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Variable Tolerance Magnetic Read Circuitry Insensitive to Amplifier Phase Shifting

IP.com Disclosure Number: IPCOM000082029D
Original Publication Date: 1974-Sep-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 7 page(s) / 185K

Publishing Venue

IBM

Related People

Dillinger, JR: AUTHOR [+3]

Abstract

Reading of magnetic data written on the magnetic stripe of a strip of tickets 10 (Fig. 12) passing across a write head 66 (Fig. 11) and then across a read head 68, is used to verify magnetic encoding on the tickets as they are made. The circuitry may also be used to enter data to a connected system from the tickets 10 being processed. The read circuitry recognizes level transitions of the "read signal" from read head 68, and counts the number of strobes or clock signals from a read emitter 12 between transitions in the same direction. This eliminates the effects of phase shifting in amplifier 14. Additionally, the customer engineer or repairman can reduce the tolerance on acceptable read strobe counts, to provide quicker identification of a machine which is only marginally reading.

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Variable Tolerance Magnetic Read Circuitry Insensitive to Amplifier Phase Shifting

Reading of magnetic data written on the magnetic stripe of a strip of tickets 10 (Fig. 12) passing across a write head 66 (Fig. 11) and then across a read head 68, is used to verify magnetic encoding on the tickets as they are made. The circuitry may also be used to enter data to a connected system from the tickets 10 being processed. The read circuitry recognizes level transitions of the "read signal" from read head 68, and counts the number of strobes or clock signals from a read emitter 12 between transitions in the same direction. This eliminates the effects of phase shifting in amplifier 14. Additionally, the customer engineer or repairman can reduce the tolerance on acceptable read strobe counts, to provide quicker identification of a machine which is only marginally reading.

Figs. 8 and 9 illustrate generally the operation of the read circuitry. The read head output (amplifier input) is shown on curve 21 of Fig. 8, and the read signal (output of amplifier 14) is shown in curves 23 and 25 assuming two different switching levels A and B of amplifier 14. These may be at either a plus voltage level or at a minus voltage level. If the threshold switching level of the read signal (output of amplifier 14) is at voltage A, the transitions are shown by curve 25, while if the threshold switching level is at voltage B, the transitions are indicated by curve 23.

The difference between curves 23 and 25 is caused by amplifier phase shifting. Obviously, the up level of curve 25 is considerably longer than the up level of curve 23. Nevertheless, the time between the transitions from 0 to 1 of curve 25 (indicated by Y) is the same as the time between the same transitions for curve 23 (also indicated as Y). Likewise, the time between successive transitions from 1 to 0 in curve 23 and in curve 25 are also the same (both indicated by Z).

Thus, the effect of phase shifting has been eliminated by the read circuitry, since amplifier 14 has a constant threshold level at which switching takes place during the time a single ticket 10 passes over read head 68. A given amplifier 14 will have a switching level somewhere between A and B, depending upon variations in the amplifier components.

A zero character, for example, determined from the read signal from amplifier 14 may be indicated by four successive overlapping medium size gaps. These gaps may be determined by 0 to 1 transitions as shown initially in curve portion 27a of Fig. 9, or they may be determined by 1 to 0 transitions as shown by curve portion 27b. Other characters are indicated by long, medium and short gaps. The 3 character, for example, may be indicated by a long gap, a succeeding medium gap, and then two succeeding short gaps as is shown by curve portion 27c.

A short gap consists nominally of 16 50-microsecond emitter counts; a medium gap consists nominally of 24 emitter counts, and a long gap consists ...