Power Management
even slight inconsistencies in their construction will impinge on their overall accuracy. Also as there will be a certain amount of power dissipation through the packaging of these components there can still be issues in terms of its operational lifespan.
Other issues that need to be taken into consideration include a tendency in such implementations for sensitivity to drift with temperature (due to heat
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.
Figure 3: Triaxis Hall Sensor
dissipation that is proportional to the current to be measured), plus inrush current (as a high inrush current will saturate the ferrite core and result in a significant hysteresis when going back to zero current). This will clearly be compounded in datacenter environments, where servers are packed tightly together and large quantities of heat are constantly being generated. Even with highly efficient cooling mechanisms in place the effect of temperature on the accuracy of some sensing systems means that the quality of the data acquired is not as high as it should be. As the demands being put onto PDUs get tougher to satisfy using conventional sensing methodologies, the need for a more sophisticated approach heightens. This is encouraging a migration towards more innovative sensor implementations. The Triaxis current sensors from Melexis present a non-intrusive solution that can be used to 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 analogue output of a Triaxis sensor can support a response time of 4 µs. This translates into a 200 kHz
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The contactless sensing solution outlined here, based on proprietary Triaxis technology, is suited to provide 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. 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 realised, displaying greater accuracy and reliability while taking up less space. Thanks to the 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.
Melexis |
www.melexis.com
Robert Racz and Mathieu Ackermann are product marketing engineers at Melexis
Components in Electronics October 2012 23
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