Patent GB-1163441-A (GB)
Title: Method and Apparatus for Analysing Time Dependent Functions
Inventor: KAISER NIELS EDMUND GULDBAEK
IPC: G06G7/00
Filed: 1966-08-26
Abstract: 1,163,441. Reverse correlation. N. E. G. KAISER. Aug. 26, 1966 [Aug. 26, 1965], No.38347/66. Heading G1U. [Also in Divisions G3 and G4] In an apparatus for detecting periodicity in two time varying functions (possibly identical), f 1  (t) and f 2  (t), representing a single physical quantity, the functions being represented in or on an information carrier or recorded in a store, a time window, comprising a scanning arrangement relative to which a function to be scanned is moved, is established, the time for which any particular value in the function is scanned being determined by the dimensions of the arrangement and the rate of movement, and the functions (or their representations) are moved relative to the window in such a way that the values of the respective functions which correspond to the same time instant are displaced by equal amounts to opposite sides of the centre of the window, the values of the respective functions which appear at the same positions in the window being simultaneously or sequentially multiplied and simultaneously or sequentially integrated. The apparatus carries out "reverse correlation", i. e. the evaluation of the integral by determining the integral The function γ(t) indicates periodicity in f(t), and # represents delay between the two multiplied functions to a maximum # max . Fig. 1 illustrates the application of equation (2). The two functions to be reverse correlated are recorded (at 1 and 4) on tapes moving in opposite directions past a window defined by the distance L between the recording arrangements. The values recorded at any particular instant lie by equal amounts to opposite sides of the centre line of the window. Relative to the centre line of the window they correspond to Œ # respectively. All such values are multiplied and summed to provide a function related to the reverse correlation integral. In a hybrid computer system for determining the reverse correlation function, Fig. 2 values of an input function are received at 7, converted to digital form at 8 and entered serially into a store 9. The store is read out from each end in opposite directions on instructions from a programme unit 10 and the results stored in positive and backward decoder registers 11a, 11b respectively. The outputs from these at each instant pass through digital analogue converters and delays 12a, 12b to a multiplier 13. The output from this passes via a regulating link 14 and filter 15 to an integrator connected at 16. Other arrangements may be of optical type in which light is passed through a carrier on which information is represented by different degrees of transparency and reflected back through the carrier in inverted form. Alternatively a light beam may be passed through two carriers moving in opposite directions. The resulting double modulated signals are received and integrated by suitable photo-cell arrangements. Two liquid filled tubes may be vibrated in accordance with the two functions to produce measurable capacitive or resistive changes in the medium between the tubes Fig. 6 (not shown). Magnetic tapes may be moved in opposite directions in juxta-position and their interaction detected by the induced effects in an adjacent wire Fig. 7 (not shown). In pneumatic arrangements, a string may be vibrated in accordance with one function close to an orifice through which air subjected to pressure changes representing the other function is pumped, or alternatively the string may be vibrated in accordance with both functions, one in each of vibrational planes at right angles, while the air pressure is not modulated. In a completely pneumatic arrangement air is streamed through an aperture at a pressure modulated in accordance with one function past orifices to which air streams modulated in accordance with the other function are applied, so that a double modulated stream is eventually obtained.