4 TECHNICAL DATA
Nonetheless, the reference block of the readhead’s integrated circuit allows for electrical adjust-
ment of the width and position of the RS485 square output-signal in such a manner that the ref-
erence indication equals one period only. The separation between neighbouring reference marks
should be greater than 1.5 mm in order to avoid overlapping of the detection areas.
The METIRIO can be used with scales comprising only one track, for instance only the incremental
track or only the reference track. It is not neccessary to utilize both information. In case of incre-
mental track, the user will only have incremental position information. In case of the reference
track the user will have no indication of the position except from the reference positions with an
accuracy of 20 µm or worse.
4.5.2 Rotary Scale Specifications
optical centerline
A/2
incremental track
reference track
track separation line
B
A
radial from disc center
resulting in radial fanout
d
OC
d
TS
Figure 4.16: Main parameters of rotary scales
• The main characteristic of a rotary scale is the optical diameter d
OC
.
• The reference track is always at the inside of the disc.
• The incremental track is a radial fanout periodic grating.
• The optical centerline is always on a radius 0.7 mm grater than the radius of the track sepa-
ration line, regardless of the track widths A and B.
• For this reason for rotary scales the track widths are reasonably limited to A = B = 1.4 mm.
The diameter of the optical centerline, the so called optical diameter is always 1.4 mm
grater than the diameter of the track separation line. The following equation holds for
every scale, regardless of the other dimensions A, B, outer diameter etc.:
d
OC
= d
TS
+ 1.4 mm. (4.1)
For rotary scales only discrete values for the optical diameter are callowed, because of the fan-out
of the scale pitch P. The number of Counts Per Revolution (CPR) or periods per 360 degrees,
determines the scale pitch P in combination with the optical diameter.
www.smaract.com | Page 41Metirio Encoder User Manual
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