Patent GB-633127-A (GB)
Title: Improvements in electrical measuring apparatus
IPC: H03F3/40
Filed: 1946-03-07
Abstract: 633,127. Automatic temperature control systems. KENT, Ltd., G., and MEDLOCK, R. S. March 7, 1946, No. 7215. [Class 38 (iv)] [Also in Groups XXXVI and XXXVIII] Apparatus for producing an indication or a control in accordance with the magnitude of a quantity to be indicated, detected or controlled comprises an oscillator generating a frequency f which is alternately damped to extinction and supplied with an electric potential corresponding to the quantity, the frequency of alternation being <#, so that the oscillator develops trains of pulses of increasing amplitude, the level from which each train starts being determined by the magnitude of the quantity. Measuring magnitude and sign of voltage.- Valve V1, Fig. 1, is connected to generate oscillations when contact 2 is opened, the values of condenser C2 and resistance R2 being such that the amplitude of oscillation increases slowly. Contact 2 is opened for short periods at a frequency less than the frequency of oscillation of VI. If a potential difference exists between the thermocouple TC and the tapping of potentiometer S1, the opening of contact 2 results in a pulse in winding L1 which starts V1 oscillating at an amplitude related to the magnitude of the pulse, the oscillations increasing in amplitude until the closure of the contact 2 stops V1 oscillating. Thus, the output of V1 consists of trains of pulses whose mean amplitude is related to the potential of TC and which are applied to an indicator 4, e.g. a rectifier type of moving-coil instrument. The phase of the oscillations generated by V1 when the potential due to TC is greater than that due to S1 will be 180 degrees different to the phase when the potential due to S1 is greater than that due to Tc, and in Fig. 2 this is utilized to indicate the sign of the potential difference between S1 and TC; a further oscillator V2, identical with V1 but controlled by a constant source E, is interrupted synchronously with V1 at contact 2 and the outputs of V1 and V2 are applied to a dynamometer or induction instrument I of the centre zero type, whose deflection indicates sign and magnitude of the potential difference between S1 and TC. The outputs of V1, V2 may be applied to the windings of an induction motor controlling the tapping on the potentiometer, so 'that the potential of S1 and TC is automatically equalized and the position of the tapping is a measure of the potential developed by TC, Fig. 3, not shown. In such an arrangement, anti-hunting can be effected by connecting a generator to be driven by the motor, and feeding its output back in series opposition to the out-of-balance voltage from TC and S1. The thermocouple and potentiometer may be replaced by an A.C. bridge whose A.C. out-ofbalance current is to be measured, Figs. 4, 4A, not shown. Controlling.-In the arrangement of Fig. 5, the sign of the potential difference between S1 and TC determines the direction of energization of differential relay 3; 4 which can control the heat supplied to the furnace whose temperature is being measured by TC. A multivibrator V1 feeds two thyratrons V2, V3 energized with A.C., which also energizes relay 5 operating contacts 2 in the input circuit of the multivibrator VI; when contact 2 is opened, a pulse is applied to multi-vibrator V1 of sign according to whether the potential of TC is greater or less than that of potentiometer P; the phase of the oscillation developed by V1 is thus determined by the potential of TC and determines which of thyratrons V2, V3 fires to energize relay 3; the ignited thyratron is rendered non-conducting by the reversal of the A.C. on the anode in synchronism with the closing of contact 2, so that the other thyratron fires only when the potential difference between P and TC changes sign.