24 000 min Example Rotary encoder with 2048 sinusoidal signal periods per revolution: One signal period corresponds to approx. 600". This results in maximum position deviations within one signal period of approx. ± 6".The position error of the encoder within one signal period always affects the calcu- lation of the actual speed on the basis of the actual position values of two succes- sive sampling cycles. The position error of the encoder within one revolution is rele- vant for the speed control loop only if no more than a few actual position values per revolution are being evaluated. For exam-ple: a sampling time of 250 µs and a speed of n Position errors within one revolution become apparent in larger angular motions. Position errors within one signal period already become apparent in very small angular motions and in repeated measurements. They especially lead to speed ripples in the rotational-speed control loop. HEIDENHAIN rotary encoders with integral bearing permit interpolation of the sinusoi-dal output signal with subdivision accura-cies of better than ± 1 % of the signal peri- od. ••

Measuring Accuracy

The quantities infl uencing the accuracy of linear encoders and Exposed Linear Industrial encoders are listed in the Linear En-coders for Numerically Controlled Machine tools cata-logs.The accuracy of angular measurement is mainly determined by:1. Quality of the graduation2. Quality of scanning 3. Quality of the signal processing electronics4. Eccentricity of the graduation to the bearing5. Error due to radial deviation of the bearing6. Elasticity of the encoder shaft and its coupling with the drive shaft7. Elasticity of the stator coupling (RON, RPN, RCN) or shaft coupling (ROD)In positioning tasks, the accuracy of the an-gular measurement determines the accura- cy of the positioning of a rotary axis. The system accuracy given in the Specifi ca-tions applies to a temperature of 20 °C, and is defi ned as follows: The extreme values of the total deviations of a position are—referenced to their mean value—within the system accuracy ± a.
–1 result in only 10 sam-ples per revolution.Temperatures as high as 120 °C, which can typically be found in motors, cause only a very small position error in HEIDENHAIN encoders.Encoders with square-wave output signals have a position error of approx. ± 3% of the signal period. These signals are suitable for up to 100-fold phase-locked loop subdi- vision. For rotary encoders with integral bearing and integrated stator coupling, this value also includes the deviation due to the shaft coupling.• For rotary encoders with integral bearing and separate shaft coupling, the angle error of the coupling must be added. For rotary encoders without integral bearing, deviations resulting from mount- ing, from the bearing of the drive shaft, and from adjustment of the scanning head must be expected in addition to the system error (see next page).The system accuracy refl ects position er-rors within one revolution as well as those within one signal period. Position error within one signal period Position errors within one revolution Signal period360° elec.
Signal level Position error Position error Position error within one signal period Position

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