Lenord+Bauer GEL 211CS0 Betriebsanleitung Seite 131

Lenord+Bauer
Using this signal a control system is able to determine the absolute angular posi-
tion of the measuring scale after the first revolution, without the need to undertake
a reference search routine.
What should the reference signal look like?
The reference signal can be a square wave or sine wave. An ideal
reference signal has a signal width of 270° within one tooth period. The middle
point is close to 0° at the position where the SIN and COS signal cross. The devia-
tion from this ideal position is termed the signal deviation.
Two further significant points are determined starting from the middle point. The
first point is the point at which the reference signal crosses the x axis on the rising
edge, which should be at around -135°. The second point is the point at which the
reference signal crosses the x axis on the falling edge; this point should be at
around +135°.
Along with the position of the signal, the amplitude is important. Lower amplitudes
will not generate a valid reference signal, while excessively high amplitudes will re-
sult in so-called "clipping" (truncation of the signal). An ideal amplitude (Vp) is
around 500 mV with an offset of around -350 mV.
What affects the reference signal?
Like the SIN/COS signals the reference signal is primarily affected by imprecise
mounting in relation to the target wheel or an imprecisely manufactured target
wheel. While mounting inaccuracies primarily generate amplitude errors, defects
on the gear wheel are primarily apparent as phase errors.
Gear wheel analysis
What does the gear wheel analysis produce?
During the gear wheel analysis the sine signal is evaluated once per revolution
(from reference pulse to reference pulse).
Manufacturing and mounting inaccuracies on the target wheel limit the overall ac-
curacy of the angle measuring system. To be able to make a quantitative state-
ment here, a so-called BQ value (evaluation quotient) is determined that repre-
sents a measure of the precision of the overall angle measuring system.
In an ideal measuring system the fluctuation on the BQ value is zero, i.e. there are
no deviations around the average value. In practice, this situation however is not
achieved.
If the standard deviation and the maximum swings (ΔBQ) are now evaluated once
per revolution, a meaningful evaluation criterion for the accuracy of the angle mea-
suring system is obtained. In this way the quality of the target wheel used and the
installation situation can be evaluated, documented and compared.
The limits for BQ standard deviations and ΔBQ depend on numerous factors: num-
ber of teeth, quality of the teeth, shape of the teeth, concentricity, bearing play etc.
The following values are determined:
GEL 211CS0
Glossary
131