Measuring accuracy

As an open angle-measuring system, in which the system components, Measuring scale and scanning head possibly also the evaluation electronics) are supplied separately, and in which there is no mechanical connection requireing own bearings, the precision can be assigned to these components as follows:1. Scale accuracy - determined by the precision of the Measuring scale on the measuring flange, and by deviations of the measuring flange mechanics from an ideal cylindrical form2. Precision within one grating pitch - primarily determined in the scanning head, depending on the quality of the sensor signal and its evaluation electronics.The following should also be considered for the measuring systems with a 1 Vpp output interface:3. Precision of the analog/digital conversion at the input stage of the subsequent electronics (in the controller)4. Noise coupled into the output signals as it is transferred from the scanning head to the subsequent electronicsA detailed description of these aspects follows: 1. Scale accuracy Every measuring flange is measured on an angle test bench, and a test certificate, quoting the precision class in accordance with specification, is completed. Although the absolute angular deviation for an open measuring system depends on the precision with which the measuring flange is centred on the axes being measured, it is to possible supply a measuring diagram (registered under ideal assembly conditions), as follows.
Abweichung ["]Error ["]0102030 -30-20-10 Winkel [Grad]Angle [Degree] For applications requiring the greatest precision, the measuring flange should be centred as accurately as possible. The precision of the angular measurement depends on the graduation error and on the concentricity of the assembly. Systematic (long-wave) errors resulting from this can be compensated for in the controller.In a special available system configuration two diametrically opposed measuring heads can be used scanning one flange in order to suppress eccentricity errors through the averaging of the angle information in a dedicated electronic box. 2. Precision within the grating pitch The deviations from the ideal sinus wave of the signal, apeared in the generation and evaluation of the primar measuring information, are mainly periodical and as already mentioned for the AMOSIN-System within 1 µm arclength (1/1000 of the pitch of 1000 µm). This high accuracy level is achieves not just for the ideal, nominal mounting and environmental conditions but for the whole specificated functional range of geometrical mounting deviations or tenperature.In order to suppress the errors discussed above under points "3" and "4", a new output interface has been implemented in the new
® generation of AMOSIN systems, in which the sine, cosine and reference signals, for the 1 Vpp output interface delivered over line drivers (see signal diagram on Page 26). The real time covertion of the original signal (e.g. 1000 µm) in finer sine wave periods down to less than 40 µm. arc length is realised over a programmable factor "D". The effect of any possible deviation in the evaluation (A/D conversion) in the subsequent electronics (controller etc.), is reduced in this signal interface by exactly the dividing factor (D) 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.Additionally, the signal dividing reduces the effect of interfered noise on the signal transfer line in proportion to the dividing factor "D"; in other words, an improved signal/noise ratio is achieved.
® The metrological principle on which the AMOSIN systems operate means that they are entirely free from hysteresis and don´t lead to a "backlash effect".
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