Monitor using transceiver and memory - compares radiation returned and altered by transducer carried by object or subject in supervised zone

摘要

The closed circuit TV monitor identifies objects inside a certain zone. It has a radiation transmitter and receiver, sending the radiation into, and receiving it from the zone. The objects carrys a transducer (65) which affects the radiation in the zone received by the receiver (32). The transducers have properties which have different influences on the radiation. A memory (73) stores these properties, and a comparator (74) compares the received radiation with the stored properties in order to detect which transducer (65) is in the zone. A store stores the previous determination of the transducer (65) position or place, and a comparator compares the stored with the current values, in order to find which transducer (65) has entered or left the zone between the preceding and current time interval. The current determination is stored for further use.