GB1204525A - Improvements in or relating to power control systems - Google Patents

Abstract

1,204,525. Automatic temperature control systems. DIAMOND H CONTROLS Ltd. Oct.11, 1968 [Oct.13, 1967], No.46851/67. Heading G3R. [Also in Division H2] An arrangement for providing to a load, groups of half cycles corresponding in number to the magnitude of a variable parameter has a source of first pulses of constant amplitude which are modified in magnitude by a control element, a breakdown switch which transmits the modified pulses to a ramp generator, a chopper circuit also fed with the first pulses which provide second pulses of instantaneous value equal to the ramp voltage, and an output device which provides a pulse each time a second pulse exceeds a threshhold value. The parameter may be developed manually e.g. a potential divider or automatically e.g. from a temperature sensitive resistor or a tachogenerator representative of motor speed. Pulses from a full wave rectifier 1 are clipped by a circuit 3-7 and passed through a transistor 15 with unchanging amplitude, the output pulses from which are stabilized by a Zener diode 16 and passed to a potential divider comprising a temperature sensitive resistor 17, and a setting resist- or 18. When the potential at the junction of 17, 18 exceeds the break-over voltage of a device 21, a capacitor 22 charges to the junction potential, which charge passes through a diode 24 to another capacitor 25. The charge on capacitor 22 blocks the device 21 until the charge falls to a releasing value. Discharge of capacitor 22 through resistor 23 and capacitor 25 through resistors 26, 27 produce ramp signals, that from capacitor 25 being applied together with constant amplitude pulses to control electrodes of a transistor 28 which develops instantaneous pulses equal in height to the ramp voltage. When these are greater than a voltage developed across a resistor 31, a transistor 32 conducts to produce constant amplitude pulses in a thyristor firing transformer 33. As temperature sensitive resistor 17 receives pulses, its heat dissipation is less than that produced by a constant current. Resistor 23 varies the proportional band.