Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – Magnetic saturation
Reexamination Certificate
2002-06-11
2004-07-06
Tang, Minh N. (Department: 2829)
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
Magnetic saturation
C324S11700H, C324S127000
Reexamination Certificate
active
06759840
ABSTRACT:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not applicable.
BACKGROUND OF THE INVENTION
The field of the invention is Hall effect current sensors and more specifically methods and apparatus for mounting a magnetic field sensor within a gap formed by a core or flux guide that surrounds a conductor.
When current passes through a conductor, the current generates a magnetic field including flux that encircles the conductor and that is directed along flux lines in a direction consistent with the well known right hand rule. The field strength is strongest at locations in close proximity to the conductor. The magnitude of current passing through the conductor is directly proportional to the total strength of the magnetic field generated thereby. Thus, if the magnetic flux generated by the current can be accurately determined, then the magnitude of the current passing through that conductor can also be determined.
One way to determine the magnetic flux and hence conductor current has been to design a sensor configuration that relies upon the well known Hall effect electromagnetic principle. To this end, in 1879, Edwin Hall discovered that equal-potential lines in a current carrying conductor are skewed when put in the presence of a magnetic field. This effect was observed as a voltage (Hall voltage) perpendicular to the direction of current flow. Today, Hall effect devices for measuring the Hall voltage and hence a corresponding magnetic field are packaged as single Hall effect chips and are sold as high volume commodity items.
A typical current sensor utilizing Hall effect technology consists of a toroid or rectangular shaped gapped core and a Hall effect chip. Exemplary cores typically include either a laminated stack or a high resistivity solid ferrite material designed to prevent unwanted eddy currents. A single current carrying conductor is positioned within the core such that the permeable core directs the magnetic flux through the core and across the gap. A Hall effect chip is placed within the gap to sense the flux density passing there across. In a well-designed Hall effect current sensor, the measured flux density is linear and directly proportional to the current flowing through the current carrying conductor.
One design challenge routinely faced when designing Hall effect sensors has been finding a cost effective and mechanically robust way in which to mount the Hall effect chip within a core gap. One other challenge has been to configure a sensor that has a relatively small volume footprint. With respect to cost, as with most mechanical products, minimal piece count, less and simplified manufacturing steps and less manufacturing time are all advantageous. In addition, smaller components size typically translates into reduced costs. With respect to robustness, many Hall effect sensors are designed to be employed in rugged environments such as industrial control applications where shock and vibration are routine.
The industry has devised several Hall effect sensor configurations. For instance, in one configuration, a donut shaped and gapped ferrite core is positioned over a vertically mounted Hall effect chip which is soldered to a circuit board. In this case the ferrite core is typically manually positioned with respect to the chip and is then glued to the circuit board. While this solution can be used to provide a robust sensor configuration, this solution has several shortcomings. First, sensor manufacturing experience has revealed that it is relatively difficult to accurately position and glue a donut shaped core relative to the circuit board mounted Hall effect chip. Also, in this regard, where the sensor is subjected to vibrations and shock, any loosening or shifting of the bond between the core and board can compromise the accuracy of the current sensor.
Second, the manual labor to glue a core to a board is not very efficient or cost effective and the glue curing cycle is typically relatively long. Labor and curing costs increase the overall costs associated with providing these types of Hall effect current sensors.
One other approach to mounting a Hall effect chip within a core gap has been to mount the chip on a board, position the core in a housing cavity with the circuit board mounted chip appropriately juxtaposed within the gap, fill the cavity with epoxy potting compound and bake the filled housing for several hours to completely cure the epoxy. As in the case of the glued donut shaped core, the manual labor required to pot the core and board is relatively expensive. Moreover, the baking time required to cure the epoxy reduces manufacturing throughput. Furthermore, the requirement for a housing increases parts count and hence overall configuration costs.
Yet one other approach to mounting a Hall effect chip within a core gap has been to mount a circuit board within a bobbin and mount a Hall effect chip to the circuit board where right angle pin connectors from the chip protrude out of apertures in the bobbin for connection to one or more other circuit boards. A core lamination stack is inserted into the bobbin with the bobbin formed to arrange the core and chip with respect to each other such that the chip is within the gap. Thereafter, the bobbin, core, chip and board are inserted into a first piece of a housing with the pin connectors protruding out housing apertures and a second housing piece is snapped together with the first piece to secure all of the components inside. The housed configuration forms a complete Hall effect current sensor.
This solution, unfortunately, requires a relatively large number of components and therefore increases costs appreciably. In addition, the pin connectors used with this type of assembly are relatively flimsy and have been known to break when used in typical industrial environments. Moreover, the pin connectors are often bent prior to installation or may be located imperfectly and therefore make installation relatively difficult. Furthermore, if the laminations are not clamped tightly by the housing, the laminations may shift laterally or rotate within the housing due to shock or vibrations. Such shifting and rotation will often result in changing the size of the core gap which alters the sensitivity of the sensor configuration.
One constraint on core size is the required dimensions of the conductor that passes through the core. To this end, conductors are typically selected based on the expected maximum steady state current passing through the conductors to ensure that heat generated by I
2
R losses or eddy currents does not cause the conductor temperature to exceed maximum limits defined by UL or IEC specifications. Heat generated by conductor I
2
R losses varies inversely with conductor cross-sectional area and with the square of current. Therefore, if conductor temperature is to be maintained, doubling the current requires a conductor with four times the original cross-sectional area.
In addition to current considerations, one other factor that may dictate conductor characteristics is the type of application in which the conductor is employed. For instance, in some applications a conductor may form a bus bar where ends of the bus bar have to have certain dimensions in order to facilitate hookup of other components via common size terminal lugs and mounting hardware that conforms with industry standards.
In some soft motor control (SMC) modular applications (e.g., high amp power pole sub-assemblies), bus bars are designed to minimize I
2
R have the largest area possible to facilitate maximum heat dissipation. For instance, where a module footprint is twelve inches by two inches, the bus bar may be designed to be thirteen inches long and two inches wide, the additional inch in length provided so that the bar extends from a module housing for linking to other system components. In such a case the core of a hall effect current sensor must have dimensions that can accommodate the required bus bar width. Thus, in the case of a torroidal core the core diameter would have to be greater than two inches to a
Annis Jeff
Marasch Richard
Rushmer Bob
Gerasimow Alexander M.
Quarles & Brady LLP
Rockwell Automation Technologies Inc.
Tang Minh N.
LandOfFree
Hall effect conductor/core method and apparatus does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Hall effect conductor/core method and apparatus, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Hall effect conductor/core method and apparatus will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3243083