GB1261355A - Improvements in or relating to transfer function analysis - Google Patents

Abstract

1,261,355. Determining normalized phase slope. SOLARTRON ELECTRONIC GROUP Ltd. Sept.19, 1969 [Sept.20, 1968], No.44896/68. Heading G1U. To enable normalized phase slope to be determined at a given frequency for an apparatus such as a closed loop servo in whose transfer function high-frequency resonances may occur in regions of the response-frequency curve showing substantial attenuation, so that such resonances may be made more apparent a sinusoidal oscillation of frequency f is applied to the apparatus and a signal representing the phase angle # 1 between its response and the applied oscillation is derived. A second oscillation of frequency f Π#f is then applied, #f/f being a small predetermined ratio irrespective of f, and a signal representing the phase angle # 2 between the response and applied second oscillation is derived. The difference between # 1 and # 2 is then obtained. This enables a plot of normalized phase slope (# 1 -# 2 )f/#f against frequency to be prepared, which prominently indicates any resonances in the transfer function. The apparatus 12 to be tested may be coupled to a digital transfer function analyser 13 of the type described in Specification 1,074,624. At each frequency point to be tested, a start pulse is applied at 20 to a bi-stable 17 which is set to initiate a pulse from a generator 18 to cause the analyser 13 to operate to deliver a signal # 1 in digital form corresponding to the phase lag between a sinusoidal signal e.g. at frequency f applied by the analyser to the apparatus under test and the output from the apparatus. This signal is held in a store 14. When the analyser has completed operation, it delivers a reset pulse to the bi-stable 17, which energizes a frequency shift circuit 19 to deliver a control signal to the transfer function analyser to adjust the test by an amount #f in a predetermined proportion #f/f, and also initiates a further pulse from the generator 18 to cause the analyser to operate again. The analyser operation is repeated and a second phase signal # 2 is delivered. This is subtracted from the stored value of # 1 , and the difference signal converted to radian measure and displayed at 16. A plot of such difference against frequency provides a response curve clearly indicating any resonances even if they are masked in the normal transfer function by heavy attenuation.