Short circuit protection device for electrical apparatus - measures internal resistance of circuit using transistors in circuit with phototransistors

摘要

Circuits of this type have particular application in the flame control of boilers. The internal resistance of the circuit is dependent upon external influences and the internal voltage drop is measured by a detector which in turn operates on the external controls and can eliminate voltage reductions caused by the external control circuits. For example in a flame control device for a boiler phototransistors are influenced by flame brightness and the emitter-collector voltage is measured by a monitor. Increasing brightness reduces the emitter-collector voltage to a point where the detector signals the fuel control (R11) to take corrective action.