Patent GB-1111331-A (GB)
Title: Correlation of variables
Inventor: LERWILL WILLIAM EDWARD
IPC: G06G7/19
Filed: 1964-04-24
Abstract: 1,111,331. Correlation techniques. SEISMOGRAPH SERVICE (ENGLAND) Ltd. April 23, 1965 [April 24, 1964], No.17061/64. Heading G1U. An apparatus for correlating two variables comprises at least one transducer 3 of extended length having a member formed of magneto-resistive material extending along it, and arrangements for producing two magnetic fields, at least one of which may be caused to travel along the transducer, which extend through the magneto-resistive material, variations in the fields along the transducer representing the variables to be correlated. A signal is derived, from circuits including the transducer, which represents a correlation of the two variables. The arrangements for producing the two magnetic fields comprise endless magnetic tapes 1 and 2 upon which the signals are recorded via the heads 8 and 9. The tape 1 is moved so that the signal recorded on it overlies the transducer 3 and stopped. The tape 2 travels across it, the tapes having their oxide coatings adjacent. At any given position adjacent the transducer 3, the magnetic induction permeating an element of the magneto-resistive strip is where g(x) and r(x) represent the functions to be correlated, x being a distance along the magnetic tapes, while # represents the instantaneous displacement of one tape relative to the other. The fractional change in the resistance of the magneto-resistive material is related to the square of the magnetic induction, i. e. where R is the resistance of the material and M is the coefficient of magneto-resistance. Hence over the entire length of the magneto-resistive head the fractional change in resistance is The final term in this expression is proportional to the desired cross correlation function, the first term is proportional to the energy in the first signal within the integration interval, which is constant, and the second term is proportional to the energy in the second signal, which is constant with a superimposed ripple representing the difference in the part of the signal just entering the integration interval and the part just leaving it. The ripple is small and may usually be neglected. The fractional changes in resistance are detected using a Wheatstone bridge arrangement, the bridge output being passed to an amplifier 16a. By using capacitive coupling in the amplifier the constant terms may be eliminated, and the amplifier output gives the required correlation function. The constant and ripple voltages may be eliminated by using a transducing head having two separate resistive strips and using tapes having two corresponding tracks. On one of the tapes the same signal is recorded on both tracks, but on the other the appropriate signal is recorded normally on one track and inversely on the other. Thus the induction which affects one magneto-resistive strip is proportional to the sum of the two signals while that affecting the other strip is proportional to their difference. By subtracting the output of one magneto-resistive transducing head from the output of the other, a signal proportional only to the correlation function is derived. The transducing heads are made from a magnetic material which is a high permeability, high resistivity magnetic ceramic, on which magnetoresistive strips of indium antimonide are mounted.