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Tuesday, January 17, 2017
The Motion Control Community Forum, sponsored by Control Technology Corporation.
Absolute Encoder SSI Interface and Grey Code
How does an absolute encoder works with the SSI interface and what is grey code all about?


Can anyone please explain how an absolute encoder works with the SSI interface and what grey code is all about?

Is reducing number of errors the main reason for grey code?

Who's the top vendor for SSI absolute encoders?

To make it simple Grey code just changes one position at a time.

In binary if you go from 1 (001) to 2 (010) you have to change the 2nd digit to 1 and the end digit to 0.

In grey code only one bit position changes 1 (001) to 2 (011), all that changes is the middle bit.

In the first instance (binary) you will see that as the code changes from 1 to 2 the encoder must turn off bit 0 and turn on bit 1. If bit 0 turns off slightly before bit 1 turns on then the output briefly becomes 0. If bit 1 turns on slightly before bit 0 turns off then it briefly becomes 3. With larger numbers these errors can become huge. Grey code only requires one bit to change for each increment so the errors are eliminated.

Kuebler from Germany probably makes the best SSI absolute encoders that I have used. It's pricey and there's not much representation in the US though.