Patent GB-836822-A (GB)
Title: Improvements in or relating to cyclic telemetering systems
IPC: G08C15/10
Filed: 1956-08-30
Abstract: 836,822. Electric correspondence control. COMPAGNIE POUR LA FABRICATION DES COMPTEURS ET MATERIEL D'USINES A GAZ. Aug. 30, 1956 [Sept. 6, 1955], No. 26512/56. Class 40 (1). In a time-multiplexed telemetering system the transmitter includes a magnetic amplifier AM for each measurement channel, these amplifiers being energized sequentially by a distributer D which energizes them with alternating current of frequency Fm, the output of the magnetic amplifiers being applied to an oscillator OFM to frequency - modulate it. As shown in Fig. 1, the measurements to be transmitted are converted to direct current amplitudemodulated signals by converters C1, C2 ... Cn. These direct currents are applied to the magnetic amplifiers AM1, AM2... AMn, where they are converted to amplitude-modulated alternating current signals having the same frequency as the alternating current supplied to the magnetic amplifiers by the distributer D when it energizes them. The outputs of the magnetic amplifiers are paralleled and after amplification in a variable-gain amplifier A1 are applied to a modulator M1 which is supplied with a phase reference signal of the same frequency as that supplied to the distributer D. In the modulator, the signals are converted to amplitudemodulated D.C. signals, the sign of which corresponds to their original sign and these signals after amplification by a magnetic amplifier MMg are applied to the oscillator OFM to vary its frequency. The frequency-modulated signals from the oscillator OFM are amplified by an amplifier E and then transmitted over a line L. The distributer D consists of a ring of bi-stable multivibrators, only one of which at any time is in the state for energizing the corresponding magnetic amplifier AM. The multivibrators are switched successively by synchronizing signals from a multivibrator or blocking oscillator generator SG and these signals are also applied to the power amplifier E to cut it off so that no signals are sent to line during the period of the synchronizing signals. The distributer has two more sections n+1 and n+2 than those required for the measurement channels. The n+1 section supplies alternating current to a bridge comparator CMo which once per cycle adjusts the frequency of the oscillator OFM so that its unmodulated frequency bears a fixed relation to the frequency of a fixed frequency reference oscillator Fo. The comparator CMo comprises two transformers, the secondaries of which form adjacent bridge arms and two equal resistors forming the other bridge arms. The primary of one of the transformers and the amplifier A1 are fed with a D.C. reference current Io derived from a reference converter and magnetic amplifiers (not shown) which determines the base frequency of the oscillator OFM and the primary of the other transformer is fed with a D.C. current from a converter Ca, the amplitude of which depends upon the difference in frequency between the base frequency of the oscillator OFM and the fixed frequency of the oscillator Fo, both of which are fed to the converter. The two D.C. currents change the inductances of the two bridge arms and if they are different unbalance the bridge. The error signal from the bridge is an alternating current signal and after amplification in an amplifier A2 this is applied to a modulator M2 which is fed from the distributer section n+1 with a phase reference signal of the same frequency and which converts the error signal into a D.C. voltage, the amplitude of which corresponds to that of the original error signal and the sign upon whether the error signal was in phase with or out of phase with the reference signal. This D.C. voltage charges a condenser K1 in the grid circuit of the oscillator OFM and adjusts its frequency until the error signal is reduced to zero; the charge on the condenser keeps the base frequency of the oscillator substantially constant during the part of the cycle that the comparator CMo is not in circuit. The section n+2 of the distributer controls a comparator CMmax which is identical with the comparator CMo and which determines the maximum frequency deviation of the oscillator OFM. It does this by comparing a current Imax which determines the maximum frequency deviation with the current produced by the auxiliary converter Ca; the current Imax is derived from a reference converter and magnetic amplifiers (not shown) and is also fed to the amplifier A1 ; the error signal after amplification by the amplifier A2 and conversion to D.C. in a modulator M3 is applied to a condenser K2 in the grid circuit of the amplifier A1 to vary its gain. When the distributer reaches the section n+1 it initiates a cycle conclusion signal from a trigger circuit CC which is terminated by the passage of the distributer from stage n+2 to stage 1. This signal cuts off the amplifier E for a sufficient time to suppress the n+2 synchronizing signal so that the synchronizing signals sent to the line consist of a number of short synchronizing signals corresponding to the number of measurement channels and a long synchronizing signal which indicates the end of each cycle. In the receiver, the line signals first pass through a filter F and then through a mixer-amplifier MF where they are mixed with the output of a local oscillator OR which is controlled so that it operates at the same frequency as the base frequency of the oscillator OFM in the transmitter. The difference frequency signals are applied in parallel to converters C<1>1, C<1>2 ... C<1>n, where they are converted into amplitude-modulated D.C. signals and after amplification in amplifiers A<1>1, A<1>2 ... A<1>n these signals are passed to indicating or recording devices. The converters are switched sequentially by a distributer D1 which consists of a ring of bi-stable multivibrators as in the transmitter but having only n+1 stages. The sections of the distributer are kept in synchronism with the corresponding sections in the transmitter by the synchronizing signals which are separated by circuits SFC and SPP for the section synchronizing signals and the cycle conclusion synchronizing signals respectively, the arrangement being such that the cycle cannot commence until the cycle conclusion synchronizing signal has been received which allows operation of the first section of the distributer. Control of the frequency of the local oscillator OR is carried out when the distributer reaches the n+1 stage. Difference frequency signals from the mixer MF are applied to a converter CR which applies a corresponding direct current to a secondary winding of a comparator CMR identical with those in the transmitter. A second secondary winding of the comparator is supplied with a direct current from a reference source RC which has the same value as Io in the transmitter. The comparator is only energized when the distributer reaches the n+1 section since one diagonal of the comparator bridge is fed with an alternating current of frequency Fm from an amplifier AR which is only energized when the distributer reaches the n+1 section. The error signal from the comparator is applied to a balanced modulator MR which adjusts the frequency of the oscillator OR until the oscillator is in synchronism with the oscillator OFM in the transmitter.