Patent GB-769431-A (GB)
Title: Improvements in or relating to electric computing apparatus
Inventor: HAMBLIN CHARLES LEONARD
IPC: G06G7/186
Filed: 1953-10-13
Abstract: 769,431. Tracking systems. GENERAL ELECTRIC CO., Ltd. Oct. 6, 1954 [Oct. 13, 1953], No. 28170/53. Class 40(7) Relates to a manually controlled " rate aided " tracking device for maintaining an index coincident with a moving object, e.g. an echo image on the screen of a C.R.T., in which the position of the index is directly proportional to the voltage output from terminal 19 of an integrating amplifier 1, Fig. 1, having a feedback capacitor 2, the input voltage V to the amplifier 1 being applied through a parallel R.C. network 6 of time constant t<SP>1</SP> so that when V is constant the velocity of the index is proportional thereto but when V is changed by an amount SV then the position of the index changes by an amount proportional to SV. When applied to radar range tracking the final value of V indicates the target velocity but such indication is subject to a time-lag of the order of t<SP>1</SP> which may be as great as 20 secs. when smooth tracking is required and according to the present invention such time lag is reduced by making the input voltage V=b Vo(1-e <SP>t/t1</SP>)where Vo is constant and b is an adjustable parameter. As shown in Fig. 1 the apparatus includes a three-pole double-throw switch 3 and the input to network 6 is applied from the slider 9 of a potentiometer 10 in the output of an integrating amplifier 12 having a parallel R.C. feedback network 13, 14 of time constant t<SP>1</SP>, a stabilized voltage Vo being applied through resistor 16 to the input of amplifier 12. When switch 3 is OF, amplifier 12 is short circuited and feedback capacitor 2 and network 6 are disconnected from the input, of amplifier 1 which then functions as a linear amplifier with resistance feedback 4 so that the output from terminal 19 is directly proportional to the setting of slider 18 of potentiometer 5 which is adjusted to align the index roughly with the image. The slider 9 of potentiometer 10 is initially set at earth potential. Switch 3 is then turned ON thereby causing amplifiers 1 and 12 to function as integrators and the voltage V at the slider 9 of potentiometer 10 is then equal to b Vo(1-e<SP>t/t1</SP>) where b depends on the setting of slider 9. In a modification, Fig. 2, a voltage b Vo is applied across potentiometer 10 and when switch 3 is turned ON the slider 9 of potentiometer 10 is moved upwards from earth to its maximum position by means of a D.C. motor 21 according to the time function (1-e<SP>-t1/t</SP> ). As shown the slider 9 of potentiometer 10 is ganged to the slider 26 of a potentiometer 27 which is connected through a capacitor 30 to the input of an amplifier 31 whose output controls motor 21 actuating sliders 9 and 26 such that when a resultant positive voltage is applied to the input of amplifier 31 the sliders are moved upwards. The top of potentiometer 27 is earthed and the bottom is connected to a positive voltage 28. When switch 3 is OFF the slider 26 of potentiometer 27 is connected to a negative voltage source 36 through two equal resistors 34, 35 whose junction is connected to the input of amplifier 31 and motor 21 then moves the sliders 9 and 27 down until the voltage input to amplifier 31 is zero, the constants being such that slider 9 is then at the earthed terminal of potentiometer 10. When switch 3 is turned ON the input of amplifier 31 is disconnected from the negative source 36 and resistor 29 is connected in parallel with capacitor 30 (time constant of network 29, 30 = t<SP>1</SP>) so that motor 21 then moves the sliders 9 and 26 up to the top terminals of potentiometers 10 and 27 respectively according to the required time function (1-e<SP>-t1/t1</SP>). The value of b is determined by the setting of potentiometer 25. When 'applied to tracking a target image on a P.P.I. display separate amplifiers 1 and potentiometers 10 are provided to control the N-S and E-W components of the index position. If the Fig. 2 embodiment is employed a single potentiometer 25 is used and its output is applied in push-pull to opposite ends of a sine-cosine potentiometer whose setting is controlled by a target course control, the resolved outputs being applied respectively to the separate potentiometers 10.