Omron V680 Series User Manual page 289

 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-HMD63-ETN Reader/Writer
 V680S-HMD64-ETN Reader/Writer
 V680S-HMD66-ETN Reader/Writer
54 mm min.
90 mm min.
110 mm min.
54 mm min.
90 mm min.
110 mm min.
Section 11
Appendices
RFID System
287
User's Manual
(Modbus TCP)