| 摘要 |
A reader for checking magnetically encoded security thread incorporated or to be incorporated into sheet material comprises a housing 1 which includes a magnetic reading head, 13, a rotary member, 6, which is rotatable by frictional engagement either with a surface of the thread or of sheet material containing the thread to be checked, and an encoder, coupled to the rotary member, for providing electrical signals indicating units of relative movement between the housing and the surface, in synchronism with electrical signals from the reading head. The housing may be portable for manual movement over the thread and includes circuit means including an ADC responsive to electrical signals from the magnetic reading head to decode same and provide signals indicative of the magnetic pattern detected by the magnetic reading head, for comparison with signals stored in a memory, a second memory in which a signal comparison algorithm is stored, and a microprocessor operating in accordance with the comparison algorithm to compare the stored data with the digital signals from the ADC to produce an output signal indicative of the result of the comparison. A mean unit of length as computed from the second length is compared with stored data relating to the true unit length for the thread, to determine if the scanned thread has suffered stretch or is otherwise not within the specification for the thread. |
