Improvements relating to supervisory circuit arrangements

1,068,027. Tunnel diode switch circuits. ASSOCIATED ELECTRICAL INDUSTRIES Ltd. Feb. 11, 1964 [April 11, 1963], No. 14616/63. HeadingH3T. [Also in Division H2] A supervisory circuit for monitoring a voltage E comprises a resistor R, an inductor L and a tunnel diode D arranged so that the " load line " of the circuit intersects the region of negative resistance of the tunnel diode voltage/current characteristic only when the monitored voltage is within predetermined limits and the supervisory circuit itself is free from fault. Thus under normal conditions an oscillation is produced across the diode, this being applied through an amplifier AMP, capacitor C and rectifier RE to a relay RA which is maintained energized until the oscillation voltage ceases. An emitter follower transistor may be interposed between the supervisory circuit and the circuit having the voltage to be monitored so as to present a high impedance to the latter circuit, Fig. 3 (not shown).