TTi Iprober 520 Positional Current Probe
The Aim I-prober 520 positional current probe is unlike any other current measurement device available.
Calibrated measurement of current normally requires the current 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 that 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 I-prober 520 positional current probe is unlike any other current measurement device available.
Calibrated measurement of current normally requires the current 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 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 magnitude of the signal from a positional current probe is critically related to its position relative to the conductor. The size of the conductor (e.g. the width of a PCB track) also has a significant effect.
This means that the sensitivity of the I-prober has to be adjusted to match the track width when quantitative measurements are required. A calibrator within the control box enables sensitivity adjustment in conjunction with a calibration graph.
The measurement result will also include other field effects present at the tip of the probe and not just that coming from the current through the conductor. This may include DC effects from adjacent magnetized components and the earth's magnetic field, plus AC effects from transformers and other field radiating sources.
Current in adjacent tracks or tracks on the opposite side of the PCB will also affect the measurement. There are solutions to these potential problems. The unwanted DC can be nulled out by observing the measurement without power to the circuit, whilst AC interference can be attenuated using bandwidth filters. The I-prober control box includes a wide range of DC offset control and switchable filters.
Nevertheless, the use of the I-prober 520 requires an interpretation based upon a proper understanding of circuits and systems. It is a tool for the professional engineer.
Closed-loop current measurement
Whereas the primary purpose of the I-prober 520 is as a positional current probe, the are many circumstances where current measurements can be made conventionally by enclosing the conductor.
To increase its overall usefulness, the I-prober 520 is supplied with a clip-on toroid assembly which converts it into a closed magnetic circuit probe for measuring current in a wire.
The toroid is open until the probe is attached, allowing the insertion of the wire without disconnection. The wide bandwidth, dynamic range and low noise of the probe are retained but higher accuracy, repeatability and unwanted field rejection are achieved.
Minimal circuit disturbance
With many high-frequency switching circuits and high bandwidth signal paths, inserting even a short loop of wire into the track path can change the inductance sufficiently to alter the circuit performance. Unlike a conventional current probe, the I-prober 520 has an extremely low insertion impedance and negligible stray capacitance. This enables current observations and measurements to be made without disturbance to the circuit.
Safe for higher voltage use
The I-prober 520 is safety rated to 300V CAT 11 (600V CAT 1). This enables it to be used on circuits with a direct connection to the AC line at up to 300V RMS, and on isolated circuits at voltages up to 600V RMS. A finger guard is incorporated to maintain user safety at higher voltages.
The probe can be used to measure high-temperature PCB tracks and component leads up to 120oC continuous or 150oC short term.
Measurement of the electromagnetic field
The very small size of the field sensor within the I-prober 520 gives it some unique capabilities when used to measure magnetic fields.
The variation of the field with position can be accurately determined to enable the precise source of fields to be located and their variation in space measured. A switch on the control box re-scales the output voltage to measure in Teslas or amps per meter.