creates a momentary event, a retained event, or a diversion count. Do not clear steady orange until the rule for multiple diverted parts has been satisfied. Prove the sequence by attempting acknowledgement and reset while the initiating condition is still active; the indication must continue to communicate the unresolved state.
Control-Logic and Wiring Checks
Map each documented state to a physical output and compare the program command with the electrical result. A correct PLC state with the wrong lamp illuminated points to output mapping, wiring, lamp-module placement, or field-voltage problems rather than sequence logic.
- Place the equipment in an approved commissioning condition and inspect the installed color order and output assignments against the electrical drawings.
- Command each lamp individually through the authorized test method. Confirm the commanded output, output-module indication, field voltage, and illuminated color agree.
- Test blinking orange as a controlled flash command rather than an incidental program-scan effect. Select and document a plant-approved flash behavior; no flash rate is specified here.
- Remove the test command and trigger the real process condition. Confirm the same output activates from sequence logic.
- Cycle control power where the commissioning plan permits it. Confirm retained warnings and diversion information follow the documented retention rule rather than clearing unpredictably or returning stale.
Do not move on until every physical segment passes both an individual output test and a process-driven test.
End-to-End Commissioning Verification
Run the complete response workflow with production, maintenance, quality, and controls representatives present. Use controlled test conditions and record the actual trigger, displayed indication, responder, correction, reset behavior, and restored state.
- Start from the normal running condition and confirm green is on while red and yellow are off.
- Create a valid potential-issue condition and confirm yellow appears, the assigned responder accepts it, and green follows the documented coexistence rule.
- Escalate or create a valid stopped condition and confirm red takes priority without deleting the unresolved yellow state.
- Remove the stop cause, perform the approved reset and restart, and confirm yellow reappears if its cause remains.
- At a vision-equipped station, divert one part and confirm blinking orange. Create the documented multiple-diversion condition and confirm steady orange, response ownership, and part reconciliation.
- Clear every corrected condition, restart the line, and confirm the final display is green only when the line has returned to its defined running state.
FAQ
What happens if red and yellow conditions exist at the same time?
Red should take display priority for the stopped line, while the control logic retains the yellow cause. After red clears, yellow must return if the potential issue remains active.
What happens if an operator resets yellow before fixing the cause?
The active trigger should keep yellow on or immediately restore it. Test this behavior during commissioning so acknowledgement cannot conceal an unresolved process condition.
What happens if a lamp passes the PLC output test but fails during production?
Trace the real process condition through its input, sequence state, priority logic, and output command. Complete the final verification by recreating the process trigger, clearing its cause, executing the approved restart, and confirming green appears only after the line is running normally.