GB972702A - Improvements in or relating to transistor switching devices - Google Patents

Abstract

972,702. Measuring temperature. BAILEY METERS & CONTROLS Ltd. May 17, 1961 [May 23, 1960], No. 18053/60. Heading G1N. [Also in Divisions G4, H2, H3 and H4] A switching circuit (see Divisions H3 and H4) is used in and electronic commutator circuit for connecting each of a plurality of thermocouples in turn to a load and provision is made for stopping the commutating action and connecting any selected thermocouple to the load. In Fig. 1 the thermocouples 1 are connected in series with reference voltages 2 to a common output line labelled "switched output" in succession by rendering the corresponding pairs of silicon transistors 3, 4 conducting. This may be effected by bringing into operation successively one at a time the oscillators 9 and feeding their output either directly or through a rectifier circuit 5, 6 to the corresponding transistors 3 and 4. The oscillators are of a type which upon receipt of a triggering pulse will commence operation and remain so until switched off by a quenching pulse and will remain off until retriggered into the operating condition. Quenching pulses are supplied from a common oscillator 10 in parallel to each oscillator 9 so that the operative oscillator is switched off. The resulting surge in the collector current produces a pulse which is fed to the next oscillator to initiate operation and this continues until the next quenching pulse occurs when this switches off and the next is switched on so causing the oscillation state to switch round the ring of oscillators. An individual circuit may be brought into operation by operating a switch 12. This disconnects the quenching supply from the selected oscillator and connects instead a negative voltage which brings the oscillator into operation. A further contact on the switch interrupts the quenching supply to the other oscillators. In an alternative embodiment (Fig. 5, not shown) operation of a selecting button 12 causes the repetition frequency of the quenching pulses from source 10 to increase so that the circuit rapidly switches round to the selected oscillator. A rectified output of this oscillator is connected through a further contact of switch 12 to a transistor which short circuits the supply of quenching pulses so that the circuit remains switched to this condition. In a further embodiment (Fig. 6, not shown) each oscillator is replaced by a pair of cross coupled transistors forming a bi-stable circuit and outputs from the bi-stable circuits are connected to gating transistors which connect a common oscillating source to the appropriate one of the transistors 3, 4 of Fig. 1.