Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – Frequency of cyclic current or voltage
Patent
1974-12-16
1976-02-17
Smith, Alfred E.
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
Frequency of cyclic current or voltage
340214, G01R 3122
Patent
active
039393984
ABSTRACT:
A circuit, having protection against current feedback when a component fails, for testing indicator lights whereby multiple lights may be tested simultaneously by pressing one pushbutton and closing one set of normally open contacts. The test pushbutton and the indicator signal operate at a higher voltage such as 120 volts AC and the indicator lamp is operated at a low voltage such as 6 volts, providing safety and allowing the use of inexpensive incandescent indicator bulbs. Only one indicator transformer is required for each indicator light. In one embodiment of the invention a pair of diodes are provided on the high voltage connection to indicator transformer to permit a test signal or a normal operating signal to activate the indicator bulb without affecting the rest of the circuit. A single common return line is used to provide a return line for the test circuit and the operating signal circuit. A transformer diode is connected across the primary of the indicator transformer, and fuses are disposed in series with each of the pair of diode provided on the high voltage side connection to the indicator transformer. When a signal diode or a test diode failure occurs a surge of current flows through the transformer diode and blows the appropriate fuse. The fuse blowing isolates the test circuit from the signal circuit. In another embodiment of the invention a single fuse is provided in the signal line connection to the high voltage side of the indicator transformer. A Zener diode is also provided in series with the transformer diode in a back-to-back relationship. This allows kick back to flow in the primary winding of the transformer which is less than the Zener breakdown level. It is important to allow this inductive kick back to flow for two reasons. One is that transformed to the secondary, it contributes to overall greater brilliance in the lamp and; second is that it tends to demagnetize the iron in the transformer core. However, when either the test or signal diode fails, the potential rises to a value greater than the Zener breakdown level, across the Zener diode and transformer diode which conduct, blowing the associated fuse. This then isolates the test circuit from the signal circuit. The disclosed invention prevents a failure of the test or signal diode from adversely affecting other circuits connected to the signal lamp test circuit.
REFERENCES:
patent: 2839741 (1958-06-01), Kratville
patent: 3040243 (1962-06-01), Weiss
patent: 3840801 (1974-10-01), Kellogg et al.
Elchik W. A.
Hille Rolf
Smith Alfred E.
Westinghouse Electric Corporation
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