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Magnetic Head Baseline Shift Automatic Measurement Technique

IP.com Disclosure Number: IPCOM000090809D
Original Publication Date: 1969-Jul-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 3 page(s) / 46K

Publishing Venue

IBM

Related People

Lucero, JC: AUTHOR [+2]

Abstract

The baseline shift of a read-back signal 10 induced in read head 11 associated with a magnetic tape, not shown, is measured. The period of signals 10 is shown as Tx, indicating that the period can be varied for the tester. In other words, various frequencies of recordings can be utilized in the tester for testing a variety of magnetic reproducing heads. The period is defined as the elapsed time between two successive signal peaks in the read-back signal of like polarity, that is, between two successive positive peaks or two successive negative peaks. Baseline shift is determined from clamped read-back signal 12 supplied from clamp circuit 13.

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Magnetic Head Baseline Shift Automatic Measurement Technique

The baseline shift of a read-back signal 10 induced in read head 11 associated with a magnetic tape, not shown, is measured. The period of signals 10 is shown as Tx, indicating that the period can be varied for the tester. In other words, various frequencies of recordings can be utilized in the tester for testing a variety of magnetic reproducing heads. The period is defined as the elapsed time between two successive signal peaks in the read-back signal of like polarity, that is, between two successive positive peaks or two successive negative peaks. Baseline shift is determined from clamped read-back signal 12 supplied from clamp circuit 13. Clamping facilitates making measurements by raising both segments of the baseline above reference level, thus removing the ambiguity caused by both baselines being less than the reference level. Baseline shift is defined as the ratio of a voltage difference Vb of two successive flattened portions of signal 12 between two successively occurring like-polarity signal peaks and the peak-to-peak voltage Vp.

The system is controlled by a program in computer 14. Data and control signals are exchanged between computer 14 and control logic and computer interface unit 14B over cable 14A. Unit 14B contains an instruction register for receiving operation instructions from computer 14 Logic circuits in unit 14B are responsive to received instructions to sequence the tester operations. Necessary interfacing circuits, including buffer registers are also included in unit 14B.

During a first pass of the tape past the read head, the peak-to-peak voltage amplitude Vp is measured and stored in computer 14. Unit 14B supplies an activating signal over line 15 to peak-to-peak amplitude detection circuit 16. This supplies an analog peak-to-peak voltage to A-D converter 17 which digitizes the amplitude for supply to computer 14.

The intermediate voltages indicated by samples 18 and 19 are then successively measured during second and third passes of the tape past the read head. The time or strobe samples 18 always occur after a positive peak and are first measured and digitized for computer 14. Positive peak time detector 20 generates rectangular signals 21. These have positive transitions in time coincidence with the positive peaks and negative transitions in time coincidence with the negative peaks. And 22 is opened by a signal supplied during the entire sample 18 measurement period over line 23 from unit 14B. Square wave 21 is supplied through Or 24 to actuate one of a plurality of strobe generating channels
25. One of these is selected by activating signals supplied by unit 14B over cable 26 to the plurality of gates 27. One, and only one, channel 25 is activated at a given time.

Each channel is used for a different frequency of recording. For example, channel 25 labeled T1 is used for measuring baseline shift in a magnetic head caused by a signal having...