Encoder Position Is Exactly Four Times Wrong? Check Quadrature Evaluation
An exact factor-of-two or factor-of-four position error often points to counting conventions. Match encoder pulse specification, receiver evaluation, and engineering-unit scaling.
Original counting example; terminology varies by encoder and receiver.
What is happening?
Quadrature receivers can count selected edges or multiple edges from the A/B signals. Pulses per revolution and evaluated counts per revolution are therefore not always interchangeable terms. The installed configuration defines the actual count scale.
Check these five things
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Read how the encoder defines its resolution.
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Check receiver edge-evaluation mode.
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Determine evaluated counts per mechanical revolution.
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Include gearing and travel per revolution in the conversion.
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Verify against a known displacement using the approved method.
Worked example
A teaching encoder produces 1000 A-channel cycles per revolution. A receiver evaluating four quadrature edges per cycle produces 4000 counts per revolution. Software that divides by 1000 would report four revolutions for one actual revolution.
Quick diagnostic reference
| Term | Example |
|---|---|
| Cycles per revolution | 1000 |
| Evaluation multiplier | 4 |
| Counts per revolution | 4000 |
The mistake to avoid
Do not change the scale until the resolution terminology is confirmed. Some datasheets already state the evaluated count value.
How to verify the fix
Check direction and scale over multiple approved distances, including a full revolution where practical. Preserve the complete conversion in documentation.
Field-work boundary: These are educational diagnostic guides. Use the exact equipment manuals and approved site procedures. Electrical testing and machinery changes belong to qualified, authorized personnel; control hazardous energy and validate affected functions before release.
Technical reference
Beckhoff: EL5101 incremental encoder interface. The examples and diagnostic tables above are original teaching material; they do not replace the product manual.