I-prober 520 positional current probe
Unique technology enabling current measurement in PCB tracks
bandwidth of DC to 5MHz, dynamic range of 10mA to 20A pk-pk
useable with any normal oscilloscope, safety rated to 300V Cat II
aimtti.com
investigates waveforms in any conductor including ground planes
aimtti.co.uk | aimtti.us
AIM & THURLBY THANDAR INSTRUMENTS
Aim I-prober 520 - a breakthrough in current measurement technology !
Key Features
Current measurement from insulated probing of conductor
Suitable for observation and measurement of current in
PCB tracks, component leads and ground planes
Wide dynamic range of 10mA to 20A peak to peak
Wide bandwidth of DC to 5MHz
Low noise figure equivalent to <6mA rms at full bandwidth
Safety rated to 300V Cat II (600V Cat I)
Suitable for connection to any oscilloscope
High accuracy general purpose H-field probe
Converts to standard ‘closed magnetic circuit’ current probe
A technology breakthrough
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.
Unique Capabilities
No requirement to break or surround the conductor
Observe and measure currents in PCB tracks directly
Minimal disturbance to circuit conditions through very
low insertion impedance and stray capacitance
Useable in confined and difficult to access spaces
Measures current into surface mount components,
IC legs and short component leads
Can observe currents flowing within ground planes
Useable on high voltage conductors and in high
temperature areas
Observe & measure currents in PCB tracks, captive component leads & ground planes
Current measurement techniques
True measurement of current requires the circuit to be broken and a current
measurement device inserted (e.g. a shunt that converts current to voltage).
However, breaking the circuit is impractical in many circumstances and, in the
case of PCB tracks, may be impossible.
Closed magnetic circuit current measurement
DC capable current probes do not measure current, they measure field density.
Current flowing through a conductor creates an H field which is directly
proportional to the current.
If a conductor is surrounded by a closed magnetic circuit of high Mu material
the whole of the field is ‘captured’ by the magnetic circuit and the field density
can be scaled to represent current.
Conventional current probes achieve this by concentrating the field into a gap
within a loop of high Mu material. The field is then measured by a field sensor
inserted into the gap, often a Hall effect device.
Alternatively ac current can be
measured by transformer action
whereby the loop of magnetic
material creates a one turn
primary from the conductor that is
enclosed. Hybrid devices typically
use a field sensor for dc and low
frequencies plus a transformer for
higher frequencies.
Normally the probe provides a method
of mechanically splitting the magnetic
circuit to enable the conductor to be
inserted.
The position of the conductor
within the loop has relatively little effect
upon the measurement
.
PCB track current measurement
Measuring current in a PCB track presents particular difficulties because
it normally not possible either to break the track or to enclose it within a
magnetic circuit. Typically engineers have to guess at the current flowing in a
track from voltage measurements made in other parts of the circuit..
As electronic design moves towards ever higher densities, development omits
the “bread board” stage and goes straight to PCB design. The inability to
observe and measure currents in a circuit under development can pose a
serious problem for engineers.
Illustration shows high performance
current probes from Tektronix Inc.
Engineering a Solution
The only practical way to observe and measure the current in a PCB track is
by sensing the field in very close proximity to the track.
We refer to this type of current probe as a
positional current probe
.
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.
The Fluxgate Magnetometer
- updating an established principle
The I-prober 520 uses the well established principle of a fluxgate
magnetometer to measure field.
Conventional fluxgate magnetometers are relatively large with bandwidths
limited to a few kHz. They are typically used for precision measurement of
fields within geophysics and bio-electromagnetics.
By contrast, the sensor within the
I-prober 520 uses a patented miniature
fluxgate magnetometer of sub-
millimetre size incorporating a highly
advanced core material.
This enables it to use an excitation
frequency of several tens of MHz
resulting in a sensor with a bandwidth
of dc to 5MHz combined with low noise
and wide dynamic range.
The illustration shows the main part of
the magnetometer. The field sensing
element is of sub-millimetre dimensions
and is placed at the tip of the sensor.
Making PCB current measurement a reality
The concept of a positional
current probe is not entirely
new. However, previous
attempts have been physically
large and suitable only for
measuring high currents at low
bandwidth.
The high excitation frequency
miniature sensor within the
I-prober 520 provides it with
levels of positional accuracy,
sensitivity, bandwidth and
dynamic range that are superior
to anything previously achieved
by several orders of magnitude.
In consequence, the Aim I-prober 520 is the first and only probe
that can be used to measure currents from amps down to milliamps
at frequencies from DC up to MHz, making practical measurement
of PCB track currents a reality.
Modern high-density electronic PCB layouts make
current observation and measurement increasingly difficult
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 in the conventional way 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 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.
Measurement of 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
field with position
can be accurately
determined enabling
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
in amps per metre.
The I-prober 520 in use
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 magnetised components and from
the earths 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 DC offset control and switchable
filters.
Nevertheless, the use of the I-prober
520 requires interpretation based upon
a proper understanding of circuits and
systems. It is a tool for the professional
engineer.
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 direct
connection to 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.
Aim I-prober 520 - a innovative and flexible measurement tool
Designed and built in Europe by:
Thurlby Thandar Instruments Ltd.
