Author:
Reported by Cliff Keys, Editorial Director, PSD
Date
09/01/2011
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I had the pleasure of an interview with Mark Edwards, Sales Director of Aim-TTi, Thurlby Thandar Instruments Ltd, based in Huntingdon, Cambridgeshire, UK. The 13 year close links with Cambridge University research has now come to fruition.
Traditionally, measuring current on a PCB has been a tricky process. The newly launched I-prober 520 achieves something radically new. It can observe and measure currents in PCB tracks and other conductors where conventional current probes can't be used. This includes captive wires into components, the legs of integrated circuits, and PCB ground planes. Conventionally, current can only be measured by either breaking the circuit to insert a shunt resistor or by surrounding the conductor by a loop of magnetic material as in a standard current probe. The I-prober 520 enables currents, from dc up to 5MHz, to be observed and measured simply by placing its insulated tip onto the conductor. The company's new I-prober 520 is the culmination of over ten years of research and development in conjunction with the University of Cambridge. Initially intended for launch in 2009, the I-prober has been subject to continuous revision to improve manufacturability. Now, following large pilot builds and beta testing, the company is now ready to launch this unique product. I-prober 520 is the only product in the world capable of observing and measuring currents in PCB tracks, captive component leads and ground planes. The detailed information on how the I-prober 520 works can be viewed on the company's web site at: www.aimtti.com/go/iprober
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The Aim I-prober 520 positional current probe uses a patented technology to observe and measure current without the need to break or surround the conductor. Calibrated measurement of current normally requires either the insertion of a shunt resistor, or for the conductor to be passed through a closed magnetic loop. Typically this is done using some form of split clamp device. Whereas this is suitable for individual wires, it is of no use for measuring current in PCB tracks. The I-prober 520 is a compact hand-held probe which is used with an oscilloscope. By placing the insulated tip of the probe onto a PCB track, the current flowing in the track can be observed and measured. The probe has a bandwidth of DC to 5MHz and a dynamic range of 10mA to 20A pk-pk. It is safety rate to 300V Cat II (600V Cat I) and is suitable for connection to any 1MOhm input oscilloscope. The Aim I-prober 520 operates by sensing the field in very close proximity to the track. To achieve a calibrated measurement, the field sensor must be capable of maintaining a precise distance from the track. To achieve good sensitivity this distance must be very small because field reduces with the square of distance (to a first order approximation). To create a practical current measurement probe, a very special type of miniaturised sensor was needed. The requirements included very small size with precision dimensions, dc sensing capability, wide ac bandwidth, and low noise. None of the existing sensor technologies used within field and current probes was suitable for this. Instead the I-prober 520 uses a patented miniaturised version of a fluxgate magnetometer, developed in conjunction with Cambridge University. It is the patented miniaturisation that enables it to measure the field at a precise point in space. In addition, the miniature sensor has much lower noise and much wider bandwidth than a conventional fluxgate magnetometer. As well as measuring currents in PCB tracks, the probe can be used on component leads or any other current carrying conductor. An interesting example is ground planes where it can be used to observe circulating currents, interference injection points and hot spots in order to optimise design. Customers and Applications Current observation and measurement is a large market, and companies such as Tektronix enjoy a substantial turnover from current probe sales. Conventional high performance current probes (i.e. wide bandwidth, wide dynamic range) are relatively expensive, normally costing €1,000 upwards. This is a reflection of the precision mechanics that are incorporated. I-prober 520 is not a replacement for a conventional current probe when measuring current in wire. Although it can act as a conventional "closed loop" probe by using the supplied toroid attachment, it is less convenient to use and has lower rejection of external fields. The primary purpose of the I-prober 520 is as a "positional" current probe for observation and measurement in the many situations where a conventional probe can not be used. Aim-TTi expects the unique capabilities to create considerable potential demand, but that some qualification of customer applications will be necessary. It is not a simple and straightforward probe to use. To obtain useful measurement results requires an understanding both of how the probe works, and the circuit and environment in which it is being used. Potential customers need to have an application where conventional current measurement is not possible, plus some understanding of possible limitations of the probe in their application. Aim-TTi intends to produce an explanatory video which can be sent to potential customers in order to ensure that the product is likely to meet their expectations. In the meantime, customers should be encouraged to visit the web site and read/download the detailed information. The Aim I-prober 520 is supplied with a control box and calibrator, power supply, and a clip on toroid assembly which can convert it into a convention closed magnetic loop current probe. The price in the UK is £495. Thurlby Thandar Instruments Ltd. Glebe Road, Huntingdon, Cambs. PE29 7DR United Kingdom Tel: +44 1480 412451. Email: info@aimtti.com www.aimtti.com
