Electricity: measuring and testing – Conductor identification or location – Inaccessible
Reexamination Certificate
1998-07-24
2001-04-24
Oda, Christine (Department: 2862)
Electricity: measuring and testing
Conductor identification or location
Inaccessible
C324S326000, C324S424000
Reexamination Certificate
active
06222358
ABSTRACT:
DESCRIPTION
Technical Field
The present invention relates generally to AC power line testing equipment and, more particularly, to an AC power circuit identifying device. Specifically, the present invention is used to identify the circuit interrupter device associated with a particular power outlet receptacle, thereby performing a calibration process automatically.
BACKGROUND OF THE INVENTION
When work is performed on an electrical system in a building or facility, it is necessary to trace and identify which circuit interrupter device (e.g., circuit breaker or fuse) is supplying power to a particular power outlet receptacle or electrical component. Manual identification of the fuse or circuit breaker can be accomplished by removing each fuse or opening each circuit breaker, thereby disrupting the power flow through the circuit. Each outlet must subsequently be examined to determine whether the power to the outlet has been disconnected. This method is not only time consuming, but also may not be feasible in situations where it would be hazardous to interrupt the power flow to certain outlets, e.g., in a hospital or in an environment where computers are in use with no backup power.
Alternatively, a variety of circuit testers are available for identifying the fuse or circuit breaker that is supplying power to a particular outlet receptacle. These testers employ an assortment of techniques to distinguish one circuit breaker from the rest. For example, the testers disclosed in U.S. Pat. Nos. 4,906,93 8 and 5,497,094 use a relaxation oscillator to apply an identification signal comprising a large amplitude current pulse of very short duration to the circuit. A schematic diagram of the transmitter
10
disclosed in U.S. Pat. No. 4,906,938 is shown in FIG.
1
. The terminals
12
,
14
of transmitter
10
are connected to the outlet or light fixture to be tested. Diode
16
acts as a half-wave rectifier. Specifically, if the voltage across diode
16
is positive, diode
16
acts as a short circuit, and if the voltage across diode
16
is negative, diode
16
acts as an open circuit. Sidac
18
is a short circuit when the voltage thereacross reaches its threshold value of 120-135 volts, and is an open circuit when the current through sidac
18
drops below the minimum holding current of the device. Thus, in this arrangement, sidac
18
acts as a trigger switch.
If a conventional power line voltage is applied to transmitter
10
, sidac
18
will initially go into conduction when the line voltage reaches approximately 120 volts. This causes capacitor
20
to immediately charge to the line voltage, resulting in a large amplitude current pulse which is used to identify the circuit. Sidac
18
will continue conducting until the current approaches 0 amps, i.e., approximately 50-150 milliamps, which occurs near the peak of the power line voltage. When sidac
18
is switched off, capacitor
20
will be charged at a voltage level close to the peak voltage, i.e., approximately 150 volts, and can only discharge through resistor
22
. Due to the relatively large resistance of resistor
22
, the discharge of capacitor
20
will be slow.
Because capacitor
20
remains charged at approximately 150 volts, as the line voltage decreases from 150 volts to 0 volts and continues through its negative cycle, the voltage across diode
16
is negative. Thus, diode
16
remains an open circuit and capacitor
20
continues to discharge slowly through resistor
22
.
During the next cycle, diode
16
becomes a short circuit when the line voltage surpasses the charge on the capacitor
20
. Sidac
18
will remain an open circuit, however, because the voltage across sidac
18
, which is the difference between the line voltage and the voltage across capacitor
20
, will not reach its threshold value. Thus, transmitter
10
will not conduct any current until the voltage across capacitor
20
has time to discharge through resistor
22
, which does not occur for a number of cycles. This results in a frequency of current spikes less than the power line frequency of 60 hertz.
The identification signal develops a strong magnetic field that will likely be sensed in the vicinity of a number of circuit interrupter devices, including the one that is actually connected to the transmitter. In order to isolate the specific circuit interrupter device, the end user must manually adjust the gain or amplifier of the receiver, and re-scan the circuit interrupter devices with the receiver. This procedure is repeated until only one circuit breaker triggers a response by the receiver. The circuit interrupter device connected to the transmitter may also be identified by monitoring a signal strength meter or bar-graph display. These devices require the user to select the circuit interrupter device with the strongest magnetic field. Receivers which require manual adjustment of the gain or amplifier of the receiver, and signal strength meters having analog or digital readouts can be quite difficult to use, especially if the end user has no prior experience with such instruments.
SUMMARY OF THE INVENTION
The present invention is directed to an electronic system for identifying the associated dedicated circuit interrupting device. Particularly, a transmitting device is plugged into the power outlet receptacle in question, and an identification signal is transmitted over the circuit wiring from the electrical panel.
Unlike most existing circuit identifiers currently on the market, the automatic circuit locator of the present invention does not require input from the end user to identify the correct circuit interrupting device. The automatic circuit locator performs the calibration process, thereby eliminating the need for the end user to do so.
According to a first aspect of the present invention, an identification signal is transmitted from an outlet to produce a magnetic field around a plurality of power lines. A receiver senses the strength of the magnetic fields around the power lines, and stores the largest value. The user is alerted when the receiver senses the stored value.
Other features and advantages of the invention will be apparent from the following detailed description taken in conjunction with the drawings.
REFERENCES:
patent: 3916301 (1975-10-01), Vild et al.
patent: 4642556 (1987-02-01), Pecukonis
patent: 4979070 (1990-12-01), Bodkin
patent: 5422564 (1995-06-01), Earle et al.
patent: 5590012 (1996-12-01), Dollar, II
patent: 5969516 (1999-10-01), Wottrich
NTC, Inc.
Oda Christine
Wallenstein & Wagner
Zaveri Subhash
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