New type of probe measures current in PCB tracks directly

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 5 MHz and a dynamic range of 10 mA to 20 A peak to peak. It is safety rated to 300 V Cat II (600 V Cat I) and is suitable for connection to any 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 occurs in ground planes, where it can be used to observe circulating currents, interference injection points and “hot spots” in order to optimise design.

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.