Motion and state
Its rotary state can be driven from a PLC output so speed and direction remain visible during a scan.
PLC control pattern
Commission it by proving active feedback before accepting enable.
Fault practice
Inject stuck-on, stuck-off, misaligned states and require the PLC sequence to detect, stop and recover deliberately.
PLC integration guide
How to use a rotary encoder with a PLC
Use the high-speed counter path
Encoder pulses can change faster than the normal PLC scan can sample. Wire the channels to inputs and instructions specifically rated for the required frequency, then configure the counter mode for A/B quadrature and the desired multiplication. A normal contact instruction may miss edges even though it appears to work at hand-turned speed. Shielding, grounding and differential signalling matter as cable length and electrical noise increase.
Convert counts into engineering units explicitly
Document the encoder resolution, whether the counter uses one, two or four edges per cycle, gearbox ratio, wheel circumference and sign convention. Position is accumulated counts divided by counts per engineering unit. Speed is count change over a stable sample interval. Avoid burying these constants across rungs; keep them together and expose raw count, scaled value and status for diagnosis.
Plan reference, rollover and loss detection
An incremental encoder does not inherently know absolute position after power loss. Use a home sensor, index pulse or retained position strategy that matches the machine. Handle counter rollover and reverse motion mathematically. When motion is commanded, compare the expected count change with a timeout or following-error band so a broken coupling, damaged cable or stalled shaft becomes a meaningful fault.
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.
Open the quadrature encoder signal labSignal map
I/O you can reason about
PLC output Enable; PLC input Active feedback
| Signal | PLC direction | Type / range |
|---|---|---|
| Enable enable | output | bool |
| Active feedback active | input | bool |
Field checklist
Commissioning sequence
- 01Confirm output electrical type, supply, pulses per revolution, maximum frequency and PLC high-speed-input compatibility.
- 02Turn the shaft slowly in the positive direction and verify A/B direction and count sign.
- 03Rotate one known revolution and compare the count change with the configured edge multiplier.
- 04Scale counts into the real distance or angle, then validate across several known positions.
- 05Disconnect one channel and simulate stalled feedback to prove channel and no-motion diagnostics.
Fault finding
Symptoms and first checks
| Symptom | Check |
|---|---|
| Count direction is reversed | Swap A and B only if permitted by the wiring design, or change the configured direction convention consistently. |
| Counts are missed at speed | Check input frequency rating, filter time, high-speed-counter configuration, cable shielding and signal level. |
| Position is correct near zero but drifts with travel | Verify pulses per revolution, edge multiplier, gearing, circumference and mechanical slip. |
Fault and recovery exercise
Make abnormal states part of the sequence
Inject stuck-on, stuck-off, misaligned states and require the PLC sequence to detect, stop and recover deliberately.
stuck-onstuck-offmisaligned
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
Rotary encoder FAQ
Why are encoder channels A and B offset?
Their phase relationship reveals direction. The sequence of A and B edges changes when the shaft reverses.
What does encoder PPR mean?
Pulses per revolution describes the base signal cycles. A quadrature counter may count multiple edges per cycle, so configured counts per revolution can be higher than the stated PPR.
Does an incremental encoder retain position?
The encoder provides relative movement. Absolute machine position normally requires homing, an index strategy, retained state with validation, or an absolute encoder.
Free first success
Put the rotary encoder 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
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