Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – Magnetic saturation
Reexamination Certificate
2002-09-03
2004-05-04
Le, N. (Department: 2858)
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
Magnetic saturation
Reexamination Certificate
active
06731105
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to current sensors, and more particularly to corrected noncontacting current sensors which tend to be insensitive to transverse installation misalignment.
BACKGROUND OF THE INVENTION
In systems including a large number of interconnected devices, any one of which is liable to fail, troubleshooting can be difficult. Various techniques are used to aid in locating defective components. In the context of discrete circuits using bipolar transistors or FETs, it was previously common to place a moderate-value resistor in series with the base or gate, so that a short-circuit from the emitter or collector, or the source or drain, respectively, to the base or gate, could be detected by noting the voltage across the resistor so added. The value of the resistor was selected so that its effect on the operation of the circuit was minuscule during normal operation of the device. With the increased usage of microcircuits, this simple approach has become less useful.
There are systems in which large numbers of generally identical electrical units are operated in parallel. These systems are ordinarily located in bays of large racks, where the packing density of the units makes access difficult. In such arrangements, it is desirable to individually monitor the current flow to each module, as for example by associating a current sensor with each module. Each current sensor may be as simple as, again, a series resistor through which the current to be monitored flows, and which generates a voltage attributable to the power supply current flow to the module. A gross failure of a module might be readily identifiable by the existence of a relatively large voltage across the series resistor.
A more subtle failure, such as that of a single component within the module, might be identifiable as a momentary surge of the supply current as the failed component draws excessive current and then fails in an open-circuited state. Monitoring for such failures may require that a running record be kept of the supply current of each module. However, when a gross defect is noted, such as might occur when someone enters a room filled with racks of such equipment, and smells an “electrical fire” odor. Naturally, an immediate remedy is to cut all power to the equipment in the room. However, there is then the problem of tracking down the source of the odor. Since the odor vanishes shortly after the removal of power, and even were it present is not a good indicator of exact location, it may be difficult to locate the problem. In such an instance, it would be very valuable to have available a record of the moment-to-moment current in each module during the time in question, so as to be able to identify any current surges. With the use of microcircuits, mounted on printed-circuit boards, such a scheme would be quite possible, and might be relatively inexpensive to implement.
Naval and other ships contain large numbers of electrically driven motors, servos and the like, distributed throughout the various compartments of the ship. Many of these electrically driven devices could be styled as “heavy machinery.” The same problem as that described above, namely that of locating a defective device within numerous other devices in close quarters, exists in the shipboard context. However, the problem is not as easy to solve in the ship context, because the currents involved are too large for ordinary printed circuits to withstand. This, in turn, means that the mounting of current sensors cannot be accomplished by simply connecting a circuit board in-circuit with the current to be sensed or measured, but instead the current sensor must be custom-installed on or adjacent the large conductor. Such installations tend to be labor-intensive and therefore expensive, and additionally are subject to installation errors which may compromise the measurements.
Improved current measurement techniques are desired, as for example for fault monitoring.
SUMMARY OF THE INVENTION
An electrical current sensor arrangement according to a general aspect of the invention is for sensing the current in an elongated conductor. The arrangement comprises first and second current sensing devices which can be magnetically coupled to the current to be sensed, for generating sensed signals relating to the magnitude of the current being sensed. Each of the first and second current sensing devices has a preferred magnetic sensing axis, which in general is oriented relative to the current flow in the conductor so as to provide a signal. A nonmagnetic physical mounting is physically coupled to the first and second current sensors, for holding the first and second current sensors with their preferred sensing axes one of (a) parallel and (b) orthogonal, thereby defining a sensor plane in which the current sensing devices lie. The fact that the current sensing devices lie in the same plane necessitates or requires a spacing therebetween, which spacing remains fixed. The physical mounting is adapted for mounting adjacent an electrical conductor, with the sensor plane parallel with a tangent with an outer surface of the electrical conductor, and for, when so mounted, holding the preferred sensing axes of the sensors relative to the direction of current flow in the conductor so as to produce a sensed signal in at least one, and preferably both, of the current sensing devices, in response to current flow in the conductor. As a result, each of the current sensing devices senses magnetic fields related to less than the total current flowing through the electrical conductor, or at least gives an indication which is less than it would give if properly located and oriented. The arrangement includes electrical coupling means coupled to the first and second current sensors, for processing the sensed signals produced by the first and second current sensors, to thereby produce a signal representative of the total current in the electrical conductor. In one embodiment, the conductor has a generally circular cross-section. Ideally, the current sensors are corrected for at least one of (a) temperature effects and (b) unit-to-unit variation in sensitivity. In the version in which the sensing axes of the current sensors are parallel, a transverse separation of the sensors is desirable.
In one version of the arrangement according to an aspect of the invention, the electrical coupling means algebraically sums the currents represented by the signals generated by the first and second current sensing devices to produce the signal representative of total current in the electrical conductor.
According to another aspect of the invention, the physical mounting comprises a first physical mounting portion physically coupled to the first and second current sensors, for holding the first and second current sensors with their preferred sensing axes (a) parallel or (b) mutually orthogonal, thereby defining a sensor plane, and with a fixed or known spacing between the preferred sensing axes. According to this aspect of the invention, a second physical mounting portion is provided for mounting adjacent an electrical conductor. The second physical mounting portion includes means for holding the first physical mounting portion with the sensor plane parallel with a tangent with (or to) an outer surface of the electrical conductor, and for, when so mounted, holds the preferred sensing axes (a) generally parallel with the direction of current flow in the electrical conductor or (b) at 45° to the direction of current flow. In one version of this aspect of the invention, the first physical mounting portion comprises a printed-circuit board, and the second physical mounting portion comprises a nonmagnetic structure including a printed circuit mounting portion defining a plane, and also including a depression shaped to the exterior of the conductor. The depression defines a longitudinal axis parallel with the plane of the printed circuit mounting portion.
In a kit of nonmagnetic mounting arrangements according to another avatar of the invention, each of the mounting arr
Berkcan Ertugrul
Hoyle Scott Baxter
Duane Morris LLP
Le N.
Nguyen Vincent Q.
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