Motion and state
Its travel is animated along the validated local axis and can expose command and end-state feedback.
PLC control pattern
Commission it by proving selected before accepting the next sequence state.
Fault practice
Inject stuck-on, stuck-off states and require the PLC sequence to detect, stop and recover deliberately.
PLC integration guide
How to use a selector switch with a PLC
Decode the contacts into one valid mode
Do not scatter raw selector inputs throughout the program. Convert them once into a mode state and an invalid-state flag. A three-position switch may use two PLC inputs: neither on for OFF, one on for MANUAL and the other for AUTO. If both are on because of a short, mapping error or transition overlap, the machine should not guess. The valid combinations depend on the actual contact blocks and break-before-make or make-before-break construction.
Define command authority in every mode
AUTO normally permits the sequence to command outputs when all interlocks are healthy. MANUAL permits explicit maintenance controls, often with reduced motion, hold-to-run action or additional permissives. OFF removes normal command authority. Safety functions remain active in every mode. Keep the mode decision separate from equipment commands so it is possible to audit exactly why an output energised.
Prevent surprising transitions
Changing from MANUAL to AUTO should not replay a stale automatic request, and switching into MANUAL should not inherit an automatic output without a deliberate command. Clear or reconcile latched requests at the transition edge. For equipment with stored state, define a bumpless transfer rule and show the selected mode prominently on the HMI along with any reason the new mode is not yet ready.
Learn the physical principle first
The reference above focuses on PLC integration. The interactive school lesson shows the device, signal or mechanism before you write the control sequence.
Learn how industrial control contacts change stateSignal map
I/O you can reason about
PLC input Selected
| Signal | PLC direction | Type / range |
|---|---|---|
| Selected selected | input | bool |
Field checklist
Commissioning sequence
- 01Check contact-block arrangement and continuity in every detent with power isolated.
- 02Map raw inputs and verify every physical position creates the documented combination.
- 03Force each valid and invalid combination in the PLC test plan and confirm deterministic mode decoding.
- 04Change modes during idle and active states while observing command ownership and output transitions.
- 05Cycle controller power in each switch position and verify the restart behaviour matches the machine specification.
Fault finding
Symptoms and first checks
| Symptom | Check |
|---|---|
| HMI mode disagrees with the switch | Check physical contact blocks, raw input states, tag mapping and decode truth table. |
| Equipment starts when AUTO is selected | Remove stale run requests, require a valid transition or fresh start and verify restart policy. |
| Two modes appear active | Inspect make-before-break overlap, shorted conductors and logic that uses raw inputs independently. |
Fault and recovery exercise
Make abnormal states part of the sequence
Inject stuck-on, stuck-off states and require the PLC sequence to detect, stop and recover deliberately.
stuck-onstuck-off
Engineering boundary
The model teaches PLC sequence behaviour and diagnosis. Confirm ratings, wiring, guarding, process calculations and commissioning limits against the real manufacturer documentation and site design.
Plain-English answers
Selector switch FAQ
Is a selector switch a safety device?
A standard mode selector is a control device, not automatically a safety-rated selector. Safety-related mode selection requires suitable hardware, architecture and validation.
Should manual mode bypass interlocks?
Safety and equipment-protection interlocks should not be casually bypassed. Any maintenance override needs explicit engineering, indication, access control and risk assessment.
What is bumpless transfer?
It is a planned change of control authority that avoids an abrupt or unintended output change when the selected mode or controller changes.
Free first success
Put the selector switch into a working control sequence
Open a related browser scenario, run the PLC logic and see the component state respond. Start without installing software or entering a card.
No installNo credit cardImmediate pass/fail feedback
Keep building
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