Patent GB-583792-A (GB)
Title: Improvements in or relating to the measurement of short intervals of time
IPC: G01S1/02
Filed: 1942-06-05
Abstract: 583,792. Radiolocation; cathode-ray oscillographs. COCKCROFT, J. D., and PLETTS, J. W. June 5, 1942, No. 7679. [Class 40 (v)] [Also in Group XXXVI] In apparatus for measuring short time intervals by comparing an exponential time base voltage with the voltage obtained from a potentiometer, particularly applicable to radiolocation systems, and of the type described in Specification 582,170, a resistance in series with the potentiometer is adapted to shift the time indicated by any setting of the potentiometer by more than the difference between the times indicated by extreme settings of the potentiometer, without introducing any change in the magnitude of this difference. In the application of such a range-measuring potentiometer of extended range to a radiolocation system, the need for the potentiometer wiper arm to return to the commencement of its travel each time the series resistance is varied, is overcome by providing two parallel paths a1, b1, c10, c11 and a2, b2, c20, c21. The potentiometer resistances b1 and b2 each covers a range difference of 950 yards in 50 yard steps, the contact 5 being connected to the deflecting plate 6 of the cathode-ray tube 4. The wiper 10 is geared to wiper 5 and is arranged to pass from one stud to the next to alter the value of resistance c21 while wiper 5 is traversing resistance b1 and to alter resistance' c11 while wiper 5 is traversing resistance b2. Resistances c10 and c11 together cover the range difference 2000-28,000 yards in 2000 yard steps, c10 being such that the voltage at the lower end of resistance b1 represents a range of 2000 yards when resistance c11 is short-circuited. Resistances c20, c21, together cover the range 3000-29,000 yards in 2000 yard steps, resistance c20 ensuring that the voltage on the upper end of resistance b2 represents a range of 3000 yards when resistance c21 is short-circuited. The time base voltage applied to plate 3 of the cathode may tube is developed across condenser 2, the valve 1 being made non-conducting on the occurrence of each transmitted pulse. The range of a particular echo pulse is determined by the setting of the potentiometer required to bring the echo pulse to the centre of the cathode-ray tube screen. To compensate for the potential drop across valve 1 when conducting, a value for the valve resistance is assumed and the values of resistances c10, c20 and the steps of resistances c11, c21 are calculated accordingly. Resistance c10 is split into two parts, the part 14 being chosen so that the voltage drop across it is equal to the anode voltage of valve 1 when conducting, this equality being ensured by adjustment of the valve resistance by potentiometer 17, or a variable anode resistance, until the origin of the cathode-ray tube trace is brought to the centre of the screen when switch 15 is closed and switch 16 in its lower position. A current limiter valve 18 is connected in series with the H.T. supply 19 to prevent excessive current at low range settings when the potentiometer resistance is reduced. In order to keep the deflecting plate 6 at approximately earth potential, a potentiometer comprising the constant current valve 21 and the cathode follower valve 20 is connected across the H.T. supply as described in Specification 582,170.