And here's Mike's teardown for those who may want to watch that as well:
I'm trialing a new menu annotation system at the start of the video, let me know what you think.
Dave.
I never thought about current paths before, although I find it interesting. What determines the width of such a current path?
Regarding the menu annotation system: I like the idea, but it looks a little messy. Also I don't think I will ever use it. Maybe someone else will. It would be a good system for combined teardown / review videos. So maybe just two or three buttons on the bottom for major sections.
You could place all the links to websites and other videos at the end of the video. Took me quite a while to find the link for Mike's teardown again.
I found the trick Mike used with the LED and long exposure very neat. Really helps to visualise the way the current takes.
Regarding the menu I think the idea isn't bad as such, just the way you did it looked awful. Maybe put it on a splash screen (for example the EEVBlog logo) at the beginning of the video for a few seconds instead of plastering it all over your talking head?
Dave, at about 30mins mark i started hearing some 1KHz switching noise ... Where did it come from?
Re patent for Flux Gate Magnetometer - Not sure if this is the one but look for GB 2461437, Paul Robertson is listed as Inventor, and he worked at Camb. Engineering on this device. I have attached the pdf of the above patent.
Steve
I'm trialing a new menu annotation system at the start of the video, let me know what you think.
Dave.
Because of my OCD tendencies, I'm bugged by the fact that the boxes are not perfectly aligned. But it is what it is I guess. I'm also not sure I like the embossed "impact" style annotation.
As for the instrument, I wonder how long it will take before the coils get cheap enough to put in a second coil to compensate for Earth's magnetic field.
I never thought about current paths before, although I find it interesting. What determines the width of such a current path?
frequency.
for Dc they go wherever they feel like. as frequency goes up they follow the path of the signal above.
Wonder how they make the sensors? They must be using some ultra thin wire and old core memory ferrites.
more likely to be a vacuum deposited multilayer inductor
I never thought about current paths before, although I find it interesting. What determines the width of such a current path?
frequency.
for Dc they go wherever they feel like. as frequency goes up they follow the path of the signal above.
Yes, and no.
As I showed, DC (1KHz I used is close enough) does not just go "wherever they feel like" into the dead end voids etc.
Dave.
Wonder how they make the sensors? They must be using some ultra thin wire and old core memory ferrites.
Read the link I put on the video notes.
Dave.
Back in the early 80's maybe earlier HP had a current tracer for logic IC pins on PCBs - the HP 547A Current Tracer, it didn't hook up to a scope, or provide current readings,
it was just used to find out where the current sincs were.
reason I mentioned it it that it had a small tip that was placed onto the track in interest.
www.hparchive.com/Bench_Briefs/HP-Bench-Briefs-1977-09-10.pdf
Back in the early 80's maybe earlier HP had a current tracer for logic IC pins on PCBs - the HP 547A Current Tracer, it didn't hook up to a scope, or provide current readings,
it was just used to find out where the current sincs were.
reason I mentioned it it that it had a small tip that was placed onto the track in interest.
www.hparchive.com/Bench_Briefs/HP-Bench-Briefs-1977-09-10.pdf
Inspired by the HP Journal article on the current tracer, I actually made one for myself. Filed down a piece of ferrite to make the core. If I were making it today, I would probably try a hard drive head as the sensor.
http://www.hpl.hp.com/hpjournal/pdfs/IssuePDFs/1976-12.pdfThe big problem with the HP-type sensor is that its sensitivity increases with frequency, so it was pretty useless at seeing an accurate current waveform. HP used the sensor to detect transients (ie switching waveform edges) so they were not concerned with the frequency response of the sensor. The beauty of the fluxgate sensor is it has a flat frequency response all the way to DC.
Richard.
for Dc they go wherever they feel like. as frequency goes up they follow the path of the signal above.
Yes, and no.
As I showed, DC (1KHz I used is close enough) does not just go "wherever they feel like" into the dead end voids etc.
Dave.
[/quote]
let me rephrase that.
for low frequencies they will attempt to follow the most direct line between source and destination. they travel in a relatively wide band. of course they won't go in sticking-out-swaths of copper if there is no point in going there.
as frequencies increase they will tend to follow the path of the source signal.
DC
________________________________
| |
( top layer) in ------ |
--------- out
|______________________________|
(plane) GND ------------------------------------------------------------------------------- GNd return
RF
________________________________
| |
( top layer) in ------ |
--------- out
|______________________________|
________________________________
| |
( plane) in ------ |
--------- out
|______________________________|
kind of hard to do in ascii ..
if you have a meander trace over a solid plane : for DC or low frequency the ground return current ( current coming back from the load , through the ground , to the source ) will flow in a straight line. ( top drawing )
for RF : the return current will follow the shape of the meander above the plane. it will not go for the beeline but run exactly in the same shape as the trace above, even if there is a solid plane and no reason to do that.
Dave, if you have a known current flow through the PCB trace (100 mA as measured by the Fluke 87), why not just calibrate the probe to the trace instead? Adjust the PCB Sensitivity knob until the o-scope reads 100 mV. Then you can bump up the current flow through the trace to 200 mA or 500 mA and see if the probe is accurate at those levels.
Dave, if you have a known current flow through the PCB trace (100 mA as measured by the Fluke 87), why not just calibrate the probe to the trace instead? Adjust the PCB Sensitivity knob until the o-scope reads 100 mV. Then you can bump up the current flow through the trace to 200 mA or 500 mA and see if the probe is accurate at those levels.
Good point. I should have done that.
Dave.
let me rephrase that.
for low frequencies they will attempt to follow the most direct line between source and destination. they travel in a relatively wide band. of course they won't go in sticking-out-swaths of copper if there is no point in going there.
as frequencies increase they will tend to follow the path of the source signal.
DC
________________________________
| |
( top layer) in ------ |
--------- out
|______________________________|
(plane) GND ------------------------------------------------------------------------------- GNd return
RF
________________________________
| |
( top layer) in ------ |
--------- out
|______________________________|
________________________________
| |
( plane) in ------ |
--------- out
|______________________________|
kind of hard to do in ascii ..
if you have a meander trace over a solid plane : for DC or low frequency the ground return current ( current coming back from the load , through the ground , to the source ) will flow in a straight line. ( top drawing )
for RF : the return current will follow the shape of the meander above the plane. it will not go for the beeline but run exactly in the same shape as the trace above, even if there is a solid plane and no reason to do that.
Yes, it does that because at RF the loop inductance in the ground plane just below the trace is the lowest, hence more current will flow there instead of wider out in the ground plane.
Just wanted to clarify that at DC, current just doesn't flow everywhere equally, as I showed in the video.
Dave.
Interesting ! a search through the UK TTi web-site shows no I-prober 520 being available... looks like they consider UK purchase of this device, not worth marketing in the UK;
or is this a patent distribution, partnership-consortium issue ?... as Dave say's Go Figure.
Okay I-prober own up... just found the product on the their UK site, via the site-map; would have thought it should be easier to find, without deep searching.
I remember experimenting some years ago using a cassette player record-playback head as a current tracer.
Interesting ! a search through the UK TTi web-site shows no I-prober 520 being available... looks like they consider UK purchase of this device, not worth marketing in the UK;
or is this a patent distribution, partnership-consortium issue ?... as Dave say's Go Figure.
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