Absolute Encoder Values Jump Strangely? Check Gray Versus Binary
An SSI encoder can communicate reliably while its position is decoded incorrectly. Confirm the encoding before blaming noise or mechanics.
Original three-bit example; use the exact encoder frame specification.
What is happening?
Gray and binary coding assign different bit patterns to positions. Frame length, status bits, single-turn and multi-turn fields also affect decoding. A plausible value at one position does not prove the complete format is correct.
Check these five things
-
Read the encoder output-code specification.
-
Check receiver Gray-to-binary conversion settings.
-
Confirm frame length and data-field placement.
-
Separate status bits from position bits.
-
Compare a sequence of known positions in a test setup.
Worked example
In a three-bit teaching example, binary position 3 is 011 while its reflected Gray code is 010. Treating the Gray pattern as ordinary binary produces 2. Multiple positions are needed to expose the resulting nonlinear interpretation.
Quick diagnostic reference
| Setting | Check |
|---|---|
| Coding | Gray or binary |
| Frame width | Total transmitted bits |
| Field layout | Position versus status |
The mistake to avoid
A simple scale factor cannot correct a coding mismatch across the entire range. Fix the documented decoding arrangement first.
How to verify the fix
Verify monotonic movement, rollover, multi-turn behavior where applicable, and diagnostic bits before enabling dependent motion functions.
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: SSI encoder coding and frame configuration. The examples and diagnostic tables above are original teaching material; they do not replace the product manual.