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Measuring Accuracy

The total measurement error of a measuring encoder is caused by the errors listed below:

  • Graduation Pattern Accuracy – Determined by the quality of the measuring scale.
  • Accuracy within the Graduation Pitch – Determined primarily by the quality of the sensor signal sensing the graduation pattern pitch, and the quality of the evaluation electronics of the scanning head.

In addition, for the measuring encoders with output interface 1 Vpp to consider the following:

  • Accuracy of analog / digital conversion in the input stage of the subsequent electronics (control side)
  • Coupling of noise on the encoder output signal in the transmission of the sine wave signals to the subsequent electronics.

Pitch accuracy

Each linear/angular  scale is calibrated on a test bench and has a test certificate, which indicates the accuracy class meets the customer specified requirement. Optionally, an accuracy chart (measured under ideal assembly conditions) can be supplied.

Accuracy within the grating period

AMO offers three different pitch sizes for the scales (500μm, 1000μm and 3000µm), with the appropriate pitch selected depending on the application. The periodic error occurring within one pitch is small due to the high quality of inductive sinusoidal waveform and the excellent signal acquisition and interpolation, and is only 0.1% of the pitch (eg:. maximum deviation of 0.5 microns for a grating period of 500μm). This high accuracy is not only for the ideal mounting of the encoder head, but also is true when the encoder head is mounted anywhere within the mounting tolerances and operating temperature range, due to auto offset and gain compensation. Each scanning head is adjusted in accordance with these high quality criteria.

For the suppression of the error mentioned above under item “3” and “4”, we have implemented in the new generation of AMOSIN ® systems, a new output interface in which the Sin, Cos and reference index signals with 1 Vpp output are divided and offered with a line driver output. These differential signals (with programmable interpolation) are generated in real-time with signal periods down to 20µm.

The effect of any possible deviation to the encoder signal in the subsequent electronics (controller etc.) is reduced exactly by the dividing factor that is applied.

In addition, this reduced sinusoidal signal period leads to finer quantisation in the subsequent electronics, which is of particularly great importance to demanding high stability, high stiffness drive applications.

In addition, by subdividing, the influence of disturbances (noise, …) on the signal transmission reduces proportional to the dividing factor, ie an improved signal to noise ratio.

Due to the metrological characteristic of AMOSIN ® systems that work completely without hysteresis.