Glebe Road, Huntingdon, Cambridgeshire. PE29 7DR United Kingdom
Tel: +44 (0)1480 412451 Fax: +44 (0)1480 450409
Email: info@aimtti.com Web: www.aimtti.com
Brochure Part No. 82100-1440 Iss. 1A
Technical Specifications
GENERAL SPECIFICATIONS (All Modes)
Output Signal
Maximum Output: ± 10V .
Oscilloscope Input: Suitable for an input impedance of 1MW in parallel with < 30pF.
Trace Position: Wide range DC offset control within control box.
Safety
Max. Circuit Voltage 300V Cat II (on AC line circuits).
600V (on uncategorised secondary circuits inside equipment).
Max. Tip Temperature 150ºC maximum allowable temperature at probe tip.
Conformance Complies with EN61010-1 & EN61010-031
Bandwidth Control
Switch Position Full 500kHz 2Hz
Nominal Bandwidth: DC to 5MHz DC to 500kHz DC to 2Hz
Risetime: <70ns 700ns 175ms
Aberrations: <±5% <±1% <±1%.
Noise (Typical)*: 6mA rms 3mA rms 1.5mA rms
* This is the noise level for current measurement using the Toroid attachment. For PCB track
measurement the equivalent noise will depend upon the track width and gain setting but will
be similar to the Toroid measurement figure for a track width of 0.5mm.
HF Performance (bandwidth switch at Full)
Propagation Delay 60ns typical (to 10%).
Bandwidth: DC to 5MHz (small signal)
Slew Rate: 15A/µs (equivalent).
Overload Indication
Indicator Threshold: Indicator LED within control box will light if output voltage exceeds
± 10V or if large magnetic fields cause the system to saturate.
Power Source
Power Supply: 5.2V at up to 5 watts from AC line adaptor (supplied).
Mechanical
Probe Dimensions 155mm x 38mm x 28mm max; 2.8mm x 1.8mm at tip
Cable Length 2m from probe tip to output BNC
EMC
Conformance Complies with EN61326
MAGNETIC FIELD MEASUREMENT (Mode = Field)
Scaling Factor: 250µT (or 200A/m) per Volt.
Accuracy and Linearity: ±3%
Maximum Field: ±2·5mT (2000A/m).
CURRENT MEASUREMENT USING TOROID (Mode = Wire)
Scaling Factor: 1 Amp per Volt.
Accuracy and Linearity: ±5%
Current Range: ±10mA to ±10A (DC + peak)
Max. Wire Diameter: 3.5mm (unbroken) or 6mm (end fed)
CURRENT MEASUREMENT IN PCB TRACKS (Mode = PCB Track)
Scaling Factor: Adjustable to 1 Amp per Volt for track widths 0·2mm to 3.5mm
(0·007” to 0·14”) and 2 Amp per volt for track widths 3mm to
6.5mm (0·125” to 0·25”) using Calibrator and compensation graph.
Sensor Spacing: 0.7mm distance from sensor to PCB track set by probe design.
Calibrator: Built-in calibrator within the control box providing an AC or DC
calibration current through a 0.5mm track.
Accuracy specifications apply for the temperature range 18
o
C to 28
o
C after one hour warm-up.
Thurlby Thandar Instruments Ltd. operates a policy of continuous development and reserves the
right to alter specifications without prior notice.
The I-prober 520 is supplied complete with a fitted carrying case
which accommodates all of the items including the power supply,
instruction manual and calibration graph.
The power supply has a universal voltage input (100V to 240V) and has inter-
changeable plugs for UK, Europe, USA and Australia.
Thurlby Thandar Instruments Ltd.
Glebe Road, Huntingdon, Cambridgeshire PE29 7DR England (United Kingdom)
Tel: +44 (0)1480 412451 Fax: +44 (0)1480 450409
Email: info@aimtti.com Web: www.aimtti.com
Designed and built in Europe by:
Company name and product brands
Thurlby Thandar Instruments Ltd. (TTi) is one of Europe’s leading
manufacturers of test and measurement instruments.
Products have been sold under two brand names:
TTi and Aim.
In the future, however, the full product range will be branded Aim-TTi.
This changeover will be gradual and many products will continue to carry
the TTi or Aim brands for some time to come.
Web Addresses (URLs)
The preferred URL for obtaining information concerning Aim-TTi products
is:
www.aimtti.com (international customers)
Customers in the UK should use the URL:
www.aimtti.co.uk
Customers in the USA should use the URL:
www.aimtti.us
Note that previous URLs such as www.tti-test.com will continue to operate
for the time being.
Product Summary
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Bench and system power supplies from 30 watts up to
1200 watts using linear, mixed-mode and PowerFlex
regulation technologies.
Waveform Generators
Analog and digital (DDS) function generators, true
arbitrary generators, arbitrary/function generators and
pulse generators.
Precision Measurement Instruments
Benchtop DMMs, frequency counters, component
measurement instruments (LCR), electronic dc loads,
current probes.
RF and EMC Test Equipment
Spectrum analyzers, signal generators, frequency counters,
power meters, emc measurement instruments.
