GB1462055A - Prevention of double processing in object identification sytems - Google Patents

Abstract

1462055 Vehicle identification systems NATIONAL RESEARCH DEVELOPMENT CORP 27 Aug 1974 [4 Sept 1973] 41446/73 Heading H4L An object identification system is of the kind wherein a transmitter on the object transmits signals representing identifying codes to receivers located on a route taken by the object and wherein storage arrangements are coupled to store the codes received by each receiver, the stores being interrogated by a scanning arrangement which passes the codes to a processor which provides identifying information. In such systems it is possible for the identification codes from a particular object to be recorded twice, e.g. because the code is picked up simultaneously by two or more receivers or because during the repeated transmission of the same code by the same receiver, an error occurs such that a following code appears as a new record. To prevent this possibility, code signals from different receivers are compared, or at least three closely successive codes from the same receivers are compared, or both these comparisons are performed, and logic arrangements are coupled to the comparator to prevent the same code being passed more than once to the processor, when the same code is received concurrently from more than one receiver or when after a change in code occurs a reversion to a previous code takes place. In the described embodiments, the invention is applied to a road vehicle detection system. In one arrangement (Fig. 1) a vehicle may cross two receiver loops 14, 12 and be detected by both. The detected code is stored in both of registers 17, 18. The corresponding storage positions of these are coupled to exclusive OR gates 19-22. If all of these gates give zero output showing complete equivalence of store contents, AND gate 23 is operated, the inverter 24 gives a null output and thus AND gate 25 is turned off to prevent the signal from receiver 26 being passed to the scanning arrangement in the processor. In a second embodiment, for dealing with successive code signals (Fig. 2) the signals pass to a series of registers 30, 31, 32 and the code stored in the final register is compared with that in the preceding registers and in the register before that by respective comparators 33, 36. A scanner control prevents a record being made of any code until it changes. This control is not operated until enabled by AND gate 35 and this requires both comparators 33, 36 to show a difference in the codes compared.