Patent GB-630670-A (GB)
Title: Improvements in measuring and controlling apparatus
IPC: H03C3/09
Filed: 1945-06-07
Abstract: 630,670. Automatic control of frequency. BROWN INSTRUMENT CO. June 7, 1945, No. 14445. Convention date, May 26, 1944. [Class 38 (iv)] [Also in Group XXXVIII] Frequency sensitive electrical apparatus comprises a high-frequency generator the output from which is interrupted at a regular relatively low frequency before being applied to a discriminator, so that the discriminator output is an oscillation at the said L.F. having a magnitude and phase sense corresponding to the magnitude and sense of the difference between the generated H.F. and that to which the discriminator is tuned. As shown in Fig. 1, for indicating, recording and, or, controlling the fluid flow in a pipe 1, variations in the flow act through a manometer 2 to vary correspondingly a condenser 3 to detune an electronic oscillator 4 associated with a frequency discriminator whereby a motor 5 is driven in accordance with the sense and magnitude of the oscillator frequency deviation, and, through gearing 25, 26 a spring-tensioned cord 30 and drum 34, adjusts a condenser 6 to retune the oscillator when the motor comes to rest. The angular position of the gear 26 thus corresponds to the fluid flow which may be indicated by a pointer driven by gear 26. In addition the gear 26 may drive through gear 40 and a sector plate 41 an arm 43 carrying a pen which records the flow on a time driven chart 44. The gear sector 41 also operates an arm 45 which through a pneumatic device 46, 48, as described in U.S.A. Specification 2,125,081 adjusts through a pneumatic motor 52 a valve 53 for maintaining the fluid flow in pipe 1, constant. The angular movement of gear 26 is limited in either direction by a projection 28 thereon, and the plates of condenser 6 may be shaped to give a linear record or indication of fluid-flow. Electronic control, Fig. 2. The condensers 3, 6 are both arranged in the parallel tuned grid circuit of oscillator 54 the H.F. output of which is interrupted at low frequency, for example, by connecting the screen-grid 79 directly to the secondary 65 of the 60 cycle mains transformer 58. The oscillator delivers output to the discriminator 55 only during alternate half cycles of the mains supply, the output during these alternations being substantially constant. To ensure that the modulation envelope more closely approaches a square wave a gaseous discharge tube 90 may be connected by switch 93 across the oscillator screen-grid and cathode. The oscillator output is, in known manner, coupled inductively and capacitatively to the discriminator 55 which delivers a D.C. control voltage output across the diode load resistors 104, 105, pulsating at mains frequency and of magnitude and sense dependent on the magnitude and sense of the frequency deviation of oscillator 54 from that of the resonant frequency of the discriminating parallel tuned circuit 101, 102, 114. The discriminator output is fed through an amplifier and limiter 56 and power amplifier 57 to the control winding 24 of the induction motor 5 the other winding 23 of which is fed directly from the supply mains 61. The motor circuit arrangement described in Specification 568,204 is such that both windings 23, 24 take current but the rotor is electrically braked to a standstill for zero output from the discriminator and is rotated in a corrective sense when condenser 3 detunes the oscillator until the motor driven condenser 6 retunes the oscillator. The datum fluid flow may be adjusted by means .of a variable condenser 86 in the tuned grid circuit of the oscillator. Modifications. The detuning and, or, retuning of the oscillator 54 may be effected, alternatively, by variable inductances having iron-dust cores or combinations of inductive and capacity reactances. The detuning and retuning means may operate on separate moving plates of the same condenser 3, Fig. 8 (not shown), particularly for torque amplifying applications of the invention, or on separate iron cores in the same tuning coil 85, Fig. 7 (not shown). Where the recording, indicating and retuning means is located remote from the manometer and detuning means 3, the latter may, for short distances, be connected in the oscillator circuit of Fig. 2 by concentric line, Fig. 9 (not shown). For greater distances the fluid flow or other variable to be indicated or recorded detunes an adjacent oscillator such as 54 which however is not modulated as in Fig. 2. The variable H.F. so produced is transmitted by land line, Fig. 11 (not shown), or by radio to the receiver where the signal is amplified and amplitude modulated at mains frequency as in the Fig. 2 arrangement and then fed to the discriminator. The motor 5 functions as before to drive an indicator and recorder and also operates to retune the discriminator resonant circuit to the incoming frequency, e.g. by adjusting the condenser 114 of Fig. 2, or some other frequency determining parameter(s). In another modification, Fig. 14 (not shown), the oscillator frequency is maintained constant but amplitude modulated at L.F. as in Fig. 2, the variable to be indicated detuning the discriminator resonant circuit, e.g. by varying a condenser such as 114 of Fig. 2 and the motor 5 operates to retune this circuit, e.g. by adjusting a further condenser. Other frequency determining parameters, Figs. 15 to 19 (not shown), may however be varied for detuning and retuning. In a further modification, Fig. 20, two similar oscillators 54a, 54b are employed. The frequency of oscillator 54a only is varied by the fluid flow or other variable and the outputs of the two oscillators are connected alternately to the discriminator 55a by a vibratory interrupter 178 operated at mains frequency. During the mains alternations when constant frequency oscillator 54b is connected to the discriminator, the output of the latter is zero. During the other alternations when oscillator 54a is connected thereto the discriminator yields a D.C. pulsating output corresponding to the variable being measured or controlled and functions-to effect retuning of the oscillator 54a by motor 5 as in the Fig. 2 arrangement. The invention is applicable to the remote indicating and recording of temperature, pressure, liquid level, and to boat steering, telemetering or repeater positioning. U.S.A.Specification 2,423,524 also is referred to.