Electrical transmission or interconnection systems – Switching systems – Condition responsive
Reexamination Certificate
1998-02-02
2001-03-13
Fleming, Fritz (Department: 2836)
Electrical transmission or interconnection systems
Switching systems
Condition responsive
C307S130000, C307S125000
Reexamination Certificate
active
06201320
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to power supply circuits, and in particular to an automatic power turn-on circuit for a battery-powered voltage measurement apparatus.
Conventional battery-powered voltage measuring instruments, such as voltmeters and the like, typically have power switches that connect and disconnect internal batteries to and from measurement processing circuits in order for them to operate and display the measurement. Typically associated with this type of instrument is a pair of test leads, one for providing a common reference such as ground, and the other for receiving the voltage to be measured. An operator must first turn the power on and then touch the test leads to desired points in the electrical circuit being measured. Of course, all the time that the instrument is turned on, the batteries are draining. If the instrument is left on for an extended period of time without making measurements, or if the instrument is unintentionally left on, battery life is shortened appreciably.
Continuity checkers are known in the art that are powered by a circuit under test and do no more than energize an indicator light. Another prior art approach is that of the type that is taught in U.S. Pat. No. 3,919,631, which discloses a battery-powered leadless probe that detects the presence of voltage by means of a sensor or conductive tip connected to an electronic switch that connects a battery to a light bulb. These prior art devices merely indicate that a voltage is present, and turn off as soon as they are removed from the voltage field.
It would be desirable to provide a battery-powered apparatus capable of automatically turning on in order to provide measurement or indication of a number of different voltages over a predetermined voltage range. Moreover, it would be desirable to provide a battery-powered apparatus that would remain turned on for a predetermined time period following a voltage measurement so that a series of measurements could be made without the apparatus turning on and off for each measurement.
SUMMARY OF THE INVENTION
In accordance with the present invention, an automatic power turn-on circuit is provided for a battery-powered measurement instrument. Instrument power is normally off, conserving the power of an internal battery. When the input leads of the instrument are connected to a voltage potential to be measured or verified, or even when the input leads are touched together, the voltage potenial that is sensed thereby activates an electronic switch that in turn connects the battery power to the processing and display circuits of the instrument. The voltage sense circuitry includes circuits for sensing potentials of either a positive or a negative polarity, or ground, and biasing a driver transistor into conduction. The driver transistor in turn activates the switch to connect the battery voltage to a power supply output node. An RC network holds the switch in the “on” position for a short period of time after the voltage potential to be measured or verified is removed from the inputs of the instrument.
It is therefore one object of the present invention to provide an automatic power turn-on circuit for a battery powered measurement instrument.
It is another object to provide a measurement instrument that automatically turns on when its inputs are connected to a voltage potential to be measured or verified.
Other objects, features, and advantages of the present invention will become obvious to those having ordinary skill in the art upon a reading of the following description when taken in conjunction with the accompanying drawings.
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Fleming Fritz
Fluke Corporation
Noe Goege T.
LandOfFree
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