90 INSTRUMENTATION IN SCIENTIFIC RESEARCH [Chap. 1 



disk D with transparent and opaque segments. Depending upon the 

 position of the disk, some of the light beams will reach the photo 

 transducers and cause an output signal; the result appears in binary 

 digits (e.g., 1, 1,0). 



An encoder disk with 10 concentric arrays of segments, for 10-digit 

 information, is shown in Fig. (1-2)72; a disk of this type gives a 



Fig. (1-2)72. Encoder disk for 10 digits. 



different output for each of the 2 10 possible configurations, i.e., it 

 furnishes information of the angular-disk position with an accuracy 

 of 360°/l,024, or an angle of about 0.35°. Systems of this type have 

 been built with disks of 10 in. diameter having up to 17 concentric 

 segments. An accuracy as high as 10 sec of arc has been obtained. 

 Instantaneous reading of rotating disks is accomplished by pulse 

 operation of the light source. 1 



1 Information by courtesy of Wayne-George Corporation, Boston, Mass. 



