flux probe

FluxProbe is a test prod for measuring currents without touching the conductor it is flowing through. More acurately it is measuring the magnetic flux. This way you can measure currents on PCB traces without having to put a resistor in between.

This test gear enables you to trace faults in your PCB (for example search for a short circuit). This is usefull for commissioning of you circuit for example.

Do you remember this awefull measuring technique? : Strommessung "in Circuit" In much cases this is not needed when your lab is equipped with a flux probe ;-)

There are similar current probes like this: I-prober 520. The prices of these might make them unaffordable to hobbyists, which is the intended audience for the flux probe tool.

theory of operation

The central part of the circuit is a hall sensor. These sensors detect (static of altenating) magnetic fields. Thus these can measure DC current contrary to coil based measuring principles.

The physics behind these sensors are explained at wikipedia perfectly - so I will spare this part here.

circuit explanation

A part called A1324 (oder similar like A1321) is used for the hall sensor. This one is available in a SOT-23W footprint which enables me to put it on the edge of the pcb.

Because the sensor has a heavily offsetted voltage, which is about VCC/2 offset at a used voltage difference of some mV for Amps measuring. This voltage can not be read accurately using multimeters or oscilloscopes. This is why I inserted a offset compensating circuit.

The offset compensation is done by a programmable voltage reference DS4303 (programmed by a button press) and an instrument amplifier subtracting the reference voltage from our signal coming from the hall sensor.



These are the first measurements I made. The settings for the following pictures are:

horizontal: 10ms/div


  • red: 200mV/div (output of the flux probe)
  • yellow: 33,3mA/div (current that was measured) / 10V/div (voltage fed into the resistor)

at 50Hz:

at 10Hz:


probe coming from the left: signal in to the resistor

probe going to the right: signal measurement to the DSO

Resistor: 300 Ohms.


The Probe is still very „touchy“ - I did not get reliable results in some cases, depending on how i hold the probe.

Remember this is just the first prototype. In a few days I will have a second revision of the pcb, which will include voltage generation from a single AA battery as well as a standard bnc or sma connector.

en/prokekte/fluxprobe.txt · Zuletzt geändert: 2017/04/15 22:59 (Externe Bearbeitung)
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