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Design Features
The Role of Hall Effect Sensors in Power Distribution Infrastructure
Page 2
The Melexis Triaxis current sensors can measure the current directly from a PCB trace (normally 5 A to 50 A) or a bus bar (normally 50 A to 1000 A). What differentiates these devices is their ability to sense the field generated in a PCB trace or bus bar without need of a ferrite toroid or steel lamination stacks. This is thanks to the patented IMC™ (Integrated Magnetic Concentrator) ferromagnetic film which is deposited onto the chip. When used in conjunction with complex mathematical algorithms, it allows the density of magnetic flux parallel to the sensor to be precisely and rapidly determined. This proprietary technology and subsequent implementation of the sensing elements intrinsically result in their magnetic sensitivity being magnified.
The analog output of a Triaxis sensor can supports a response time of 4 µs. This translates into a 200 kHz bandwidth compared with 50 kHz for conventional Hall Effect sensors. While there will normally be 2-3% non-linearity with conventional devices due to the ring’s construction and some hysteresis effects, Triaxis devices have non-linearity of just 0.5 % In addition, the temperature drift will also be reduced considerably if a Triaxis device is used instead of a conventional Hall Effect sensor.
The contactless sensing solution outlined here, based on proprietary Triaxis technology, is highly suited to accurate and reliable monitoring of PDU input/outputs. It has the strong linearity and responsiveness needed to obtain meaningful results, as well as allowing effective temperature compensation to be implemented. As no ferrite core is required, it fits into a package, thus saving board space. Furthermore, as it is programmable it is easy to adapt to different current ratings, thus offering a high degree of flexibility. As an upshot of this is that different designs are possible from a single platform.
Figure 4: PCB Showing Isolation Mechanism
As we have seen there are many challenges that engineers face when implementing a PDU design. These include protection against voltage transients, the handling of current inrush, dealing with space constraints, lowering systems costs and ensuring reliability. Non-intrusive sensing solutions which are capable of offering intrinsic isolation and protection against high transient voltages or inrush currents have a clear advantage over the more tradition approaches. Furthermore, sensors which can combine this with the capacity to detect magnetic flux parallel to the board will enable more streamlined implementations to be realized, displaying greater accuracy and reliability while taking up less space. Thanks to the unique IMC technology employed by the Triaxis sensor devices it is possible to amplify the magnetic field incident on the sensor chip, so that its sensitivity levels are enhanced and noise is kept to a minimum.
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