Measuring accuracy

The total error of a measuring system is caused by the following measuring inaccuracies:1. Precision of the graduation - determined by the precision of the measuring scale2. Precision within one grating pitch - primarily determined by 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 scale is measured on a linear test bench, and a test certificate, quoting the precision class in accordance with specification, is completed. Optionally a measuring diagram (measured under ideal mounting conditions) can be supplied, as follows. 2. Precision within one grating pitch These errors are extremely small on AMOSIN systems, and are in the region of 0.1 % of the grating pitch (corresponding 1 µm for a grating pitch of 1000 µm). This maximum precision is not just relevant to the ideal set-up, but is also retained when the mounting tolerances and working temperature range are exploited. Every scanning head is adjusted and tested on the basis of these tight criteria of quality.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, are divided and over line drivers (see signal diagram on Page 23).The dividing of the grating pitch (D) generates a signal corresponding to a pitch of 40 µm in real-time, if a measuring scale with a grating pitch of 1000 µm is used.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 dynamic and stiff drive applications.Additionally, the signal division reduces the effect of noise coupling 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.
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