Omron V680S Series User Manual page 229

 Mutual Interference of RF Tags
If you use more than one RF Tag, separate them by at least the interval shown below to prevent
malfunctions due to mutual interference.
If the distance between the RF tags is too short, read / write distance will be reduced.
 V680S-HMD64-ETN Reader/Writer
 V680S-HMD66-ETN Reader/Writer
120 mm min.
110 mm min.
150 mm min.
140 mm min.
120 mm min.
110 mm min.
150 mm min.
140 mm min.
Section 8
Appendices
RFID System
227
User's Manual