" The size of the actual MR sensor chip with the four permalloy strips on silicon is 1 mm by 22 mm , the distance between the two arms of the bridge being 1.6 mm (see Photo 2). It is mounted2 with the electronics on a 23 mm by 35 mm single in-line hybrid circuit designed for through- hole PCB mounting with very low profile. The NT-xx product family from Sensitec includessensors for nominal currents of 5 A, 15 A, 25 A, and 50 A.Figure 3. Magnetoresistive current sensors detect changes in magneticfields but are insensitive to homogeneous fields. The orientation of thebarber poles on the two arms of the bridge has been modified from theconfiguration shown in Figure 2.Among the advantages of these sensors are:• Significantly smaller volume and weight compared to conventional current sensors, permittinggreater flexibility in application-specific design• No remanence in the event of overload• Measurement of DC and AC currents without additional loss16• Wide frequency range due to low inductive design• No auxiliary supply necessary on the level of current to bemeasured• Low system costsPhoto 2. The actual sensingelement consists ofInitially developed for use in inverters (see Photo 3) andmagnetoresistive Permalloy stripsservo-regulators, MR current sensors have a broad range ofintegrated onto a silicon chip.other applications: energy distribution; power electronicssystems such as inverters and mains receivers; batterymanagement (charge and discharge currents); solar technology; electrical vehicles;uninterruptable power supplies; robotics; automotive (e.g, drive-by-wire); and safety devices.The signal conditioning electronics of the NT-xx family isadiscrete circuit; in the new NTS-xxFigure 4. In this cross section of amagnetoresistive sensor withcompensation, the isolatedaluminum compensation17family, it has been integrated into an ASIC operating atconductor can be seen above thefrequencies up to 100 kHz. The output signal is scalable toPermalloy strips and barber poles.meet the requirements of external A/D converters.Additional functions are a comparator I/O with adjustable trigger level for short-circuit detection,an open-drain concept that permits three-phase monitoring, and a true rms output for powermeasurement and protection. These sensors are supplied with a unipolar voltage of +5 V,compatible with most digital interfaces. Since no core is used to concentrate the magnetic field,there is no remanence, which means that overcurrents produce no permanent offset changes. Thecompensation method guarantees a high linearity. The profile on the PCB board is low, and themounting is very easy.The ASIC allows digital calibration of the current measurement system even after installation inan application. The calibration data are stored on the chip. The MR sensor is located on a secondchip. A co-integration of sensor and interface electronics on the same silicon substrate is possiblebut is not yet cost effective. The principal application areas will be in electronic systems for theautomotive industry (see ?Current Sensors in Tomorrow‘sCars?), motion control,Figure 5. The magnetic field linesand the position of the two18 "