in which the interrogator is operated interrogator units are capable of interrogating multiple tags within their reading field and discriminating between the tags without misreading interrogators employing tag response levels as a method of discriminating between multiple tags may accomplish this by distance differential and or position relative to the antenna pattern error detection is used to ensure reading accuracy the system detects for the presence and direction of movement of each individual unit of rolling stock and shall provide suitable output words for missing and incorrect tags and incorrect characters if appropriate the equipment detector function provides for sensing the following conditions 1 equipment presence detecting each unit of rail rolling stock whether equipped with a tag or not including cars locomotives and cabooses and 2 train presence transitioning the system from idle to active mode upon the approach of a train or a cut of cars or a single car upon the train or car s leaving the system the system shall provide a 34 clean list 34 report on the net movement of equipment and the system shall transition to the idle mode this 34 clean list 34 will contain no duplications or omissions of rolling stock initials and numbers due to stops and reverse moves before the interrogator the radio communication system 70 described consists of a reader system 54 rf module 44 and tags 30 the tags are placed on objects to be identified and readers antennas and rf modules are installed at points to record the passing of tagged objects the system is designed for localized application where the tag passes by the reader system the block diagram of fig3 indicates the function of each component rf module 44 transmits.