" automation, or energy management in buildings.sensing elements are shown in across section of a sensor capableIn the standard sensor types described thus far, the nominalof measuring a broad range ofcurrent is set by the geometry of the primary conductor thatcurrents simply by adapting theis part of the system and by the distance between the MRgeometry of the conductor.chip and the conductor. Recent investigations, however, havedemonstrated that the high-current bus bar need not beinterrupted or guided through a hole, as required with Hall transducers. Instead, it can simply beshaped in the form of a bus bar plate. A sensor module realized as a dual in-line surface mountdevice component can be mounted on the power PCB board placed above the bus bar plate sothat the current flow can be directly measured.A very clever and cost-effective solution for the measurement of high currents, especially inseries applications, was presented at PCIM‘99 in Nuremberg, Germany, where it drewconsiderable attention. In this execution, the current is directly measured in the primaryconductor (flat conductor,Photo 4. The latest type ofmagnetoresistive current sensor isplaced into a slot in a straight19PCB) and the sensor module is then simply clipped into aconductor, in this case a 200 Aslot made in the conductor (see Photo 4). The result is acopper bus bar.differential field measurement system that is insensitive tohomogeneous external magnetic perturbations. The sensors and the ASIC are mounted on anappropriate substrate and encapsulated in a plastic package (see Figure 5). With this sensor, abroad range of currents can be measured simply by adapting the geometry of the conductor.Potentially heterogeneous perturbation fields can easily be shielded.The advantages are obvious:these current sensors are not only small, compact, and light, but also cheap and easy to mount.The primary current conductor can be part of the application and need not be mountedseparately. This opens the way to completely new construction possibilities for developers ofpower electronic modules and devices such as for mains receivers and frequency inverters.The Magnetoresistive EffectThe anisotropic magnetoresistive effect (AMR effect) is known to be present in a whole family offerromagnetic alloys. Most of these alloys are composed of iron (Fe), nickel (Ni), and chromium(Cr), and may be binary (two components) or ternary (three components). They have in common amore or less strong anisotropy in their magnetic properties. Whenever these materials are exposedto a magnetic field during crystal formation, a preferred orientation in magnetization will result.The same happens when the materials are forced into shape, i.e., a mechanical anisotropy isimposed.20Long before chip or even thin film technologies were developed, simple wires drawn of NiFewere known to possess an orientation of their magnetization, a magnetic moment, along theirlinear axes. Interestingly, it was found that changing the orientation of the magnetic moment inthe wire caused a current passing through it to change correspondingly. The orientation could bechanged by applying an external magnetic field, and generally an increase in current (i.e., adecrease in resistance) was observed. This phenomenon was called anisotropic magnetoresistiveeffect.Today, the ferromagnetic materials can be deposited as thinfilms and structured into small strips that are typically 40 nmthick, 10 mm wide, and 100 mm long. A magnetic field isapplied during the process. In modern device fabrication analloy commonly called Permalloy (81% Ni, 19% Fe) turnsFigure 6. The Permalloy strip hasout to be the best compromise in terms of device sensitivity,an orientation of the innerlongevity, and reproducibility.magnetic moment, M0, parallel toits long axis. When an externalFigure 6 shows the position of a Permalloy strip. As does thefield is applied, the totalwire, the strip has an orientation of the inner magneticmagnetization of the strip ismoment, M0, parallel to its long axis. When an external fieldturned at an angle, u.is applied, the total magnetization, M, of the strip is turned atan angle, f.In the most general case, the electrical resistance of AMR material depends on the angle, u,between the direction of the magnetization, M, and the direction of the current going through it.21 "