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Menu 3
Digitax ST Advanced User Guide 41
Issue Number: 1 www.controltechniques.com
5.5 Menu 3: Speed feedback and speed control
Menu 3 relates to different functions which are:-
• Speed feedback
• Speed controller
• “Zero speed”, “at speed” and overspeed detectors
• Drive encoder.
Speed accuracy and resolution
Digital reference resolution
When a preset speed is used the reference resolution is 0.1rpm. Improved resolution can be obtained by using the precision reference (0.001rpm).
Analog reference resolution
The resolution from analog input 1 is better than 16bits plus sign provided the speed reference is routed via Pr 1.36, Pr 1.37 or Pr 3.22 in high speed
update mode. The resolution from analog inputs 2 or 3 is 10bits plus sign.
Accuracy
The absolute speed accuracy depends on the accuracy of the crystal used with the drive microprocessor. The accuracy of the crystal is 100ppm, and
so the absolute speed accuracy is 100ppm (0.01%) of the reference, when a preset speed is used. If an analog input is used the absolute accuracy is
further limited by the absolute accuracy and non-linearity of the analog input.
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