Best way to measure current through a PCB trace

[wardenclyffe]

I was wondering what is the best way to measure current through a PCB trace. I guess ideally if you were designing your own board you would include test points with jumpers, but what trying to troubleshoot existing consumer products. How can you measure the current without cutting traces? Is there special equipment that exists to do the job or am I missing some obvious way to go about it?

[Time]

http://www.tti-test.com/go/iprober/index.htm

[IanB]

It's not easy. Must diagnostic tests can be done by measuring voltages or looking at signals at various points on the board without having to break the circuit. The need to measure actual current is quite rare. If it must be done I think you would have to de-solder a component and insert your meter in the circuit at the break. This was easier to do with through-hole components than with SMT components.

[DaveW]

This works brilliantly-I've been playing around with one for the last few days-I can do a quick review if people are interested.
There are also other probes that work by using the track itself as a resistor and measuring the voltage drop, using a oddly shaped head, however these are rendered useless by solder resist or similar, and like the TTI, you have to put in the width of the track.

The only other method I've used is definitely fiddly-measure the resistance of the track using accurate meter, then place a wire of the same resistance in parallel with the track, measure the current through the wire and multiply by two. Have to careful of the different tempco of the two paths though

http://www.tti-test.com/go/iprober/index.htm

[Psi]

There are HALL effect ICs which detect current through any pcb trace that runs under the IC on the board

I doubt they are very accurate in the mA range but might be worth a look.

[wardenclyffe]

This works brilliantly-I've been playing around with one for the last few days-I can do a quick review if people are interested.
There are also other probes that work by using the track itself as a resistor and measuring the voltage drop, using a oddly shaped head, however these are rendered useless by solder resist or similar, and like the TTI, you have to put in the width of the track.

The only other method I've used is definitely fiddly-measure the resistance of the track using accurate meter, then place a wire of the same resistance in parallel with the track, measure the current through the wire and multiply by two. Have to careful of the different tempco of the two paths though

http://www.tti-test.com/go/iprober/index.htm

Thanks for all the replies everybody. I would be interested in seeing a review of this product if you are up for it. I am not sure I quite understand how it works.