9300 Feedback systems: Resolution and accuracy of encoder systems

Question:
With indicating accuracies more and more questions due to different indications in the interplay with 9300 drive controller arise. How do the indications in the data books arise?

Answer:
Encoder systems differ in terms of resolution, static accuracy (positioning accuracy) and dynamic accuracy.

The resolution is determined by the maximally distinguishable number of the encoder systems' positions.

In case of static accuracy production tolerances and wrong mountings are added.

The dynamic accuracy is additionally determined by the dynamic capacities of the evaluation system.

1. Resolver:

Measuring signal: Two carrier frequency voltages electrically offset by 90 °, whose amplitude depends on the sine and cosine of the orientation angle of the rotor. These signals are conditioned with a resolution of 11 bits, which corresponds to 2048 steps.
If an encoder revolution (360 ° * 60 ´) is divided by 2048, this results in a resolution of 10 ´.
The static accuracy corresponds to ± 10 ´ compensated and ± 20 ´ uncompensated (´ = minute of arc), the dynamic accuracy corresponds to ± 15 ´ compensated and ± 30 ´ uncompensated. (Compensation of the resolver error see 20032600).

2. Incremental encoder:

Measuring signal: Two sequences offset by 90 ° of high-low-signals (created via Schmitt trigger), whose frequency is proportional to the speed. A four-fold evaluation (from these signals four unique status' can be created) for an encoder with 2048 lines results in an internal resolution of 8192 steps.
If an encoder revolution (360 ° * 60 ´) is divided by 8192, this results in a resolution of 2.6´.
The static accuracy of this system corresponds to ± 2.6 ´, the dynamic accuracy corresponds to ± 20 ´.

3. Sine-cosine encoder:

Measurement signal: Structure like incremental encoder. The signal is, however, not created via Schmitt trigger, but a sine sequence (e. g. with 512 periods) is given electronically to the unconditioned signal (triangular).
Sine-cosine-encoder with 512 sine-cosine signals supplies a value with a 512 times higher resolution than the resolver mentioned above.
The resolution in the 9300 drive controller is limited by the internal resolution 16 bits = 65536 steps.
If an encoder revolution (360 ° * 60 ´) is divided by 65536, this results in a resolution of 0.33 ´.
Here the best values can be achieved with ± 0.8 ´ static and ± 10 ´ of dynamic accuracy.

In order to evaluate the accuracy you have to distinguish between resolution (ideal accuracy) and actual accuracy in the static and in the dynamic case.

Further notes see Application Report No. 100.16.1.

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