Patent GB-798181-A (GB)
Abstract: 798,181. Frequency and phase measurement. ENGLISH ELECTRIC CO. Oct. 14, 1955 [Oct. 15, 1954], No. 29757/54. Class 40 (5). An apparatus for measuring the frequency of an electrical input signal first generates a single pulse of fixed amplitude and of duration equal to the duration of a complete cycle of the input signal, and then integrates this pulse to provide an output signal having a strength proportional to the said duration. The apparatus also measures the phase between an alternating input signal and an alternating reference signal by generating a second pulse of fixed amplitude and of duration equal to the time interval between a particular event in the cycle of change of the input signal and a corresponding event in the cycle of change of the reference signal, integrating this second pulse to provide a signal having a strength proportional to said duration, and comparing the strength of this output signal with that of the output signal related to frequency. It is stated that the apparatus is suitable for measurements in the range 0.01 to 100 cycles per second. As shown in Figs. 1 and 2, the input signal 10, Fig. 2 (a), is amplified at 11 and supplied to a flip-flop 14 which supplies rectangular pulses, Fig. 2 (b), (c), which generate trigger pulses (d) for operating trigger 17 and trigger pulses (e) for operating triggers 15, 16. A signal (f), which is derived from a source 18 via a tapping key, is also applied to the trigger 15, the dotted line representing the instant at which the key is pressed. The output (g) from the trigger 15, which is only present when the key is depressed, is applied through a cathode follower 19 to the trigger 17 to produce output (h) which in turn is applied to trigger 16 to produce output (i). The step-waves (g) and (i) are combined to form a signal (j) of fixed amplitude and of duration equal to one complete period of the input signal, and applied to a Miller integrator 20 which provides an output (k) having a steady amplitude V proportional to the duration of a complete period. In order to provide a signal of voltage proportional to frequency, a voltage inversely proportional to the output (k) is required. The step-wave (i) is fed to a clamp circuit 21 and conditions a trigger 22 to produce pulses (1) of the frequency of a standard supply 23 which are supplied to a circuit 24 incorporating a transitron-Miller valve whose grid is fed by the voltage output from the integrator 20. The output (m) from circuit 24 consists of pulses having a duration which is inversely proportional to the steady voltage V which are passed through a circuit 25 to fix the amplitude of the pulses before the signal (m) is smoothed and its mean strength measured by a meter 26 to indicate the frequency. In measuring phase, a reference signal 12 is amplified at 13 and supplied to a flip-flop 27 producing a square wave output, Fig. 3 (d). Fig. 3 (a) and (b) shows the input 10 and reference 12 respectively, and Fig. 3 (c) shows the output from source 18 via cathode follower 19 when the key is depressed. Pulses (e) are derived from the waveform (d) and supplied to trigger 28 together with the output from cathode follower 19, which through cathode follower 29 provide a step-wave (f). The output from cathode follower 29 and the output (g) from trigger 16 are supplied to a Miller integrator 30, the circuit integrating a signal of waveform (h) to provide an output (i) resulting in a steady signal of strength v, the dotted line showing the corresponding output from the integrator 20. Fig. 3 (j) shows the output signal from circuit 24 which is amplitude modulated by the output from 30 in an amplifier unit 31 to provide an output (k), which, when steady, has pulses of regular amplitude proportion to v and of duration proportional to 1/V. The mean value of the output signal (k) is proportional to v/V and is measured by the meter 32 whereby an indication of the phase angle between the two waves (a) and (b) is obtained. The Specification includes a detailed circuit diagram giving component values.